A Place to Paint
We've all heard of cars that received a fantastic show-winning finish while being sprayed in a garage, barn, or even a driveway or carport. The fact is that quality painting requires a quality environment to work in-and safety recommends the use of a professional spray booth for all painting activities. True, few of us have the good fortune of a pro-quality paint booth for our one-off project ambitions, but nearly anyone can find access to a booth with a little legwork. Often a pro facility will be willing to rent booth time to hobbyists at a nominal fee. A pro facility will usually come with a professional-level air supply, the specific lighting needed, and most importantly, the proper ventilation system that ensures a safe paint project. The modern paint booth contains high powered fans that draw the air through filters, and downward, taking the unwanted overspray away from the vehicle being painted.
A clean supply of clean, dry...
A clean supply of clean, dry air in sufficient capacity is a key requirement in automotive spray painting. This huge two-stage compressor is operated by a 20hp industrial three-phase electric motor and supplies this shop with all the air required. For most requirements, compare the air consumption figures of the equipment to be used versus the rating of the compressor, and add a 50 percent margin of capacity.
A need that is a vital part of any paint project is, of course, a compressed air source to operate the spray equipment at the time the paint and primer materials are applied. Further, most autobody power tools are traditionally air powered, running the range from air sanders and body files, to reciprocating saws, grinders, and in some instances, even the buffers and polishers. The bottom line is that a paint project requires a reliable and ample supply of air. When it comes to compressors, it is typically the case that too much is never a problem, but falling short in terms of required air delivery at a critical point of the job can spell disaster.
Air compressors are most commonly rated in terms of volume by Standard Cubic Feet per Minute (SCFM), which is a measure of the volume of air delivered per minute of run time. Be aware that the volume delivered is greater at low pressure than at higher output pressures, so it's important to note the pressure (PSI) at which the volume (SCFM) specification is rated. For instance, a compressor may put out 11 SCFM at 40 psi, but at 125 psi, that output may be only 5-6 SCFM. Another consideration is the size of the storage tank which receives the compressed air. A larger tank will considerably cut down on the duty cycle of a properly-sized compressor, while providing a more stable air supply.
How much compressor is enough? At a minimum, this will depend upon the requirements of the tools being used, and fortunately most are also rated in SCFM for air consumption. As with the compressor output, it's important to note the pressure at which the tool's air consumption is rated. It also pays to figure a margin of about 50 percent over capacity when comparing the compressor output to the requirements of the tools. When it comes to compressors, the golden rule is that bigger is almost always better, and that goes for both capacity and storage tank size.
A professional shop installation...
A professional shop installation will have a moisture trap system of varying complexity to remove impurities from the air, ensuring that the supply is clean and dry. Here we have a piped system with multiple downlegs and separators. A main system pressure regulator should also be found as part of the compressor installation.
Presuming air of sufficient quantity is available, the next and equally important factor is air quality. Compressed air can often contain moisture that will condense into water at the tool or spray equipment, and water will certainly foul the paint. Oil contamination is also a possibility, often from worn or inadequately maintained compressors. The key here is to make sure the air compressor is in good mechanical condition, and the air delivery system is set up with a minimum of one water trap/separator. Another item that should be included in the air delivery system is a true pressure regulator. This will provide a stable and constant air pressure to the spray gun or equipment independent of the pressure fluctuations in the storage tank. A further regulator or choke is used at the spray equipment to set the air pressure at the tool.
Spray Equipment: Paint Guns
It used to be that just a few standard units dominated the field of autobody refinishing. These guns were predominantly conventional suction-feed types manufactured by DeVilbiss, Binks, and Sharpe. The landscape changed with the introduction of High Volume Low Pressure (HVLP) equipment more than a decade ago, initially introduced to cut waste and emissions from spray equipment in keeping with regulatory requirements. While the older conventional-style equipment is still capable of providing excellent results, the modern HVLP equipment has come to dominate the industry.