Engineered Materials Group
Engineered Polymer Systems (EPS) Division

Tech Talk: Technical Data Sheets for PTFE Seal Materials

Session Replay & Transcript


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PTFE Material Data Sheet (Example)

Parker portfolio of PTFE material categories


  • 0100 Series:  Virgin PTFE, pigmented PTFE and mineral-filled PTFE
  • 0200 Series:  Fiberglass-filled formulations with versions that include pigmented, unpigmented, speckled and some mixed formulations with glass and moly (MoS2) compounds
  • 0300 Series:  Carbon-based compounds. This can be soft carbon, hard carbon or graphite type of material plus mixtures
  • 0400 Series:  Metal-filled materials which are primarily varying percentages of bronze-filled, but also included stainless steel
  • 0600 Series:  Nonabrasive and filled with polymeric fillers including aromatic polyesters, PPS (Polyphenylene sulfide), polyimides, and PEEK
  • 0700 Series:  Advanced formulations utilizing modified PTFE (mPTFE)
Verbatim Transcript

Time Stamp: [00:00:06.880]

Welcome to today's Tech Talk Session from Parker Engineered Polymer Systems Division. Today, we're discussing how EPS Division's Quality Laboratory follows standardized ASTM test methods to generate technical data sheets for EPS Division Seal materials. Our guest speaker will review how each of the line items found on a technical data sheet relate to physical and mechanical properties, as well as performance requirements of PTFE sealing materials. Our speaker is PTFE expert, and material scientist Aydin Aykanat, Ph.D. who holds the position of principal research and development engineer at Parker EPS Division.

 
[00:00:48.460]

Welcome Aydin.

 
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OK, before actually going into these like properties for Parker EPS PTFEs, we do have seven different categories.

 

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You have 100 series 200, three, four or five all the way up to like 600 series.

 

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100 series is mostly it's Virgin PTFE Pigmented PTFE along with also that we have some mineral filled PTFEs there.

 

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200 series is primarily actually glass filled formulations that are like 15, 25, 30 percent like glass with all pigmented and pigmented glass, also like speckled versions. In addition, there are also some like a little bit like mixed formulations with like Glass and Moly (MoS2) compounds there.

 

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300 is basically carbon based compounds. This can be like soft carbon, hard carbon or graphite type of like material.

 

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It's plus also like they are mixtures. We have 0307 material, which is 23 carbon to graphite mix.

 

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400 Series is the metal filled ones metallic like fillers in it, and primarily it is bronze-filled. But we do have a couple of formulations with stainless steel also. And in addition to like standard like bronze-filled compounds like 40 percent and 60 percent bronze, we do also have bronze with like moly mixed compounds like fifty-five bronze, five moly (MoS2), which makes like total like 60 percent filler in it.

 

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500 series is carbon fiber based ones are like popular compound, which is like 0502 is 10 percent carbon fiber plus two percent the yellow pigment in it. That's actually very popular and very good performing material. Other than that, we do have 10 and 15 percent standard carbon fiber compounds there.

 

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600 series is filled with polymeric fillers like aromatic polyester PPS, which is polyphenyline sulfide. We have polyimides, we have PEEK filled ones. These are actually great for soft counter surfaces. Like if you are going to be using against like aluminum, these are actually great 600 series are great material because they are not abrasive like glass fiber or unlike like glass fiber or like metals.

 

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And 700 series is more like advanced a little bit more expensive because it uses a special type of PTFE, which is called like Modify PTFE. And we do have all different type of kinds of formulations, compounds actually in that 700 category.

 

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Now, going back back to this technical data sheet, like I mentioned, 400 series is like bronze filled and 0401 is one of the most common PTFE compounds. This is like forty percent bronze. And the type of bronze, the shape, the size -- these are for this type of high end applications for challenging applications -- these are all optimized the particle size of bronze and distribution shape and whether it's oxidized or non oxidized. So these all have a huge, big impact on all like physical, mechanical and thermal properties.

 

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OK, first, let's start with the typical like physical properties. Specific gravity.

 

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Normally Virgin PTFE is like two point fourteen. If it is like hundred percent, its like two point fourteen (2.14). And PTFE is actually I guess it's the heaviest among like all the polymeric materials. It's all because of the fluorine structures on it and can actually put different types of like filler into PTFE. Some of those fillers, they can reduce the specific gravity, some of them, they can actually almost keep the same level. But of course, like since metals are also like heavy, they actually increase the specific gravity.

