Hydraulic Bearings – Bearing the Load

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Deconstructing An ASTM D2000 Line Callout

Whitepapers On Whiteboard

 

EXPERT LEVEL:

2 of 5

LENGTH:

8:31

INSTRUCTOR:

Andrew Rommann

 

SUMMARY

The Society of Automotive Engineers (SAE) and the American Society for Testing and Materials (ASTM) established ASTM D2000 to help provide guidance when determining elastomer compounds. By using a method called the “line callout,” engineers have a readily available classification system.

Andrew Rommann breaks down the individual elements that compose this “line callout” and the benefits of using this method.


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VIDEO TRANSCRIPT

In many elastomer products, ASTM D2000 is utilized as the standard to communicate the performance requirements of the materials based on the customer’s expectations or the demands of the application.

 

An ASTM D2000 Line Callout

An ASTM D2000 line callout looks like this and is the entire line that you can see between my arrows. We have a specification that applies to the line call out. We have some basic requirements information and then we have what’s known as the suffix requirements portion of the line call out.

 

The Basic Requirements

So, within the line call out, within the basic requirements:

  • You have usually proceeding with an M which indicates metric units, so SI units.
  • You have a number following the M that indicates the grade of the material.
  • The first letter following that number is the type. The type for the materials is actually based on resistance to heat aging.
  • After that, you have class. The class is based on resistance to oil swelling.
  • Following that, we have a single digit that is representative of the hardness of the rubber. This has a 7 that could be a 70 durometer material plus or minus five. It also could be a 65 durometer material plus or minus 5, it could be a 75 durometer material plus or minus five.

So we’ll see that the durometer if that is a specific target you’re going for, you may need to add an additional suffix requirement to explain that.

  • Then the last two digits are actually representing the tensile strength of the material given in megapascals.

What you see on the left-hand side of the line call out – this is actually the minimum requirement that you need to specify an ASTM D2000 material. With this requirement, there is a set of basic requirements automatically imposed regardless of the grade of the material and without the existence of any of the suffix requirements. Those basic requirements include tests and performance results for heat aging, oil immersion, and compression set.

 

The Suffix Requirements

The suffix requirements as you can see the line call out is actually the greatest portion. What I have written on the board is the longest standard line call out that you could come up with for a M2BG710 material. This is a nitrile compound. Grade 2 correlates to the performance results of each one of these tests. For a grade 2, a grade 3, grade 4, 5, and 6, each grade will have different applicable suffix requirements. It will also have different levels of minimum performance to qualify as that grade of material.

In the suffix requirements section we see that we have a preceding letter or set of letters for each suffix requirement.

  • And so B14 and B34 with the B letter – they actually are both compression set tests.
  • EA 14 with the EA preceding this is a resistance to an aqueous fluid or water resistance.
  • We have EF and this is fluid resistance. Specifically, fuel resistance.
  • We have EO 14 E0 34. These are both oil resistance tests.
  • F17 is the low-temperature requirement.
  • And our Z call-outs at the very end Z 1, 2, and 3 in this case – are what we call special requirements.

 

Special Requirements

These special requirements are very powerful to help clarify specific items that may be required by a manufacturing process. A typical Z could be in this case for Z1. I wanted to clarify that the seven in the durometer call out is actually applicable to a durometer of 75 plus or minus five. I wanted to make that clear so I added the Z1 call out for that.

Z2, this could be the special processing in the manufacturing that I was referring to so maybe this elastomer component goes on to an assembly that goes through a paint line and ultimately through a paint oven there could be a small degree a small amount of time short duration or we have an elevated temperature and you wanted to evaluate the effects of that Temperature of the paint booth on the elastomer itself. So in this case, I’ve included a Z2 call out to say this ASTM method D 573 and I want to check it one hour at 125 degrees Celsius.

And then Z3 in this case. I wanted to come up with something a little bit out of the ordinary and this one I wrote down is must smell like vanilla birthday cake. It’s very unlikely that you actually need your product to have a certain fragrance, but it is possible to create a Z call out to impose any special requirement of any kind on the material. Keep in mind in doing that, you can prescribe a Z call out that is impossible to meet or could have a major cost impact on the overall material price.

So with these Z callouts, you want to make sure that you’re using what is applicable to your needs and not imposing anything above and beyond your requirements on the material.

