Trepanning NRV washers.

Except the theory only applies in theory!!! Anyone remember Challenger? Cold O-rings = faulty sealing abilities.

Anybody that actually claims a rubberband works better at minus 100 deg C, than at 25 deg C, might just need a ground survey at ear level! How come winter tires are made of a softer compound than summer rubber?

 

Hi Henrik, this is a complex subject and any discussion inevitably involves the use of simplified ideas and illustrations. There can be no doubt that temperature does affect the elasticity of rubber, and the vast majority of scientists will tell you that, within strict temperature limits, cold rubber stretches more than hot rubber. Obviously if you go to high temperatures rubber melts and then burns. At temperatures below -70 deg C, rubber undergoes a transition and can behave in a brittle manner.

"On cooling, rubber undergoes a liquid-glass transition, which has also been called a rubber-glass transition. For example, the Space Shuttle Challenger disaster was caused by rubber O-rings that were being used well below their glass transition temperature on an unusually cold Florida morning, and thus could not flex adequately to form proper seals between sections of the two solid-fuel rocket boosters."

Tyre compound formulation is a science in its own right and the properties of the tyre depend on the nature and amount of fillers, and the degree of polymer cross-linking created in the "vulcanisation" process.

I am sorry if you have difficulty in accepting the facts about the effect of temperature on the elasticity of rubber. However, the great thing about science is that you can always repeat the experiment, and if you find differently, try to get your results published.

Best Regards,
Kerophile.

 

No problems here mate

My "issue" is that the linked answer is strictly on a theoretical basis, and can't by any means be applied to reality. For instance no mention of said type of rubber or it's compound, no mention of temperature range, no mention of any other relations. So it's strictly theoretically! If it applied in real life makers of O-rings would not need to state a lower working temperature?

http://www.pspglobal.com/teflon-oring.html

Quote: "It is interesting to note that the resistance to petroleum based oils and hydrocarbons increases when the nitrile content is increased in the elastomer (the elastomer may have a low, medium or a high content). At the same time, the low temperature flexibility decreases when you increase the content."

So it is not black and white at all, that's my point kerophile

 

Clever. I have a bad valve in my Carlson stove. I was thinking of using leather. where would I find nitrile?

 

Part of the problem with natural rubber compounds is that they continue to cure (vulcanise) at ambient temperatures. If you then elevate the temperatures they cure even faster. As all (black)rubber compounds contain varying amounts of carbon black, depending upon the hardness, the rubber will eventually carbonise (go brittle) and crumble.
For elevated temperatures, synthetic compounds (nitrile, viton) are best as they have resistance to oils and fuels.

Hope this helps

Bean

 

i used a bit of cork jammed in the end of the valve and works fine so far,

 

I've found an automotive antenna (the old collapsible type) has several sizes of tubing suitable for making different sized pips or gaskets this way.

Thread necromancy, beh