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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Vacuum Furnace with Oil Quench

Hardening of steel is one of the main heat treatment processes. In this process, which is initially carried out using aqueous solutions, the quenching medium affects the final properties of the steel and can therefore be controlled to optimize the hardness, microstructure and degree of deformation of the treated part.

Oil quenching problem
Like any hardening process, the purpose of oil quenching is to transform the austenite phase into martensite structure through rapid cooling to achieve the desired hardness index.
Depending on the steel type and cooling regime, a variety of different structures can be obtained. When austenitic parts are immersed in oil, the cooling process will consist of several consecutive stages.

Advantages of vacuum oil quenching
When heated in a vacuum furnace, the surface of the component is reliably protected and oxidation or decarburization is completely avoided. The easy control of the gas partial pressure is a further advantage. The partial pressure of inert gases (nitrogen, argon) inhibits the sublimation of alloy elements. In addition, the partial pressure of active gas provides the possibility for carburizing or carbonitriding under low pressure and high temperature conditions, helping to shorten process cycle times.

Cooling control
When the furnace is vacuum purged, since the transfer of the charge is carried out under vacuum or inert gas conditions, the surface of the components is always protected until completely immersed in the quenching oil. Regardless of whether oil quenching or gas quenching is used, the surface protection conditions are basically the same.
The main advantage compared to traditional atmosphere oil quenching solutions is the ability to precisely control cooling parameters. When using a vacuum furnace, it is possible to adjust the standard quenching parameters – temperature and stirring intensity – and also to adjust the pressure above the quenching tank.
Adjusting the pressure above the quenching tank can create a pressure difference inside the oil bath, thereby changing the oil cooling efficiency curve obtained at atmospheric pressure. The highest cooling efficiency is of course the boiling stage. Changes in quenching oil pressure will change the evaporation effect caused by the heat of the charge.

Technical principles of oil quenching vacuum furnace
Vacuum oil quenching furnace technology is very similar to vacuum air-cooled furnace:
All or part of the outer furnace shell is cooled by double-wall water circulation.
Graphite is mainly used as the manufacturing material and insulation material of the heating chamber. Can be equipped with a convection fan to improve circulation at low temperatures (<750°C).
The pump unit ensures reliable emptying of the furnace shell.
Oil quenching equipment was added to the system. Additional equipment includes:
A quenching tank equipped with stirring paddle, heating element and cooling heat exchanger
A charge transfer device can automatically and quickly transfer the charge between the charging/discharging area, heating chamber and quenching tank.

Factors to Consider in Furnace Type Selection
In recent years, the types of oil quenching vacuum furnaces have increased significantly. There are now many options to choose from, and users must find the most suitable equipment for their production needs through careful analysis. The following factors must be considered:
Volume and total charge: they are the first parameters to be determined, based on the size, shape and output of the most troublesome parts. Depending on the furnace type (single chamber or dual chamber), the process cycle time will change, which also affects the furnace capacity.
Vacuum level requirements: Although a rough vacuum can usually meet the requirements for hardening low-alloy steel, some more special applications may require a higher vacuum level. A diffusion pump can be added to the double chamber furnace.
Cooling flexibility: Oil quenching can be supplemented by inert gas forced convection to accelerate cooling, which enables processes such as carburizing and annealing. The oil quenching/gas quenching process can be equipped with a high-pressure cooling chamber to expand the range of steel types and improve the versatility of the equipment.
Necessity of Charge Thermocouples: Some applications (such as aerospace component processing) may require these high temperature measurements. However, the complexity of the system and the short life of oil-cooled thermocouples greatly restrict their use.
Charge transfer time: Low hardenability alloys require very short transfer times. Although almost all modern furnace models are capable of achieving transfer times of 20 – 40 seconds, the requirement for transfer times shorter than 15 – 20 seconds limits the range of equipment available on the market.