GB1594167A - Workpiece support systems for heat-treatment furnaces - Google Patents

Description

(54) WORKPIECE SUPPORT SYSTEMS FOR HEAT-TREATMENT FURNACES (71) We, KOPPERS-WISTR AOFENBAU GESELLSCHAFT MIS BESCHRANKTER HAFTUNG a Company of the Federal Republic of Germany of Wiesenstrasse 134, 4000 Dusseldorf-Heerdt, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns the workpiece support beams of heat-treatment furnaces.

Heat-treatment furnaces in which steel is heated to rolling temperature usually provide for both top and bottom heating of the workpieces in the case of heavy duty furnaces and particularly when the workpieces have thick cross-sections. The workpieces rest in the furnace on a support system comprising beams through which a coolant flows. Various support system constructions have been used or proposed.

An advantageous known support system is one in which a support beam, extending in the direction of workpiece conveyance in the furnace, is rigidly fixed at one of its ends to a structure situated outside the furnace and is mounted so as to be capable of longitudinal displacement on supports such as uprights in the furnace. The workpiece support system consists of one or at most two such support beams that extend continuously from one end of the furnace to the other.

The support beams of such a system are stressed mechanically by the weight and by the horizontal and vertical movement of the workpieces. The horizontal movement transversely of the direction of workpiece conveyance is produced by the expansion of the workpieces on heating and results in the workpieces sliding laterally on the support rails when they are not moving in the conveyance direction. The beams and their supports have therefore to be adequately massive and appropriately constructed to resist these stresses, but the greater the cross-section of the beams the greater is the tendency for shading of parts of the workpieces from heat radiation.

When cooled support beams are used in addition to shading effects a further heat loss to the workpiece occurs due to the heat conducted to the beams from the workpiece. These shading and heat loss effects cause undesirable temperature differences to occur in the workpieces.

Another disadvantage is that heat is lost from the furnace to the entire support beam surface and to the surface of the cooled structure supporting the beam.

An object of the invention is to provide a support system in which the shading of the heat radiation from workpieces by the support beams is reduced, as is also the surface of the heat-dissipating cooled structural parts.

The horizontal forces stressing the support system as a result of thermal expansion of the workpiece cannot exceed the product of workpiece weight multiplied by the friction coefficient: because the latter will be less than unity in the conditions of interest, the horizontal forces cannot exceed, and will usually be substantially less than, the workpiece weight.

It has therefore been proposed (DOS 2 502 130) that the load-bearing cross-section of a support beam should be much taller than it is wide. In respect of the shading of the workpieces by the support beam, beam section width is of much greater importance than section height. This proposed construction therefore results in a reduction of the undesirable shading. However, such a beam section has low flexural stiffness about a vertical axis in comparison with a wider section and to compensate it has been proposed to stiffen the beam supporting uprights by transverse tubes that interconnect the uprights of adjacent beams or connect them to the furnace wall.This construction, however, leads both to an increase in the heat-absorbing surfaces of the system and to a structural stiffness that is much less in the longitudinal direction of the furnace than in the transverse direction of the furnace. There is no justification for this having regard to the magnitude of the shearing forces in a pusher furnace and the acceleration forces in an under-fired walking beam furnace.

It has also been proposed (German Utility Model 76 20 266) to connect the beam rigidly to the supporting uprights, both beam and uprights then having the same cross-section and there being no stiffening by means of transverse tubes. The disadvantage of this construction is that the stiffness of the support system in the transverse direction of the furnace is much less than in the longitudinal direction, because the rigidly connected uprights and beam constitute a frame structure of substantial longitudinal stiffness with but little transverse stiffness.

In a support system according to the invention, a beam is rigidly fixed at one of its ends to structure located outside the fumace and is mounted so as to be capable of longitudinal displacement on uprights in the furnace, the system being characterised by the features that the beam rests solely on uprights that extend substantially vertically that the height of the continuous load-bearing cross-section of the beam is more than 1.4 times the width of the section, and that the substantially horizontal load-bearing cross-section of the uprights has a dimension in every direction more than 1.5 times the width of the load-bearing cross-section of the beam.

