Webinar: How To Read A Rubber Seal Test Report

How to Read a Test Report Webinar_Parker OES_2-22-2022.mp4 - powered by Happy Scribe

Thank you for joining us and welcome to Parker's Tech Webinar on How to Read a Test Report. My name is Samantha Sexton and I'm the Marketing Communications Manager at Parker O-Ring & Engineered Seals Division. Before we get started, I'd like to point out a few housekeeping items. All participants will be placed on mute during the webinar. Please take a moment to check your audio settings and ensure you are in listen only mode. We will have a Q & A session at the end, so if you have questions during the webinar, please submit these via the Q & A feature in your Zoom panel. Also, this webinar will be recorded. A recording will be available at www.parker.com/OES located under the Solutions tab. We will also send you a link to the recording via email. And lastly, there will be a short survey at the end of the webinar. Please take time to fill this out so that we can bring you future topics of interest. And now I'll hand the discussion over to our speakers, Shannon Wood and Nathan Tangyunyong.

Shannon

I'm Shannon Wood.

An applications engineer for the O Ring & Engineered Seals Division. I've been with Parker for over a year now. In this role, we receive hundreds of questions about materials each week and guide customers to the best choice for their particular application.

Hello, my name is Nathan Tangyumyong. I'm also an applications engineer for the O-Ring & Engineering Seals Division and I've also been with the company for about a year. Parker is a global company with a local focus. We have over 56,000 team members worldwide in 50 different countries with over 450,000 customers worldwide.

Selecting an appropriate material is key for success in your sealing application. Parker offers hundreds of elastomer material choices, and understanding material characteristics from the test report is key to choosing a suitable material. Today, we'll take a look at how to read physical properties including tensile strength, heat age, fluid resistance, temperature retractions, and other important considerations before a live Q & A. Accurate and comparable material test results can arm you with powerful data to help evaluate and ultimately predict relative performance of materials in many applications. But with so much data, we often hear what does all that test data really mean? To interpret test results, it's important to understand the tests and methodologies used to ensure that the data is gained by following an established testing protocol. Each material Parker offers will have a material test report like the one shown on screen to describe the material properties. This presentation will feature VM125-75, which is one of our low temperature fluorocarbon materials. The test report will start out with general information such as the compound name and color, as well as any specifications the material may need. This could be approvals for many different things such as food and water use, like FDA or NSF approvals to medical or military specifications.

In general, Parker labs use ASTM test methodologies to evaluate our compounds. Often test reports include an ASTM D 2000 call out like the one shown under specification to show which tests will follow. Today, we'll focus on the meaning of those tests. Within each test report, basic material properties are quantified. Typical test reports include original physical properties, heat age, compression set, fluid resistance, and low temperature testing. Today, we'll take a deeper look at how these tests are performed and how the results translate to performance in your application. Before taking a look at these materials, it's important to know your particular application details. In order to select a material, you will need to know your temperature limits, high and low, the pressure, and the fluids in contact with the seals. These parameters are the ones we need to know to compare to material test reports for suitability,

Hardness, tensile strength, and elongation, are physical property tests that form the starting point for material testing. These results are listed first on test reports and material spec sheets and provide basic material details. Hardness, also called durometer, is the measurement of deformation with a specified force. Results are commonly presented as Shore A hardness. A standard plus or minus five points tolerance is established to allow for realistic range and allow for variance experience while measuring the durometer. Results are given on a scale of 0 to 100, with 100 being the hardest. 70 durometer is the most common hardness for O-ring materials, with some O-rings being as soft as 40 durometer and as hard as 95 durometer. Other hardness measurements, such as Shore M and IRHD are also used. While similar, there's no conversion factor from one method to the other, and it's important to note that Short M or IRHD cannot be easily compared to Shore A results. In a rubber seal application, hardness is a primary predicator of pressure resistance and compressive load force. In a properly designed groove, an average 70 durometer material should be able to resist about 1500 PSI of fluid pressure without damage.

