High-frequency induction annealing machine "specializes" in the cracking defect of press screw keyway

The pressing screw is a key part of the 200A-3 oil press. During operation, the surface spiral surface bears the dual effects of extrusion force and friction. The core requires good toughness, and the surface requires high hardness, high strength and excellent wear resistance. The stress state of the workpiece and the service environment are relatively harsh. The original process of pressing snails adopts 20 steel carburizing and quenching treatment. The thickness of the carburized layer is 1.5-2mm, the hardness is 55-62HRC, and the parallelism deviation of both ends of the workpiece is less than 0.15mm:100mm. During production, it was found that the overall strength of the workpiece after the original process was low, the wear was fast, and the working life was short, with an average of only 3 months. In order to improve product quality and performance, a high-frequency annealing machine is used to improve the heat treatment process to strengthen the overall strength of the snails and extend their service life.

Analysis: The main reason for the low working life of the screw is that the overall strength of 20 steel is low. Although the surface of the workpiece has been carburized and quenched, the core is not strong enough. The improved process is to use a high-frequency annealing machine for overall heating and quenching heat treatment, and the workpiece hardness is 50-55HRC. However, it was discovered during production that during overall quenching, due to the complex structure of the workpiece and the influence of processing factors, residual stress existed at the keyway. The phase change stress and thermal stress generated during quenching caused stress concentration there, and cracks were found many times at the right angles of the keyway. Phenomenon. To this end, a special fixture for screw quenching was experimentally designed. Use a fixture to quench and cool it to 200°C before water can be released, lay down the inclined wedge, and then put in the second workpiece for quenching.

After clamp quenching, due to the rapid heat transfer between the clamp mandrel and the flat pad, the inner hole and both end faces of the screw are cooled quickly, and the temperature of the surface layer changes slowly, so the stress is reduced and surface cracks are avoided. The surface hardness of the workpiece after quenching is above 55HRC, and the hardness after low-temperature tempering is about 50-55HRC. No cracking or cracking of the screw was found.

After heat treatment using an improved process, the performance of the press screw has been greatly improved, quenching crack defects have been eliminated, and the overall strength and toughness of the workpiece has been enhanced. The working life of the press screw has reached more than 6 months, more than doubled, and the production is running well.