Causes and Countermeasures of Induction Hardening Hardened Layer of Gears

Hardened Layer is Too Shallow or Too Deep

Reason 1：

The hardenability of the gear material is too low or too high, and the carbon content is too high or too low.

Countermeasures:

1. Choose suitable hardenable steel according to gear size and technical requirements.

2. The carbon content of gears should meet the requirements of GB/T 699-1999 and GB/T 3077-1999, and the component deviation should meet the requirements of GB/T 222-2006.

Reason 2：

Improper selection of induction heating frequency, too high or too low, and in this case did not choose a reasonable specific power and heating time, the current penetration depth is too thin or too deep, directly affecting the depth of the heating layer, resulting in hardening The layer depth does not meet the technical requirements.

Countermeasures:

1. The induction heating frequency should be selected reasonably according to the requirements of the hardened layer depth. The relationship between the depth of various hardened layers and the current frequency will be gradually introduced in the future.

2. When the depth of the hardened layer is required to be greater than the current penetration depth that the frequency of the existing equipment can achieve, the following methods can be used to obtain a deeper hardened layer under the condition that the surface is not overheated.

2.1 Reduce the specific power and extend the heating time. If it is continuous heating and quenching, the relative movement speed between the inductor and the gear can be reduced.

2.2 Properly increase the gap between the gear and the inductor to extend the heating time, or use intermittent heating when heating at the same time to increase the heat transfer time.

2.3 Before induction heating, the gears are preheated in the inductor.

2.4 When heating continuously, double-turn or multi-turn inductors are used.

2.5 When the gear size is large and the equipment power is insufficient, continuous sequential heating and quenching should be used to minimize the heated surface area in the inductor to increase the specific power and take preheating measures at the same time.

Reason 3：

The induction heating time is too short or too long, which has a greater effect on the heating temperature and heating depth of the gear surface, and determines the depth of the hardened layer.

Countermeasures.

Reasonably set the induction heating time according to the requirements of the gear hardened layer depth.

Reason 4：

The unit power is too high or too low, and the length of heating time affects the surface heating temperature and heating speed as well as the austenitizing temperature of the material.

Countermeasures.

Choose the unit power reasonably according to the requirements of the gear hardened layer depth.

Reason 5：

The gap between the inductor and the gear is too small or too large, resulting in different heating depths, so the depth of the hardened layer is significantly different.

Countermeasures.

According to the size of the gear and the depth of the hardened layer, select the appropriate gap between the inductor and the gear, and determine the best gap through experiments. Please pay attention to the heat treatment ecosystem, which will be introduced gradually.

Reason 6：

The gear (or inductor) moving speed is too fast or too slow during continuous quenching.

Countermeasure:

When the gear adopts continuous quenching method, the appropriate moving speed can be determined through experiments.

Reason 7：

Improper quenching and cooling process, such as improper selection of temperature, pressure and composition of quenching cooling medium.

Countermeasures:

Improve the quenching cooling process, increase the cooling rate, and adopt a preheating method.

Causes of Uneven Hardened Layer

Reason 1：

When the gear is heated at the same time, its placement position is eccentric.

Countermeasure:

When the simultaneous heating method is adopted, the gear position should be straightened.

Reason 2：

The spray holes of the sensor are uneven.

Countermeasures:

During the design and manufacture of the inductor, the spray holes should be evenly distributed to ensure that the hardened parts can be evenly cooled.
Reason 3：

The upper and lower centers of the quenching machine are not concentric.

Countermeasure:

The concentricity of the upper and lower centers of the quenching machine tool should be less than 0.05mm.
Reason 4：

The internal organization of the gear raw material is unqualified (such as serious band structure and network carbide).

Countermeasures:

Ensure the quality of raw materials, and conduct inspections such as high magnification; gears should be normalized or quenched and tempered before induction hardening.

The Depth of the Hardened Layer Exceeds the Required Range

Reason 1：

Gear material factors. In addition to the changes in the content of C and Mn, other alloying elements, especially Mo, Cr and other elements, greatly affect the hardenability of the material. If the cutting gear inspection finds that the depth of the heating layer is similar, but the hardenability depth changes greatly, it may be a material factor. .

Countermeasures:

Ensure the quality of raw materials, check the composition of chemical elements that affect hardenability, and the deviation of the main chemical composition should meet the requirements of GB/T 222-1999.

Reason 2：

The pressure, flow, liquid temperature and concentration of the quenching cooling medium will affect the depth of the hardened layer and must be checked.

Countermeasures:

Strictly implement quenching and cooling specifications. Check whether the pressure, flow, liquid temperature and concentration of the quenching cooling medium meet the requirements.

Reason 3：

There is a big change in the electric specification of induction heating, and the moving speed of the continuously hardened gear carrier has changed.

Countermeasures:

Check whether the electrical specifications of induction heating have changed greatly. Continuously hardened gears should ensure that the carriage moves at a steady speed.、

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