Liquid Coatings Q&A: Improving an Operation’s Transfer Efficiency
Q. What is the best way to achieve transfer efficiency optimization in our operation?
A. To properly answer this question we must first look at all the things that can affect transfer efficiency, including the application device, air pressure and gun settings, the booth’s air flow and application technique.
When possible, using an electrostatic spray device will positively impact transfer efficiently because the paint particles are being charged, enabling them to attract to a grounded work piece. This will, in many cases, lead to a wraparound effect where the paint overspray will “wrap” around and coat the backside of the part. Electrostatics can improve transfer efficiency by as much as 20 to 30 percent and even more in cases where part geometry lends well to electrostatics.
The air pressure settings are typically overused and misunderstood. The air distributes or propels the paint to the part. The idea is to make sure it is collected on the substrate being coated and not blown pass by the part. However, the lower the air pressure, in other words, slowing the velocity, the better chance of increasing the amount of paint deposited on the part. Also, make sure the spray patterned in optimal for the part geometry. Not too large for small parts or too small for large parts.
Air flow of the booth can assist as well. You want the air to flow from the back of the applicator, moving the paint particles passed the part being coated and drawn to the filters. These filters must be maintained to optimize air flow and the booth should be sized to meet NFPA 33. Too much airflow pulls paint particles passed the part. Keep in mind that a booth is typically sized without parts in the booth. If you place a large part that takes up a great deal of space, the air flow of that booth will be increased proportionally and dramatically. Where transfer efficiency is optimized, a VFD to offset these variables can be very beneficial.
Technique is the fastest way to impact transfer efficiency. The goal is to keep the same distance between the applicator and the part surface during the entire coating process, making sure the nozzle is perpendicular to the part, not angled. Trigger off the part enough to keep from getting a burst of paint on the edge and pull off the trigger only after leaving the part surface.
In a coating operation, over-sprayed material wastes money and optimizing transfer efficiency can reduce the cost of coating a part and enhance quality.
Steve Houston is the chief marketing officer at Col-Met Engineered Finishing Solutions. Visit colmetsb.com or call 972-772-1919.
Bryan Willis, director of controls for Col-Met Engineered Finishing Solutions, also contributed to this article.
Originally published in the June 2016 issue.
How do you measure the surface area of a threaded fastener? How much coating would you put on it? How thick of a coating? What about non-threaded fasteners? The U.S. Department of Agriculture’s Forest Service, of all people, may have come up with the solution for those pondering how to coat sometimes-difficult small pieces using computer imaging and software to compute the area.
A more realistic way to perform salt spray tests.
This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2012 in Las Vegas, Nev., on June 13, 2012.