Background Art In general, hot materials 110 such as slabs and billets are heated up to a predetermined temperature while being carried in a reheating furnace 100 before they are hot rolled. As shown in Fig. 1, the reheating furnace 100 contains a skid apparatus 120 for supporting and carrying the hot materials 110 within the reheating furnace 100, a plurality of burners 122 functioning as heat sources and an exhaust duct unit 130 for exhausting atmospheric gas out of the reheating furnace 100.

The skid apparatus 120 includes stationary beam skids 124

and movable beam skids 126 for moving the hot materials 110, in which the movable beam skids 126 carry out a transport cycle including elevation, advancement, descent and retreat to carry the hot materials 110 within the reheating furnace 100 toward an exit while the stationary beam skids 124 support the hot materials 110.

The skid apparatus 120 has coolant pipes 140 which are placed on top portions of the skid beams, as shown in Figs. 2 and 3, each surrounded by a heat insulation layer 142 for allowing passage of coolant through the same. On the coolant pipes 140, there are mounted a plurality of skid members 150 made of ceramic composite or special refractory steel for supporting the hot materials 110.

Each of the skid members 150 may be in the form of a column having a polygonal cross-sectional configuration, such as a hexagonal section as shown in Fig. 4a, a circular cross-sectional configuration as shown in Fig. 4c or a quadrangular cross-sectional configuration as shown in Fig. 4d.

Also, as shown in Fig. 4b, the skid member 150 may be shaped as a circular column having heat-absorbing fins 150a mounted on the top thereof.

As shown in Fig. 5a, the skid member 150 may have a stationary rail structure extended longitudinally along the coolant pipe 140, which is suitable for pushing the hot materials into the furnace through an entrance so that the hot materials are slid on the stationary rail.

Also as shown in Figs. 5b and 5c, the skid member 150 comprises assembling structures 143 projected from the coolant pipe 140 and a rider 144 coupled with the assembling structures 143 along the length of the coolant pipe 140.

In the skid apparatus 120 of the conventional reheating furnace 100, the skid members 150 are cooled down with coolants such as cold water or steam, etc. , while they support the hot materials 110. As a result, when a top portion 161 of each skid member 150 supports an underside region of each hot material 110, the underside region is cooled down with coolant to form a skid mark 160 having a temperature lower than other regions of the hot material 110. That is, the skid mark 160 is formed in the underside region of the hot material 110 contacted with the top portion 161 of the skid member 150, in which the contacted underside region of the hot material 110 has a temperature lower than other regions of the hot material, thereby creating temperature difference to the hot material.

Therefore, the prior art maintains the temperature difference of about at least 20 to 30C between the skid mark 160 and other regions of the hot material. Since the skid mark 160 has such a large value of temperature difference, this causes difference of elongation to the hot material 110 in a subsequent hot rolling process thereby degrading precision of rolling thickness and width.

Such degraded precision of rolling thickness creates a localized thick portion to the hot material in a finishing mill process which is requiring a precise rolling control of thickness, this is caused by the increase of deformation resistance at the skid mark of low temperature while the hot material is rolled under tension between hot rolling stands.

On the contrary, when the hot finishing mill process is performed to a steel strip or plate of ultra low carbon content in a temperature range (860 to 890C) below the transformation

point (Ar3 : about 910C) where a skid mark region undergoes phase-transformation (e. g. , from austenite to ferrite), deformation resistance decreases rapidly in the longitudinal direction of rolled steel to worsen rolling threading ability or to reduce strip or plate thickness radically thereby tearing them off.

If'the temperature of the hot rolled strip or plate is raised to avoid the foregoing problems, energy is consumed excessively. Also, the surface of the hot rolled strip or plate may be scaled and rolls suffer from heavy thermal fatigue.

Therefore, in the prior art, heating time is prolonged or the temperature of the reheating furnace 100 is raised excessively in order to decrease the temperature difference associated with the skid mark 160. However, temperature rise in the reheating furnace 100 consumes fuel by a large quantity thereby raising the production cost of steel products with the reheating furnace 100. Also, the hot material is overheated thereby increasing scales as well as lowering the yield of steel products. Further, even though the scales formed on the surface of the hot material are removed via impact of high-pressure water, some of scales remain on the surface causing surface defects to the rolled hot material.

In order to prevent problems related with hot rolling and subsequent processes, it is required to maintain the temperature difference associated with the skid mark 160 within about 20C, preferably, about 18 C.

Several improvements have been proposed in the prior art, to solve the problems related with subsequent processes caused by the skid mark.

Japanese Laid-Open Patent Publication Serial No. H2-85322 discloses a laser apparatus capable of detecting the temperature of a skid mark in a rolled slab and emitting a laser beam to the skid mark from the exit side of a reheating furnace to further heat the skid mark so that the temperature of the skid mark rises equal to that of the slab. Since the laser apparatus is provided in addition to the reheating furnace, this technique requires additional cost for the laser apparatus.

Japanese Laid-Open Patent Publication Serial Nos.

H3-207808 and H5-179339 propose techniques for mounting a skid mark burner in the exit side of a reheating furnace to heat a corresponding region of a slab to remove any skid mark from the slab and providing the skid mark burner with excellent endurance.

According these techniques, the burner is installed within the reheating furnace to be use exclusively for the skid mark, and the burner also increases installation cost.

Japanese Laid-Open Patent Publication Serial Nos. <BR> <BR> <BR> <BR> <P>H3-47913 and H4-131318 disclose a skid button. Thisskidbutton has an internal space and is partitioned into two or three vertical sections, in which an upper section is made of a material excellent in heat conductivity and a lower section is made of material excellent in endurance and structural strength.

However, such partitioned skid button is structurally unstable, and causes high fabrication price thereby raising cost.

Also, Japanese Patent Publication Serial No. H4-57727 discloses a cylindrical skid member within a skid member holder on a skid coolant pipe, in which the skid member is made of heat insulation material such as non-oxide ceramic and has a hollow space or an upward opening. However, this skid member also has a partitioned structure and thus disadvantageously increases

installation cost. Further, scales are deposited in the <BR> <BR> <BR> <BR> opening to fill the same, resultantly giving an effect of filling the opening with insulation material.

Japanese Laid-Open Patent Publication Serial No.

H6-306453 discloses an apparatus comprising a burner installed in a lower portion of the exit side of a reheating furnace, a local heating controller for controlling the burner and a time predicting controller in order to minimize the temperature difference between a skid mark and other regions of a slab based upon the temperature of the skid mark. This apparatus also requires extension of equipment installation.

Another Japanese Laid-Open Patent Publication Serial No.

H9-268314 discloses skid button having a cylindrical short pipe installed on a skid member holder extended from a skid pipe, in which refractory castable is filled into the pipe remaining a gap in an upper portion thereof. However, since the short pipe reduced in sectional area only supports the contact region of a slab, a large quantity of surface pressure is applied to the contact region of the slab'potentially leaving a mark on the contact region of the slab. In this skid button, while the gap and the refractory castable block heat generated from the slab to prevent creation of a skid mark in an initial stage, as the time goes by, scales are deposited in the gap filling the same thereby disabling the effect of the gap to a certain degree.

Japanese Laid-Open Patent Publication Serial No. <BR> <BR> <BR> <BR> <P>H10-140246 proposes an apparatus which comprises a water cooling pipe arranged inside a skid beam under a tempering zone of a reheating furnace and an auxiliary heating gas line incorporating a gas supplying pipe extended upwardly through

a refractory layer and having a nozzle placed right below a slab for heating a skid mark of the slab. This apparatus can remove the skid mark through. localized heating to the slab, but needs extension of installations thereby causing rise in equipment price and running cost.

Another Japanese Laid-Open Patent Publication Serial No.

H10-140247 installs a plurality of regenerative burners above a tempering zone in a reheating furnace to further heat a skid mark on a slab thereby reducing the temperature difference between the skid mark and other regions of the slab. However, this technique requires additional regenerative burners thereby raising installation cost by a large quantity as well as manufacturing cost through additional heating.

Japanese Laid-Open Patent Publication Serial No.

H10-306313 discloses a technique for heating skid beams with fuel supplying pipes installed in one of the skid beams thereby to prevent a skid mark in an underside region of a slab supported by the skid beams. Since this technique of the prior art also requires the fuel supplying pipes on the skid beam, there are problems that extension of installations consumes a large amount of cost as well as complicates a system design.

Furthermore, Japanese Laid-Open Patent Publication Serial No. 2000-61503 provides a solenoid-induced heating apparatus between a prime rolling mill and a finishing mill to heat a low temperature region of a slab over other regions thereof. This conventional technique also needs additional heating units.

Object of the Invention

The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the invention to provide an improved method and a skid member for reducing temperature difference in a hot material to be heated and a skid apparatus using the same, more particularly, which reduces the heat transfer area from the hot material toward a lower portion of the skid member and forms a ventilation channel enlarging an area in contact with hot gas to increase the quantity of heat introduced into the skid member, thereby reducing heat loss from an upper portion of the skid member to the lower portion thereof with the ventilation channel and thus imparting compensatory heating to the upper portion of the skid member.

It is another object of the invention to provide an improved method and a skid member for reducing temperature difference in a hot material to be heated and a skid apparatus using the same, more particularly, which reduces the temperature difference between a skid mark and other regions of a hot material to be heated through simple structural improvement so that the hot material can be heated at a uniform temperature to improve the hot rolling threading ability and quality of the hot material in subsequent processes.

It is yet another object of the invention to provide an improved method and a skid member for reducing temperature difference in a hot material to be heated and a skid apparatus using the same, more particularly, which introduces hot gas within a reheating furnace into the skid member while maintaining the contour of the skid member to reduce temperature difference associated with a skid mark, thereby improving percentile thickness and width within tolerances and

restraining creation of scales to minimize descaling operation, improve rolling yield and save manufacturing cost.

Disclosure of the Invention According to an aspect of the invention for realizing the foregoing objects, there is provided a method for reducing temperature difference in a hot material to be heated which is supported and/or carried by a skid member within a reheating furnace, the method comprising the following steps of: circulating hot gas for heating the hot material into a space formed within the skid member; and compensating heat loss of an upper portion of the skid member with a portion of heat transferred from the hot gas which is introduced into the space and transferring a residual of the transferred heat to a coolant pipe, whereby the temperature of the upper portion of the skid member is maintained higher than a temperature inevitably creating a skid mark in the hot material.

According to another aspect of the invention for realizing the foregoing objects, there is provided a'skid member for supporting and/or carrying a hot material to be heated within a reheating furnace, comprising: a top face contacting an underside region of the hot material; and at least one ventilation channel formed in the skid member for introducing hot gas through the same to reduce temperature difference between the underside region of the hot material in contact with the top face of the skid member and a non-contact region of the hot material.

According to further another aspect of the invention for

realizing the foregoing objects, there is provided a skid member <BR> <BR> <BR> <BR> for supporting and/or carrying a hot material to be heated within a reheating furnace comprising: a top face for supporting the hot material ; a lateral hollow space of a predetermined size formed within the skid member; and a lateral vent hole formed in the skid member, whereby the quantity of heat transferred from the hot material to a coolant pipe is reduced and the quantity of heat introduced from hot gas is increased to reduce temperature difference between an underside region of the hot material in contact with the top portion of the skid member and a non-contact region thereof.

According to further another aspect of the invention for realizing the foregoing objects, there is provided a skid member for supporting and/or carrying a hot material to be heated within a reheating furnace comprising: a top face for supporting the hot material; a blind lateral vent hole formed within the skid member at a predetermined size ; and a stopper blocking an opening of the vent hole to define a hollow space within the skid member, whereby the quantity of heat transferred from the hot material to a coolant pipe is reduced to decrease temperature difference between an underside region of the hot material in contact with the top portion of the skid member and a non-contact region of thereof.

