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The truth about these application myths...
When it comes to powder coating equipment and application, just like the actual powder, there are some myths out there. Out tech service team explode some of the most common powder application myths.
1. Myth: All powder coating guns have a positive charge.
Corona powder coating guns almost always charge the powder with a negative polarity. You can get positive charging multipliers, but normally negative charging guns do not arc as much and they charge the powder better. If you are using a corona charging gun in tandem with a tribo gun (positive charging) you should use a positive charging multiplier.
2. Myth: The Technical Data Sheet (TDS) cure schedule is air temperature not part temperature.
The TDS cure information is based on Peak Metal Temperature (PMT), not air temperature. In other words, the part needs to reach the suggested temperature and hold that temperature for the required duration. Please remember that the thicker the metal the longer it takes for it to reach the proper temperature.
3. Myth: Run all application guns at 100 kV and 100 micro amps, always.
Depending on the powder application, running the powder coating equipment at its highest settings may not always be the best method. Coating recessed areas with the electrostatic settings too high can cause problems with back ionization (a rough orange peel effect). Also, when recoating previously coated parts the settings should be adjusted down.
4. Myth: All powders cure at the same oven settings.
Referring to the Technical Data Sheets (TDS) is always important when curing a thermoset powder coating. Some powder coatings will cure for 10 minutes @ 400˚F. and some for 10 minutes @ 340˚F. (PMT). Other products may have a different cure schedule than the two previously mentioned. In some cases curing a low cure powder (10 minutes @ 340˚F.) at a higher oven setting can cause the powder to cure too quickly giving it an orange peel appearance. It can also cause the powder to not flow out over the surface of the substrate, which can potentially cause adhesion problems.
5. Myth: All ovens are balanced with no hot or cold spots.
When installing a new or used oven for powder coating it is always a good idea to have the oven checked for hot or cold spots. These hot or cold spots can occur as a result of improperly placed duct work or louvers placed in the wrong location or direction on the duct work. An oven should be ±5˚F. in the top, middle and bottom as well as the front, middle and back. A good way to check for consistent temperature distribution is to run an oven recorder. Another way to check an ovens cure potential is to run test parts and follow with a solvent rub test. This method is less accurate but may be more available to some shops than the oven recorder method. In fact, sticking with ovens, another myth often put about is that a balanced oven stays balanced, it does not change over time. This is not the case. Ovens should be checked periodically to be sure they are maintaining the right temperature. Day-to-day operation and constant heat produced can cause wear on thermal couples, belts and motors. Duct work can be damaged over time and the gas-to-air mixture of the burner can start to change. It is always a good idea to practice regular preventive maintenance (PM) versus waiting for a problem to occur. Every shop should have a defined preventive maintenance process and schedule. Periodic checks with an oven recorder or frequent solvent rub tests are good ways to maintain a powder cure oven. If a shop does not have access to an oven recorder solvent rub tests should be conducted once a week if not more frequently, particularly if running parts of various thicknesses.