Description

APPARATUS FOR FORMING CIRCLE SHAPE OF THICK STEEL PLATE FOR MAKING PIPE AND METHOD THEREOF

Technical Field

[1] The present invention relates, in general, to apparatuses and methods for forming thick steel plates into rolled shapes for making pipes having relatively large diameters and, more particularly, to an apparatus and a method for forming a thick steel plate into a rolled shape in which one side of the thick steel plate from an edge to a medial portion is formed into an arc shape by rolling and pressing and, thereafter, the other side of the thick steel plate from an opposite edge to the medial portion is formed into an arc shape, thus forming the thick steel plate into a rolled shape having a circular cross section. Background Art

[2] Generally, methods for manufacturing pipes using steel plates are classified depending on whether the steel plates are thin steel plates or thick steel plates. In the case of the thin steel plates, methods for manufacturing pipes are classified into a spiral forming method, in which a steel band, which does not require a particularly large force to bend it, is wound into a spiral shape with a predetermined lead and, thereafter, a spiral junction is processed by welding, and a rolling method, in which a process of passing a thin steel plate between three rollers, which are disposed in a triangular arrangement when viewed in a side view and which rotate in predetermined directions, is repeated several times, so that the thin steel plate is formed into a rolled shape having a circular cross section, and, thereafter, the rolled shaped structure is welded while being held by a shaping die or jig such that it maintains a perfectly circular cross-sectioned shape.

[3] However, in the case of the rolling method, because pressing force is relatively weak, only steel plates having thicknesses of several mm or less can be processed. As such, because the thickness of a steel plate to be processed is limited to a predetermined range, productivity and workability are reduced. Particularly, due to structural characteristics of a mechanical frame for supporting the rollers, the lengths of the rollers are limited. Therefore, the rolling method is inefficient and thus unsuitable for manufacturing a pipe required in the construction of a relatively long pipeline.

[4] In the case of the spiral forming method, because a continuous process is possible, whereby it is easily adapted to mass production, unlike the rolling method, there is an advantage in that the cost of manufacturing pipes is reduced. However, the thickness

range of the wall of a pipe, within which this forming process can be conducted, is limited to several mm or less, as in the rolling method.

[5] Meanwhile, in methods for manufacturing pipes using thick steel plates, a method using a press and a UO forming method have been well known. In the case of the method using the press, as shown in FIG. 1, a rectangular steel plate 100, which has a width corresponding to the circumference of a pipe to be formed and has a length corresponding to the length of the pipe, is provided, and a plurality of marks 101, which section the width of the steel plate 100, corresponding to the circumference of the pipe to be formed, into regular intervals, is provided on an edge of the steel plate 100. Thereafter, a portion of the steel plate 100 corresponding to each mark 101 is pressed by a pressing head in sequence from an edge thereof to the central line thereof, so that half of the steel plate 100, from an edge thereof to the central line thereof, is formed into a rolled shape having a curvature corresponding to the radius of the pipe to be formed. Subsequently, every marked portion of the other half of the steel plate 100 is pressed by the pressing head moving from the opposite edge to the central line. Thus, a pipe medium 103, which is open at one side, is obtained. Thereafter, the pipe medium 103 is welded while being held by a shaping die or jig such that it maintains a perfectly circular cross-sectioned shape, thus obtaining the pipe.

[6] In the UO forming method, as shown in FIG. 2, a rectangular steel plate 100, which has a width corresponding to the circumference of the pipe to be formed and has a length corresponding to the length of the pipe, is provided. Thereafter, opposite edges of the steel plate 100, between which the circumference of the pipe is defined, are bent upwards at predetermined angles or are formed into arc shapes, thus forming shaped edge regions 104. Thereafter, the steel plate 100 is formed into a U shape using a U shape forming die, thus forming a semicircular cross section part 105. The structure manufactured through the above-mentioned processes is formed into a rolled shape having a circular cross section using an O shape forming die, thus obtaining a pipe medium 103. Subsequently, the pipe medium 103 is welded while being held by a shaping die or jig such that it maintains a perfectly circular cross-sectioned shape, thus obtaining the pipe. Disclosure of Invention Technical Problem

[7] In the method using the press, because the consecutive forming operation is conducted by pressing every portion of the steel plate 100 corresponding to each mark 101 using the pressing head, the processing speed of the work is slow. Furthermore, because the equipment used in this method is large and heavy, there is a problem in that it is very difficult to move the equipment.

