Automotive paint and body shops use compressed air in nearly every step of the automotive body repair process. Including various sanding steps (rough to wet finishing), multiple paint applications, (primer coats, base coats and finishing clear coats) and they all consume compressed air. As a result, compressed air plays a critical role in auto body repair, so the choice of air compressor should be considered carefully.
To achieve the best results with your paint application, it’s important to understand the requirements of your paint process, including the type of paint required. Water-based paints and solvent-based paints are unique and require different levels of compressed air quality.
Water-based paints require clean, oil-free, dry air in order to achieve the best paint results without potential fish-eyes or other imperfections. These can lead to a lot of additional re-work or a complete re-paint. Oil-free compressed air is recommended for water-based paint applications because it eliminates the risk of oil-vapor in the compressed air, and oil coming into contact with the paint. If you do not have an oil-free compressor, be sure to use proper activated carbon filtration in your system, either directly after your air compressor or at the point of use.
Solvent-based paints require clean dry air as well, but oil-free air is not a requirement. In either case, you should use a coalescing filter (for liquids) and a particulate filter to remove impurities from your compressed air, as these contaminants will damage paint surfaces.
Compressor Sizing and Installation Considerations:
There are a few things you should consider when sizing your compressor:
Pressure needs — Consider each tool in your shop that requires compressed air and follow the manufactures recommended guidelines for the required operating psi. Using an incorrect pressure can result in poor tool performance or adversely affect your paint application.
Air demand — Be sure to determine the size of your compressor based on your specific compressed air requirements, including psi and CFM. When sizing your compressor you should take in to account the operating pressure and sum of your average CFM requirement for each piece of equipment in your shop. For example, if you use a spray gun that requires eight CFM with a use factor of 50 percent, that tool would require four CFM from the total compressed are delivery. To create an accurate estimate of your total air demand, do this for each tool in your shop.
Compressed air storage — A general rule of thumb for compressed air storage is to have four to five gallons of air storage per one CFM of compressed air delivered from your compressor. However, this can vary depending on your specific application and equipment requirements. Take a look at the example below:
In this example, we see that 124 CFM is required. This is the minimum air required based on current usage. An air system should always be designed to provide ten to 20 percent more than the current usage requirement to handle peaks and/or future growth. Site elevation and relative humidity can also impact your air system as seen in the example above. If you have questions or concerns about your air demand and usage, always reach out to your local compressed air representative.
Question to Ask:
Do you need oil-free air or is an oil-lubricated compressor acceptable? If you don't care about small amounts of oil in your process, then oil-lubricated is perfectly fine. If oil in your process is an issue, you will also need to consider filtration or an oil-free compressor.
Do you need dry air? All air compressors create condensate, but condensate can cause problems in some applications. To reduce or eliminate this condensate, you should consider a compressed air dryer. Dryers reduce moisture in the delivered air, yielding a better paint process.
Smaller body shops typically will not use any filtration, though most medium to large shops will use at least point-of-use membrane or desiccant style dryers and a point-of-use carbon filter at the paint booth, as well as drip legs and in-line filters to capture condensate. Additionally, FRLs (filter, regulator and lubricators) are used to keep tools oiled.
This practice, however common, can be costly and requires frequent replacement of your filtration media in multiple places. A best practice is to install a refrigerated, membrane or desiccant compressed air dryer and to use coalescing, particulate and carbon filtration for the entire system to minimize cost and cut-down on short-term filter media change-outs.
Ideally, your compressor should be installed on a solid, level surface. You should adhere to the recommended guidelines for spacing around and above the compressor to allow for the proper air flow and maintenance access. The unit should be kept away from dusty environments to guard against shortened air inlet filter life, poor compressor performance and diminished compressed air quality.
Piston compressors: Look for a heavy-duty piston compressor that is built for durability. For a more in-depth look at piston compressors, read this.
Rotary screw compressors: Screw compressors are built to run 100 percent of the time and provide full rated CFM continuously.
Air treatment: Consider using coalescing two-stage filtration to remove liquids and particulates, and choose activated carbon filtration to remove oil vapor.