EP0039630B1 - Skid provided with refractory ledges for a walking beam furnace - Google Patents

Description

The invention relates to beam ovens and relates more particularly to studs or refractory buttons for such ovens.

For a few years now, ovens with cooled mobile beams have tended to replace push furnaces for reheating slabs, blooms or steel billets due in particular to their superior production capacity, their good reliability and their economic interest.

In the beams ovens, the load (slabs, blooms or billets) to be heated passes successively from the moving beams to fixed beams, without friction, by controlled installation and removal on spaced studs or buttons, integral with the beams and protruding from the top of said beams. The longitudinal members being made up of a metal tube (with a diameter of approximately 130 to 220 mm) internally cooled by a circulation of water and a relatively thick insulating refractory lining (approximately 60 mm) sheathing said tube, there would be advantage that the studs or buttons are as high as possible so that their upper face is at a temperature as close as possible to that of the lower face of the load. Also, the higher the studs or buttons, the less there is to fear the shadow effect that the side members and their insulating lining can exert on the heating of the load by the lower side burners.

However, the studs or buttons currently used, which are made of an alloy with 50% of cobalt, 30% of chromium and 20% of iron, tend to crush, due to an insufficient creep resistance, after a few months of operation when their height exceeds a certain value (approximately 90 mm), passing from an initial cylindrical shape to that of a mushroom, owing to the fact that the stresses which can be supported by the metal decrease when the temperature in service of the metal increases , which is the case when increasing the height of the studs or buttons. For this reason, the height of the current studs is in the range of 70 to 90 mm. To remedy this drawback, it has been proposed to use a nickel-rich alloy in place of the above-mentioned alloy, but the results obtained have not been, to the knowledge of the Applicant, fully satisfactory. In addition, it should be noted that the alloy studs or buttons used until now are very expensive.

There is therefore a need for pads or buttons of relatively large height for beam ovens which are more efficient than the pads or buttons currently used and which are less expensive than the latter.

The object of the present invention is to satisfy this need by providing a new stud or button for longitudinal beam ovens.

The invention relates to a stud or button for longitudinal beam ovens comprising a body of refractory material based on oxides, and a jacket of refractory metal alloy surrounding the periphery of the body, means being provided to prevent tearing up. of the body compared to his shirt.

Preferably, the body protrudes slightly at its upper part relative to the shirt.

According to a preferred embodiment, the stud or button further comprises a metal reinforcement embedded in the body of refractory material.

By "pad or button" is meant both elements of generally circular shape and of generally square, rectangular or other shape.

Means must be provided to prevent the body from being torn off in order to prevent the body, under the effect of sticking with the load to be reheated, from being torn off from its shirt. We have, in fact, found that such an undesirable phenomenon could occur in the case of bodies simply shrunk in a cylindrical jacket. The anti-tearing means may consist in giving the shirt a section which decreases from its base to its top, for example in giving the shirt a frustoconical or pyramidal shape. Alternatively, one could give the shirt a wavy shape or provide protrusions on the inner surface of the shirt intended to hold the body against any force aimed at tearing it from its shirt.

• - une matière réfractaire fondue et coulée dont la composition chimique est approximativement, en poids, 73% d'A1₂0₃, 5% de Zr0₂, 20% de Si0₂, 0,5% de Ti0₂, 0,3% de CaO, 0,5% de Fe₂0₃ et 0,7% de Na₂0, et dont la composition cristallographique est, en poids, 43% de corindon, 5% de zircone, 37% de mullite et 15% de phase vitreuse. Cette matière est dispondible dans le commerce sous la marque MAGMALOX^O et est largement utilisée pour la construction des soles de fours poussants;
• - les matières réfractaires fondues et coulées, recommandées dans le brevet français FR-A-2 295 930 ou le brevet US-A-4139 394 pour le garnissage des soles de fours poussants et dont la composition chimique est, en poids, de 10 à 28% de Zr0₂, 3 à 12% de Si0₂, 60 à 80% d'A1₂0₃, 0,3 à 1,5% de Na₂0, jusqu'à 5% au total de Fe₂0₃, Ti0₂, CaO et MgO avec la condition que le rapport pondéral
  
  et dont la composition cristallographique, en poids, est de 60 à 80% de corindon, 10 à 28% de zircone et 5 à 19% de phase vitreuse, la somme corindon+zircone+phase vitreuse constituant au moins 99% de la composition et la somme zircone +2,5 (phase vitreuse) étant comprise entre 33 et 57,5%.