[8] In the UO forming method, the processes of forming the steel plate into a U shape and an O shape must be conducted using dies. Hence, several dies are required to provide various diameters of pipes to be formed. As a result, equipment becomes large and heavy, so that it is very difficult to move the equipment. Technical Solution

[9] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus which includes a slider, which is provided on a support base so as to be movable in a lateral direction, a movable base, which vertically moves on the slider, two support rollers, which are reversibly rotated on the movable base and the distance between which is adjustable, and a pressing head, which is placed above the medial portion between the two rollers so as to be movable in a lateral direction and presses a thick steel plate downwards, thus having the advantages of the conventional rolling method and pressing method, thereby easily forming the thick steel plate into a rolled shape for making a pipe, and a method of forming the thick steel plate into the rolled shape using the apparatus.

[10] In other words, an object of the present invention is to provide an apparatus and method in which, after a first edge region of the thick steel plate is placed on the two support rollers, the thick steel plate is formed into an arc shape from the first edge region to the medial portion thereof, and, thereafter, the thick steel plate is moved, or the slider, the movable base, the support rollers and the pressing head are moved while the upper and lower surfaces of the thick steel plate are supported, so that a second edge region of the thick steel plate is placed on the two support rollers, and, subsequently, the thick steel plate is formed into an arc shape from the second edge region to the medial portion thereof, thus easily forming the thick steel plate into a rolled shape having a circular cross section.

Advantageous Effects

[11] As described above, in an apparatus and a method for forming a thick steel plate into a rolled shape for making a pipe according to the present invention, a slider is provided on a support base so as to be movable in a lateral direction, and a movable base vertically moves on the slider. Furthermore, two support rollers are reversibly rotated on the movable base and the distance between them is adjustable, and a pressing head is placed above the medial portion between the two rollers so as to be movable in a lateral direction and presses a thick steel plate downwards. Thus, after a first edge region of the thick steel plate is placed on the two support rollers, the thick steel plate is formed into an arc shape from the first edge region to the medial portion thereof. Thereafter, the thick steel plate is moved, or the slider, the movable base, the

support rollers and the pressing head are moved while the upper and lower surfaces of the thick steel plate are supported. Subsequently, a second edge region of the thick steel plate is placed on the two support rollers, and the thick steel plate is formed into an arc shape from the second edge region to the medial portion thereof. As such, the present invention incorporates the advantages of the conventional rolling method and pressing method and makes it possible to easily form the thick steel plate into a rolled shape having a circular cross section using the advantages. Brief Description of the Drawings

[12] FIGS. 1 and 2 are views schematically showing processes of forming thick steel plates into rolled shapes for making pipes according to conventional methods;

[13] FIG. 3 is a front view schematically showing an apparatus for forming a thick steel plate into a rolled shape for making a pipe, according to the present invention;

[14] FIG. 4 is a sectional view showing a lower forming unit of the apparatus according to the present invention;

[15] FIG. 5 is a sectional view showing another embodiment of the lower forming unit of the present invention;

[16] FIGS. 6 and 7 are views showing a support roller of the lower forming unit of FIG.