A harder 90 durometer compound can typically handle about 3000 PSI in the same mating hardware. The ability to resist pressure is a product of several variables, but hardness is generally a good predictor of the results if all factors are kept constant. Tensile strength, reported in English or metric units, is simply the maximum stress achieved during a tensile test. With rubber materials, it typically occurs at the point of breakage. The tensile strength is one quality assurance measurement used to ensure compound uniformity. This property can be tested using O-rings or test platens. Because O-rings are seldom stretched more than a few percent in application, tensile strength is generally less critical than other properties when evaluating rubber O-rings. It has more importance with other types of rubber components like diaphragm and duckbill valves. The ultimate elongation is defined as the increase in length expressed in a percentage compared to the original length. The ultimate elongation value is determined at the point of breakage and is often reported along with tensile strength as the test to determine these two values is the same. The test method most commonly used to test these two properties is ASTM D412. Elongation is often used to help determine how much a component can be stretched during installation.

Like tensile strength, the elongation is another quality assurance measurement used to ensure compound uniformity.

In a traditional compressed seal application, the rate of flattening out is a critical indicator to determine how long a seal will last. Compression set is defined by the amount of permanent deformation after removal from a compressive load. 0% compression set means that the seal would regain its circular shaped cross section completely. 100% compression set means that the seal is now fixed in its compressed state, which would look flattened or oval shaped rather than circular. In most static seal applications, it's the flattening out of the seal which causes the end of life failure. Unfortunately, mathematical calculations have not yet linked compression set values with actual service life, but general statements and comparisons can be drawn from the applicable data. Compression set testing is a simple test. This snippet from the VM125 test report shows a compression set test to our typical standard ASTM D395 method B. A sample of a known thickness is compressed 25% and held in place for a predetermined length of time at a set temperature. After cooling to room temperature, the sample is measured. The amount of compression set is reported as a percent of the compression that has been permanently lost.

Again, a 0% compression set means that the sample rebounded to a completely circular cross section. 100% compression set means that the sample has permanently deformed to the compressed thickness. As shown here, higher temperatures lead to more compression set. Now, compression set can be tested on samples of different dimensions. When comparing compression sets results, it's essential that the sample size be identical. The resulting value is roughly inversely proportional to the original thickness for samples of identical composition. Standard half inch thick buttons of material exhibit the best compression set value. A stack of .075 inch thickness will be slightly worse than a solid button. Small O-rings with .070 inch cross section will have the highest result. When all test variables are equal, the material with a lower compression set value can be expected to last longer in application, assuming no other failure mechanisms occur. However, but because there's no mathematical correlations that exist, there's no way of quantifying how much longer one material will last than another. Experience has shown that the leakage often occurs around the 80% compression set value. However, this is a very rough rule of thumb that does not apply in all applications.

Materials ability to withstand elevated temperatures is another area of interest in evaluating the performance of a rubber compound. Primarily, the changes in physical properties are measured. Heat aging is performed by placing either O-rings or platens in an oven for a planned time or temperature. To accelerate the aging effect, these tests are usually performed at or near the upper operating temperature limit of the material. Historically, these tests are specified to last 70 hours, but many recent specifications require durations of 1000 or even 2000 hours to evaluate long term effects. The physical properties, such as the hardness, tensile strength, and elongation, are measured after the specimens are removed from the oven and cooled - and compared to the original physical properties before heat age testing. Hardness results are reported as the points difference, while tensile strength and elongation are measured as a percent difference. Substantial changes in the physical properties of a sample indicate a degradation of the material. Although most seal materials hardened during heat aging, there are a few exceptions. Particularly when the temperature exceeds the recommended temperature limit of the material. Therefore, both hardening and softening of the material is of interest. Changes larger than about ten points Shore A may indicate significant damage to material.

As a rubber material hardens or softens, the tensile strength and elongation typically change as well. Changes in the tensile properties larger than about 25% should be further investigated.

Weather exposure is deliberate or accidental, every rubber seal will come in contact with a liquid, gas, or solid that could chemically interact with it. Fortunately, few solids or gases interact significantly with rubber, so testing is primarily focused on liquids. Three different interactions occur simultaneously when a rubber material is exposed to a fluid. Swelling is the most well known phenomenon. Negative volume change, which is shrinkage, is caused by the extraction of liquid phase constituents from a rubber material. Lastly, chemical reaction is a direct degradation of the seal material. Ultimately, minimizing all three interactions is critical to maximizing overall performance.

