Sintering furnace and silicon nitride powder sintering method

Abstract

The sintering furnace includes a furnace shell, a heat-insulating cylinder installed in the furnace shell, and a temperature-equalizing cylinder installed in the heat-insulating cylinder. A gas flow chamber is formed between the temperature-equalizing cylinder and the heat-insulating cylinder. The gas flow chamber is equipped with an induction heating element controlled by an external controller and having heating and temperature sensing functions. The characteristic is that the furnace shell is equipped with an internal circulation component for pumping the gas in the temperature-equalizing cylinder to circulate between the temperature-equalizing cylinder and the gas flow chamber, and the internal circulation component is controlled and operated by an external controller. The present invention avoids the focus of high heat in the temperature-equalizing cylinder, improves the reliability of sintering, and thus enhances the sintering activity of the powder; it can effectively prevent the excessive temperature in the temperature-equalizing cylinder from affecting the product, and can also reduce energy consumption; the gas flow direction in the heat-insulating cylinder changes dynamically in an undirected manner, so that the quality of the sintered products at different positions in the temperature-equalizing cylinder tends to be stable and consistent, thereby improving the reliability of sintering. The present invention also provides a method for sintering silicon nitride powder.

Description

Technical Field

[0001] The invention relates to a sintering furnace and a silicon nitride powder sintering method, belonging to the technical field of sintering furnaces. Background Art

[0002] The sintering furnace is suitable for high-pressure sintering of materials such as silicon nitride and cemented carbide. It can increase the sintering density of the material and improve the mechanical properties of the material. It is a heat treatment furnace that can provide a specific temperature and pressure environment for the material. The sintering furnace can promote the mutual bonding of certain solid particles in the material, grain growth, gradual reduction of voids (pores) and grain boundaries, shrinkage of the total volume of the material, increase of density, and finally become a dense polycrystalline sintered body with a certain microstructure. The existing sintering furnace generally includes an insulation tube and a temperature-equalizing tube, and the temperature-equalizing tube is arranged in the inner cavity of the insulation tube. Among them, the insulation tube mainly plays a role of heat preservation, and the temperature-equalizing tube is used to load the material to be processed and provide the material with a specific processing temperature and pressure. In the specific use process, in order to provide a specific pressure environment for the material, a high-pressure inert gas is often required to be input into the temperature-equalizing tube. During the air intake process, the internal pressure of the temperature-equalizing tube will gradually increase. Once it exceeds the rated point, the relative balance of the temperature-equalizing tube will be destroyed, and the temperature-equalizing tube will be squeezed and damaged due to the excessive pressure difference between the inside and the outside.

[0003] At present, the preparation of silicon nitride powder usually adopts the silicon powder nitriding method. Its basic principle is that silicon powder and nitrogen react at high temperature in an atmosphere sintering furnace to generate silicon nitride. The process flow of its operation mainly includes: filling silicon powder into a sagger, sending multiple saggers into the sintering furnace in turn, continuously introducing nitrogen-containing reaction gas into the sintering furnace, gradually heating to about 1300 degrees Celsius, keeping warm for a certain time to cause nitriding reaction, and then cooling to below 50 degrees, removing the sintered sagger from the sintering furnace, removing the generated silicon nitride plate from the sagger, and crushing it to a certain particle size to obtain silicon nitride powder. In actual production, it was found that the α-phase and β-phase content of the silicon nitride at the bottom and top of the sagger were inconsistent, and the impurity content of carbides in the silicon nitride also had regular differences, which led to differences in the final silicon nitride powder quality. The powder quality was uncontrollable, especially after the sintering furnace had undergone a major overhaul, the product quality was unstable. After analyzing the reasons, it was found that during sintering, nitrogen usually maintains a continuous directional flow in a single direction in the sintering furnace. The directional flow of the gas will cause differences in the performance of the product in the flow direction. There are many influencing factors, such as trace impurities in the gas, the influence of volatiles in the furnace, and the flow state of the gas in the furnace. Although the principle of the silicon powder nitriding process is simple, the actual reaction is very complex. To obtain silicon nitride powder with a high α-phase content, the key is to control the temperature, pressure, and gas process during the process. The silicon powder nitriding process is an exothermic process. As the reaction proceeds, the large amount of heat released will increase the local temperature of the material. The unidirectional airflow will aggravate the temperature rise at the rear. The α-phase in silicon nitride powder is a high-temperature unstable phase. If the rear is overheated, the generated α-phase silicon nitride powder can easily be partially converted into the β-phase, thereby affecting the sintering activity of the powder. Summary of the Invention