According to yet another aspect of the invention for realizing the foregoing objects, there is provided a skid apparatus for supporting and/or carrying a hot material to be heated within a reheating furnace comprising: a coolant pipe for allowing passage of coolant through the same ; a heat insulation layer surrounding an exterior of the coolant pipe; and at least one skid member having a bottom connected with the

coolant pipe, a top face for supporting the hot material and at least one ventilation channel for allowing passage of hot gas within the reheating furnace into the skid member, whereby temperature difference between an underside region of the hot material in contact with the top face of the skid member and a non-contact region thereof is reduced.

Brief Description of the Drawings Fig. 1 is a side sectional view for illustrating slabs carried in a general reheating furnace ; Fig. 2 is a longitudinal sectional view for illustrating stationary beam skids and movable beam skids in the reheating furnace shown in Fig. 1, which support and carry heated objects; Fig. 3 is a sectional view of a skid apparatus of the prior art; Figs. 4a through 4d illustrate several types of skid members of the skid apparatus of the prior art, in which Fig.

4a illustrates a polygonal cross-sectional configuration, Fig.

4b illustrates a structure with heat-absorbing fins mounted on a top portion thereof, Fig. 4c illustrates a circular column-shaped configuration, and Fig. 4d illustrates a quadrangular cross-sectional configuration; Figs. 5a through 5c illustrate several types of skid apparatus sections mounted with rail-type skid members of the prior art, in which Fig. 5a illustrates a quadrangular rail. structure, Fig. 5b illustrates a rail structure mounted with a rider, and Fig. 5c is a cross-sectional view taken along a line A-A in Fig. 5b; Figs. 6a through 6d are detailed views of a skid member

having a ventilation channel and a skid apparatus mounted with the skid member according to the invention, in which Fig. 6a is an exterior perspective view of the skid apparatus, Fig. 6b is a sectional view taken along a line A-A in Fig. 6a, Fig. 6c is a sectional view taken along a line A'-A'in Fig. 6b, and Fig. 6d is an exterior perspective view of the skid member; Figs. 7a through 7c are detailed views of a skid apparatus mounted with a skid member having a neck of the prior art, in which Fig. 7a is an exterior perspective view of the skid apparatus, Fig. 7b is a sectional view taken along a line B-B in Fig. 7a, and Fig. 7c is a sectional view taken along a line B'-B'in Fig. 7b; Figs. 8a and 8b are detailed views of a skid apparatus mounted with a stationary rail-type skid member having vent holes therein according to the invention, in which Fig. 8a is an exterior perspective view of the skid apparatus, and Fig.

8b is a sectional view taken along a line A-A in Fig. 8a; Figs. 9a through 9c are detailed views of a skid apparatus mounted with a rider-type skid member having vent holes therein according to the invention, in which Fig. 9a is an exterior perspective view of the skid apparatus, Fig. 9b is a sectional view taken along a line A-A in Fig. 9b, and Fig. 9c is a sectional view taken along a line A'-A'in Fig. 9b; Figs. 10a through 10c are detailed views of a skid apparatus mounted with a skid member having one inclined ventilation channel formed therein according to the invention, in which Fig. 10a is an exterior perspective view of the skid apparatus, Fig. 10b is a sectional view taken along a line C-C in Fig. 10a, and Fig. 10c is a sectional view taken along a line C'-C'in Fig. lOb ;

Figs. lla and llb are detailed views of a skid apparatus mounted with a stationary rail-type skid member having a plurality of inclined ventilation channels formed therein according to the invention, in which Fig. lla is an exterior perspective view of the skid apparatus, and Fig. llb is a sectional view taken along a line C-C in Fig. lla ; Figs. 12a through 12c are detailed views of a skid apparatus mounted with a skid member having a plurality of horizontal ventilation channels formed therein according to the invention, in which Fig. 12a is an exterior perspective view of the skid apparatus, Fig. 12b is a sectional view taken along a line D-D in Fig. 12a, and Fig. 12c is a sectional view taken along a line D'-D'in Fig. 12b; Figs. 13a through 13c are detailed views of a skid apparatus mounted with a skid member having a plurality of inclined ventilation channels formed therein according to an alternative embodiment of the invention, in which Fig. 13a is an exterior perspective view of the skid apparatus, Fig. 13b is a sectional view taken along a line E-E in Fig. 13a, and Fig.

13c is a sectional view taken along a line E'-E'in Fig. 13b; Figs. 14a through 14c are detailed views of a skid apparatus mounted with a skid member having a plurality of intersected ventilation channels formed therein according to another alternative embodiment of the invention, in which Fig.

14a is an exterior perspective view of the skid apparatus, Fig.

14b is a sectional view taken along a line F-F in Fig. 14a, and Fig. 14c is a sectional view taken along a line F'-F'in Fig.

14b ; Figs. 15a and 15b are detailed views of a skid apparatus mounted with a stationary rail-type skid member having a

plurality of ventilation channels diagonally inclined therein according to further another alternative embodiment of the invention, in which Fig. 15a is an exterior perspective view of the skid apparatus, and Fig. 15b is a sectional view taken along a line F-F in Fig. 15a; Figs. 16a through 16c are detailed views of a skid apparatus mounted with a skid member having a plurality of ventilation channels inclined diagonally and intersected with each other according to another alternative embodiment of the invention, in which Fig. 16a is an exterior perspective view of the skid apparatus, Fig. 16b is a sectional view taken along a line G-G in Fig. 16a, and Fig. 16c is a sectional view taken along a line G'-G'in Fig. 16b; Figs. 17a through 17c are detailed views of a skid apparatus mounted with a skid member including a plurality of vent holes having different heights and communicating with each other according to another alternative embodiment of the invention, in which Fig. 17a is an exterior perspective view of the skid apparatus, Fig. 17b is a sectional view taken along a line H-H in Fig. 17a, and Fig. 17c is a sectional view taken along a line H'-H'in Fig. 17b; Figs. 18a through 18c are detailed views of a skid apparatus mounted with a skid member according to further another alternative embodiment of the invention, in which Fig.

18a is an exterior perspective view of the skid apparatus, Fig.

18b is a sectional view taken along a line I-I in Fig. 18a, and Fig. 18c is a sectional view taken along a line I'-I' in Fig.

18b; Figs. 19a and 19b are detailed views of a skid apparatus mounted with a skid member having a plurality of vent holes

intersected with each other at a same height according to an alternative embodiment of the invention, in which Fig. 19a is an exterior perspective view of the skid apparatus, and Fig.

19b is a sectional view taken along a line J-J in Fig. 19a ; Figs. 20a and 20b are detailed views of a skid apparatus mounted with a stationary rail-type skid member having a longitudinal vent hole and a plurality of lateral vent holes formed at a same height therein according to another alternative embodiment of the invention, in which Fig. 20a is an exterior perspective view of the skid apparatus, and Fig. 20b is a sectional view taken along a line J-J in Fig. 20a; Figs. 21a and 21b are detailed views of a skid apparatus mounted with a skid member having a plurality of vent holes inclined laterally and intersected with each other according to another alternative embodiment of the invention, in which Fig. 21a is an exterior perspective view of the skid apparatus, and Fig. 21b is a sectional view taken along a line K-K in Fig.

21a; Figs. 22a and 22b are detailed views of a skid apparatus mounted with a skid member having a lateral vent hole and a vertical vent hole extended from the lateral vent hole to a top face of the skid member according to another alternative embodiment of the invention, in which Fig. 22a is an exterior perspective view of the skid apparatus, and Fig. 22b is a sectional view taken along a line L-L in Fig. 22a; Figs. 23a and 23b are detailed views of a skid apparatus mounted with a stationary rail-type skid member having a longitudinal vent hole and a plurality of vertical vent holes extended from the longitudinal vent hole to a top face of the skid member according to another alternative embodiment of the

invention, in which Fig. 23a is an exterior perspective view of the skid apparatus, and Fig. 23b is a sectional view taken along a line L-L in Fig. 23a ; Figs. 24a and 24b are detailed views of a skid apparatus mounted with a stationary rail-type skid member having lateral vent holes and vertical vent holes extended from the lateral vent holes to a top face of the skid member according to another alternative embodiment of the invention, in which Fig. 24a is an exterior perspective view of the skid apparatus, and Fig.

24b is a sectional view taken along a line L-L in Fig. 24a ; Figs. 25a and 25b are detailed views of a skid apparatus mounted with a skid member having an inclined vent hole extended through the skid member and a vertical vent hole extended from the inclined vent hole to a top face of the skid member according to another alternative embodiment of the invention, in which Fig. 25a is an exterior perspective view of the skid apparatus, and Fig. 25b is a sectional view taken along a line M-M in Fig.

25a; Figs. 26a and 26b are detailed views of a skid apparatus mounted with a skid member having a plurality of vent holes diagonally intersected with each other and a vertical vent hole extended from the diagonal vent holes to a top face of the skid member according to another alternative embodiment of the invention, in which Fig. 26a is an exterior perspective view of the skid apparatus, and Fig. 26b is a sectional view taken along a line N-N in Fig. 26a; Figs. 27a and 27b are detailed views of a skid apparatus mounted with a skid member having a plurality of vent holes inclined diagonally and intersected with each other and a vertical vent hole extended from the diagonal vent holes to a

top face of the skid member according to another alternative embodiment of the invention, in which Fig. 27a is an exterior perspective view of the skid apparatus, and Fig. 27b is a sectional view taken along a line 0-0 in Fig. 27a; Figs. 28a and 28b are detailed views of a skid apparatus mounted with a skid member having a plurality of lateral vent holes formed at different heights and a vertical vent hole extended from the vent holes to a top face of the skid member according to another alternative embodiment of the invention, in which Fig. 28a is an exterior perspective view of the skid apparatus, and Fig. 28b is a sectional view taken along a line P-P in Fig. 28a; Figs. 29a and 29b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus mounted with a skid member having a first group of vent holes extended diagonally one above another alternating with one another in the skid member, a second group of upper vent holes extended to lateral faces of the skid member and a vertical vent hole extended to a top face of the skid member, in which Fig. 29a is an exterior perspective view of the skid apparatus, and Fig. 29b is a sectional view taken along a line Q-Q in Fig. 29a; Figs. 30a and 30b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus mounted with a skid member having a lateral vent hole extended through the skid member, a vertical vent hole extended from the lateral vent hole to a top face of the skid member and a scale exit hole extended downward from the holes, in which Fig. 30a is an exterior perspective view of the skid apparatus, and Fig. 30b is a sectional view taken along a line

R-R in Fig. 30a; Figs. 31a and 31b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a stationary rail-type skid member comprising a longitudinal vent hole extended through the skid member, a plurality of vertical vent holes extended from the longitudinal vent hole to a top face of the skid member and a scale exit hole extended downward from the holes, in which Fig.

31a is an exterior perspective view of the skid apparatus, and Fig. 31b is a sectional view taken along a line R-R in Fig. 31a; Figs. 32a and 32b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a stationary rail-type skid member comprising a plurality of longitudinal vent holes extended through the skid member, a plurality of vertical vent holes extended from the longitudinal vent holes to a top face of the skid member and scale exit holes extended downward from the holes to a side, in which Fig. 32a is an exterior perspective view of the skid apparatus, and Fig. 32b is a sectional view taken along a line R-R in Fig. 32a; Figs. 33a and 33b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an inclined vent hole extended through the skid member, a plurality of vertical vent holes extended from the vent hole to a top face of the skid member and a scale exit hole extended downward from the holes to a side, in which Fig. 33a is an exterior perspective view of the skid apparatus, and Fig. 33b is a sectional view taken along a line S-S in Fig. 33a; Figs. 34a and 34b are detailed views of a skid apparatus

according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a plurality of vent holes extended diagonally crossing one another at a same height in the skid member, a vertical vent hole extended from the vent holes to a top face of the skid member and a scale exit hole extended downward from the holes, in which Fig. 34a is an exterior perspective view of the skid apparatus, and Fig. 34b is a sectional view taken along a line T-T in Fig. 34a; Figs. 35a and 35b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a plurality of vent holes extended at different heights, a vertical vent hole extended from the vent holes to a top face of the skid member and a scale exit hole extended downward from the holes, in which Fig. 35a is an exterior perspective view of the skid apparatus, and Fig. 35b is a sectional view taken along a line U-U in Fig.

