Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Patent
1981-07-16
1984-05-01
Robinson, Ellis P.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
241183, 241300, 241DIG30, 264261, 4284239, 4284248, 428492, 428493, B02C 1722, B32B 2508
Patent
active
044461925
DESCRIPTION:
BRIEF SUMMARY
Wear-resistant rubber products are used to a large extent in the mining industry, especially in chutes and, primarily, in mills for grinding ore. In such mills, use is made of a wear-resistant lining consisting of shell plates and so-called lifters which extend into the drum mill and stir the charge within the rotating mill drum and which therefore are subjected to an exceptionally high wear. In view hereof, the lifters must be replaced on more than one occasion during the life of the mill lining or, strictly speaking, the shell plates. Normally, the worn lifters are replaced by new ones, and the worn lifters frequently are scrapped. The worn-out lifters usually still carry large quantities of rubber since the lifters must be replaced before the grinding capacity which is dependent upon the lifter geometry, has decreased to an unacceptably low level. In order to reduce waste of lifter material, it has therefore been suggested, for instance in U.S. Pat. No. 3,191,875 and Swedish patent specification No. 335,460, gradually to raise the lifters in relation to the shell plates, thereby to use up as much rubber as possible. It has also been tried to recap rubber lifters by using recapping methods well known in connection with the recapping of motor vehicle tires, the strength requirements necessitating the technique of hot recapping.
However, the recapping methods used in the tire industry are not readily adapted to the recapping of lifters because the worn rubber lifter must be thoroughly buffed and washed and given a primer coating and because vulcanization must be carried out for a considerable period of time under heat and pressure in expensive vulcanizing moulds of steel in order to produce a bond of sufficient strength. Furthermore, some of the known recapping methods require access to special equipment. The application of pre-vulcanized treads to used carcasses requires careful shaping (abrading) of the rubber surface of the used detail to make it conform to the shape of the new vulcanized rubber detail which is vulcanized to the old rubber detail.
It therefore is an object of the present invention to provide a new wear-resistant rubber product which has the properties of the original product and which, besides, is readily manufactured. Furthermore, the invention comprises a novel method of making this product.
According to the invention, a wear-resistant rubber product which is to be used as, for example, a lifter in grinding mills thus comprises at least two prefabricated parts interconnected by means of a binder layer of in situ cast and vulcanized polyurethane having a thickness of at least 2 mm (preferably at least 5 mm). The wear-resistant rubber product is made by placing the prefabricated vulcanized rubber parts at a distance of at least 2 mm (preferably at least 5 mm) from one another and filling the gap with a reacting urethane rubber composition with excess isocyanate so that the prefabricated parts on either side of the gap are contacted substantially simultaneously by said urethane rubber composition. The characteristic features of the invention are stated in the claims.
The wear-resistant rubber product may be either a new product or a recapped product in which parts of a used corresponding wear-resistant rubber product have been connected with at least one prefabricated vulcanized wear-resistant rubber body by means of the in situ cast and vulcanized urethane rubber layer, said prefabricated and vulcanized rubber body having a profile adapted to that of the future product. Since the conditions of prefabricating this rubber body are far more readily controlled, a high-quality wear-resistant rubber body can be obtained. Hot recapping by vulcanizing an uncured rubber compound to an old and worn product in a vulcanizing mould always necessitates a compromise between on one hand the vulcanization of the newly supplied rubber compound and thus the properties and adhesive power of said compound in the vulcanized state and, on the other hand, the risk of overcuring or scorching of the rubber mater
REFERENCES:
patent: 3686389 (1972-08-01), Beneze
patent: 3895146 (1975-07-01), Nishimaki
patent: 4064215 (1977-12-01), Halada
patent: 4240852 (1980-12-01), Gomberg
patent: 4311181 (1982-01-01), Hausch
patent: 4327138 (1982-04-01), Hausch
Robinson Ellis P.
Trelleborg AB
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