Wood Finishing: What is Transfer Efficiency?

By Bernie Bottens | Posted: 06/13/2013 10:29AM

 

Bernie Bottens how to finish wood Do you really know transfer efficiency is? Do you really think about it when you have the gun in your hand? Do you have any idea about how T.E. can affect the bottom line over the course of a year’s time in the booth?

You should be able to answer yes to all of those questions. Let me help you understand what you need to know.

Transfer efficiency, T.E., is the amount of coating that actually lands on the item that you are spraying. That efficiency is discussed as a percentage. 100% means that everything that left the tip of the gun made it onto your project. It’s downhill from there to what reality truly is. Reaching 100% T.E. is not easy.

What affects that number? Well, first of all we would want to take a look at the coating that you are spraying and the surface that you are spraying onto. The thicker the coating, the more energy that will be needed to shear the coating. The thicker the coating, the harder it may be to break it up into small enough droplets. The more energy exerted, the more bounce back and overspray that will occur. Bounce back and overspray tend to end up on you, on the floor, and on the booth filters.

Obviously, a flat surface perfectly positioned for you to spray will allow you the potential for the highest T.E. with the least amount of “messing around.” If it’s curved, has openings in it, etc., then things become more challenging and your T.E. may suffer.

You also need to understand that different types of application systems demonstrate the ability to transfer coatings at varying percentages. My friends at CA Technologies have a really useful chart that shows approximate transfer efficiencies for various types of guns. Here’s their chart.

Bernie Bottens transfer efficiency spray guns

The magical transfer efficiency number is, as the chart shows, 65%. Why that number? Because HVLP guns are designed to have a minimum transfer efficiency of 65%. Can I make an HVLP gun shoot at a lower percentage? Yes. Can I make one shoot at a higher percentage than 65? Yes. It all comes down to proper setup and use of the gun.

 

About the Author

Bernie Bottens

Bernie Bottens (WoodworkingNetwork.com/blogs)writes and teaches on the subject of wood and wood finishing in industrial woodworking. He and his wife, Carol, live in Vancouver, WA. Bernie has been teaching wood finishing to shop owners, shop foremen, spray technicians and finishers all over Oregon, southwest Washington, and northern California for the past 9 years. Prior to that, he owned his own cabinet shop. His shop credentials include apprenticing and becoming a journeyman exhibit builder. Before that he taught in the public schools for 20 years. Bernie is the owner of Kapellmeister Enterprises, Inc. and Kap Coatings Consulting. Reach him at kapenterprises@msn.com.

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