 

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So from two point fourteen (2.14), when you put like forty percent like bronze, it goes up to like three point ten (3.10). And of course, like for 60 percent like bronze formulation, this is even higher. I think it should be about two point twenty five (2.25), two point thirty (2.30) specific gravity levels.

 

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The next one, let's talk a little bit on Tensile Strength against the elongation properties, which is like stress, strain behavior.

 

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PTFE is actually different than all other thermoplastics or even like Thermosets. PTFE is a very, very inert material. So nothing in nature actually reacts with PTFE. So when compounding, let's say like epoxies or any other like. Polymeric materials, when you put like a certain type of soft fillers, let's say like glass fiber, those glass fibers , for other thermal plastics, they are actually surface modified so that they are compatible with the polymeric matrix actually, they are going in.

 

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But since PTFE doesn't have any reaction with any other material, whatever you put it in, PTFE becomes just like a filler. So there is no like chemical bond between the filler and the PTFE. Now, going back to that, your tensile strength, why am I saying this?

 

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Virgin PTFE typically has around like 4500 to 5500 tensile strength. So when you put any type of like filler in it, since there is no bonding between the fillers and PTFE and the strength only comes from the polymeric side - polymeric material- you're going to actually see a drop in the tensile strength from like, let's say, like 5000 psi. For Virgin PTFE, when you put like 40 percent bronze, it drops down to like 3200 psi, which is tensile strength that break.

 

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And similarly for Virgin PTFE, it's around like 450 to 500 percent like elongation. That also drops down to like a 250 percent level for this compound. Of course, actually, the more filler you put it in, this number is going to go down more and more. And we try to actually like a good performing one should compound a good performing even like very highly filled should still have at least like 1500 psi tensile strength, plus almost like around like 80 to 100 percent like elongation.

 

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So when I actually am going back to the mechanical testing this tensile elongation. What we do is we we follow ASTM D638 test method, which for PTFE we used like mini dog bone samples and the pull rate is two inches per minute. We attach those ones into like Instron machine and then we actually pull it with two inches per minute head speed and whenever there is any break, so the machine stops and it measured at that point it measures the tensile strength which is at break and also like elongation at break.

 

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In addition to those properties, we also keep stress strain curves and we can also like measure like tensile modulus, which is also called like elastic modulus. We can also measure yield point. It's the point actually where the material starts, like yielding where actually from like a plastic region to elastic region.

 

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Also like some other like properties like toughness, which is the area under the curve. We can all like measure those ones. But the important one here is tensile and elongation. In addition to those like standard ASTM test methods, we also do tensile elongation testing on the final parts, which is most of the time like in the form of like rings. So we can do like ring pull tests depends on actually customer specifications, like different pull rates, different geometries.

 

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So we can also like do all kinds of like a different tensile elongation testing on both on by using standard test method or also the customer specified test methods.

 

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The next one, Hardness. For PTFE actually use again like a standard ASTM D2240 by using like Shore D. It's actually very sharp pin that penetrates into PTFE or PTFE compounds and from there actually you measure the the hardness.

 

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Virgin PTFE is typically around like 55 56 Shore D. The highest hardness material of among like all the PTFE compounds is around like 67, 68 range. And those are like heavily, highly filled both like metal and sometimes those molys let's say like this 40 percent bronze is like 64. If you look at actually 55 bronze five moly, that should be probably around 66 to 67 hardness Shore D hardness range.

 

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This hardness is normally calculated at immediately as soon as there is a spike in the scale. But we also like do after. It also comes to equilibrium, after fifteen seconds. Some customers also like they ask for that type of like information you might actually see in some of those technical data sheets you might see like initial hardness or after like ten seconds or 15 seconds. And typically actually after ten, 15 seconds the hardness actually dropped between five to seven Shore D range.

 

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So if this one is that initially like 64, probably after ten seconds, it might go down to like around 59 or 58.

 

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Coefficient of Friction. Let me explain that one at the bottom, actually, with wear coefficient and how do we measure those? Because both of them, they are related to each other.

 

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OK, service temperature range, OK, this is very subjective. Basically, there's no, like, specific test to determine the real service temperature range for any type of like polymers or any type of like plastics. The reason is for each application, the application, conditions are different. For most of our applications, there is like pressure involved. There is heat involved. There is a speed involved. In addition, also, like there might be also chemicals involved.

 

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But in general, for PTFE by far among, like all the polymeric material, has the widest range of temperature resistance. Typically it can be used like plus minus 500 degrees F. Virgin PTFE. So whenever actually you start like putting fillers in it and the amount of like the fillers and the type of fillers is also important that let's say like we are looking at let's say look, we look at actually the upper temperature, virgin PTFE is around, like I mentioned, it's around like 500 degrees where there is no there's not too much like pressure on it and not so much like high speeds, pretty much just static environments or low PV dynamic environments like Virgin PTFE can resist all the way up to like 500 degrees.