4;

[17] FIG. 8 is a sectional view showing an upper forming unit of the apparatus according to the present invention;

[18] FIG. 9 is a sectional view showing an actuating means of the upper forming unit of

FIG. 8;

[19] FIG. 10 is a perspective view showing another embodiment of the upper forming unit of the present invention; and

[20] FIGS. 11 through 18 are views illustrating a process for forming a thick steel plate into a rolled shape for making a pipe using the rolled thick steel plate forming apparatus according to the present invention. Best Mode for Carrying Out the Invention

[21] In order to accomplish the above objects, the present invention provides an apparatus for forming a thick steel plate into a rolled shape, including: a lower forming unit having a support base provided on a bottom of a frame, and two support rollers provided on the support base at opposite sides; and an upper forming unit provided in the frame above the lower forming unit and having a pressing head provided so as to be vertically movable by an actuator. The apparatus further includes a rotation drive means for reversibly rotating the support rollers in place; and a vertical and lateral motion drive unit to move the support rollers in vertical and lateral directions.

[22] The vertical and lateral motion drive unit for the support rollers includes a slider

provided on the support base so as to be movable in a lateral direction, a first screw shaft rotatably coupled through the slider to move the slider in the lateral direction, a first screw drive motor coupled to an end of the first screw shaft to reversibly rotate the first screw shaft, and a movable base provided on the slider so as to be vertically movable by an actuator.

[23] Furthermore, a die may be provided between the support rollers. As such, in the case that the die is provided, the lowermost position of the pressing head is limited by the die, so that the curvature radius of the thick steel plate can be set at a predetermined value, thus more precisely forming a pipe having a circular cross section.

[24] As well, an oil supply passage is formed in the support base or in the slider to supply oil to the interface between the support base and the slider, thus forming an oil film at the interface between the support base and the slider, thereby minimizing friction therebetween.

[25] The upper forming unit is movable along a guide rail at an upper position in the frame in a lateral direction by a lateral motion drive unit, in the same manner as that of the slider. The lateral motion drive unit includes a second screw shaft, which is rotatably coupled through the upper forming unit, and first and second screw drive motors, which are coupled to an end of the second screw shaft and reversibly rotates the second screw shaft.

[26] The pressing head of the upper forming unit may be removably coupled to a head body using a coupling member such that the pressing head can be removed from the head body and replaced with a new one depending on the object to be formed.

[27] Preferably, the upper forming unit and the lower forming unit may be provided in the frame having a tunnel shape without protruding outside the frame. Then, several apparatuses may be continuously coupled to each other to accommodate the length of a steel plate to be shaped. As such, because each apparatus comprises one individual unit, the apparatus of the present invention can be relatively easily transported and installed, compared to the conventional apparatus, which is large heavy equipment.

[28] In another aspect, the present invention provides a method for forming a thick steel plate into a rolled shape, including: a first step of supplying the thick steel plate such that a first edge region of the thick steel plate to be formed into the rolled shape is placed on two support rollers, and manipulating a pressing head such that the pressing head presses the first edge region of the thick steel downwards using weight thereof at a central position between the support rollers; a second step of pressing the first edge region of the thick steel plate by moving the two support rollers upwards or by moving the pressing head downwards, thus shaping the first edge region of the thick steel plate to have a predetermined curvature radius; a third step of moving the thick steel plate by a predetermined pitch between the support rollers and the pressing head by rotating the

support rollers or the pressing head while the thick steel plate is supported and pressed only by the weight of the pressing head through manipulation of the support rollers or the pressing head after the first edge region of the thick steel plate is shaped at the second step; a fourth step of forming the first edge region of the thick steel plate into a semicircular rolled shape by repeating a process of pressing and shaping part of the first edge region of the thick steel plate to have the predetermined curvature radius by moving the two support rollers upwards or by moving the pressing head downwards after the thick steel plate is moved by one pitch at the third step, and of stopping the pressing and forming process when the first edge region of the thick steel plate approaches a head body; a fifth step of placing an unshaped second edge region of the thick steel plate on the support rollers by rotating the support rollers or the pressing head while the portion of the thick steel plate shaped in the fourth step is supported and pressed only by the weight of the pressing head; a sixth step of shaping a remaining unshaped part of the thick steel plate to have the predetermined curvature radius by consecutively conducting the second, third and fourth steps, thus obtaining a pipe medium, which is a semi-finished product and has a circular cross-section that is open at one side (an upper side) thereof; and a seventh step of lifting the pressing head along with the pipe medium to a predetermined height from the support rollers, of removing the pipe medium from the pressing head, and of carrying the pipe medium to a subsequent process.

