PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Development of Large High Temperature Vacuum Annealing Furnace

Buttons are refractory metals that have been widely used in cutting-edge industries. Among them, it can be used to manufacture button capacitors and launch tube electrodes in the electronics industry; it can be used as a heating element and a heat shield in a high vacuum resistance furnace; it can be used as a variety of corrosion-resistant containers in the chemical industry. The button material must be subjected to high vacuum annealing treatment after pressure processing. One is to improve the surface quality, and the other is to eliminate machining stress and improve physical properties.

Metal saws have a series of excellent properties such as high melting point, low vapor pressure, good cold working performance, high chemical stability, strong resistance to liquid metal and acid and alkali corrosion, and small thermal neutron capture section. , cemented carbide, atomic energy and aerospace industry, modern strategic weapons, superconducting technology, scientific research and medical equipment and other fields, is an important engineering material. In general, the processing materials of metallic silver are supplied in the annealed state.

1 Main technical parameters of the equipment

(1) Effective working size in the furnace: 1100 mm×800 mm×3200 mm (WxHxL);

(2) Maximum loading capacity: 600 kg;

(3) Maximum temperature: 1550 ℃;

(4) Working temperature: 1450 C;

(5) Temperature uniformity: ≤+5°C (empty furnace 1 350°C);

(6) Vacuum degree: cold limit vacuum 5×10-4Pa;

(7) Thermal vacuum: better than 3×10-3 Pa.

2 Summary of technical difficulties

(1) The effective working size in the furnace is large. Most of the vacuum furnace shells adopt a cylindrical double-layer water-cooling structure, which has high structural strength, easy processing, less welding seams and material saving. In order to meet the effective working size of the furnace, the inner diameter of the furnace shell reaches 2 meters, the diameter of the heating body in the furnace is 1.5 meters, and the innermost diameter of the heat shield is 1.66 meters. Due to the high working temperature of the system, high temperature molybdenum material is required as the heating element and heat shield material. For the heating element with an unfolded length of 4.712 meters, the whole molybdenum strip cannot be used, and only the method of splicing multiple molybdenum strips can be used. Similarly, the high-temperature molybdenum heat shield needs to be spliced not only in the circumferential direction, but also in the length direction, which causes great difficulties in the processing and assembly of the heating element and the heat shield.

(2) The working temperature in the furnace is high, and the design of the feeding and discharging mechanism is difficult. Due to the relatively high temperature of the material to be vacuum annealed, for the support structure of the feeding and discharging mechanism, only materials with high temperature resistance and certain strength at high temperatures can be selected. The more commonly used materials are molybdenum, tungsten, graphite, etc. Molybdenum, tungsten, graphite and other materials have high hardness and good static strength at high temperature, but they are brittle and easy to break when subjected to impact force. Therefore, the feeding and discharging mechanism of high temperature vacuum annealing furnace is different from other annealing furnaces. The system selects molybdenum material as workpiece support and material tray.

3 Equipment structure and characteristics

The vacuum furnace is mainly composed of furnace body, vacuum system, feeding car, cooling water system, compressed air system and electric control system, as shown in the figure.

3.1 Furnace body

The furnace body mainly includes a furnace shell, a furnace gallbladder, a heat insulation reflection screen, a heating body, a workpiece support and a material tray. The furnace shell is a double-layer water-cooling jacket structure, and the flange, inner wall, outer wall and support are made of carbon steel. The jacket has undergone strict pressure test and leak detection, and has good air tightness and temperature stability. The cooling water in the water jacket circulates well to avoid the uneven temperature of the furnace shell and the influence of excessive temperature on the furnace shell. The inner wall of the vacuum chamber is polished to ensure the cleanliness of the vacuum heating system and at the same time provide a guarantee for the heating system to obtain a higher vacuum degree. The rest of the accessories on the furnace body include vacuum gauge, cooling gas backfill valve, charging air valve, vacuum pressure gauge, etc.

3.2 Heater

3.2.1 Selection of heating element material

There are two types of heating materials for vacuum heating. Metal materials include nickel-chromium alloy, iron-chromium alloy, molybdenum, tungsten and button, etc., and non-metallic materials include silicon carbide and graphite. The selection of electric heating element material mainly considers the maximum operating temperature of the furnace, and at the same time, it is necessary to reasonably select the electric heating element voltage under vacuum to prevent the phenomenon of vacuum discharge and electric breakdown, and finally determine the appropriate electric heating element surface load. The maximum temperature of the equipment is 1 550 ℃, and molybdenum, tungsten, button and graphite materials can be considered. However, the processing performance of tungsten material is not good, the large-sized strip is even more difficult to process, and the material cost is high. The button material has good processing performance and high operating temperature, but the material cost is expensive. Due to the large effective working space of the system, the corresponding furnace shell, heat shield and heating element are also large in size. If graphite is used as the heating element material, the size of the furnace shell, the heat shield and the heating element will be larger than that of the metal heating element. Big and expensive. Moreover, the system selects high temperature molybdenum material as the heating element material.

3.2.2 Structure design of heating element

After the electric heating element is selected, the appropriate heating element structure should be selected according to the power of the vacuum furnace and the shape, size and form of the heating chamber.

In order to facilitate temperature uniformity control and later maintenance, the form of three-stage heating is selected in the length direction, and the three stages are independently controlled. . There is no heating element in the front and rear furnace doors. In order to ensure the size of the uniform temperature zone, the temperature compensation is performed by lengthening the three-stage heating element in the middle cylinder. The heating body of this equipment is designed as a rib-type cylindrical structure, and each rib is connected end to end as a whole, as shown in the figure below.

Equipment selection of vacuum annealing furnace: RVA vacuum annealing furnace produced by SIMUWU is an excellent choice for completing this type of process. Its process performance can fully meet the needs of such thermal processing, with good temperature control accuracy, temperature uniformity and annealing uniformity. High process repeatability, stable production, quality output can be guaranteed.