 

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But like I mentioned, whenever actually you start like putting fillers in it and the type of filler, the amount of filler, shape, size, those are also like very important.

 

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You can stretch that upper temperature range all the way up to, let's say, five-seventy five degrees (575°F) Fahrenheit.

 

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Virgin PTFE, the melt temperature, not the service temperature. The temperature is around 628, 630 degrees. You don't want to be actually too close to the melt point because the material actually softens a lot and loses a lot of like mechanical properties. But let's say for this type of like material which has like high density and high compressive strength, it can actually resist all the way up to like five hundred seventy five (575°) degrees. And it can be warm and not only resist, but also function well without losing a lot of its performance and properties at certain pressures, temperatures and velocities. It can perform well up to those temperatures.

 

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Like a couple of different examples I can give. We rate actually our PTFE compounds from 500 to 575°F. Let's say like 10 percent graphite filled, which is our like 0301 material. It has like less percentage of filler in it, 10 percent plus graphite is not in fibrous form. It's more like under it's basically like slippery because it's a dry lubricant. The service temperature range for that material is around like 525°F.

 

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If you use like certain 600 series material, let's say like 10 percent aromatic polyester or even like maybe 15 percent PPS, that will be actually pretty much around like 550 range. But the ones that have, like, highly, heavily loaded, like 40 percent bronze or let's say like our 0718 material, which is used for high PV applications. It has both carbon fiber in it, a metal filler in it, and some dry lubricants and also like heavily loaded, almost more than 40 percent. That's also like rated up to 575 degrees Fahrenheit service temperature.

 

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On the low side, normally Virgin PTFE and modified PTFE (mPTFE), which is 0701 material. They are the best performing ones at very low cryogenic temperatures. You can still go up to below like almost like 300 degrees Fahrenheit (-300°F). For those two materials, especially modified PTFE is actually great for cryogenic purposes. Any time actually you start like putting some fillers in it, it makes actually the material a little bit like more brittle so that from -300°F it goes all the way up to -200° Fahrenheit. So that's actually the service temperature range.

 

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One thing I need to mention that differs from all the other thermoplastics or all the other like polymeric materials is the melting point or PTFE. It's 630 degrees. All other thermoplastic, when they reach to their, like, melt temperature, they immediately become like water. So their viscosity goes down like significantly. But PTFE, even though we call it melt temperature, in theory, actually it's not a melt temp -- it's called also like gel temperature.

 

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It does not melt. It gels. Gels means it's it doesn't become like water. It doesn't become like a low viscosity fluid. It still maintains its structural integrity. And the reason is it has like extremely high melt viscosity. So even at melt temperature, or gel temperature, the material doesn't flow.

 

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So why is it important? There are certain applications, especially like sometimes like dry running or non-lubricated environments, sometimes you might actually see big spikes in the test environment or in the application. The temperature might go up to 700 degrees.

 

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PTFE will still survive at 700 degrees or even beyond sometimes like even like 800 degrees. You don't want to actually go too high because of the some degradation properties starts actually after like 750 degrees F. But even after beyond melt temperature, PTFE can still, for a short period of time, maintain some of its mechanical properties. This is very important, actually. We do have some data actually on that one, comparing our PTFE High, which is 0718 material against PEEK, Polyethylethylketone for very high PV applications, where both of the materials, almost like melt temperatures are the same. But as soon as actually PEEK reaches up to like 630, 640 degrees F, --Boom,-- like it fails immediately, like catastrophically, but PTFE it still goes on and on and on and even at 800, 850 degrees, it can still actually keep going.

 

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So that's very important. Just to actually, I wanted to mention about here, when we talk about like service temperature, this is like long term temperature. But PTFE can still be used for beyond these temperatures for a short period of time or any type of spikes happening in the application.

 

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OK, thermal conductivity, Thermal Conductivity. Why is it important? PTFE is very non conductive. It's an insulating material. Even some of the fillers that you put it in there also like insulating. But for some applications, both thermal conductivity and electrical conductivity is very important. Why is important? Since PTFE, virgin PTFE is like insulating depends on the application, there might be actually big heat build up, heat generation, and that generated heat can build up actually under seal or on the part.

 

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So you want to actually dissipate at certain applications, that generated heat from the contact surface, from the bore and from the shaft to the outside.

