Thermoplastic engine intake pipes etc. - produced by injection moulding e.g. straight pipes for easy demoulding and then hot forming them into bends required

摘要

Bent hollow plastic articles, and pipes in particular such as intake pipes for i.c. engines, are produced in an injection mould by moulding them first to a readily demoulded shape (particularly straight) and then bending them to requirements in a second operation. In an example a cylinder with two end flanges is first injection moulded in conventional manner and demoulded. The pipe made (R) is then placed in a mould (5) consisting of two halves. Here the pipe is introduced while hot and is bent and then cooled. If necessary the preliminary pipe is heated specially before final moulding. The flanges can be injection moulded in the first phase or injected on in an additional phase. A variant on the process whereby a spring is incorporated by placing it in the injection mould first has the spring embedded in the second stage, and its insertion prevents the finished pipe from forming kinks or buckling. ADVANTAGE - The method avoids the drawbacks of using a lost core type of process or those of moulding in two halves plus bonding them together. The products can be stiffened by placing a spiral spring in the mould before injecting the polymer. The pipe can be bent while internally pressurised (eg., with compressed air).