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Hydraulic Sealing Basics

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Hydraulic Sealing Basics

Whitepapers On Whiteboard

 

EXPERT LEVEL:

Beginner

LENGTH:

5:45

INSTRUCTOR:

Jesse Thomas

 

SUMMARY

The function of hydraulic seals goes far beyond preventing leaks. Hydraulic applications require seals to withstand high pressures, extreme temperatures and transverse forces within the cylinder.

As an introduction, Jesse Thomas breaks down the different types of seals, glands, and considerations when designing your cylinder.


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VIDEO TRANSCRIPT

This video is intended for first-time hydraulics users, but we’re going to be diving into each of these topics in much more detail in future videos.

 

Anatomy Of A Hydraulic Cylinder

PISTON

To begin, we have the anatomy of a hydraulic cylinder. Starting with this chamber, the hydraulic fluid that is pressurized is provided through an inlet/outlet port. That pressurized fluid exerts its work on the piston and the rod to which it is bolted – which allows it to actuate linearly. To take full advantage of that pressurized fluid we are going to need to stop leaking across the cylinder piston.

We’ve got a leak path here between the piston and the bore and between the piston and rod. But these are two different problems. Between the piston the rod there’s no relative motion so we can just use an o-ring, but between the piston and the bore, we’ve got the opposite. We’ve got a sliding movement and for that reason, we’re going to need special geometries and materials to make a seal that can last.

This component here is the wear ring – simply is a strip, usually thin of plastic often nylon – that reduces the chance for metal on metal contact and damage. You could also see wear rings appear on the rod head gland side.

HEAD

The head gland on this cylinder has been threaded in. Giving us similar problems to what we saw on the piston and the rod. We have a zero dynamic motion application up here. We can just use an o-ring again between the bore and the head and then like the piston seal we’re going to need a rod seal between any sliding rod and static piston. This is especially important in a bi-directional cylinder where both chambers are occasionally pressurized.

Another component you’re going to see is the wiper. The wipers are particularly important in applications where the environment has debris that could enter your cylinder and damage your components.
To keep these components in the right place we machine glands into our metal parts.

 

Types Of Glands

 

OPEN GLAND

The most basic of which is the open gland. Open gland often used for wipers far at the front of the head. It is just a counterbore into the head and then you press in a metal OD wiper. The press-fit provides for retention and stability.

SPLIT GLAND

Split gland begins as an open gland and it’s used for difficult to install components in the head and also used for very small diameters – 5 mm / 6 mm. Instead of bending it into a certain shape and then installing it and allowing it to expand like you would for a typical rod seal or wiper, you just install it and it’s round shape before bolting on a faceplate to achieve a closed gland.

CLOSED GLAND

A truly closed gland is the most important of the glands because this provides the most control when you’re trying to seal something. That’s because you know the distance between the diameter where the gland ends, and the diameter of your rod bore – whatever you’re sealing against. As you’ll see in future videos this is extremely important for increasing the pressure rating of your system.

 

Considerations When Designing Your Cylinder

 

TEMPERATURE

Speaking of other design considerations, you want to look at the temperature. If you are in Arctic conditions or are using farm implements out in Iowa, you’re going to need to be aware of the temperature rating of your elastomer materials. A lot of these rubbers are going to lose their elasticity at low temperatures. You need to be aware of that.

SPEED & Ra/Rz/Rq

Speed of the rod, as well as the surface, finish your seals are sliding against. If it’s too rough, too fast, you’re going to be wearing out in no time.

ASSEMBLY & SIDE LOAD

– Have you understood the tools used to install these components?
– Do you understand that people are going to be stretching piston seals over a piston? You need to be aware of that to build a realistic hydraulic cylinder.
– Is there going to be a weight causing a cantilever motion that’s going to be forcing your piston against your bore? You need to be designing your wear rings to handle that.

MEDIA & CONTAMINATION

A lot of these elastomer materials do have chemical compatibility issues. You need to be aware of what fluids you are using, fluids you are going to be seeing out here, and what your customers going to be cleaning the cylinder with. Perhaps, it could have an impact on the lifetime of your seals. Contamination, same thing. If there’s solid ice on your rod when you start up the cylinder, you’re going to need a specially designed wiper for that application.