[29] In the method for forming the thick steel plate into the rolled shape according to the present invention, at the fifth step, when the second edge region of the thick steel plate is moved towards the support rollers after the first edge region of the thick steel plate is shaped, while the support rollers and the pressing head are moved, the support rollers and the pressing head may be rotated at speeds corresponding to movement speeds thereof such that the thick steel plate remains in place.

[30] In the method for forming the thick steel plate into the rolled shape according to the present invention, at each step, when the thick steel plate is shaped to have the predetermined curvature radius, the thick steel plate may be pressed and shaped by both the support rollers and the pressing head press at the same time, rather than by one selected from the support rollers and the pressing head. Mode for the Invention

[31] Hereinafter, an apparatus for forming a thick steel plate into a rolled shape according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[32] FIG. 3 is a front view schematically showing the apparatus for forming the thick steel plate into the rolled shape for making the pipe according to the present invention.

FIGS. 4 through 10 are views illustrating upper and lower forming units of the rolled thick steel plate forming apparatus of the present invention.

[33] As shown in the drawings, a frame 10 is provided in a rectangular tunnel shape, having inclined upper corners opposite each other. A support base 12, which has a planar upper surface, is provided on the bottom of the frame 10. A slider 20 is provided on the support base 12 so as to be movable in a lateral direction. A movable base 30 is provided on the slider 20 so as to be vertically movable by an actuator 23. Here, the slider 20 and the movable base 30 must be respectively movable in lateral and vertical directions without being rotated.

[34] Furthermore, an oil supply passage 21, through which oil is supplied from an oil pump of a hydraulic system 40, is horizontally formed at a lower position in the slider 20. A plurality of oil discharge passages 22 vertically extends from the oil supply passage 21 to a lower surface of the slider 20, so that oil is supplied to an interface between the support base 12 and the slider 20. Thanks to the supply of oil to the interface between the support base 12 and the slider 20, an oil film is formed between the support base 12 and the slider 20, thus minimizing friction therebetween, thereby ensuring smooth movement of the slider 20.

[35] The hydraulic system 40 must be controllable and be connected to the oil supply passage 21 of the slider 20, a fluid passage 23c of the actuator 23, which is provided on the slider 20, and a fluid passage 63c of an actuator 63, which is provided in an upper forming unit 60, such that oil can be supplied to them at appropriate pressure.

[36] Furthermore, in the present invention, a lateral motion drive unit for moving the slider 20 in a lateral direction is provided. The lateral motion drive unit includes a first screw shaft 24, which is coupled through the slider 20 so as to be rotatable with respect to the slider 20, and a first screw drive motor 25, which is coupled to an end of the first screw shaft 24 to reversibly rotate the first screw shaft 24.

[37] As well, a guide (not shown), which guides the slider 20 such that the slider 20 is prevented from undesirably moving when it is moved in a lateral direction, may be provided on the slider 20 or the support base 12, or on both the slider 20 and the support base 12.

[38] As shown in FIG. 4, the actuator 23, which vertically moves the movable base 30, includes a piston 23 a, which extends a predetermined length downwards from a lower surface of the movable base 30, a piston hole 23b, which is formed in the slider 20 and into which the piston 23a is inserted, and the fluid passage 23c, which is formed in the slider 20 at the lower end of the piston hole 23b.

[39] The movable base 30 has sidewalls 31 at opposite side ends thereof. The lower forming unit 50 is provided between the sidewalls 31 of the movable base 30. The lower forming unit 50 includes two support rollers 52a and 52b, which are provided at

a medial portion between the sidewalls 31 and spaced apart from each other by a predetermined distance, a spacer 56, which supports each support roller 52a, 52b, and a screw 57, which pushes or pulls each spacer 56.