 

Additional Suffix Letters

Some additional suffix letters are shown here. In addition to the ones that I’ve had this particular call out did not include a C12 call out and the C suffix would indicate an ozone resistance test. You could also have a G call out which is an air resistance test and there’s a small list of additional suffix letters that correspond to different types of tests that can be applied to different types of material. The combinations of grade, type and class could have a different list of suffix letters applied.

 

Benefits Of Using An ASTM D2000 Line Callout

So with all of this, based around the ASTM D2000 standard, and included on your drawing the major benefits of using it –

  • provides us a standard language to communicate our performance expectations and the performance requirements demanded by the application.
  • It defines the test methods that you’re going to use so that the testing can be done at any accredited laboratory and it can be done consistently, and results can be comparable.
  • it also defines the performance requirements by the combination of grade and type/class.

So with those things defined -both the grade, type, and class – along with the ASTM D2000 suffice requirements, we know exactly what tests need to be performed on the material and what the minimum requirements of those tests need to be to qualify for this requirement. It provides very clear information to the design team, to the manufacturer, and also to the quality assurance teams for products.

The Importance of the PV Value

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The Importance of the PV Value When Selecting A Seal

Whitepapers On Whiteboard

 

EXPERT LEVEL:

Intermediate

LENGTH:

4:25

INSTRUCTOR:

Jason Huff

 

SUMMARY

Pressure velocity, or PV value, is the combination of the pressure of the application and the speed of either the rotating or reciprocating shaft. The PV limit is the maximum value of that combination where the seal will function and wear normally. If we exceed that value, we’re going to see excessive wear which will lead to sealing failure.


There are several factors to consider when selecting a seal. Each factor has a direct impact on the performance and lifespan of your application. One of the most significant, but often overlooked, is the pressure-velocity, or PV, of your seal.

Jason Huff spends some time defining pressure-velocity, the calculations, and walking through examples to show its significance.


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VIDEO TRANSCRIPT

When selecting a seal, there are several factors that we need to consider. Including pressure, speed, temperature, the media you’re trying to seal, the hardness, and surface finish of the mating hardware.

And arguably one of the most important things that we need to take into consideration is the PV value or pressure velocity.

This is the combination of the pressure of the application and the speed of either the rotating or reciprocating shaft. The PV limit is the maximum value of that combination where the seal will function and wear normally. If we exceed that value, we’re going to see excessive wear which will lead to sealing failure.

 

Reciprocating PV Calculation

For a reciprocating application, to calculate the PV value:
– take the stroke length in feet
– multiply that by the cycle rate in cycles per minute
– multiply that by the pressure in PSI

 

Reciprocating Example

recip-calcseal-selection-chart

If we had an application that had a stroke length of 3-inches and a cycle rate of 80 cycles per minute and a pressure of 600 PSI:
– 600 PSI should be no problem for a quad ring
– A u-cup will handle 600 PSI – no problem
– And then obviously these two versions of a cap seal can handle 600 PSI

The issue becomes when we combine that with the speed of 80 cycles per minute, which is fast for a reciprocating application.

We’re going to take our:
– three-inch stroke length divide that by 12 to get it in feet
– multiply that by 2 to capture the entire distance traveled
– multiply the 80 cycles per minute
– multiply 600 PSI

That puts our PV value at 24,000.

When we reference our seal selection chart you can see both the quad ring and u-cup are no longer viable options and we’re going to have to stick to one of these cap seal options.

 

Rotary PV Calculation

 

Similarly, if we want to calculate the PV value for a rotary application, we’re going to take:
– the circumference of our shaft in feet
– multiply that by the speed in RPM
– multiply that by the pressure in PSI

 

Rotary Example

seal-selection-chart

If we had a 2-inch diameter shaft, and it was rotating at 1500 RPM and a pressure of 30 PSI:
– 1500 RPM for a traditional rotary lip seal – no problem
– A Flexi-lip or PTFE lip seal – no problem
– The same with these spring energized PTFE seals

Now that we have to consider 30 PSI that automatically puts are rotary lip seal out because that’s exceeding its max range – 30 PSI for the PTFE lip seal is no problem. Not a problem for the spring energized PTFE seals either.

But, when we combine the two:

– our 2-inch shaft divided by 12 so that we’re in units of feet
– multiply that by pi to get the circumference
– multiply 1500 RPM
– multiply 30 PSI

That puts our PV value at 23,562.

Again, now it eliminates those first two options as being acceptable seals.

 

Summary

It’s very important to not only consider the pressure and velocity independently – we need to combine the two so that we get a true understanding of what the seal is going to see in application.