PRESSURE & GAP

The pressure is the first thing we think of. A lot of these seals come with catalog entries that have a pressure rating for the seal. However, like we’re going to see in future videos, the pressure rating is only as good as the gap – the extrusion gap. The difference between the diameter of the component with the gland and the diameter of whatever you’re sealing against. If that gap is too large, it doesn’t matter what pressure is going to be coming at it. It could easily extrude the component even though it’s pressure rating said it was to something much higher.
As I said, we are going over these in more detail in future videos, but that is hydraulic sealing basics.

Hydraulic Bearings – Bearing the Load

orings2

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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

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 seal 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.

Shaft Lead A.K.A “Twist”

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Shaft Lead A.K.A “Twist”

Whitepapers On Whiteboard

 

EXPERT LEVEL:

3 of 5

LENGTH:

8:45

INSTRUCTOR:

Andrew Rommann

 

SUMMARY

For optimum performance of seals, the shaft surface texture must be optimal. A rough surface texture will cause the seal to wear out quickly, while a smooth texture will cause the seal to bed incorrectly. The shaft lead, also called twist, is formed during the manufacture of shafts and has to be ideally zero.

Andrew Rommann explains the different types of shaft lead, what it does to a sealing system, and methods to measure.


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VIDEO TRANSCRIPT

Shaft lead also known as twist. Shaft lead, if not well understood and defined on your specifications, can have a detrimental impact to the performance of a dynamic sealing system.

Typical rotary applications have an elastomeric sealing element interfacing with a rotating shaft. On the shaft surface, the characteristics are very important and critical to the proper operation of the sealing system.  One of those characteristics is shaft lead.

 

Macro Shaft Lead

A typical manufacturing process may be the use of a single point tool against a rotating shaft where the tools actually traversing the surface of the shaft. This operation will result in a spiraling groove pattern around the circumference of the shaft. In this type of pattern, we refer to it as macro lead – has a continuous thread-like structure.

 

Micro Shaft Lead

An alternative process maybe traverse grinding.

In this case, we don’t have a single point tool rather a stone with multiple points that contact the rotating shaft. The stone is still traversing along the surface of the shaft and it does result in micro lead. The threadlike structures are not continuous, but they do have a deviation from the circumferential direction of the surface of the shaft resulting in shaft lead.

 

Two Orientations of Shaft Lead

Shaft lead can have two orientations. It can be a right-hand orientation. Where it’s shown here on the moving from the bottom right to the top left corner of the image and left-hand lead where you’re actually the threadlike pattern is from the bottom left to the top right.

 

Results In A Sealing System

So what does this do in a sealing system?

Again, in a rotary sealing system, we have an elastomeric sealing element that is interfacing with a rotating shaft.

If we look closer at the surface of the shaft and in this illustration, I actually have drawn a right-hand lead type structure. We can see where the oil is in contact with the shaft surface and the sealing lip.

As the shaft rotates depending on the direction of rotation, it will actually transport oil from left to right or right to left. Because this is right-hand twist if we have a right-hand rotation – so the top of the shaft moving towards the bore – we will actually end up with movement of the oil from left to right. So in this case out of the sealed system resulting in leakage.

If we have left-hand rotation, so in this case, the top of the shaft moving out away from the bore you will result in movement from right to left. So left-hand transport. This will help retain the oil in the system.

However, if it’s aggressive enough transportation of the oil it will actually result in a lack of proper lubrication at the interface between the sealing lip and the shaft surface could lead to premature wear of the sealing lip.

 

Twist, Rotation, Transport

 So again right-hand twist right-hand rotation – the transport is to the right. A right-hand twist with a left-hand rotation – the transportation is to the left.

 

String Method & Optical Method

So how can we measure and hopefully quantify shaft lead on an actual physical component? There are two major categories out there. There are a lot of different methods developed over the years, but the oldest and most well-known method is referred to as the string method or the thread method.

In this method, you mount a shaft in a rotating device. You drape a thread with a weight attached to it over the shaft. From the side view as you slowly rotate the shaft you may observe movement to the left or to the right from its original position.

If you do observe movement, you are observing that the shaft likely has lead. You cannot easily and precisely quantify accurately the amount of lead that exists in the shaft, but you can get a qualitative sense of whether or not you have left-hand or right-hand shaft lead.

A more precise and accurate method of measurement is using an optical method. In an optical method, you are creating a 3D mapping or 3D profiling of the entire surface of the shaft.

Software can then collect the data and process it to produce a representation of the effective shaft lead of the system.