Swelling of a seal material is caused by absorption of the test fluid. This process usually reaches equilibrium within the first 24 to 48 hours. As a result, fluid immersion testing is typically conducted for 70 hours, just like the test shown here with VM125. Some specifications can require much longer 1000 or 2000 hours immersions. Every rubber specification with a fluid immersion requirement should include volume swell limitations. VM125 meets the requirements of 0 to 10% volume increase with only a 6% volume increase. In the event that such limits are not present, the following guidelines can be used for interpreting the results.

Fluids are considered compatible if they have less than 20% volume change. They're considered moderately compatible with 20% to 40% volume change, and fluids are considered incompatible if they result in greater than 40% volume change. For fluids with moderately compatible results, we caution you to use this material only in a static environment and to avoid using it in a critical safety application if a more suitable material exist. Negative volume change or shrinkage is a factor to consider in many cases, it affects the volume swell results. Many rubber compounds contain liquid plasticizers for improved low temperature performance or processing. During fluid immersion testing, the plasticizers can dissolve into the application fluid, resulting in shrinkage of the seal material. This process happens within the first few days of exposure. At the same time, swelling occurs. As the plasticizers migrate out of the rubber compound, they are replaced with the application fluid. The resulting net volume change will be lower than that seen for an otherwise identical material that does not contain plasticizers. A compound with negative volume change is an application fluid; will often experience premature failure as the seal material shrinks and pulls away from the mating surfaces.

Changes in physical property should also be considered in fluid immersion testing. For example, high temperature steam seldom causes materials to swell, but it can cause catastrophic damage. Steam can react with the rubber material through oxidation. It is not uncommon for this to result in an 80% loss in tensile strength and elongation values without appreciable swelling. Other chemical reactions can cause significant changes in hardness or tensile properties, but there are no universally accepted limits for interpreting these results. In general, hardness changes of less than 10 points and tensile strength or elongation changes of less than about 30% are typically considered acceptable. Hardness changes of 10 to 20 points are questionable, as our tensile and elongation losses of 30% to 50%. Changes larger than this are generally indications of incompatibility. There are several exceptions to these rules, so if there are any questions, reach out to Parker for sealing expertise for your particular application.

Seal function at low temperature is becoming increasingly critical. Aircraft flying at higher altitudes and oil drilling at higher latitudes may be the most visible, but practically every industry utilizing rubber seals is looking for the next big improvement in low temperature seal performance. Low temperature brittleness using ASTM test Method D2137 measures the crack resistance of a material at low temperatures. A sample is cooled, typically to negative 40 degrees Celsius, struck with a specified force, and then evaluate for cracking and/or breaking. Materials that don't crack or break are given a pass rating. This common method is useful for some mechanical applications. For example, automotive steering boots must withstand impact from rocks and road debris at low temperatures without fracturing. However, it has very little direct relevance to the function of a conventional seal. Seal materials that pass the test may not maintain enough rubberiness at that temperature to maintain a reliable seal. Conversely, it is also possible for seal material to maintain seal function at temperatures well below the temperature at which it fails an impact brittleness test. For this reason, low temperature impact brittleness is a poor indicator of seal function at low temperatures. A variation of this method is to bend or twist a sample at low temperatures.

This tends to be less severe than ASTM D2137. A material that fails to impact brittleness test may bend flat onto itself or round a manual without cracking at the same temperature. However, it still has little direct relevance to seal function. Determination of glass transition, or TG, using ASTM test method D3418 is another common method for evaluating thermoplastic materials. All polymeric materials undergo a low temperature phase change similar to freezing. Below this point, the material is glassy, brittle, and easily fractured. However, there are two fundamental problems with applying this method to rubber materials. The glass transition of most rubber materials is a gradual process that occurs over a range of several degrees, and there's also no widely accepted correlation between glass transition and loss of seal function. The midpoint of glass transition process is usually reported, but a published value could instead be the onset. The warmest temperature or final coldest temperature point of the transition. Leakage would occur at temperatures below the final point of the glass transition, but the specified portion of the transition in which seal function is lost varies dramatically among rubber materials. The temperature attraction method, also known as the TR-10 method, is currently the most reliable method of testing the low temperature sealing performance.

