The mouth of the small tube is annealed and heat treated using high-frequency induction annealing equipment

The small tube undergoes cold work hardening after stretching. In order to close the mouth in the next process, the mouth of the small tube must be recrystallized and annealed. The material of the small tube is low carbon steel, the wall thickness is 0.25-0.4mm, and the length of the annealed part is 10-14mm, so high-frequency annealing equipment is used for annealing. Compared with the previously used resistance furnace heating and annealing, the productivity has increased by more than 12 times, the power consumption has remained at 60%-70%, the product quality has been improved, and the scrap rate has been reduced from 0.1% for resistance furnaces to 0.02%. The operation is simple and the working conditions are improved.

1. High frequency induction heating mouth annealing equipment

High-frequency induction heating mouth annealing adopts the method of sequential and continuous heating. The annealing machine tool is automatically heated by the inductor one by one through the mechanical total device. The sensor is connected to the step-down transformer of the high-frequency power supply. The transmission screw makes the small tube move linearly through the sensor. Driven by the friction of the screw, the small tube rotates itself, ensuring uniform heating temperature at the mouth of the small tube. The high-frequency generator used is type 260 with a power of 60KW. The inductor has an 8-row parallel wire structure and the output can reach 900-1100 pieces/min.

2. High frequency induction heating mouth annealing temperature

The mouth of the small tube is annealed in a resistance furnace, and the maximum temperature of the furnace is 840°C; when using high-frequency induction heating, in order to achieve the purpose of recrystallization, the actual heating temperature of the mouth of the lower pass is 840°C.

3. Heating time for high-frequency induction heating mouth annealing

The time of sequential heating depends on the length of the inductor and the speed of the small tube passing through the inductor. Through experiments, the same performance can be obtained if the heating time is in the range of 2.4-13.6S. The 8-row high-frequency annealing machine uses 6-8S.

4.Multiple rows of sequential heating sensors

The inductor is made of 11.2mmx9.4mm rectangular pure copper tube. The length of the inductor is based on the heating time required when the small tube is heated. It should also match the parameters of the high-frequency generator. The two inductors are connected in parallel to the high-frequency generator. Step-down transformer. The connection method between multiple rows of inductor wires can be connected sequentially or cross-connected. The magnetic field distribution of the two connection methods is different. The magnetic field of the cross-connected stranded wires is in the working area where the magnetic field lines are concentrated, and in the non-working spacing. There are no magnetic field lines, so energy utilization is higher. In an inductor with cross-connected wires, the magnetic field strength of the middle two rows is higher than the magnetic length of the two side rows. In order to obtain the same mouth annealing quality for each row, the length of the outer two rows of the inductor is longer than the middle one. 7.5% longer, which increases the heating time of the two outer rows of the sensor.