The image on the left you can see as you move in the circumferential direction from 0 to 360 Degrees. You actually have axial movement along the shaft. In the one on the right-hand side you can see as you move from 0 to 360 Degrees, you actually have zero movement along the axial position of the shaft. This one we would refer to as having right hand lead this one having zero lead.

Using the optical methods, you can get a precise and accurate quantification of the lead angle, which can be useful when you are inspecting or qualifying components for a new product.

 

Industry Specifications

Some of the specifications that exist and are used in the industry that you may see include ISO 6194 – 1 and DIN 3760. Both of which specify zero lead. RMA OS-1-1 actually does tolerate lead to a very small level.

There are other specifications out there. There are also specifications that exist for most major OEMs where they have expanded on the information that’s available in the industry standard specifications.

 

Conclusion

 

The main thing to remember is that if you are not aware of what your tolerances for shaft lead in your sealing system, or you’re not aware of what your actual lead is, you could end up with performance issues that are not easy to identify the root cause.

And in many cases we find that in a situation where you’re not able to identify the root cause of a sealing system failure in a rotating system – if it’s not a tribute attributable to the elastomeric seal or to other obvious installation design issues – in some cases it’s actually result of the presence of lead that is hard to detect and again not very well understood.

Durometer Scales – The Basics

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Durometer Scales – The Basics

Whitepapers On Whiteboard

 

EXPERT LEVEL:

1 of 5

LENGTH:

4:10

INSTRUCTOR:

Jason Huff

 

SUMMARY

Today we’re going to talk about durometer of rubber products. Durometer is a measurement of hardness and like other hardness test measures the depth of indentation in the material created by a given Force using a standardized pressure foot. The ASTM D 2240 standard recognizes 12 different durometer scales.

 

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VIDEO TRANSCRIPT

Shore Hardness Scales


Shore OO Durometer Scale:

duro-shore-oo

If we look at some of the most common scales used across the industry, we can start with the Shore OO The indenture for the Shore OO is the conical bottom there in this scale is used for extra soft rubbers. Some examples of this would be like sponge rubber or Gummy Bears or even the gel insoles for your shoes.

Shore A Durometer Scale:

duro-shore-a
Another very common durometer scale used in the industry is the shore A durometer scale. You can see that the indenture for this one is a truncated cone. This durometer scale is going to cover your soft medium and hard rubbers. Some soft rubbers could be like rubber bands or a pencil eraser. Some more medium hardness rubbers would be car tires or a little bit harder than that, maybe the sole of your shoe.

Shore D Durometer Scale:

duro-shore-d

And then after that, for much harder materials, we’re going to jump up to the shore D. You can see this is a 30-degree cone. Some examples of products you would use the shore D hardness tester on would be like a shopping cart wheel, which is a very hard rubber or even some plastics when you get to the higher range of the shore D –  like a hard hat or something like that.

IRHD Durometer Scale:

Another very common durometer scale used in the industry is the IRHD – the international rubber hardness degree. This scale is very closely aligned with the shore A but it is not exactly equivalent. We can’t compare an IRHD to the shore A and think that their equivalent.

Important Note For Testing:

One important aspect to note is the test methods used when testing durometer.

When you’re using any of these Shore OO, Shore A , or D, or the IRHD scales, you need to be using a large thick flat piece of rubber. The piece of rubber needs to be a minimum of six mm thick and large enough that all of your measurements can be taken at least 12 mm from the edge of the material. This can create some obstacles when you’re trying to measure small rubber products such as o-rings. Most O-rings don’t have a 6 mm thickness. So if you’re trying to use a Shore A durometer tester on the typical o-ring that’s going to be an incorrect measurement method. It’s not valid.

Shore M Durometer Scale:

In the case that you do need to measure physical parts with small cross sections, you’re going to have to use the shore M durometer scale. Again, you can see that this is a 30 degree cone. It is a little bit smaller diameter than the short D and also would have a different spring force applied to it. But with this scale you can measure samples as little as a 1.25 mm in diameter.

Understanding AS568 Aerospace Standard

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Understanding AS568 Aerospace Standard

Whitepapers On Whiteboard

 

EXPERT LEVEL:

1 of 5

LENGTH:

6:02

INSTRUCTOR:

DJ Rodman

 

SUMMARY

The AS568 o-ring size chart, published by the Society of Automotive Engineers (S.A.E), sets a standard for universal o-ring sizing. The chart specifies the inside diameters, cross-sections, tolerances, and size identification codes for 349 o-rings used in sealing applications.


