How is the vacuum degree of the sintering furnace achieved?

Sintering furnace is a kind of equipment used to heat and sinter powder materials to densify them and form materials or products with specific properties, and vacuum is an extremely critical environmental factor in its operation. To create a vacuum environment in the sintering furnace, a vacuum system composed of vacuum pumps, vacuum valves, high-quality vacuum pipes and connectors is used to gradually establish a corresponding vacuum degree by removing the air and other gases in the furnace. Such a vacuum environment plays an important role. On the one hand, it can prevent the material from chemically reacting with oxygen in the air during high-temperature sintering, ensuring that the sintered material has good purity and performance; on the other hand, it can effectively reduce the interference of gas on heat transfer, facilitate uniform heat distribution, make the sintering process more stable and efficient, and thus accurately achieve the process requirements for sintering and forming of various materials.
Furnace body structure and sealing guarantee
Overall furnace body structure
Double-layer or multi-layer furnace wall design: The furnace body of the sintering furnace often adopts a double-layer or even multi-layer structure. The outer layer is a steel structure to provide overall strength and support, and the inner layer is a high-temperature resistant and airtight material (such as stainless steel, etc.) that directly contacts the furnace environment. The interlayer in the middle can be evacuated or filled with inert gas to form an insulation layer. While reducing the heat transfer to the outer layer, it also helps prevent the outside air from penetrating into the furnace through the furnace wall, ensuring the stability of the internal vacuum environment.
Furnace body welding and sealing: For the assembly of the furnace body, a large number of welding processes are used, especially for the inner tank. High-quality welding (such as argon arc welding, etc.) is used to ensure the sealing of the welds to avoid defects such as tiny pores and cracks that cause gas leakage. After the welding is completed, non-destructive testing (such as helium mass spectrometry leak detection, X-ray flaw detection, etc.) will be carried out to verify the sealing of the welds to ensure that the furnace body itself has a good airtight foundation.
Furnace door and opening sealing
Furnace door sealing structure: The furnace door is the key link in the sealing of the entire furnace body. Generally, heavy-duty hinges are used to connect to the furnace body to facilitate the switch operation while ensuring the stability of the installation. A sealing groove is set on the edge of the furnace door, and a high-temperature resistant, wear-resistant and elastic sealing material, such as a graphite sealing gasket, is placed in the groove. When the furnace door is closed, a uniform pressing force is applied through hydraulic, pneumatic or mechanical levers to make the sealing gasket fit tightly with the furnace door frame, effectively blocking the gas in and out. Some advanced furnace door designs are also equipped with auxiliary sealing enhancement devices. For example, after the furnace door is closed, an inert gas curtain can be formed around the sealing gasket, and the gas pressure is used to further prevent the outside air from penetrating into the furnace.
Observation window sealing: The observation window must ensure that the sintering situation in the furnace can be clearly observed, and a good seal must be maintained. It is usually made of multi-layer glass or quartz material, and is sealed and connected to the furnace body through a special metal frame. Sealant, sealing gasket, etc. are used to seal between the metal frame and the furnace body and between the glass or quartz sheet. The sealant is selected from a material that is resistant to high temperature, aging and has good adhesion to ensure that there will be no gaps for gas leakage in the observation window during long-term use.
Sealing of electrodes, inlets and outlets and other openings: The electrodes need to pass through the furnace wall to power the heating elements in the furnace. The sealing here is achieved by using ceramic insulating seals. Ceramics have both insulating properties and can form a tight sealing structure with metal electrodes and furnace walls to prevent gas leakage from the electrodes. If the inlet and outlet are used intermittently, they can be designed as sealed doors or sealing plugs. High-quality sealing materials and reasonable clamping mechanisms are also used to ensure the sealing when closed; if it is a sintering furnace with continuous inlet and outlet, complex dynamic sealing devices will be used, such as magnetic fluid seals, rotary seals and other special technologies to ensure that the vacuum degree in the furnace is not affected during the continuous inlet and outlet of materials.
Vacuum degree control and guarantee in the process of exhaust process control
Pre-exhaust stage: Before sintering begins, first start the mechanical vacuum pump to pre-exhaust the furnace, and gradually reduce the air pressure in the furnace according to the set exhaust rate and time. At this stage, we should pay close attention to the changes in the readings of the vacuum gauge, and check the operating status of all components of the entire vacuum system to ensure that there are no abnormal gas leakage points, so that the air and other gases in the furnace can be smoothly pumped out until the mechanical vacuum pump reaches the lowest vacuum that can be achieved or the transition vacuum required for the next operation (such as starting the diffusion vacuum pump).
High vacuum acquisition stage: When the pre-exhaust reaches a certain level, according to the vacuum requirements of the sintering process, a higher-performance vacuum pump such as a diffusion vacuum pump or a molecular pump is started in time to further remove the residual gas in the furnace and increase the vacuum to the specified level. In this process, it is necessary to accurately control the operating parameters of each vacuum pump, such as the speed and exhaust flow rate, and reasonably adjust the gas flow direction and the air pressure distribution of each part through the cooperation of the vacuum valve to avoid the situation where air flow turbulence or local air pressure abnormality affects the vacuum improvement.
Vacuum maintenance and dynamic adjustment
Monitoring and feedback during sintering: During the entire sintering process, the vacuum gauge continuously monitors the vacuum in the furnace in real time. Once the vacuum fluctuates and deviates from the process requirements, the control system will respond immediately. For example, if the vacuum degree decreases, it may be due to a small leak in the furnace, material degassing, or a decrease in the performance of the vacuum pump. At this time, the control system will first check for leaks (by checking the sealing parts, pipe connections, etc.), and adjust the power of the vacuum pump as needed, open or close the relevant vacuum valves to adjust the pumping rate, and try to restore the vacuum degree to the normal range; if the vacuum degree is too high or too low and affects the quality of the sintered product, it will also be fine-tuned accordingly. Vacuum guarantee during feeding and discharging and process adjustment: For situations where materials need to be fed in and out during the sintering process, special feeding and discharging devices and operating procedures will be used to minimize the impact on the vacuum degree. For example, at the moment of feeding and discharging, the gas influx caused by the short opening can be compensated by quickly closing the local vacuum valve, starting the standby vacuum pump, or increasing the pumping speed of the existing vacuum pump, so as to quickly restore the vacuum degree in the furnace. In the process adjustment stage, when changing parameters such as sintering temperature and time, attention should also be paid to changes in vacuum degree, because these parameter changes may cause changes in the material degassing characteristics, which in turn affect the vacuum degree, so timely measures should be taken to ensure the stability of the vacuum environment.

Vacuum Sintering Furnace