We have a lot of spent powder that we have to dispose of in a landfill. Are you aware of any facilities that can take spent powder and reuse use it as a raw material or have another use for it in lieu of disposing of it?
--Sandra Forsyth, EHS Specialist, McLaughlin Body Co.
For years the powder coating industry has looked for a means to eliminate obsolete powder. For a while it was thought that perhaps the concrete industry could bleed some old powder into their mixes, but this wasn’t possible due to quality issues. The use of spent powder was also pursued as a fuel for industrial processes. However, I don’t think this application materialized. I’ve encountered companies that buy and resell unwanted powder. Surplus Coatings in Grandville, MI, is one example.
A couple of entrepreneurs in Akron, OH, have pioneered a novel process that uses obsolete paint, powder, plastics and even synthetic carpet as feedstock to a cracking process that produces a variety of petrochemicals. We featured this technology in the December 2006 issue of Finishing Today (“True Recycling of Scrap Paint & Powder,” online at www.finishingtodaymag.com). The company isn’t expected to be operational until 2008, but it could provide a viable solution at that point.
If any of our readers has an idea regarding how to manage spent powder, we would love to hear from you. E-mail me email@example.com.
We are a manufacturer of paint racks for plastic parts. One of our automotive customers paints left- and right-hand parts at the same time on the same rack. They occasionally need to paint only one hand, leaving the other hand empty. This causes heavy paint buildup on the hand not being painted. Is there a way to mask the holder so that paint buildup is not a problem?
--Mike Freeman, FCF Custom Fab
Have you tried silicone plugs? I can't exactly envision your rack design, but you may be able to cover the holder with a silicone plug/cover. A thick silicone cover will insulate the holder, and the oversprayed paint can be removed easily from the cover. Another idea is to design a few extra racks that only accommodate one side of the parts. Still another idea is to design a universal holder that can accept right- and left-hand parts on either side of the rack.
I hope that this helps. Not knowing the exact dimensions and design of the parts and racks makes it difficult to determine whether any of these suggestions will solve your problem.
Are there any issues with using aluminum versus steel panels to do system sprayouts? We use a polyester epoxy blend powder.
--Paulo Dos Santos
The panel type shouldn't make much of a difference. Remember that aluminum is a better heat conductor so the metal heats up faster than steel. The mass of the panels will also affect the heat-up rate - obviously heavier panels heat up more slowly. You should also ensure that the panels are always clean, oil- and dust-free.
Our facility is in Houston. I understand that “fish eyes” are usually caused by oil, grease, and other contaminants that are incompatible with the coating, but it appears that humidity also can cause these crater-like defects to occur. We store our powder at temperatures below 74ºF. In discussions with some powder suppliers about product shelf life and storage, there seems to be a general consensus that if a powder sprays, it is okay even if it is beyond the 12-month “shelf life.” Since powder is hygroscopic and it is not stored in airtight, sealed boxes, is the humidity likely to contribute to coating issues, particularly in older, stored coatings?
--Brian Gurney, S&S Technology
First of all, it’s important to define our terms. Fish eyes, a coater’s worst nightmare, are relatively large, crater-like disruptions in the powder coated surface. They’re caused by a large differential in surface tension between the powder and the contaminant. Contaminants that cause fisheyes can be silicones, acrylic powders, greases, lubricants (including WD-40), hand creams, antiperspirants, forming oils and metal processing fluids, to name but a few. Moisture in powder causes pinholes, which look like sharply defined microholes in the surface. Pinholes can be numerous and are usually fairly evenly spaced apart.
Powder shelf life can span years under the proper conditions. Virtually all powder suppliers deliver their products in lined containers. The lining is typically a 4-mil-thick polyethylene bag which, when sealed, is impervious to atmospheric humidity. Powder only attracts moisture if it is exposed to a humid environment over a period of time. This can happen if containers are left open and also in the application area (e.g., hoppers, reclaim systems, etc).
If you feel that you are observing fish eyes, water probably is not the culprit. Your air supply may be contaminated. This can be the incoming air to the booth or the compressed air used for your application system. Make sure the compressed air is being properly dried and filtered prior to entering your application system. You might also need to increase the capacity of your dryer; in the summer, the dryer is taxed more by the increased ambient humidity.
If you still are experiencing fish eyes and the compressed air appears clean, then start looking for extraneous contaminants like those mentioned above. If you feel you are experiencing pinholes, then moisture may be the source. The moisture may emanate from incompletely dried parts or improperly stored powder.
Ask Joe Powder is a regular feature of Finishing Today magazine. Please send your questions to firstname.lastname@example.org.
FINISHING ANSWERS: Ask Joe Powder
June 1, 2007