[40] It is preferable that the distance between the support rollers 52a and 52b be adjustable depending on the diameter of the pipe to be formed. For example, when the diameter of the pipe is relatively small, the distance between the support rollers 52a and 52b must be reduced, and, when the diameter of the pipe to be formed is relatively large, the distance between the support rollers 52a and 52b must be increased.

[41] Particularly, regardless of the distance between the support rollers 52a and 52b, the curvature radius of the thick steel plate may be controlled by adjusting the position of a pressing head 65, which is provided above the medial position between the support rollers 52a and 52b, so that the thick steel plate can be formed into a pipe having various diameters.

[42] As shown in FIG. 5, a die 51 may be provided at a medial position between the support rollers 52a and 52b. As such, in the case that the die 5_1 is provided, the lowermost position of the pressing head 65 is limited by the die 58, so that the curvature radius of the thick steel plate can be set at a predetermined value.

[43] For convenience of work, a rotation drive means, which rotates each support roller

52a, 52b, is provided on opposite ends of each support roller 52a, 52b. As shown in FIGS. 6 and 7, the rotation drive means includes a roller housing 53, which is provided on each of opposite ends of each roller 52a, 52b, a plurality of rotation prevention protrusions 54, which are provided on each roller housing 53 to prevent the roller housing 53 from rotating when the support roller 52a, 52b is rotated, and a reversible roller drive motor 55, which is provided on one roller housing 53 of each support roller 52a, 52b and is coupled to the support roller 52a, 52b to rotate the support roller 52a, 52b about its own axis.

[44] In this embodiment, the rotation drive means, which rotates each support roller 52a,

52b, is provided on the ends of each support roller 52a, 52b. However, in place of the rotation drive means, a separate carrying means, which moves the thick steel plate in increments of a predetermined pitch, may be provided on each support roller 52a, 52b.

[45] The spacer 56 is placed between each sidewall 31 of the movable base 30 and each support roller 52a, 52b. In the case that the distance between the support rollers 52a and 52b is relatively short, because the distance between each sidewall 31 and each support roller 52a, 52b is increased, another spacer having a thickness corresponding to the increased distance is inserted therebetween. Conversely, in the case that the distance between the support rollers 52a and 52b is relatively short, remaining spacers, other than the spacer that is in contact with each support roller 52a, 52b, are removed.

[46] Meanwhile, two guide rails 14, which are parallel to each other, are provided above

the lower forming unit 50 in the frame 10. The upper forming unit 60 is provided on the guide rails 14 so as to be movable in a lateral direction. The upper forming unit 60 includes an upper body 61, which is suspended on the guide rails 14 through moving rollers 62 so as to be movable in a lateral direction, and a head body 64, which has a pressing head 65 and is coupled to the upper body 61 so as to be vertically movable using the actuator 63. A piston 63a is provided on an upper end of the head body 64. A piston hole 63b, which receives the piston 63a therein, is formed in a lower end of the upper body 61. The fluid passage 63c, through which oil is supplied from the hydraulic system 40, is formed in the upper body 61 at each of upper and lower positions of the piston hole 63b.

[47] Furthermore, the upper forming unit 60 includes a lateral motion drive unit, which moves the upper forming unit 60 in a lateral direction, in the same manner as that of the slider 20. As shown in FIGS. 8 and 9, the lateral motion drive unit of the upper forming unit 60 includes a second screw shaft 66, which is coupled through the upper body 61 so as to be rotatable with respect to the upper body 61, and a second screw drive motor 67, which is coupled to an end of the second screw shaft 66 to reversibly rotate the second screw shaft 66.