[0004] The sintering furnace and silicon nitride powder sintering method provided by the present invention avoid high heat focusing in the temperature-isolating cylinder, improve the reliability of sintering, and enhance the sintering activity of the powder; effectively prevent the excessive temperature in the temperature-isolating cylinder from affecting the product, and reduce energy consumption; the gas flow direction in the temperature-isolating cylinder changes dynamically in an undirectional manner, so that the quality of the sintered products at different positions in the temperature-isolating cylinder tends to be stable and consistent, thereby improving the reliability of sintering.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The sintering furnace includes a furnace shell, an insulation tube installed in the furnace shell, and a temperature-equalizing tube installed in the insulation tube. A gas flow chamber is formed between the temperature-equalizing tube and the insulation tube. The gas flow chamber is equipped with an induction heating element controlled by an external controller and having heating and temperature sensing functions. It is characterized in that the furnace shell is equipped with an internal circulation component that pumps the gas in the temperature-equalizing tube to circulate between the temperature-equalizing tube and the gas flow chamber, and the internal circulation component is controlled and operated by an external controller.

[0007] Preferably, the internal circulation component includes an exhaust fan for extracting the gas in the temperature-isolating cylinder and a wind hood for limiting the gas extracted by the exhaust fan from flowing out of the temperature-isolating cylinder.

[0008] Preferably, one end of the temperature-averaging cylinder is provided with an exhaust port for an exhaust fan to extract gas, and the other end is provided with a reflux inlet for gas to flow back into the temperature-averaging cylinder.

[0009] Preferably, the temperature-averaging cylinder includes a temperature-averaging cylinder body, a temperature-averaging door 1 cooperating with one end of the temperature-averaging cylinder body, and a temperature-averaging door 2 cooperating with the other end of the temperature-averaging cylinder body, and the exhaust port is opened on the temperature-averaging door 1.

[0010] Preferably, the temperature-averaging door 1 and the temperature-averaging door 2 are movable doors controlled by an external controller. The temperature-averaging door 2 moves in the insulation cylinder and separates from the temperature-averaging cylinder, forming a return air inlet between the temperature-averaging cylinder and the temperature-averaging door 2.

[0011] Preferably, the insulation cylinder includes an insulation cylinder body, an insulation door 1 cooperated with one end of the insulation cylinder body, and an insulation door 2 cooperated with the other end of the insulation cylinder body, the insulation door 1 is arranged on the same side as the uniform temperature door, the insulation door 2 is arranged on the same side as the uniform temperature door 2, the exhaust fan is arranged along the central axis, the motor end of the exhaust fan is positioned on the furnace shell, and the exhaust blade end of the exhaust fan passes through the insulation door 1 and extends into the exhaust port.

[0012] Preferably, the wind cover is installed on the heat-insulating cylinder to cover the heat-insulating door at one end, and the exhaust fan passes through the wind cover and the heat-insulating door and extends into the exhaust port.

[0013] The silicon nitride powder sintering method of the sintering furnace described above is adopted, the silicon powder is loaded into the temperature-equalizing cylinder and the reaction atmosphere gas is input into the gas flow chamber, and the induction heating element is controlled by an external controller to heat up the temperature in the temperature-equalizing cylinder to sinter the silicon powder. It is characterized in that: during the sintering process, the external controller controls the internal circulation component to extract the gas from the temperature-equalizing cylinder into the gas flow chamber, and the gas flows in the gas flow chamber and then flows back to the temperature-equalizing cylinder, forming an internal circulation of the gas between the temperature-equalizing cylinder and the gas flow chamber.

[0014] Preferably, the gas temperature in the inner gas flow cavity is monitored in real time by the induction heating element and sent to an external controller, and the external controller adjusts the output power of the induction heating element according to the received gas temperature information.

[0015] Preferably, the real-time air pressure in the gas flow chamber is monitored and sent to an external controller. The external controller adjusts the output power of the exhaust fan, the size of the return air inlet, and the flow rate and velocity of the input reaction atmosphere gas according to the received air pressure information to adjust the flow rate, flow rate and flow direction of the gas between the temperature equalizing cylinder and the gas flow chamber.

