Rubber Moulds and Plastic Moulds: The Differences and Their Various Uses

June 3, 2015
Rubber Moulds and Plastic Moulds: The Differences and Their Various Uses

The technology behind rubber and plastic moulding is influenced by different industries and competing technologies, with early adopters of the rubber moulding process declaring the technique as crude when compared to an equivalent plastics production cycle. While once true, new rubber production environments are popping up, and we need some way of differentiating the two methods. The apparent material differences notwithstanding, let’s take a closer look at just how the two moulding methodologies diverge when seen in a manufacturing environment.

First of all, an advantage that’s considered near and dear to any financial department, the total cost of the process. Thermoplastic production machinery has been in place for over half a century now, and that period has seen the method become essential throughout every industrial sector. Because of this established process, plastic moulding machinery and the principles that drive that machinery have seen the thermoplastic injection moulding process perfected and expanded to encompass hundreds if not thousands of differently graded thermoplastic materials. On the other hand, rubber moulded products didn’t truly become established as a viable production technology until the 1960s. Even then, the market was subject to substandard components made from low grade natural and synthetic rubbers.

The gap between the two moulding techniques remained dramatically wide until recent years. The advent of advanced rubber moulding solutions had arrived. Synthetic rubber was easier to manufacture and liquid silicone injection (LSR) had come of age. Still, as highly detailed as these parts can now be manufactured within a rubber moulding assembly, there are still production-related issues to conquer. More pressure is typically required to set an elastomer within a mould cavity. In addition, we’re also faced with a curing period after the process is finished and the part has cooled. Thermoplastics require less pressure and a straightforward cooling period.

Moving on to our next article of proof, the geometries of both plastic and rubber moulded parts can assume complex shapes, each with any amount of detail. Unfortunately, there’s a number of factors that determine a more expensive and advanced shape when it comes to the rubber mould. Flashing, for example, occurs if the mould isn’t properly sealed. This phenomenon is eliminated by keeping the mould gap at or below 0.002 inches (0.05 mm), but the rubber mould requires higher tolerances, a reduced gap of as little as 0.001 inches (0.025 mm). This ramps up the engineering skills required to produce a top-functioning rubber mould, a fact that is reflected in the additional costs.

Despite vulcanizing issues, the need for advanced flashing solutions, venting attachments and tooling differences, there’s much demand for moulded rubber. Tiny moulded rubber valve seals and ‘O’ rings grant elastic-like properties to medical instruments. Meanwhile, moulded plastics safeguard the other end of the spectrum, delivering a certain amount of elasticity alongside the abrasion-resistant and chemical-proof factors that make engineering plastics the most viable solution in today’s industrial applications. Meanwhile, check out the advantages of compression-manufactured rubber parts as rollers and bumpers, the essential components that take the brunt of our impact-heavy world.