Rubber and silicone goods are usually made in moulds, and there are several technologies for doing this. Alternative approaches include rotational moulding, blow moulding, extrusion moulding, thermoforming, resin transfer, injection moulding and compression moulding.
In compression moulding, a mould is made in two (or more) parts. Typically, the lower part is filled with moulding material and heated while pressure is applied through the top part. In rubber injection moulding, the liquefied material is injected under pressure into a complete pre-assembled mould.
Both techniques can produce similar goods in large quantities. Creating the initial moulds, especially for injection moulding, can be difficult and relatively expensive, but once it’s in operation, parts can be produced quickly at low costs.
The products from both production methods are strong and durable. Consequently, both methods are used to produce goods like automotive gaskets, seals and grommets, and diaphragms for industrial pressure gauges. You can see a range of typical products at https://www.meadex.co.uk/rubber-moulding/.
Rubber injection moulding pros and cons
Generally speaking, injection moulding is capable of creating more detailed, higher-quality and more uniform parts. It is possible to build sophisticated features into the product simply via the mould design, such as by building anti-tamper features into bottle caps.
Production speeds depend on your equipment, but injection moulding can be significantly faster. Some thin-walled parts that cool quickly take as little as two seconds to produce. In addition, few or no post-moulding processes (like trimming) are normally required, which further reduces your time, labour and costs.
On the other hand, the initial tooling of an injection mould often takes more time and incurs a higher cost. This also means a longer lead time before a new order can begin its first production run.
Compression moulding pros and cons
There are believed to be 85,000 formulations available for injection moulding, but there are sometimes cheaper options for compression moulding.
Tooling compression moulds is often easier, quicker and cheaper, and the wider choice of materials includes thermosetting resins of higher molecular weight.
The production rate is often significantly slower than injection moulding; it can be several minutes before a mould can be reused.
Compression moulding leaves no flow lines or knitting seams. However, resin is prone to escape into mould joints, necessitating additional manual work to trim it and further reducing the production rate.