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Vacuum heat treatment process for gear quality control

The heat treatment quality problems that may occur during the gear vacuum quenching and cooling process mainly include:

1.Insufficient hardness 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 vacuum 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. highlighted.

Gear quenching and tempering process and quality control: quenching and tempering equipment

1.Heating equipment

The heating equipment can control the furnace temperature according to the process requirements. In the effective heating area of the equipment, the maximum temperature deviation of the insulation does not exceed +15°C.

2.Cooling equipment and medium

The vacuum quenching and cooling equipment should have a circulating cooling device or a stirring device to ensure sufficient and uniform cooling of the gear blank. When the gear blank is vacuum quenched and cooled, the medium temperature should be controlled at: water temperature < 40 °C; oil temperature < 80 °C.

Gear vacuum heat treatment process regulations

1.Before loading the furnace, the surface quality of the workpiece should be checked, and defects such as cracks, folds, and severe bumps are not allowed

2.There should be a reasonable machining allowance for the post-quenched and tempered gear blank

3.The sharp corners of the gear blanks should be chamfered, and the sudden changes in the cross-section should be transitioned with circular arcs.

4.The gear blanks should be placed in the effective heating area of the equipment, and there should be a certain distance between them.

5.After vacuum quenching, it should be vacuum tempered in time, and the general interval should not exceed 4 hours.

6.When vacuum quenching and cooling, the gear blanks should not be stacked in the cooling tank to prevent uneven cooling and excessive deformation.

Gear gas carburizing heat treatment process and its quality control

1.Technical requirements for vacuum heat treatment equipment

For heating equipment such as converters, sealed box furnaces and well-type gas carburizing furnaces, the temperature in the effective heating zone should be controlled within +10°C of the predetermined value.

2.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.

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

4.Process control

① When loading the furnace, for medium and small modulus thin-walled gears, fixtures in the form of hanging or pads should be used, and 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.

The carburizing temperature is generally 890~930°C.

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.

②Carbon potential control principle

Carbon potential control in the intensive infiltration period: In general, under the premise that there is no carbon black and the level of carbides on the working surface is allowed, the furnace should have the highest carbon potential in the intensive infiltration period to obtain the fastest infiltration rate.

Carbon potential control during the diffusion period: Generally, the carbon potential in the furnace is determined by the carbon concentration on the surface of the workpiece reaching the design requirements.

③Vacuum quenching process specification

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

④ 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 high-nickel-chromium steel large gears, it is necessary to fully temper, generally 10 to 20 hours. For high-precision gears, stress relief and tempering should be carried out after gear grinding at a temperature of 140-160°C, and the holding time should not be 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.