Prodn. of insulated screwdrivers - by positioning and gripping blade in mould, injecting thermoplastic shot, raising pressure, withdrawing grips and letting shot fill space

摘要

Screw drivers are produced by positioning a long blade in an injection mould and injecting polymer into the cavity to form the handle and to insulate the blade. The blade is held in position with grips which are withdrawn whilst pressure is applied to the shot, so that the space which it leaves is filled with polymer. The blade (15) is held in the two-part (11, 12) mould which has a feed runner (14) for the polymer shot. The handle end (16) is not supported in position, so that it becomes completely encapsulated in polymer. The blade end (16) is held, but the blade is mainly locked in position by two grips (20, 21) which can be moved radially to the cavity (13). Initially these grips (20, 21) are advanced in unison so that their ends engage the blade (15) and hold it centrally. E.g. cellulose acetate or cellulose acetobutyrate is injected (14) into the cavity (13). When this is full the applied pressure is raised to 1,000 bars for 2 mins., The grips (20, 21) remain in position for about one third of this time, by which time the insulating sleeve (23) round the shaft has set hard and holds it in position. The grips (20, 21) are then partly withdrawn, the shot cooled, and the mould. ADVANTAGE - The method produces the screw driver in a simple manner and few stages.