Bunna o-ring channel depth??

[migueld]

I'm making a channel for the bunna o-ring and I'm trying to figure out how deep should the channel go. My estimate is 80% of the diameter of the o-ring, regardless of diameter size, but I'm not sure, can anyone help? Before I show numbers let me warn that this is for a giant block, 8x18" for a passive radiator and that the smallest width our CNC can make is .25". Here's a simple sketch of the channel and o-ring's cross section:

[Dryadsoul]

Que passo Miguel, got no numbers but that looks more than do-able.

[migueld]

On a smaller block I tried making the channel 50% deep from the o-ring diameter and that didn't go well, the o-ring didn't compress as much as I thought it would leaving a space between the top plate and the plastic. So I want to avoid that, and I wanted to know how much percentage is usual with o-rings.

And about numbers, they are in the picture

[JAxen]

Could this be it?
http://forums.procooling.com/vbb/sho...1&postcount=23

[migueld]

Originally Posted by JAxen

Could this be it?
http://forums.procooling.com/vbb/sho...1&postcount=23

Hmm, I can't see it being 67%-70%, I did try 80% and it's still no good. I'm leaning to go with 90% because I want the plate to make full contact with the base, I don't want any space in between. It may have to do with the fact that my o-ring has a large diameter whereas with smaller diameters a lower percentage may be better. Still not sure.

Good find though, thanks JAxen.

[blue68f100]

Without a Parker O ring hand book handy, I think you only need around 0.025" - 0.050" for a static seal and this may be too much. You are not looking at high pressure. You need to use a low duromoter compound (60-70 or less), you will find it easy to assemble and seal.

[migueld]

Originally Posted by blue68f100

Without a Parker O ring hand book handy, I think you only need around 0.025" - 0.050" for a static seal and this may be too much. You are not looking at high pressure. You need to use a low duromoter compound (60-70 or less), you will find it easy to assemble and seal.

What do you mean by the durometer compound?

[blue68f100]

Durometer is the hardness of the rubber.

Lower the softer and easier it is to seal. You only need the 80+ if you are using high pressure and high temps. I have used a lot in the 40-50 which is harder to come by.

Here is the link for Parker O-rings handbook. It has engineering data for design/machining.

http://www.parker.com/ead/cm2.asp?cmid=3903&

[BGP Spook]

Was about to suggest something like that.

I could analyze your O-ring for deformations at different loadings if you could tell me what it's Young Modulus is and it's hardness number.

I doubt you would have that information though.

blue68f100, has the right idea.

[jaydee]

I have always used 75%. If that does not work then there maybe something wrong with your mounting system or an inconsistent O-ring groove or flatness of the material the groove is going in. Make sure your bolt pattern holding the 2 pieces together is not spread to far apart to cause the o-ring to bend the material you are trying to seal. Had that problem on a few water blocks. Simple solution add more bolts.

Without knowing the specs of what you are doing we can not limit the problem to just the channel depth.

[migueld]

Thanks for the info guys, I now have a few more variables to play with. The hardness of the o-ring is 70-75 so it's somewhat hard unfortunately and I might have to get another type. I couldn't find the Young Modulus, but I think it should be available somewhere online, the rubber I'm using is Bunna-N/Nitrile. From McMaster it's item 9679K21.

With this additional info it seems that one of my mistakes was not making the channel wide enough, that coupled with the durometer being 70-75 and 80% depth channel maybe less isn't allowing for the sort of compression that I need.