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Vacuum Heat Treatment Furnace

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Special equipment industry gear vacuum heat treatment

As a key part of special equipment such as cranes and amusement facilities, gears are mainly used to transmit power and motion, and change the transmission speed ratio through them. Due to the constantly changing speed, the working conditions of the gears are very complicated, which requires the gears to have good quality. Therefore, vacuum heat treatment is very necessary.

1.Commonly used materials for gears

The basic requirements for gear materials are: the tooth surface should have sufficient hardness and wear resistance, and the tooth center should have sufficient toughness to prevent various failures of the tooth surface. At the same time, it should have good cold and hot processing technology. In order to meet the various technical requirements of the gear.

Commonly used gear materials are various grades of high-quality carbon structural steel (such as 45 steel), alloy structural steel (such as 40Cr), etc.

According to the hardness of the tooth surface after vacuum heat treatment, the gear can be divided into soft tooth surface gear (≤350HBS) and hard tooth surface gear (>350HBS). Generally required gear transmission can use soft tooth surface gear.

2.Why vacuum heat treatment

The quality of vacuum heat treatment is the key to determine the quality of the gear, and it is the key factor for the gear to achieve low noise, high precision and long life. Vacuum heat treatment includes: one is ordinary vacuum heat treatment, such as vacuum annealing, normalizing, vacuum quenching, vacuum tempering, quenching and tempering; the other is surface heat treatment, which includes surface hardening (such as induction hardening, laser hardening, etc.) and chemical vacuum heat treatment ( Such as carburizing, carbonitriding, nitriding, nitrocarburizing, etc.).

The performance of high-quality carbon steel and alloy structural steel is not only related to chemical composition, but also depends to a large extent on proper vacuum heat treatment. If the part does not require vacuum heat treatment, it is enough to choose carbon structural steel, provided that the mechanical strength meets the requirements. If the parts need vacuum heat treatment, high-quality carbon steel or alloy structural steel must be selected. There is no way to determine the vacuum heat treatment process if the chemical composition is unstable. High-quality carbon steel or alloy structural steel must be vacuum heat treated.

3.Vacuum heat treatment process commonly used for gears

(1) Vacuum tempering

Quenching and tempering is a double vacuum heat treatment of vacuum quenching and high temperature vacuum tempering. The gear is vacuum quenched and then subjected to high temperature (500~650°C) vacuum tempering. The purpose is to make the workpiece have good comprehensive mechanical properties.

Quenching and tempering treatment is often used for gears made of high-quality carbon steel (such as 45 steel) or alloy steel (such as 40Cr) with a carbon content of 0.3%~0.5% (mass fraction). The carbon content of 40Cr steel is 0.37% to 0.44%, slightly lower than 0.42% to 0.50% of 45 steel.

Quenching and tempering can refine grains, and obtain uniform, certain dispersion and excellent mechanical properties. The overall performance of quenched and tempered gears is better than that of normalized gears.

(2) Surface quenching

Surface hardening is often used in medium carbon steel or alloy steel, such as 45, 40Cr steel, etc., mainly including induction hardening, laser hardening and flame hardening.

Gear surface hardening mainly adopts induction hardening process. The induction heating speed is fast, there is almost no oxidation and decarburization, the gear deformation is small, and it is easy to realize local heating and automatic production, and the cost of vacuum heat treatment is low. Therefore, it is widely used in the special equipment industry.

4.The sequence of quenching and tempering and vacuum quenching

Generally, the vacuum heat treatment process of gears is first quenched and tempered and then finished, and the tooth surface is vacuum quenched after the gears are processed. If the order is reversed, the tooth surface is high-frequency quenched first and then heat-treated and tempered, then the overall hardness of the gear is the hardness of quenched and tempered, which is not high compared to the high-frequency quenched hardness. Therefore, in order to further improve the strength of the gear core, quenching and tempering treatment is often carried out before surface quenching.

Since the hardness of the gear is not high after quenching and tempering, the finishing of the gear teeth can be carried out after vacuum heat treatment. Quenching and tempering is often used for preparatory vacuum heat treatment of gears (such as nitriding, quenching and tempering before induction hardening).

Typical machining process for surface hardened gears:

Blank→forged billet normalizing (or vacuum annealing)→mechanical rough machining→quenching and tempering→mechanical semi-finishing (blank making) and gear making→surface quenching→vacuum tempering→mechanical finishing→finished product.