Rubber O-Rings: Hardness, Strength & Compression Stress

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Discussion Overview

The discussion revolves around the properties and design considerations of rubber O-rings, particularly in the context of sealing applications under water pressure. Participants explore the relationship between rubber hardness, strength, and the effects of compression stress in O-rings.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant queries how the hardness of rubber affects sealing effectiveness in O-rings under pressure, specifically asking for equations related to compression stress.
  • Another participant suggests consulting O-ring catalogues for specific pressure and environmental conditions, noting that hardness and strength are related but also highlighting the complexity of rubber properties.
  • It is mentioned that properly designed grooves for O-rings should prevent overtightening from affecting the seal, although deformation of flanges could lead to sealing issues.
  • A participant with extensive experience recommends contacting manufacturers for detailed answers and emphasizes the importance of adhering to recommended torque values to avoid overtightening.
  • A later reply indicates that design handbooks have been found, leading to a better understanding of the complexities involved in O-ring design.

Areas of Agreement / Disagreement

Participants generally agree on the importance of consulting manufacturers and design resources for O-ring applications. However, there is no consensus on the specific relationship between hardness and strength, nor on the effects of overtightening, as these points remain somewhat contested.

Contextual Notes

Participants express uncertainty regarding the exact equations for stress in O-rings and the specific effects of hardness on sealing effectiveness, indicating a need for further exploration of these topics.

Who May Find This Useful

Individuals involved in engineering, design, or maintenance of sealing systems, particularly those working with rubber O-rings in pressurized applications.

RKD89
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Hi guys

I have a general query regarding Rubber O-rings.

For an application , say seal between 2 mating flanges of pipes ,with water pressure say about 10bars,

How exactly does the hardness of rubber effect the the sealing?

Is there a direct relation between hardness & strength ?

Can some one give me equations for the stress in O-rings when in compression?

A decent link would help, I have looked through stuff online , but still haven't found what I was looking for .

And how over tightening of the bolts on Flanges would effect the O-ring
 
Engineering news on Phys.org
Get a catalogue for Orings.

James Walker
busak + shamban

etc.

Look for your pressure, look for the environment. It even shows you how to design the grooves that it sits in.Hardness and strength are kind of related, but also not. Rubbers are odd like that. I realize this isn't a massively helpful answer, but the exact chemistry used to make the polymers means properties can be tailored.

O-rings sit in grooves, designed to give a certain operating compression. A correctly designed groove means that overtightening shouldn't affect the sealing at all. If you are overtighening to the point of the flanges (or whatever) deforming, then obviously there will be a sealign issue.
 
RDK89, During over 20 years experience with sonar systems I dealt with lots of "O" rings. xxChrisxx above is exactly correct...contact the manufacturer. They will answer all your questions. One tip: learn the recommended torque to apply and NEVER overtighten!
 
Thanks guys...I have found design Handbooks on O-rings...and now I understand why such a simple thing is a bit complicated to design
 

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