PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Gear gas carburizing

Basic requirements for gear materials

1.The tooth surface should be hard and the tooth core should be tough

2.Easy to process and vacuum heat treatment

3.It has sufficient bending strength under alternating load and impact load.

Generally for low-carbon steel and low-carbon alloy steel, increase the carbon content on the surface of the workpiece to improve the strength and hardness of vacuum quenching.

Quality problems and solutions in vacuum quenching and cooling Whether it is vacuum carburizing and quenching, carbonitriding or overall heating vacuum quenching, the quality problems of vacuum heat treatment that may occur during vacuum quenching and cooling of gears mainly include:

1.The hardness is insufficient after vacuum quenching, the hardness of vacuum quenching is uneven, and the depth of vacuum quenching hardening is not enough

2.The hardness of the core is too high after vacuum quenching

3.Vacuum quenching deformation is out of tolerance

4.Vacuum quenching cracking

5.The surface brightness is not enough after oil quenching

Such quality problems are often related to gear material, pretreatment, vacuum quenching heating and vacuum quenching cooling. After eliminating the problems in materials, pretreatment and vacuum quenching heating, the role of vacuum quenching medium and related technologies is very special. highlights:

1.Insufficient hardness and insufficient hardening depth

The low cooling rate of vacuum quenching is the cause of insufficient hardness, uneven hardness and insufficient hardening depth of gears. For vacuum quenching oil, the vapor film stage of oil is short, the cooling rate at medium temperature is fast, and the cooling rate at low temperature is fast, so it can often be obtained High and uniform vacuum quenching hardness and sufficient quenching depth.

The way the workpiece is mounted also has a significant impact on the effect of vacuum quenching. Only by making the flow of vacuum quenching oil smooth and equipped with a good stirring device can better results be obtained.

2.The hardness of the core is too high after vacuum quenching

This kind of problem is related to the cooling rate of the selected medium is too fast or the low temperature cooling rate of the medium is too high. One of the solutions is to change the vacuum quenching oil to meet the requirements. The second is to add appropriate additives to reduce the medium and low temperature cooling rate of vacuum quenching oil. The third method is to switch to steel with lower hardenability.

3.The problem of vacuum quenching deformation

Vacuum quenching deformation is the most troublesome problem in vacuum heat treatment of gears. Because this involves many aspects, it is also a comprehensive measure to solve it. The main reason is insufficient cooling speed and uneven cooling. The solution is to increase the cooling speed and try to achieve uniform cooling. It is best to use isothermal graded oil to control deformation.

4.Vacuum quenching and cracking of gears

It mainly occurs in induction heating vacuum quenching. If a good water-based vacuum quenching medium is selected, this problem can be solved.

Vacuum quenching cooling equipment and cooling medium

Vacuum quenching cooling equipment should have controllable heating, cooling circulation system and stirring device. The cooling medium should have the cooling capacity required by the gear vacuum quenching, and it is not easy to age.

Vacuum tempering equipment: Vacuum tempering can use continuous or periodic furnaces, and the temperature of the effective heating zone in the furnace should be controlled within +10°C of the predetermined value.

Gear gas carburizing process control

1.Gas carburizing process specification

For the thin-walled gears with medium and small modulus, fixtures in the form of hanging or pads should be used when loading the furnace, and the gears with spline holes should be properly supported. When the gear is installed on the fixture, there must be no overlap between the teeth, and there should be enough clearance between the working surfaces of the gear.

Gas carburizing temperature is generally 890 ~ 930 ℃. For gears that require a gentle gradient in the seepage layer, diffusion should be carried out after strong infiltration. However, when the effective hardened layer depth is required to be less than 1mm, diffusion may not be performed.

2.Vacuum quenching process specification

After the gear is carburized by gas, it is cooled to 840°C to 860°C in the carburizing furnace for 0.5 to 1 hour, and then put into a vacuum quenching medium to cool.

3.Vacuum tempering process specification

After the gear is cleaned, it should be tempered at low temperature in time, and the general interval should not exceed 4 hours. For large gears made of high-nickel-chromium steel, full vacuum tempering is required, usually for 10 to 20 hours. For high-precision gears, stress relief tempering should be carried out after gear grinding, the temperature is 140-160 °C, and the holding time is not less than 2 hours.

Gear Vacuum Heat Treatment Quality Inspection

1.After the gear is vacuum heat treated, the surface must not have defects such as scale, bruising, peeling, and corrosion.

2.After vacuum heat treatment and gear grinding, gears with high reliability requirements should be 100% inspected, and general gears should be randomly inspected. Cracks are generally not allowed on the surface after grinding.

3.Process specification

For carbonitriding gears with a depth of carburizing layer less than 0.5mm, the carburizing temperature is generally 820~840°C

For carbonitriding gears with a depth of carburizing layer of 0.5-0.8mm, the carburizing temperature is generally 860-880°C

When the depth of the carburized layer is greater than 0.8mm, it is recommended to adopt two-stage process specifications. The first stage uses carbonitriding or carburizing at a higher temperature of 900-920°C, and then lowers it to 840-860°C for medium-temperature carbonitriding, and then directly Heating Vacuum Quenching

4.Quality control and inspection methods

Appearance: After carbonitriding of gears, the surface shall not have defects such as scale, bruising, peeling, and rust.

Carbon and nitrogen concentration: from the surface of the carbonitriding layer to the first surface at a depth of 0.1 mm, the average carbon concentration should be controlled at 0.75% to 0.95%, and the average nitrogen concentration should be controlled at 0.15% to 0.30%.

Hardness: generally not less than 57IRC, the hardness difference of the same batch of gears shall not be greater than 5HRC. The hardness of the core shall generally not be less than 30HRC.