Warning: Powder Coatings Zone

From D+D Online, March 2011

by Walter R. Scarborough

The mere mention of powder coatings elicits a wide variety of responses from the stakeholders of the design professions and construction industry....
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Tagged categories: Coatings technology; Good Technical Practice; Powder coatings

Comment from Robert Pfaffmann, (3/10/2011, 8:34 AM)

Of the hundreds maybe thousands of areas of knowledge and architect must have, I appreciate the quality of information coming from D&D. As the owner of a small "Boutique design firm" I do resent the implication that the architect only cares about his/her design. There are a lot of us out there that care deeply about every aspect, and focus on the detail. Part of the problem is the need to reflect the values of our clients project and thus design a process that of education that prioritizes which issues we bring to their attention and which we must just take care of quietly.


Comment from Kevin Biller, (3/16/2011, 3:32 PM)

This is an interesting article Mr. Scarborough. It's good to hear the perspective of a building specifier. Your explanation that powder coating refers to a technique and not a material is helpful, however the materials are ambiguously known by the same moniker. It is vital to specify not just a "powder coating" but a powder coating that specifically meets the appropriate specification. In the powder industry this is the approach nearly always followed. Virtually all OEM's have internal specifications which must be met to qualify for supply. Architectural specifiers would be well-advised to either utilize the appropriate AAMA standard and/or their own internally generated specification. As for some of your technical comments: - Substrates are typically cleaned then chemically converted and dried prior to application of powder. The cleaning is typically an alkaline solution followed by a water rinse. If the substrate is ferrous, then an iron or zinc phosphate stage follows. If the substrate is an aluminum alloy phosphating does not work. Instead a deoxidization stage (typically acidic) is used followed by a rinse then a chromate conversion step. - Powder coatings used for exterior architectural applications in Europe are no better and often inferior to the powders used in North America. The majority of Europe lies significantly further north than The United States and hence the UV intensity is much less than even some of our northern states. - Powder coating technology based on fluoropolymer chemistry possesses equal or better durability compared to liquid coatings. This technology is well-known and well-proven. The polymers used are chemically equivalent to the polymers used in liquid paints. - Powder coatings are not just "heated to its melting point". Curing a powder coating requires exceeding its melt point and holding the material at a temperature long enough to cure (chemically react). Melt may take a minute or two depending on substrate mass whereas proper cure requires 15 to 30 minutes depending upon chemistry. - Powder coatings typically require cure temperatures equal to or higher than those typically used for industrial liquid coatings. - Applying powder coatings can be less expense than many liquid paints because of the elimination of wastes streams, pollution abatement, permitting, hazardous material handling and overall better efficiency. Your conclusion about the specifier selecting the right chemistry is right on the money however. It is imperative to ensure that the powder performance meets the requirements of the job.


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