Solutions 2Q07

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Solutions Current Issues > April/May/June 2007 > Testing Capabilities

Testing Capabilities

We conduct chemical, physical, and mechanical tests.

by Rick Hudson

How do you verify that a material is what you expect it to be, or that it will perform as you need it to perform in a given application? The answer is simple: you test it. Testing is an increasingly important part of what we do here at RL Hudson.

When I founded this company back in 1980, I honestly had no idea it would someday grow to what it has become. I look at all we do today – the wide range of products we offer and the sophisticated services we provide – and I can hardly believe that it all started in a single room in my home. RL Hudson has grown far beyond my wildest dreams over the past twenty-seven years, and for that I am extremely grateful.

As we’ve grown, more and more of our customers have asked us to assist them with material and product testing. In response, we have established our own in-house material development and testing laboratories at our Engineering & Research Center in Oklahoma. We have our very own Banbury® mixer, as well as a mill on which to flatten mixed rubber into thin sheets. Samples from these sheets can be taken for testing. We also have our own press, which allows us to test-mold compounds into slabs.

We also conduct a wide array of testing. Our in-house testing capabilities can be divided into three main categories: chemical testing of material stock, physical testing of material stock, and mechanical testing of finished parts. Here’s a closer look at our testing capabilities:

CHEMICAL TESTING We utilize a Fourier Transform InfraRed (FTIR) spectrometer to analyze rubber and plastic samples. The samples are subjected to a beam of infrared radiation to produce a recordable spectrum, one that is unique to that material, like a fingerprint. Analysis of this spectrum allows us to identify and verify material ingredients. Plus, we can store the infrared spectrum in the form of a graph for future reference, giving us the ability to compare a material sample to all subsequent batches of that material, and thus verify consistency.

We also use a Thermogravimetric Analyzer (TGA) on material samples. By fractionation (material separation) at elevated temperatures, our TGA helps us determine the quantities of ingredients in a given sample.

Our Melt Point Indicator allows us to confirm material purity by identifying the melt point of a sample. Comparing this melt point to the melt point of a reference sample known to be pure allows us to verify purity.

PHYSICAL TESTING The most commonly referenced physical property is material hardness as expressed in either durometer points or International Rubber Hardness Degrees (IRHD). We can conduct durometer tests per ASTM D 2240 and IRHD tests per ASTM D 1415.

Our Instron® tensile / compression tester allows us to conduct in-house tensile tests per ASTM D 412. Our Instron allows us to place a rubber specimen (in the form of a 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 breakage is the sample’s tensile strength. Our tester also features a compression load cell, enabling us to run compression-deflection tests as described in ASTM D 575. Comparing test results allows us to verify material consistency and to predict material performance.

We have six elevated temperature Blue M® ovens. These are horizontal airflow convection ovens, and they feature microprocessor-based controls. Air is heated to a precise temperature, then circulated over material samples inside specially designed chambers. These ovens allow us to anticipate material performance in high temperatures based on the results of tests described in ASTM D 573.

Our Blue M ovens also facilitate compression set testing, and we have our own compression set test fixtures. These fixtures allows molded (or die-cut and plied) cylindrical test specimens or O-rings to be placed between steel plates, which are then forced together using a bolt-tightening device and steel spacers. Compression is held for a set period of time at a set temperature (with these variables based on anticipated service conditions), then the compression is released. Measurements are taken to see how much set the sample has undergone. Because compression set can cause an elastomeric part (such as an O-ring) to lose sealability, gauging compression set characteristics via tests described in ASTM D 395 can be very helpful when selecting a material.

We have a heating block manufactured by Akron Rubber Development Laboratory (ARDL) that lets us conduct elevated temperature fluid resistance tests as detailed in ASTM D 471. Our block features a digital temperature controller (with a maximum operating temperature of 400° C) and holds up to ten test tubes simultaneously. Fluid resistance tests enable us to evaluate how well a material will withstand the potentially degrading effects of fluids in simulated service conditions. We use a fume hood for solvent capture during flammable fluid tests.

Use of a Bashore resiliometer allows us to determine the resilience of a cured material by vertical rebound. As described in ASTM D 2632, resilience testing is important because it reflects a sample’s ability to regain its original size and shape after temporary deformation. The need for a material with good resilience can be critical in dynamic seal applications.

MECHANICAL TESTING We have two shaft seal endurance testers with multiple variable controls that allow us to test the effectiveness of seal designs. Our testers let us control test head temperature, shaft speed and rotational direction, shaft-to-bore misalignment, dynamic runout, and sump temperature, all with an eye toward simulating anticipated service conditions. New designs can be evaluated and existing designs refined based on the results of this testing.

On the subject of shaft seal testing, we can also gauge radial lip force using an electronic split-shaft tester. One half of the shaft is held stationary, while the other half is free to move, allowing it to reflect how much force is being exerted on it by the lip of a shaft seal. As described in RMA Handbook OS-6, lip force tests are important because they can help make sure that a shaft seal lip will not exert either too much or too little force on the shaft.

Our hydrostatic tester with chamber allows us to run hose burst tests per ASTM D 380. Our tester features a 48”-long tank and a dual pump system that allows both 0-1000 psi and 0-3000 psi testing. Because they record the pressure at which a hose sample ruptures, burst tests give a very clear indication of a hose’s ability to withstand a given pressure situation. We can also conduct coupling and outside diameter (O.D.) swell tests.

Because some parts will be expected to function in extreme cold or extreme heat (or, in some very severe applications, both), we employ a Thermotron® environmental test chamber to conduct high and low temperature tests. Our test chamber can handle hot-cold cycling from -73° C to 177° C (-100° F to 350° F).

We use a Differential Scanning Calorimeter (DSC) to verify the proper state of cure for a given part. Our DSC also allows us to gauge the glass transition temperature (Tg) for materials or compounds.

LOOKING FORWARD And that’s not all. We also have the ability to conduct fuel / fluid soaks, to study the leak flow of valves, to conduct heat-cold combined with pressure-vacuum life cycles, and to build and operate real-world simulation fixtures. We’re adding to our capabilities almost constantly, so by the time you read this, we will have probably added yet another testing device.

Why do we do this much testing? It’s certainly not to save effort or money, at least not for us! Testing equipment is extremely expensive, as is providing highly-trained personnel to oversee the labor-intensive tests. RL Hudson has made significant investments – in both equipment and personnel – over the past five years in order to expand our capabilities to what they are today. We’ve done all of this because we firmly believe that our customers deserve nothing less than the very best rubber and plastic parts available anywhere. As we hope is evident, we’re willing to do whatever it takes to make sure that the words “quality” and “RL Hudson” remain synonymous. Please do not hesitate to call us at 1-800-722-6766 if we can help you with a compounding or testing concern. We’ll be happy to put our expertise to work for you!