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TESTING THE LIMITS
Sample Stretch: Engineering Test Technician Wes
Lyon conducts a
tensile test using our Instron machine.
Open Oven: Quality Inspector Scott Bielby examines
our Blue M oven
and compression set test fixture.
Expanding our testing capabilities is an ongoing process.
by Rick Hudson
It has been said that success is a journey, not a destination. The same is true, I think, of quality. Providing quality products is an ongoing process that never really ends. But I also believe that a company’s willingness to seek out progress will determine both their quality and their success. I’m proud that we at RL Hudson are dedicated to continuous improvement. We are ISO 9001 and QS 9000 certified, and Quality Assurance Manager Richard Stanaland leads a skilled quality team. We also have our own in-house rubber chemist, Director of Materials Sam Burgess. Always seeking advancement, we’ve recently added several pieces of testing equipment. Let me tell you about our new capabilities.
TENSILE AND COMPRESSION TESTS We now have a tensile / compression tester made by Instron®, a worldwide leader in advanced testing instrumentation. Shown in the photo below left, our Instron allows us to place a rubber specimen (molded dumbbell) between a pair of grips (jaws). When the tester is activated, the dumbbell is pulled steadily until it breaks. The force being exerted on the sample at the time of rupture is that sample’s tensile strength. Tensile tests are fully described in American Society for Testing and Materials (ASTM) document D 412. Our Instron also features a compression load cell, enabling us to conduct compression-deflection tests on molded, cylindrical disk specimens or actual finished parts. Compression-deflection tests are detailed in ASTM D 575.
Why are tensile and compression tests important? Tensile tests let us gauge not only tensile strength but also a sample’s modulus (the force required to produce a certain elongation, such as 100% elongation) and ultimate elongation (elongation when the sample breaks). All of these characteristics are calculated and plotted via computer onto a tensile curve. Comparing a new sample’s tensile curve to a curve previously generated by a reference sample lets us verify material consistency. Compression-deflection data is imported into our Abaqus® Finite Element Analysis (FEA) software. Our engineers use FEA to simulate actual operating conditions and better predict the performance and life of a rubber part.
TEMPERATURE TESTS Another recent acquisition is a Blue M® horizontal airflow convection oven. Shown in the photo below right, our oven features a microprocessor-based controller. If you’re not familiar with how testing ovens work, the concept is simple: air is heated to a precisely controlled temperature, then passed over material samples inside a specially designed chamber. Air oven tests are detailed in ASTM D 573.
Why are temperature tests important? Most physical and chemical properties are impacted when an elastomeric compound meets high temperatures, especially with prolonged exposure. How a sample reacts to a heated test environment (Does it harden? Crack? Exhibit other changes?) is a good indicator of how that material will function in high temperature service conditions.
COMPRESSION SET TESTS Our Blue M oven also facilitates compression set testing, and we now have our own compression set test fixtures. These fixtures allow molded (or die-cut and plied) cylindrical test specimens or O-rings to be placed between steel plates. The plates are then forced together using a bolt-tightening device and steel spacers. Compression (typically 25% of original thickness) is held for a given time (for example, 22 hours) at a specific temperature (for example, 100° C), with both variables based on anticipated service conditions. Once the compression is released, measurements tell us how much set the samples have undergone. ASTM D 395 describes compression set tests.
Why are compression set tests important? Compression set is the result of progressive stress relaxation, a steady decline in sealing force that results when an elastomeric material is compressed over time. An elastomeric part (like an O-ring) that has undergone excessive compression set cannot seal effectively, so gauging a material’s compression set characteristics in a given environment is vital to seal selection.
AND THE PROCESS CONTINUES… I’m out of space for this issue; being CEO guarantees me only so much! Still, we have other new devices, including two shaft seal endurance testers, a hose burst test chamber, and an enhanced video imaging measurement system. I’ll describe them next time. Until then, please do not hesitate to call us at 1-800-722-6766 if we can help you solve a quality or performance issue. Rest assured, even as we at RL Hudson prepare to celebrate our twenty-fifth anniversary in 2005, we remain as dedicated as ever to the ongoing process of quality.
