Guide rails are grooves or ridges made of metal or other materials that can bear, secure, guide and reduce friction of moving devices or equipment. Guide rails are also called slide rails, linear guide rails, and linear slide rails. They are used in linear reciprocating motion situations. They have a higher rated load than linear bearings. They can also bear a certain amount of torque and can achieve high-precision linear motion under high loads. . Therefore, guide rails generally require quenching heat treatment to improve their hardness, wear resistance and service life. After the guide rail is subjected to medium frequency induction quenching, it will be affected by many factors and will produce quenching cracks and other defects. Today, the editor will take the stator guide rail as an example to tell you the reasons for the quenching cracks and their preventive measures.
The NJM type oil motor stator guide rail is an important part of the oil motor, and its material is ZG35Mn. In order to meet the needs of the work, we choose 200kw medium frequency heating equipment for medium-frequency induction heating and quenching equipment. The stator and inductor are immersed in the water tank for heating and quenching at the same time. The preliminary heat treatment before medium frequency induction heating quenching is normalizing at 840-880℃ + tempering at 560℃-570℃. After tempering, the furnace is cooled to 450℃ and air-cooled out of the furnace. However, during production, we found that after the surface of the stator guide rail is quenched, some micro-cracks will appear. These cracks are not easy to detect with the naked eye, but after surface flaw detection, the existence of micro-cracks can be found. These cracks propagate during high-load stress operations in hydraulic components, often leading to early product failure and even production accidents. Therefore, it is crucial to master its preventive measures.
Analysis shows that the main causes of quenching cracks in the stator guide rail are as follows: casting defects, such as bubbles and inclusions in castings; surface quality of parts; workpiece shape and complexity factors and quenching heating and cooling treatment methods, etc. From the analysis of quenching cracks in this product, the main cause of stator quenching cracks is improper selection of quenching medium. After medium-frequency induction heating and cooling, for ZG35Mn cast steel, water quenching and cooling are too intense. Especially at temperatures below Ms, it is easy to cause quenching cracks in quenched parts due to drastic changes in quenching stress.
In view of the above problems of stator quenching, the test uses a synthetic quenching agent with slow cooling performance (polyvinyl alcohol aqueous solution with a mass fraction of 0.1%~0.4%) to quench and cool the stator. The purpose is to control the cooling rate during quenching so as not to be too large and reduce the Thermal stress and tissue stress. The cooling rate of synthetic quenching agent in the high-temperature section is close to that of water, while the cooling rate in the low-temperature section is slower and gentler. In terms of process operation, in order to reduce residual stress and brittleness after quenching, the stator should be tempered in time after quenching. In addition, the specific power of quenching heating should be appropriately adjusted in terms of process parameters. After adopting the improved process, the quenching hardness of the stator guide rail meets the requirements (53-58HRC), quenching cracks are eliminated, and the effect is good.
Oil motors are widely used in life. The quality of the stator guide rail is closely related to the quality of the oil motor. Therefore, it is very important to produce high-quality stator guide rails. Today, we analyzed the causes of cracks in the stator guide rail during the quenching process and shared with you the preventive measures. We hope you can apply these in production.
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GS-ZP-1200
