Take a closer look at North American Rubber Technology. We did...
Nitrile O-Rings are so prevalent now, there is a tendency to think of them as a commodity which can be purchased from the cheapest source in the world. There seems
to be a belief that all Nitrile O-Rings are created equal. Zatkoff Seals and Packings, being one of the largest, full line Seal Distributors in North America, took a leadership
role in challenging this belief. In part through the efforts of Zatkoff, Parker Seal Group compound N674-70 is recognized as the best industrial Nitrile rubber material. However,
the belief that all Nitrile O-Rings are the same encouraged us to investigate the performance of foreign, particularly Asian sourced O-Rings. Zatkoff personnel went to
several Asian O-Ring suppliers and we sampled O-Rings of various standard cross sections from the best of the many suppliers surveyed and visited.
The most important performance property of an O-Ring is its resistance to compression set. Simply put, resistance to compression set measures the resistance of the
O-Ring to flattening during squeeze in the application. We are all familiar with the leaky faucet or fitting which, when taken apart, has a flattened O-Ring no longer capable of
sealing the joint or fitting. Compression set testing was done on the various standard cross section O-Rings per ASTM D395 Method B procedures. The testing time and
temperature were 70 hours at 100oC which is an accurate measure of Nitrile O-Ring performance. In standard compression set testing, a section of the O-Ring is squeezed
to 25% deflection, oven aged for the desired time and temperature, removed from the fixture and cooled to room temperature prior to measurement. Compression set is expressed
as the percentage of the original squeeze lost during the testing. In other words, the percent compression set is the amount of seal interference lost. The lower
the compression set, the better the O-Ring will retain its sealing interference and the longer the O-Ring life in the joint or fitting.
In the figure below, we have plotted the results from compression set testing done by Zatkoff. With every standard O-Ring cross section tested, Parker’s N674-70 was
clearly superior to the Asian sourced O-Rings for resistance to compression set. If we set the standard of performance at 50% maximum compression set, which is a reasonable
expectation for Nitrile O-Rings, the smaller cross section Asian O-Rings have a particularly difficult time meeting this expectation. Parker’s N674-70 meets this expectation
easily and is very robust across the range of standard O-Ring cross sections. The O-Rings from the Asian Source 1 even showed a worse resistance to compression
set at the standard 400 series, 0.275" cross section. This is indicative of utilizing ingredients strictly for cost reduction and shortening the critical process cycles to further
reduce costs. The process controls and traceability of the Parker process for N674-70 is clearly demonstrated in the compression set results.