Galvanic Corrosion w/ Shim Stock?

[Doggert]

Hi - I'm a ChE + need some verification on the subject of shim stock.

I need to order shim stock for a mill which is comprised mainly of stainless and carbon steel.

I've come across some laminated aluminum shims that look like they may be much easier to use, as they just require our maintenance guys to peel off layers until they hit the correct shim size.

Is there a problem with using Aluminum shims on a spindle in a mainly stainless/carbon steel machine?

I'm not sure if galvanic corrosion would play a role here. The environment is the interior of an air classification mill which involves air (no humidity control) and metallic soaps as product (milling these to a powder).

Do I have anything to worry about as far as using Aluminum shims (related to galvanic corrosion), or should I stick with stainless?

Thanks.

 

[WoodyPE]

You can always seal the aluminum with some kind of coating.

If you annodize the aluminum, this should greatly reduce any risk of corrosion, galvanic or otherwise.

http://www.angelfire.com/planet/gadgetforum/index.html

 

[MikeHalloran]

The maintenance crew is not going to take the time to anodize or coat shims.

To make their job easier, I'd stock both stainless and plastic shim stock, and tools appropriate to cut and punch each.





Mike Halloran
Pembroke Pines, FL, USA

 

[WoodyPE]

Polypropylene will hold up to about anything. We use it with 100% sulfuric acid vitrol -- no problem whatsoever.

http://www.angelfire.com/planet/gadgetforum/index.html

 

[MintJulep]

It doesn't matter what the machine "mainly" is.

What are the materials that will be in contact with the shims?

Use plastic shims only in joints that carry no or very small loads. Plastic will flow over time, resulting in a loose fit.

 

[Doggert]

Thanks for your help guys.

I decided to play it safe and go with the stainless. I agree with Mike that our maintenance will more than likely not take the extra steps to coat the aluminum.

The actual material in contact is stainless.

Thanks!

 

[dimjim]

We used stainless steel shims in our wire race
bearings for years. The upper and lower rings
were aluminum usually 7075 or 6061. Do not know
that we had any corrosion problems. We opted
also not to use plastic shims for the same reasons
mentioned that they would flow or not support
the loads imposed on the rings.

 

[WoodyPE]

Plastic typically cold flows -- I agree. Why not stainless steel? It costs more, but how big is a shim?

http://www.angelfire.com/planet/gadgetforum/index.html

 

[WoodyPE]

BTW, without a picture, I really don't know what you're doing with the shims. How do you shim a spindle bearing? Does the shim conform to a round shape or a flat shape?

Sounds like you guys have it figured out anyway.

http://www.angelfire.com/planet/gadgetforum/index.html