[0016] The beneficial effects of the invention are:

[0017] The sintering furnace of the present invention controls the heating of the induction heating element through an external controller to increase the temperature in the temperature-equalizing cylinder to sinter the product in the furnace; an internal circulation component is installed in the furnace shell, and the gas in the temperature-equalizing cylinder is pumped by the internal circulation component to circulate between the temperature-equalizing cylinder and the gas flow chamber, and the high-temperature gas in the temperature-equalizing cylinder is driven to flow to the gas flow chamber during the sintering process, so that the heat released during the nitriding process of the silicon powder flows from the temperature-equalizing cylinder to the gas flow chamber, avoiding the high heat from focusing in the temperature-equalizing cylinder, and effectively preventing the generated α-phase silicon nitride powder from being partially converted into β-phase due to overheating in the temperature-equalizing cylinder, thereby improving the reliability of sintering and enhancing the sintering activity of the powder; the internal circulation component pumps the high-temperature gas in the temperature-equalizing cylinder into the annular cavity, and the external control system can timely grasp the gas temperature in the temperature-equalizing cylinder through the induction of the induction heating element, and appropriately reduce the output power of the induction heating element when the real-time temperature sensed by the induction heating element rises sharply, that is, when the silicon powder nitridation starts to release heat, to slow down the heating rate in the temperature-equalizing cylinder. degree, which can effectively prevent the temperature in the temperature-equalizing cylinder from exceeding the limit and affecting the product, and can also reduce energy consumption; the gas has strong fluidity between the gas flow chamber and the temperature-equalizing cylinder, which can effectively improve the reaction rate of the gas and powder, make the contact between the powder and the gas more uniform, improve the uniformity, sufficiency and efficiency of the reaction, and thus improve the sintering quality; the internal circulation component draws the gas in the temperature-equalizing cylinder into the gas flow chamber, which is exactly opposite to the gas input direction of the reaction atmosphere gas input into the gas flow chamber and then flowing into the temperature-equalizing cylinder, causing the air pressure in the temperature-equalizing cylinder and the gas flow chamber to fluctuate. During the sintering process, the gas moves from the end with high air pressure to the end with low air pressure. As the air pressure of the temperature-equalizing cylinder and the gas flow chamber fluctuates, the gas flow direction in the insulation cylinder changes dynamically in an undirectional manner, avoiding the phenomenon of uneven and unstable product quality caused by continuous directional flow of gas in the sintering furnace, making the quality of sintered products at different positions in the temperature-equalizing cylinder tend to be stable and consistent, thereby improving the reliability of sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the sintering furnace of the present invention. DETAILED DESCRIPTION

[0019] The following combination Figure 1 The embodiments of the present invention are described in detail.

[0020] The sintering furnace includes a furnace shell 1, an insulation tube 2 installed in the furnace shell 1, and a temperature-equalizing tube 3 installed in the insulation tube 2. A gas flow chamber 4 is formed between the temperature-equalizing tube 3 and the insulation tube 2. The gas flow chamber 4 is equipped with an induction heating element 5 controlled by an external controller and having heating and temperature sensing functions. It is characterized in that the furnace shell 1 is equipped with an internal circulation component 6 for pumping the gas in the temperature-equalizing tube 3 to circulate between the temperature-equalizing tube 3 and the gas flow chamber 4, and the internal circulation component 6 is controlled and operated by an external controller.

