SELECTING THE PROPER ELASTOMER

There are four primary considerations in elastomer selection: temperature, chemical compatibility, physical attributes (including abrasion and tear resistance) and cost. The first step in selecting the proper elastomer is determining which polymer family best suits the application. The following is an outline of physical and chemical characteristics pertaining to deVries International’s nine most commonly used polymers.

In determining the correct polymer family for your application, the first consideration should be the system’s operating temperature. If the upper limit of the temperature range is exceeded, a chemical reaction within the elastomer will cause it to change permanently, resulting in loss of elastic properties needed for effective sealing. Temperatures below the lower limit of the elastomer cause only a non-permanent hardening. As the elastomer warms back within its temperature limits all of its original properties will return.

A seal’s compatibility with the fluid to be sealed is determined by the elastomer’s stability while immersed in that fluid. Changes in the elastomer’s hardness, tensile, elongation, and volume are measured after immersion in the fluid with the smallest changes in these properties identifying the most suitable seal material. A “1” rating reflects maximum stability while a “3” rating shows the greatest physical change and a material not recommended for use in that fluid. (See Fluid Compatibility Chart.) The outline of polymer families below will also provide an indication of physical strength as well as relative costs.