LU86176A1 - METHOD FOR MANUFACTURING A CYLINDER FOR A COAL BRIQUETRY MANUFACTURING INSTALLATION AND CYLINDER MANUFACTURED ACCORDING TO THIS METHOD - Google Patents

Description

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Method of manufacturing a cylinder for an installation for manufacturing coal briquettes and cylinder manufactured according to this method.

The present invention relates to a method of manufacturing a cylinder serving as a mold in a plant for the production of coal briquettes, mixed with other materials, the external surface of which comprises cells, the shape of which corresponds to that of the briquettes. and which are produced by an electro-chemical erosion process, known per se. The invention also relates to a cylinder obtained by this process.

The invention relates in particular to installations 10 for manufacturing small briquettes, of an ellipsoidal shape having a length of a few centimeters and a thickness of about two centimeters and which are intended both for industrial use and for use spare. These briquettes are formed, as described in patent DE-Ps 15 84 752, from carbon powder which, mixed with other abrasive materials, creates an atmosphere of the order of 500 ° C. between two cylinders juxtaposed rotating-, counter-rotating and tangential contact. The over-! faces of the two cylinders have complementary molds, i.e. alveoli having the shape of a half ellipsoid with a depth of about ten millimeters.

By the rotation of the two cylinders, the cells, of complementary shape, are brought in synchronism one opposite the other in the contact zone of the cylinders r 25 after having been filled with the mixture of coal powder and other abrasive materials. just above the contact area. The mixture is thus transformed into briquettes: quets under the effect of temperature and pressure; when the complementary cells close one on the other like two half-shells.

The surface of the cylinders which is provided with these cells or molds is exposed to relatively great wear and the frequency of replacement of the cylinders obviously has repercussions on the cost price of the | I:. j 40 briquette manufacturing. 'j é I # i -2-

Up to now, these cylinders have been produced exclusively by fixing a ring whose external surface is provided with these cells on a metallic cylindrical core i. The ring is made of a special alloy which has undergone a heat treatment process to give it the required hardness and in the surface of which the cells have been formed by an electro-chemical erosion process known per se. Heat treatment is a quenching process, the effects of which are essentially limited to the surface of the alloy, i.e. that the hardness gradually decreases in depth. As a result, the alveoli present in the outer region, i.e. along their edge, a hardness for example of approximately 50 Rockwell C and in the bottom a substantially lower hardness, for example, 35 Rockwell C. It follows that the cells rapidly deform in the bottom and become in particular deeper and deeper. In addition, this wear gradually accelerates as the resistance di-20 decreases due to the gradual decrease in hardness in depth. As a result, the cylinders, or at least their peripheral strip, must be replaced after the production of approximately 15,000 tonnes of bricks.

The object of the present invention is to provide a new method for manufacturing the cylinders described.

Above, which allows better resistance to wear and, therefore, less frequent replacement.

To achieve this objective, the method proposed by the present invention is essentially characterized in that, before the electro-chemical erosion, one applies to the exterior surface of a metal cylinder, by a known hard hardening method. per se, a uniform layer of a resistant carbide-based alloy, of a thickness at least equal to that of the depth of the cells and in what is subjected; to this layer a heat treatment process so that it has a uniform hardness in depth of at least i ~ Tl __: __ i

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-3- 0 "J" minus 50 Rockwell C.

The invention also proposes a new cylinder serving as a mold in an installation for manufacturing coal briquettes and the outer surface of which comprising X cells which serve as a mold for the production of briquettes is produced according to the above process.

The essential characteristic of the layer deposited by hard surfacing is that, unlike that obtained by a surface quenching process, it exhibits a uniform hardness in depth of approximately 50 Rockwell C. This process allows the formation of layers of thickness up to 150 millimeters.

This results in two essential advantages, the effects of which are complementary for lengthening the duration of the cylinders and reducing the frequency of their replacement.

Indeed, the cells, unlike those produced in conventional cylinders, have the same hardness at the bottom as at the surface. Consequently, these wear out less quickly in the bottom, and the time when their wear no longer allows effective use is significantly delayed.

The other advantage is that, when the cells or molds have reached the critical wear stage, it is possible to remove the surface layer until partial or total erasure of the cells and to produce on the remaining layer, again, alveoli by the same electro-chemical erosion process. One can thus practice successive recoveries until exhaustion; - total of the resistant peripheral layer deposited by hard surfacing. These new cells always have the same degree of hardness as 50 Rockwell C 35 both on the surface and in depth. Although this layer! could theoretically reach a thickness of 150 i millimeters or more, it is planned to achieve one! ! ^ hard reload of approximately 60 millimeters, which

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Λ »* * -4- allows to practice two to three successive bites in the same layer and thus to double or triple the duration of use of the cylinders.

The cylinders produced according to the method proposed by the present invention have still other advantages. One of these is that the method is cheaper than the conventional method of manufacturing the cylinders since the ring, i.e. the base material is normal alloy steel. Another advantage is that the resistance of the hardfacing layer is not very sensitive to temperature changes. On the other hand, the resistance of the surface layer of the rolls produced according to the conventional method decreases appreciably at the working temperatures which are of the order of 450 to 550 ° C.

The invention will be explained below in more detail with the aid of a nonlimiting example of the production of a cylinder which can be used for the production of coal briquettes.

20 On a rotating metal cylinder preheated to 420 ° C, the hardfacing layer is applied by welding. For this purpose, a consumable flux-cored wire of the SARCLAD type, well known in the field of welding, is used as the electrode. These are strips 25 folded in mild steel containing a powder constituting the particular alloy for the intended use. In the application concerned by the present invention, it is essential that the resurfacing does not have any cracks in view of the process for producing the molds by electro-chemical erosion. To this end, it has been found that the most suitable material is that of the SARCLAD 4 type, ’the welded deposit of which has the following nominal composition as a percentage: 35 C: 0.65 i

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Ni: 0.06

Cr: 5

MB: 1

Nb: 3.3, the remainder being Fe 5 The welding is carried out using a current of 350 to 650 A for a single wire electrode and from 750 to 1350 A for double wires. Several successive coats can thus be applied, the maximum interpass temperature being 650 ° C. The surfacing by welding 10 is finished when the layer reaches approximately 60 millimeters in thickness.

The cylinder then undergoes slow cooling without cover to ambient temperature followed by a stress relief annealing at 520OC for 8 hours with progressive cooling to give the hardfacing layer a martensitic structure with a uniform hardness of 52 Rockwell C on all its thickness.

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Claims (3)

1.- Method of manufacturing a cylinder serving as a mold in an installation for manufacturing briquettes of coal mixed with other abrasive materials, the external surface of which comprises cells 5, the shape of which corresponds to that of the briquettes and which are produced by an electro-chemical erosion process known per se, characterized in that, before the electro-chemical erosion, a hard reloading process, known per se, is applied to the outer surface of a metal cylinder uniform layer of a resistant carbide-based alloy, of a thickness at least equal to that of the depth of the cells and in that this layer is subjected to a heat treatment process so that it has a hardness 15 uniform in depth of at least 50 Rockwell C. 2. Method according to claim 1, characterized in that said layer deposited by hard surfacing has a thickness of at least 60 millimeters. 3. Cylinder serving as a mold in a process for manufacturing coal briquettes obtained by the process according to one of claims 1 or 2. S ~ 1