The high-frequency induction annealing machine is used to treat the shrinkage of the boring gear box with out-of-tolerance

When boring the gear box body, a group of holes with a diameter of 90mm is bored to a size of 0.01-0.02mm, which will cause batches of workpieces to be scrapped according to technical regulations. In order to save this batch of artifacts, repair measures were taken, useful experience was gained, and finally this batch of artifacts was successfully repaired. So what equipment is used? let us wait and see.

After analysis, it is believed that the inner holes of sleeve and ring parts shrink and deform under the action of thermal stress. The local shape of the 9Omm diameter hole in the gear box is similar to a ring-like part, and its stress state and thermal stress changes should be similar. It is feasible to use thermal stress to restore the shrinkage hole to its original size.

As we all know, thermal stress occurs, one is caused by uneven heating temperature. The box body is composed of the inner hole surface layer A and the inner layer B, as shown in the figure below. If only the inner hole surface is heated, the temperature of part A is high, the temperature of part B is low, the expansion of A is large, and the expansion of B is small, resulting in Internal stress, expansion at point A is limited by point B, which is subject to compressive stress. When the temperature of part A is higher than 500°C, it enters the plastic zone and plastically shortens under compressive stress, causing the hole to shrink. When cooled to room temperature, only elastic deformation occurs, and the original size is restored after cooling, thus causing the inner hole to shrink.

The shrinkage process of wheel box parts is as follows. A high-frequency induction annealing machine is used to heat the inner hole with a diameter of 90mm. The temperature in the middle zone is lower than the phase transition temperature Ac1 and higher than the plastic starting temperature of 500°C. Select 650-700°C. Select the anode voltage to be 11000V, the anode current to be 5.5A, and the gate current to be 1.lA. When the inner hole is out of tolerance 0.01-0.02mm, heat for 15-20s. When the inner hole is out of tolerance 0.02-0.03mm, the first heating is 15-20s, the second heating is 10s, and the interval between the two times is 0.5-1min.

Using the above process, the 90mm hole diameter of the out-of-tolerance gear box returned to normal size, and the box shrinkage treatment was all qualified.

The key points of implementing shrinkage cavity treatment are as follows:

(1) Use thermal stress to shrink the gear box hole slightly. The thermal stress generated should be small. Use rapid heating. The temperature should not be too high, but moderate is better.

(2) The cooling speed should not be too fast

(3) Before heating, check the hole out-of-tolerance condition, correctly determine the process parameters, such as voltage, current, heating time and temperature, and strictly control the process execution.

(4) The sensor should be placed in the center of the hole to ensure uniform heating and cooling and achieve better results in workpiece processing.

After many tests, it was concluded that the use of high-frequency induction annealing machine to heat treat the gear box body avoids various defects caused by traditional heat treatment. The produced gear box body is of good quality, meets the work requirements, and is suitable for large-scale production in large quantities.