US3706448A

US3706448A - Skids or beams for furnaces

Info

Publication number: US3706448A
Application number: US108407A
Authority: US
Inventors: Frank Michael Salter; John Edwin Dibley
Original assignee: British Iron and Steel Research Association BISRA
Current assignee: British Iron and Steel Research Association BISRA
Priority date: 1970-03-23
Filing date: 1971-01-21
Publication date: 1972-12-19
Anticipated expiration: 1989-12-19
Also published as: SE363847B; CA933352A; DE2113666B2; NL7103857A; GB1321302A; DE2113666A1; ZA71360B; BE764650A; FR2084354A5

Abstract

A skid or beam for a slab reheating furnace has a hollow water cooled pipe with a rail welded along the top of the pipe on which the slabs bear. The rail is of inverted channel section with two outer limbs extending downwardly from an upper portion. The lower ends of the outer limbs are welded to the pipe. Preformed grooves extend across the bearing surface of the rail at spaced locations along its length. The channel shaped rail minimizes conduction of heat from the slabs to the pipe and in use the grooves crack and relieve stresses caused by the temperature differences across the rail.

Description

United States Patent Salter et al.

[ 51 Dec. 19, 1972 [54] SKIDS OR BEAMS FOR FURNACES [73] Assignee: The British Iron and Steel Research Association, London, England [22] Filed: Jan. 21,1971

[21] Appl.No.: 108,407

[30] Foreign Application Priority Data March 23, 1970 Great Britain ..l3,923/70 [56] References Cited UNITED STATES PATENTS 2,044,165 6/1936 Halliwell ..75/l23 K 2,105,838 1/1938 McCormick ..263/6 B 2,553,609 v 5/1951 Schmidt ..75/l23 K 2,757,084 7/1956 Cape et al.. 75/123 K 3,214,152 10/1965 Molz ..263/6 B 3,236,507 2/1966 McKie 266/5 H 3,552,729 l/l97l Hepp et a1 ..263/6 B Primary lixaminer-Gcrald A. Dost Attorney-Bacon & Thomas 157] ABSTRACT A skid or beam for a slab reheating furnace has a hollow water cooled pipe with a rail welded along the top of the pipe on which the slabs bear. The rail is of inverted channel section with two outer limbs extending downwardly from an upper portion. The lower ends of the outer limbs are welded to the pipe. Preformed grooves extend across the bearing surface of the rail at spaced locations along its length. The channel shaped rail minimizes conduction of heat from the slabs to the pipe and in use the grooves crack and relieve stresses caused by the temperature differences across'the rail.

3,544,094 12/1970 Knaak ..266/5 H 3,304,070 2/1967 Jones ,.266/5 H 11 Claims, 6 Drawing Figures 1 I, I, z I I, l L I,

SKlDS OR BEAMS FOR FURNACES In steel making it is known to use furnaces for reheating stock, such as billets or slabs, with burners both above and below the stock and with skids or beams for supporting the stock. The skids or beams include a water cooled pipe and a rail supported on the pipe which provides a wearing surface and on which the stock bears. In a pusher furnace there are skids for supporting the stock, and the stock is pushed through the furnace and rubs along the rails. In a walking beam furnace there are moving beams and stationary beams and the stock is advanced by being successfully raised off the stationary beams and deposited again further along the stationary beams by the moving beams.

The water cooling, which is necessary to maintain the strength of the pipes, causes cooler regions in the stock known as skid marks. One way of minimizing these skid marks is for the rail to be as hot as possible and therefore high temperature alloys are necessary. With these materials there are difficulties in attaching the rails to the pipe.

Attempts have been made to overcome these attachment problems by interlocking the rail and pipe without welding them together, but such solutions require large rails and are expensive.

An object of this invention is to provide a simple skid or beam in which the flow of heat from the stock to the pipe is small.

of the pipe, the rail providing a bearing surface for the stock to be heated, is characterized in that the rail is of inverted channel section with two outer limbs extending downwardly from an upper portion, the lower ends of the outer limbs being welded to the pipe, and in that the upper portion of the rail has a number of stress relieving discontinuities spaced along its length.

Previous attempts in which rails of high temperature alloys have been welded directly to the pipe have resulted in the rail becoming separated from the pipe. We have realized that the reason, for this is that when the skid rail is in use thetop of the rail becomes hot whereas the bottom is maintained at a low temperature because it is welded to the water cooled pipe. This temperature difference causes the top part'of the skid rail to be compressed, and under the stresses set up, plastic deformation occurs, thereby relieving these stresses. When the furnace temperature is lowered the rail cools and the top contracts and comes under tension. This results in the rail tending to curve upwardly at its ends thus applying tensions to the weld so that either the rail, or the weld cracks or both the rail and weld crack. In a pusher furnace the stock is pushed along the rails with a force of hundreds of tons and the stock can catch on a raised portion of the rail that has cracked and bowed and easily tears the rail from the pipe.

