CN117190679A - High-temperature vacuum nitriding furnace for efficiently producing nitriding material and manufacturing method thereof - Google Patents
High-temperature vacuum nitriding furnace for efficiently producing nitriding material and manufacturing method thereof Download PDFInfo
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims abstract description 19
- 239000007789 gas Substances 0.000 claims abstract description 17
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Abstract
The invention discloses a high-temperature vacuum nitriding furnace for producing nitriding materials with high efficiency and a manufacturing method thereof, wherein an electric heating mode controlled by silicon controlled rectifier is adopted, compared with a traditional natural gas heating mode, the heating temperature is more stable, the quality of nitriding calcined products is excellent, the surface is free from pollution, and the exhaust gas and dust emission is greatly reduced. The nitrogen ventilation mode adopts a silicon nitride slit type dispersion ventilation mode, so that the upper surface, the lower surface, the left surface and the right surface of a nitrided product are uniformly contacted with nitrogen, the nitriding efficiency is improved by 30%, the quality qualification rate of the nitrided product is up to more than 98%, the energy utilization rate is improved to more than 85%, the yield of a single kiln is improved by 50%, and the production cost of a nitrided material is reduced by 25%. The production varieties of the nitriding materials cover varieties from low-end, low-temperature silicon nitride, silicon manganese nitride, manganese nitride to high-end, high-temperature titanium nitride, vanadium nitride, niobium nitride, aluminum nitride and the like.
Description
Technical Field
The invention belongs to the field of production of nitriding materials. In particular to a high-temperature vacuum nitriding furnace for efficiently producing nitriding materials and a manufacturing method thereof. Has wide application prospect in the production fields of artificial synthetic materials, high-end manufacturing fields, aerospace, medical treatment, metallurgy and the like.
Background
The nitride generated by nitriding reaction of elements with extremely strong affinity to nonmetallic nitrogen such as silicon, aluminum, titanium, vanadium and the like is called as high-temperature nitride structural ceramic material under the condition of vacuum and nitrogen atmosphere.
The silicon nitride which is most widely applied in the ceramic material with the high-temperature nitride structure is an artificial synthetic material, the Mohs hardness is 9-9.5, the Vickers hardness is 2200, and the hardness is close to that of diamond; the elastic modulus is 28420-46060 MPa, the compressive strength is 490MPa, and the bending strength is 147MPa; the linear expansion coefficient is 2.8-3.2X10-6/DEG C at 1000 ℃; is insoluble in water and has extremely strong acid and alkali resistance. The temperature of the oxidation starting in the air is 1300-1400 ℃ and the melting point is 1900 ℃ (under pressure).
Silicon nitride is a superhard material and has excellent characteristics such as lubricity, wear resistance, oxidation resistance, thermochemical stability, super corrosion resistance, ultra high temperature, ultra high strength, and ultra hardness.
In nineties of the twentieth century, as an important application and research technical result of silicon nitride as a high-temperature structural ceramic material, the silicon nitride high-temperature structural ceramic material is rapidly popularized and developed, and developed countries have begun to widely apply the silicon nitride high-temperature structural ceramic material to the processing and production of ultrahigh-temperature, corrosion-resistant and wear-resistant parts; a steel-making microalloying production process; high-end manufacturing industries such as high-speed cutting tools, missile tail nozzles, artificial joints, high-temperature spray coatings of aeroengines and the like, and the application fields relate to industries such as metallurgy, machinery, chemical industry, medicine, electronics and aviation and the like.
At present, the main process for producing the silicon nitride raw material in China comprises the following steps: direct nitridation, carbothermal reduction nitridation, vapor deposition, thermal decomposition, flash combustion, and the like.
The carbothermic reduction nitriding method adopts a method that quartz ore, carbon powder and iron powder are firstly reduced in a high-temperature nitriding furnace and then nitrided to produce silicon nitride. The carbon proportioning requirement in the production process is very accurately controlled, the carbon powder quantity is too high, and partial silicon carbide is easy to generate; low carbon content, incomplete reduction and high free silicon oxide in the product. The control of technological parameters such as carbon partial pressure, nitrogen partial pressure balance, reduction temperature, nitriding temperature and the like in the furnace is complex, and the exhaust gas and dust emission is enlarged.
The vapor deposition method and the thermal decomposition method adopt ammonium salt and silicon chloride to carry out high-temperature vaporization or decomposition synthesis, and the produced silicon nitride has high purity and small granularity (reaching the nanometer level). However, the generated waste gas has high toxicity, complex recovery treatment process and high production cost, and is not suitable for mass production of enterprises.
The flash combustion method sprays ferrosilicon and industrial silicon powder into a closed container, and the ferrosilicon and the industrial silicon powder react with nitrogen in a furnace to generate silicon nitride by utilizing heat generated by combustion and gravity descending process of the ferrosilicon and the industrial silicon powder through ignition combustion. The flash combustion method has low energy consumption, low cost and high yield. But has large pollution to flue gas and dust, complex production process and equipment structure and large one-time investment. The specific gravity of the produced silicon nitride is small (about 2.0g/cm 3), and the silicon nitride can only be limited to the production and use of refractory materials, and is difficult to meet the production process requirements (the specific gravity is greater than 2.5g/cm 3) of nitrogen alloy products for steelmaking.
