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Automotive Functional Parts

Corrosion, chemical and mechanical resistance for functional parts

Automotive functional parts include brake components, filters, engine brackets, springs and other metal parts. Continuous oil contact, heat and vibration place high demands on oil resistance, heat resistance and adhesion.

Veri Coating offers textured and smooth pure epoxy powders and smooth epoxy-polyester hybrid powders, with GT0 adhesion, 50 kg-cm impact resistance, more than 1,000 hours of salt-spray resistance and low-temperature curing down to 120°C.

Application notes: Castings should be preheated for degassing, while edge coverage and compatibility with subsequent assembly should be verified; the recommended film thickness is 60-90 um.

Typical Powder Coating Challenges for Automotive Functional Parts

Outgassing from Die CastingsOutgassing blisters require preheating and controlled powder reactivity.

Outgassing from Die Castings

Porosity, residual release agent and moisture within aluminium- or zinc-alloy die castings escape during heat-up and cure, producing pinholes, blisters, craters or localised surface depressions. Defects are more likely in thick sections, recycled aluminium and complex ribbed areas, and worsen as film thickness increases.

Formulation Design

  1. Use an outgassing-tolerant system with an extended flow window and slower surface closure, balancing melt viscosity and gas-release capability.
  2. Control degassing-agent loading to avoid cratering, gloss loss or reduced intercoat adhesion from excessive addition.

Process Control

  1. Preheat parts for outgassing before coating, setting temperature and time from actual part thickness.
  2. Strengthen degreasing, rinsing and drying to prevent residual release agent and moisture.
  3. Control film thickness; where necessary, apply multiple thin coats and verify intercoat adhesion.
Validation Focus
  • Pinholes/blister count
  • Defects before and after preheating
  • Film-thickness sensitivity
  • Adhesion retention
Coating Delamination During Subsequent MachiningHole-edge delamination requires better adhesion and toughness with optimised machining.

Coating Delamination During Subsequent Machining

When coated functional parts are drilled, milled, tapped or press-fitted, the coating at hole entries and cut edges may chip, lift or delaminate in sheets. Common causes include inadequate coating toughness, poor substrate pretreatment, undercure, blunt tooling and excessive machining heat.

Formulation Design

  1. Improve resin-system toughness and adhesion to the metal substrate rather than pursuing hardness alone.
  2. Optimise crosslink density and pigment and extender loading so the coating remains intact under cutting impact.

Process Control

  1. Mask machining areas or machine before coating; where the sequence cannot change, use sharp tools and a stable feed rate.
  2. Strictly control pretreatment and degree of cure to prevent complete separation at the coating-substrate interface.
  3. Chamfer hole edges to reduce stress concentration at sharp edges.
Validation Focus
  • Width of chipping around holes
  • Cross-hatch adhesion
  • Impact/bend
  • Corrosion spread after machining