The channel section of the rail according to the invention has the result that less heat is conducted to the, pipe than would have been conducted by a solid rail of the same dimensions, so that the skid marks are small. The top of the rail is therefore hotter than in a conventional rail with a correspondingly greater tendency to curve but this problem is reduced by the provision of stress relieving discontinuities spaced along the rail.

When the rail according to the invention is in use the upper portion expands and is thus compressed and under this compressive force plastic deformation occurs. On cooling the upper portion contracts and comes under tension which is relieved by the spaced discontinuities. We have found that a rail according to the invention produces smaller skid marks than a conventional rail and is not torn off the pipe in use.

After a slab or billet emerges from a reheating furnace it is rolled, and for the rolling to be satisfactory the whole of the slab or billet must be above a certain temperature. The coolest parts of the slab, namely the skid marks, have to be raised above this certain temperature and therefore the rest of the slab has to be.

raised to a higher temperature than is necessary for satisfactory rolling. By diminishing the skid marks by use of skids according to the invention it is thus possible to lowerthe overall furnace temperature which results in a saving in fuel and an increased life for the refractory materials lining the furnace.

The stress relieving discontinuities can take many forms which are capable of preventing buildup of stress between opposite ends of the upper portion of the rail. For example the discontinuities could be formed by complete cuts extending laterally through the upper portion of the rail at spaced locations along the rail, the cuts being made after the rail is cast. The discontinuities could also be formed by laterally extending rows of holes drilled through the upper portion to form cracking points along which the rail cracks when under tension. Preferably the discontinuities include grooves extending right across thebearing .surface of the rail. The walls of the grooves preferably meet the bearing surface at an obtuse angle to reduce the likelihood of stock catching on to the edge of the groove. The grooves are preferably V shaped and can be formed when the rail is cast. When the rail contracts it can crack along one or more of the grooves, and the grooves are so designed that they will crack before either the rail or the weld are otherwise damaged. Preferably the discontinuites extend down at least part of the outer surfaces of the two outer limbs and terminate in holes passing right through the outer limbs to prevent the cracks from spreading.

The discontinuities can include grooves extending across the underside of the upper portion of the rail. Where there are grooves on the underside of the upper portion as well as on the bearing surface there is preferably a groove on the underside directly under each groove on the bearing surface. This promotes cracking.

The rails are preferably made of 50 or 51 percent cobalt steel alloy. The rail is preferably made up of a series of rail lengths welded together.

In a walking beam furnace it is not essential for the rail to be continuous along the length of the beam although this is preferred. It is possible to have a series of rail lengths spaced apart from one another, but in accordance with the invention'each rail length would have spaced discontinuities.

The pipeis preferably covered with insulating material having two generally flat upper surfaces inclined to one another and converging towards the rail. This produces less shielding to the slab from burners beneath the slab than a circular skid. The pipe can have a generally triangular cross section. The skid or beam can have more than one pipe. For example three circular pipes can be welded together with their axes parallel, each pipe contacting the othertwo. In this way an effectively triangular skid can be fabricated using circular pipes.

In the accompanying drawings:-

FIG. 1 is a cross section of a pusher furnace with skids embodying the invention,

FIG. 2 is a cross section of one skid embodying the invention,

FIG. 3 is a perspective view of a rail length for the skid of FIG. 2,

FIG. 4 is a side view of another rail length,

' FIG. 5 is a cross section on the line V V of FIG. 4,

and Y FIG. 6 is an end view of the rail of FIG. 4.

' FIG. 1 showsa slab reheating pusher furnace with six skids 1, each supported on a supporting structure 2. A slab of steel stock 3 is shown supported on the skids l. Thereare burners 5 above and below the skids l and heat is radiated to the slabs 3 from the burner flames and from the walls 6 of the furnace.

FIG. 2 shows one of the skids 1 in more detail. The skid 1 includes a hollow skid pipe 9 adapted to allow a cooling fluid to be passed therethrough, and a rail 10 welded on top of the pipe 9, the rail providing a bearing surface 11 for the stock to be heated. The rail 10 is of inverted channel section with two outer limbs 12 extending downwardly from an upper portion 13. The

outer limbs 12 are supported on the pipe 9 so'that a space 14 is enclosed by the rail 10 and pipe 9. The lower ends of the outer limbs 12 are welded with weld material 15 to the pipe'9. The width of the limbs 12 is such that the horizontal cross sectional area of the limbs 12 per unit length of rail is substantially less than the area per unit length of the upper surface 11 of the upper portion 13.

The rail 10 is cast from 50 or 51 percent cobalt steel alloy which is a wear resisting material which can. be operated for long periods at high temperature such as 1,000C. The pipe 9 has two generally flat surfaces 16 inclined to one another and converging towards the rail 10 over a major portion of the height of the pipe 9. The maximum height of the pipe exceeds its maximum width. A layer of thermal insulating-material 17 surrounds the pipe 9 for insulating the pipe and the insulating material also has two generally flat surfaces inclined to one another at converging towards the rail. The insulating material 17 has reinforcing mesh 18 provided within it which is welded at 18 to the pipe to secure the material 17 to the pipe. Refractory filling material 19 is used to fill the gaps between the top of the material 17 and the bottom of the rail 10.

