There is more than one method to test whether the workpiece surface is clean, among which the most common one is the “water break free” test. In the test, observe whether water is fully sheets over the clean part or draws away from certain parts of the surface. Other methods include cloth swabs, alcohol drops and sophisticated laboratory methods.

For powder coatings, iron phosphate is the most commonly applied pretreatment method. It can be used for almost any materials. With the same pretreatment method, powder coatings can perform better than liquid paint. Sometimes, zinc phosphate is also used for pretreatments. But it costs more. And the use of heavy metals will produce lots of sludge.

When a perfect fluidization is achieved, the coated materials should look like fluid. It’s like water simmering on low heat. It should not be boiled for long time.

The failure of the powder to adhere to the workpiece may be caused by:
1. Failure in the generation of high voltage electrostatic due to the coating gun or the controller.
2. The workpiece is poorly grounded due to a dirty hanger or a poorly grounded convey.
3. Poor electrode contact or excessive powder buildup.

In many countries, powder used for electrostatic powder coating is not considered hazardous. The treatment for the powders is similar to that of conventional non-hazardous wastes. For this concern, it is advisable to consult your local authority for more accurate information.

Faraday cage effect defines the condition when there are recesses, inside corners, channels, or protrusions on the surface of a workpiece. It is an area that an external electric field cannot penetrate. To achieve an effective coating in Faraday areas, the following conditions should be met:
1. Powders should be well charged.
2. The air flow should be enough to deliver the powder into the recess, but not too much to cause a powder deposition.
3. The external electric field needs to be controlled so as to reduce the push for the powder particles to deposit in the Faraday cage.

Size of the particles can affect the process of powder coating, including fluidization, powder transport in hoses, powder movement in air, electrostatic charging, transfer efficiency, Faraday cage penetration and the smoothness of the film. The appearance of cured surfaces can also be affected by particle size.

The adhesion of coatings is affected by the cleanliness of workpiece surface, pretreatment method, melting and curing of powder coating. Adhesion can be tested using a variety of methods, one of which is by using of cross hatch and tapes. In the test, firstly, make some crossed cuts on the surface. Then stick the tape to the cuts and quickly rip it off. Coating adhesion can be obtained by judging how much coatings can remain. In the coating process for a workpiece, the intercoat adhesion for different coatings varies. Epoxy powders tend to be harder and more prone to intercoat adhesion problem, especially after being overbaked. But polyester and epoxy-polyester can be recoated well.

The selection of the coating should be a cooperation between the user and the supplier of the powder. For a specific coating application, there should always be some considerations. If the coatings require a higher pencil hardness and weatherability, then flexibility will be reduced. If chemical resistance is preferred, then weatherability and over bake yellowing resistance should be compromised. Additionally, cure time, temperature, materials of the workpiece and application methods also need to be considered.

Precoated or recoated workpieces often have 1-2 mils of coatings already. When a coating of 4-5 mil is achieved, powder may start to repel itself. It is time to reduce the voltage of the powder coating gun by at least 1/2 to prevent the newly coated materials from repelling or back ionization. To achieve better recoating effect, it is recommended to consult the supplier of the powder to ensure a proper intercoat adhesion.

The cycle time of the oven is composed of bring-up time and dwell time. The bring-up time refers to the time required to reach the curing temperature of the workpiece, while dwell time is the time required to keep the workpiece at curing temperature. In some powder coating applications, the workpiece can be heated quickly to reach a higher curing temperatures and shorten the dwell time. By doing this, the oven cycle time can be shortened.

You are advised to consult a manufacturer of air compressors. You should have a good oil and water extractors as well as a refrigerant or a desiccant dryer system. Whatever you choose, you should prepare an oil coalescing filter with automatic drain and particulate filter.

A powder coating gun should be cleaned after each change of a color. After a day’s coating work is completed, powder coating gun, pump, and hose should be purged to prevent the existence of moisture in the powder and from causing blockage for the next use. A deep cleaning is necessary once a week and worn parts should be replaced according to how frequently it is used.

Depending on wearing or contamination caused by the powder, powder hoses should be replaced at least once a year. A regular inspection can help to find any possible cracks in time.

A rod should be vertically inserted into the ground and a grounding strap should be directly attached to the booth. You can contact the local electrical contractor to get a standard grounding rod, which is usually made of copper.