Session: 03-05-01: Materials Processing and Characterization

Paper Number: 68181

Start Time: Wednesday, 10:45 AM

68181 - Compressive Stress Relaxation (CSR) Testing of Elastomers 

This paper presents Compressive Stress Relaxation (CSR) results for various elastomer samples to ascertain their performance in sealing applications. The paper presents results of percent retained sealing force (%RSF) behavior and its relationship with compression set and hardness.  Materials studied are used in critical piping and medical seal applications.  CSR methodology is used to benchmark various materials in terms of sealing performance.  Potential problems with the current standard of testing have also been identified that can affect the resolution and variability of the test. 

In low pressure seals, leakage occurs when the fluid pressure exceeds the sealing pressure.  In high pressure seals, when there is a loss in fluid pressure and movement of seals is allowed, a compressive force is necessary to maintain the position or engagement of the seals. Currently, compression set is used to identify materials that can perform the function of compressive seals. Given that it is an indirect indicator of material performance, variability in its measurement will lead to greater variability in seal performance and life. For high-precision applications such as in the medical industry, a more direct and reliable test, such as %Retained Sealing Force (%RSF), measured using Compressive Stress Relaxation (CSR) tests is necessary to quantify material performance over time and under specific working environments.

This paper seeks to test a set of different materials and understand how %RSF varies with compression set and hardness. It also seeks to highlight certain issues present in current CSR testing and provide potential remedies to improve the reproducibility and precision of CSR tests. Post curing elastomeric parts is generally done to improve compression set and sealing performance. This paper summarizes CSR testing performed on both standard specimens and specimens that have been post cured to determine if there is an improvement in performance.  The paper explores differences in %RSF for various families of elastomers commonly used in seals.  These elastomers include natural rubber, polybutadiene rubber styrene butadiene rubber and flourocarbon elastomer. 

The paper details all the steps involved to perform accurate CSR testing.  The paper discusses advantages and disadvantages CSR testing might have over conventional tests used to verify seal performance such as compression set.

This is only an introductory study and requires further tests with the same elastomers subjected to other process conditions, such as heat aging are also studied to understand how they affect %RSF. This can also be expanded to other materials to build a database of standard %RSF behavior under identical conditions.

Presenting Author: Robert Michael Gannon University

Authors:

Dilip Menon Gannon University
Robert J. Michael Gannon University
David Gee Gannon University