Cryo freezing bearings...........

[barthautala]

I have an ap where I need to press a bearing into a sleeve. I want to use liquid nitrogen to cool the bearing before pressing. where can I find a spray unit to accomplish this task? Has anyone done this? any advice?

 

[unclesyd]

Come back with a little more information.

What type of bearing?

A plain bearing probably while it's generally a no-no for ball roller bearings.

 

[iainuts]

We've been dunking bearings in LIN for a long time and haven't seen any obvious negative affects. Bearings are not sealed of course, and have no grease on them at the time of being dunked.

You can purchase a dewar of LIN from your local industrial gas supplier and just pour it into an insulated container. We use a stainless pipe cap placed inside a wooded box with fiberglass insulation around it.

 

[barthautala]

I meant to say bushing...........I know doing this to needle/roller/ball ect would not be smart.

Currently we're dipping them but doing manualy resulting in varying temps. Im going to build a fixture and spray them for a length of time to get consistent temps to ensure quality. Im pretty sure theyre brass........but Im not sure of the exact alloy. I looking at some drawings right now to figure this out.

 

[barthautala]

Im pretty sure that anything the LN2 comes into prolonged contact with needs to be stainless correct?

Because of the way the liquid evaporates you can place it into any container and it them becomes a pressure vessel. Am I correct in assuming that? Does the LN2 level off aftre a certain pressure? Would any vessel need a relief valve in case of over pressurization?

Thank you all for your help. Im LN2 stupid.

 

[unclesyd]

Do not close up a container of LN2.

Your supplier should have some information on handling LN2 or have someone instruct you on the proper procedures.

The aforementioned small Dewar comes with a very light foam cap that easily relieves any pressure in the container. These are used for handling small amount of LN2.

If you have a use for any amount you will get an LN2 cylinder from you gas supplier that is fully equipped to handle LN2 safely.

You would normally have an open top container to hold LN2 used to cool your bearing. When you immerse a warm object into LN2 there will vigorous boiling and splashing LN2.
Proper personal safety equipment is required when working with LN2.

When you drop a cold bearing in place let it warm up naturally, do not add heat.

Nitrogen is a hazardous gas and can cause death in very short time if not handled properly. All work with LN2 should be done in a well ventilated area.

Don't be afraid to ask questions.

 

[Junior33]

why would cryofreezing a roller bearing be a bad idea? traditionally the materials in the race and the rollers are the same so thermal contraction shouldn't be an issue?

that said I've never tried it, else I'd not be asking.

as far as handling LN2 goes. Would it make sense to use a mesh tray (forgive the crummy example, but like what they use in a deep frier at a fast food place to make your french fries) in order to dip parts?

 

[unclesyd]

There is nothing that prevents one from cooling a roller bearing to LN2 or any temperature. The problem comes in that the bearing materials are extremely brittle at these temperatures so it want take much to crack the bearing components. In warming up the bearings thermal gradients can get quite high.
There is a process to split bearings using cryogenic temperatures.

We use a SS baseket to hold bronze bearings for the cooling process. The idea is to keep the mass being immeresed as low as possible to mitigate boiling of the LN2.

PS:
All the mechanics will be using the LN2 to remove warts.

 

[barthautala]

Ive talked to a couple of other people over the weekend. They exlpained that dipping might be a better solution to the situation. However, this situation occurs in an automated workcell. The idea of spraying something automatically rather than having a container that opens and closes all the time seems more favorable to me.

The evaporation of LN2 is was causes pressure in the container correct?

 

[iainuts]

The closest thing to a commercial spray type unit I've heard of would be used in the medical industry such as this one:

http://www.delasco.com/pcat/1/Cryosurgery/FrigiSpray_Unit/dlmif020/

The only other relativly commercial unit that sprays liquid nitrogen I've heard of is used for spraying parts that are being machined. You can see something about it here:

http://www.manufacturingcenter.com/man/articles/0807/0807cryo.asp

If you're looking for some kind of automated unit that can spray parts with liquid nitrogen, I don't think you're going to find anything off-the-shelf. I'd suggest having something made. You could do this two ways.
1. Call your industrial gas supplier and tell them what you want and let them make it for you. Air Products for example, developed the unit used for spraying machined parts, but I suspect Praxair, BOC, Linde or any of them could do it.
2. Have the unit manufactured and buy it through a cryogenic manufacturer. I'd suggest looking through ThomasNet:

http://www.thomasnet.com/seealso.html?cov=NA&heading=21130208&sa=58390204&navsec=relbox

I can personally vouch for Technifab and ACME Cryogenics. I think either of them could do it.

http://www.technifab.com/

http://www.acmecryo.com/