The construction according to the invention combines the advantageous effects of the features used and avoids their disadvantages.

The narrow shading zone of a narrow and tall beam section with its favourable effect in respect of the desirable reduction of temperature differences in the workpieces is adopted but the lack of flexural stiffness of such a beam section about a vertical axis is compensated for by the uprights being of thick construction in relation to the width of the beam.

The upright cross-section being larger than the beam section width ensures the transverse stiffness of the beam without resulting in a wider shading throughout the beam length with corresponding streaks forming on the workpieces and without the heat-absorbing surface being increased by the use of transverse tubes.

The beam is preferably longitudinally internally divided into superposed separate coolant flow passages. With this construction, coolant may be introduced into one of these flow passages in the vicinity of the fixed end of the beam outside the fumace, the coolant flowing in that passage to the other end of the beam where it is directed into the other passage to return therein to the fixed end of the beam.

This avoids the need for coolant connections in the furnace and the need for such connections to accommodate longitudinal movement of the beam.

The beam is desirably fitted with prismatic skids of high temperature-resistant metal having recesses accommodating a web welded to the beam and bolted to the skids.

The beam-supporting uprights may extend through the bottom of the furnace to mountings permitting the uprights to rock about a horizontal axis parallel with the beam, means being provided to effect such rocking of the uprights.

This construction is especially useful in a walking beam furnace, as will be explained.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section of a furnace having top and bottom heating and comprising a support system in accordance with the invention; Figure 2 is a detail of the section A-A in Figure 1, showing the two support beams and uprights of a walking beam furnace provided with a support system according to the invention; Figure 3 illustrates a preferred beam construction; and Figure 4 illustrates the provision of beam rocking in a system embodying the invention.

Figure 1 shows a furnace chamber 1 fitted with a longitudinal beam 2 carried on uprights 3 within the furnace and having one end fixed to structure 4 outside the furnace. In accordance with the invention, the cross-section of the beam 2 within the chamber 1 has a section height that is more than 1.4 times the section width, while the uprights 3 have a cross-section (in plan) the dimensions of which, in both longitudinal and transverse directions of the beam 2, are more than 1.5 times the width of the beam cross-section.In practice, there will usually be at least two similarly supported beams extending parallel with one another throughout the length of the furnace chamber 1 and in the case of a walking beam furnace each beam will be constituted by a pair of parallel beams one of which is fixed, at least longitudinally, whereas the other is arranged to rise above the fixed beam, move forward in the conveying direction, descend to a level below the fixed beam and thereafter return to its starting position so as to lift workpieces from the fixed beam, carry them forward and replace them on the fixed beam, at each cycle.

Figure 2 shows, diagrammatically a pair of parallel beams of a walking beam furnace, that designated 2 being supported by uprights 3 that are carried by a suitable mobile structure, shown at 3a, to move the beam 2 in the required manner.

Figure 3 illustrates a preferred beam section the interior of which is divided into two superposed passages for flow of coolant from an entry near the fixed end of the beam, through one passage to the other end of the beam and thence back to an exit, near the fixed end, through the other passage.

This Figure also shows a skid 5 of heatresistant metal straddling a web 6 welded to the beam, the skid being attached to the web 6 by a bolt 7.

The spacing between two beams 2 in a furnace limits the dimensions of the workpieces undergoing heat treatment in the furnace during normal operation. Of course the workpieces must not be shorter than the distance between two beams. However, depending upon the thickness of the material, it may exceed the distance between the beams only by a certain amount, because otherwise the ends of the workpiece may droop excessively under the influence of their weight, particularly in the event of interruptions to operation. Suitable beam spacing requirements are difficult to meet, particularly in walking beam furnaces, because on the one hand these furnaces require twice as many beams as pusher furnaces while on the other hand the beams may not be less than a minimum distance apart if sufficient heat radiation pathways to the workpieces are to be left between the beams.

