Powder coating is a dry finishing system made from resin, pigment, curing agents and performance additives. Electrostatically charged particles are typically sprayed onto a grounded part. The part then enters an oven, where the powder melts, flows across the surface and chemically cures into a continuous film.
Its solvent-free nature, broad range of colours and finishes, recovery potential and high mechanical performance make powder coating suitable for many areas of the metal industry. Yet describing powder coating as durable does not mean every application will automatically succeed.
Powder coating quality is created across the entire line—from the surface and hanging system to the spray gun and curing oven.
How does a powder coating system work?
An industrial powder coating process generally includes:
- Selecting a coating system suited to the part’s service conditions
- Cleaning and pretreating the metal surface
- Drying the part completely
- Applying the powder electrostatically
- Building a balanced film thickness
- Curing the part at the time and temperature required by the coating system
- Cooling, visual inspection and performance testing
A deviation at any point in this chain can lead to adhesion loss, orange peel, pinholes, craters, colour or gloss variation and inadequate corrosion resistance.
How should the right powder coating be selected?
Selection should not be based on a RAL colour or gloss level alone. Indoor or outdoor use, exposure to sunlight, chemical and mechanical loads, required appearance, substrate and available curing conditions must all be considered.
Epoxy systems
Epoxy-based systems can be considered for indoor applications where adhesion, chemical resistance and mechanical durability are priorities. Because prolonged ultraviolet exposure can change colour and gloss, they are generally not the first choice for appearance-critical outdoor use.
Epoxy-polyester hybrid systems
Hybrid systems are widely used for indoor finishes that require a balanced appearance and general industrial performance. Office furniture, shelving, electrical cabinets and interior metal components are typical examples.
Polyester systems
Polyester powder coatings are preferred where ultraviolet resistance and outdoor performance are required. For outdoor furniture, agricultural equipment, façade components and sun-exposed parts, the product’s durability class and project specification should guide selection.
The resin family matters, but it is not enough on its own. Two coatings from the same chemical family may differ in appearance, cure response, flexibility, chemical resistance or weathering performance. Selection should therefore be based on the technical data sheet and verified project conditions.
How does surface preparation affect coating performance?
Oil, rust, weld residue, moisture or pretreatment residue can prevent a stable bond between the coating and the metal. Proper degreasing, rinsing and conversion coating support adhesion and corrosion resistance.
The pretreated part must be fully dry before entering the booth. Water trapped in hanging pockets, joints or closed profiles can evaporate in the oven and cause pinholes, blisters and crater-like defects.
Why is grounding important in electrostatic application?
During electrostatic spraying, powder particles are electrically charged and attracted to the grounded part. Poor contact to ground can reduce transfer efficiency, create uneven film build and make recessed areas harder to coat.
Cured powder accumulating on racks and hooks forms an insulating layer over time. Regular cleaning of contact points, checking earth connections and securely hanging parts are therefore fundamental to process continuity.
What is the Faraday cage effect?
In corners, narrow channels, deep recesses and enclosed geometries, the electric field can concentrate at the outer edges. Powder builds quickly on exposed areas while struggling to reach recesses. This is known as the Faraday cage effect.
Increasing voltage or powder output is not always the answer. Excess charge can increase back ionisation and surface defects. Gun angle, distance, air volume, voltage and current limits should be optimised together for the part geometry. Manual pre-touch-up or changes to automatic gun positions may also be required.
Why must film thickness be controlled?
Film thickness can affect colour coverage, gloss, appearance, adhesion, flexibility, impact resistance and assembly tolerances. A thin film may give poor coverage and protection, while excessive build can cause orange peel, pinholes, brittleness or assembly problems.
There is no universal film thickness for every product. The target should be set from the manufacturer’s technical data, surface type, part geometry and customer specification. The gauge must suit the substrate and be verified regularly.
How is correct curing achieved?
Cure cannot be verified from oven air temperature alone. The metal itself must reach the required temperature and remain under the specified conditions for the required time.
Thin sheet and a heavy welded assembly do not heat at the same rate. Conveyor speed, part mass, hanging density, oven temperature distribution and air circulation all change the actual metal temperature profile. Oven profiling with a temperature data logger should therefore verify the cure schedule for different part families.
Under-curing can lead to poor adhesion, low hardness and weak chemical resistance. Unnecessary over-curing may change colour or gloss, waste energy and, in some systems, impair mechanical properties.
Common powder coating defects
Orange peel
A wavy surface resembling orange skin. Film thickness, powder flow characteristics, part heating rate, gun settings and curing conditions should be checked together.
Pinholes and blisters
Outgassing, moisture on the part, oil or water in compressed air, surface contamination and excessive film thickness can cause these defects. Outgassing risk should be assessed separately for porous castings and galvanised surfaces.
Craters and fisheyes
Contaminants such as silicone, oil and incompatible powder particles can disrupt film wetting. Booth cleanliness, colour-change discipline, compressed-air quality and nearby auxiliary materials should be investigated.
Colour and gloss variation
Variable film thickness, differing metal temperature profiles, under- or over-curing, cross-colour contamination and batch management can all create colour or gloss differences.
Poor adhesion
Insufficient cleaning, unsuitable pretreatment, moisture or residue, incomplete cure and incompatibility between coating and substrate should be checked first.
What can be checked in quality control?
The inspection plan should reflect the part’s service environment and customer specification. Common checks include:
- Visual surface, colour and gloss inspection
- Dry film thickness measurement with a suitable gauge
- Verification of the oven profile and actual metal temperature
- Assessment of coating separation by cross-cut testing
- Project-specific impact, bend, hardness and chemical resistance tests
- Corrosion testing where required by the specification
Cross-cut results are not a tensile force measurement; they classify how the coating separates at the cut areas. For salt spray testing, duration and acceptance criteria must be defined by the relevant product or customer specification.
CONCLUSION
Consistent quality comes from managing the entire process together.
A successful powder coating application depends on the right resin system, a clean and dry surface, effective grounding, balanced application, controlled film thickness and a verified curing profile working together.
Ferovant evaluates coating selection not only through colour and price, but through the part’s service environment, pretreatment line, application equipment and performance target.
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