Rubber Moulding Process and the Mould Making Compounds

October 13, 2017
Rubber Moulding Process and the Mould Making Compounds

The march of a rubber component, from concept to realisation, begins with a discussion brief and a set of specifications. Technical drawings then provide an outline of a three-dimensional product, a physical prototype. Of course, the rubber moulding process employs state-of-the-art rapid prototyping services, with new 3D printing systems taking over from older methods, but this is where the project splits, for the moulding of rubber can be accomplished through three alternative manufacturing methods.

Compression Rubber Moulding

This is the grandfather of polymer processing, a method of inserting rubber blanks into an open cavity. Heat and hydraulically driven pressure close the mould and shape the uncured rubber. While this method is common, it’s not suitable for complex production cycles. Also, the process has found a home in the manufacturing of larger parts due to the relatively primitive shapes expelled by the presses.

Injection Rubber Moulding

The shortcomings of the compression moulding technique are offset by the precisely controlled nature of this evolved rubber moulding process. Molten rubber is injected under pressure, forced into the moulds by pistons, at which point the viscous rubber cools and cures. Injection moulding is used in high speed, high volume production cycles and is the de facto choice when intricate components need to be manufactured.

Transfer Rubber Moulding

As with the injection method, transfer machinery varies in size and complexity. It’s also based on a sealed mould format, the same as injection moulding, but a special transfer pot is employed to deliver the preheated rubber blanks into each of its moulds. The ram-to-cylinder configuration in this machinery creates parts that are more intricately detailed than the compression method, and the provision of rubber blanks means less heat is required, thus curing time is reduced.

A Brief Anatomy on Mould Compounds

It’s a complex production environment, one that requires polymer mould compounds to properly distribute and cure the processed rubber. Computer-assisted controls aid in eliminating mixing errors here, with automated programs reducing or increasing heat settings. Sensors monitor the formulations consistency and adjust the pressure and heat of the machinery to finely adjust curing and ensure the mix is uniformly distributed throughout the mould. Catalysts are added to the mould compounds as well, platinum among them, and these additives trigger rapid vulcanization, at which point the mould is ejected.

Three distinctly different processes partner with a source rubber, catalysts, and rubber compounds to produce the optimal, client-specified rubber product, one that excels in its chosen application.