[48] As shown in FIG. 10, it is preferable that the pressing head 65 of the upper forming unit 60 be removably coupled to the head body 64 so that the pressing head 65 can be replaced with another one, depending on the object to be formed, after it is removed from the head body 64. For example, when it is desired to bend a thick steel plate, which has been formed into a rolled shape by the pressing head comprising a roller, as shown in the above drawing, to form angle steel to be used as a pillar of a steel-frame structure, the pressing head comprising the roller must be able to be replaced with a bending blade type pressing head appropriate to the above process.

[49] Preferably, the upper forming unit 50 and the lower forming unit 60 are placed in the frame 10 such that they do not protrude outside the frame 10 in the direction of the center line between the support rollers 52a and 52b. Then, several apparatuses of the present invention can be continuously coupled to each other to extend the length to accommodate the length of the thick steel plate to be formed. As such, because each apparatus comprises one individual unit, the apparatus of the present invention can be relatively easily transported and installed, compared to the conventional apparatus, which is large heavy equipment.

[50] A method of forming a thick steel plate into a rolled shape using the rolled thick steel plate forming apparatus having the above-mentioned construction will be explained in detail herein below. First, in consideration of the thickness of the thick steel plate 100, the distance between the support rollers 52a and 52b is adjusted to be appropriate to the diameter of the pipe to be formed. Preferably, the distance between

the support rollers 52a and 52b is adjusted in the smallest possible increments. In the present invention, the distance between the support rollers 52a and 52b is appropriately adjusted by increasing or reducing the number of spacers 56, which are placed between each sidewall 31 of the movable base 30 and each support roller 52a, 52b.

[51] In this state, as shown in FIG. 11, the thick steel plate 100 to be formed into a rolled shape is supplied such that a first edge thereof is placed on the two support rollers 52a and 52b. Thereafter, the actuator 63 of the upper forming unit 60 is manipulated such that the thick steel plate 100 is pushed downwards at a medial position between the support rollers 52a and 52b by the weight of the pressing head 65 constituting the upper forming unit 60.

[52] Here, both the actuator 23 of the slider 20 and the actuator 63 of the upper forming unit 60 are operated. In detail, the pistons 23a and 63a protrude because oil is supplied into the piston holes 23b and 63b at high pressures by the hydraulic system 40, so that the movable base 30 is moved upwards and, simultaneously, the pressing head 65 is moved downwards. Therefore, the thick steel plate 100 is formed into a downward convex shape by the support rollers 52a and 52b and the pressing head 65, as shown in FIG. 12. At this time, the curvature radius of the thick steel plate 100 is determined depending on the degree of overlap between the pressing head 65 and the support rollers 52a and 52b.

[53] Although a process of pressing and forming the thick steel plate 100 has been described as being conducted by simultaneously operating the movable base 30 and the pressing head 65 in opposite directions, the thick steel plate 100 may be pressed and formed by moving only the movable base 30 or by moving only the pressing head 65.

[54] After part of the thick steel plate 100 has been bent through the above-mentioned process, the actuators 23 and 63 of the slider 20 and the upper forming unit 60 are operated to move the movable base 30 slightly downwards or to move the upper forming unit 60 slightly upwards, so that the pressing head 65 maintains the state of smoothly pressing and supporting the thick steel plate 100 using only the weight of the pressing head 65.

[55] In this state, the reversible roller drive motors 55 of the support rollers 52a and 52b are operated for a time. Then, the support rollers 52a and 52b are rotated in counterclockwise directions, so that the thick steel plate 100, which is undergoing the forming process, is moved by a predetermined pitch between the pressing head 65 and the support rollers 52a and 52b, as shown in FIG. 13. Here, one pitch means the distance between a position at which the pressing head 65 presses the thick steel plate 100 downwards and a subsequent position at which the pressing head 65 presses the thick steel plate 100 downwards.

[56] As such, after the thick steel plate 100 has been moved by one pitch, the actuators

23 and 62 of the slider 20 and the upper forming unit 60 are again operated, as illustrated in FIG. 12, such that the movable base 30 is moved upwards and, simultaneously, the pressing head 65 is moved downwards, thus forming the thick steel plate 100 at a predetermined curvature radius. By repeating this operation, the thick steel plate 100 is bent at a predetermined curvature radius. When the first edge of the thick steel plate 100 reaches a position adjacent to the pressing head 65, as shown in FIG. 14, the above-mentioned repeated operation is stopped.