 

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This is actually great material for this application because it's bronze-filled. Bronze is like metal and whenever actually put metal fillers in PTFE. Both the thermal conductivity and also the electrical conductivity also increases. For Virgin PTFE, I think it's around like zero point three (0.3) levels thermal conductivity, but using like 40 percent bronze, it improves almost like 50 percent higher. The percentage of like bronze you can it's still like going up to like 60 percent bronze. You can actually stretch that one to more than point five (0.5), basically thermal conductivity. So this is important. Like the low conductivity just dissipate, like heat build up, like in the environment. If not if you don't, the amount of like heat buildup can start to actually reduce the performance of the seal or the part because of course, at higher temperatures, the mechanical properties wear property, tribological properties, and most of the physical properties, they go down significantly. So that actually helps a lot, those type of like metal fillers to conduct the heat from the system.

 

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Thermal expansion coefficient.

 

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Why is it important, unlike metals or ceramic, polymeric materials actually, they expand with heat. Right.

 

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Like if I have certain length of like material polymeric material at room temperature, if I heat it up, that's not going to be the same length actually at 200 degrees compared to the room temperature. Why is it important?

 

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So in the applications, of course, there's always like heat there, especially like when the application engineers or design engineers, when they design certain seals, they need to consider how much the material is going to expand in application because not all the applications are run at room temperature. So they are running at certain temperatures. This is actually important thermal property that needs to be considered when designing actually a fixture.

 

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One important thing here is the parts are not always isotropic. When I say isotropic, it means the properties are not the same in a radial direction, in a longitudinal or in molding direction. So those like properties can change. Depends on actually what type of material that you are talking about. You need to consider this thermal expansion coefficient is important in which direction actually you are looking at. Even though here we only publish one most of the time we do tests in two different directions, both like molding direction or I mean, depends on the direction of molding -- longitudinal basically -- or like transverse direction.

 

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So this can be also different from each other, like I mentioned, depends on what type of like process you are using. A lot of customers, even though we use like Standard D- 696 test method by using our DMA, which is dynamic mechanical analyzer, and it's super, super sensitive, we do also test according to customer specifications in two different directions. And we can also like do it on the final parts, the seals, and also like do it on the radial side, when we do the billets or when we do skive sheets, we can also like test the material on the radial direction for thermal expansion.

 

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For thermal expansion, sometimes for certain compounds, we also display between different temperature ranges, room temperature to 150, room temperature to 200, 250 or also like 300. Because thermal expansion is not linear. So it's a little bit like exponential. So that's why different ranges needs to be specified for certain applications and for certain compounds.

 

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The next one is deformation under load. Deformation under load is very important actually for PTFE Virgin PTFE.

 

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OK, even though he has the best chemical resistance, temperature range plus minus 250 C, which is plus plus or minus 500 degrees F, and also like the lowest coefficient of friction among like all the polymeric materials, and that's why actually it's a great material for dynamic applications, one of the important drawback of PTFE is the formation under load. So whenever actually you apply a force or pressure on PTFE, the material, the PTFE is going to actually flow -- meaning that it's going to creep, which is like deform under pressure.

 

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That's why actually Virgin PTFE is not commonly a good material to be used for, like high pressures and velocity applications.

 

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In order to improve this property, we use actually different type of like fillers in it. Like this can be like fibrous, like glass fiber or carbon fiber. It can be like particles like carbon, soft part graphite, metal particles like a bronze or stainless steel, we can use like silica in it, moly (MoS2) -- these all actually improve creep or deformation under load properties of PTFE. So we do actually two different tests on deformation under load. Here we only actually show one of them.

 

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We either do at room temperature, which is like 70 degrees F at 200 psi, like pressure on the material. We do it for like 24 hours and we look at the amount of deformation under load. So we measure what's the percentage of change when we apply this much of load at room temperature after 24 hours, which is like four point four (4.4). And then we release the load, we actually wait for a certain amount of time. And because of the bounce-back properties, the material actually relaxes back and we measure that one after that, which is --- actually four point four (4.4) is the permanent deformation, six point two (6.2) is the deformation under load. It's the measure because it's higher. So when it's when it is like deformed six percent (6%) under pressure, the load is removed and then the material actually recovers one point eight percent (1.8%) and that ends up like four point four (4.4) after the pressure is released.

 

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In addition to room temperature and 2000 PSI, another standard condition is 500 degrees F and 600 PSI. Again, like for 24 hours. We can also like do at higher temperature. We have like large oven that we can actually put a test fixture in it and test it also for high temperature and 600 psi.

 

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That's also like according to D-621.

