COVER FOR STRAND SINTERING EQUIPMENT PROVIDED WITH A CONTINUOUS STRAND SINTERING TRACK

FIELD OF THE INVENTION The invention relates to the cover defined in the preamble of Claim 1.

BACKGROUND OF THE INVENTION

Continuous strand sintering is used after pelletizing concentrate powder to agglomerate the pellets, improving their strength and reactivity. As an example of the strand sintering technique, a strand sintering furnace could be mentioned, which is used in the production of ferro-chromium and divided into sev- eral sequential zones, different temperature conditions prevailing in each one of them. The strand sintering equipment includes a perforated steel belt, which is directed as an endless loop around two deflector rolls. At the forward end of the furnace, wet fresh pellets are fed onto the steel belt to form a bed with a thickness of a few decimetres. The steel belt conveys the bed of pellets through the drying, heating, and sintering zones of the furnace and to a stabilizing or equalizing zone, after which the bed of pellets further travels through sequential cooling zones. After travelling through the cooling zones, the pellets in a sintered form exit the strand sintering equipment at its tail. To optimize the energy economy, the energy contained in the cooling gases of the tail of the furnace is used in drying, heating and sintering at the forward end of the furnace, which is why the strand sintering equipment includes a number of gas ducts to implement the gas circulation mentioned above. For this purpose, the drying, heating, and sin- tering zones and the cooling zones comprise covers

that are provided with gas units . There is no gas unit in the cover of the equalizing zone.

In particular, the invention relates to the cover of the equalizing zone, which does not have the gas unit, and which in the known technology usually has a structure that includes a cover with side walls and an essentially horizontal flat roof, which extends between the side walls on top of the sintering track. Inside the steel-framed cover, there is a refractory lining. The refractory lining is usually made of heavy ceramic material that withstands high temperatures. Furthermore, the lining is poor in withstanding tension. Flexural tensile stresses are formed in the planar lining layer, which is why the steel frame that supports the lining must be very stiff, wherefore it becomes extremely heavy.

THE PURPOSE OF THE INVENTION

The purpose of the invention is to eliminate the disadvantages mentioned above.

In particular, the purpose of the invention is to disclose a cover, which enables the use of a lighter skeleton structure of the cover than before.

A further purpose of the invention is to dis- close a cover, wherein the tensile stresses exerted on the refractory lining are smaller than before and the strength of the lining can be improved.

SUMMARY OP THE INVENTION The cover according to the invention is characterized in that which is presented in Claim 1.

According to the invention, the cover includes a vaulted part that extends on top of the strand sintering track. Because of the vault structure, the tensile stresses exerted on the cover become small, and mainly

compression stresses occur in the vault. Thus, it is possible to obtain a lighter cover than before. Furthermore, any tensile stresses exerted on the refractory lining become smaller than before and the strength of the lining can be improved.

In one embodiment of the cover, the cover includes side walls and a roof that extends between the side walls, the roof including the said vaulted part.

In one embodiment of the cover, the cover in- eludes a metal frame, which in the area of the vaulted part of the cover is arched like a vault and which includes a lower side on the side of the strand sintering track. The refractory lining is supported by a number of anchoring members to the lower side of the metal frame as a vault-like, arched layer. The metal frame can be made lighter than before, and in the hard and fragile lining that is good in withstanding compression but poor in withstanding tension, mainly only minor tensile stresses and mainly compression stresses occur.

In one embodiment of the cover, the metal frame includes a set of coolant channels for cooling the cover with a cooling intermediate agent conducted through the set of coolant channels. The cooling fur- ther improves the durability of the lining and the anchor members of the lining.

In one embodiment of the cover, the vault- like part is an arched barrel-vault structure in the lateral direction of the strand sintering track, its centre of curvature being in the longitudinal middle plane of the strand sintering track.

In one embodiment of the cover, the vault- like part has a cross section of the shape of a circle segment . In one embodiment of the cover, the vault- like part is elliptical or has the shape of a parabolic arch.

In one embodiment of the invention, the vault-like part has the shape of an inverted catenarian curve, i.e., a hyperbolical cosine. No tensile stresses occur in such an ideal vault shape. In one embodiment of the cover, the cover is the cover of the equalizing zone of the strand sintering equipment.

LIST OF FIGURES In the following, the invention is described in detail by means of exemplary embodiments and with reference to the appended drawing, in which

Fig. 1 shows schematically a side view of the strand sintering equipment comprising an embodiment of the cover according to the invention,

Fig. 2 shows the cross section II-II of the strand sintering equipment of Fig. 1,

Fig. 3 shows a perspective view of the cover of Fig. 3, and Fig. 4 shows the section IV-IV of Fig. 3.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows an example of an application of the cover, which is a strand sintering furnace that is used in the production of ferro-chromium and which is divided into several sequential zones I - VII, different temperature conditions prevailing in each one of them. The strand sintering equipment includes a perforated steel belt 12, which is conveyed as an endless loop around two deflector rolls 13 an 14, at least one of which being a used roll. Wet fresh pellets are fed at the forward end of the furnace (left in the figure) on top of the steel belt 12 to form a bed with a thickness of several decimetres. The steel belt 12 carries the bed of pellets through the drying zone (I, a temperature of about 350 ⁰ C) , the heating zone (II, a

temperature of about 1150 ⁰ C), and the sintering zone (III, a temperature of about 1350 ⁰ C) of the furnace to the stabilizing or equalizing zone (IV) , after which the bed of pellets further travels through a sequen- tial first cooling zone (V, a temperature of about 125O ⁰ C), second cooling zone (VI, a temperature of about 1150 ⁰ C) and third cooling zone (VII, a temperature of about 400 ⁰ C) . After travelling through the cooling zones, the pellets in the sintered form exit the strand sintering equipment at its tail. The strand sintering equipment includes a number of gas ducts 15, 16, 17 to implement the gas circulation mentioned above. For this purpose, the drying, heating and sintering zones as well as the cooling zones comprise covers that are provided with gas units. There is no gas unit in the cover 1 of the equalizing zone.

Referring to Figs. 2 to 4, the cross- sectional drawing of Fig. 2 comprises the cover 1 of the equalizing zone IV, comprising a vaulted part 4 that extends on top of the strand sintering track 2. Cover 1 includes side walls 5 and a roof 6, which forms the vaulted part 4 and extends between the side walls 5. Cover 1 includes a metal frame 7, which in the area of the vaulted part 4 of the cover is arched like a vault. A refractory lining 9 is supported by a number of anchor elements 10 (see Fig. 4) to the lower side 8 of the metal frame 7 as a uniform layer that is arched like a vault. As seen in Figs. 2 and 3, the metal frame 7 comprises, in the area of both the roof 6 and the side walls 5, sets of coolant channels 11 for cooling the cover 1 with the cooling intermediate agent that is conducted through the sets of coolant channels. As seen in Fig. 2, the vaulted roof 6 is a barrel-vault structure, which is arched in the lateral direction of the strand sintering track 2, its cross section having the shape of a circle segment, and its centre of curvature being on the longitudinal middle

plane of the strand sintering track 2. In another application, the vaulted part can be elliptical, have the shape of a parabolic arch or the shape of an inverted catenarian curve, i.e., a hyperbolic cosine.

The invention is not limited to the above exemplary embodiments only, but many variations are possible within the inventive idea defined by the claims.