[57] Subsequently, the actuators 23 and 63 of the slider 20 and the upper forming unit 60 are operated such that the pressing head 65 maintains the state of smoothly pressing and supporting the thick steel plate 100 using only the weight of the pressing head 65. In this state, the movable base 30 is moved to the left and, simultaneously, the support rollers 52a and 52b provided on the movable base 30 are rotated in counterclockwise directions, such that the thick steel plate 100 remains in place without moving. Then, the movable base 30 and the support rollers 52a and 52b are moved towards a second edge region of the thick steel plate 100 which is not yet shaped. Furthermore, movement of the movable base 30 and the support rollers 52a and 52b stops when the second edge region of the thick steel plate 100, which is not yet shaped, is disposed on the support rollers 52a and 52b, as shown in FIG. 15.

[58] In a detailed description of the process of moving the movable base 30 while the thick steel plate 100 remains in place, the first screw shaft 24 is rotated by the operation of the first screw drive motor 25, so that the slider 20 is moved along with the movable base 30. Simultaneously, the support rollers 52a and 52b are rotated by the operation of the reversible roller drive motor 55, such that the thick steel plate 100 moves with respect to the slider 20 at a speed corresponding to the moving speed of the slider 20.

[59] In other words, in the same state as that when the thick steel plate is processed at the initial stage, the second edge region of the thick steel plate 100, which is not yet shaped, is placed on the support rollers 52a and 52b, and the medial portion of the thick steel plate 100 is pushed only by the weight of the pressing head 65 of the upper forming unit 60.

[60] In this state, the actuators 23 and 63 of the slider 20 and the upper forming unit 60 are operated such that the movable base 30 is moved upwards and, simultaneously, the pressing head 65 is moved downwards. Then, the thick steel plate 100 is pressed and formed into a downwards convex shape by the support rollers 52a and 52b and the pressing head 65, as shown in FIG. 16. At this time, the curvature radius of the thick steel plate 100 is determined depending on the degree of overlap between the pressing head 65 and the support rollers 52a and 52b.

[61] As such, after part of the thick steel plate 100 has been bent through the above-

mentioned process, the actuators 23 and 63 of the slider 20 and the upper forming unit 60 are operated to move the movable base 30 slightly downwards or to move the upper forming unit 60 slightly upwards, so that the pressing head 65 maintains the state of smoothly pressing and supporting the thick steel plate 100 using only the weight of the pressing head 65.

[62] In this state, the reversible roller drive motors 55 of the support rollers 52a and 52b are operated for a time. Then, the support rollers 52a and 52b are rotated in counterclockwise directions, so that the thick steel plate 100, which is undergoing the forming process, is moved by a predetermined pitch between the pressing head 65 and the support rollers 52a and 52b, as shown in FIG. 17.

[63] As such, after the thick steel plate 100 has been moved by one pitch, the actuators

23 and 62 of the slider 20 and the upper forming unit 60 are again operated, as illustrated in FIG. 16, such that the movable base 30 is moved upwards and, simultaneously, the pressing head 65 is moved downwards, thus forming the thick steel plate 100 to have a predetermined curvature radius.

[64] By repeating this operation, the second edge region of the thick steel plate 100 is also shaped to have a predetermined curvature radius. Ss shown in FIG. 18, when the second edge of the thick steel plate 100 is placed adjacent to the head body 64, the operation is stopped. As a result, the cross-section of the thick steel plate 100 is formed into a circle shape, which is open at one side (an upper side) thereof.