35a ; Figs. 36a and 36b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a vertical vent hole extended upward and a scale exit hole extended downward from the hole to a side of the skid member communicating with the vertical vent hole, in which Fig. 36a is an exterior perspective view of the skid apparatus, and Fig. 36b is a sectional view taken along a line AB-AB in Fig. 36a; Figs. 37a and 37b are detailed views of. a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a stationary rail-type skid member comprising a plurality of vertical vent holes extended upward and a plurality of scale exit holes extended downward from the

holes to both sides of the skid member in a communicating type, in which Fig. 37a is an exterior perspective view of the skid apparatus, and Fig. 37b is a sectional view taken along a line AB-AB in Fig. 37a ; Figs. 38a and 38b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an oval hollow space and a vent hole extended from the hollow space to a side of the skid member, in which Fig. 38a is an exterior perspective view of the skid apparatus, and Fig. 38b is a sectional view taken along a line W-W in Fig. 38a; Figs. 39a and 39b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an oval hollow space and a plurality of vent holes extended at inclinations from the hollow space to front and rear sides of the skid member, in which Fig. 39a is an exterior perspective view of the skid apparatus, and Fig. 39b is a sectional view taken along a line X-X in Fig. 39a ; Figs. 40a and 40b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an oval hollow space, a plurality of vent holes extended at inclinations from the hollow space to a top face of the skid member and a scale exit hole extended to a lateral side of the skid member, in which Fig. 40a is an exterior perspective view of the skid apparatus, and Fig. 40b is a sectional view taken along a line Y-Y in Fig.

40a ; Figs. 41a and 41b are detailed views of a skid apparatus according to another alternative embodiment of the invention,

the skid apparatus having a skid member comprising an oval hollow space, a vent hole extended from the hollow space to front and rear faces of the skid member, a plurality of vent holes extended at inclinations from the hollow space to a top face of the skid member and a scale exit hole extended to a lateral side of the skid member, in which Fig. 41a is an exterior perspective view of the skid apparatus, and Fig. 41b is a sectional view taken along a line Z-Z in Fig. 41a ; Figs. 42a and 42b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a lateral vent hole, a vertical vent hole extended from the lateral vent hole to a top face of the skid member and a scale exit hole extended downward to a side of the skid member so that holes communicate together, in which Fig. 42a is an exterior perspective view of the skid apparatus, and Fig. 42b is a sectional view taken along a line AA-AA in Fig. 42a; Figs. 43a and 43b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a stationary rail-type skid member comprising a plurality of lateral vent holes, vertical vent holes extended from the lateral vent holes to a top face of the skid member and scale exit holes each communicating with corresponding lateral and vertical vent holes and extended downward to a side of the skid member, in which Fig. 43a is an exterior perspective view of the skid apparatus, and Fig. 43b is a sectional view taken along a line AA-AA in Fig. 43a ; Figs. 44a and 44b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a horizontal

blind vent hole formed within the skid member and a stopper blocking an opening of the vent hole to define a hollow space within the skid member, in which Fig. 44a is an exterior perspective view of the skid apparatus, and Fig. 44b is a sectional view taken along a line V-V in Fig. 44a; Figs. 45a and 45d are detailed views of a skid apparatus according to another alternative embodiment of the invention having ventilation channels of discrete vent holes, in which Fig. 45a is an exterior perspective view of the skid apparatus, Fig. 45b is a sectional view taken along a line A2'-A2'in Fig.

45a, Fig. 45c is a detailed view of a ventilation channel with a closed upper end and an opening inclined downward to a side, and Fig. 45d is a sectional view taken along a line AB'-AB'in Fig. 45c ; Figs. 46a and 46b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an inclined vent hole extended through the skid member and a combustion gas pipe with a leading end extended into the vent hole, in which Fig. 46a is an exterior perspective view of the skid apparatus, Fig. 46b is a sectional view taken along a line AC-AC in Fig.

46a; Figs. 47a and 47b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising an inclined vent hole extended through the skid member, a vertical vent hole extended from the inclined vent hole to a top face of the skid member and a scale exit hole extended downward from the holes and a combustion gas pipe with a leading end extended into the vent hole, in which Fig. 47a is an exterior perspective view

of the skid apparatus, Fig. 47b is a sectional view taken along a line AD-AD in Fig. 47a; Figs. 48a and 48b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a hollow space, an inclined vent hole extended from the hollow space to front and rear faces of the skid member, a vertical vent hole extended from the hollow space to a top face of the skid member and a scale exit hole extended downward from the holes to a side of the skid member and a combustion gas pipe with a leading end extended into the vent hole, in which Fig. 48a is an exterior perspective view of the skid apparatus, Fig. 48b is a sectional view taken along a line AE-AE in Fig. 48a; Figs. 49a and 49b are detailed views of a skid apparatus according to another alternative embodiment of the invention, the skid apparatus having a skid member comprising a hollow space, a lateral vent hole extended from the hollow space to front and rear faces of the skid member, a plurality of vertical vent holes extended from the hollow space to a top face of the skid member and a combustion gas pipe with a leading end extended into the vent hole, in which Fig. 49a is an exterior perspective view of the skid apparatus, Fig. 49b is a sectional view taken along a line AE-AE in Fig. 49a; Fig. 50 is a graph illustrating results of Example 1 according to a structure of the invention and a conventional structure, in which temperature differences between a skid members contact region and a non-contact region of a hot material are plotted; Fig. 51 illustrates an arrangement of the hot material, skid members and thermometers used in Examples 2 and 3 according

to the invention; Fig. 52 is a graph illustrating temperature profiles at points #1, #3 and #5 in Fig. 51 according to results of Example 2; Fig. 53 is a graph illustrating temperature profiles at points #2, #4 and #6 in Fig. 51 according to results of Example 2 ; Fig. 54 is a graph illustrating temperature difference profiles produced by deducting temperatures at 60mm from an underside of a hot material from temperatures at 10mm from the underside of the hot material according to results of Example 2; Fig. 55 is a graph according to results of Example 2, illustrating temperature differences between the points #5 and #1 at 10mm above the underside of the hot material and between the points #6 and #2 at 60mm above the underside of the hot material, in which the points #5 and #6 were supported by the skid member of the invention and the points #1 and #2 were supported by the skid member of the prior art; Fig. 56 is a graph illustrating temperature profiles based on time at points #1, #3 and #5 in Fig. 51 according to results of Example 3; Fig. 57 is a graph illustrating temperature profiles based on time at points #2, #4 and #6 in Fig. 51 according to results of Example 3; Fig. 58 is a graph illustrating temperature difference profiles produced by deducting temperatures at 60mm above an underside of a hot material from temperatures at 10mm above the underside of the hot material according to results of Example 3 ;

Fig. 59 is a graph according to results of Example 3, illustrating temperature differences between the points #5 and #1 at 10mm above the underside of the hot material and between the points #6 and #2 at 60mm above the underside of the hot material, in which the points #5 and #6 were supported by the skid member of the invention and the points #1 and #2 were supported by the skid member of the prior art ; Figs. 60a through 60c are detailed views of a conventional skid member as a comparative example and skid members of the invention, illustrating positions for measuring stress point temperatures ; Fig. 61 is a graph for illustrating a temperature profile of a skid member of the invention with respect to the sectional area of circular and elliptic ventilation channels when a conventional skid member reaches a predetermined temperature 1100C ; Figs. 62a through 62c are detailed views of a conventional skid member as a comparative example and skid members of the invention used in Example 5 ; Fig. 63 is a graph of temperature difference profiles according to results of Example 5 in a structure having a ventilation channel formed in an upper portion, illustrating temperature differences between the points #3 and #1, the points #3 and #5, the points #4 and #2 and the points #4 and #6 at 40mm and 100mm positions, in which the points #5 and #6 are supported by the skid member of the invention, the points #3 and #4 are in central non-contact section of a hot material, and the points #1 and #2 are supported by the conventional skid member; and Fig. 64 is a graph of temperature profiles according to results of Example 5 in a structure having a ventilation channel

formed in a lower portion, illustrating temperature differences between the points #3 and #1, the points #3 and #5, the points #4 and #2 and the points #4 and #6 at 40mm and 100mm positions, in which the points #5 and #6 are supported by the skid member of the invention, the points #3 and #4 are in central non-contact section of a hot material, and the points #1 and #2 are supported by the conventional skid member.

Best Mode for Carrying out the Invention The following detailed description will present the present invention in conjunction with the accompanying drawings.

The present invention provides a method for reducing temperature difference in a hot material to be heated such as a slab and billet with a skid member 5 as shown in Figs. 6a through 6c. The skid member 5 includes a ventilation channel 7 formed therein to reduce heat transfer from an upper portion to a lower portion of the skid member. The ventilation channel 7 allows passage of hot atmospheric gas from the reheating furnace which heats the hot material 110 so that heat absorbed via the ventilation channel can compensate heat loss in the upper portion 162 of the skid member, and be transferred toward a coolant pipe to further reduce heat transfer from the upper portion 162 of the skid member. As a result, the temperature of the skid member upper portion 162 is maintained over a predetermined temperature inevitably creating a skid mark 160 in the hot material 110.

The skid apparatus 1 of the invention adopted in the method of the invention is applicable to a stationary beam skid 124

and a movable beam skid 126, which in common comprise a coolant pipe 140 for allowing passage of coolant through the same. The coolant pipe 140 is surrounded by a heat insulation layer 142, and connected with a plurality of other skid members 5 which also have ventilation channels 7 formed therein.

Generally, as a structure for seating the skid member 5 on the coolant pipe, the skid member 5 comprises bosses 5a having an extended width at its bottom and a plurality of clip receiving portions 5b formed at both lateral upper sides of the bosses 5a. Alternatively, skid member holders may be provided to readily seat the skid member on the coolant pipe 140.

The ventilation channel 7 is extended longitudinally or laterally through the skid member 5 of the invention so that gas within the reheating furnace can be introduced into the ventilation channel 7. The ventilation channel 7 has a structure of a lateral vent hole 10 which is extended from one side of the skid member to one of the other sides thereof as shown in Fig. 6b. Alternatively, as shown in Figs. 45b and 45d, the ventilation channel may have a structure of blind vent holes 10 and 10a, which are extended horizontally or at an inclination to a side of the skid member. Also, the ventilation channel may be formed diagonally extending through corners.

The vent hole 10 has a circular cross section but is not limited to the same. For example, the cross section of the vent hole 10 may be in the form of any polygon such as a triangle, quadrangle, hexagon and octagon or an ellipse. Further, the number of the vent hole 10 may be varied, or radiator fins may be formed in the inner periphery of the vent hole to increase the surface area of the vent hole 10.

The upper portion of the skid member 5 rises in temperature

as the diameter of the circular or elliptic ventilation channel 7 increases, thus it is more preferred that the ventilation channel is placed higher in the skid member.

The uppermost point of the ventilation channel 7 is preferably placed about at least 40mm from the uppermost portion of the coolant pipe 140.

The ventilation channel 7 is perforated in a direction that hot atmospheric gas flows within the reheating furnace, as in Fig. 6, it may follows the longitudinal direction of the coolant pipe 140. However, the ventilation channel 7 may be oriented different from the longitudinal direction of the coolant pipe 140. Since flow of hot gas is directed toward a section of the reheating furnace 100 communicating with an exhaust duct unit 130 as shown in Fig. 1, it is preferred to make the ventilation channel 7 follow the direction of hot gas determined according to the arrangement of the reheating furnace 100.

