Transfer Efficiency Varies Depending on the Spray Applicator
What Is Transfer Efficiency?
The term transfer efficiency refers to the amount of paint that is deposited on the part compared to how much material sprays past the part and is wasted. Transfer efficiency is expressed as a percentage. A 60% transfer efficiency means that 60% of the material sprayed actually reached the target. The balance of 40% was lost to the spray booth or other areas during the spray finishing process.
There are two primary test standards when measuring transfer efficiency – ASTM and EN13699. The ASTM test standard simulates a conveyor system. For conventional spraying, ASTM never has a transfer efficiency greater than 50%.
The second type of test standard is the EN13699, which is performed by spraying a pattern in the middle of a large target. The EN standard produces higher results for the same gun due to the way the test is performed. For example, an HVLP gun tested to the ASTM standard has a range of 25 – 32% transfer efficiency. The same HVLP gun tested to the EN standard has a range of 70 – 78% transfer efficiency.
Why is Transfer Efficiency Important?
Transfer efficiency is critical to the spray finishing industry from both a cost and a regulatory standpoint. Although transfer efficiency is a relatively simple concept, it can lead to considerable confusion (or even deception) if it is not clearly understood. To serve your customers well, you need to know more about transfer efficiency and how it is used in the industry, beyond its simple definition.
By increasing transfer efficiency we reduce the amount of paint sprayed. This leads to a reduction in released VOC’s as well as improves the life of your booth filters. Transfer efficiency can be increased as a result of using different spray applicators. By maximizing transfer efficiency, and spraying less paint, manufactures not only save money, but it also means less maintenance, clean-up, lower filter costs and VOC emissions.
What Determines Transfer Efficiency?
This biggest factor in achieving high transfer efficiency is choosing the right spray gun. Selecting the most efficient spray gun for the intended application is important in optimizing the efficiency of your spray operation. Conventional air spray, compliant, HVLP, air assist and electrostatic and rotary atomizer all offer excellent benefits depending on the application.
Other factors can impact applicator transfer efficiency too, such as operator techniques and proper setup. Operator technique can affect transfer efficiency by 10% to 30%. Because of this, operators should be trained on proper spray techniques so transfer efficiency is maximized. Training should include spraying the right distance from the part, spraying perpendicular to the part, plus triggering and detriggering at the proper time. Using a paint robot, the spray technique is consistent each time and transfer efficiency will be optimized.
To get the full benefit of your spray applicator, ensure you have proper setup. The proper air pressure and fluid pressure is critical for transfer efficiency. Too much air pressure will cause turbulence in the sprayed material, resulting in excessive overspray and reduced transfer efficiency. The key is to use enough air pressure to get a high quality spray pattern, but low enough to optimize transfer efficiency. Fluid pressure should be minimized to reduce bounce back of material on the substrate.
Spray pattern height is also important. Your spray pattern height needs to match the part you are spraying. Material blow-by from too large of a spray pattern reduces transfer efficiency. The tip size should be sized to the largest spray pattern height for your parts, but not bigger. You should also purchase a spray gun with a fan pattern adjustment knob, so as your part size varies, the operator can adjust the spray pattern height down to match the part size.
Overall, there are advantages and disadvantages to each spray technology. Determining the highest requirement for your production line will assist you in identifying which spray technology will fit your application. By exploiting transfer efficiency, manufactures can save money, reduce maintenance, lower filter costs and VOC emissions.