DJ Rodman spends some time covering these attributes at a high-level.


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VIDEO TRANSCRIPT

 

Today we’re going to talk o-rings. We get frequent calls, request for quotes, emails, regarding o-ring and o-ring sizing. Today we are going to run through and explain how o-rings are sized and talk a little bit about the language of o-ring sizing. O-rings are sized using AS568; which is an aerospace standard that was published back in the seventies. The original AS568 was published in 1971, since then there have been several versions A through D – you can see the years that they were published – 1995, 2001, 2008, and 2014 is the latest.

The Three O-Ring Sizing Dimensions

When we talk o-rings, we are of course are talking about circular seals, but more importantly, when we say o-ring, we mean the o-shaped cross-section – or round cross-section. Because a number of seals are round but the cross sections are not circular. So today we are talking about the circular cross-section seals.

O-rings are sized using three different dimensions. There’s the ID which is the inner diameter. There is the OD which is the outer or outside diameter, and then there’s the cross-section which is also known as the width. So those are the three dimensions that are most important.

AS568 Universal Table

 As we look at the standards themselves. The first thing that I do want to clarify is that sizing is important when it comes to o-rings. You can get close to dimensions, but you want to be careful because those o-rings are sized using a squeeze and fill percentage, which is critical in sealing and it does affect the overall sealing of the application. So if you have questions about the groove or groove size console an application engineer.

The AS568 dash numbers refer to a specific ID and cross-section. The OD is listed when you look at tables, or in particular when you look at the tables for a manufacturer, but it’s not necessarily needed.

The AS568 numbers are uniform across manufacturers. It does not matter who. You are going to see the same dimensions and you’re also going to see the same tolerances.

So in our example, we’re looking at a -001 o-ring. That o-ring has a 1/32 inch ID and it has a 1/32 inch cross-section. We can look at it from a nominal standpoint and we can also look at it from an actual standpoint. That actual standpoint- it would be an ID of .029 inches with a tolerance of + or – .004. The cross section would be .040 with a tolerance of .003 inches. Again, this is universal across manufacturers. As long as it’s AS568 referenced, all of these dimensions should be the same.

As you look at the dash numbers – as they go up higher you get into thicker cross-sections. So for instance, a -120 o-ring is 1 in by 3/32 of an inch – actually translates to .987 + or – .010 with a cross section of .103 + or – .003.

Again, use the table, use any manufacturer – we have Parker in particular – use the table provided by the manufacturer and then use tools. We don’t necessarily recommend a caliper, although you can get close to those dimensions. Also, you can use an o-ring cone which would get you the actual AS568 reference for that part.

All in total, there are 349 AS568 dash numbers that are available – these are tooled-up. Any o-ring manufacturer should have 349 sizes available.

Non-Standard O-ring Sizes

Now in addition to your standard AS568 dash numbers, when it comes to o-rings, I do also want to reference that there are 3-9XX sizes available – few limited. These are considered boss or the tube-fitting o-rings – sized specifically for threads and the end tube fittings.

There are also nonstandard sizes that are available, and those sizes depend on the manufacturer. They’ll be a list of available sizes that have been tooled up outside of the AS568 references.

One last note as you’re talking about AS568 sizes, do keep in mind that tooling for these sizes at manufacturers is unique to the material or the compound that the o-ring is made up of and this is due to shrinkage rates and shrinkage rates on material varying. So the tooling itself will have to vary with that.

I appreciate the time. If you have any questions, feel free to contact our website at espint.com or industrial seal.com.

Deconstructing An ASTM D2000 Line Callout

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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.


Click on the image to open in a New Tab.

 

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.

Not All O-rings Are Created Equal! Part II (Elongation)

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Not All O-rings Are Created Equal! Part II (Elongation)

Whitepapers On Whiteboard

 

EXPERT LEVEL:

1 of 5

LENGTH:

5:46

INSTRUCTOR:

Don Grawe

 

SUMMARY

In most applications, to create an effective seal an o-ring must be slightly smaller than the groove it sits on – stretched during installation. But how much can it stretch and still be effective?

In the second part of Not All O-Rings Are Created Equal, Don Grawe covers elongation – how it’s defined and how it’s impacted by the base polymer, hardness, and curing process.


