Reminder: Blame the Weather
Q. This summer we had a number of days when our plating processes did not seem to work properly. Some days our production would go well with no problems, and other days we were tearing our hair out trying to resolve such things as water spots and other defects. I have been in the plating business for nearly 30 years and suggested that some of the problems have to do with the strange weather we experienced on the East Coast. Could you comment on this? K.B.
A. I have not discussed the influence of weather on plating results in a number of years. Since I’ve received a number of questions over the last few months regarding weather and its influence on plating processes this is a good time to repeat what I wrote in an earlier column:
Your question touches on one of the greatest unacknowledged variables in electroplating, the weather. To those uninitiated in plating processes, blaming the weather sounds like another weak excuse for poor plating results. This is not the case. Unless your plant is completely climate controlled you more than likely will have some weather related problems. (I might point out that weather plays a role in many manufacturing processes, not just electroplating.)
Lawrence J. Durney in his book, Trouble in Your Tank? Third Edition addresses this subject in a very clear, detailed manner.
One of the most obvious weather issues is temperature. Parts may be stored in a cold warehouse before processing. The plating area usually is much warmer and very humid. Some of the parts will condense water vapor on their surfaces. The results are flash rust or other corrosion products on the surface. Sometimes you will even have etching of the surface.
What about the summer versus winter temperatures of the plating room? A plating room may be a comfortable 65–75°F in the winter months but can be 100–110°F in summer. How does this affect the temperature of your plating baths? A bath operating at 140°F probably won’t suffer, but a bath that is supposed to operate at 85°F will get hotter during the day.
Weather can affect drying of parts. When humidity is low, parts can easily partially dry off during their movement from tank to tank. The end result is staining of the parts. If the humidity is high, then the parts won’t stain, but instead are difficult to dry.
As pointed out in Durney’s book, the apparent randomness of this staining problem can be explained by the absolute humidity of the atmosphere. Absolute humidity is a measure of actual concentration of water in the atmosphere. It is important to remember that absolute humidity is not the same as relative humidity. Relative humidity is used by the weatherman, but does not tell you how much water is in the atmosphere and quite often does not correlate well with staining and spotting out problems.
One last item to consider is barometric pressure. The barometric pressure affects the solubility of gases in water. An example of this effect is classic brass plating using ammonia as one of the components of the bath. If barometric pressure changes, the amount of ammonia in the bath will change and in turn, the color of the brass deposit will change.
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