What Are the Types and Basic Requirements of Cast Polyurethane Rollers?
Polyurethane rollers are generally classified into three types based on the primary raw material of their flexible segments: polyester-based, polyether-based, and polycaprolactone-based.
Polyester-based polyurethane is commonly used for low to medium hardness rollers. It offers high physical and mechanical properties and good solvent resistance, making it suitable for applications in the non-ferrous metal industry.
Polyether-based polyurethane is ideal for high-speed and high-hardness rollers. It provides excellent water resistance, low-temperature resistance, and good processability, and is widely used in wire drawing and printing rollers.
Polycaprolactone-based polyurethane exhibits superior overall performance. It has excellent low-temperature and hydrolysis resistance and is used in demanding applications such as squeezing rollers.
1. Basic Requirements for Polyurethane Materials in Rollers
Physical and Mechanical Properties: Must meet the specific mechanical performance standards for different roller applications.
Bonding to Core: Requires strong adhesion to the metal core to support bonding and molding processes.
Hardness: The hardness of the roller should be uniform and meet specified requirements. Leather rollers typically have a hardness of 50–60 Shore A.
Surface Quality: The roller surface must be free from bubbles, contaminants, or mechanical damage.
Surface Finish: The surface should be smooth or treated according to functional needs.
Taper (Conicity): The difference in diameter between the center and the ends of the roller helps compensate for deflection in longer rollers. The taper increases with roller length.
2. Metal Core Pretreatment
Cleaning: The surface must be thoroughly cleaned to remove oils, lubricants, and organic residues from oxidation. Solvents such as trichloroethylene can be used.
Rust and Oxide Removal: Sandblasting is used to remove rust and oxide layers. For steel cores, 80–100 mesh aluminum oxide abrasive is recommended; for aluminum cores, 140–320 mesh abrasive should be used with wet blasting. After sandblasting, any residual dust should be removed with solvent. Steel cores should be bonded within 4 hours and aluminum cores within 72 hours.
Adhesive Application: Suitable adhesives like NA-1, Chemlock-218, or Thixon 422 should be applied. After application, the adhesive should air dry for 20 minutes and then be cured at 90±10°C for one hour before casting polyurethane.