Compression moulding

In compression molding, the rubber mixture is first formed into a substance which is then placed in the cavities. In order to ensure that the cavity is filled, a certain "overload" of the order of 5 - 10% is required.

The blanks placed in the cavities are produced by a cutting process directly from rubber compound plates or the rubber compound is extruded through a die that forms a profile that is cut to suitable lengths.

The heat input between the tool and the rubber mixture is crucial for the vulcanization process to start. As the thermal conductivity of the rubber is low, the heating is slow and the curing time is therefore relatively long.

Typical curing times are from 3 minutes for thin goods to hours for thick-walled products. In the latter case, it is effective to preheat the rubber in, for example, a heating oven or by extruding the rubber mixture.

The advantages of compression molding are mainly the following:
1. The method is simple with relatively cheap tools. Suitable for small series.
2. Enables molding of several different components and materials.
3. Suitable for products with large area or wide spread.
4. Can be used for rubber compounds with high viscosity and poor flowability.

The disadvantages of compression molding are as follows:
1. Subject preparation and positioning of subjects in the tool can be time-consuming.
2. Complicated details can be difficult to get completely filled.
3. Beard formation is extensive and the tolerances on non-form-bound dimensions are worse compared to injection molding.
4. The production rate is relatively low.