Not-All-Orings-Are-Created-Equal---Part-2--high

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VIDEO TRANSCRIPT

Welcome to our next installment of how all o-rings are not created equal. Today we are going to talk about elongation and to start us off we’re going to use the trusty Parker handbook to give their definition and then go from there.

Parker defines elongation, as it pertains to o-rings: as an increase in the length expressed numerically as a percent of initial length. It is generally reported as ultimate elongation and further, like tensile strength, elongation is used throughout the industry as a quality assurance measure on production batches of elastomer materials.*

Okay, what’s all that really saying?

 

Elongation comes down to how far can my o-rings stretch?

What we need to know when looking at how far an o-ring can stretch is:

  • How far do you need it to stretch?
  • What are the other variables that go into selecting o-ring materials and the like?

The primary reason that’s important is especially the smaller the o-ring gets, there are applications where you have to be able to stretch it over a fitting, over some type of a ledge to get to the groove that you ultimately need to be able to get to.

Always consider the elongation when it comes to installation. With that, elongation gets measured by ASTM requirements in our physical properties. We talked about compression set, when we talked about tensile strength, we talked about abrasion resistance – they all fall within the ASTM D2000 requirements.

How that affects the different materials and the ratings for elongation. Let’s look at three of the most common materials that you work within the industrial marketplace. That being nitrile or NBR, FKM or fluorocarbon, and EPDM.

 

From a pure polymer standpoint, elongation is as the definition, a numerical number or a percentage of the original size that the o-ring will stretch.

A 70 durometer NBR o-ring, typically by ASTM D2000 requirements, will stretch 250%. In practicality, most quality compounds will exceed that significantly. In the case of a 70 durometer EPDM, you’re looking at a 200% stretch. Again, most compounds, quality compounds, will exceed that by a good measure.

The closer you get down to 100%, the tighter those variances will be. With an FKM or a fluorocarbon material – 75 durometer very common – now you’re looking at only 150% stretch. So from a pure base polymer standpoint standard compounds, these are your norms.

 

How does the effect of hardness of the o-ring impact elongation?

Let’s stay with the two common NBRs and FKMs. If the only thing I change is hardness and go from a 70 durometer nitrile to a 90 durometer nitrile, look what happens to my elongation. Now, my elongation is only 100%. Common applications for fittings and couplings etc. 90 durometer is a common durometer because of the properties that that hardness will give but also understand you can’t stretch it near as much as you can the 70 durometer nitrile. In the case of fkm also a significant hit from 150% for 75 durometer to only 100% for the 90 durometer.

Let’s throw one more variable in there. If compression set is a significant factor in your application, a peroxide cure o-ring is a common go to when it comes to compounds and materials.

 

How does the curing process within the manufacturing of the o-ring impact elongation?

Well, a sulfur-cured 70 durometer nitrile is really the baseline that we were comparing over here at 250%. But by going to a peroxide cure material, higher compression set material, one with a little higher tensile strength – look what happens to your elongation at the same 70 durometer hardness. Drops from 250% down to 125%

Base polymer, hardness, curing process all have an impact on elongation.

 

One last thing I want to point out.

There’s some give and take as there is with most compounds and most elastomers when you’re trying to reach a particular physical property within that. Elongation just like any of the others.

To get performance in one property sometimes means giving up performance in another physical property.

You want elongation, you got to stretch this part significantly without breaking, but in order to get that based on the other criteria:

  • Do I have to give up compression set?
  • Do I have to give up tensile strength?
  • Do I give up abrasion resistance?
  • What are the give and takes?

Know the basics – elongation- how far can I stretch but what else do I need my material to do?

Again, not all o-rings are created equal!

SOURCES: *Parker Hannifin Corporation, “Parker O-Ring Handbook – ORD 5700”

Obtaining Elastomer Shelf Life

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Obtaining Elastomer Shelf Life

Whitepapers On Whiteboard

 

EXPERT LEVEL:

2 of 5

LENGTH:

2:08

INSTRUCTOR:

Hanna Nguyen

 

SUMMARY

“Shelf life” is the maximum time (beginning with manufacture date) that an o-ring or elastomeric seal – with proper packaging and storage, becomes unable to meet its original specifications.


Aerospace Recommended Practice (AP 5316) is the most comprehensive basis for establishing shelf life, however, it is not a binding specification.


Let’s look at a few Methods at which shelf life is being calculated.