A rubber seal material sample is stretched 50% clamped in position and frozen. The clamps are then released and the temperature slowly increased. The temperatures of which the material has regained enough resilience to recover 10% of the original stretch is reported as a TR-10 point. This test directly evaluates the material, stops being rubbery, and starts behaving more like a soft plastic. As a result, it has proven to be an accurate predictor of low temperature behavior. In general, rubber seal materials can be expected to function reliably down to their TR-10 point in dynamic applications. In static applications, rubber seal materials can typically maintain a seal to 15 degrees Fahrenheit below their TR-10 temperature.

Rubber test reports provide a significant amount of useful engineering information about a rubber compound, and it's important to understand what all that data means. Be sure to note the following when reviewing test reports. The time and temperature of the test, size and shape of the sample, and the test methods must be the same for useful comparisons to be made. Test data should be gathered from a reputable test laboratory with substantial experience in working with rubber. Parker's test facilities are accredited to ISO 17025. In this presentation, we reference ASTM procedures. The corresponding GIS, DIN, and ISO procedures typically produce similar results, but they're not identical in all cases. Do keep in mind that test report and accuracy can and do exist. Rubber test reports are a good fundamental starting point for material selection or comparison, but actual performance testing should always be performed to verify the suitability of a seal material in a particular application. This information from test reports can be used as a benchmark to evaluate materials suitability for your application's fluids, temperatures, and pressures. As a user of seals, you should never hesitate to contact Parker and our applications engineers for assistance in understanding test reports and interpreting the results.

Thank you for joining us for our How to Read a Test Report Basics. You can scan the QR code to learn more about Parker O_Ring & Engineered Seals, we've provided our technical support email if you'd like to reach out for us at this time, we'll segue to our question and answer section.

Thank you, Shannon. So like Shannon mentioned, we're going to start a question and answer section. So our first question is, Where can I find a copy of a test report for a Parker compound? So some of our compounds have test reports that are listed on our website. However, not all of them unfortunately are listed. So if you ever have a Parker compound, or if you're looking for the newest one that we have, you can always reach out to us at oesmailboxcom@parker.com and we'd be happy to give you a copy of a test report.

Our second question is when discussing hardness, we talked about short A hardness, but there's another type of hardness, IRHD hardness. So this is really just a different test method for measuring hardness. Shore A uses more of a cone style depressor, while IRHD uses a sphere to press into the surface with a certain mass. So these are just different conventions of measuring the hardness of rubbers, but we usually use Shore A here at Parker.

The next question is do you do ozone testing? If so, how's this done? So there's a couple of different test methods when it comes to ozone testing. The one that we use most commonly is Per ASTM D1171. So we don't do this for every compound, but basically you take a specimen and you put it into a ozone environment, high ozone environment, and then after a certain amount of time, you're going to be able to see if there's any cracks that have come on the surface of the rubber material. So Parker does have the ability to test it. However, it's not something that we do for every single test report.

Another question is where are the data sheets located on the website? If you go to www.parkerorings.com, you can search for a relevant test report under the Support tab. If you ever find that the test report isn't the most updated or you're looking for additional information, don't hesitate to reach out to us. On our chat function, we'll speak with one of our applications engineers like Nathan Or. I.

The next question is why don't you include compressive stress relaxation results in your data sheets? So compressive stress relaxation results aren't part of ASTM and D2000, which is the normal test method we usually tested for. And typically we only do it for certain customers. Most commonly we do for automotive customers. Additionally, this is a very long test. Most CSR tests are thousand hours or longer, and so it's not something that we have decided to do for every single compound. But there are certain compounds, such as a lot of our AEMs and certain fluorocarbons that are common in the automotive industry that we have test data for compressive stress relaxation results.

