5052-H32 Corrosion Problem

[MadMango]

Hello all,

I have a corrosion problem and I’m looking for some advice. A section view of the problem area can be found here.

Yellow- .25”thk 5052-H32, powder coated tray
Pink- 14ga 304 SST, powder coated pocket
Red- 3/16” 304 SST, passivated AMS-QQ-P-35 Type II
Dark Gray- Oilite Bronze Bearing
Light Gray- 304 SST threaded insert
Light Gray Thrust Washer- Oilite Bronze

I have about .125” clearance around the aluminum part and the SST pocket. This product was installed in a city transit bus between 24-36 months, and had severe corrosion to the yellow tray. So severe, that the oilite bronze bearing and thrust washers were gone, and the material thickness of the tray was reduced to about .030”. I know that aluminum tray should probably be anodized instead of powder-coated, but due to costs, we cannot change this aspect.

I know I probably haven’t provided enough information, so I will try to provide more as required. I’m looking for advice on material changes to reduce or eliminate this corrosion issue. Thanks.

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
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[unclesyd]

You link is working one gets the "Access Denied" "the access control is configured correctly."

 

[MadMango]

Thanks unclesyd, let's try this...

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[btrueblood]

Mango,

My $.02: can you change the Alum. tray to stainless? From what I can see, that's probably the root of your trouble. Alternatively, you need to completely galvanically isolate the alum. and stainless parts, using either rubber or plastic bushings. Even a stainless fastener has to be kept isolated with a sleeve or bushing to prevent contact with the alum. And don't count on the powder coating being an isolator, it can have porosity and/or wear away over time.

 

[EdStainless]

Lots of crevices, lots of dissimilar metals, galvanic corrosion will happen.
Real isolation is your only option, unless you can change materials.
Is there any corrosion on other parts?
Can you look at some of these that have not rotted away to see how they are failing?

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[MadMango]

Unfortunately we can't change the material due to weight considerations, but could change the grade (posibly 7000 series?).

There is no other corrosion with any of the SST parts. It is hard to fully isolate the aluminum tray, due to mechanical fastening of the tray to a piano hinge for rotation of the tray. We haven't seen such severe corrosion at this location, only where the SST pivot and oilite bushing is located.

We are thinking about changing the oilite bushing and thrust washer to some other material.

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[boo1]

Consider wet assembling the fasteners with Proseal 870 sealant.

We have changing to 5059 Al alloy to reduce pitting corrosion

 

[unclesyd]

You have one of the worst cases of copper worms I've ever seen. This is so bad the material looks like partially covered 2024 in or around salt water.

It looks like you are getting pitting, from Cu ions, a good distance from the bearing flanges. This takes away from isolating the bushing to mitigate problem.
What did the flanges of the Oilite bushing look like?


Are the loads on the bearing high enough to preclude a non-metallic bearing?

Would you be able to use an Al bushing?