O-ring groove design for non-circular groove 4

[RayJ2]

Hi,

I am designing a static seal with an o-ring.
The particularity is that the groove is non-circular. It has an oval-like shape (see picture in link below).
I am wondering how to calculate groove dimensions.

The medium is compressed air of 10 bar.
Pressure is on the inside, so the o-ring is pressed to the outermost groove wall.

I was thinking to calculate the groove the standard way as if the o-ring was placed in a circular groove, using some online calculator or the Parker Handbook.
Then, I would calculate my oval groove so that the outside wall ('outside circumference') of the oval groove has the same length as the outside wall of the circular groove.
Groove width and depth according to the standard calculations.
Would this be an acceptable calculation method?

Kind regards
Ray

 

[israelkk]

Do not use cyanoacrylate glue!! If the o-ring is not a silicone rubber you can use a silicon grease (-70C to 400C if I remember correctly). But to my opinion grease is not necessary. A grease is mostly used when the o-ring is installed in pistons and cylinder and rubs against the cylinder wall during installation to lower installation friction forces but is not needed is a face seal.

 

[saplanti]

I do nothave any question on the o-ring and its compression in the groove.
However there are certain surface quality is required for the o-ring grooves. In your case, I guess, there are some machining problems for the oval shape to meet the surface quality required. Are you sure that you can obtain the required surface quality with the oval shape? What kind of tool do you consider to manufacture this shape? Discuss it with your manufacturer to make sure you are on the right way.

Ibrahim Demir

 

[RayJ2]

@Ibrahim,
That is a good remark.
According to o-ring suppliers specifications, surface roughness for grooves should range from 0.8 to 1.6 um Ra (micrometer Ra).
That can be achieved with milling.

 

[racookpe1978]

Timely post. Good information above. Thank you.

---...---...

Related problem, different job.

I've got a oil-to-water heat exchanger here in Spain ( no 1/4 inch O-rings available) on a crit path job with no assembly drawings for the heat exchanger or maintenance spec's. Low pressure (40 - 60 psi) on both sides.

Only available O-ring kit has 6.0 mm tubing. (We believe the grove is designed for 6.5 mm (1/4 inch nominal) O-ring (3/16 deep x 9/32 wide).

O-ring groove measures at 4.5 mm deep by 7.5 mm wide.


Compression of a 6 mm O-ring = 6/4.5 = 33% (Good, based on comments above)

Area of 6 ring = 28.26 mm2
Area of 6.5 ring = 33.16 mm2
Area of 7 ring = 38.46 mm2
Area of groove = 33.75
It appears a 7 mm o-ring is too large.

Do I approve the 6 mm O-ring?

 

[tbuelna]

racookpe1978,

As long as your o-ring elastomer compound is of average hardness (60 or 70 durometer) then 1.5mm compression of a 6.0mm nominal section o-ring cord is more than adequate for sealing a deltaP of 60 psi. Most manufacturers recommend a maximum compression value of 35% for most situations. A static face seal type o-ring seals against the groove at the top and bottom points of contact. If you calculate the amount of friction force holding the o-ring in place, created by compressing the o-ring over its linear length, you'll be surprised at how much pressure differential it would actually take to push the o-ring out against one side of the groove.

Also, you mention that your o-ring is sealing an interface between oil and water. Take care to ensure that the elastomer you use is compatible with both fluids.

Good luck.
Terry

The 6.0mm o-ring x-section area is about 84% of your groove x-section area. This is a little bit more than optimum for a low pressure seal, but still should be OK.

 

[racookpe1978]

Understand, thank you very much. Will write it up that way for dayshift lead engineer to approve.

About 45 minutes from now. 8<)

 

[hydtools]

racookpe1978, the squeeze is 100*(6 - 4.5)/6 = 25%. Still OK. or (1 - 4.5/6)*100 = 25%

Here is the Parker o-ring handbook for future reference:

http://www.parker.com/literature/ORD 5700 Parker_O-Ring_Handbook.pdf

Ted

 

[racookpe1978]

For info: Air tests on both the oil coolers passed sat.

Thank you.

 

[hydtools]

Thanks for the feedback.

Ted