FT Archives

Roobol on Painting

Thinking About Adding Powder Coating?

My husband and I have owned a small paint shop for eight years. We do various jobs for people and companies around here, especially repainting cars and trucks. We have now decided to do powder coating as well because we are frequently asked to powder coat parts and there is nobody within 50 miles who do it. So we have just purchased a very large oven that will heat the temperature higher than 525°F. Powder coating is new to us. Are there any classes on this, or can you send us information on how to powder coat?

While I don't very often telephone folks who submit finishing questions, this time I'm glad I did. When I asked a few questions, I quickly discovered that you didn't recognize the term "phosphating" or know anything about what the phosphating process involved. Likewise, you had never done any electrostatic spraying or know about any of the requirements for electrostatic application. Most surprising was the realization that neither you nor your husband had ever seen powder coating being done. I told you to visit a powder coating operation as soon as possible to get an idea of the scope of what was involved.

My next advice was to put on hold any plans to powder coat until you had a reasonably complete knowledge of what powder coating encompasses. I suggested you contact the Powder Coating Institute and visit its Web site, which you had already done. You wondered about attending powder coating classes, but I urged you to first read books on the subject. Then if you still felt it prudent for your shop to proceed on such a venture, a powder coating class would be a logical next step.

I haven't gone into much of all the numerous suggestions and many details of our conversation, but I did want to give enough information here so that others may learn from it. The major lesson is that wise decisions can only be made from sufficient knowledge. A possible secondary truism is that wise people ask questions.

Moisture Levels in Compressed Air

I read a question somewhere else regarding the proper dryness of compressed air for applying paint and powder coatings so that color and gloss problems are obviated. The answer was rather vague and unhelpful, so that got us discussing how moisture levels are measured in compressed air. It seems unlikely the dry bulb/wet bulb method would be suitable. What is the correct degree of dryness to have, and how is it measured? I can't imagine any manufacturing plants actually take readings of exactly how dry their compressed air is.

Yes, the dry bulb/wet bulb method will determine the relative humidity of noncompressed air. Compressed air dryness is expressed by the dew point, the temperature of a cold surface onto which moisture will condense out of the air. Most compressed air dryers are the refrigerated types and these are generally able to reduce the dew point to around 20°F, and for most coating applications this is acceptable dryness. For critical applications, regenerative desiccant dryers are employed since these devices can readily achieve minus 30°F (and for pharmaceutical and micro-electronic manufacturing, far lower dew points) dew points.

No, you normally would not measure the dew point, rather you need to rely on the dryer manufacturer to accurately state the dew points achievable for the typical ranges of air temperatures and air pressures used at your operation. I hope this answer is more instructive than the other one you mentioned. You can find more in the compressed air section of INDUSTRIAL PAINTING & POWDERCOATING, Principles and Practices, 3rd Edition.

Got Hydrographics Information?

I've been waiting to hear more details on hydrographics, which you promised to give us several months ago. When can we expect to see this news in the magazine?

Well, I've been waiting, too. The person who asked if I wanted more hydrographics information has not yet responded to my request that they send it along so I could put it in my column. This may be because they have forgotten, or more likely it is because their company decided they should not at this time reveal that knowledge. Just as soon as I receive it from them, or if someone else can provide more material on this topic, I'll ask the editor to put it in the column immediately. Thanks for asking about it.