A big concern for many wood finishing companies is saving material.  Generally when purchasing a spray gun, the transfer efficiency of the gun is a major consideration.  While the spray gun is part of the transfer efficiency equation, there are other factors which should also be examined including:

1. Gun 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. 

To correctly set the air pressure, turn the air pressure down and spray a test pattern. If there are “tails” at the end of the pattern or if the particle size is not even, turn up the air pressure 5 psi, then test again.  Repeat this procedure until the “tails” are gone or the particle size is consistent.  The key is to use enough air pressure to get a high-quality spray pattern, but low enough to optimize transfer efficiency.

Regarding fluid pressure, it should be minimized to reduce bounce back of material on the substrate.

2. Size and shape of the part – To improve transfer efficiency, it is important that your spray pattern height matches 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. It is also important to 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.

3. Operator technique – Operator technique can affect transfer efficiency by 10% to 30%. An operator should be trained on proper spray techniques so transfer efficiency is increased.  Training should include, but not be limited to: spraying the right distance from the part, spraying parallel to the part and triggering and detriggering at the proper time.

4. Proper booth conditions – The air conditions in the spray booth also impact transfer efficiency. Conditions include humidity, temperature, air flow and air velocity.

 Wendy Hartley is the product marketing manager for Graco Inc. For more information visit Graco.com or call (877) 844-7226.