Patent GB-743452-A (GB)
Title: Improvements in and relating to method and apparatus for curing friction compositions
IPC: B29C35/02
Filed: 1953-09-29
Abstract: 743,452. Moulding brake linings etc.; fibrous compositions. RAYBESTOS CO. Sept. 29, 1953 [Oct. 8, 1952], No..26709/53. Classes 70 and 87 (2). A composition of fibrous asbestos friction material for brake linings, containing a heathardenable binder, is heat-hardened by a method which comprises heating the composition for a period of 1-6 minutes in a zone heated to a temperature of 450-600‹ F. while confining it in the zone between opposed faces of an edgwise open low-pressure shaping clamp. The binders may be an elastomer, vulcanized or unvulcanized, or a thermosetting resin, natural or synthetic; or a mixture of both in, e.g. a hydrocarbon solvent with a'drying oil. Volatilization may give rise to soft spots in the material unless the curing is slow; but on the other hand rapid curing is desirable to guard against deformation of the material on reheating. The invention therefore uses preformed strips which may have already been heated, e.g. by infra-red or radio-frequency heat, to remove volatile contents, but not at a temperature high enough to harden the binder, and these preforms are moulded into their final shape under light pressure only, in a pre-heated oven to give a rapid final cure, and between shaped clamps which form moulds open at their sides and ends to permit any remaining volatiles to escape. The preforms or segments 10 are fed to a shoot 13 and drop one by one into the spaces between arcuate clamp sections 15, 16 which are moved in pairs on a succession of plates 17 by an endless conveyer 18. The segments are dropped by the inter-related action of air cylinders 20, 21 whose pistons project each through one wall of the shoot, their action also being related to the movement of the conveyer 18. The clamp section 15 is fixed to its plate 17 but the clamp section 16 is slidable on the plate to and from the section 15. As the conveyer 18 advances, the section 16 passes behind a leg 26 depending from the piston of a cylinder 25 which then acts to draw it towards the section 15 and deform the interposed segment 10 to the arc of the mould sections. A pivoted lever 27 at each end of the section 16 rides over a pin 28 projecting from each end of the section 15 and is held down by springs 30 to lock the sections 15, 16 together. The clamping pressure is just enough to overcome the vapour pressure due to volatilization, e.g. 10-20 lb. per sq. in. All these movements take place in an oven 14 heated to 450‹ F.- 600‹ F., the segments being in the oven from 1 to 6 minutes. Continuing with the movement of the conveyer the mould assemblies emerge through an opening in the end of the oven and return underneath it, upside down, Fig. 2, and the locking levers 27 meet the ends of fixed brackets 32 and are thereby tilted to release the sections 16, while the piston of a cylinder 34 rises into the path of each section 16 in succession and so cause it to recede from its corresponding section 15 as the latter moves on. The cured brake lining segments 10 drop out for discharge and the mould sections re-enter the oven. After the segments have been discharged they may be heated to cure the drying oil binder by oxidation especially when the binder is rubber. The Specification recites examples of compositions, with suitable treatment for each before and after the moulding operation. Binders specified are rubber and peptized rubber material, phenol-formaldehyde resin powdered or in aqueous solution; the fibres are asbestos; other materials mentioned in the examples are: mineral spirits solvent, e.g. gasoline, friction material filling, lubricant, resin cure accelerator and sulphur. The invention may also be applied to the production of clutch faces and other rings, gaskets and insulators.