Pushing the Limits of Feasibility - Wacker Chemie AG

Pushing the Limits of Feasibility

Temperatures of up to 300 Degrees Celsius

Specifically for such components, WACKER has launched a new line of solid silicone rubbers that synergistically interact with heat stabilizers and thus, when cured, supply an extraordinarily high heat resistance. Sold under the name ELASTOSIL® R 756, these peroxide-crosslinking silicones can withstand temperatures of 250 degrees Celsius even over long periods of time and temperatures of 300 degrees Celsius over the medium term. Long-term exposure to extreme temperatures does not affect the good resilience of the cured rubber. Their compression set, which is a measure of resilience, remains low enough for them to act as elastic seals, for example.

Elastic Seals

That’s why good resilience after exposure to extreme temperatures is a prerequisite for the use of silicone elastomers in door gaskets of self-cleaning ovens. These kitchen appliances can clean themselves at the press of a button. This is accomplished via pyrolysis – the chemical degradation of organic substances by heating in the absence of an air supply. During the cleaning program, the oven chamber reaches a temperature of approximately 500 degrees Celsius for a certain period of time. At this temperature, grease spots, spilled gravy or cooking juices and food remnants on oven trays carbonize. All that remains is a powdery layer of soot and ash, which can easily be swept up or wiped away. This saves consumers the troublesome task of cleaning the oven manually.

The Product

The peroxide-crosslinking solid silicone is extraordinarily heat resistant. With a stabilizer, the cured rubber withstands temperatures of 250 degrees Celsius even over longer time periods and temperatures of 300 degrees Celsius over the medium term.

Hot Space

Despite the sophisticated design of the oven door, the profile gasket around it, which seals off the space between the baking chamber and the oven door, heats up. During pyrolysis, temperatures can reach 300 degrees Celsius in some areas, which is too hot for conventional silicone gaskets. Up until now, oven manufacturers have therefore mostly used a tube-shaped seal made of woven fiberglass that is reinforced on the inside with wire mesh. The wire mesh gives the gasket the necessary resilience.

In principle, the fiberglass and wire mesh can withstand the temperatures that occur during pyrolysis. However, the fiberglass gaskets wear out quickly during use. The repeated opening and closing of the oven door causes the wire mesh to lose its shape and therefore its ability to provide support. In addition, the woven fiberglass absorbs grease-laden vapors during baking and cooking, which condense, become rancid and solidify over time. This gradually causes the woven material to harden and the gasket can become brittle. Furthermore, the fiberglass gaskets cannot be cleaned, so they eventually become an eyesore.

Profile gaskets for doors made of the new heat-resistant ELASTOSIL® R 756 solid silicones provide a high-quality alternative to fiberglass gaskets. They can withstand the high temperatures they are subjected to during pyrolysis and remain elastic enough to provide an effective seal, even after many self-cleaning cycles.