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Coefficient of Thermal Expansion

Coefficient of linear expansion is the ratio of the change in length per °C to the length at 0°C. Coefficient of volumetric expansion for solids is approximately three times the linear coefficient. As a rough approximation, elastomers have a coefficient of expansion ten times that of steel (an exception to this is perfluoroelastomers). This can be a critical factor at high temperature if the gland is nearly filled with the seal, or at low temperature if squeeze is marginal. See the table below.


Coefficient of Linear Thermal Expansion of 
Typical Parker Materials and Common Materials

Family Test Range Reported CLTE (m/m/°C) Calculated CLTE (in/in/°F)
NBR 25 °C to 125 °C 1.97E-04 1.1E-04
HNBR 25 °C to 160 °C 1.95E-04 1.1E-04
AEM 25 °C to 175 °C 2.29E-04 9.5E-05
EPDM 25 °C to 125 °C 2.01E-04 1.1E-04
FKM 25 °C to 200 °C 1.98E-04 1.1E-04
Low Temperature FKM -20 °C to 200 °C 2.67E-04 1.5E-04
Aflas 25 °C to 200 °C 2.85E-04 1.6E-04
FFKM 25 °C to 320 °C 3.91E-04 2.2E-04
VMQ 25 °C to 230 °C 2.30E-04 1.3E-04
FVMQ 25 °C to 175 °C 2.00E-04 1.1E-04
Kel-F n/a 1.49E-04 8.3E-05
High-Temperature Type Aluminum, 2017 n/a 2.34E-05 1.3E-05
Stainless Steel, Type 302 n/a 1.73E-05 9.6E-06
Steel, Mild n/a 1.21E-05 6.7E-06
Invar n/a 1.08E-06 6.0E-07
Test method ASTM E831      


There are certain reactions that in some circumstances cause a seal to exert relatively high forces against the sides of a groove. These forces are generated by thermal expansion of the rubber and/or swelling effect of a fluid.

If the seal is completely confined and the gland is 100% filled, the dominating force is the force of thermal expansion of the rubber. There have been instances where a seal has ruptured a steel gland due to expansion when heated.

Effective force exerted by the seal due to fluid swell is another potentially large factor if the gland volume exceeds that of the seal by only 5 to 10% (see Figure 2-20). Depending on the interaction between the rubber and the fluid being sealed, the effect may be quite pronounced even at larger gland void conditions.


Parker Hannifin
O-Ring & Engineered Seals
2360 Palumbo Drive
Lexington, KY 40509
Ph: 859-269-2351
Fax: 859-335-5128