The failure mode of forklift forks is mainly characterized by excessive plastic deformation, brittle fracture and early fatigue fracture. In order to ensure the mechanical properties and process performance of the fork, the carbon content of the material is preferably between 0.3% and 0.4%, and SCM435 steel is recommended. In the process of preparation, forging, heat treatment, and welding, the quality requirements should be strictly guaranteed. The fork is an important carrier of the forklift. During using process, once the fork breaks, it will cause serious accidents. In order to ensure the reliable performance of the fork, besides high strength limit, yield limit, good plasticity, toughness and low temperature performance, good surface quality is required. This depends on the material selection of the fork and the quality of the process such as forging, heat treatment and welding.
Fork material must have good overall mechanical properties, including forging properties and weldability. The carbon content of the fork material is preferably between 0.3% and 0.4%. At present, the main material of forks are made of S45C steel, SCR440 steel and SCM435 steel, and they should be quenched and tempered. Their carbon content is in the medium carbon range. However, most 45 carbon steel forks have shorter life. It is worthwhile to explore whether it is appropriate to use SCR440 steel for 2-ton forks and more than 2-ton forks. Under almost the same hardness conditions, the tensile strength of 35CrMo4 steel is 10% to 14% higher than that of SCR440 steel, and the yield strength limit is 20% higher than that of SCR440 steel. Therefore, 35CrMo4 steel can also significantly reduce the tendency of temper brittleness, so from the use conditions, 35CrMo4 steel is the more suitable for the production of forklift forks.
Hot rolled steel has fewer surface defects than hot forged steel, so the raw materials for forks are mostly hot rolled steel. Before forging, the steel must be inspected and cleaned, and the cracks, hair lines or subcutaneous pores on the surface of the steel, and the folding stools should be worn away by the grinding wheel. No sharp corners or deep pits can be formed in the sanding area. When gas cutting is used, the gas cutting surface stress is very complicated. Especially in winter, the gas cutting surface is prone to cracks, and the forging elongation after forging affects the quality of the fork. Therefore, when conditions permit, sawing and cutting should be used. Most of the fork breaks are caused by forging folding, hammer marks, over-burning and cracking. Therefore, the heating temperature and heating speed of forging must be strictly controlled, and over-burning is absolutely not allowed. In order to prevent residual hammer marks, the hammer head of the forging hammer and the anvil surface should be flat. In the forging process, in order to prevent the addition of scale, it is necessary to continuously blow the scale with compressed air. A slight hammer mark or fold that has been formed must be ground with a grinding wheel.
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