The refractory materials based on oxides which can be used are all the melted and cast refractory materials which have a very low creep under the service conditions of the studs (temperature of the order of 1300 ° C. and compression forces of the order of 2 , 5 N / mm ² for example), are insensitive to oxidation, resist attack by iron oxide, therefore not very porous, and have a reduced tendency to stick with the scale present on the surface of the filler to reheat. In general, it will be possible to use the molten and cast refractory materials used to make the hearths of the push furnaces. Non-limiting examples of such materials are as follows:

• - a molten and cast refractory material whose chemical composition is approximately, by weight, 73% of A1 ₂ 0 ₃ , 5% of Zr0 ₂ , 20% of Si0 ₂ , 0.5% of Ti0 ₂ , 0.3% of CaO, 0.5% of Fe ₂ 0 ₃ and 0.7% of Na ₂ 0, the crystallographic composition of which is, by weight, 43% of corundum, 5% of zirconia, 37% of mullite and 15% of glassy phase. This material is available commercially under the brand name MAGMALOX ^O and is widely used for the construction of hearths for push ovens;
• - molten and cast refractory materials, recommended in the French patent FR-A-2 295 930 or US-A-4139 394 for the lining of the hearths of push ovens and whose chemical composition is, by weight, from 10 to 28% of Zr0 ₂ , 3 to 12% of Si0 ₂ , 60 to 80% of A1 ₂ 0 ₃ , 0.3 to 1.5% of Na ₂ 0, up to 5% in total of Fe ₂ 0 ₃ , Ti0 ₂ , CaO and MgO with the condition that the ratio weight
  
  and whose crystallographic composition, by weight, is 60 to 80% of corundum, 10 to 28% of zirconia and 5 to 19% of glassy phase, the sum of corundum + zirconia + glassy phase constituting at least 99% of the composition and the sum zirconia +2.5 (glassy phase) being between 33 and 57.5%.

Instead of molten and cast refractories, it is also possible to use refractory concretes and sintered refractory materials with a high alumina content, in particular the refractory concretes described in the French patent and addition applications FR-A-2 359 090 and FR-A-2390400 or in US-A-4111 711, especially those containing chromium oxide.

To date, however, it is preferred to use molten and cast refractory materials (also called electrofused) to constitute the body of the studs.

• - 0,5% C, 26,5% Cr, 48,5% Ni, 6,25% W et du fer pour le complément à 100%;
• - 0,4% C, 25% Cr, 20% Ni et du fer pour le complément à 100%.

The jacket is made of a refractory metal alloy having good mechanical resistance at high temperature. Non-limiting examples of suitable alloys are refractory steels such as the following:

• - 0.5% C, 26.5% Cr, 48.5% Ni, 6.25% W and iron for the complement to 100%;
• - 0.4% C, 25% Cr, 20% Ni and iron for the complement to 100%.

Preferably, the stud of the invention further comprises a metal sole on which the refractory body rests, so as to distribute the compression forces exerted on the body over a larger surface of the cooled spar.

The studs or buttons according to the invention have heights of at least about 70 mm, preferably 100 + 150 mm in order to minimize the thermal transfer of the load to be heated to the cooled beams. Such a height, which represents a significant advance compared to the 70-90 mm of the studs or buttons of the prior art, is made possible thanks to the low rate of creep at high temperature of the refractory materials used to constitute the body of the studs of the invention. MAGMALOX ^@ resists, for example, at 1300 ° C at pressures of the order of 30 N / mm ² while the compression forces exerted on the pads by the loads to be heated are of the order of 2.5 to 3 N / mm ² . Furthermore, the fact that the molten and cast refractory materials based on oxides have a much lower thermal conductivity than the metal alloys used for producing the pads of the prior art, the thermal transfer of the charge to be heated to the cooled longitudinal members is greatly minimized, which makes it possible to obtain an improved uniformity of heating.

The metallic reinforcement, optional but preferred, embedded in the body, aims to improve the resistance to mechanical and thermal shocks of the body, the refractory materials being relatively fragile to these shocks. Also, in the event of breakage of the body, this reinforcement tends to retain the pieces of the body which would otherwise risk being torn from the stud, for example as a result of bonding with the scale of the charges to be heated. The metal reinforcement can have various configurations. It may, for example, be constituted by a metal insert of cruciform shape or in the form of fins secured to a central mast. It can also consist of fins integral with the jacket and distributed over the internal surface of the latter, in which case the metal reinforcement can simultaneously fulfill the role of the anti-tearing means.

The studs or buttons of the invention can be easily attached to the side members supporting them by welding from the base of the liner to said side members.

