Vacuum chambers are used in many industries. Their largest application area in the physical vapor and directed vapor deposition, (PVD and DVD,) process industries. Here they are used for applying both decorative finishes and hard protective coatings. Vacuum eliminates contaminants that would cause oxidation or reduce purity. The cutting tool, semiconductor and nuclear industries are all big users. They’re also used in scientific research even for growing engineered diamonds.
A Difficult Sealing Environment
The gaskets used for sealing these chambers are critical pieces of the equipment. They fit around access ports where they have to withstand high clamping forces as well as extremely low vacuum. That means they need strength and good compression set resistance. Another requirement is a wide temperature range and there’s also a fourth, more specialized challenge.
Emptying a vacuum chamber of air, (pumping it down,) takes time because molecules cling to the interior surfaces. These surfaces must be given time to give up these molecules in a process called “outgassing”.
Materials give up their attached air molecules at different rates, which makes outgassing behavior an important consideration when selecting gasket material for vacuum chambers. Slower outgassing means longer pump-down times, which in turn reduces chamber throughput.
Suitable Materials for Vacuum Chamber Gaskets
The most popular choice is Viton®. Technically a polymer from the fluorocarbon family, (Viton® is the DuPont trade name,) this has a wide temperature range, (-20 to +400°F) and good compression set resistance. Most importantly though, it provides shorter outgassing times than the alternatives.
These alternative materials are silicon, Butyl, Buna-N and EPDM. Silicon gasket material outgasses more slowly than Viton® but has a wider temperature range and good ozone resistance. In ultra-low vacuum applications, meaning pressures below 7.5×10-10 Torr, elastomeric gaskets are replaced by copper.
Finding the Right Material for Vacuum
Every vacuum chamber has access ports, and access ports need gaskets. An important consideration for the gasket material is outgassing behavior as this affects pump-down time. If outgassing is a concern in your gasket application, the specialists at Hennig Gasket will be happy to offer advice.