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January 19, 2009

Recommended Cleaning Cycles

The cleaning cycle recommended by ASTM and Myers has four parts: precleaning, intermediate (alkaline) cleaning, final electrolyte cleaning, and the acid dip. Not all step are needed in every case. The precleaning and intermediate cleaning may be combined in one operation, or one or the other or even both eliminated, depending on the conditions of the parts as they are received by the plating department.

The object of precleaning is to remove large excesses of soil, especially deposits of solid particles, such as pigmented drawing and buffing compounds. The types of precleaners are solvent, emulsifiable solvent, spray or soak emulsion, soap/detergent soak, alkaline spray, and alkaline soak.

The intermediate cleaning removes residual soils softened or conditioned by precleaning. This is usually accomplished by soak or spray cleaning. For soak cleaning 30 or 120 g/l of alkaline cleaner at 82oC up to boiling for 3 to 15 min in generally used. A typical soak cleaner for steel would contain:
  • Sodium dydroxide ------------------- 35% wt
  • Anhydrous sodium metasilicate --- 25% wt
  • Sodium carbonate ----------------.--- 22% wt
  • Sodium tripolyphosphate -------..--- 12% wt
  • Anionic surfactant -----------------.--- 5% wt
  • Nonionic surfactant ------------------- 1% wt
Spray cleaners are used at about 4 to 16 g/l at 68 to 74oC with spray pressure from 0.7 too 3.5 kg/cm2. only low foaming surfactants may be incorporated in spray cleaners. Fortunately a number of low foaming nonionic surfactant are available. The compression of the spray cleaner is very similar to that of the soak cleaner except for the surfactant.

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