Surface Treatment and Coating Process for Semi-Trailers

Surface Treatment and Coating Process for Semi-Trailers
Semi-trailers are long-term exposed to harsh conditions such as sun exposure, rain, sand impact and salt spray. Therefore, surface treatment and coating are critical to anti-corrosion, appearance quality and service life.
 

1. Pre-Treatment (The Foundation of Coating Life)
Shot Blasting / Sandblasting
Remove rust, oxide scale, welding spatters and impurities to reach cleanliness grade Sa2.5, creating a rough surface to improve adhesion.
Degreasing & Washing
Use alkaline cleaning agents to remove oil stains, followed by multiple rinses to avoid chemical residue.
Phosphating / Passivation
Form a dense conversion film on the steel surface to enhance anti-corrosion performance and inter-coat adhesion.
Drying
Thoroughly dry the surface to prevent bubbles, peeling or blistering in later coating.

2. Coating Process (Three-Layer Protection System)
(1) Primer
Mainly for anti-rust and anti-corrosion.
Common types: Epoxy Zinc-Rich Primer, Epoxy Iron Oxide Primer.
Provides excellent adhesion and cathodic protection, especially for chassis and structural parts.
(2) Intermediate Coat
Fills small defects, levels the surface, and improves impact resistance and inter-layer bonding.
Usually uses Epoxy Intermediate Paint to enhance the overall thickness and durability.
(3) Topcoat
Provides weather resistance, color retention, scratch resistance and aesthetics.
Common types: Polyurethane (PU) Topcoat, Acrylic Topcoat.
Features UV resistance, fading resistance, oil resistance and good gloss.

3. Curing & Quality Inspection
Baking Curing: High-temperature baking at 120–140°C to fully cure the paint film, increasing hardness and durability.
Thickness Test: Total dry film thickness generally reaches 160μm or above for heavy-duty semi-trailers.
Adhesion Test: Cross-cut test to ensure no peeling.
Appearance Inspection: Uniform color, no sagging, pinholes, wrinkles or missing coating.
4. Process for Special Semi-Trailers
Tank Semi-Trailers: Use anti-static, oil-resistant coatings; internal surfaces may use food-grade or anti-corrosion linings.
Flatbed / Container Semi-Trailers: Focus on weatherability and wear resistance, with high-hardness topcoats.
Tipper Semi-Trailers: Strengthen internal wear-resistant coating to resist impact and abrasion from bulk goods.
5. Advantages of Standard Coating Process
Effectively prevents rust and corrosion, extending service life.
Improves appearance for export and brand image.
Enhances resistance to impact, scratches, acid, alkali and salt spray.
Reduces later maintenance costs.