Therefore, as shown in Figs. 6a through 6d, the skid member 5 having the ventilation channel 7 can absorb heat from hot gas introduced within the same as well as reduce heat transfer from the upper portion 162 to the lower portion 164 based upon a ventilation channel portion 163 of the skid member 5 in order to raise the temperature of a contact region between the hot material 110 and the skid member 5.

Hot gas within the ventilation channel 7 compensates heat loss, which is transferred from the upper portion 161 at the skid member toward the coolant pipe 140 thereby to prevent over-cooling of the skid member upper portion 161. At the same time, heat transfer occurs from hot gas toward the lower portion 164 of the skid member 5 connected with the coolant pipe 140

via the ventilation channel 7 thereby to reduce the quantity of heat transferred from the upper portion 162 to the lower portion 164 of the skid member.

Such heat balance is expressed in following Equation 1: Qs + Qe + Qe'-Qc = 0----> Qs + Qe + Qe'= Qc....

Equation 1, Wherein, Qs is the quantity of heat transferred from the skid mark of the hot material to the skid member, Qe is the quantity of heat introduced from hot gas within the reheating furnace outside a skid member, Qe'is the quantity of heat introduced into the skid member from hot gas within the ventilation channel, and Qc is the quantity of heat transferred from the skid member to the coolant pipe.

The above equation shows, that the quantity of heat introduced from the ventilation channel 7 formed in a central portion of the skid member 5 is advantageous to add heating to the skid member 5. In particular, where the ventilation channel 7 is constituted of the single lateral vent hole 10 as shown in Figs. 6a through 6c, the ventilation channel 7 is extended to both lateral sides of the skid member 5 so as to ensure more excellent heating effect at the same sectional area while imparting excellent structural strength to the skid member 5.

Figs. 7a through 7c illustrate a comparative example of a skid member 150, in which elongate grooves 152 having a semi-circular section are formed symmetrically at both lateral sides of the skid member 150 to form a neck. Assuming that the diameter of the lateral vent hole 10 shown in Fig. 6a is same as that of the grooves 152 shown in Fig. 7a, the elongate grooves 152 have Qe and Qe''which are remarkably different from those

of the lateral vent hole 10 while the elongate grooves 152 form a cross sectional area equal to that of the lateral vent hole 10.

Herein the quantity of heat transfer Qe and/or the quantity of heat introduction Qe'can be expressed according to following Equation 2: Qe or Qe'= A X 6 X £ (T4-t4).... Equation 2, wherein A is the surface area of heat transfer, E is emissivity, 6 is a proportional factor such as Stefan-Boltzmann constant, that is, 5.669 X 10-8W/m2K4, T is the temperature of hot gas, and t is the temperature of the skid member.

The quantity of heat transfer Qe and/or the quantity of heat introduction Qe'are proportional to the surface area of heat transfer, that is, the surface area A of the skid member 5 exposed to hot gas. In the structure shown in Fig. 6a, the surface area exposed to hot gas is constituted of lateral faces of the skid member 5 and the inner periphery of the lateral vent hole 10. However, in the structure shown in Fig. 7a, the surface area exposed to hot gas is defined by front and rear faces of the skid member 150, the inner periphery of the elongate grooves 152 and lateral faces of the skid member 150 excluding the grooves 152. Then, it can be seen that the surface area in Fig.

7a is reduced as much as those portions corresponding to the elongate grooves 152 compared to the surface area in Fig. 6a.

As a result, in the structure in Fig. 7a having the reduced surface area of heat transfer, the quantity of heat absorbed into the skid member 5 from hot gas within the reheating furnace is also reduced compared with the structure in Fig. 6a.

Further, the structure of the invention as shown in Fig.

6a has section modulus which is remarkably larger than the structure shown in Fig. 7a to have a more strong structure resisting against bending moment and torsional moment. Such section modulus indicates the capability of resisting against bending stress and torsional stress applied to the skid member 5 from the hot material 110. Even though the skid member 5 with the vent hole 10 in Fig. 6c and the skid member 150 having the elongate grooves 152 at sides in Fig. 7c have the same sectional area, at their weakest section, the structural strengths will be remarkably different according to the magnitude of their section moduli.

That is, since the skid member 5 of the invention shown in Fig. 6c has the lateral vent hole 10 formed through the front and rear faces, the maximum bending moment and the section modulus at the weakest section can be obtained as shown in Fig.

6c according to following Equations 3 and 4: M = 6b X Z.... Equation 3, Z = hi (h23-d3)/6h2.... Equation 4, wherein M is maximum bending moment which can be resisted by the skid member, 6b is maximum bending stress of the skid member, and Z is section modulus.

At the weakest section, the skid member 150 shown in Fig.

7c has a cross sectional area same as that of the skid member shown in Fig. 6c if the elongate grooves 152 of a semi-circular section have a diameter d same as a diameter d of the vent hole 10. However, the skid member 150 will have a section modulus at the weakest section, expressed in following Equation 5: Z'= hi X (h2-d) 2/6.... Equation 5.

If hl, h2 and d in above Equations 4 and 5 are substituted by any arbitrary numbers, it can be seen that Z > Z'. Therefore,

with the structure of the invention shown in Figs. 6a through 6c, the structural strength against bending stress applied to the skid member 5 is much higher than that of the comparative example shown in Figs. 7a through 7c. Therefore, The structure of the invention has a higher resistant ability against any external stress applied to the skid member 5 from the hot material 110, and thus is more stable structurally.

Such difference in section modulus is applied equal to bending stress as well as torsional stress applied to the skid member 5, and the structural strength of the skid member 5 is varied according to the position of the lateral vent hole 10, which is an important factor in the invention.

Therefore, the invention shown in Figs. 6a through 6d has an ability of reducing the quantity of heat transfer from the upper portion to the lower portion of the skid member, which is more excellent than that of the comparative example shown in Figs. 7a through 7c. Further, the structure of the invention has a very excellent structural strength.

Figs. 8 and 9 illustrate stationary rail-type and rider-type skid apparatus each adopting the structure shown in Fig. 6 of the invention. Each of these skid apparatus has a plurality of vent holes 10 formed longitudinally and opened at lateral sides in a skid member 5 to form ventilation channels 7. These skid members 5 are excellent in heat transfer capability as well as in structural stability as described in conjunction with Fig. 6.

Fig. 10 illustrates an alternative structure of the invention which is modified from the structure of Fig. 6. In the alternative structure shown in Fig. 10, a ventilation channel 7 has an inclined lateral vent hole 17 formed from a

front face to a rear face of a skid member 5. Where the diameter d of the lateral vent hole 17 is identical with a diameter d of the lateral vent hole 10 shown in Fig. 6, the inclined structure of the lateral vent hole 17 can provide a heat transfer area defined by the lateral vent hole 17 which is larger than that of the structure shown in Fig. 6. As shown in Fig. 10c, the area of the skid member 5 cut by the vent hole 17 is smaller than that in the structure shown in Fig. 6c, thereby obtaining larger section modulus. Therefore, the ventilation channel is strengthened structurally.

Fig. 11 illustrates a stationary rail-type skid apparatus adopting the structure shown in Fig. 10. The skid apparatus of this structure has a plurality of inclined vent holes 17 formed in a stationary rail-type skid member 5. It can be understood that the skid apparatus of this structure is also excellent in heat transfer ability and structural stability as described in conjunction with Fig. 10.

Fig. 12 also illustrates another alternative structure of the invention, in which a ventilation channel 7 includes a plurality of lateral vent holes 20 which are arranged parallel with one another from a lateral face to an opposite lateral face of a skid member 5. Where the plurality of or n number of lateral vent holes 20 are configured to have a total sectional area equal to that of the single lateral vent hole 10 as shown in Fig. 6, the quantity of hot gas within the reheating furnace passing through the lateral vent holes 20 is same as that of hot gas passing through the single lateral vent hole 10. However, the lateral vent holes 20 can achieve a heat-absorbing surface area larger than that of the single lateral vent hole 10.

That is, where n number of the lateral vent holes 20 have

a diameter d1 and have a total sectional area same as that of the single vent hole 10 shown in Fig. 6, they have a total heat transfer surface area which is expressed in following Equations 6 and 7: n XTtdi =d------> di = d/n Ad = xd X 1 Adl = n X Ttdi X 1 = n X xd X l/n.... Equation 6, and Adl/Ad = n/n.... Equation 7, wherein n is the number of lateral vent holes, 1 is the length of each vent hole, Ad is the inside surface area of the single lateral vent hole, and Ad1 is the total inside surface area of the plurality of lateral vent holes.

Therefore as can be seen from above Equations 6 and 7, the total inside surface area of the lateral vent holes is larger than the inside surface area of the single lateral vent hole 10 for n/n times.

When total sectional area of the plurality of lateral vent holes 20 as shown in Fig. 12 is same as the sectional area of the single lateral hole 10 as shown in Fig. 6, the total inside surface area of the lateral vent holes 20 in contact with hot gas passing through the same is remarkably larger than the inside surface area of the single lateral hole 10. While the capability of the lateral vent holes 20 for allowing passage of hot gas is same as that of the single vent hole shown in Fig. 6, the surface area of the lateral vent holes 20 for absorbing heat from hot gas is remarkably larger than that of the single vent hole so that a large quantity of heat can be transferred from hot gas to the skid member 5 for a short time period.

Therefore, it can be understood that the structure in Fig.

12 has a heat absorbing ability more excellent than that of the structure in Fig. 6.

Moreover, as shown in Fig. 12c, the diameter of each lateral vent hole 20 defined in one planar section is smaller than that of the single lateral vent hole 10 shown in Fig. 6c, thus this structure can have a larger section modulus. As a result, this embodiment provides a more stable structure.

Fig. 13 illustrates another alternative structure of the invention which is also modified from the structure in Fig. 12.

This alternative structure has ventilation channels 7 constituted of a plurality of lateral vent holes 23 which are inclined from a face to an opposite face, e. g. , from a front face to a rear face of a skid member 5. In this inclined structure of the lateral vent holes 23, the heat transfer area defined by the lateral vent holes 23 is realized larger than that of Fig. 12. Also, as shown in Fig. 13c, this structure can obtain a section modulus larger than that shown in Fig. 10.

As a result, this embodiment allows this structure to be more stable.

Fig. 14 illustrates another alternative structure of the invention, in which at least lateral vent holes 26 of ventilation channels 7 are oriented along diagonals of a skid member 5, crossing each other. In this embodiment, n number of the lateral vent holes 26 each having a diameter d2 are formed to have a total sectional area which is equal to that of the single lateral vent hole 10 having a diameter d as shown in Fig. 6. The lateral vent holes 26 are crossed with each other rather than oriented in a same direction to allow more efficient passage or introduction of hot gas, in case that hot gas flows in various

directions rather than one direction within the reheating furnace 100.

As shown in Fig. 14c, since the diameter d2 of each lateral vent hole 26 is remarkably smaller than the diameter d of the single lateral vent hole 10, this structure has a larger section modulus and thus is more stable over the structure in Fig. 6.

Fig. 15 illustrates a stationary rail-type skid apparatus adopting the structure shown in Fig. 14. This structure includes a ventilation channel 7 constituted of a plurality of inclined vent holes 26 formed diagonally in a stationary rail-type skid member 5. This embodiment is also excellent in heat transfer ability as well as structural stability as described in conjunction with Fig. 14.

Fig. 16 illustrates a further another alternative structure of the invention in which lateral vent holes 29 of a ventilation channel 7 are arranged one above the other alternating with each other in addition to the structure shown in Fig. 14. This structure of the invention allows more efficient passage or introduction of hot gas where hot gas flows in various directions rather than one direction within the reheating furnace 100 as described in conjunction with Fig. 14.

Also, this structure is increased in heat transfer area and strengthened in section over the structure in Fig. 14, and thus excellent in heat transfer ability as well as in stability.

