Welding method for cured polymeric compositions

摘要

1,132,906. Branch fittings. CABOT CORP. 18 May, 1966 [20 May, 1965], No. 22067/66. Heading F2G. [Also in Division B5] Compositions comprising a cured polymeric material and between 20 parts and 500 parts per 100 parts by weight of the material of an electrically conductive filler are welded by localized heating of the surfaces to be welded to above the softening temperatures thereof, interposing between said surfaces an adhesive composition comprising a thermally activatable curing agent, bringing said surfaces into direct proximity with each other with only the adhesive composition therebetween, and flow sufficient electric current through the cured compositions and the adhesive to activate the adhesive. The cured or "cross-linked" polymeric composition may be a cured polymer or copolymer of a lower α-mono-olefinic hydrocarbon, e.g. polyethylene, polypropylene, ethylene/butene-1 copolymers, ethylene/propylene copolymers and mixtures thereof. The filler material is preferably a carbon black such as thermal black, acetylene black, oil furnace black, gas furnace black, channel black or a mixture thereof. Alternatively, the filler material may be a finely-divided or powdered metal or-metal alloy, such as copper, iron, nickel, chrome/nickel, aluminium or iron/nickel. Curing may be effected by gamma or ultra-violet irradiation of the composition or by thermal activation of a suitable curing agent, e.g. an organic peroxide, dispersed therein. The adhesive comprises a curing agent which may be an organic peroxide, such as di-α-cumyl peroxide, tert.-butyl-α-cumyl peroxide, tert.-butyltriphenyl methyl peroxide, decanoyl peroxide, caprylyl peroxide, or benzoyl peroxide, or may be a quinone oxime or a quinone oxime derivative. Preferably, the adhesive interlayer comprises an essentially uncured polymer containing at least 20 parts, e.g. 50-120 parts, per 100 parts by weight of the polymer of an electrically conductive filler and between 0À5 and 10 parts per 100 parts of a curing agent of one of the types specified above. Preferably, a curing agent is chosen which has an active curing temperature range at least slightly above the softening temperature of the adhesive composition. The adhesive composition may be applied to the surfaces in a finely granular or powdered form, as a solution or as a sheet or film. Prior to application of the adhesive the surfaces are heated above the softening temperature thereof to a depth of between 1/ 16 inch and ¢ inch by flame impingement or by a hot iron contoured to the shape of the surfaces. In the embodiment shown, to form a "T" pipe joint, surfaces 3, 4 of pipe portions 1, 2 to be joined are heated, an adhesive film 5 is placed between the surfaces 3, 4 and the portions 1, 2 are brought together. An air powered ram is lowered on to a surface 14 and an electric current is passed between the electrodes 6, 9 to earth to effect the welding. Thermocouples 10, 11, 12, 13 are inserted into the portions 1, 2 to measure the temperatures thereof during welding.