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The difference compression, injection, and transfer moulding

When it comes to producing quality rubber parts, the mould and moulding process play a crucial role in the final product. Discover the differences between the main moulding methods.

Injection moulding

During the injection moulding process, a strip of uncured rubber is fed through a rotating screw where the specific amount is pulled into the injection unit. Here the rubber is pre-heated and plasticised, then injected into a mould cavity. In this cavity, the rubber is held under high pressures and temperatures, resulting in vulcanisation. When curing is done, the moulded rubber part is dislodged from the mould.

Injection moulding is ideal for producing high volumes of parts requiring medium-to-high precision. Furthermore, it leads to reduced cure times because the rubber is pre-heated. This moulding method also reduces material waste and ensures high levels of control and consistency.

Transfer moulding

When it comes to transfer moulding, a specific measure of uncured rubber is placed into a pot that forms part of the mould. The mould is then closed, and a plunger compresses the material. Next, heat is applied, and the pressure forces the uncured rubber through sprues into the mould’s gaps. The mould remains closed during the curing process. Finally, the part is removed from the transfer mould and overflow material, or flash is trimmed.

Transfer moulding offers tight control of dimensional tolerances ensuring better uniformity. In addition, because the rubber enters the mould cavity at a higher and more even temperature, it starts to cure more quickly.

This process is more accurate and consistent than compression moulding but has a slower production cycle than injection moulding.

Compression moulding

Compression moulding is used to mould elastomers and durometers by placing uncured rubber in the mould’s cavity. Then, the mould is closed, and heat and pressure are applied to fill and allow excess material to overflow into its grooves. When curing is complete, the mould is opened, and flashing is removed during demoulding.

This is an excellent method for hard or difficult-to-flow materials. Compression moulding is also ideal for running low-volume applications, moulding large parts, and using expensive materials.

Compared to the other moulding methods, compression moulding has a lower tooling cost, is cost-effective for smaller runs to make parts, and excellent for large parts production. However, compression moulding isn’t as precise as injection moulding. In addition, it produces more waste, has slower process times, and as a result, can decrease the production rate while increasing the part cost.

Contact Delta Rubber for details

There are a lot more to the different moulding techniques than explained here. To discuss custom rubber moulding for your specific application, please contact a representative from Delta Rubber today.

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