Questions About Transfer Efficiency

Question:

I am the paint line supervisor in our plant. Some time ago, we switched to waterborne-paints to meet the local air quality standards, and we are in compliance. I keep hearing about transfer efficiency. I guess that is the latest “buzz” word. In fact, the plant manager just asked me about our transfer efficiency. I heard it is the ratio of the paint that goes on the product to the paint that does not go on the product. Since we are in compliance, do I have to worry about transfer efficiency? 

Answer:

If you want to save money in your painting operations, you should worry about transfer efficiency (TE). First, you heard wrong. TE has been calculated differently by different people. Simply stated, TE is the ratio of the amount of paint actually applied on a product to the total amount of paint used, multiplied by 100. TE is expressed as a percentage. You can save money by increasing your TE.

For example, consider a hypothetical product that requires 0.66 gallons of 50% solids paint for complete coverage when sprayed using equipment capable of 30% TE. If you use the same paint in equipment capable of 70% TE, you get complete coverage using only 0.28 gallon. You use 0.66 gallon – 0.28 gallon = 0.38 gallon less paint. If the paint costs $10.00/gallon, you save 0.38 gallon x $10.00/gallon = $3.80 in paint costs for every hypothetical product coated. Not only will you save material costs, you will also save labor costs because the paint will be applied in less time. Taking it a step farther, your production rate could also be increased. 

Question

What should be the expected transfer efficiency of a square transfer system composed of one e-coat bath and two permeate immersion tanks? 

Answer

The transfer efficiency is a calculation that determines the degree of utilization of the electrocoat material in the system. A transfer efficiency of 100 percent indicates that all electrocoat material has been transferred to the parts. Needless to say, achieving a transfer efficiency of 100 percent is impossible. So where does the e-coat material that is not transferred to the parts go?

The typical areas where electrocoat material is used up, besides on the parts, are in the racks, excessive film or film variation, excessive oven and cure conditions, and excessive permeate carryover and/or leaks. Other factors such as poor agitation also can contribute to poor transfer efficiencies. Low agitation or poor agitation patterns may lead to settling of paint solids.

Electrocoat industry studies and reports indicate that a transfer efficiency of 95 percent can be obtained with e-coat systems. This compares with transfer efficiencies of 45-60 percent for liquid systems and 60-80 percent for powder systems.

Maintaining high transfer efficiencies in electrocoat systems, especially in high-volume applications, can translate into significant annual savings on electrocoat resin and paste. Proper rack maintenance, good agitation, adequate cure and good ultrafiltration are typically the keys to good transfer efficiencies.