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Best solution to clean Alkaline-Tin Plated Parts

September 4, 2008

We are a machine shop that machines aluminum parts. We have several PNs that require Alkaline-Tim Plating on them, so we must tap or chase threaded holes after plating. To tap we must use oil/coolant on the tools in order to keep the tools cool and lubed.

The issue is after tapping with oil/coolant the parts become stained. What is the best solution/chemical to clean these parts? We have tried Isopropyl Alcohol, Water, Water with Aluminum Cleaner, Water with dish soap, Nue-Tri. The water just stains the part worse unless you can blow it off quickly and evenly.

Dan

Dan B
Machine Shop - SD, USA

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Not having seen the parts, from your description I'm going to guess that the tin plating is dull as plated. It's almost impossible to prevent staining on dull tin, and probably equally impossible to remove staining.

I'd suggest you use a water soluble tapping compound, one which is based on animal fats or soaps. You'll still have some staining.

If practical, you can clean the finished parts by hand with a mild abrasive like "scotch-brite" and mild detergent, followed by a good rinse in war water. A stiff plastic brush might work well too.

The burnishing of the surface will make the parts brighter, and it will also make them less susceptible to staining. You should check with your customer to make certain this burnished look is acceptable.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
September 8, 2008

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The plating is Alkaline Tin Plate with .00015 MIN Thickness with .0006 Copper Underplate per MIL-T-10727. (MATTE BISMUTH TIN PLATE with dull finish).

I doubt the customer would allow the use of scotchbrite, but I will test on a scrap and hope to not remove too much.

We currently use a water based lubricant (stains the worst) (masterchemical.com/db-docs/pdf_di/MicroSol_606.pdf)

We also use a vegetable oil on another set of machines which does not stain as much as the water based coolant.

Dan B
- Yankton, SD
September 12, 2008

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