Induction quenching and tempering treatment of variable cross-section cylindrical parts

Although many workpieces are treated by induction heating, the shapes of the workpieces are very simple. For workpieces with variable cross-sections, the heating temperature is difficult to be uniform. Especially when it is used for quenching and tempering treatment, it is difficult to ensure the quality of the workpieces after treatment. With the rapid increase of deep-processed products, a large number of variable cross-section cylindrical workpieces appear. In order to ensure the quality of the quenching and tempering treatment of the workpiece, a special intermediate frequency Induction heating furnace was developed to replace the box-type and well-type resistance furnace process equipment.

1. Workpiece shape and technical requirements

The shape of the workpiece is shown in Figure 12-13 and is made of alloy steel. After quenching and tempering, the hardness is required to be 103 ~ 228HB, and the elongation is -2.5%, which creates good conditions for subsequent processing. The mass of the workpiece is 13. 5kg.

2. Equipment configuration

It is mainly composed of induction heating furnace, intermediate frequency power supply and quenching water tank.

(1) Induction heating furnace: The structure of the induction heating furnace is shown in the figure, and its key equipment is an inductor. Since the thickness of each part of the work piece varies greatly, to meet the processing quality requirements and ensure uniform temperature, different heat must be given to each part of the work piece. Therefore, the main and main inductors are designed as single-layer coils to heat the entire workpiece. The secondary inductor is a double-layer coil that heats thick-walled parts. During operation, the workpiece is advanced according to the requirements of the quenching and tempering process with different cycle times. The bottom part enters the secondary inductor for preheating first, then enters the main inductor in turn, the whole is heated to a quenching temperature of 920 degrees, out of the furnace, and sent to the water tank for quenching; or heated to a tempering temperature of 620 degrees, out of the furnace, and air-cooled.

The inner diameter of the coil of the main inductor is 185mm and the length is 1460mm. The secondary inductor coil has an inner diameter of 185mm and a length of 140mm, all of which are wound with a square pure copper tube measuring 14mm X 14mm X 2mm. The main sensor and the sub-sensor are connected in series to supply power. The heat-resistant bushing in the induction coil is 3mm

The non-magnetic stainless steel plate is made of an open cylinder, which is wrapped with aluminum silicate fiber felt.

The water-cooled guide rail is used to support the workpiece and guide the movement of the workpiece.

(2) Intermediate frequency power supply: According to the material, size, heating characteristics and production capacity of the workpiece, the selected frequency conversion equipment is KGPS-250/1 thyristor intermediate frequency power supply. The power, voltage, current, etc. are adjustable and suitable for quenching and tempering heating processes. And different production rhythm needs.

(3) Quenching water tank: A 1200mm x 600mm x 800mm tank is formed by welding section steel and steel plate, and it is filled with a water quenching agent containing 20% NaOH, which is maintained at a temperature of 20-80^.

3. Hot state test

In order to verify the accuracy of the design calculations, the performance of the sensor, the actual heating temperature of the workpiece and the relevant electrical parameters were tested, and a thermal test was carried out.

(1) Temperature measurement: Drill 3 holes in the representative part of the workpiece (see picture), and put the end of the thermocouple of 0.3mm in the small hole. In order to protect the thermocouple, reduce the electromagnetic influence, and improve the accuracy of the test, the compensation wire is passed through a section of stainless steel tube and connected to the millivolt meter.

(2) Quenching and heating: Under the condition that the output power of the intermediate frequency power supply is 140kW, the voltage is 600V, and the current is 250A, a workpiece is pushed in for heating according to the cycle time of l-5min. The heating temperature of the workpiece is 1000°C. Because the thickness of the three parts on the workpiece is different, the heating time of the three parts in the inductor is also different. The heating time of the three parts is T:T:T3=6min:3min:4.5min, and the temperature difference is about 100℃. (3) Tempering heating: The same set of Induction heating furnace is used to temper and heat the workpiece. Under the conditions of power of 50kW, voltage of 350V, and current of 160A, a workpiece is pushed in for heating at a cycle time of 2.5min. The heating temperature of the workpiece is 750°C. The heating time of three different parts on the workpiece is T: T2: T3 = 10min: 5min: 7.5min, and the axial temperature difference is 140°C. The temperature changes of the two heating processes are consistent with the expected situation. If the power of the secondary inductor is increased, or another secondary inductor is added, the temperature difference of the variable cross-section cylindrical workpiece will be reduced. Tests have proved that the variable cross-section cylindrical workpiece can meet the requirements of technical conditions after induction heating quenching and tempering treatment.