Troubleshooting Powder Coating Problems

Aug 23,2010

Troubleshooting problems in the powder operation may be necessary from time to time in spite of good process controls and operating procedures. Troubles can occur in application, pretreatment and curing.

Knowing what to look for helps to speed up the process of correction.

Application Problems

Problems with powder charging or delivery will make it more expensive and difficult to apply the material to the part. Many times these problems can be corrected by a review of the basic function of the application system to see what is wrong. This troubleshooting section covers some of the common mistakes that cause difficulty in the application of powder coatings.

Poor Charging

When it becomes unusually difficult to get powder into the inside corners (Faraday cage areas) there are three common things that should be checked.

Grounding

Powder flow rate

Voltage

Grounding may be lost from excess build-up of coating on the hangers.

Measure the resistance from the part to the conveyor rail with an

ohmmeter. If the resistance is greater than 1 megohm, the path to

earth ground is not adequate. Check the components of the racking arrangement, find the insulated component and clean it to make good contact.

Excessive powder flow rates will cause a reduction in charging efficiency.

Check the gauges and reduce the flow rate.

The voltage at the gun tip needs to create a field of high potential.

Check voltage at the gun tip to make sure that it is compatible with

the gauge.

The Faraday cage effect describes the problem with getting the powder to adhere to the surface of an inside corner. This is the result of resistance created by the presence of an electrostatic force. The trostatic force is attracted to the prominent areas of the part where the resistance is low. Free ions and powder film build quickly on these more prominent surfaces and create additional resistance to penetration.

Faraday cage effect can be reduced by limiting the current draw of the gun, by using the correct nozzle for the task, and by control of the flow rates and gun-to-target distance.