[0021] The sintering furnace described above controls the induction heating element 5 to generate heat through an external controller, thereby raising the temperature inside the temperature-averaging cylinder 3 and sintering the product in the furnace. An internal circulation component 3 is installed in the furnace shell 1, and the gas in the temperature-averaging cylinder 3 is pumped by the internal circulation component 3 to circulate between the temperature-averaging cylinder 3 and the gas flow chamber 4. During the sintering process, the high-temperature gas in the temperature-averaging cylinder 3 is driven to flow to the gas flow chamber 4, so that the heat released during the nitridation of the silicon powder flows from the temperature-averaging cylinder 3 to the gas flow chamber 4, avoiding the high heat from being focused in the temperature-averaging cylinder 3, and effectively preventing the generated α-phase silicon nitride powder from being partially converted into β-phase due to overheating in the temperature-averaging cylinder, thereby improving the reliability of sintering and enhancing the sintering activity of the powder; the internal circulation component 6 pumps the high-temperature gas in the temperature-averaging cylinder 3 into the annular cavity 4, and through the induction of the induction heating element 5, the external control system can timely grasp the gas temperature in the temperature-averaging cylinder 3, and when the heating rate increases and the real-time temperature sensed by the induction heating element 5 rises sharply, that is, when the silicon powder nitridation begins to release heat, the output power of the induction heating element 5 is appropriately reduced to slow down the temperature-averaging The heating rate in the cylinder 3 can effectively prevent the excessive temperature in the temperature-equalizing cylinder 3 from affecting the product, and can also reduce energy consumption; the gas has strong fluidity between the gas flow chamber 4 and the temperature-equalizing cylinder 3, which can effectively improve the reaction rate of the gas and the powder, make the contact between the powder and the gas more uniform, improve the uniformity, sufficiency and efficiency of the reaction, and thus improve the sintering quality; the internal circulation component 6 extracts the gas in the temperature-equalizing cylinder 3 into the gas flow chamber, which is exactly opposite to the gas input direction (not shown in the figure) of the reaction atmosphere gas input into the gas flow chamber and then flowing into the temperature-equalizing cylinder, causing the gas pressure in the temperature-equalizing cylinder 3 and the gas flow chamber 4 to fluctuate. During the sintering process, the gas moves from the end with high pressure to the end with low pressure. As the pressure of the temperature-equalizing cylinder 3 and the gas flow chamber 4 fluctuates, the gas flow direction in the insulation cylinder changes dynamically in an undirectional manner, avoiding the phenomenon of uneven and unstable product quality caused by continuous directional flow of gas in the sintering furnace, so that the quality of the sintered products at different positions in the temperature-equalizing cylinder tends to be stable and consistent, thereby improving the reliability of sintering.

[0022] Among them, the internal circulation component 6 includes an exhaust fan 61 that extracts the gas in the temperature-equalizing cylinder 3 and a wind hood 62 that limits the gas extracted by the exhaust fan from flowing out of the heat-insulating cylinder 2. The wind hood 62 limits the gas extracted from the temperature-equalizing cylinder 3 from flowing out of the heat-insulating cylinder 2. Therefore, after the gas is extracted from the temperature-equalizing cylinder 3, it enters the gas flow chamber 4, flows in the gas flow chamber 4 and then flows back to the temperature-equalizing cylinder 3, forming an internal circulation from the temperature-equalizing cylinder 3 to the gas flow chamber 4 and then to the temperature-equalizing cylinder 3. The reaction atmosphere gas is input into the gas flow chamber 4 and then flows into the temperature-equalizing cylinder 3. During the sintering process, the input direction of the reaction atmosphere gas is opposite to the flow direction of the internal circulation component 6 that extracts the gas in the temperature-equalizing cylinder 3 into the gas flow chamber 4. Changes in the flow rate and flow velocity of the reaction atmosphere gas input and the flow rate and flow velocity of the gas extracted by the internal circulation component 6 will cause dynamic fluctuations in the air pressure in the gas flow chamber 4 and the temperature-equalizing cylinder 3. The flow direction of the gas in the gas flow chamber 4 and the temperature-equalizing cylinder 3 will change dynamically. The flow direction is unbalanced, and the reaction between the gas and the powder is more uniform, avoiding the phenomenon of uneven and unstable product quality caused by continuous directional flow of gas in the sintering furnace, so that the quality of the sintered products at different positions in the temperature-equalizing cylinder 3 tends to be stable and consistent, thereby improving the reliability of sintering.

[0023] The temperature-averaging cylinder 3 has an exhaust port 7 at one end for the exhaust fan 61 to extract the gas, and a return air inlet 8 at the other end for the gas to flow back into the temperature-averaging cylinder. Figure 1 The dotted line in the figure indicates the direction of internal circulation flow. The exhaust fan 61 draws the gas in the temperature-equalizing cylinder 3 out of the exhaust port 7 into the gas flow chamber 4, and the gas flows back to the temperature-equalizing cylinder 3 from the reflux air inlet 8 through the gas flow chamber 4, that is, the direction of internal circulation flow. An internal circulation flow of gas is formed between the gas flow chamber 4 and the temperature-equalizing cylinder 3, and the accumulated heat formed in the temperature-equalizing cylinder 3 due to heat release during the powder sintering process can be flowed into the gas flow chamber 4, avoiding the heat focusing in the temperature-equalizing cylinder 3 to cause excessive sintering of the product, thereby improving the safety and reliability of sintering.

