O-Ring Material for Molds

[wgknestrick]

We are having to replace O-rings for our molds during every service to prevent failure from O-ring compression set. We currently use 100 series Viton O-rings encapsulated in a .073" deep bore, for our static seal waterlines. General mold temps are around 320-350F. Each mold currently has about 200 O-rings that are replaced on each service, and Viton o-rings are anything but cheap.

Is there something we are doing that is leading to shortened O-ring life? Should we us Silicone over Viton or increase our pocket depth?

 

[btrueblood]

What kind of viton? A facetious question to some extent...but there are different grades, and various vendors who sell "Viton" O-rings may also blend other materials into it...and the bottom line is that regular-grade Viton is lousy in hot, hi-pressure water (it swells and cracks). Dupont will try and sell you a special grade of Viton that has better hydrolysis resistance, but good luck finding it in commerically available O-rings. You could try EPDM, but it will likely not be able to take the dry heat at 350 F. You may be forced into using something like perfluoroelastomer (FFKM) rings. Don't use silicone, it comes apart in steam and hot glycol.

 

[esqrkim]

wgknestrick,

First of all, make sure the amount of compression applied to the static seal O-ring is within the recommended amount for the O-ring width and the O-ring material. The depth of the O-ring groove in the mold would control this.

Secondly, I have never used viton in a mold before. For molds that were to be heated by hot oil (higher than 200F), I've always used 70 durometer silicone O-rings. We've never had problems with these.

Regardless of the material used, if the O-ring undergoes too much compression due to shallow O-ring grooves, then you will have problems. Parker O-ring offers very good documentation for O-ring applications.


**My comments are my opinions, and results are not guaranteed**
Eugene Kim

http://www.eeksolutions.com

 

[patprimmer]

That is an exceptionally hot mould. I find it hard to believe you would have water anywhere near it so I presume it's oil.

I wonder if you actually need any coolant and maybe the mould temperature could be controlled by electric elements and natural loss to the environment. Some controlled air circulation might help cool the hot spots.

From memory, elastomers for that temperature are silicone and fluorocarbons, but asothers have said, ask the "O" ring manufacturers.

Another possibility might be copper or aluminium "O" rings and something like a Threebond or Loctite sealing sompound.

What do they use for the oil seals on turbo charge shafts on the exhaust side?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Pud]

Gosh! Saw this post some time ago and did not realise the real temp of this tool! (max c.176)

We use tools for PPS (which we mould at 150 deg C) which are electrically heated with cartridge heaters. No probs at all with O rings as there are none!

Suggest you go down the route Pat suggested - install electric heating, insulating the tool if not already done so. Maintenance then zilch apart from a visual.

As an aside, we have a customer who insists on getting tools made elsewhere rather than involving us. It has just cost them 200 GBP to replace the cartridge heaters in a new tool as the wattage was insufficient to get up to temp within 1/2 hour.

What are you moulding - PEEK/PTFE/Thermosets?

Cheers

Harry