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rod surface finish

rod surface finish

(OP)
Is anybody aware of any standards for surface finish for rods in dynamic sealing applications? We are using a double lip seal in a pump on our rods and have continuous leakage issues. Our current rod spec calls for 8-16 Ra which I think is way too rough. I have found some various ISo standards but nothing specific. An RMA OS 1-1 spec I have found does go into some details but will have to buy it to know for sure(unless someone is familiar with it here).

When we can pinpoint a finish we want, I need to understand the best way of specifying. As just an Ra finish leads some interpretation. I would like to expand upon it with Ra, Rz and Rpm values but need to determine what those should be for this type of sealing application.

Any help that could be provided would be appreciated.

RE: rod surface finish

What's the machining process? A "lead" along the surface can cause problems. Also, too fine a finish can cause problems. We had to go with a more expensive (Chicago Rawhide) seal to stop leaks on one high speed shaft.

RE: rod surface finish

Consult with the seal manufacturer about required surface finish. For polymer seals, too smooth a surface will increase friction and wear. Lubricated or non will make a difference.

RE: rod surface finish

(OP)
Thank you. Yes, have been working with our supplier and seal manufacturer for required surface finish. A simple Ra finish is all that's ever specified.

Have you found a simple Ra designation is adequate to obtain the required finish needed? We don't appear to be getting consistent results using this alone.

RE: rod surface finish

A 32 RMS honed or polished will work. It does everyday.

You need to supply more info. If this is rotational seal I opt out as a don't design parts that use them.

- CJ

RE: rod surface finish

If this is a reciprocating rod,, Check Merkel Surface Finish Parameters. Application engineer of the sealing manufacturer should be able to help you out.

RE: rod surface finish


Do they leak from new, or after an unreasonably short time.
How are you managing the oil flow internally? Is the seal subjected to full pressure? How high is that pressure?

page 2 here -
http://www.garlock.com/download.php?obj_id=2704

surface finish and lead are discussed in some detail.

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