Powder Manufacture & Application
How is powder made?
It’s actually a pretty simple process. The raw materials are weighed out (and there are no wet ingredients in powder and no solvents, which means no VOC’s) and we mix and blend them together to start the mixing process. The mixture is put into an extruder, which uses controlled heat and pressure to completely homogenize the mix. The hot extrudite is then forced out through chilled rollers, which cool it very quickly, making cold, thin and brittle sheets of hard material. These long sheets cool on the cooling rack and then are broken up into chips and then the extruded chip is ground down into powder.
Making metallic or sparkly powders
Metallics have an extra step. The powder is made in the same way, but at IFS we bond all our metallic powders. This means that we put the powder and metallic flake through a process that makes the tiny metallic flakes stick to the powder particles. It ensures a much more even and professional finish. At IFS we do most of our bonding in house, so we don’t’ have to send it elsewhere for that process to happen.
Making adjustments to color
Because everything is heated up and mixed together during the extrusion process, then cooled and ground down, if the color is not quite right, we have to start again. Once the raw materials have been through the extruder, they are all melted together - we can’t “unmelt” them So if the color isn’t quite right, then we start all other again, adjust the pigment quantities, and create a whole new powder.
At IFS we manufacture powder, we don’t actually apply it. There are thousands of powder coaters all over the USA who do a great, high quality job of applying powder coating to metal substrates. There are a few different ways of applying powder, but the most common is electrostatic application.
In this method, the powder is placed in a hopper, which often looks like a big drum that sits on the floor of the powder spray booth. The powder is then fluidized, which essentially means we push air through the powder which makes it behave like a liquid. This means that the fluidized powder can be pumped from the hopper, through hoses which connect the hopper to a powder spray gun.
The parts to be coated are hung on a moving conveyor and they are grounded.
At the end of the spray gun there are some electrodes. When you fire the powder gun, the powder is discharged from the gun and picks up the electrostatic charge from the electrodes at the end of the gun. The electrostatically charged powder is therefore attracted towards the grounded parts. The electrostatic bod keeps the powder on the part. Once the part is covered in powder, the conveyor then carries the parts to an oven.
Each powder comes with its own cure schedule, which tells us how hot the oven should be and how long should the powder coated part stay in the oven for. The coated parts stay in the oven for the required amount of time. The powder heats up, then it melts, flows and then gels. As it gels and cools a whole new chemistry is created on the part. That is what makes powder so tough, hard and scratch resistant. A whole new chemistry is created that can’t be broken.
In tribostatic application, the powder particles are charged by rubbing along a specially designed tube on the inside of the powder gun. The particles become charged using friction and are then attracted to the grounded parts. Using a tribo gun requires a different formulation of powder than a corona gun.
Fluidized bed application
Another way of applying powder is to use a fluid bed. In this method the a fluidized powder bed is created and the parts are “dipped” into it.
Did you know we also have a whole series of videos that cover everything from application problems, appearance issues and even QC testing? Check them out here!
Pretreating the substrate before applying powder to it is important. At the very least the parts to be coated should be cleaned and have any dirt or oil etc. removed from them. If this is not done then you are going to get powder coated dirt, oil and grease and this will not only affect how the powder performs but also how the substrate performs beneath the powder.
For certain applications such as architectural applications, then a complete pretreatment program is recommended to add an additional protective barrier to the substrate. This will help both the powder and the substrate perform better. It helps clean the substrate and protect against rust or substrate degradation.
During this type of pretreatment process the parts are cleaned using water of a specific PH level. Then the chemical pretreatment is applied. With powder coatings a chrome based pretreatment or a non-chrome pretreatment can be used. Once the pretreatment chemicals have been applied, the parts are rinsed and then sent through a blast oven which quickly dries them off so they are ready to be powder coated.
With powder coatings, there is no primer - chrome based or otherwise - required after the pretreatment of aluminum. This is a huge advantage over liquid coatings as it is one less layer of paint, process, energy and time.
When coating steel, often one of the key considerations is corrosion. After a similar pretreatment process, a primer may be applied. Zinc rich powder primers help add a protective layer that will help guard against corrosion. The powder top coat can then be applied.