Fig. 17 illustrates another alternative structure of the invention in which lateral vent holes 32 are formed at various heights in front and rear faces of a skid member 5 communicating with each other in the skid member 5 to forma ventilation channel 7 between the front and rear faces of the skid member 5.

Therefore, this structure can allow passage of hot gas at a rate

equal to that of the structure in Fig. 6, and its heat transfer area is larger than that of the structure in Fig. 6. At the same time, as shown in Fig. 17c, this embodiment has a more enhanced section modulus and thus has a more stable structure.

Further, Fig. 18 illustrates a further another alternative embodiment of the invention which is modified from the structure in Fig. 14. In this embodiment, a first set of lateral vent holes 35 are arranged diagonally one above another alternating with one another in a skid member 5, and a second set of lateral vent holes 35 are formed over the first set of lateral vent holes, arranged one above the other alternating with each other and extended toward opposed lateral faces of the skid member 5, in order to form ventilation channels 7. The plurality of lateral vent holes 35 are extended toward the lateral faces of the skid member 5 alternating with one another instead of being oriented in a same direction to allow more efficient passage or introduction of hot gas where hot gas forms turbulent flow in various directions rather than one direction within the reheating furnace 100.

As shown in Fig. 18c, the diameter d3 of each vent hole 35 is remarkably smaller than the diameter d of the structure in Fig. 6. This is useful since this structure can be structurally intensified.

Fig. 19 illustrates another alternative embodiment of the invention, in which a plurality of crossed lateral vent holes 38 which are extended through opposed lateral faces to intersect each other at a same height in a skid member 5 to form a ventilation channel 7. There are advantages in that this structure also can allow more efficient passage or introduction of hot gas where hot gas forms turbulent flow in various

directions within the reheating furnace 100 and its section modulus can be further intensified structurally.

Fig. 20 illustrates a stationary rail-type skid apparatus adopting the structure shown in Fig. 19, in which a vent hole 38a is formed longitudinally and a plurality of vent holes 38b are formed laterally from the vent hole 38a in a stationary rail-type skid member 5. It can be understood that the skid apparatus of this structure also has excellent ability for reducing heat transfer and structural stability as described in conjunction with Fig. 19.

Fig. 21 illustrates another alternative embodiment of the invention, in which lateral vent holes 41 are formed in a skid member 5 to form a ventilation channel 7. The vent holes 41 each are inclined from one face to an opposite face, crossing each other. There are advantages in that this embodiment also can allow more efficient passage or introduction of hot gas where hot gas forms turbulent flow in various directions within the reheating furnace 100, and have a heat transfer area larger than that of Fig. 19. Also, the section modulus of this embodiment can be further intensified structurally.

Fig. 22 illustrates a skid apparatus 1 according to another alternative embodiment of the invention. The skid apparatus 1 comprises a lateral vent hole 10, which is horizontally extended through a skid member and a vertical vent hole 10a extended from the horizontal lateral vent hole 10 to a top face of the skid member to form a ventilation channel 7.

The vertical vent hole 10a in this structure allows hot gas within the reheating furnace to directly contact a skid upper portion 162 and an underside contact region of the hot material 110. Therefore, unlike the structure shown in Fig. 6, this

structure has excellent performance for directly heating the skid upper portion 162 and the contact region of the hot material 110 to further raise the temperature of the hot material thereby further reducing any temperature difference associated with the skid mark. Furthermore, this structure can remarkably reduce any vertical temperature variation in the hot material in contact with the skid member.

Fig. 23 illustrates a stationary rail-type skid apparatus as an alternative to the structure shown in Fig. 22. This stationary rail-type skid apparatus comprises a vent hole 10 extended longitudinally in a skid member 5 and a plurality of vertical vent holes 10a extended from the longitudinal vent hole 10 to a top face of the skid member 5. This embodiment is also excellent in heat transfer ability as well as structural stability as described in conjunction with Fig. 22.

Fig. 24 illustrates a stationary rail-type skid apparatus as another alternative to the structure shown in Fig. 22. This stationary rail-type skid apparatus comprises a plurality of longitudinal vent holes 10'which are extended longitudinally in a skid member 5 with both ends opened to sides of the skid member 5 and vertical vent holes 10a extended from the longitudinal vent holes 10'to a top face of the skid member.

This embodiment is also excellent in heat transfer ability as well as structural stability as described in conjunction with Fig. 22.

Fig. 25 illustrates a skid apparatus as further another alternative to the structure shown in Fig. 22. This skid apparatus comprises an inclined lateral vent hole 17 formed in a skid member 5 and a vertical vent hole 17a extended from the lateral vent hoe 17 to a top face of the skid member 5. It can

be understood that this embodiment is also excellent in heating ability similar to that of Fig. 22.

Fig. 26 illustrates an another alternative embodiment of the invention which comprises a plurality of lateral vent holes 26 which are formed diagonally at different heights in a skid member 5 and intersected with each other and a vertical vent hole 26a extended from the lateral vent holes 26 to a top face of the skid member 5 to form a ventilation channel 7. This embodiment is also excellent in heat transfer ability as well as structural stability as described in conjunction with Fig.

22.

Fig. 27 illustrates an alternative to the skid apparatus shown in Fig. 26 according to the invention. This skid apparatus comprises a plurality of inclined lateral vent holes 29 which are formed diagonally at different heights in a skid member 5 and intersected with each other and a vertical vent hole 29a extended from the inclined vent holes 29 to a top face of the skid member 5 to form a ventilation channel 7. This structure is also excellent in heating ability and strength.

Fig. 28 illustrates an alternative to the skid apparatus shown in Fig. 17 according to the invention. This skid apparatus comprises a plurality of lateral vent holes 32 formed at different heights in a skid member 5 and a vertical vent hole 32a extended from the lateral vent holes 32 in a communicating type to a top face of the skid member 5 thereby forming a ventilation channel 7. This embodiment has an excellent heating ability over the embodiment shown in Fig. 17.

Fig. 29 is an detailed view of an another alternative to the skid apparatus shown in Fig. 18 according to the invention.

This skid apparatus comprises a first set of lateral vent holes

35 which are arranged diagonally one above the other alternating with each other, a second set of upper lateral vent holes 35 which are arranged diagonally one above the other alternating with each other and a vertical vent hole 35a extended from the lateral vent holes 35 to a top face of the skid member 5 to form a ventilation channel 7. This embodiment has an excellent heating ability over the embodiment shown in Fig. 18.

Fig. 30 illustrates another alternative to the skid apparatus shown in Fig. 22 according to the invention. This skid apparatus comprises a horizontal lateral vent hole 10 extended through a skid member 5, a vertical vent hole 10a extended from the horizontal vent hole 10 to a top face of the skid member 5 and a scale exit hole 10b which is extended downward from the holes 10 and 10a to a side of the skid member 5 to form a ventilation channel 7. This embodiment can effectively remove foreign materials such as scale through the scale exit hole 10b out of the ventilation channel 7 and achieve more effective circulation of hot air while realizing an excellent heating effect toward the skid upper portion 161 as in Fig. 22.

Fig. 31 illustrates a stationary rail-type skid apparatus as an alternative to the structure in Fig. 30. This skid apparatus comprises a vent hole 10 extended longitudinally through a skid member 5, a plurality of vertical vent holes 10a extended from the longitudinal vent hole 10 to a top face of the skid member 5 and scale exit holes 10b which are extended downward from the holes 10 and 10a to a side of the skid member 5. This embodiment is also excellent in heat transfer ability as well as structural stability as described in conjunction with Fig. 30.

Fig. 32 illustrates another alternative to the structure

in Fig. 30 according to the invention. This skid apparatus comprises a plurality of vent holes 10 formed longitudinally in a skid member 5 and opened at both ends laterally, vertical vent holes lOa extended from the longitudinal vent holes 10 to a top face of the skid member 5 and scale exit holes lOb which are extended downward from the holes 10 and 10a to a side of the skid member 5. This embodiment has an excellent heating ability over the embodiment shown in Fig. 30.

Fig. 33 illustrates an another alternative to the skid apparatus shown in Fig. 25 according to the invention. This skid apparatus comprises an inclined lateral vent hole 17 formed in a skid member 5, a plurality of vertical vent holes 17a extended from the lateral vent hole 17 to a top face of the skid member 5 and a plurality scale exit holes 17b extended downward from the vent holes 17 and 17a to sides of the skid member to form a ventilation channel 7. This embodiment can effectively remove foreign materials such as scale through the scale exit hole lOb out of the ventilation channel 7 while realizing an excellent heating effect toward the skid upper portion 161 as in Fig. 25.

Fig. 34 illustrates an another alternative to the skid apparatus shown in Fig. 26 according to the invention. This skid apparatus comprises a plurality of lateral vent holes 26 which are formed diagonally at same heights in a skid member 5 and intersected with each other, a vertical vent hole 26a extended from the lateral vent holes 26 to a top face of the skid member 5 and a scale exit hole 26b extended downward from the vent holes 26 and 26a to a side of the skid member 5 to form a ventilation channel 7. This embodiment can effectively remove foreign materials out of the ventilation channel 7 while

realizing an excellent heating effect.

Fig. 35 illustrates an alternative to the skid apparatus shown in Fig. 28 according to the invention. This skid apparatus comprises a plurality of lateral vent holes 32 formed at different heights in a skid member 5, a vertical vent hole 32a extended from the lateral vent holes 32 to a top face of the skid member and a scale exit hole 32b extended downward from the vent holes 32 and 32a to a side of the skid member communicating with each other. This skid apparatus 1 can effectively remove foreign materials out of the ventilation channel 7 while realizing an excellent heating effect as in Fig.

28.

Figs. 36a and 36b illustrate another alternative embodiment of the invention which comprises a vertical vent hole 47a formed in a central portion of a skid member 5 and a scale exit hole 47b extended downward from the vent hole 47a in a communicating type to a side of the skid member 5 to form a ventilation channel 7.

In this structure, hot gas heats a skid upper portion 161 of the hot material overlying the skid member through the vertical vent hole 47a and foreign materials are discharged through the scale exit hole 47b.

Figs. 37a and 37b illustrate an alternative to the skid apparatus shown in Fig. 36 according to the invention. This skid apparatus comprises a plurality of vertical vent holes 47a formed in central portions of a stationary rail-type skid member 5 and scale exit holes 47b extended downward respectively from the vertical vent holes 47a in a communicating type to both sides of the skid member 5. As in Fig. 36, this skid apparatus allows hot gas to heat a contact region of a hot material 110 via the

vertical vent hole 47a, and effectively removes foreign materials through the scale exit hole 47b.

Fig. 38 illustrates another alternative embodiment of the invention which comprises a skid member 5, an oval space 50 formed inside the skid member 5 and a lateral vent hole 52 extended from the oval space 50 to a side of the skid member 5.

In this structure, the oval space 50 reduces the quantity of heat transferred from a hot material 110 to a coolant pipe 140 and the lateral vent hole 52 allows efficient passage of hot gas through the same so that the skid member 5 can compensate heat loss therein.

The oval space 50 and the lateral vent hole 52 increase the quantity of heat introduced from hot gas and effectively act to decrease heat transfer from the hot material 110 to the coolant pipe 140.

Fig. 39 illustrates an alternative to the skid apparatus shown in Fig. 38 according to the invention. This skid apparatus comprises inclined vent holes 55 extended from a hollow space 50 within a skid member 5 to front and rear faces of the skid member 5.

In this structure, the hollow space 50 reduces the quantity of heat transferred from a hot material 110 to coolant in a coolant pipe 140 while the vent holes 55 allows efficient passage of hot gas so as to internally compensate heat loss to the skid member 5 as well as to reduce heat quantity discharged from the hot material to the coolant pipe 140.

