plating, anodizing, & finishing Q&As since 1989
1100 Aluminum staining brown spots of discoloration during the cleaning process.
January 25, 2012
We are cleaning 1100 aluminum tubes .930ID x .035W in DI water at 150 °F with Brulin 815 GD soap at a minimum PH of 9.3. The tubes are immersed in the agitated soap solution for 20 minutes and are coming out with brown stains in random places. The wash tank is all 304 stainless, as well as all the fittings, the agitation pump is plastic and stainless.
We cleaned these tubes a year ago, same tubes, same heat number, same batch, same tank, same procedure without the discoloration. I just don't know what it could possibly be. So far we have had our DI water checked, put in all new filters. We tried new soap, new pump, adjusted the water temperature, and even tried tap water to no avail. I am in the process of having another tank made.
It seems the lower the agitation in the water, the darker the discoloration becomes.
Also seems the discoloration is greatest on the end of the tubes closest to the water jet and the parts closest to the heating elements.
Any help would be greatly appreciated.
Operations Manager - Leetsdale, Pennsylvania, USA
February 16, 2012
1100 is 0.95 % Iron which forms brown stains, 0.12 % copper which forms green and black stains, both of which is why heavy anodizing on 1100 comes out bronze to gray. The high pH cleaner is attacking the surface and leaving the stains of iron.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina