The difference between vacuum annealing furnace and vacuum quenching/tempering furnace

Vacuum heat treatment furnaces can be classified into vacuum quenching furnaces, vacuum tempering furnaces, vacuum annealing furnaces, etc. depending on the application. Choosing a vacuum furnace depends on the application and the performance of each component. This article simply introduces the difference and selection of vacuum quenching furnace, vacuum tempering furnace and vacuum annealing furnace.

1, vacuum quenching furnace;
Vacuum quenching furnace can be divided into vacuum oil quenching furnace and vacuum quenching furnace.

1) Vacuum oil quenching furnace is suitable for vacuum heat treatment of die steel, spring steel, stainless steel, bearing steel, high temperature alloy steel, etc.
Its main features are: wide range of applicable data, hardenability, low cost, quench oil can be used repeatedly.
The disadvantages are that the amount of deformation is relatively large, and the follow-up needs of the workpiece are clean.
Vacuum oil quenching furnace can be divided into two-chamber furnace and three-chamber furnace from the layout.

2) Vacuum high pressure gas quenching furnace is suitable for vacuum heat treatment of high-speed steel, stainless steel, die steel and some other hardenability materials. It is characterized by small deformation of parts and no need of cleaning after heat treatment. Inadequacies: Quenching gas cannot be recovered and the cost is high.

Vacuum high pressure gas quenching furnace can be divided into horizontal and vertical two kinds from the layout. Horizontal type can be divided into single room, double room and three rooms. Vertical heat treatment for ring-shaped, cylindrical and long rod-shaped parts. The high pressure gas quenching furnace vacuum quenching pressure is usually 2b a r ~ 10b a r. According to the user's needs can choose parts for the pressure of the furnace.

2, vacuum tempering furnace:
The vacuum tempering furnace can be divided into single chamber, double chamber and vertical type. Usually the nickel-chromium strip is used to heat the maximum temperature of 800°C. Vacuum tempering furnaces are generally suitable for parts with light appearance and no oxidation color after tempering.

3, vacuum annealing furnace:
Vacuum annealing furnace can be divided into single chamber, double chamber and vertical. Vacuum annealing furnace according to the part data can be selected in the high temperature and low temperature, (high temperature 800 °C ~ 1350 °C, low temperature 800 °C).

Structural composition of vacuum annealing furnace

The Vacuum Annealing Furnace adopts the pre-vacuum atmosphere protection mode. When the operation is first pumped to a certain degree of vacuum, the furnace is filled with high-purity nitrogen or ammonia to decompose the atmosphere for protection and heating, so as to achieve less oxidation-free heating and no decarburization light. The purpose of the vacuum annealing furnace is therefore used for the quenching of stainless steel products.

Structure of the Vacuum Annealing Furnace.

1, furnace body
The shell is made of 4mm steel plate and reinforced steel. The inner lining is made of aluminum silicate fiber cotton or brick and stereotyped brick. The ring is evenly placed on the brick and placed on the brick.

2, furnace cover
The furnace cover is made of 25mm steel plate, and the lower part of the furnace cover is provided with an insulating layer structure.

3, vacuum nitrogen filling pipeline
A vacuum pressure gauge is installed on the furnace cover for pipes and valves used for vacuum and nitrogen filling (plug-and-play type), and pressure safety protection device is also provided.

4, furnace tank
The tank is made of stainless steel. The bottom of the tank is welded with stiffeners. The top of the tank is equipped with a cooling water jacket, sand sealing device, and fastening bolts.

5, heating elements
Optional 0Cr25Al5, 0Cr27Al7Mo2 or Cr20Ni80 alloy wire around.

6, sealing device
The furnace lid and furnace tank are sealed with inner and outer double-layer composite structure. The inner layer is made of graphite asbestos and the outer layer is made of silicone rubber with oil resistance and temperature resistance. In order to maintain the service life of the sealing device, a water cooling device is specially provided.

7, water cooling device
By the upper and lower sets of two, respectively welded on the lid and furnace flange flange, used to protect the sealing material.

Vacuum Annealing Furnace application in annealing of titanium alloys

Titanium has metallic luster and ductility. Density 4.5 g/cm3, Melting point 1660±10°C, Boiling point 3287°C. The main features of titanium are low density, high mechanical strength, and easy processing. The plasticity of titanium depends mainly on purity. The purer the titanium, the greater the plasticity. It has good corrosion resistance and is not affected by the atmosphere and seawater. At room temperature, it will not be corroded by dilute hydrochloric acid, dilute sulfuric acid, nitric acid or dilute alkali solution; only hydrofluoric acid, hot concentrated hydrochloric acid, concentrated sulfuric acid, etc. can borke it.