To avoid these difficulties, the construction illustrated in Figure 4 may be utilised. As shown in this Figure, a beam 2 is supported by uprights 3 that have, beneath the bottom floor 8 of the furnace, a mounting permitting the uprights and the beam to pivot about a horizontal axis extending in the longitudinal direction of the furnace. This pivoting can be controlled by known mechanical, electrical or hydraulic means. The mounting itself may be constructed in any suitable form, e.g. a spindle, shaft, spring or the like and is indicated diagrammatically as comprising a pedestal bearing and a shaft 9. Figure 4 also shows a water seal 10 and a link 11 that connects the upright 3 to movement control mechanism (not shown).

The pedestal bearing for the shaft 9 is supported by a girder 12. In a typical embodiment, the arrangement permits the centre lines of the uprights 3 to be rocked to the attitude shown at 13 so that the beam 2 is shifted laterally by about 350mm.

This pivotal mounting can be used both for fixed beams and for walking beams. The pivotal mounting enables the distance between the beams to be adjusted as required to suit the dimensions of the workpieces undergoing the heat treatment in the furnace.

In the case of a walking beam furnace with the support system of the invention and including pivotal mounting of the beam-supporting uprights as just described, 'idle beams', that is, the beams that at any time are not carrying workpieces, may be rocked aside, e.g. through about 200 to 400mm, being swung back into their basic load-carrying position immediately prior to the workpieces being deposited thereon or raised thereby, as the case may be. In this way, a considerable disadvantage of prior art under-fired walking beam furnaces, i.e. the shading of the workpieces by the idle beams, is substantially avoided. Recent experiments and experience show that the influence of such shading is very important at the high temperatures of about 1250 "C in rolling-mill furnaces for steel.Rocking the idle beams out of their basic position enables the heat radiation to pass freely to the workpieces under going heating.

In walking beam furnaces the widening of the opening in the fixed fumace floor required to permit the rocking movement of the walking beam uprights is preferably provided only at one end of the opening, the walking beam when idle being moved into the relevant end position before the rocking movement is initiated. The advantage of this arrangement is that the widening of the opening in the fumace floor required for the rocking movement is limited only to part of the length of the opening and hence the heat radiation through the opening is reduced.

WHAT WE CLAIM IS: 1. A support system for heat-treatment furnaces, comprising a beam rigidly fixed at one of its ends to structure located outside the furnace, the beam being mounted so as to be capable of longitudinal displacement on uprights in the furnace, characterised by the features that the beam rests solely on uprights that extend substantially vertically. that the height of the continuous load-bearing cross-section of the beam is more than 1.4 times the width of the section, and that the substantially horizontal load-bearing cross-section of the uprights has a dimension in every direction more than 1.5 times the width of the load-bearing crosssection of the beam.

2. A support system according to claim 1 wherein said beam is longitudinally internally divided into superposed separate coolent flow passages.

3. A support system according to claim 2, including means for introducing coolant into one of said passages near the fixed end of the beam to flow therein to the other end of the beam, and means at said other end for directing the coolant into the other flow passage for return therein to said fixed end of the beam.

4. A support system according to any preceding claim, wherein the beam is fitted with prismatic skids of high temperature resistant metal having recesses accommodating a web welded to the beam and bolted to the skids.

5. A support system according to any preceding claim, wherein the beam-supporting uprights extend through the bottom floor of the furnace to mountings permitting the uprights to rock about a horizontal axis parallel with the beam, means being provided to effect such rocking of the uprights.

6. A method of operating a walking beam furnace with a support system according to claim 5, wherein beams when idle are laterally displaced from their load-carrying basic position.

7. A supporting system according to claim 5 for operation according to claim 6, wherein the walking beam uprights extend through openings in the fixed floor of the furnace, the required widening of said openings to accommodate said beam displacement being provided at one end of the openings.

