Polyester powder coating is a dry material sprayed onto a work piece and then cured to form a protective covering. This method of covering and protecting objects has a number of advantages over conventional wet coverings. Polyester powder coating creates a stronger and more durable finish and is more economical and safer for the environment than many forms of liquid coatings. As a result, powder coating systems have become very common in commercial and industrial processes.
In most cases, a polyester powder coating starts as granules of industrial polyester. These granules vary in size based on how they were made, but they are usually about the size of a marble. The granules are mixed with coloring agents and chemicals and then fed into an extruder where the mixture is heated until it melts together. The extruder pushes out the mixed material where it is rolled flat and allowed to dry. The dry sheets are broken into chips and then ground into powder.
There are two main types of polyester powder coating: thermoset and thermoplastic. A thermoset coating undergoes a chemical reaction when heated, making the coating stronger than its constituent parts. A thermoplastic coating simply melts together during the curing process. While thermoplastic coverings are not as strong as thermoset, they are stronger than most conventional wet coverings.
The most common method of using polyester powder coating is in electrostatic coating. The power is sprayed through a system that imparts a positive charge to the particles. These systems may be a simple handheld sprayer or may be a large enclosed spraying chamber. When the powder hits the work piece, the difference in electrical charge causes the particles to stick.
After the work piece is thoroughly coated, it is placed in a curing oven. These ovens are generally large conventional ovens, similar to those found in a household kitchen. Depending on the work piece, it may be in there as little as a few minutes to as long as a few days.
In addition to the greater strength, there are a number of reasons why polyester powder coating has become more popular. One of the biggest is the lower cost of the process. The greater protection of the coating results in less defective coatings, which lowers the coating costs. Second, any powder that doesn’t stick to the work piece can be gathered up and reused, unlike wet coverings where any surplus is lost. Lastly, the machinery to set up a dry powder system generally costs less than a wet system.