Compared with the traditional vacuum nitriding furnace, the electric heating high-efficiency high-temperature vacuum nitriding furnace with the double-hearth and dispersion type ventilation structure is more energy-saving and environment-friendly, and has the advantages of resource saving, product quality and higher input-output cost.
The traditional vacuum nitriding furnace has low compressive strength and poor sealing property due to the furnace body structure; the uneven temperature of the gas burning mode and the easy overburning oxidation of the flame contact surface cause uneven nitridation of the product, and the smoke emission pollutes the atmosphere and the effective utilization rate of heat energy is low; the single hearth and the single trolley are subjected to nitriding firing, the firing time is long, and the productivity is low; the quality of the nitriding product can not meet the quality requirement of the nitriding material in the high-end field; when the high-temperature nitriding material is burned at the same time, the temperature difference in the hearth is large, and the fireproof material is easy to deform, so that the hearth is damaged; meanwhile, the nitrogen gas is introduced into the hearth through the pipeline, so that the airflow in the hearth is disturbed, the nitriding effect of the nitriding material is poor, the nitriding degree of the product is uneven, and unqualified products and waste products of the nitrided product are easily caused.
Disclosure of Invention
The invention aims to provide a high-temperature vacuum nitriding furnace for efficiently producing nitriding materials and a manufacturing method thereof, which aim at the problems that the material heating, nitriding, sintering heat preservation, cooling, discharging and charging of the traditional nitriding furnace are all completed in a hearth, the nitriding reaction period is long (4-5 days), the production efficiency is low, and continuous production cannot be realized; the furnace body structure has low compressive strength, poor sealing performance and insufficient vacuum degree, and when residual oxygen exists in a hearth and leads to high-temperature nitriding reaction, metal fine powder easy to oxidize is easy to oxidize and leads to insufficient quality of nitriding products; the requirements of producing high-end nitrided products with high nitriding temperature and nitriding pressure cannot be met; the gas combustion process can produce a large amount of harmful gases such as carbon dioxide, nitride, metal gas and the like, and dust has serious pollution to the atmospheric environment, and the environmental protection treatment investment of the production process is large. The high-temperature flame generated by the fuel gas scours and erodes the surface of the nitriding product, so that the surface of the nitriding material is locally sintered, the infiltration reaction of nitrogen is influenced, the nitriding effect is caused, and the quality of the nitriding product is influenced; meanwhile, nitrogen flows into the hearth at a high speed through the pipeline, turbulence generated by mixing of the nitrogen and the fuel gas can lead to uneven distribution of the air flows at the near end and the far end of the nitrogen air inlet in the hearth, so that the nitriding quality of the nitrided product is uneven, and even defects such as waste products are generated, and the optimization and improvement are carried out.
The aim of the invention can be achieved by the following technical scheme:
the utility model provides a high temperature vacuum nitriding furnace of high efficiency production nitriding material, includes the vacuum nitriding furnace body, the inside of vacuum nitriding furnace body is provided with two inclosed furnace, and a furnace preheats the intensification, and a furnace realizes high temperature nitriding reaction and burns, adopts heat pump and heat exchanger to connect between the two inclosed furnace, and the waste heat utilization is realized to the heat-up furnace that preheats to the hot air displacement that will nitridize exothermic reaction produce, sets up three group and total 54 silicon molybdenum heating rod groups in every furnace, four faces in the control furnace evenly heat, and the difference in temperature is less than or equal to 5 ℃, has all placed the platform truck in every inclosed furnace, still be provided with air inlet system in the airtight, all install nitrogen gas inlet control pipeline on every inclosed furnace.
As a further scheme of the invention: the double-closed hearth shell adopts 18-20 mm Q345B high-temperature resistant steel plate double-sided argon arc welding, and the vacuum degree in the kiln reaches more than-0.05 MPa.
As a further scheme of the invention: the air inlet system is an air chamber cavity consisting of 5000 multiplied by 300 multiplied by 1200 mm, wherein the air chamber cavity consists of an outer layer heat-insulating light brick and an inner layer sealing loading sagger, the heat-insulating light brick and the sealing loading sagger form a nitrogen air chamber, the upper end and the lower end of the sealing loading sagger are respectively provided with a bottom air inlet and a heat exchange bottom air inlet, and both sides of the heat-insulating light brick are respectively provided with a side air inlet.
As a further scheme of the invention: the sealed loading sagger is an integral close-joint sagger made of a silicon nitride plate with the thickness of 30 mm, which is formed by high-temperature stable phase beta-Si 3N4 slurry and stainless steel short fibers through high-temperature firing at 1600 ℃.