[0024] The temperature-averaging cylinder 3 comprises a cylinder body 31, a first temperature-averaging door 32 mating with one end of the cylinder body 31, and a second temperature-averaging door 33 mating with the other end of the cylinder body 31. An exhaust port 7 is provided on the first temperature-averaging door 31. The first and second temperature-averaging doors 32 and 33 seal both ends of the cylinder body 3, creating gaps for gas flow between the first and second temperature-averaging doors 32 and 33 and the cylinder body 31. Reaction atmosphere gas is introduced into the gas flow chamber 4 and enters the cylinder body 3 through these gaps. An exhaust fan 61 draws gas from the cylinder body 3 through the exhaust port 7 on the first temperature-averaging door 32.

[0025] The first and second temperature-averaging doors 32, 33 are movable doors controlled by an external controller. The second temperature-averaging door 33 moves within the heat-insulating cylinder 2, separating from the heat-averaging cylinder 31. A return air inlet 8 is formed between the heat-averaging cylinder 31 and the second temperature-averaging door 33. Adjusting the distance between the second temperature-averaging door 33 and the heat-averaging cylinder 31 adjusts the size of the return air inlet 8, thereby regulating the internal circulation gas flow rate.

[0026] Among them, the insulation cylinder 2 includes an insulation cylinder body 21, an insulation door 22 matched with one end of the insulation cylinder body 21, and an insulation door 23 matched with the other end of the insulation cylinder body 21. The insulation door 22 and the uniform temperature door 32 are arranged on the same side, and the insulation door 23 and the uniform temperature door 33 are arranged on the same side. The exhaust fan 61 is arranged along the central axis, the motor end of the exhaust fan 61 is positioned on the furnace shell 1, and the exhaust blade end of the exhaust fan 62 passes through the insulation door 22 and extends into the exhaust port 7. The reaction atmosphere gas is input into the gas flow chamber 4, enters the temperature-equalizing cylinder 3 through the gap on the temperature-equalizing cylinder 3, and forms an input flow direction from outside to inside. The exhaust fan 61 is operated to extract the gas in the temperature-equalizing cylinder 3 from the exhaust port 7 to the gas flow chamber 4, and flows in the gas flow chamber 4 and flows back to the temperature-equalizing cylinder 3 through the return air inlet 7, forming an internal circulation flow direction from inside to outside and then from outside to inside. The combination of the input flow direction and the internal circulation flow direction causes the gas to form a non-directional flow with a dynamically changing flow direction between the temperature-equalizing cylinder 3 and the gas flow chamber 4. By changing the flow rate and flow velocity of the input reaction atmosphere gas, as well as the output power of the exhaust fan and the size of the return air inlet, the air pressure in the temperature-equalizing cylinder 3 and the gas flow chamber 4 can be adjusted, so that the air pressure fluctuations of the two change. The air pressure fluctuation causes the gas flow direction to change dynamically, avoiding the gas in the insulation cylinder 2 to flow in a constant direction. The gas has strong fluidity and the flow direction changes dynamically, which can utilize the uniform heating reaction of the product in the temperature-equalizing cylinder 3 to improve the consistency and uniformity of the product sintering, so that the powder is fully in contact with the gas and is evenly sintered, thereby improving the sintering quality.

[0027] The hood 62 is mounted on the heat-insulating cylinder 2, covering the end where the heat-insulating door 32 is located. The exhaust fan 61 extends through the hood 61 and the heat-insulating door 22 into the exhaust port 7. The gas extracted from the exhaust port 7 is blocked by the hood 62 and does not flow out through the gap between the heat-insulating door 22 and the heat-insulating cylinder 21. Instead, it flows into the gas flow chamber 4, ensuring an effective and stable internal circulation of the gas.

[0028] The silicon nitride powder sintering method of the sintering furnace described above is adopted, the silicon powder is loaded into the temperature-equalizing cylinder 3 and the reaction atmosphere gas is input into the gas flow chamber 4, and the induction heating element 5 is controlled by an external controller to generate heat to increase the temperature inside the temperature-equalizing cylinder 3 to sinter the silicon powder. It is characterized in that: during the sintering process, the external controller controls the internal circulation component 6 to extract the gas from the temperature-equalizing cylinder 3 into the gas flow chamber 4, and the gas flows in the gas flow chamber 4 and then flows back to the temperature-equalizing cylinder 3, forming an internal circulation of the gas between the temperature-equalizing cylinder and the gas flow chamber.

