Surprising results from a multi-year study could change the way seal materials are used
It’s not uncommon for seal manufacturers to test their materials in various fluids to better understand their compatibility. Most tests run from a week to about a month. They’re performed in heated fluids to simulate hydraulic applications and determine if the materials will maintain their intended properties over time.
But System Seals wondered what would happen if the tests ran longer – much longer. Would they find different results? It turns out, they did.
For the past few years, System Seals has embarked on an exhaustive fluid compatibility study that paired more than 500 combinations of seal materials with commonly used fluids. Some of the tests were performed by customer requests, while others were conducted to round out the research and store for future use.
The difference in nearly half these tests, however, was the duration. System Seals ran the simulations from 60 to 90 days, and in some cases even longer. The results were astonishing. More than 25 percent of the material-fluid combinations that safely passed the 28-day mark began to fail near or after 60 days. This meant that a quarter of all tests that are commonly performed throughout the industry are showing false results.
Figure 1. The graphs above are for the same study. Note that after 7 (and even 28) days, it appears compatible. However, the 90 days study shows incompatibility after 60 days. Thus, 90 days reduces “false positives”.
All of the materials underwent stringent testing, included breaking points, tensile strength, elongation, volume swell, abrasion resistance and hardness – all qualities required for safe seal performance and longevity. Several of the fluid-material combinations that passed successfully within 28 days and then failed afterwards are widely regarded throughout the industry as acceptable.
“One critical point we discovered was that certain materials, such as HNBR, often have many different variations, and the variants don’t all behave the same way,” said Kurt Sassmannshausen, product development manager with System Seals. “Some materials perform quite well, but because of the varying levels of ACN, fillers and degree of saturation, others in the same family start to degrade after just a couple of months.”
The research not only debunked some commonly held beliefs about fluid-material combinations, it also proved that entire material categories can no longer be grouped as one. Specific material blends must be detailed by the OEMs with recommended fluids.
Fluid compatibility is a major cause of early degradation and seal failure. This was one of several major studies performed by System Seals, which recently introduced its new Cylinder Optimization Program – a systematic process that analyses a cylinder’s properties well beyond what is commonly known by the OEMs or end users.
For more information, contact a System Seals industry expert at www.systemseals.com or call (216) 220-1800.