In recent years, rare metal pipes, especially titanium pipes, zirconium pipes, etc., have been widely used in aerospace, marine, nuclear power, petrochemical and other fields, and these industries have extremely high requirements on the quality of pipes.

Vacuum annealing is an important process for the production of intermediate and finished products. There are many ways to heat the annealing process, but annealing the titanium tube using vacuum annealing is a relatively new technology and process in the rare metal processing field.

The Vacuum Annealing Furnace frame is welded by various types of steel. The outer frame is made of channel steel as the main beam, the hoarding is made of cold thin plate, the channel steel is used as the main beam, and the bottom plate and front and rear end plates are made of midplane.

Transmission part: The trolley drive adopts motor and reducer to drive the front set of driving wheel drive through the chain. The door-to-door drive uses a combination of a worm gear reducer and a motor to electrically lift.
Sealing: The labyrinth structure is adopted for the seal between the trolley and the furnace body, and an automatic sand-sealing knife sealing device is arranged on the trolley side. The door seal adopts the roller type compression and the spring compression automatic mechanism to seal the furnace body. The furnace body part adopts the high quality refractory brick structure to ensure the sealing of the furnace. In the pressure part of the trolley, a high-alumina brick building is used, and the lower part is filled with thermal insulation bricks.
Combustion system: Several burning nozzles are installed on both sides of the oil furnace, and the heat flow circulates in the furnace to ensure the uniformity of the furnace temperature. Automatic and semi-automatic types can be selected as required.
Exhaust gas preheating device: A smoke exhaust preheating device is installed at the upper end of the furnace. When the flue gas in the furnace passes through the preheater, it is sent to the cold air for preheating by the fan, and then sent to the burning nozzle for combustion by the pipeline. Install a manual disc valve at the outlet, which regulates the pressure in the furnace.

How to choose an energy-saving vacuum annealing furnace?

I. Choose high quality vacuum annealing furnace lining material

The furnace lining adopts aluminum silicate and ceramic fiber, which has the advantages of compact structure, small volume, light weight, good heat insulation, small heat storage loss, fast heating and cooling speed, less heat loss from the furnace body, and energy saving. The fiber cotton is compressed into a square folding bag and is fixed on the furnace top and wall of the annealing furnace with stainless steel riveting hardware. The riveting hardware is hidden in the folding bag and the heat is not transmitted to the furnace wall through the riveting firmware.

II. To strengthen the vacuum annealing furnace door, trolley and furnace body seal, greatly reducing the heat loss.

The upper and lower sides of the furnace door are along the guide rails on both sides. The upper end of the guide rail is fixed on the cross beam of the door frame, and the lower end is connected with two electric push rods. Fiber-cotton blankets are attached around the door and the furnace panel, and the electric push rod tensions the guide rails. The rail presses the furnace door so that the furnace door is in close contact with the furnace panel without any gap. The trolley adopts a soft seal structure of a fire-resistant fiber blanket pressed by an electric push rod, so that a tightly sealed requirement is achieved between the trolley and the furnace body, and heat loss is greatly reduced.

III. Control vacuum annealing furnace furnace pressure

The furnace pressure is generally controlled in the range of 100Pa. Micro differential pressure sensors are used to generate digital signals and meters. In-furnace pressure can be displayed. The high pressure in the furnace can increase the speed of the flue gas draft fan and increase the opening of the flue electric valve, and vice versa. This control can be done automatically or manually.

IV. Pulse Annealing Furnace

As the flame of the burner is blown out at its exit at a very high speed, a strong stirring effect is generated in the furnace, so that the temperature inside the furnace is always kept uniform, and at the same time, 10 burners in the furnace are controlled by the PLC in an orderly manner from the small fire. Changing the fire, so that the furnace temperature is even and save energy, the temperature of the various parts of the furnace and the combustion of each burner, at a glance on the computer's main screen.

V. The vacuum annealing furnace adopts the air-fuel ratio valve to automatically control the ratio of gas to air so that the gas can be fully burned, energy can be saved, and pollutant gas emissions can be reduced.

VI. Selection of vacuum annealing furnace flue outlet After the furnace, the well is built with a refractory brick wall in front of the flue to reduce the discharge of heat in the furnace.

VII. Use flue gas heat. Preheat the 4200m/h combustion air to about 350°C, and the annealing furnace can save energy by 20%.