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Vacuum Heat Treating for Gear Manufacturing

Whether it is carburizing, hardening, carbonitriding or overall heating of vacuum hardening gears, the main heat treatment quality problems that may occur during the vacuum hardening and cooling process are:
1. Insufficient hardness after vacuum hardening, uneven hardening hardness, and insufficient quenching hardening depth
2. The core hardness is too high after vacuum hardening
3. Vacuum hardening deformation is out of tolerance
4. Vacuum hardening cracking
5. The surface brightness is not enough after vacuum oil quenching

Such quality problems in factories are often related to the material pretreatment of gears, vacuum quenching heating and quenching cooling. After eliminating the problems in material pretreatment and quenching heating, the role of quenching media and related technologies becomes particularly prominent.
1. Insufficient hardness and insufficient hardening depth
The low cooling rate of vacuum hardening is the reason for insufficient hardness of the gear, uneven hardness and insufficient hardening depth. For quenching oil, the vapor film stage of the oil is short, the cooling rate is fast at medium temperature, and the cooling rate at low temperature is fast. High and uniform quenching hardness and sufficient quenching depth can often be obtained. The way the workpiece is hung also has a significant impact on the vacuum hardening effect. To achieve better results, the quenching oil must flow smoothly and a stirring device must be equipped and used.
2. The core hardness is too high after vacuum hardening
This type of problem is related to the cooling rate of the selected medium being too fast or the low-temperature cooling rate of the medium being too high. One solution is to change the quenching oil to meet the requirements. The second is to add appropriate additives to reduce the medium and low temperature cooling speed of kerosene. The third method is to switch to steel with lower hardenability.
3. The problem of vacuum hardening deformation
Vacuum hardening deformation is the most troublesome problem in vacuum heat treatment of gears. Because it involves many aspects, the solution is to adopt comprehensive measures. The main reason is insufficient cooling rate and uneven cooling. The solution is to increase the cooling rate and try to achieve uniform cooling. It is best to use isothermal graded oil to control deformation.
4.Hardening cracking of gears
It mainly occurs in induction heating quenching. If you choose a good water-based quenching medium, this problem can be solved.
5.Light problem
Where there are requirements in this regard, bright quenching oil or rapid bright quenching oil should be selected. Generally, if the quenching oil has good brightness, the cooling rate is not high enough, while if the cooling rate is high, the brightness is often poor. In addition, the brightness of hot oil is generally poor, so you can replace it with new oil or add brightness additives.

Gear hardening and tempering process and quality control
Hardening and tempering equipment
1. Heating equipment
The heating equipment controls the temperature of the vacuum furnace according to process requirements. Within the effective heating area of the equipment, the maximum insulation temperature deviation does not exceed ±15°C.
2. Cooling equipment and media
The vacuum quenching cooling equipment should have a circulating cooling device or a stirring device to ensure that the gear hair is sufficiently and evenly cooled. tooth.
When quenching and cooling the damaged gear, the medium temperature should be controlled at: water temperature 40C; oil temperature 80C.

Gear hardening and tempering heat treatment process procedures
1. The surface quality of the workpiece should be checked before installing the furnace. Defects such as cracks, folds, serious bumps, etc. are not allowed.
2. There should be a reasonable machining allowance for the gear blank that has been roughened and tempered.
3. The sharp corners of the gear blank should be chamfered, and the sudden changes in the section should be transitioned with arcs.
4. The gear hairs should also be placed within the effective heating area of the equipment, with a certain distance between them.
5. Vacuum tempering should be carried out in time after vacuum quenching, and the general interval should not exceed 4 hours.
6. During vacuum hardening and cooling, broken gears should not be stacked in the cooling tank to prevent uneven cooling and excessive deformation.