Rubber material advice needed 1

[scoboni]

I'm having what appears to be flex cracking issues with some compression molded NBR elastomers I'm using on a bicycle seat post project. The NBR we're using performs well even with the surface cracks that have developed. We'd like to find a material that will perform like NBR but have a higher resistance to the cracking. I've attached a photo of the cracks in question. I've no in depth rubber engineering experience and am hoping to connect with someone here that can help on a professional basis. Please feel free to contact me directly at: scoboni@comcast.net

Thank you!
Ross Shafer
Six-Nine Design
707 765 1236

http://www.six-ninedesign.com

 

[GrahamBennett]

You've come to the right place scoboni.

The photograph looks like ozone cracking to me. Does your compound have to be red in colour? If it does, your options are limited to the use of non-staining antidegradants, which are not as powerful as the staining varieties. Staining varieties include the p-phenylenediamine (PPD) family, which provides high levels of dynamic flex cracking resistance.

Having a black compound will give you certain advantages including in-built UV resistance, the ability to use powerful but staining antidegradants, possibly reduced costs. I would suggest using about 2phr of 6PPD (Santoflex 13) + 1 or 2 phr of a blooming wax such as Sunproof Improved (static antiozonznt) as a starting point.

 

[tom1953]

If you don't need oil resistance, you might consider EPDM rubber, as it's inherently very resistant to ozone cracking. If you need oil resistance (is that why a nitrile is being used?), then a NBR/PVC (e.g., Paracril OZO) would give ozone resistance, but set might be defensive. Urethanes, castable or millable, are inherently very oil and ozone resistant, but moisture/water resistance might be defensive, especially with polyester urethanes.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[scoboni]

Thank you guys...your help is much appreciated!

 

[SealGuru]

Or better yet, you can choose which rubber material best suits your application in this <a href=”

http://mykin.com/index.php/rubber-properties”>rubber

properties chart</a>. The chart allows you to choose which rubber properties that are important to you. Remember, choosing the right rubber material is always a compromise. There is no one material that satisfies all criteria.

Best,
Michael

http://mykin.com

 

[Ltormento1]

Due to the clear color NBR is prone to be attacked by Ozone and Oxygen and have the cracks.
I suggest you to blend the NBR with EPDM or make the parts with CPE (as CPE is cured by peroxides a post treatment to eliminate odor is recommended).

Please check the interaction of the filler and the rubber it could be a source of the problem, too.

 

[Vicbowling]

SealGuru,

Thanks for posting that chart, it's pretty useful. I guess we're still waiting on that miracle material too.

custom rubber molding

http://www.meererubbermolding.com