Vacuum Furnace Technology:

Vacuum furnaces are used for processes such as annealing, degassing, solution heat treatment, quenching, tempering, and precipitation hardening. They can also be utilized for chemical heat treatment after introducing an appropriate medium.

Vacuum annealing, degassing, and solution heat treatment in vacuum furnaces are primarily used for workpieces with high purity or surface quality requirements, such as softening and stress relief of refractory metals, solution heat treatment of stainless steel and nickel-based alloys, degassing treatment of titanium and titanium alloys, annealing to improve the magnetic permeability and coercivity of soft magnetic alloys, as well as bright annealing of bright carbon steel, low-alloy steel, and copper, etc. Vacuum quenching comes in two types: gas quenching and liquid quenching. Gas quenching involves cooling the workpiece in a cooling chamber filled with high-purity inert gas (such as nitrogen) after vacuum heating. It is suitable for materials with lower martensite critical cooling rates, such as high-speed steel and high-carbon, high-chromium steel. Liquid quenching is the process of transferring the heated workpiece to the cooling chamber, filling it with high-purity nitrogen, and then immediately immersing it in a quenching oil bath for rapid cooling. If high surface quality is required, the tempering and precipitation hardening of the workpiece after vacuum quenching and solution heat treatment should still be carried out in a vacuum furnace.

Vacuum carburizing involves placing workpieces in a vacuum furnace, then evacuating and heating it to purify the environment and reach the carburizing temperature. Carbon-hydrocarbon compounds (such as propane) are introduced for carburizing once the temperature is achieved. After a set period, the carburizing agent is cut off, and vacuum is re-established for diffusion. This method allows for high-temperature carburizing (up to 1040℃) while shortening the carburizing time. Internal oxidation does not occur in the carburizing layer, and there's no issue of lower carbon content in the carburizing layer surface compared to the underlying layer. Pulse vacuum carburizing can also be used to ensure uniform carburizing layers in blind and small holes.

The vacuum furnace's vacuum heat treatment is a comprehensive technology that combines vacuum technology with heat treatment, referring to the entire or partial heat treatment process being conducted under a vacuum state. In China, vacuum is categorized into low, medium, high, and ultra-high vacuum.

Types of vacuum furnaces:

Vacuum Resistance Furnace

1. External Heat Vacuum Furnace: (Place a vacuum furnace pot inside a normal pit furnace chamber)

Mainly performs annealing operations, which can be cooled by removing the vacuum pipe and lifting the crucible. Prepare several vacuum crucibles for continuous operations.

2. Internal heat vacuum furnace: (The furnace pot is under vacuum, and there is also a vacuum between the furnace pot and the furnace body.)

Feature: Achieves consistent internal and external pressure within the furnace pot, reducing the thickness of the pot wall

B. Infrared heating: Resistance wires are suspended inside the cylindrical furnace chamber.

Note: The difference between internal heating and external heating: In internal heating, the resistance wire and furnace lining are both in a vacuum. In external heating, the resistance wire and furnace lining are not in a vacuum.

C. Types: Carbon tube furnace, double-chamber vacuum furnace, high-pressure gas quenching furnace

Carbon Tube Furnace: Insulation screen with inner molybdenum sheet (0.3mm) and outer stainless steel.

The material becomes shiny upon exposure to high heat, reflecting radiant energy back and thus maintaining heat. Additionally, it has a low gas content, making it suitable for high vacuum conditions.

b. Twin-chamber vacuum furnace: This furnace is horizontal, divided into a front and rear chamber, both in a vacuum state, separated by a vacuum gate. The rear chamber contains a sealed pot for the workpiece to be heated. Once heated, the vacuum gate is opened, and the workpiece is pulled into the front chamber, along with the gas escaping from the carbon felt. The vacuum gate is then closed, and the furnace door is opened to discharge the material. After feeding the material, the front chamber is first evacuated, then the vacuum gate is opened to push the material into the rear chamber for heating. It can also be used for quenching treatment by introducing protective gas and adding an oil bath.

c. High-pressure gas quenching furnace: Utilizes high-pressure gas to quench workpieces, suitable for high-speed steel.

Vacuum Induction Furnace

The Semi-Continuous Vacuum Induction Furnace: The crucible can continuously pour several molds without waiting for the furnace to cool down. Compared to the periodic vacuum furnace, it does not require repeated vacuum pumping of the heating chamber, allowing the heating chamber to remain in a vacuum state at all times. Additionally, there is no need to wait for the furnace to cool down before removing the molds.

What is semi-continuous casting: It relies on the movement of small carts to enter and exit, completing the process. The carts are removed after casting, changed to a new mold, and then enter the heating chamber for casting.