There are about fifteen different processes for coating metal products. However, only a few of them give you the possibility to apply whatever color finish you have in mind on the product. For these, you can choose from a wide palette of RAL colors to achieve the finish you require. The powder coating process allows you to work with multiple layers to achieve a very special, custom appearance.
Powder Coating Beginnings
The powder coating process is among today’s leading techniques for applying colors on objects. Its predecessor was called „flame spraying“, which is a technique that was experimented with in the 1940s. It was the first application of thermoplastic powders directly to metal with the help of heat.
In the 1950s, a breakthrough was made by German scientist Dr. Erwin Gemmer, who first developed the fluidized bed process. It was the first step towards modern powder coating processes and was patented in 1962. This process introduced a finish to the world that was easily reproducible and practical. It also significantly reduced negative impacts to the environment compared to traditional liquid painting that utilized volatile solvents.
Consequently, huge leaps in the development of electrostatic spraying techniques were made and the foundations for a new coating industry were laid down. This method has become widely adopted by many industries over the years and now represents one of the most popular finishing processes around the world.
Electrostatic Spraying
A crucial method that makes the powder coating process possible is electrostatic spraying, which requires the use of a magnetic field to apply paint to metals and plastics. It operates on the principle of polarity, where opposites are attracted to each other.
Paint is pulled toward the object by applying a negative charge to the object and a positive charge to the paint, resulting in a strong, smooth, and durable finish. An electrostatic field works like a magnetic field. When two items have opposing electric charges, they will be pulled towards each other. Simple as it sounds, this is the basic principle behind the electrostatic spraying method.
How does powder coating work?
Basically, all you need to successfully carry out the powder coating process on metal or plastic is the powder in any RAL color, a powder application system (spray gun), an oven or heat lamps, and a place where you can comfortably and professionally coat the product.
Cleaning
The product needs to be properly cleaned before application of the powder. This means all smudges, oils, and impurities need to be removed. Generally, the item needs to be degreased by spraying it with gasoline and then wiping it down with a clean cloth. Although this works for most smaller items, some of the larger truss segments require degreasing baths of various sizes. These large items are dipped into the bath to ensure complete degreasing. It’s an efficient process that saves a lot of labor and time.
Powder Application
The actual powder is made of polyester and pigment. The powder is inserted into a powder coating spray gun that is connected to an air pressure machine, which pushes the powder through the gun. The powder is then positively charged up to 50,000 volts by an electromagnetic coil within the gun.
That gets us back to the electrostatic painting method that applies powder to the object by using positive and negative electrons, so the coating is attracted to the object. This method ensures less overspray than traditional spray painting. The object to be coated must be grounded and have a negative charge. Charging is very important, as the object then attracts the polarized powder, retains it, and somehow automatically levels the layer of powder on its surface.
Curing or Baking
Once the product is properly painted with the powder, it’s time for the oven to work its magic. The product is placed into an oven and cured/baked at 200° C for at least 20 minutes. During this time, the powder liquifies and the curing process changes the molecular structure of the powder into a durable and elastic plastic coating. To describe it in more detail, the powder goes through two changes during the baking process. It transitions from a solid to a liquid and then back to a solid again, creating a smooth, even, and durable coating on the product.
Powder Coating vs. Paint
Painting objects with standard paint is a tried and true method of achieving a desired finish or color on any product. However, the relatively new process of powder coating is successfully utilized in many different industries and is thus rising to the top position of product finishing methods. Listed below are a few advantages and disadvantages of the powder coating method.
Pros:
- Powder coating is durable and flexible, which is why it is commonly utilized for suspension components that are constantly moving or under continuous use
- One layer is sufficient for full coverage of the object, but it is also possible to apply multiple layers to achieve a special or custom appearance
- Does not contain high levels of chemicals or solvents
- During application of powder to the object, it is possible that some inconsistencies could appear in the finish. In this case, it is extremely easy to remove the powder and start over if you realize your mistake before the beginning of the baking process. Just remove the powder from the object with air pressure gun and start again.
- The coating is evenly distributed on the surface of the object, ensuring a more uniform finish
Cons:
- Powder coating adds a significantly thick layer to the object, which might be an issue with products that need to maintain a precise size. For these cases, traditional paint would be a better solution.
- In situations where you would need to cover some parts of the object to keep certain areas free of the coating, the use of temperature-resistant plugs and tapes would be necessary.
- The bigger the object, the larger the oven you would need. There are limits to what size objects can be powder coated.
- Materials that can be coated by this method must withstand high temperatures during the baking process, i.e. plastic and wood are not suitable for powder coating
Powder Coating Truss
For several years, there has been an ever-increasing demand from the event production industry for truss structures in various colors, with standard black being the most popular. Truss can be powder coated in any RAL color, with several different levels of gloss for the finish.
There are two reasons why black is so popular. First, it ensures that there are no reflections from the truss, which is very important for events that are filmed (TV shows, live broadcasts, concerts, etc.). The second reason is that black powder coated truss becomes almost invisible as far as live concerts are concerned and does not cause any distractions during the event. In general, the standard black powder finish comes out as a smooth coating on the surface of the truss. The coating is uniform and suitable for high end installations, where design matters the most.
For touring and rentals, we would recommend the so called “structural powder coating”, where the coat is more robust and the overall finish shows more plasticity. It is harder to remove, scratch, or dent. Since this coating is more damage-resistant and durable, it’s a better fit for repeated assembly and temporary installations.
