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Automotive Wheels

High flow, filling corrosion protection and multilayer compatibility

Automotive wheel applications mainly involve surface coating of passenger-car aluminium-alloy wheels. Direct exposure to road-stone impact, rain and brake dust places high demands on flow, filling ability and compatibility with other coating layers.

Veri Coating offers an epoxy-polyester matt wheel primer designed for aluminium wheels, with good powder penetration into bolt cavities, strong flow and filling performance, and compatibility with acrylic high-gloss clear powder for appearance and long-term protection.

Application notes: Aluminium wheels should be degreased and chromated, with a recommended film thickness of 80-100 um and curing at 180°C for 15 minutes; recoat adhesion should also be verified.

Typical Powder Coating Challenges for Automotive Wheels

Insufficient Deposition in Spoke Corners and Bolt HolesLow film build in holes requires better penetration and optimised touch-up settings.

Insufficient Deposition in Spoke Corners and Bolt Holes

The Faraday cage effect makes it difficult for powder to penetrate spoke roots, included angles, bolt holes and deep rim channels, causing exposed substrate or low film build while outer flats become too thick. Complex geometry can also produce local colour variation and subsequent corrosion risk.

Formulation Design

  1. Optimise particle-size distribution, charging and melt flow to improve penetration and deposition in deep channels and holes.
  2. For wheel powder primers, improve penetration into bolt recesses while retaining filling and flow.

Process Control

  1. Coat deep channels, holes and spoke roots at lower voltage before coating the outer surfaces.
  2. Adjust gun angle, gun distance and powder output to avoid back ionization at high voltage.
  3. Establish film-thickness checkpoints in critical areas and apply targeted touch-up to thin zones.
Validation Focus
  • Minimum film thickness in bolt holes
  • Spoke-root coverage
  • Film-thickness uniformity
  • Failure of thin areas after salt spray
Compatibility of Powder Primer with Liquid Basecoat and ClearcoatIntercoat mismatch requires validation of the powder primer, basecoat and clearcoat system.

Compatibility of Powder Primer with Liquid Basecoat and Clearcoat

Poor compatibility between a wheel powder primer, liquid basecoat and clearcoat can cause craters, solvent attack, intercoat delamination, adhesion loss or blistering after baking. Performance depends closely on the primer surface condition, degree of cure, recoat interval and solvent system of the liquid coatings.

Formulation Design

  1. Select a wheel-specific powder primer with suitable surface wetting and intercoat adhesion, controlling migration of waxes and surface additives.
  2. Balance primer cure to avoid residues from undercure and loss of intercoat adhesion from overcure.

Process Control

  1. Conduct system-compatibility tests with the customer's actual basecoat, clearcoat and complete bake schedule.
  2. Control the waiting time and surface cleanliness after primer cure, preventing oil, silicone and touch contamination.
  3. Verify intercoat performance after both a single cure and multiple bake cycles.
Validation Focus
  • Intercoat adhesion
  • Cratering/solvent attack
  • Blistering after multiple bakes
  • Delamination after damp heat and salt spray
High-Flow Decorative FinishPoor flow requires a balance of levelling, outgassing and decorative appearance.

High-Flow Decorative Finish

High-gloss or premium decorative wheel surfaces accentuate orange peel, craters, particles, waviness and local film-thickness differences. Complex curvature, die-casting outgassing, powder reactivity and oven uniformity jointly affect image clarity and batch consistency.

Formulation Design

  1. Use a high-flow wheel powder primer or topcoat, optimising resin viscosity, flow-control agent, degassing agent and cure rate.
  2. Control pigment and extender dispersion and particle-size distribution to reduce gel particles, coarse particles and particulate defects.

Process Control

  1. Strengthen preheating and outgassing of die castings, powder sieving and booth-cleanliness control.
  2. Stabilise film thickness and verify the part heat-up profile to provide sufficient flow time.
  3. Assess orange peel, distinctness of image (DOI) and particles under a standard light source using limit panels.
Validation Focus
  • PCI smoothness rating ≥ 8
  • DOI or image clarity
  • Particle count
  • Batch gloss and appearance