Why choose to use ultrasonic induction heating equipment for quenching heat treatment of cast iron rails?
Cast iron guide rails, which are generally used in machine tools, are an important working surface of machine tools. Guide rails generally require high wear resistance, high scratch resistance and high fatigue strength. Therefore, we usually use quenching to improve the hardness of the guide rail. Regarding the quenching heat treatment of the guide rail, three methods are available: induction heating surface quenching, flame heating surface quenching and contact resistance heating surface quenching. However, the most common application now is the induction heating surface quenching of cast iron guide rails using ultrasonic frequency induction heating equipment.
The gray cast iron used for induction heating surface quenching shall meet the requirements of JB/T3997 "Technical Conditions for Gray Cast Iron of Metal Cutting Machine Tools". The compound carbon is between 0.6%-0.8% (mass fraction). Surface hardness of the guide rail: when the length of the guide rail is less than or equal to 2500mm, it should be greater than or equal to 190HBW; when the length of the guide rail is greater than 2500mm or the quality is greater than 3t, it should be greater than or equal to 180HBW. Unless there are special requirements, all edges and sharp corners should be chamfered.
After the guide rail is quenched by super audio frequency induction heating equipment, the depth of the hardened layer can reach 1.5 ~ 2.5mm. The super audio frequency induction heating equipment is complex and technically strong, but the quenching hardness is uniform, the consistency is good, and the production efficiency is high, suitable for batches. production, which has been widely used at home and abroad.
Flame heating surface quenching is to use oxygen-acetylene (or oxygen-other combustible gas) flame to burn through a special burner, so that the flame nozzle and water spray device move along the surface of the guide rail to continuously perform surface quenching. During the heating process, the pressure of acetylene and oxygen must be kept stable, the flame nozzle is vertical to the surface of the guide rail, and the moving speed is uniform. The depth of the hardened layer obtained by this method can reach 1-3mm. The phenomenon of surface overheating and melting occurs, the hardness distribution is not as uniform as that of induction heating surface quenching, and the deformation after quenching is large, so it is only suitable for single-piece small batch production. The technical requirements for flame-heated case-hardened gray cast iron are the same as those for induction-heated case-hardening. Due to poor process stability and difficult to control heating temperature, manual flame heating surface quenching is rarely used in rail quenching.
Contact resistance heating surface quenching is to use current to pass through the contact resistance between the electrode and the surface of the bed to heat the surface of the workpiece, and then move the electrode to cool it with the help of the heat conduction of the workpiece itself to achieve the purpose of surface quenching. The advantage is that the equipment and process are simple and easy to operate. After quenching of the ordinary gray cast iron machine tool guide rail, the wear resistance of the guide rail without quenching can be doubled, and the scratch resistance ability is significantly improved. The depth of the hardened layer is 0.2 to 0.25 mm, the quenched structure is fine needle-like martensite, the hardness can reach more than 600HV, and the quenching deformation is extremely small. However, its disadvantage is that the production efficiency is low, only part of the guide rail surface is hardened, and the hardened area is small, which is resistant to quenching, and the hardened layer is very shallow, which is prone to fire burns. In the maintenance of batch products or machine tool guides. For cast iron guide rails with electrical contact surface quenching, the requirements for gray cast iron materials are the same as those for induction heating surface quenching. The surface of the guide rails should be cleaned of oil before quenching.
Through a comprehensive comparison, the use of ultrasonic induction heating equipment for induction hardening is the most used. However, this is not to tell you that as long as the guide rail is quenched, it should be carried out with ultrasonic induction heating equipment. We should flexibly choose the quenching method suitable for our workpiece according to the actual situation.
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