Fig. 40 illustrates an alternative to the skid apparatus shown in Fig. 39 according to the invention which comprises a plurality of vent holes 55a extended from a hollow space 50

within a skid member 5 to a top face of the skid member 5 and a scale exit hole 55b formed at an inclination from the hollow space 50 to a side of the skid member 5.

In this structure, the hollow space 50 reduces the quantity of heat transferred from a hot material 110 to coolant in a coolant pipe 140, the vent holes 55 allows efficient passage of hot gas, and hot gas directly contacts a skid upper portion 162 and a contact region of the hot material via the vent holes 55a so as to further improve heating ability.

Fig. 41 illustrates an alternative to the skid apparatus shown in Fig. 40 according to the invention which comprises through holes 57 extended from a hollow space 50 within a skid member 5 to front and rear faces of the skid member 5, a plurality of vent holes 57a extended from a hollow space 50 within the skid member 5 at an inclination to a top face of the skid member 5 and a scale exit hole 57b extended downward from the hollow space 50 to a side of the skid member 5.

This structure allows foreign materials to be efficiently discharged through the scale exit hole 57a out of the hollow space 50 so that hot gas can be more efficiently introduced through the vent holes 57 in addition to the operation and effect in Fig. 40.

Fig. 42 illustrates a skid apparatus according to another alternative embodiment of the invention. The skid apparatus of this embodiment comprises a. lateral vent hole 43 extended from an inner portion of a skid member 5 to a face thereof, a vertical vent hole 43a extended from the lateral vent hole 43 to a top face of the skid member 5 and a scale exit hole 43b extended downward from the vent holes 43 and 43a communicating with the vent holes 43 and 43a to a side of the skid member 5

to form a ventilation channel 7.

The holes are sized in the order of the scale exit hole 43b, the lateral vent hole 43 and the vertical vent hole 43a.

Preferably, the scale vent hole 43b may be flared downward in diameter.

This skid apparatus allows hot gas to efficiently circulate through the vent holes 43 and 43a and the scale exit hole 43b as well as to directly heat skit marks 160 of a hot material 110 seated on the skid member 5.

When the hot material is carried with the skid apparatus, vibration is created assisting foreign materials introduced into the holes 43,43a and 43b to be smoothly discharged through the scale exit hole 43b.

Fig. 43 illustrates an alternative to the skid apparatus shown in Fig. 42 according to the invention. The skid apparatus of this embodiment comprises a plurality of lateral vent holes 43 formed in a stationary rail-type skid member 5, vertical vent holes 43a extended from the lateral vent holes 43 to a top face of the skid member 5 and inclined scale exit holes 43b communicating with corresponding lateral and vertical vent holes 43 and 43a.

This skid apparatus allows foreign materials introduced into the holes 43,43a and 43b to be smoothly discharged through the scale exit hole 43b.

Fig. 44 illustrates a skid apparatus according to another alternative embodiment of the invention. The skid apparatus comprises a skid member 5 with an upper face for supporting a hot material 110, a blind vent hole formed within the skid member 5 at a predetermined size and a stopper 50a blocking an opening of the vent hole to define a hollow space 50 within the skid

member 5. This structure decreases the quantity of heat transferred from a hot material 110 to a coolant pipe 140 to reduce the temperature difference between a region of the hot material 110 contacting the top portion of the skid member 5 and other regions thereof which are not in contact with the skid member 5.

The hollow space 50 is defined within the skid member 5 of a uniform material by forming the blind vent hole horizontally within the skid member 5 and blocking the opening of the blind vent hole with the stopper 50a.

The stopper 50a is preferably of a cowl for example made of insulation material. This structure having the space in a central portion of the skid member 5 reduces the section modulus of the skid member 5 only to a small value thereby minimizing strength degradation compared to a conventional solid structure without the hollow space 50.

Fig. 45 illustrates another alternative embodiment of the invention having a discrete ventilation channel 7. That is, as shown in Figs. 45a and 45b, the vent holes 10 are extended into a skid member 5 from front and rear faces thereof but stopped in middle portions of the skid member 5 to form the discrete ventilation channel 7. However, this structure can also prevent temperature difference in a hot material 110 since the vent holes 10 effectively keep the heat of the skid member 5.

Furthermore, as shown in Figs. 45c and 45d, a ventilation channel 7 having a blind upper end is formed in a central portion of the skid member 5. The ventilation channel 7 has an downward portion which is extended downward at an inclination from a lateral portion of the ventilation channel 7.

This structure also effectively acts to reduce the

quantity of heat transferred to a coolant pipe 140 from the hot material 110 since hot gas circulates into the skid member through the ventilation channel 7.

Fig. 46 illustrates another alternative to the skid apparatus shown in Fig. 10 according to the invention. This skid apparatus comprises a lateral vent hole 17 extended through a skid member 5 and a combustion gas pipe 60 with a leading end extended into the lateral vent hole 17.

This structure feeds a small quantity of combustion gas through the combustion gas pipe 60 into the lateral vent hole 17 so that flame heats the skid member 5 through the lateral vent hole 17 to enable indirect heating of a hot material 110 via the skid member 5.

That is, the leading end of the combustion gas pipe 60 is extended into an end of the lateral vent hole 17 so that combustion gas is fed into the lateral vent hole 17 to perform direct and indirect heating through the skid member 5 to a portion of the hot material in contact with the skid member 5 while enhancing heating effect to above the skid member 5 via the vent hole.

Fig. 47 illustrates another alternative to the skid apparatus shown in Fig. 30 according to the invention. This skid apparatus comprises a horizontal lateral vent hole 17 extended through a skid member 5, a vertical vent hole 17a extended from the horizontal vent hole 17 to a top face of the skid member 5, a scale exit hole 17b which is extended downward from the lateral vent hole 17 to a side of the skid member 5 and a combustion gas pipe 60 with a leading end extended into the lateral vent hole 17.

This embodiment can effectively remove foreign materials

such as scale through the scale exit hole 17b out of the vertical vent hole 17a while realizing an excellent heating effect toward a skid mark 160 through the vertical vent hole 17a as in Fig.

30. Also a small quantity of combustion gas is fed through the combustion gas pipe 60 into the vertical vent hole 17a so that the skid mark 160 can be heated directly with flame through the vertical vent hole 17a or indirectly through the skid member 5.

The combustion gas pipe 60 may be extended into the scale exit hole 17b instead of the lateral vent hole 17 to obtain substantially equal effect.

Fig. 48 illustrates another alternative embodiment to the skid apparatus of the invention. This skid apparatus comprises a skid member 5, a hollow space 50 within the skid member 5, a lateral vent hole 17 extended from the hollow space 50 to front and rear faces of the skid member 5, a vertical vent hole 17a extended from the hollow space 50 to a top face of the skid member 5, a scale exit hole 17b extended from the hollow space 50 to a side of the skid member 5 and a combustion gas pipe 60 with a leading end extended into the lateral vent hole 17.

According to this structure, the hollow space 50 minimizes heat transfer from a hot material 110 toward a coolant pipe 140.

This embodiment can effectively remove foreign materials such as scale through the scale exit hole 17b out of the vertical vent hole 17a while realizing an excellent heating effect toward a skid mark 160 through the vertical vent hole 17a as in Fig.

30. Also a small quantity of combustion gas is fed through the combustion gas pipe 60 into the vertical vent hole 17a so that the skid mark 160 can be heated directly with flame through the vertical vent hole 17a or indirectly through the skid member

5.

Fig. 49 illustrates another alternative embodiment to the skid apparatus of the invention. This skid apparatus comprises a skid member 5, a hollow space 50 within the skid member 5, a lateral vent hole 10 extended from the hollow space 50 to front and rear faces of the skid member 5, at least one vent hole 10a extended from the hollow space 50 to a top face of the skid member 5 and a combustion gas pipe 60 with a leading end extended into the lateral vent hole 10.

According to this structure, the hollow space 50 minimizes heat transfer from a hot material 110 toward a coolant pipe 140.

The vent holes 10a enhance heating effect toward a skid upper portion 161 and allow direct heating of an underside contact region of the hot material 110 or indirect heating via the skid member 5.

Example 1 A conventional skid apparatus shown in Fig. 3 and a skid apparatus having a lateral vent hole 10 of the invention as shown in Fig. 6 were prepared in order to examine actual effects of the invention in association with temperature difference reduction in skid marks, and results were measured with a Solid Model analysis system.

In Example 1, an experimental reheating furnace was maintained at a temperature of about 1250 °C. Temperatures were measured at regions of a hot material, i. e. , slab 110 on the skid apparatus of the invention and the conventional skid apparatus for every 30 minutes to measure temperature differences between underside regions of the slab 110 in contact

with the skid members and central regions thereof not in contact with the same. Experiments were performed twice in the same manner to obtain results as reported in Table 1 below.

Table 1. Temperature Difference in Skid Marks Experiment 1 Experiment 2 Classifi (Temp. difference : C) (Temp. difference : C) cation Conv. Inv. Improvement Conv. Inv. Improvement 30 min 16 23 +7 12 20 +8 60 min 71 67 _4 63 56-6 90 min 90 82-8 55 46-9 120 min 52 43 _9 36 26-10 150 min 33 16-17 32 17-15 180 min 30 14-16 30 13-17 According to Table 1 above, the invention shows an improvement of about 15 to 17 C in the temperature difference between the contact region and the non-contact central region of the slab compared with the prior art after a lapse of 150 minutes in heating time because the slab 110 of a typical type requires a heating time for about at least 150 minutes. The distribution of the temperatures measured in Example 1 is shown in a graph of Fig. 50.

As can be seen from above, the temperature difference between the contact regions of the slab, i. e. , a region of the slab overlying the skid member 5 and the non-contact central region of the slab were maintained within about 20 C, preferably within about 18°C. Thus, the invention can prevent quality defects for example in the rolling thickness and width of the slab 110, which were observed in the prior art where the

temperature difference was beyond the above range.

Table 2 below quantitatively reports a percentile thickness and width within tolerances and deviations of rolling thickness and width of the hot rolled strip, which was produced with improvement in temperature difference according to the invention as above in comparison to those of the prior art.

Table 2. the percentile thickness and width within tolerances and Deviation of Rolling Thickness and Width Owing to Temperature Deviation of Skid Contact Regions Percentile thickness and Deviation (m, mm) Classification width within tolerances (%) Conv. Inv. Conv. Inv. Thickness (+50Am) 99.7 100.0 8.9 5.0 Width (0-10mm) 85.7 100.0 7.5 2.0 As afore described, the invention prevents excessive temperature difference associated with the skid upper portion 161, thereby improving the percentile thickness and width within tolerances and reducing their deviations.

Furthermore, the invention can drop the operating temperature of the reheating furnace which was raised in the prior art in order to prevent temperature difference at the skid mark 160 on the underside of the slab 110, thereby saving the cost of fuel consumed in the reheating furnace. The invention also can restrict creation of scales to improve the yield of rolled products.

Example 2 In Example 2, a burner was used to feed flame having a temperature of about 1450C into an experimental reheating furnace to maintain the temperature within the experimental reheating furnace at a temperature of about 1230 C. As shown in Fig. 51, a skid member of the invention was loaded into the reheating furnace together with a skid member of the prior art under same conditions. Then, temperatures were measured at regions of a slab (sample) on the skid member of the invention and the conventional skid member to obtain temperature differences between skid marks and other regions of the slab.

That is, after the skid member of the invention was mounted on one side of a skid pipe and the conventional skid member was mounted on the other side of the skid pipe, the slab was placed on both the skid member of the invention and the conventional skid member. Then, the slab was heated with the burner without moving the slab.

The slab used in Example 2 had dimensions of 115T X 400W X 900L, the skid members of the invention and the prior art had dimensions of 55W X 140L X 135H. The skid member of the invention had a laterally inclined channel structure as shown in Fig. 10, in which the circular ventilation channel had a diameter of about 20mm. That is, the ventilation channel 7 had the single lateral vent hole 17 extended at an inclination to front and rear faces of the skid member 5.