The manufacture of a stud or button of the invention, when a melted and cast refractory material is used to constitute the body of the stud, can be carried out by pouring into the jacket resting on its base the melted refractory material and by l 'allowing it to solidify, a counterweight being provided on the top of the shirt forming the mold so as to locate the recess cavity therein. After cooling, the solidified part corresponding to the counterweight is sawed, the saw line being slightly above the top of the shirt.

One could also, of course, pour the refractory body apart and introduce it later into the jacket.

Preferably, the refractory body is made to rest on a metal soleplate which distributes the stress over a larger area of the cooled spar.

• Les figures 1 a et 1 b sont des vues en coupe verticale et horizontale, respectivement, d'un plot selon l'invention; les figures 2a et 2b sont des vues en coupe verticale et horizontale, respectivement, d'un autre plot selon l'invention; les figures 3a et 3b sont des vues en coupe verticale et horizontale, respectivement, d'encore un autre plot selon l'invention.

The description which follows, made with reference to the drawings, will make the invention clear. In the drawings:

• Figures 1a and 1b are views in vertical and horizontal section, respectively, of a pad according to the invention; Figures 2a and 2b are views in vertical and horizontal section, respectively, of another pad according to the invention; Figures 3a and 3b are views in vertical and horizontal section, respectively, of yet another pad according to the invention.

In FIGS. 1 a and 1 b, we see a part of a longron made up of a metal tube 1 cooled by a circulation of water and of a refractory thermal insulation 2. This spar carries at its upper part a stud, designated by the general reference 3, consisting of a body 4 of melted and cast refractory material, of a jacket 5 of refractory steel of generally frustoconical shape surrounding the body and of an insert 6 of refractory steel constituting a cruciform piece 7 welded at its base to a round steel sole 8, the cruciform part being embedded in the refractory material of the body. The stud 3 is fixed by welding the base of the shirt 5 to the tube 1, and the body protrudes slightly, at its upper part, relative to the shirt. As an indication, the stud may have a height of 120 mm and a diameter at its top of 110 mm and at its base of 130 mm. The projection of the body relative to the shirt can be of the order of 2 mm. The tapered shape of the shirt prevents the body from being torn off.

In FIGS. 2a and 2b, which illustrate an alternative embodiment of the pad of the invention, there is seen a pad, designated by the general reference 13, consisting of a body 14 made of melted and cast refractory material and surrounded by a jacket 15 in refractory steel of generally cylindrical shape. The jacket 15 carries on its internal face a plurality of fins 16 made of refractory steel, for example in the form of groups of 3 or 4 fins distributed at 90 ° from one another as shown in FIG. 2b, the fins of opposite groups being offset from each other in the height direction as shown in Figure 2a. These fins are embedded in the molten refractory material and poured during the manufacture of the stud and prevent any tearing of the body in service.

Figures 3a and 3b illustrate yet another type of stud according to the invention. This stud, designated by the general reference 23, has a rectangular shape in horizontal section and consists of a body 24 of molten and cast refractory material, of a jacket 25 of refractory steel in the general shape of a pyramid trunk based rectangular, and an insert 26 of refractory steel consisting of a rectangular plate 27 carrying fins 28 distributed on its faces.

The type of studs in Figures 3a and 3b is more particularly suitable for reheating narrow parts (billets) which impose almost continuous support along the side members.

It goes without saying that the embodiments described are only examples and that it would be possible to modify them, in particular by substitution of technical equivalents, without departing from the scope of the invention.

Claims (8)

1. A skid button for walking beam furnaces, characterized in that it comprises a body (4, 14, 24) of a refractory oxide-based material and a shell (5, 15, 25) made of a refractory metal alloy surrounding the periphery of the mody, and means to prevent detachment upwardly of said body from said shell.

2. A skid button according to claim 1, characterized in that it further comprises a metallic reinforcement member (6, 16, 26) embedded in the body of refractory material.

3. A skid button according to claim 1, characterized in that the shell has the shape of a cone frustum or a pyramide frustum.

4. A skid button according to claim 1, characterized in that the shell is of cylindrical shape and is provided on the internal surface thereof, with projecting elements.

5. A skid button according to claim 2, characterized in that the metallic reinforcement member is crossshaped.

6. A skid button according to claim 2, characterized in that the metallic reinforcement member comprises a central winged element.

7. A skid button according to any of claims 1 to 6, characterized in that it is at least 100 mm high.

8. A skid button according to any of claims 1 to 7, characterized in that it further comprises a metallic base (8) on which the body rests.

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