Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1997-04-17
1998-10-13
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164114, 164118, B22D 1916, B22D 2704, B22D 1304
Patent
active
058198385
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a bimetallic grinding wheel of generally frustoconical or cylindrical shape, comprising a cast support made of machinable ductile cast iron in the outer surface of which are embedded, longitudinally, in the direction of the generatrix, wear inserts made of a material having a high wear resistance, the said inserts being retained in the support by mechanical bonding. The invention also relates to a grinding wheel obtained by the implementation of this method.
Grinding wheels consisting of an outer wear layer which is supported by a more ductile core are known. These wheels are produced by successive casting of the wear layer and of the supporting core in order to form a metallurgical bond between the two materials. Given that this method of manufacture can be implemented only for a few pairs of compatible materials for a metallurgical bond, the choice of materials, both for the wear layer and for the supporting core, is limited. To produce the metallurgical bond furthermore requires perfect synchronization of the casting operations and good control of the casting temperature.
Document EP 0,476,496 A1 recommends the technique of using inserts for the manufacture of grinding wheels by the implementation of a method as described in the preamble.
According to this document, the inserts are cast separately in first moulds and subsequently placed in a sand mould into which the supporting core is poured in order to form a mechanical bond between the two materials. Contrary to the metallurgical bond, the mechanical bond does not involve constraints from the choice-of-materials standpoint, so that it is possible to choose harder alloys for the inserts, for example high-alloy chromium cast irons or any other highly wear-resistant material, and more suitable alloys for the core, such as spheroidal graphite cast iron.
This technique also enables the casting capacity to be doubled, given that the inserts are cast separately and may be stored for the purpose of the second casting.
However, this technique often comes up against other difficulties. When the second casting is carried out into the sand mould on cold inserts, these run the risk of cracking induced by heat shock. In order to avoid this risk, or at least to reduce it, it is necessary to preheat the inserts to a temperature of the order of 400.degree. to 500.degree. C. Now, this preheating is not easy to perform given that it must entail bringing bulky heating equipment close to the sand mould and, in addition, the necessary temperature to be reached generally causes the binder used for the mould sand to be destroyed.
It is also necessary to fix the inserts temporarily in the sand mould in order to prevent them from moving during casting. For this purpose, a destructible temporary support may be provided or, they may be simply wedged against each other in order to jam them by a vault effect.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel method of manufacturing bimetallic grinding wheels which enables the drawbacks associated with the known method to be eliminated or at least reduced, while still keeping their advantages.
In order to achieve this objective, the invention provides a method of the kind described in the preamble, which is characterized in that a mould is used which consists of a transportable shell made of metal or any other material capable of withstanding a temperature of at least 400.degree. C., in that the inserts are stood up at the periphery of the shell, in that the shell and the inserts are preheated in an oven, in that the shell together with the inserts are rapidly removed from the oven and placed on a centrifugal casting machine which is set in rotation, in that the ductile cast iron is poured and in that demoulding takes place after cooling.
The ductile cast iron is preferably a lamellar or nodular grey cast iron, while the inserts are preferably made of chromium cast iron or a highly wear-resistant material.
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REFERENCES:
patent: 4932460 (1990-06-01), High
De Vylder Jean
Guerard Norbert
Lin Kuang Y.
Magotteaux International
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