Our last article went over the vacuum baking process and why that is critical for high and ultra-high vacuum applications. Parts and fasteners for these applications are required to be free from volatile materials that would lead to contamination of the entire vacuum system. However, can you use an untreated O-ring in a vacuum system even though tests have shown that untreated O-rings will outgass under vacuum?
 
 
Quick Overview of Outgassing
Outgassing (or offgassing) refers to releasing gas that is trapped, frozen, dissolved, or absorbed in some other material. Outgassing is a common problem when creating and maintaining a clean high-vacuum environment. High-vacuum and high-temperature environments increase the rate of outgassing due to vapor pressure and an increase in chemical reactions in the polymers. With proper preparation, and the right parts, you can drastically reduce the amount of outgassing in your vacuum system.
 

Figure 1 : O-Ring Bake-Out Residue
 
 
Virgin/Untreated O-Rings
There are a variety of O-rings on the market today which vary widely from manufacturer to manufacturer, the source of the materials used, and even from lot to lot. A new O-ring can potentially contain trace amounts of contaminants such as solvents, water / water vapor, volatile curing agents, unreacted monomers, and more.
 
New, untreated, O-rings require long-term room temperature pumping periods to remove water contaminates from the polymer. Contaminates slowly diffuse to the surface and then desorb which can take weeks (and even months) to properly condition. Treating the O-rings by baking out the water vapor prior to installation will drastically reduce the possibility of outgassing.
 
 
Baked vs Non-Baked
As you can see in the table (figure 2) below, the outgassing rate decreases dramatically with pump time utilizing baked O-rings versus non-baked O-rings. The rate shown here is representative of the common variations, though practical outgassing will fall somewhere between the two curves.
 

Figure 2 : O-Ring Gas Loads
 
 
Using untreated O-rings in vacuum applications have been proven to outgas; one of the best, and easiest, ways to help reduce outgassing is the use of specifically formulated and treated O-rings in HV, UHV, and EUV environments.
 
 
We Offer Top Quality Solutions
Our RediVac® O-rings are specially processed for immediate use in High Vacuum and Ultra High Vacuum equipment. All of our fasteners and O-rings are cleaned and packaged in our certified Class 100/ISO Class 5 Cleanroom. This process is based on typical requirements for pre-cleaning elastomer seals prior to installation for vacuum service. The Vacuum Baking Process is also just one of the finish options that UC Components, Inc. offers for our family of RediVac® precision cleaned and clean-packaged fasteners, washers, nuts, and O-ring products.
 
Request a quote or contact UC Components, Inc. for more information and to place an order.
www.uccomponents.com