Rubber O-Rings: Hardness, Strength & Compression Stress

In summary, the conversation discusses a query regarding the use of Rubber O-rings for sealing between two mating flanges of pipes under water pressure. The participant is curious about the relationship between the hardness of the rubber and its sealing capabilities, and is looking for equations and a catalogue to aid in the design process. There is also a discussion on the impact of over tightening the bolts on the flanges on the O-rings. The expert advice suggests consulting the manufacturer for specific information and learning the recommended torque for proper application.
  • #1
RKD89
78
1
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
 
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  • #2
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.
 
  • #3
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!
 
  • #4
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
 

1. What is the purpose of measuring the hardness of rubber O-rings?

The hardness of rubber O-rings is measured to determine their resistance to indentation or deformation under pressure. This is important in applications where the O-rings are subject to compression stress, as it ensures that they will maintain their shape and seal effectively.

2. What factors affect the strength of rubber O-rings?

The strength of rubber O-rings can be affected by various factors, including the type and quality of rubber used, the manufacturing process, and the dimensions of the O-ring. Different rubber compounds have varying levels of strength and resistance to compression stress, so it is important to select the appropriate type for the intended application.

3. How do you determine the ideal hardness for a rubber O-ring?

The ideal hardness for a rubber O-ring depends on the specific application and the amount of compression stress it will be subjected to. Generally, a higher hardness (measured in durometer) indicates a stronger O-ring, but it may also mean less flexibility and potential for cracking. It is important to consult with a rubber engineer to determine the appropriate hardness for your specific needs.

4. What is the recommended compression stress for rubber O-rings?

The recommended compression stress for rubber O-rings varies depending on the type of rubber and the dimensions of the O-ring. Generally, a compression stress of 15-25% is recommended for most applications. However, it is important to consult with a rubber engineer to determine the appropriate compression stress for your specific application.

5. How can I ensure the longevity of rubber O-rings?

To ensure the longevity of rubber O-rings, it is important to select the right type and quality of rubber, as well as the appropriate hardness and compression stress. It is also essential to store the O-rings properly and replace them periodically before they become worn or damaged. Regular inspection and maintenance can also help to prolong the lifespan of rubber O-rings.

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