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Reduce Time and Cost of Damping Testing- Here’s How


Li Wan

Application Engineer, China

How Long Does it Take You to Test for Damping Properties During a Production Run?

Not to dampen your spirits, but until recently the state of testing for the damping properties of rubber was weak. Damping is a property that reduces the amplitude or even prevents oscillations in a system by a mechanism that opposes the changes in it. Simply put, damping represents a material’s capacity for energy absorption. In a wide variety of modern applications, rubber damping material is used for shock absorption or anti-vibration because of its unique viscoelastic properties. To reach different levels of shock absorption, rubber material needs to have corresponding damping properties such as stiffness and damping coefficient, and must be able to meet those needs over a wide temperature range. Therefore, the analysis of damping properties is of primary concern in designing rubber absorbers. 

Damping capability is influenced by many factors such as the nature of material, modulus, frequency, and temperature. Rubber absorbers and anti-vibration systems are usually used in a wide range of temperatures and frequencies, which have profound impact on the material’s damping capabilities. If the temperature decreases or frequency increases enough, rubber absorbers will become very stiff and brittle, losing much of their damping properties and resulting in little or no shock absorption. Glass transition temperature Tg or brittleness temperature Tb are often used to evaluate those properties. Generally, all rubbers have their Tg or Tb below room temperature. 

To determine these properties of the rubber material, many methods or instruments are used, such as the rebound tester, and dynamic and static stiffness tester. However, these test methods have a hard time keeping up with a production environment where testing not only requires timely analysis but also a high level of accuracy and repeatability. It’s clear that a more accurate and efficient testing method to predict damping properties of rubber material is urgently needed. 

Pretty Good Damping Property Analysis, but at a Big Price

Meanwhile. the dynamic mechanical analyzer (DMA), is commonly used in measuring the damping properties of rubber material, as it can be run in a wide range of temperatures and frequencies. The material damping coefficient related parameters Tan δ and modulus (stiffness) related parameters E can be measured at different frequencies and temperatures using a DMA and time-temperature superposition, as described in ASTM D5992. But the DMA is expensive – both the cost of equipment and trained technicians to run it – and slow. The DMA can only give you the ability to evaluate the post cure properties of rubber. This may make the expensive instrument you bought idle most of the time. But, what other options are available to you?

Consider the Premier RPA with Sub-Zero Technology

For many years, Alpha’s Premier™ RPA has been famous for its powerful capabilities and simple operation. Premier RPA can measure your compounds before, during and after cure in a single test, which is especially valuable in the characterization of rubber processing properties. That’s why we call it Rubber Processing Analyzer  – the test temperature range of an RPA can well cover the processing temperature range of rubber. However, when characterizing the post cure properties of rubber, due to the limits of test temperature (minimum test temperature is room temperature), it cannot meet the requirements of test temperature well, because you can’t put and operate an RPA in the refrigerator.

Image of the Premier RPA with Sub-Zero Technology from Alpha Technologies

But now, by adding Sub-Zero Technology to RPA, you enter a whole new world. Your RPA is not only a Rubber Processing Analyzer, but also a more powerful Dynamic Properties Analyzer. RPA with Sub-Zero Technology is capable of testing down to -25°C. This means the sub-ambient dynamic properties testing requirements of rubber are well covered. You can characterize the damping properties like you did on DMA. The storage modulus(G’), loss modulus(G’’), and loss factor (Tan δ) can be obtained. The change characteristics of modulus and loss factor with temperature, frequency, and other conditions can be tested. What’s more, all of those can be done easier and faster with one test, with no additional sample preparation, no highly trained technical staff needed. We call it a “foolproof instrument”, that can operate like an MDR, and is extremely suitable in a quality release or production environment.

The Accuracy You Need at a Price You Can Afford.

What? You are more concerned about whether the test results are consistently accurate. We did the comparison of test results from DMA and RPA with Sub-Zero Technology (see ig. 1). E* and Tan δ tested by DMA in tension correlates well with G* and Tan δ tested by RPA in shear with expected linear relationship, which show RPA’s powerful capability in dynamic properties analysis.

What’s more, by leveraging the exclusive Precision Dynamic Modulus (PDM) technology, you can achieve even greater accuracy with improved repeatability and reproducibility. Due to these advantages, the Premier RPA Sub-Zero can directly replace traditional DMA for dynamic analysis and QC of rubber material, saving time, material, and indirect costs. The RPA with Sub-Zero Technology continues Alpha Technologies’ leadership and innovation in the rubber analysis and testing industry.

Comparison of test results from DMA and RPA with Sub-Zero Technology

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