Full definition
Polyurethane coating is a highly durable layer applied to metal surfaces in various industrial applications, particularly in mining and material handling. The coating is formed from a wear-resistant polyurethane (PU) material, which is known for its exceptional fine-particle abrasion resistance. The typical hardness of polyurethane coatings ranges from 85 to 95 Shore A, allowing them to withstand significant wear while still maintaining a degree of elasticity. The thickness of the coating can vary between 3 mm to 25 mm, depending on the specific application and expected wear life of the component. This adaptability makes PU coatings an ideal choice for environments where fine particles are prevalent, as they provide an extended lifespan compared to traditional materials such as rubber and steel.
The application methods for polyurethane coatings are diverse, including centrifugal casting, spray coating, and adhesive bonding. Centrifugal casting involves pouring PU liquid into a rotating drum or pipe, where it cures against the inner surface due to centrifugal force. This method is particularly useful for lining pipes and cylindrical components. In contrast, spray coating involves applying a two-component fast-setting PU in layers onto prepared metal surfaces, making it suitable for large and irregularly shaped surfaces like chutes and hoppers. Adhesive bonding allows for the use of pre-cast PU sheets that are secured to metal surfaces using polyurethane or epoxy adhesives, facilitating field repairs and modular system designs.
Surface preparation is crucial for achieving optimal adhesion and performance of the PU coating. This typically involves grit blasting to a standard of SA 2.5, with a primer applied within four hours to ensure proper bonding. Polyurethane coatings excel particularly in applications involving fine-particle sliding abrasion, where they can provide 3 to 10 times the lifespan of rubber and 5 to 20 times that of steel under similar conditions. However, there are limitations to consider; polyurethane coatings exhibit lower impact resistance compared to natural rubber, as they tend to tear rather than rebound under high-impact angles, and they have a temperature limit of 80°C. Furthermore, these coatings can be adversely affected by hot water exposure, necessitating careful consideration of environmental conditions during application and use.