White Dust After Cleaning

What causes white dust on the tops of degreased components?

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Q. We have a nine-tank cleaning process. After the degreasing process the top surface of the components forms a white dust. Why does this happen and what can we do to correct it? –P.H.

A. All aqueous cleaning processes use “builders” that provide alkalinity to buffer the pH and saponify fatty acids that can be found as an ingredient in industrial lubricants. These builders are generally sodium and potassium salts of carbonates, complex phosphates, hydroxides and others. Since they are by nature a salt, if not rinsed reasonably quickly, these builders can dry down on the surface of the parts. It is possible to confirm this by wetting pH paper with deionized water, then gently rubbing it across the surface of the residue. If it is residual cleaner, the pH paper will show it to be alkaline.

This cleaner residue can be avoided if parts are processed between tanks more quickly. Also, lowering the temperature in the cleaning tank can significantly mitigate this. It is possible that if the cleaning tank temperature is greater than about 170 - 180°F, the aqueous cleaner could be drying onto the surface very quickly. Lowering this temperature about 20° may eliminate the problem. If that is not successful, it may be possible to erect rinse risers over the cleaning tank or between cleaning and rinsing, which will start to rinse and cool the part to reduce or eliminate the residue. This rinse water can be collected and used as make-up for evaporative losses in the cleaning tank.

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