low temperature O-ring seals

[Onno]

Hello to all

I am involved in a low temperature application of O-ring seals. A tank of 1 m length and 50 cm diameter has a flange at each side at must be sealed. Tank vacuum: better than 1e-5 mbar. Temperature range : -40 C to + 60 C. Gas permeability from atmosphere to vacuum is an issue.
At present I am using EPDM O-rings: hardness 70 Shore. diameter 329.57 mm and thickness 6.99 mm. First tests with these rings when cooling down seem to indicate that the acceptable cooling rate for the 2 flange halves and ring is limited to 0.1 degree C /min or lower in the temperature range -20 to -30 C.
This may sound impratical but our application allows for 12 hours to go from room temperature to operating temperature.
I am looking for some alternatives to EPDM and possibly some more information on low temperature use of O-rings.

Greetings

Onno

 

[flexibox]

Try Viton GLT or GLFT. I think min temp limit is 35C though and may be boarderline for your application.

Carboxilated Nitrile
(-54 C to +135 C) A nitrile elastomer with low temperature and excellent abrasion resistance. Commonly used in Downhole applications. petroleum oils, water brake fluid, phosphate esters. availability may be a problem.

trust this helps

 

[flexibox]

Found some more information:

Ethylene Propylene:
-54 C to +150 C Ethylene Propylene has excellent ozone and chemical resistance characteristics. Generally used in automotive brake systems. brake fluids, refrigerants, steam petroleum oils, diester lubricants

Fluorosilicone:
-56 C to +204 C Fluorosilicone combines the good high and low temperature stability of silicone with the fuel, oil, and solvent resistance of fluorocarbon. petroleum oils, gasoline acetone, ethyl acetate

Neoprene:
-40 C to +135 C Due to its excellent resistance to freon and ammonia, Neoprene is widely accepted as a preferred elastomer for refrigeration seals. refrigerants, alcohol, ozone petroleum oils, Toluene

Nitrile (Buna-N)
-40 C to +135 C

Nitrile (Low-Temp)
-65 C to +120 C Presently the seal industry's most widely used elastomer. Nitrile combines excellent resistance to petroleum based oils and fuels, silicone greases, hydraulic fluids, water and alcohols. It has a good balance of working properties such as low compression set, high tensile strength, high abrasion resistance, combined with a low cost. petroleum oils,
water, hydraulic oils brake fluid, ketones, phosphate esters

Polyurethane:
-40 C to +105 C An excellent elastomer with high abrasion resistance characteristics and high tensile strength. Used in high pressure hydraulic systems where highly stressed parts are subject to wear. petroleum oils,
hydraulic oils brake fluid

Silicone:
-65 C to +260 C Silicone elastomer is resistant to high, dry heat, in primarily static applications. It has low compression set characteristics and a wide temperature range. dry heat, alcohol, vegetable oil petroleum oils & fuels

 

[Onno]

Dear flexibox

Thank you for this nice overview. I have some comments on it.

-Ethylene Propylene: -54 C to +150 C
This is what I am testing at the moment. As said I have done two tests with EPDM and they seem to loose their seal at -20 - 30 C. However, yesterday I found a small hard spot on the flange and removed it. It was so small I only found it with a magnifying lens. The ring was also vacuum cleaned (outgassed)at 105 C for 24 hours. Tomorrow I will continue testing.

-Nitrile-low temperature: our supllier does not know the low temperature quality. Their regular quality of NBR (NBR-nitrile butadien rubber) has a temperature resistance between -30C and 120 C. This qulaity has my interest.

-Silicone: I can order this quality from the supplier. I completely missed it when going over the suplliers database. Thank you for reminding me on this quality.

In general: -40 C is a temperature which must be handled by the seal in our set up. That is why I concentrate on the seal materials with a temperaure resistance below -40 C

Anyway thank you. It was very helpfull.