The skid pipe mounted with the skid members in Example 2 had outside diameter of about 170mm, inside diameter of about 130mm, thickness of about 20mm and castable thickness of about 75mm. Coolant of a room temperature was fed into the skid pipe.

Thermometers T/C were mounted on points #1 through #6, as shown in Fig. 51, to detect temperatures of these points.

The points #1, #3 and #5 designate three points distanced for 10mm from the underside of the slab. The points #2, #4 and #6 designate three points distanced for 60mm from the underside of the slab, that is, for 50mm from the top portion of the slab.

Also, the points #1 and #2 are placed right above the skid member of the prior art, the points #5 and #6 are placed right above the skid member of the invention, and the points #3 and #4 are in central sections (non-contact sections) which are not supported by any of the skid members.

Fig. 52 is a graph illustrating temperatures at the points #1, #3 and #5 with respect to time, and Fig. 53 is a graph illustrating temperatures at the points #2, #4 and #6 with respect to time.

Referring to Fig. 52, after a lapse of 8000 seconds, the point #1 at 10mm from the underside of the slab supported by the conventional skid member had a measured temperature of 1085 °C,' the point #3 at 10mm from the underside of the slab in the central section which was not supported by any of the skid members had a measured temperature of 1119 C, and the point &num 5 at 10mm from the underside of the slab supported by the skid member of the invention had a measured temperature of 1107 C.

This shows that the region of the slab supported by the skid member of the invention had a temperature difference of only 12 C from the central region of the slab, whereas the region of the slab supported by the conventional skid member had a temperature difference of 34 C from the central region of the slab. This result is similar to the effect of the skid member

of the invention which was observed in Example 1.

Further, referring to Fig. 53, after a lapse of 8000 seconds, the point #2 at 60mm from the underside of the slab supported by the conventional skid member had a measured temperature of 1104C, the point #4 at 60mm from the underside of the slab in the central section which was not supported by any of the skid members had a measured temperature of 1132°C, and the point #6 at 60mm from the underside of the slab supported by the skid member of the invention had a measured temperature of 1124C.

This shows that the contact region of the slab supported by the skid member of the invention had a temperature difference of only 8 C from the central region of the slab, whereas the region of the slab supported by the conventional skid member had a temperature difference of 28°C from the central region of the slab. This result shows that the invention can allow remarkably uniform heating to the slab over the prior art.

Fig. 54 illustrates temperature difference profiles produced by deducting temperatures at the three points 60mm above the underside of the slab from the temperatures at the three points 10mm above the underside of the slab right under the first three points when the slab was heated as above.

The profiles were obtained on basis of Figs. 52 and 53.

The temperature differences were large owing to heat transfer through contact between the skid members and the slab before a time lapse of about 1 hour (3600 seconds), whereas the temperature differences were steady after about 1 hour.

Measured values were obtained between 3600 to 8000 seconds.

The central section of the slab which was not supported

by any of the skid members had temperature differences of only about 12 to 13 C between the points #3 and #4, the slab supported by the conventional skid member had temperature differences of about 19 to 20 C between the points #1 and #2, and the slab supported by the skid member of the invention had temperature differences of about 16 to 18 C between the points #5 and #6.

The points #2, #4 and #6 had temperatures higher than those of the points #1, #3 and #5 because the burner is placed in an upper portion of the experimental reheating furnace, the slab (sample) is relatively thin, and heat is transferred from the top portion to the bottom of the slab. However, in an actual reheating furnace, the points #3 and #4 in the slab which were not supported by any of the skid members have substantially equal temperatures (e. g. , temperature differences of about 2 to 5C).

As can be seen from Example 2, the temperature differences between the points #5 and #6 in the slab section supported by the skid member of the invention further approach the temperature differences between points #3 and #4 in the slab section without any of the skid members compared with the temperature differences between the points #1 and #2 in the slab section supported by the conventional skid member. As a result, the invention achieves an effect of reducing the temperature differences for about 2 to 3C.

Reduction in the temperature differences as above means that the slab was heated uniformly so that the skid member of the invention has an excellent effect of heating the slab more uniformly than the skid member of the prior art.

Fig. 55 illustrates temperature differences between the points #5 and #1 at 10mm above the'underside of the slab and

between the points #6 and #2 at 60mm above the underside of the slab, in which the points #5 and #6 were supported by the skid member of the invention and the points #1 and #2 were supported by the skid member of the prior art.

The temperature differences were large owing to heat transfer through contact between the skid members 5 and the slab before a time lapse of about 1 hour (3600 seconds), whereas the temperature differences were steady after about 1 hour.

Measured values were obtained between 3600 to 8000 seconds, and resultant values were obtained from the temperature differences.

As can be seen from the above results, the temperatures at the points #5 and #6 supported by the skid member of the invention were higher than the temperatures at the points #1 and #2 supported by the conventional skid member so that the skid member of the invention can support the slab at more uniform temperatures. In particular, the effect of uniformly regulating the temperature was more prominent in the points #5 and #1 at 10mm above the underside of the slab than in the points #6 and #2 at 60mm above the underside of the slab.

Figs. 56 through 58 illustrate experimental results achieved with the alternative structures to the skid member of the invention.

Example 3 In'Example 3, an experimental reheating furnace same as that used in Example 2 was prepared. To carry out a series of experiments, the experimental reheating furnace was maintained at a temperature of about 1170 C and then raised to a temperature

of about 1285 C at a point Kl in Fig. 56. The skid member shown in Fig. 10 used in Example 2, was replaced by the skid member shown in Fig. 30. That is, the skid member comprises a vent hole 10 extended longitudinally through the skid member 5, a vertical vent hole 10a extended from the longitudinal vent hole 10 to a top face of the skid member 5 and a scale exit hole 10b extended downward from the holes 10 and 10a to a side of the skid member 5.

Temperatures of the slab (sample) in Example 3 are illustrated as a graph of temperature profiles at the points #1, #3 and #5 with respect to time in Fig. 56, and a graph of temperature profiles at the points #2, #4 and #6 with respect to time in Fig. 57.

Referring to Fig. 56, after a lapse of about 10500 seconds, the point #1 at 10mm from the underside of the slab supported by the conventional skid member had a measured temperature of 1103'C, the point #3 at 10mm from the underside of the slab in the central section which was not supported by any of the skid members had a measured temperature of 1157 C, and the point #5 at 10mm from the underside of the slab supported by the skid member of the invention had a measured temperature of 1150C.

Regarding the above graphs, it can be seen that the temperature difference between a non-contact region and the point of the slab supported by the skid member 5 of the invention (i. e. , the temperature at the point #3-the temperature at the point #5) was only 7°C.

The skid member of the invention used in Example 3 can further reduce the temperature difference for about 5 C over

the skid member of the invention used in Example 2 (i. e. , shown in Fig. 10) because atmospheric gas within the reheating furnace can directly heat the underside of the slab through the vertical vent hole lOa extended from the horizontal lateral vent hole 10 to the top face of the skid member.

Furthermore, in Fig. 56, in order to reach a temperature corresponding to the point Kl on the temperature profile of the point #5, the slab section supported by the conventional skid member is further heated for about 10 minutes (600 seconds) in order to reach a point K2 on the temperature profile of point #1 which has same temperature at point K1.

According to the skid member 5 of the invention as above, the slab can reach a desired temperature at a relatively small heat quantity compared with the conventional skid member.

Thus, the skid member 5 of the invention can lower a slab-heating temperature within a reheating furnace than the prior art thereby saving the fuel cost of the reheating furnace as well as to shorten a slab heating process for at least about 10 minutes thereby imparting a higher flexibility thereto.

Further, as in Fig. 57, after a lapse of about 10500 seconds, the point #2 at 60mm from the underside of the slab supported by the conventional skid member had a measured temperature of 1119C, the point #4 at 60mm from the underside of the slab in the central section which was not supported by any of the skid members had a measured temperature of 1157 C, and the point #6 at 10mm from the underside of the slab supported by the skid member of the invention had a measured temperature of 1156C.

This shows the temperature difference between the point #6 in the slab supported by the skid member 5 of the invention

and the point #4 in the slab is only 1C, whereas the temperature difference between the point #2 in the slab supported by the conventional skid member and the point #4 in the slab reaches 38 C. This result shows that the invention allows remarkably uniform heating to the slab over the prior art.

The skid member of the invention used in Example 3 can further reduce the temperature difference for about 7 C over the skid member of the invention used in Example 2 because the vertical vent hole 10a functions very effectively to directly heat the underside of the slab.

Furthermore, in Fig. 57, in order to reach a temperature corresponding to the point K3 on the temperature profile of the point #6, the slab section supported by the conventional skid member is further heated for about 8.5 minutes (510 seconds) in order to reach a point K4 on the temperature profile of point #2.

Fig. 58 illustrates temperature difference profiles produced by deducting temperatures at the three points 60mm above the underside of the slab from the temperatures at the three points 10mm above the underside of the slab right under the first three points when the slab was heated as above.

The profiles were obtained on basis of Figs. 56 and 57 in a fashion similar to Fig. 54. The temperature differences were large owing to heat transfer through contact between the skid members and the slab before a time lapse of about 1 hour (3600 seconds), whereas the temperature differences were steady between 3600 to 8000 seconds after a lapse of about 1 hour.

Referring Fig. 58, at a time point of elapsing 10000 seconds, the central section of the slab without contacting any

of the skid members had a small value of temperature difference between the points #3 and #4, the slab supported by the conventional skid member had a temperature difference of about 16°C between the points #1 and #2, and the slab supported by the skid member of the invention had temperature differences of about 6 C between the points #5 and #6.

As a result, the skid member used in Example 3 of the invention can reduce the temperature difference in a vertical direction with respect to the skid member for about 5°C compared with the skid member used in Example 2, and for about 7 C compared with the conventional skid member. Therefore, the skid member in Example 3 can reduce the vertical temperature difference of the slab thereby to improve rolling threading ability and steel plate configuration.

Fig. 59 illustrates temperature differences between the points #5 and #1 at 10mm above the underside of the slab and between the points #6 and #2 at 60mm above the underside of the slab, in which the points #5 and #6 were supported by the skid member of the invention and the points #1 and #2 were supported by the skid member of the prior art.

The temperature differences were large owing to heat transfer through contact between the skid members and the slab before a time lapse of about 1 hour (3600 seconds), whereas the temperature differences were steady after about 1 hour.

Measured values were obtained between 3600 to 10000 seconds, and resultant values were obtained from the temperature differences.

As can be seen from the above results, the temperatures at the points #5 and #6 supported by the skid member of the

invention were higher than the temperatures at the points #1 and #2 supported by the conventional skid member so that the skid member of the invention can support the slab at more uniform temperatures. In particular, the effect of uniformly regulating the heating temperature of the slab was more prominent in the points #5 and #1 at 10mm above the underside of the slab than in the points #6 and #2 at 60mm above the underside of the slab.

The skid member of the invention used in Example 3 is proved more excellent over the conventional skid member since the skid member of Example 3 regulates the heating temperature of the slab more uniformly. Furthermore, the skid member of Example 3 can achieve an effect of further raising the temperature in the contact region between the slab and the top portion of the skid member over the skid member of Example 2.

According to Examples 1 through 3 above, when applied to the actual reheating furnace, the invention had effects of reducing the temperature difference for about at least 50% compared with the conventional skid member while raising the temperature of the skid mark for about at least 10 C.

Example 4 In Example 4, computer simulation was performed to skid members 5 of the invention having a circular ventilation channel 7 and an elliptic ventilation channel 7 as shown in Figs. 60a through 60c, and results were reported in Table 3 below.

Fig. 60a illustrates a conventional skid member 150 as a comparative example, and Figs. 60b and 60c illustrate the skid members of the invention.