[0029] The silicon nitride powder sintering method described above pumps the gas in the temperature-equalizing cylinder 3 to circulate between the temperature-equalizing cylinder 3 and the gas flow chamber 4 through the internal circulation component 3, and drives the high-temperature gas in the temperature-equalizing cylinder 3 to flow to the gas flow chamber 4 during the sintering process, so that the heat released during the nitriding process of the silicon powder flows from the temperature-equalizing cylinder 3 to the gas flow chamber 4, avoiding the high heat from focusing in the temperature-equalizing cylinder 3, and effectively preventing the generated α-phase silicon nitride powder from being partially converted into β-phase due to overheating in the temperature-equalizing cylinder, thereby improving the reliability of sintering and enhancing the sintering activity of the powder; the gas has strong fluidity between the gas flow chamber 4 and the temperature-equalizing cylinder 3, which can effectively improve the reaction rate of the gas and the powder, make the contact between the powder and the gas more uniform, and improve the uniformity of the reaction. Sufficiency and efficiency are enhanced to improve the sintering quality; the internal circulation component 6 draws the gas in the temperature-equalizing cylinder 3 into the gas flow chamber, which is exactly opposite to the gas input direction (not shown in the figure) of the reaction atmosphere gas input into the gas flow chamber and then flowing into the temperature-equalizing cylinder, causing the air pressure in the temperature-equalizing cylinder 3 and the gas flow chamber 4 to fluctuate. During the sintering process, the gas moves from the end with high air pressure to the end with low air pressure. As the air pressure in the temperature-equalizing cylinder 3 and the gas flow chamber 4 fluctuates, the gas flow direction in the insulation cylinder changes dynamically and non-directionally, avoiding the phenomenon of uneven and unstable product quality caused by continuous directional flow of gas in the sintering furnace, so that the quality of sintered products at different positions in the temperature-equalizing cylinder tends to be stable and consistent, thereby improving the reliability of sintering.

[0030] The induction heating element 5 monitors the gas temperature in the inner gas flow cavity in real time and sends it to the external controller. The external controller adjusts the output power of the induction heating element according to the received gas temperature information. The internal circulation component 6 draws the high-temperature gas in the temperature-equalizing cylinder 3 into the annular cavity 4. The induction heating element 5 senses the gas temperature in the temperature-equalizing cylinder 3, so that the external control system can timely grasp the gas temperature in the temperature-equalizing cylinder 3. When the real-time temperature sensed by the induction heating element 5 rises sharply, that is, when the silicon powder nitriding begins to release heat, the output power of the induction heating element 5 is appropriately reduced, and the heating rate in the temperature-equalizing cylinder 3 is slowed down. This can effectively prevent the excessive temperature in the temperature-equalizing cylinder 3 from affecting the product and reduce energy consumption.

[0031] Among them, the real-time air pressure in the gas flow chamber 4 is monitored and sent to the external controller. The external controller adjusts the output power of the exhaust fan 61, the size of the return air inlet, and the flow rate and velocity of the input reaction atmosphere gas according to the received air pressure information, so as to adjust the velocity, flow rate and flow direction of the gas between the temperature-equalizing cylinder 3 and the gas flow chamber 4. The reaction atmosphere gas is introduced into the gas flow chamber 4, enters the temperature-equalizing cylinder 3 through the gap on the temperature-equalizing cylinder 3, and forms an input flow direction from outside to inside. The exhaust fan 61 is operated to extract the gas in the temperature-equalizing cylinder 3 from the exhaust port 7 into the gas flow chamber 4, and then flows in the gas fluid chamber 4 and flows back to the temperature-equalizing cylinder 3 through the return air inlet 7, forming an internal circulation flow direction from inside to outside and then from outside to inside. The combination of the input flow direction and the internal circulation flow direction causes the gas to form an omnidirectional flow with a dynamically changing flow direction between the temperature-equalizing cylinder 3 and the gas flow chamber 4. By changing the flow rate and flow velocity of the input reaction atmosphere gas, as well as the output power of the exhaust fan and the size of the return air inlet, the air pressure in the temperature-equalizing cylinder 3 and the gas flow chamber 4 can be adjusted, so that the air pressure fluctuations of the two change. The air pressure fluctuation causes the gas flow direction to change dynamically, avoiding the gas in the insulation cylinder 2 to flow in a constant direction. The gas has strong fluidity and the flow direction changes dynamically, which can utilize the uniform heating reaction of the product in the temperature-equalizing cylinder 3 to improve the consistency and uniformity of the product sintering, so that the powder is fully in contact with the gas and is evenly sintered, thereby improving the sintering quality.

