A Paint Guru’s Take on the Paint Booth
For a guy whose first passion was corrosion, Ron Joseph is an unlikely paint expert. Trained as a corrosion engineer in his native South Africa, job openings led him to Plascon-Evans Paints, a South African manufacturer of architectural paints and high-performance coatings. There, he got hooked on the challenges and complexities of paints and coatings.
Today Joseph, who lives in Saratoga, Calif., covers all aspects of paint technology, from spray booth design to painting processes, as a consultant. He is a senior manager in the mechanical engineering and materials/metallurgy practice for failure analysis firm Exponent. He is also the organic coatings editor for Metal Finishing Journal and the Organic Coatings Guidebook and Directory.
With nearly 40 years in the field, Joseph says he’s still learning about technology that can lead to beautiful high-performance coatings or catastrophic paint defects. Here, he tells us what shop operators need to know to get a good finish.
Let’s start with what may draw the most ire from painters, and may be most eye-opening for shop owners: What don’t the pros know—but ought to—when it comes to spraying paint?
I am most surprised by how little painters, and first- and second-line managers, know about paint technology and the root causes of paint defects. I am often amazed these folks do not know why a spray booth is fitted with a manometer or Magnehelic gauge. They have not been taught to zero-out these instruments, nor do they know how to read or interpret the results.
The majority of painters have not been properly taught to set up a spray gun from scratch. They tend to set up their guns by trial and error, turning one knob and then the next, until they get the finish they desire. Setting up a spray gun is not only an art; there is some science to it.
Painters need to know the relationship between the velocity or volume of atomizing air passing through the spray gun and the velocity or fluid flow rate of the paint passing through the orifice. The ratio between the two is critical to providing an excellent wet, smooth finish.
Give us the dirt on dirt problems. What’s the most important thing a collision center operator can do to ward them off?
It’s critical that spray booths have proper airflow. High density air intake filters allow the incoming air to enter the booth uniformly. With some of the less expensive filters, the incoming air channels its way through the booth, potentially causing turbulence that can pull loose, dry paint particles off walls, ceilings, floors and exhaust filters, and redeposit these dust particles onto freshly applied paint.
Similarly, exhaust filters shouldn’t be allowed to build up with overspray that can change the booth air balance. A spray booth is properly balanced when the volume of air entering and leaving are approximately the same. If slightly more air enters than leaves, the booth exhibits a slightly positive pressure. When more air is exhausted than enters, the booth is negative. For an automotive collision repair center the trend is to operate at a slightly negative pressure of 0.03- to 0.07-inch water column.Most of the larger collision repair centers have dampers or variable frequency drives that constantly monitor the pressure differential between inside and outside the spray booth and increase or decrease the revolution per minute of one of the air exhaust fans to maintain booth air balance. Smaller body shops might not have the luxury of these devices; they’re expensive.
When airflow is out of whack, what happens?
I’ve been in spray booths that operated with such high negative pressures that when a painter opened one of the access doors, masking paper, masking tape, dirt and dust could be seen flying into the booth. On the other hand, I’ve been in spray booths that were under such high positive pressures the access doors opened on their own. This can’t possibly result in excellent, dust-free finishes.
What else helps with dust?
Daily spray booth maintenance is a must if dirt and dust defects are to be prevented. The walls, ceiling, floors and other surfaces that catch overspray must be washed daily. Exhaust filters must be monitored and replaced before they build up a significant resistance to airflow that results in reduced air velocity through the spray booth. The compressor must be monitored on a regular basis to ensure the air remains dry and free of rust. In older installations, galvanized pipes carrying compressed air to the spray booth can corrode; I’ve seen many regulators and filters plugged with rust. Even after years of use, nobody opened the filter to clean it.
So it’s up to painters to keep their booth in good working order. Will the booth designs of the future be any help with that?
Spray booths of the future will be designed for better energy conservation. Already, newer spray booths have the ability to change airflow in different modes of operation: spraying, flash drying, force drying. This trend will become more sophisticated. Software programs that operate at the touch of a screen will produce preconfigured menus for specific primers, basecoats and clear coats.
Built-in controls will monitor pressure differentials across air supply and exhaust filters and forewarn operators when it is time to replace the filters. Monitors will detect if someone is spraying inside the spray booth, and gas and electricity consumption will be reduced by as much as 30 percent during down periods.
New, inexpensive equipment is available to direct high-velocity air through nozzles toward freshly painted surfaces. The nozzles can be directed in almost any direction to follow the contours of a vehicle. These devices can be retrofitted into an existing booth and provide the benefit of reducing the flash-off time for freshly applied paint.
New or retrofitted spray booths, then, lead to greater efficiency. How about painters themselves? What signs should a shop owner monitor to be sure the folks in the paint department are spraying efficiently and effectively?
Transfer efficiency (TE). It’s measured by the amount of paint deposited on a vehicle relative to the total amount of paint used. When you use a paint brush, the TE is approximately 100 percent, but when a spray gun is used the TE drops dramatically, sometimes to well under half. In collision repair shops, where painters often turn up their atomizing air pressure to apply metallic colors, TE can be as low as 40 percent.
When I train painters my goal is to improve TE by at least 15 percent. If I’m successful, the shop owner immediately enjoys a 15 percent reduction in VOC emissions, more than 15 percent reduction in hazardous waste, fewer spray booth filter changes, improved appearance of paint finish due to less overspray and 15 percent reduction in paint usage. When you add up all these savings, the total can be impressive.
How many technicians are properly applying paint?
I would estimate that well over 60 percent of all collision repair operators do not achieve optimum TE. In even the best shops, I believe a 5 to 10 percent savings can be reaped. For the remainder, I believe 10 to 30 percent savings are waiting to be enjoyed.
That sounds like a lot of operators have an opportunity to improve the balance sheet associated with paint. How can they do that?
In my opinion, painter training is the most important thing an owner can do to improve efficiency.
In most cases, however, painters attend a class, are “gung-ho,” but within days, they go back to their old habits because there is nobody to enforce or reinforce what they have learned. So the shop owner or manager should also attend a training program [in order to be able to] enforce what the painters have learned and to set up quiz sheets and logs to periodically measure the standard of their painters.
If you ran a collision repair operation, what are the top three things you would make sure your painters knew?
I would immediately train them to understand the VOC regulations, including the National Emission Standard for Hazardous Air Pollutants, and the types of violations that result in environmental pollution and massive fines.
From a production perspective, I would train them to apply paints at the highest reasonable transfer efficiency for a particular application. That includes methods for properly setting up a spray gun and measuring fluid flow rate.
The third approach would be to train them to better understand the components of a spray booth: how to measure pressure differentials, change filters, minimize air turbulence and eliminate moisture from the compressed air lines.