Metal finishing Q&As since 1989

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Barrel burnishing aluminum/zinc

We are having trouble obtaining a satisfactory burnished finish on Aluminium (various grades) and zinc based materials (myzac etc) with a rotary barrel polisher.

We have moved from mainly carbon/stainless steel polishing and so have been using carbon steel mixed shot with various compounds, all of which are resulting in some form of staining (either grey or yellow) on the parts. I have been advised to try stainless shot and/or a different compound

We are a little unclear as to whether we really need to change to stainless shot (obviously more expensive) or whether we can just use a different compound, we are looking for a burnished mirror finish.

Any advice would be appreciated.

Thanks in advance,

Will Hamlyn
Logic plc - London, UK
2001

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Will, the yellow/gold staining you see on the aluminum and zinc is probably due to immersion plating of iron for your steel shot. When you were finishing other ferrous parts, immersion plating was not a problem. Now that you are finishing aluminum and zinc, both more chemical active than iron, any soluble iron plates out on the more active aluminum or zinc. The plated iron gives the part the gold color.

To prevent this, you need to switch to a more chemically inert shot. It will be very difficult to solve this problem with another compound. In addition to stainless steel, you may want to consider ceramic shot.

Roy Nuss
Trevose, Pennsylvania, USA
2001

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Suspected that may be the case, thanks for your advice, time for some new supplies.

Regards,

Will Hamlyn
Logic plc - London, UK
2001

Have you looked into low plasticity burnishing? it provides the mirror finish and compressive stresses without the need for shot peening. may solve your problem without needing to buy different supplies or change materials.

Julie Prevey
- Cincinnati, Ohio, United States
June 29, 2009