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VIDEO TRANSCRIPT

 

5 Methods to Obtain Elastomer Shelf Life

Some materials are listed as unlimited, however unlimited is not equal to forever. For some companies, they use 25 to 30 years as unlimited shelf life. According to the study EPRI NP-6608, which is one of the references in ARP 5316, which replaced by Aerospace Standard 5316, in the study it talks about five different methods to obtain elastomer shelf-life.

1. Method A: MANUFACTURERS RECOMMENDATION

shelf-life_method-a
It is acceptable to use field experiences data or lab test data, however, using military standardization handbook or rubber products or warranty, then other methods are recommended.

2. Method B: NATURAL AGING

shelf-life_method-b

Data is collected by products being stored for a number of years in an average room temperature. This method is time-consuming and yet it is a case-by-case basis.

3. Method C: ARRHENIUS CALCULATION

shelf-life_method-c

Shelf life can be obtained by using this extrapolated graph or EST equation, which requires materials in qualification data or using EDT equation and only materials data is needed.

 

4. Method D: ACCELERATED AGING

shelf-life_method-d

By using a test chamber at a given temperature, data can be obtained by measuring critical properties periodically until data drop below acceptable values. Then the EST equation can be used to estimate the shelf life.

 

5. Method E: APPENDIX B

shelf-life_method-e

Appendix B is where roughly 70 generic materials were summarized by using Method A, B, and c and is listed in years.

Metal Face Seal Basics

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Metal Face Seal Basics

Whitepapers On Whiteboard

 

EXPERT LEVEL:

1 of 5

LENGTH:

4:18

INSTRUCTOR:

Jason Huff

 

SUMMARY

Metal Face Seals provide superior performance in extreme applications where positive lubricant retention and the ability to keep out damaging and/or abrasive materials are essential. This level of durability has become a choice of OEM earth-moving equipment and machinery. The high cost of equipment downtime requires the best available seal.


Let’s start today with the basics of metal face seals: the components, profiles, materials, and common applications.

 

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VIDEO TRANSCRIPT

Metal Face Seal Components:

Today we’re going to talk about Metal Face Seals, otherwise known as duo-cone seals. What they consist of is two metal rings and two large o-rings, or toric rings. They come in seal sets. This would be one half of the seal set – one metal ring and one o-ring. Each half is then installed into the housing [you can see here] and then the two halves of the housing are brought together and it creates an axial load between the metal seal rings. So the actual dynamic movement will be between the two metal rings. You’ll have one side of the housing that is stationary and one side of the housing that rotates. There is no relative motion between the seal ring and the o-ring or between the o-ring and the housing.

Profile Options:



They come in a couple different profile options:

  1. Traditional Duo-Cone Style
  2. The Trapezoidal Elastomer Ring Style


Some advantages of the trapezoidal rings style would be that you get to machine just a square step in your bore to receive the seal rather than machining in this complicated geometry that’s necessary for the duo-cone option. These types of seals are very heavy duty. They’re used in extreme service environments where you would not be able to use a traditional elastomer lip style seal. They just wouldn’t survive. The contaminants are too harsh and they would chew that style of seal up.

Materials:



Some of the different material options that we have available for the METAL RINGS


– we use cast iron for ours with graphite inclusions in there. This allows us to run at higher speeds than the steel forged counterparts that are out there on the market as well. We’re able to do anywhere from very small two very large sizes (50 mm up to 1-1/2 meters. The cast iron is also very corrosion and wear resistant as well.


Some of the different material options that we have available for the ELASTOMER OR TORIC RINGS


– are the NBR material. It’s got good oil compatibility and compression set resistance. If we need to we can bump up to an HNBR that gives you a little bit higher temperature capability and also gives you some ozone resistance as well. If we need a higher temperature yet, then we’ll jump up to FKM, but you do sacrifice a little bit of that low temp capability versus the NBR or HNBR. If you’ve got very high-temperature extremes from very low or to very hot, we can go to silicone but with silicone, we have to take special consideration with the type of oil that you use.

Applications:



These types of seals are used in a wide variety of applications – most commonly in the construction field. Your bulldozers or your excavators – anything with a track drive is typically going to use these metal face seals. But they’re used in a variety of other applications as well; mine haul trucks, they’ve got tunnel and boring equipment that use these a lot, we’re getting into the agriculture market more, and even some offshore applications as well with dredgers and tidal turbines also a good fit for the seals as well and pumps.

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