The first step in either painting process is to sandblast the product after fabrication is complete. Sandblasting is used to remove mill scale, oil, and rust which commonly comes on freshly manufactured steel. On projects getting repainted, sandblasting is used to remove any old coatings still on the product. The medium used for sandblasting can range widely from biodegradable options such as walnut shells to manufactured steel grit. Most mediums can be re-used a few times before disposal and each have their own advantages and specific applications. Sandblasting, strips all the surface oxidization off of steel so it will rust within hours when exposed to the correct atmosphere. Keeping this in mind, it will important for the product to stay inside a dry environment after it is sandblasted.
The next stage is to start applying the powder. The operator will begin with a zink based primer which is applied through a special electrostatic or corona gun. The electrostatic gun applies a +charge to the powder as it is discharged from the gun. These positively charged powder particles are attracted to the negatively (grounded) work piece. This causes two interesting phenomenons that help the paint process. First, the powder is physically attracted to the work piece so there is minimal over spray. Second, if you try and apply the powder coat too thick in an area, the density of the positive charge will actually repel the powder and prevent it from being applied too thick.
Once the powder is applied evenly to the work piece, it is moved from the powder coating bay into the oven where it is heated up to gel the primer. It is important to note that you will need a plan to move the product around gently as the powder is not adhered to the work piece (it clings using static electricity). Touching it or bumping the work piece too hard will cause a defect in the finish. The work piece will stay in the oven for a predetermined amount of time which is based on volume of steel being heated.
After the primer is heated up or “gelled” it is moved back into the powder coating booth where the finish coat is applied. The final coat is usually a customer-driven color and is applied in the same manner as the primer.
The last stage is to bake the product in the oven until it is completely cured and ready to go to the next stage of manufacturing.
There are many benefits to powder coating products over traditional wet paint techniques. At Sparta, we exclusively use powder coating on our products.