Letter 2737

Waterspots on zinc phosphated black dichromated metal  

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Experiencing a problem with water spots on a zinc phosphated black dichromated part (immersion rack line). this part has a class "a' finish requirement and no spots are allowed. the final rinse bath is ambient,could the spotting result from the decline in temperature due to winter months? the blowoff is forced air but the dwell time from the rinse bath to the blow off is app. 2 minutes, the parts are the dried in a radiant heat drier. we are currently experiementing with wetting agents, heating the rinse bath and air knife installation (blowoff stage)any additional suggestions would be greatly appreciated. thanks

Ron Roy - Somerset, KY

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Hi Ron , I would hazard a guess that your rinsing is leaving a little to be desired in terms of efficiency & Total Dissolved salts suggest that you try the following 1 ) Agitating the final water rinse with a low pressure air blower at the rate of 2 cubic feet of air per minute per square foot of surface area of the tank . 2 ) try using demineralised water as a final rinse . Best regards


John Tenison - Woods
- Victoria Australia

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