The variable cross-section cylindrical parts quenching and tempering by medium frequency induction heating power

Most of the variable cross-section cylindrical parts are made of alloy steel. After quenching and tempering treatment, the hardness is required to be 103-228HB and the elongation is ≥2.5%. In order to meet the above requirements, many manufacturers use medium frequency induction heating power for heat treatment, with good results.

1. Equipment configuration

Medium frequency induction heating power is used for quenching and tempering heat treatment, and the key equipment is the inductor. Since the thickness of each part of the workpiece varies greatly, to meet the heat treatment quality requirements and ensure uniform temperature, different amounts of heat must be given to each part of the workpiece. Therefore, the main and secondary sensors are designed.

The main inductor is a single-layer coil that heats the entire workpiece. The secondary inductor is a double-layer coil that heats thick-walled areas. During operation, the workpiece is advanced according to the quenching and tempering process requirements and at different cycle times. The bottom first enters the auxiliary inductor for preheating, and then enters the main inductor in sequence. The whole is heated to the quenching temperature of 920°C, comes out of the furnace, and is sent to the water tank for quenching. Or heat it to the tempering temperature of 620℃, release it, and air-cool it.

The coil inner diameter of the main sensor is φ185mm and the length is 1460mm. The inner diameter of the secondary inductor coil is φ185mm and the length is 140mm. They are all wound with square pure copper tubes of 14mmx14mmx2mm. The main sensor and the secondary sensor are powered in series. The heat-resistant bushing in the induction coil is an open cylinder made of 3mm non-magnetic stainless steel plate, which is wrapped with aluminum silicate fiber felt. There are two water-cooled guide rails inside the heat-resistant bushing to support the workpiece and guide its movement.

2. Heat treatment process

(1) Quenching and heating. Under the condition that the output power of the medium frequency induction heating power supply is 120kw and the current is 180A, a workpiece is pushed in for heating at a cycle time of 1.5 minutes. The heating temperature of the workpiece is 1000°C. Since the thickness of the three parts on the workpiece is different, the heating time of the three parts in the sensor is also different. The heating time of the three parts is T1:T2:T3=6min:3min:4.5min, and the temperature difference is about 100℃.

(2) Tempering heating. The same set of induction heating equipment is used to temper and heat the workpiece. Under the conditions of power 50kw and current 75A, a workpiece is pushed in for heating according to a cycle time of 2.5 minutes. The heating temperature of the workpiece is 750°C. Three different parts of the workpiece are placed. The heating time is T1:T2:T3=10min:5min:7.5min, and the axial temperature difference is 140℃.

Many manufacturers use the above process for quenching and tempering heat treatment, and the variable-section cylindrical parts produced are of good quality and meet the requirements of technical conditions.