Fatigue fracture resistance is a core performance indicator of H-type polyurethane timing belts, directly impacting the reliability and service life of the transmission system. Improving performance requires coordinated improvements in four dimensions: material optimization, structural design, manufacturing process, and maintenance. By enhancing material toughness, dispersing stress concentrations, reducing microdefects, and optimizing operating conditions, fatigue fracture resistance can be significantly improved.
Material selection is fundamental to fatigue resistance. The tensile layer of an H-type polyurethane timing belt typically utilizes multi-strand steel wire rope or high-strength polyester cord. Its tensile strength and bending fatigue resistance directly impact its overall service life. Steel wire ropes must be made of high-carbon steel, cold-drawn to form a dense oxide layer on the surface, enhancing corrosion and wear resistance. Polyester cords require a high twist process to enhance intermolecular forces and prevent fiber breakage caused by prolonged bending. The polyurethane matrix material must possess a high elastic modulus and low compression set. By adjusting the ratio of polyether to polyester polyurethane, a balance between flexibility and oil resistance can be achieved to prevent crack propagation caused by material hardening. Furthermore, adding reinforcements such as nano-silica or carbon fibers to the matrix can form a three-dimensional network structure, effectively dissipating stress and inhibiting crack initiation.
Optimizing structural design is key to dissipating stress concentration. The tooth profile of an H-type polyurethane timing belt must conform to trapezoidal tooth standards, with precise control of the tooth tip width and root fillet radius to avoid stress concentration caused by geometric abrupt changes. The joint between the connecting ring belt and the polyurethane timing belt should utilize a circular transition design to reduce localized stress peaks caused by right-angle bends. The helical winding angle of the tensile layer steel wire rope must align with the direction of belt movement, typically adopting a 15°-20° skew layout to reduce bending fatigue. Sharp grooves on the inner surface of the belt back not only improve flexural performance but also allow air to escape during operation, reducing belt vibration caused by pressure fluctuations and thus reducing the impact of dynamic loads on the connecting rings.
Manufacturing process control directly impacts microdefect density. The composite of the steel wire rope and the polyurethane matrix requires a high-temperature, high-pressure vulcanization process. The vulcanization temperature must be controlled at 160-180°C and the pressure maintained at 2-3 MPa to ensure full interfacial fusion and prevent delamination. Injection molding utilizes a multi-stage injection technique, initially filling the mold cavity at a low speed and then compacting the belt at a high speed to reduce internal bubbles and shrinkage defects. A heat setting step is added to the post-processing process, where the polyurethane timing belt is subjected to a constant temperature treatment at 80-100°C for 4-6 hours to eliminate internal stress and stabilize dimensional accuracy. Furthermore, a rigorous quality inspection system is essential. The uniformity of the steel wire rope arrangement must be inspected using an X-ray flaw detector, and the tooth surface roughness must be observed using a laser confocal microscope to ensure an Ra value of ≤0.8μm.
Optimizing operating and maintenance conditions can extend fatigue life. During installation, the parallelism error between the two pulley axes must be ≤0.5mm/m to prevent misalignment and unilateral stress on the connecting ring. The tension must be controlled within ±5% of the design value. Too loose can cause tooth skipping, while too tight can accelerate fatigue of the tensile layer. The operating environment must be kept dry and clean to prevent oil and dust from entering the tooth grooves and to prevent impact loads caused by changes in the friction coefficient. For polyurethane timing belts operating at high speeds for extended periods, nondestructive testing is recommended every 2,000 hours of operation, focusing on checking the edges of the connecting rings for microcracks or plastic deformation. Any components with potential problems should be replaced promptly.