Another question we have is how often are these typical tests ran for a compound? The data sheets can be from different years. So what's great about Parker is we've been offering some of the materials the same materials for decades, so we don't retest the materials every year since the formula has not changed. So that's a reason why some of the data sheets are a bit older. But we do periodically retest the sheet if there's something additionally that you need to know about the material or are just looking for an update.

The next one is when testing for compression percentage. If a seal has permanent damage, how often can that percentage be repeated? As in the first test shows 10% permanent damage. If you repeat the test on the same O-ring, we'll continue to lose 10% on repeat. Or are there diminishing results? So that's kind of a hard question to answer. Normally when we try to test compression set, we try to have a very controlled environment and so we want to have the same kind of result when we test it. So normally we test on a fresh specimen, so it's kind of hard to tell. It probably lose more compression set once it starts being compression set. However, it's something that we want to test with a fresh specimen to get consistent results.

We have a question about the fluids used in ASTM D2000. So there are typically a couple of common fluids, IRM 901, IRM 902, IRM 903, and a couple of fuel blends. So these blends give you a good idea of how the rubber would perform across different compatibility. So based on IRM 903, we have a good idea of assessing how that would perform in many different fuel types. So the ASTM D 2000 spec gives us a good idea of how something might apply to your specific application. And if you need help interpreting these results, don't hesitate to contact us.

So the next question is, is your software inPHorm software still available? This has been proven to be very useful for me in the past, so unfortunately our Inform software as the software is not available. However, on our website Parkerings.com, if you go to our website and our web page, we have a mobile version of inPHorm that is all the same features that inPHorm had. You also definitely have another tool that you can use called the seal selector. So this is another tool that you can use. That the same thing as Inform software did just now online that you're able to use it.

We have the question, does Parker have the ability to test seals with methanol and ammonia fluids? So we are consistently getting questions about testing in specific fluids. This testing can be quoted depending on the fluid itself. So with something like methanol, we do have the capability to test that in our Parker facility. But please reach out to your distributor or your sales associates and they should be able to connect them with our applications team, and we can work with the lab to set up any additional testing requirements that your customer may have specifically.

Our next question. Is material compliance information like Reach/RoHS available on the park website? So we do have it on our website if you search for it. However, Reach and RoHS are continually being updated, and so what's on our website might be a little bit outdated. For instance, Reach was updated last month, and so for the newest and greatest version of our compliance statements. For this, you can always reach out to us at oesmailbox@parker.com.

We have a question. How do test results vary if using an actual O-ring when conducting tests versus samples that are not O rings like the testing buttons or samples cut from a molded sheet. So the rubber should have very similar performance. The test report is based on a specific geometry, so a thicker specimen may perform better than something that is a smaller cross section. So typically we're looking at a larger cross section for the test report values. But this can kind of be thought of as a benchmark for performance when comparing to an O-ring in actual application.

So it looks like this is our last question. So the question is, oh, there's one word that came in. We'll answer this after, but my customer has a test support for ISO standards. Are Parker test reports applicable. So I mentioned in the webinar most of our testing is per ASTM test methods, which are the common test methods we use here in North America. ISO standards are commonly used in Europe, and so the tests are similar. However, there are some key differences between tests that are testing the same sort of thing like compression set or food resistance. Normally, these test methods have different procedures, different hardware is used, and so it's a nice reference when you're trying to slide to a material. However, when we're doing the quoting process, when we as application engineers are looking at a material, we usually take exceptions to ISO test methods, and we usually either take exception or we quote testing to ISO standards. So it's a nice reference. However, it's not perfect one to one match.

All right. And let's wrap up with this last question. Has Parker done explosive compression testing with hydrogen? If so, which compounds and where can we find the results? So we have a great reference guide called the Oil and Gas Industry Reference Guide, and that is ORD 5801. And this sheet lists all of our compounds that we recommend for oil and gas applications. And this includes certifications for RGB testing to ISO 23936, as well as older standards such as NORSOK, M71-10 and the API 6A testing. So this would also be listed under the support tab. And if you have any other specific questions, don't hesitate to reach out. Thank you so much for joining us for our how to test report webinar. We really appreciate you taking the time today.