The rail 10 is formed of a series of rail lengths each having a number of stress relieving discontinuities 20 spaced along its length as can be seen in FIG. 3. The rail length is 0.45 meters long and the discontinuities 20 are spaced at about 5 centimeter intervals.

The discontinuities 20 are formed when the rail lengths are cast and consist of V shaped grooves extending right across the bearing surface 11 of the rail and down at least part of the outer surfaces 21 of the two outer limbs 12. The grooves 20 terminate in holes the grooves are V" shaped the walls of the grooves meet the bearing surface 1 1 at an obtuse angle.

Each end of each rail length is chamfered at 23 along its upper portion so that when two rail lengths are welded together a stress relieving discontinuity is formed between the two adjacent rail lengths.

Similarly each end of each rail length is formed with semi-circular recesses 25 in the outer limbs 12 so that when two adjacent rail lengths are welded together the recesses 25 on adjacent limbs together form holes passing right through the outer limbs 12 similar to the holes 22. v

The bottom end of each limb 12 is chamfered at 26 to allow it to be welded to the pipe 9 with weld material 15 as can be seen in FIG. 2. The ends of each raillength are provided with welding chamfers 27 on the portion of the limbs 12 below the recesses 25 to allow adjacent rail lengths to be welded together.

I The rail 31 length shown in FIGS. 4 to 6 differs from that in FIG. 3 in three respects. The first difference is that in addition to the grooves 20 there are grooves 30 extending across the underside of the upper portion 13 of the rail. The grooves 30 are directly under the grooves 20. The second difference is that the holes 22 are nearer the bottom of the outer limbs 12. The third difference is that the ends 32'of the rail length 31 do not coincide with one of the discontinuities. Instead the ends 32' are such that when two rail lengths 31 are welded together the weld is mid way between two grooves 20. Each end 32 has a face 34 at right angles to the length of the rail 31 and two

inclined faces

36 and 38. To connect two rail lengths the face 32 of one length is butted against the similar face of the next adjacent rail lengths and the groove formed by the

faces

36 and 38 is completely filled with weld metal.

After use of the'skid according to the invention it is found that therail has cracked along at least some of the grooves .20. These cracks are contained and cause no disadvantage. The V shaped grooves 20 ensure that there is no tendency for stock to catch on to a portion of rail 10 and hence tear the rail 10 off the pipe 9. The rail is also found to reduce the skid marks in comparison with known rails.

- We claim:-

1. A skid'or beam for a furnace includinga hollow.

pipe adapted to allow a cooling fluid to be passed therethrough and a rail welded on top of the pipe, the rail providing a bearing surface for the stock to be heated, in which the improvement comprises a rail of inverted channel section with two outer limbs extending downwardly from an upper portion, the lower ends of the outer limbs being continuous throughout the length of the rail and being welded to the pipe, and the upper portion of the rail having a number of stress relieving discontinuities spaced along its length.

2. A skid or beam as claimed in claim 1 in which the discontinuities include grooves extending right across the bearing surface of the rail.

3. A skid or beam as claimed in claim 2 in which the walls of the grooves meet the bearing surface at an obtuse angle.

4. A skid or beam as claimed in claim 1 in which the discontinuities include grooves extending across the underside of the upper portion of the rail.

5. A skid or beam as claimed in claim 2 in which the discontinuities further include a groove extending across the underside of the upper portion directly under each groove on the bearing surface.

6. A skid or beam as claimed in claim 1 in which the discontinuities extend down at least part of the outer surfaces of the two outer limbs andterminate in holes passing right through the outer limbs.

7. A skid or beam as claimed in claim 1 in which the rail is made of 50 or 51 percent cobalt steel alloy.

8. A skid or beam as claimed in claim 1 including a layer of thermal insulating material for insulating the pipe.

9. A skid or beam as claimed in claim 1 in which the rail is made up of a series of rail lengths welded together.

10. A skid or beam as claimed in claim 1 in combination with a furnace which has heating means disposed both below and above the skid or beam.

11. A skid or beam as claimed in claim 1 wherein said stress relieving discontinuities are provided in the bearing surface of the rail.

l060ll 0216

Claims

1. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough and a rail welded on top of the pipe, the rail providing a bearing surface for the stock to be heated, in which the improvement comprises a rail of inverted channel section with two outer limbs extending downwardly from an upper portion, the lower ends of the outer limbs being continuous throughout the length of the rail and being welded to the pipe, and the upper portion of the rail having a number of stress relieving discontinuities spaced along its length.

6. A skid or beam as claimed in claim 1 in which the discontinuities extend down at least part of the outer surfaces of the two outer limbs and terminate in holes passing right through the outer limbs.