Complete Guide to Caliper Coating Process: Key Steps in Surface Preparation, Coating Selection, and Curing

Complete Guide to Caliper Coating Process: Key Steps in Surface Preparation, Coating Selection, and Curing

Calipers (especially automotive brake calipers) are long-term exposed to high temperatures, high humidity, and brake dust erosion. Therefore, the coating process must balance protection and durability. Meticulous control of every step, from surface preparation to curing, directly affects the coating effect, and strict adherence to standardized procedures is essential.

Surface preparation is the foundation of coating quality, with the core goal of removing impurities and enhancing coating adhesion. It involves three key steps: First, "degreasing and derusting" – soak the calipers in an alkaline cleaning agent (e.g., sodium hydroxide solution) for 10-15 minutes to remove surface oil stains. Then, use sandblasting equipment (with 80-120 mesh quartz sand) to perform sandblasting on the caliper surface, controlling the sandblasting pressure at 0.4-0.6 MPa until the surface shows a uniformly rough off-white finish (roughness Ra 50-80 μm), thoroughly removing rust and oxide layers. Second, "phosphating treatment" – immerse the calipers in a zinc-based phosphating solution (at 50-60 °C) for 8-12 minutes to form a 5-8 μm thick phosphating film, which improves rust resistance and coating adhesion. Third, "cleaning and drying" – use compressed air to blow off residual phosphating solution and impurities on the caliper surface, then place the calipers in an oven at 60-80 °C for 30 minutes to dry, ensuring no moisture remains on the surface to prevent blistering in subsequent coating.

Coating selection must match the caliper application scenario, with a focus on high-temperature resistance and wear resistance: For automotive brake calipers, priority should be given to silicone high-temperature resistant paint (temperature resistance range: 200-600 °C) or ceramic high-temperature resistant paint (temperature resistance up to 800 °C). These coatings can withstand high-temperature baking during braking and have excellent weather resistance. For industrial machinery calipers (e.g., hydraulic calipers) that require both rust resistance and impact resistance, a combination of zinc-rich epoxy primer (zinc content ≥ 80%) and acrylic polyurethane topcoat is suitable – the primer enhances rust resistance, while the topcoat improves scratch resistance. In terms of color selection, high-temperature stable color pastes must be used to avoid fading under high temperatures. Common high-temperature resistant color pastes in red and yellow should pass a 24-hour temperature resistance test at 200 °C.

Curing determines the performance stability of the coating, and temperature and time control are crucial: For one-component coatings (e.g., silicone high-temperature resistant paint), curing is divided into two stages – first, pre-bake at 80-100 °C for 20 minutes to volatilize solvents, then raise the temperature to 180-220 °C and bake for 60-90 minutes to ensure complete curing of the coating. For two-component coatings (e.g., epoxy paint), first bake at 60-80 °C for 30 minutes, then raise the temperature to 120-150 °C and keep it warm for 40-50 minutes to avoid coating cracking caused by too fast curing. During the baking process, ensure uniform temperature inside the oven (temperature difference ≤ ±5 °C), and maintain a distance of no less than 10 cm between the calipers and the oven wall to prevent local overheating. After curing, allow the calipers to cool naturally to room temperature (approximately 2-3 hours), then conduct an adhesion test (the cross-cut test should meet Grade 1 standards) to ensure no peeling or wrinkling of the coating.