Onno

 

[hella]

Try Creavey Seal Co
You want an energized O-ring for those temperatures
Also consider Helicoflex

 

[tom1953]

One thing to note regarding the low, and high, temperature properties of the various rubber types is that within a type of rubber the low/high temperature properties can vary considerably.
For example, within the EPDM family, the ethylene (the "E" in EPDM) / propylene (the "P") ratio can vary from about 50/50 to about 75/25. The polymers with lower ethylene content (the 50/50's) have much better low temperature properties than the higher ethylene polymers (e.g., 75/25 E/P). To give another example, with nitrile rubber (NBR: acryloNitrile Butadiene Rubber), the low acrylonitrile/high butadiene versions have better low temperature properties than high acrylonitrile/low butadiene polymers (BUT not as good oil resistance).
My company produces millable urethane rubber, and, similarly, there are grades that are much better for low temp properties than others.

So, with whatever polymer family you choose, make sure the rubber is formulated for the best low temp properties, or whatever other properties are important, by proper choice of the rubber grade and other ingredients.


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[Onno]

Thank you Tom

That is very valuable information. It primarily shows that I have to look for another supplier i.e. a supplier with a more detailed and knowledgeable character. The one we use now is more a off the shelf (just try it and see if it works) supplier.

I have a deep freezer now (-45 C) that has a built in temperature ramp function, connected to Helium leaktester. testing will start 1 february next year due to all kinds of in between impracticalities.

Beste regards

Onno

 

[sreid]

I go to Parker first for special o ring applications.

http://parker.mediaroom.com/index.php?s=press_releases&item=1003

 

[linamar]

I would suggest graphite, as it handles well both high and low temperatures.
I do believe your application is stationary, i.e. there is no rotation between the surfaces being sealed.

 

[Onno]

Dear all

I finished the first series of measurements on the application of EPDM O-rings for use down to -40 C in static vacuum sealing. A report is attached to this post.Thank you all for your interest and suggestions.

Onno

Summarized this the result:

An environmental chamber to be used in the testing of ExoMars Raman-LIBS system components under a Martian atmosphere (4-12 mbar CO2 pressure; -40 to +60 °C) is being
developed at the Vrije Universiteit. 1,2 The chamber will be sealed off from the earth’satmosphere using 2 flange/door pairs that are mounted on the left- and right side of a tubular shaped chamber (L = 1 m and D = 50 cm) (figure 1). Elastomer O-rings will be used to create
the seal. Most rubbers have a limited low temperature resistance. EPDM O-rings (copolymer of ethylene, propylene and diene), with a low temperature limit of around -50 °C, were selected from the supplier’s delivery program Using a helium leak tester and an especially developed test setup, tests under vacuum conditions at temperatures between +
60 and – 40 °C were performed. The temperature difference over the O-ring seal ranged from 0 to +60 °C. Warm-up and cool-down rates were between -1 and +1.5 C/min. EPDM provided a leak-tight seal under all conditions. The only drawback in application of the EPDM rings may lie in the amount of outgassing. An accepted material used in high vacuum sealing,Viton,was also tested. As expected, Viton is not suitable for low temperature sealing applications.

 

[israelkk]

The outgassing is a real problem. You should check NASA documents and outgassibg database. All sealing compounds used by NASA are for very low to high temperature due to the fact that temperatures in space can go very low far beyond the low temperatures in the atmosphere.

 

[azigue]

Silicone (depends on manufacturer compounds) is the best rubber for low temperature.
Otherwise you can use PTFE, graphite our metallic seals.

 

[kevindurette]

Have you looked at urethane? I saw a vendor recommend it down to -54°C. It has excellent abrasion resistance, but it has poor chemical resistance, compression set, and shelf life.

 

[msouza]

Parker V1289-75 can be used until -55°C. This is also known as Cryogenic Buna or Nitrile.
I hope it helps you!!!

Mario Souza
Application & Product Engineering
WMF Solutions Brazil

http://www.wmfsolutions.com