Anodized Aluminum Water Jacket Corrosion

[SMF1964]

Does anybody have any thoughts on mitigation of corrosion of an anodized aluminum water jacket? This is a chamber that fits around a metallographic mounting press to cool the mold chamber after the plastic mount is finished "baking". The temperature of the mold is 300°F when the process's heating cycle completes, tap water (local city water, not well water) then passes through the chamber to cool the mold down to 150°F. The jacket lasted about 3½ years and corroded through the aluminum from the inside. The pH is 7.2 for the tap water. If I switch over to a demin water, can I expect the replacement jacket to last? I don't have the option of changing the jacket material and any polymer coating I put on the inside of the jacket cannot interfere with the O-rings or dimensional tolerances and must be able to take the heat of the mold.

 

[unclesyd]

Once you added organics, especially the acids, the dissolution is straight forward in a hurry.
About the only thing you could do with the jacket as stated in your post would be to put on a chromate conversion coat and periodically renew it. The ideal coating would be Xylan.

We had solid Al cooling jackets that we kept in the lab freezer or the sub zero box,if we were in hurry. Also we pushed the sample hot and use an air blast to the mold.

Your corrosion is probably occuring if the jacket is kept wet.

 

[SMF1964]

Yes, the jacket is kept wet - there is no mechanism for us to drain the cooling jacket. The whole assembly (mold, jacket, etc.) is an automatic machine. Removing the jacket requires disassembly of the machine and the process automatically starts/stops the cooling water. I'll look into the chromate conversion coating.

 

[Metalguy]

I'd give demin. water a try-it might allow enough life for you. Good auto antifreeze has corr. inhibitors which give very low corr. levels--IF you can use them.

 

[CoryPad]

unclesyd,

Can you explain why Xylan would be the ideal choice?

SMF1964,

Three years for a metallographic mounting press is pitiful performance. The manufacturer probably only warrants for one year. Can you tell us who the manufacturer is? I want to avoid their product is that is typical performance.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

Here are some company papers. We had excellent results in a similar application. We are seeing very good results on fasteners exposed to seawater/ or costal enviroment. There are numerous formulations so a call to Whitford would be in order.

http://www.whitfordww.com/

http://search.atomz.com/search/?sp-a=sp1002e8e0&sp-q=xylan

 

[SMF1964]

I've replaced the corroded parts. We are replumbing the cooling water to draw off of the lab's demin water system. I'll let you know what happens...