First of all: What is transfer efficiency?
Transfer efficiency is the ratio of the amount of powder deposited on the part to the amount of powder directed to the part. transfer efficiency is given as a percentage and 100% is optimal. Any manufacturer wants to have as much as 100% of the powder adhered to the metal surface during the first spraying process. No excess powder needs to be recycled and parts can go directly into the curing oven. But in real life, it is not true.
During actual process, there are usually a large amount of powders not covered on the object and dropped on the booth floor, we called them "overspray powders". Therefore, increase the transfer efficiency is to reduce overspray, is to improve the utilization of raw materials, reduce costs and increase profits.
Although the recycling system used today is very efficient, but this does not improve the transfer rate of the initial powder coating. What we should do is to reduce the cost by improving the first pass transfer efficiency.
So what factors will affect the first transfer rate? and How can we improve it
1. Choose appropriate size of powders
In the actual spraying process, the powder paticles have various sizes, too large or too small may affect the transfer efficiency. Generally, particles whose diameter is from 25 to 75 microns have a transfer efficiency of up to about 70% or greater. Powder particles whose diameter is from 0 to 25 microns may cause the powder to be charged and fluidized difficultly. For powder particles whose diameter is 75 microns or larger, they may not be able to maintain a uniform charge, result in a rough spray surface effect.
2. Apply right high voltage for different parts.
For effective spraying work, powder particles require static electricity to work properly. The most common powder coating guns rely on corona charging. The powder particles acquire charge while being from the gun to the part. A universal corona gun can provide 100kV high voltage or higher when in use.
However, for different sprayed workpieces, the required voltage is different. The first pass transfer efficiency can be improved only by understanding the suitable voltage range of different workpieces correctly.
The normal workpiece is sprayed at voltage from 80 to 85KV; the general plate is 70-80KV, and the groove workpiece or complex workpiece is 30-50KV. In addition, the distance between spray gun and painted workpiece, the distance between sprayed workpiece and ground are all influential factors, and the distance of 8-12 inches is generally suitable.