Both the skid members 5 had dimensions of 60W X 140L X 135H. The highest temperature of the conventional skid member 150, that is, the temperature at a top portion, thereof was set 1, 100 C as a reference value. The same force of 0. 29kg/mm2 as that of the prior art was applied to top portions of the skid members 5 of the invention.

The ventilation channels 7 were formed at 30mm from the top faces of the skid members 5 in Figs. 60b and 60c. The elliptic section was formed longitudinally, with a short diameter in a lateral direction and a long diameter in a vertical direction.

As a result of simulating stress distribution in the circular or elliptic ventilation channel, it was observed that stress was concentrated on the horizontal maximum diameter Zl.

Therefore, regarding the result in Example 2, simulation was performed to the temperature at the top portion of the skid member 5 of the invention, the maximum stress thereof and the temperature at the stress concentration point on the maximum diameter Z1 in reference to the set temperature of 1, 100C at the top portion of the conventional skid member, in which heat quantity introduced into the skid member shown in Fig. 10 and heat quantity discharged to the coolant pipe were fixed and the sectional area of the vent hole 7 was varied. Results in Table 3 below were obtained as relative temperature rise at the top portion of the skid member with respect to the variation of sectional area of the ventilation channel.

The computer simulation was performed according to following Equations 8 and 9, disclosed in"FORMULAS FOR STRESS, STRAIN, AND STRUCTURAL MATRICES", by Walter D. Pilkey, published by JOHN WILEY & SONS, INC. , in which Equation 8 is described

in page 272, and Equation 9 was described in page 278: max = CA = f07tioin = P l [t (D-d)] = 3. 000-3. 140 (d/D) + 3. 667 (d/D) 2 _ 1. 527 (d/D) 3 for 0 d/D-< 1.... Equation 8, and 6max-A-Kt rrom norn- ll-2b l D) 2 3 Ki = Cl + C2 (-) +C4 ( D D D 1. 0 < b/a < 8. 0 1. 0 b/a 8. 0 C1 1. 109-0. 188 la + 2. 086b/a C2-0. 486 + 0. 213 fla-2. 588b/a C3 3. 816-5. 510 bila + 4. 638b/a C4-2. 438 + 5. 485 fla-4. 126b/a ... Equation 9.

Table 3 Upper Stress Upper Stress Circle portion Stress point Ellipse portion Stress point temp. temp. temp. temp. Diam. C kg/mm2 C Ratio* °C kg/mm2 4 1100 0.87 854 4/8 1110 0.60 840 6 1110 0.88 849 6/12 1110 0.61 827 8 1110 0.88 844 8/16 1120 0.62 816 10 1120 0.89 840 10/20 1130 0.63 806 12 1130 0.91 837 12/24 1150 0.64 798 14 1140 0.93 835 14/28 1160 0.66 791 16 1160 0.95 833 16/32 1190 0.68 786 18 1170 0.97 833 18/36 1210 0.71 783 20 1190 1.00 835 20/40 1240 0.74 782 22 1210 1.04 837 22/44 1270 0.77 783 24 1230 1.08 841 24/48 1310 0.81 787 26 1260 1.13 847 26/52 1360 0.86 794 28 1290 1.18 854 28/56 1410 0. 92 804 Note: * means ratio of short diameter to long diameter

Fig. 61 is a graph for illustrating a temperature profile at the top portion of the skid member 5 of the invention with respect to the sectional area of the ventilation channel among values obtained as in Table 3.

It can be understood that highest temperatures of the skid members 5 rise in proportion to the increase of diameters of both the circular and elliptic ventilation channels 7. Further, the elliptic ventilation channel 7 can more readily raise the temperature of the skid member than the circular ventilation channel 7, thereby preventing local temperature drop of the slab.

This means that the temperature at the top portion of the skid member 5 can be adjusted via the ventilation channel 7 of the invention.

In Table 3 above, the temperature variation at the stress concentration point on diameter Z1 of the ventilation channel is not proportional to the size of the ventilation channel. Heat transfer from the slab to the coolant pipe is performed mainly through the width of the skid member excluding the sectional area of the ventilation channel. At a small diameter of the ventilation channel, the quantity of heat transfer tends to

increase to raise the temperature at the stress concentration point on diameter Z1. At a large diameter of the ventilation channel, the quantity of heat transfer decreases. Also, since the quantity of heat discharged from the lower portion of the skid member to the coolant pipe is substantially equal, the quantity of heat possessed by the lower portion of the skid member decreases. Thus, this influences the lower portion 164 of the skid member under the ventilation channel to lower the temperature at the stress concentration point on diameter Z1.

That is, since the ventilation channel 7 formed in the skid member blocks (or restrains) heat transfer from the upper portion 162 of the skid member to the coolant pipe, heat loss at the lower portion of the skid member is not sufficiently compensated.

However, where the diameter of the ventilation channel 7 reaches at least a predetermined value increasing the internal sectional area, a large quantity of heat introduction is made from hot gas introduced into the ventilation channel 7 to sufficiently compensate the heat loss of the lower portion 164 of the skid member. A residual quantity of introduced heat raises the temperature at the stress concentration point on diameter Z1 and compensates the heat loss of the upper portion 162 of the skid member to raise the temperature thereof.

Since the elliptic ventilation channel has an internal sectional area larger than that of the circular ventilation channel and is formed vertically, it can be understood that the elliptic ventilation channel more effectively contributes to dispersion of stress and smooth temperature distribution in a vertical direction of the skid member.

Since all the maximum stresses corresponding to the

temperatures at the stress points exist in a tolerable stress range of general material for skid member, the skid member 5 of the invention is structurally stable. It is also known that the maximum stress is varied according to variation in width of the skid member.

Example 5 In Example 5, computer simulation was performed to temperature variation in the regions of a slab contacting with skid members with respect to the position of ventilation channels in skid members.

Fig. 62a illustrates a conventional skid member as a comparative example, and Figs. 62b and 62c illustrate skid members of the invention.

Temperature differences were measured at skid marks and the slab (sample) in an arrangement as shown in Fig. 51 under equal conditions to the skid members of the invention and the conventional skid member. That is, each of the skid members of the invention was mounted on one of the skid pipes and the conventional skid member was mounted on another one of the skid pipes, and then the slab was seated on the skid members without movement, in which only radiant heat transfer was considered.

In Example 5, the reheating furnace had an atmospheric temperature of about 1250°C, and the slab had a temperature of about 1150°C. The slab was sized of 200T X 400W X 900L. The skid member of the invention in Fig. 62b was sized of 55W X 140L X 135H, in which a circular ventilation channel having a diameter of 25mm was formed at 15mm from the top face of the skid member.

In Example 5, the skid pipes mounted with the skid members

had outside diameter of 170mm, inside diameter of 130mm, thickness of 20mm and castable thickness of 75mm. Coolant of a room temperature was fed into the skid pipe.

Thermometers T/C were mounted on points #1 through #6, as shown in Fig. 51, to detect temperatures of these points.

The points #1, #3 and #5 designate three points distanced for 40mm from the underside of the slab. The points #2, #4 and #6 designate three points distanced for 100mm from the underside of the slab, that is, for 100mm from the top face of the slab.

Also, the points #1 and #2 are placed right above the skid member of the prior art (refer to Fig. 62a), the points #5 and #6 are placed right above the skid member of the invention (refer to Fig. 62b), and the points #3 and #4 are in central sections (non-contact sections) which are not supported by any of the skid members.

Fig. 63 is a graph of temperature profiles illustrating temperature differences between the points #3 and #1, the points #3 and #5, the points #4 and #2 and the points #4 and #6 with respect to time.

This shows that the temperature differences between the points #3 and #5 and between the points #4 and &num 6 are remarkably smaller than those between the points #3 and #1 and between the points #4 and #2, in which the points #5 and #6 are supported by the skid member of the invention, the points #3 and #4 are not supported by any of the skid members and the points #1 and #2 are supported the conventional skid member. It can be understood that the skid member of the invention has an effect of reducing the temperature difference more excellent than that of the conventional skid member.

Further,. the ventilation channel shown in Fig. 62c was

arranged in a lower portion of the skid member, in particular, the cylindrical ventilation channel having a diameter of 25mm was formed at 40mm from the bottom of the skid member.

In Fig. 64, a graph of temperature profiles illustrates temperature differences between the points #3 and #1, the points #3 and #5, the points #4 and #2 and the points #4 and #6 with respect to time.

This shows that the temperature differences between the points #3 and #5 and between the points #4 and #6 are remarkably smaller than those between the points #3 and #1 and between the points #4 and #2, in which the points #5 and #6 are supported by the skid member of the invention, the points #3 and #4 are not supported by any of the skid members and the points #1 and #2 are supported the conventional skid member. It can be understood that the skid member of the invention has an effect of reducing the temperature difference more excellent than that of the conventional skid member.

As shown in Fig. 64, where the top portion of the ventilation channel was formed at 40mm from the bottom of the skid member, the temperature difference between the points #3 and #1 obtained with the conventional skid member was about 48 C, but the temperature difference between the points #3 and #5 obtained with the skid member of the invention was about 42 C.

This shows that the invention achieved improvement in temperature for about 6C.

Even though this skid member achieved an effect of temperature improvement for about 6°C, it can be seen that this skid member was degraded in heat compensation compared with the structure as shown in Fig. 63, that the ventilation channel was

formed in the upper portion of the skid member.

From results of Figs. 63 and 64, it can be understood that the skid member achieves more excellent heating effect as the ventilation channel is formed higher in the skid member.

Further, it is preferred that the top portion of the ventilation channel is placed at 40mm or higher from the top portion of the skid cooling means.

While this invention has been described in connection with the various embodiments in the specification of the invention, the invention is not limited or restricted to the foregoing vent hole structures. It is also understood that the foregoing structures are disclosed for illustrative purposes only for describing the invention in detail but various modifications and variations can be made without departing from the scope of the invention. For example, the vent holes may be in the form of triangle, quadrangle, hexagon, octagon, polygon and ellipse, or varied in numbers. Also, radiator fins can-be formed in inner peripheries of the vent holes in order to increase the surface area of the vent holes.

While the skid members 5 are illustrated to have the ventilation channels 7 extended from the front face to the rear face, to the top face or diagonally, the invention is not limited thereto. The vent hole may have an L-shaped section extended to an adjacent side of the skid member. Furthermore, the vent hole may be curved rather than linear. Such variations may be made readily from the spirit of the invention.

Therefore, these various modifications and variations can be apparently made from the disclosure of the invention without departing from the spirit and scope of the invention.

Industrial Applicability According to the invention as set forth above, the temperature difference associated with the skid mark can be reduced through simple improvement to the structure of the skid member 5 so that hot material 110 can be heated at a uniform temperature so as to save excessive cost consumed for improving the skid apparatus or eliminate necessity for additional maintenance. Furthermore, the invention achieves an effect, which allows the rolling quality of the hot material such as the hot rolling threading ability, size and configuration of the hot rolled strip or plate to be improved in subsequent processes.

The invention forms the ventilation channel 7 while maintaining the contour of the skid member 5 so that the skid member 5 can receive heat from hot gas within the reheating furnace during introduction of hot gas into the same to reduce the quantity of heat transfer toward the coolant pipe 140 as well as compensate heat, thereby effectively preventing the temperature difference associated with the skid upper portion 161.

Since the reheating furnace is not heated excessively and thus the slab or hot material is not overheated, creation of excessive scale is restricted to minimize descaling, thereby raising the yield of rolling while saving production cost.

Moreover, the invention may feed a small quantity of combustion gas through the combustion gas pipe 60 arranged adjacent to the vent hole or the scale exit hole of the skid member so that flame directly heats the skid mark 160 of the hot material 110 through the vertical vent hole or indirectly heats the hot material 110 through the skid member 5 so as to minimize the temperature difference between the hot material and the skid mark.