Powder Coating Defects and Solutions- pre-treatment defects
When using powder coatings, problems occur before, during and after powder application which we are going to discuss briefly in the articles on powder coating defects and Solutions.
Primarily we will expand problems related to the pre-treatment stage. Proper pre-treatment is fundamental to having the desired final coating quality.
One of the common methods of pre-treatment in powder coating use is phosphating the metal substrate.
This method has its own challenges and we have detailed some of its problems and their causes below:
Pre-Treatment Problems and Defects (Iron phosphate)
- Poor coverage: happens when the pH level of the solution is not in the correct range.
- Poor de-greasing: possibly due to low temperature, low density and insufficient duration of de-greasing.
- Presence of stains on the coating: usually due to water contamination in the rinsing tank and insufficient duration for phosphating. It can also be traced to poor de-greasing, low density of the phosphating or the accelerator solutions.
- Rusting: due to lightness of coating, or slow dry-up of substrate
- Foaming of solution: combination of phosphating solution with solutions in the previous stages, very high pressure in the material and very high velocity of air suction can cause the solution to foam.
- Poor powder coating adhesion: high thickness of the phosphate coat, poor de-greasing, presence of contaminants and low quality steel cause poor adhesion of powder coating to substrate.
- High or low weight of coating: among the causes of low weight or high weight phosphate coat are very low or very high density phosphate solution or accelerator, low or high temperature, and short or long phosphating process duration.
- Powder is visible on the coating: poor rinsing, a lot of algae in the tank and high accelerator density are causes of powder being visible on the coating.
In the next article we will discuss defects of powder coating and solotions related to powder application. We will analyze the causes for each defect.
Prepared by: Mojtaba Zeinal