Tempering

What does tempering mean?

Tempering is a subsequent heat treatment of already cross-linked rubber molded parts , O-rings , or seals following the actual molding process.

Why is tempering necessary?

During tempering, rubber molded parts are exposed to elevated temperatures in order to achieve complete cross-linking of the elastomer, improve the physical properties and remove the remaining volatile components and decomposition products of the cross-linking reactions by evaporation. The optimal tempering parameters (temperature and duration) depend on the material type, the cross-linking system and the desired use of the rubber molded part.

Tempering is normally carried out on rubber products with peroxide or bisphenol crosslinkers. However, it can also be carried out on seals made from rubber compounds with sulphur-containing crosslinkers in order to improve certain physical properties.

In the case of molded parts, O-rings or seals with a peroxide-containing crosslinker, tempering removes volatile substances and decomposition products of the peroxide. The tempered parts have little or no odor. If the seal is intended for contact with food or drinking water, tempering is absolutely necessary in order to be able to meet the requirements of the FDA, BfR, KTW or WRAS standards with the elastomer used.

Silicones with platinum -based crosslinkers do not contain peroxide. However, in order to meet the requirements for contact with food, these silicone seals are also tempered. This removes volatile substances from the silicone and improves the physical and mechanical properties, in particular the compression set and stability at high operating temperatures.

What should you pay attention to when tempering?

The greatest improvement in physical and mechanical properties is usually achieved within the first 2 – 4 hours in the tempering oven. With tempering times beyond this, only minor improvements in properties are achieved.

The appropriate gradation of time or temperature in the oven depends on the thickness of the molded part. Products with a thickness of more than 4 mm require longer tempering times. When tempering, ensure that sufficient air can flow around each individual article

Even if the tempering conditions are the same, different elastomer products are not tempered together in the same tempering oven. Ideally, material-specific ovens are used to avoid contamination of the individual material types through outgassing.

Synonym: Post-Curing