 

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Compressive strength. Compressive strength is also related with deformation under load, the amount of stress, the maximum stress. Also unlike actually tensile strength or tensile strain, compressive strength is more on the compressive loads, how much actually load is required actually to basically deform or like to break the actual material.

 

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This is not a very common test for PTFE because PTFE is not that brittle. Normally it is mostly important for like amorphous or like brittle polymeric materials.

 

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The important one is now the bottom one wear coefficient.

 

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This is more like an application property. This is more like a tribological property. We do have Lewis tribometer where we can actually test any type of material, including PTFE, Rubbers, and also like resins, or any other engineered polymers or ultra high performing plastic materials like PEEKs or polyimide imids or Torlons in that machine, for their wear performance along with also coefficient of friction. We use like standard ASTM D-3702 test method and it's, it's run at dry running conditions. There is no lubrication there. There's a certain test specimen size and shape. Also like the material is run against a certain type of steel with certain surface roughness. I think it was like Ra number is twelve plus minus four. And you basically apply pressure to the test specimen and it rotates against on a countersurface at a certain speed. Typically like 10000 PV is a standard number for some of the PTFE compounds. If you look at actually the ASTM 3702 for PTFE the range is between 1000 PV to 10000 PV. 1000 is typically for Virgin PTFE or low percentage of filled PTFE formulations. In between either twenty five hundred or five thousand PV can be used for like mid-level filler content, like let's say like 15 percent graphite filled formulations are good for those range. But for highly filled formulations, the standard. Is a 10000 PV, which is 50 PSI and 200 feet per minute speeds.

 

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Those are like rotating speeds. And at the end and the test duration is typically one week. But sometimes actually we stop the test after three or four days depends on actually whether the material comes to equilibrium. And at the end of the test, we basically first plot wear the amount of like wear versus time, coefficient of friction versus time, and running temperature versus time. The amount of wear is measured through the change in the thickness of the lip when it was actually running against that, the countersurface.

 

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So the machine is super, super sensitive. So even like less than one 10,000th of an inch (1/10000").

 

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So it can actually measure the thickness change. So from the amount of thickness change, we measure the wear rate. Similarly, the machine also measures the coefficient of friction. But coefficient of friction is all depends on the test condition. So the coefficient of friction that will be obtained from ASTM D3702 is not going to be the same as the standard coefficient of friction, the static quotient operation that we use to measure the coefficient of friction.

 

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The real numbers for PTFE that you are going to see in the literature, the numbers that you achieve through those like Instron testing. Because Lewis Tester is more like the application. But if you compare, let's say, nylon versus PTFE, you have to look at the instrument data in the literature. All the companies, when they publish their result, it's based on Instron like that type of like testing. That's the standard testing, comparing apples to apples. But for me, actually Lewis testing is more like an application testing. There's a standard procedure we follow, ASTM D2702 method predetermined by that test method. Everything is like predetermined, like the size of the test specimens and the pull rate, the amount of weight actually you put it on. So from there, it's very standard. You want to it's better actually on the Lewis Tester, it's more like application and the more customer, I would say specify testing.

 

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Along with, like all PTFE compounds, we pretty much actually test all other engineered polymers, rubbers urethane by using our like Lewis LRI Tribometer.

 

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It's a great tool. It's a great instrument machine, actually, to compare the work performance of different compounds at different conditions. Like we can actually vary the speed. You can go all the way up to like more than 5000 rpm with very high pressures.

 

[00:29:47.770]

As I mentioned, according to this ASTM test method, typically it's recommended like 10000 PV, but for some of the highly filled PTFE compounds, it's difficult, actually, to get reliable information at those PV ratings, because those are actually becoming very low numbers. So we actually like to test at much higher PV values like a hundred thousand PV, which is super, super, super aggressive environment. And that's also even like recommended by some of our top customers, like automotive customers. They prefer us to test our materials because they are so wear resistant PTFE compounds, highly filled PTFE compounds. Like a good example is like PTFE 0718 material, which is also like known for like high PV applications that goes into like automatic transmissions.

 

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So that can actually handle 100,000 PV values.

 

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So this is actually covers pretty much all physical, mechanical, thermal properties.

 

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Thank you, Aydin. We appreciate your time. That concludes this session of Parker Engineered Polymer Systems Divisions Tech talk.

 

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To learn more about Parker EPS Division and our engineered materials and products, please visit our website at w w w dot parker dot com forward slash E P S.

 

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Thank you.

Parker Hannifin Corporation
Engineered Polymer Systems Division
2220 South 3600 West, Salt Lake City, UT 84119 USA
(801) 972-3000

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