Powder Coating Smoothness
Making powder coated surface smooth.
Powder coatings can be formulated to provide a very wide range of surface smoothness from glassy smooth to rough textures. The appearance properties and smoothness of the powder are impacted by a number of factors. Each factor must be controlled to provide consistent results.
The specific formulation of the powder material is an important factor that determines smoothness of the powder film. Different ingredients can be used to affect the flow of the powder as it cures. Typically, more flow will provide smoother finish and less flow will show more orange peel. The ingredients used in a particular coating are selected based on the customer requirements for finish appearance. If the customer requires a very smooth appearance the formulator will use ingredients that will provide the correct flow and other attributes to achieve the target smoothness.
Powder coatings are formulated to achieve the desired results when applied within a specific range of film thickness. Within this range, the coating should provide a consistent surface appearance. Orange peel may be greater if the film thickness is too light or too heavy. A typical film thickness range may be a full 25 or even 50 micron of powder from the low end to the high end.
The smoothness of a cured powder coating film can be affected by the application process. Consistent appearance relies on consistent application technique and film-build. If the operator moves the spray gun in an irregular pattern it may cause back-ionization or inconsistent film thickness. The resulting appearance may be inconsistent with areas inconsistent gloss and texture. Smooth and consistent gun strokes are needed to provide the correct smoothness in appearance.
Substrate Surface & Shape
The smoothness will also be affected the condition of the substrate. Rough castings, hot-rolled steel and other surfaces cannot be hidden by a layer of powder and serious blemishes on the part surface will show up readily in the finished film. Contamination on the part surface can cause pin-holes or other surface defects. A smooth powder appearance requires a clean and smooth substrate surface.
Coating smoothness can also be affected by cure time and temperature profile and by the rate of increase in the temperature. The specific powder material and the flow additives can be affected by the profile in the cure oven. The powder supplier can be consulted on the right cure cycle and testing should be performed to determine the best settings for a particular powder.
Powder coatings will not hide dirt or significant imperfections in the coating. Very small particles may be hidden in an average film but even small particles will likely show in a high-gloss, smooth-texture powder film. The plant area, especially the application area and the cure oven must be kept clean and controlled in order to effectively run a very smooth powder without a lot of defects or rejects.