Powder Particle Size

When power coatings are manufactured they the dry-blended materials are melted in an extruder. The extruder uses heat and pressure to melt and combine the dry ingredients into a homogenous mixture that will exit the extruder in a semi-liquid condition. As the mixture exits the extruder it is cooled by passing through a set of rollers and flattened out onto a belt to harden. At the end of the belt the now-hardened material is passed through a chipper and cracked into small pieces. These chips of powder are then put into a mill to be ground into dust. The blades in the mill and rotational speed control the average grind size of the powder particles.

When the powder exits the mill the particles above a certain target size (measured in micron) are caught in a screen and returned to the mill for further reduction. The particles below a certain size are removed using a cyclone separator. The particles that fit into the intended range of size are captured, boxed and shipped.

The process is well-set but it is not possible to completely avoid a small percentage of finer particles and percent that are larger than the target size. The average target particle size is usually between 30 and 60 microns. Some smaller particles are able to pass the cyclone and get into the box. The percentage of particles under 20 microns could be as low as 7% or as high as 13%. The percentage under 10 microns is usually around 5% to 7%.  Some particles are not able to pass through the screen but are a little larger than the target grind size. Averages vary depending on the particular powder and the properties it is being engineered to provide.

The final grind includes a wide variety of particle sizes within the target range. Collectively, the various particles can mix together at the surface and produce a good, level finish while providing good efficiency in deposition. However, if the particle size distribution changes and has a higher percentage of fines or coarser particles in can be harder to control application.