[65] After the process of forming the thick steel plate 100 into a structure that is open at one side thereof has been completed, the movable base 30 is moved downwards by the actuator 23 of the slider 20, and the pressing head 65 is moved upwards by the actuator 63 of the upper forming unit 60. Thereafter, a pipe medium 103, which is a semifinished product and has a circular cross-section that is open at one side thereof, is pushed and extracted in a longitudinal direction thereof before being carried to a subsequent process. That is, the opposite edges of the pipe medium 103 are brought into contact with each other using a jig and, simultaneously, the pipe medium 103 is finally formed such that the cross- section thereof is shaped to have a perfectly circular shape. Subsequently, the junction between the opposite edges of the pipe medium 103 is temporarily welded at predetermined intervals. Thereafter, the junction is processed through processes of welding from the inside and outside throughout the entire length of the pipe medium 103, thus forming a pipe having a circular cross-section, which is a finished product.

[66] Meanwhile, in the rolled thick steel plate forming apparatus of the present invention, in the case that a steel plate is a relatively thin, as shown in FIG. 12, in the state in which the steel plate is continuously pressed by moving the movable base 30 upwards and by moving the pressing head 65 downwards through the operation of the

actuators 23 and 63 of the slider 20 and the upper forming unit 63, the reversible roller drive motor 55 is continuously operated until the steel plate is formed into the shape of FIG. 14. Thereafter, the apparatus enters the state of FIG. 15, and the steel plate is shaped through the processes from FIG. 16 to FIG. 18. As such, the relatively thin steel plate can be formed more easily.

[67] In other words, after the forming process has started at a first edge of the steel plate

100, the support rollers 52 and 52b are rotated while maintaining the state of pressing the first edge region of the steel plate 100 downwards, thus forming the first side of the steel plate 100 into a rolled shape having a semicircular cross-section. Thereafter, the support rollers 52a and 52b are moved to a second edge region of the steel plate 100 which is not yet formed. After the forming process has again started at the second edge region of the steel plate 100, the support rollers 52 and 52b are rotated while maintaining the state of pressing the second edge region of the steel plate 100 downwards, thus forming the second side of the steel plate 100 into a rolled shape having a semicircular cross-section.

[68] Furthermore, the slider 20, which is placed on the support base 12 provided on the bottom of the frame 10, and the upper forming unit 60, which is provided on the guide rails 14 positioned at the upper portion of the frame 10, must be able to move as required. For example, to form a pipe having a relatively large diameter, because the curvature radius of a steel plate to be formed is relatively large, the slider 20 and the upper forming unit 60 must be able to move in order to actively accommodate it.

[69] To realize movement of the slider 20 and the upper forming unit 60, the first and second screw drive motors 25 and 67, which are provided at predetermined positions in the frame 10, are operated, so that the first and second screw shafts 24 and 66 are rotated. Thereby, the slider 20 and the upper forming unit 60, which are respectively screwed to the first and second screw shafts 24 and 66, are moved.

[70] Particularly, in the movement of the slider 20, to minimize friction between the support base 12 and the slider 20, oil is discharged to the interface between the support base 12 and the slider 20 from the hydraulic system 40 through the oil supply passage 21 and the oil discharge passages 22. Thus, an oil film is formed between the support base 12 and the slider 20, so that friction therebetween can be minimized. Therefore, electromotive force required by the first screw drive motor 25 is markedly reduced. Thereby, the user can easily conduct desired operation.

[71] Furthermore, the upper forming unit 60 having the pressing head 65 and the lower forming unit 50 having the support rollers 52a and 52b are provided in the frame having a tunnel shape without protruding outside the frame. Therefore, several apparatuses may be continuously coupled to each other to accommodate the length of a steel plate 100 to be formed. As such, because each apparatus comprises one individual

unit, the apparatus of the present invention can be relatively easily transported and installed, compared to the conventional apparatus, which is large heavy equipment. Industrial Applicability

[72] The present invention can be efficiently used in an industrial field for forming thick steel plates into rolled shapes for making pipes. Furthermore, the present invention enhances workability and productivity, thus increasing added value when manufacturing pipes from thick steel plates.