[0032] The above fully describes the technical solutions of the embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the embodiments described are only part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for sintering silicon nitride powder in a sintering furnace, characterized in that: The sintering furnace comprises a furnace shell, a heat-insulating cylinder installed in the furnace shell, and a temperature-equalizing cylinder installed in the heat-insulating cylinder. A gas flow chamber is formed between the temperature-equalizing cylinder and the heat-insulating cylinder. The gas flow chamber is equipped with an induction heating element controlled by an external controller and having heating and temperature sensing functions. The furnace shell is equipped with an internal circulation component for pumping gas in the temperature-equalizing cylinder to circulate between the temperature-equalizing cylinder and the gas flow chamber. The internal circulation component is controlled and operated by an external controller. The internal circulation assembly includes an exhaust fan for extracting the gas in the temperature-isolating cylinder and a wind hood for limiting the gas extracted by the exhaust fan from flowing out of the temperature-isolating cylinder; One end of the temperature-averaging cylinder is provided with an exhaust port for the exhaust fan to extract the gas, and the other end is provided with a return air inlet for the gas to flow back into the temperature-averaging cylinder; The temperature-averaging cylinder comprises a temperature-averaging cylinder body, a temperature-averaging door 1 matched with one end of the temperature-averaging cylinder body, and a temperature-averaging door 2 matched with the other end of the temperature-averaging cylinder body, and the exhaust port is opened on the temperature-averaging door 1; The temperature-averaging door 1 and the temperature-averaging door 2 are movable doors controlled by an external controller. The temperature-averaging door 2 moves in the heat preservation cylinder and separates from the temperature-averaging cylinder, forming a return air inlet between the temperature-averaging cylinder and the temperature-averaging door 2. The heat preservation cylinder includes a heat preservation cylinder body, a heat preservation door 1 matched with one end of the heat preservation cylinder body, and a heat preservation door 2 matched with the other end of the heat preservation cylinder body. The heat preservation door 1 is arranged on the same side as the temperature uniformity door, and the heat preservation door 2 is arranged on the same side as the temperature uniformity door 2. The exhaust fan is arranged along the central axis, the motor end of the exhaust fan is positioned on the furnace shell, and the exhaust blade end of the exhaust fan passes through the heat preservation door and extends into the exhaust port. The wind cover is installed on the heat preservation cylinder, covering the heat preservation door at one end, and the exhaust fan passes through the wind cover and the heat preservation door and extends into the exhaust port; Silicon powder is loaded into a temperature-equalizing cylinder and reaction atmosphere gas is input into the gas flow chamber. An external controller controls the induction heating element to heat up so that the temperature inside the temperature-equalizing cylinder is increased to sinter the silicon powder. During the sintering process, the external controller controls the internal circulation component to extract gas from the temperature-equalizing cylinder into the gas flow chamber, and the gas flows in the gas flow chamber and then flows back into the temperature-equalizing cylinder, forming an internal circulation of gas between the temperature-equalizing cylinder and the gas flow chamber. The induction heating element monitors the gas temperature in the inner gas flow cavity in real time and sends it to the external controller. The external controller adjusts the output power of the induction heating element according to the received gas temperature information. The real-time air pressure in the gas flow chamber is monitored and sent to an external controller. The external controller adjusts the output power of the exhaust fan, the size of the return air inlet, and the flow rate and velocity of the input reaction atmosphere gas according to the received air pressure information, so as to adjust the flow rate, flow rate and flow direction of the gas between the temperature-equalizing cylinder and the gas flow chamber, and adjust the air pressure in the temperature-equalizing cylinder and the gas flow chamber to cause the air pressure of the two to fluctuate. The air pressure fluctuation causes the gas flow direction to change dynamically, thereby preventing the gas in the insulation cylinder from flowing in a constant direction.

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