Improvements in plastic rivets and method of making same

摘要

Rivets with an elastic memory are formed from natural or synthetic rubber, mixed with a thermoplastic resin, the resulting composition being rigid at normal temperatures, but softening when heated to 160 DEG or 180 DEG F. The rubber may be natural rubber, quayule, balata or guttapercha or may be synthetic, such as copolymers of butadiene and styrene or acrylonitrile, neoprene or butyl. The resins may be cyclized rubber, cyclized balata, isomerized rubber or "Isolac" (Registered Trade Mark), described in U.S.A. Specification 2,158,530. Curatives and accelerators may be added. The materials are thoroughly mixed at a temperature sufficient to soften the resin and the mixture is formed into sheets that are cut into strips and moulded into round rods that are cured for 20 minutes at about 275 DEG F. and then stretched to three or more times their original length whilst at 160 DEG F. and are cooled whilst held stretched. The rivet blanks are cut from these rods and may be headed at one end. U.S.A. Specifications 1,797,188 and 2,230,359 also are referred to.ALSO:Rivets with a pronounced elastic memory are formed from natural or synthetic elastic rubber, such as No. 1 pale crepe, mixed with a thermoplastic resin, the resulting composition being rigid at normal temperatures but softening when heated to 160 or 180 DEG F. Curatives and accelerators may be added. The rubber may be natural rubber, guayule, balata or gutta percha or may be synthetic such as "Buna" S, "Buna" N, Hycar-OR-15, neoprene or butyl. The resins may be cyclized rubber such as Marbon B, cyclized balata, Marbon S, "Isolac" or plioform. One example of a mixture is Marbon B, 30 lbs., No. 1 pale crepe, 12 lbs.; stearic acid, 6 oz.; agerite white 4 oz.; zinc oxide, 1 lb. 3 oz.; "Altax," 4 oz.; and sulphur, 1 lb. The materials are thoroughly mixed at a temperature sufficient to soften the resin and the mixture is formed into sheets that are cut into strips and moulded into round rods that are cured for 20 minutes at about 275 DEG F. and then stretched to three or more times their original length whilst at 160 DEG F. and are cooled whilst held stretched. U.S.A. Specifications 1,797,188, 2,158,530 and 2,230,359 are referred to in connection with the materials specified, among the names of which "Buna," "Isolac" and "Altax" are Registered Trade Marks.