8. A support system substantially as described with reference to and as shown in Figures 1 to 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. the distance between the beams only by a certain amount, because otherwise the ends of the workpiece may droop excessively under the influence of their weight, particularly in the event of interruptions to operation. Suitable beam spacing requirements are difficult to meet, particularly in walking beam furnaces, because on the one hand these furnaces require twice as many beams as pusher furnaces while on the other hand the beams may not be less than a minimum distance apart if sufficient heat radiation pathways to the workpieces are to be left between the beams. To avoid these difficulties, the construction illustrated in Figure 4 may be utilised. As shown in this Figure, a beam 2 is supported by uprights 3 that have, beneath the bottom floor 8 of the furnace, a mounting permitting the uprights and the beam to pivot about a horizontal axis extending in the longitudinal direction of the furnace. This pivoting can be controlled by known mechanical, electrical or hydraulic means. The mounting itself may be constructed in any suitable form, e.g. a spindle, shaft, spring or the like and is indicated diagrammatically as comprising a pedestal bearing and a shaft 9. Figure 4 also shows a water seal 10 and a link 11 that connects the upright 3 to movement control mechanism (not shown). The pedestal bearing for the shaft 9 is supported by a girder 12. In a typical embodiment, the arrangement permits the centre lines of the uprights 3 to be rocked to the attitude shown at 13 so that the beam 2 is shifted laterally by about 350mm. This pivotal mounting can be used both for fixed beams and for walking beams. The pivotal mounting enables the distance between the beams to be adjusted as required to suit the dimensions of the workpieces undergoing the heat treatment in the furnace. In the case of a walking beam furnace with the support system of the invention and including pivotal mounting of the beam-supporting uprights as just described, 'idle beams', that is, the beams that at any time are not carrying workpieces, may be rocked aside, e.g. through about 200 to 400mm, being swung back into their basic load-carrying position immediately prior to the workpieces being deposited thereon or raised thereby, as the case may be. In this way, a considerable disadvantage of prior art under-fired walking beam furnaces, i.e. the shading of the workpieces by the idle beams, is substantially avoided. Recent experiments and experience show that the influence of such shading is very important at the high temperatures of about 1250 "C in rolling-mill furnaces for steel.Rocking the idle beams out of their basic position enables the heat radiation to pass freely to the workpieces under going heating. In walking beam furnaces the widening of the opening in the fixed fumace floor required to permit the rocking movement of the walking beam uprights is preferably provided only at one end of the opening, the walking beam when idle being moved into the relevant end position before the rocking movement is initiated. The advantage of this arrangement is that the widening of the opening in the fumace floor required for the rocking movement is limited only to part of the length of the opening and hence the heat radiation through the opening is reduced. WHAT WE CLAIM IS:

1. A support system for heat-treatment furnaces, comprising a beam rigidly fixed at one of its ends to structure located outside the furnace, the beam being mounted so as to be capable of longitudinal displacement on uprights in the furnace, characterised by the features that the beam rests solely on uprights that extend substantially vertically. that the height of the continuous load-bearing cross-section of the beam is more than 1.4 times the width of the section, and that the substantially horizontal load-bearing cross-section of the uprights has a dimension in every direction more than 1.5 times the width of the load-bearing crosssection of the beam.

2. A support system according to claim 1 wherein said beam is longitudinally internally divided into superposed separate coolent flow passages.

3. A support system according to claim 2, including means for introducing coolant into one of said passages near the fixed end of the beam to flow therein to the other end of the beam, and means at said other end for directing the coolant into the other flow passage for return therein to said fixed end of the beam.

4. A support system according to any preceding claim, wherein the beam is fitted with prismatic skids of high temperature resistant metal having recesses accommodating a web welded to the beam and bolted to the skids.

5. A support system according to any preceding claim, wherein the beam-supporting uprights extend through the bottom floor of the furnace to mountings permitting the uprights to rock about a horizontal axis parallel with the beam, means being provided to effect such rocking of the uprights.

6. A method of operating a walking beam furnace with a support system according to claim 5, wherein beams when idle are laterally displaced from their load-carrying basic position.

7. A supporting system according to claim 5 for operation according to claim 6, wherein the walking beam uprights extend through openings in the fixed floor of the furnace, the required widening of said openings to accommodate said beam displacement being provided at one end of the openings.

8. A support system substantially as described with reference to and as shown in Figures 1 to 3 of the accompanying drawings.

9. A support system according to claim 8,

modified substantially as described with reference to and as shown in Figure 4 of the accompanying drawings.