O-Ring Groove Issues

[QSRP]

I am working on a project that is requiring a .040 O-Ring. I have been searching the internet for any information on what the size of the O-Ring groove should be and how to calculate for it. Everything I have found I just can’t figure it out. I have tried different widths and depths but I just don’t know what is right. Should the groove be rounded or squared?

If there is anyone who has experience in this area, it would be great if you could explain how to calculate the correct groove size and profile or what it should be.

 

[stevehuckss396]

How are you using the orings? Are you sealing a diameter or using them in place of cast iron rings in a gas engine?

 

[Brian Rupnow]

Could it be a metric o-ring? A millimeter is 0.039".---Brian

 

[QSRP]

Steve

It is being used as a seal. It is a face seal.

Brian

No it is not metric. I bought the stock from McMaster-Carr. It says the fractional size is 1/32, actual size .040. The M/C p/n is 96515K11.

It could be metric because I just tried to measure it and I got .039". It's hard to measure because of it being rubber.

 

[Brian Rupnow]

QSRP--I don't think what you are seeing is uncommon. I've used a lot of 1/16" cross section viton o-rings. They actually measure 0.070" diameter.

 

[rklopp]

Google Parker Handbook. That has everything you need to know. It’s free.

 

[Jasonb]

All imperial O rings are sold as nominal size eg 1/32", 1/16, 3/32, etc but actual diameter is always larger at 0.040", 0.070", 0.103", etc So you have a 1/32" nominal O ring

As said in this application the makers suggested compression is OK to use and can be found on the net. But you will be looking in the region of 0.032" deep x 0.054 wide for a face seal.

 

[ChazzC]

Here is the link to the Parker O-Ring catalog, which has all of the info you need:

https://performanceseals.com/wp-content/uploads/2019/05/parker-o-ring-sizing-chart.pdf?msclkid=b437f65eebd112e026bc972461258de2&utm_source=bing&utm_medium=cpc&utm_campaign=**LP - Search - Parker&utm_term=parker seals&utm_content=parker seals

Face seal details are on page 4-18; although Parker O-Rings start with 1/16"/0.070", you can scale the dimensions for your 0.040" O-Ring based on the sketches at the top of the page:

O-RINGS WEST has metric O-Rings (Metric O-Ring Supplier | Metric O-Ring Sizing Chart by O-Rings West), but their groove details appear to be lifted from the Parker charts:

Groove Design - O Rings West

The important thing is to follow the ID/OD based on the direction of the pressure acting on the seal.

 

[Peter Twissell]

I use a general rule of 20 to 30% compression for static o ring seals.
For a 1mm section o ring, the groove would be 0.7 to 0.8 deep.

 

[QSRP]

Jason and Chazz

Thanks Jason And Chazz. I have the parker handbook but it does not go down .040. That is why I came to the experts on here for some help. I decided to make a few cuts and see which groove was the best. What I came up with was .020"D x .050"W (.51mmD x 1.27mmW).

Peter

Thanks for the info. 1mm and .040" are basically the same thing. So for the compression of 20 - 30 %, I am taking the .040" x .20 and .040" x .30 and I come up with .048" - .052" for the width of the groove. Does this sound right? Tomorrow I will cut some test grooves with these numbers and look at them under a scope to see how they look.

This is the first time I am cutting an o-ring groove so I am trying to figure out how to calculate the depth and width of the groove for a specific diameter of o-ring.

Because this is not an average round o-ring, it is oblong not round, so I have to use o-ring stock and cut it to the correct length and then splice. The next thing I will have to figure out is the best way to splice the 2 ends together.

 

[Asm109]

At our work we fit round orings into odd sorta rectangular shaped grooves. These are face seals. Just have to get the circumferences right with about 2-3% stretch.

 

[Jasonb]

0.040 section, 20% of that is 0.008", 30% is 0.012"

So groove depth is between 40-8 to 40-12 = 0.032" to 0.028"

Your 0.020" deep sounds far too much

Simple way to use what is in the published charts is look up a 1/16" nominal ring which is 0.070" actual and then multiply that by 40/70 to get a depth or width for your 1/32" ring. So parker is 0.050" to 0.054" , take an average of 0.052"

0.052 x 40/70 = 0.052 x 0.571 = 0.030" which is also the average of the two figures above eg between 0.032" and 0.028"

 

[QSRP]

Jason

I understand how you got the 20% and 30% and you get 0.032" to 0.028 but the in your next sentence you say my 0.020 deep is far too much. If you say it should be 0.028" to 0.032" then my 0.020 is not deep enough. what you are saying is very confusing.

From what you are saying I understand how you come up with the 0.030" depth. How do you calculate the width? I am starting to understand but still confused.

 

[Jasonb]

Your depth is giving far too much compression as it equates to 50%

Width for your 1/32" nominal ring can be based on the width for larger rings by the same pro rata calculation for depth.

1/16" ring groove width for pressure is 0.0101 to 0.107 on Parker's chart so lets take 0.104" as the average.

0.104 x 40/70 = 0.104 x 0.571 = 0.060.

This allows the o ring to take on an oval shape when compressed as it should.

As your 0.020" x 0.050" groove is shallower it will make the O ring take on more of a rounded rectangle shape as it won't be able to expand before it touches the sides of the groove. If you stick with the shallow 0.020" then the groove would likely needs to be about 0.080" wide

 

[QSRP]

Jason

Thanks for your explanation on how to calculate the depth and width. I assume you are using this chart from Parker.

By calculating the depth and width with this chart, you are saying my depth should be 0.030" and the width should be 0.060". If this is correct, I understand how you calculate them. If these are not correct, I am still confused them.

What was throwing me off is that Parker's charts do not go down to a 0.040" cross section.

 

[Jasonb]

Yes usual sort of size would be 0.030" deep x 0.060" wide.

Yes a lot of the charts start at 1/16" nominal so that is why we have to use the pro rata method to get an idea ofthe right sort of size.

You can also look up charts for metric O rings where a 1mm does actually measure 1.00mm , page 14 of this PDF for example gives depth of 0.75mm x width of 1.35mm which would be 0.0295" deep x 0.057" wide so similar to the average from the parker chart.

https://www.hitechseals.com/includes/pdf/o-ring_brochure.pdf

 

[QSRP]

Thanks Jason

I appreciate your help. I understand now how you calculate the depth and width. I new 1mm and 0.040 are basically the same and if I could have found the brochure you have linked above, I think I could have figured it out.

Again, thanks for your time in explaining helping me figure this out. Learned something new.