As a further scheme of the invention: the sealed loading sagger is provided with the micro air holes which are dispersed and uniformly distributed, so that the uniform introduction of nitrogen is facilitated.
A manufacturing method of a high-temperature vacuum nitriding furnace for efficiently producing nitriding materials comprises the following steps:
e. starting an electric heating system, heating the furnace temperature to 900-1000 ℃ of the initial nitriding reaction temperature, stopping heating, and preserving the heat for 8 hours; nitrogen enters the air chamber, and enters the hearth through micro air holes uniformly dispersed on the sagger to perform gas-solid nitriding reaction with the materials; the pressure in the hearth is reduced due to the nitriding reaction, the opening of the unidirectional nitrogen inlet control electromagnetic valve is automatically increased, and the nitrogen flow is changed from 60m 3 The rate of the reaction per hour is increased to 80m 3 And/h, constantly keeping the pressure required by the nitriding reaction of the hearth at 0.02MPa;
f. stopping heating when the heat preservation is finished and the temperature is raised to 1250 ℃ again, and preserving the heat for 24 hours; when the temperature in the furnace is increased due to the fact that a great amount of heat is continuously generated in the gas-solid violent nitriding reaction process in the furnace, materials are possibly molten, and under the condition of preventing nitriding reaction, a heat pump is started to pump high-temperature hot gas in the furnace to a heat exchanger to be led into another furnace for preheating and heating the materials, and the pumping quantity of the high-temperature hot gas is controlled to stabilize that the nitriding reaction temperature in the furnace does not continuously rise to 1250 ℃; flow of nitrogenFrom 80m 3 The height of the reactor/h is adjusted to 90m 3 And/h, controlling the pressure at 0.05MPa;
g. after the nitriding sintering reaction is finished, stopping heating to perform a heat preservation and cooling stage, switching the electric heating temperature control system to another preheating hearth, and heating to the nitriding reaction temperature to perform the nitriding sintering reaction;
h. when the nitriding sintering reaction in the first hearth is completed, after cooling to 600 ℃, opening a furnace door and pushing out the trolley; pushing the trolley with the newly loaded materials into a hearth again, sealing the furnace door, vacuumizing, filling nitrogen, and pumping high-temperature hot gas in the hearth with the second nitriding reaction to the charging hearth through a heat pump and a heat exchanger to preheat the materials; after the nitriding sintering reaction of the second hearth is finished, switching an electrothermal temperature control system to heat the preheated hearth material to the nitriding reaction temperature until the nitriding sintering reaction is finished; and (3) carrying out nitriding sintering reaction production in a circulating way in the two hearths.
The invention has the beneficial effects that:
the high-temperature vacuum nitriding furnace is a double-closed hearth, the kiln shell is welded by adopting an 18-20 mm Q345B high-temperature resistant steel plate double-sided argon arc, and the vacuum degree in the kiln can reach more than-0.05 MPa; the double-closed hearth can realize preheating and heating of one hearth and high-temperature nitriding and sintering of one hearth. The double closed hearths are connected by adopting a vacuum pump and a heat exchanger, and high-temperature hot air generated by nitriding exothermic reaction can be replaced to the preheating and heating hearths to realize waste heat utilization so as to improve the heat utilization rate. Meanwhile, compared with the traditional natural gas heating mode, the silicon controlled electric heating mode is adopted, the heating temperature is more stable, the quality of the nitriding calcined product is excellent, the surface is free from pollution, and the exhaust gas and dust emission is greatly reduced. The nitrogen ventilation mode adopts a silicon nitride slit type dispersion ventilation mode, so that the upper surface, the lower surface, the left surface and the right surface of a nitrided product are uniformly contacted with nitrogen, the nitriding efficiency is improved by 30%, the quality qualification rate of the nitrided product is up to more than 98%, the energy utilization rate is improved to more than 85%, the yield of a single kiln is improved by 50%, and the production cost of a nitrided material is reduced by 25%. The production varieties of the nitriding materials cover varieties from low-end, low-temperature silicon nitride, silicon manganese nitride, manganese nitride to high-end, high-temperature titanium nitride, vanadium nitride, niobium nitride, aluminum nitride and the like.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a schematic view of the internal structure of a high temperature vacuum nitriding furnace according to the present invention;
fig. 2 is a schematic view of the internal structure of the air intake system of the present invention.
In the figure: 1. a vacuum nitriding furnace body; 2. a furnace; 3. sealing the loading sagger; 4. a silicon molybdenum heating rod group; 5. a nitrogen inlet control pipeline; 6. a trolley; 7. a heat pump and a heat exchanger; 8. heat-insulating light brick; 9. a bottom air inlet; 10. a heat exchange bottom air port; 11. a side inlet; 12. a nitrogen chamber.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Referring to fig. 1-2, the invention discloses a high-temperature vacuum nitriding furnace for producing nitriding materials with high efficiency, which comprises a vacuum nitriding furnace body 1, wherein a double-closed hearth 2 is arranged in the vacuum nitriding furnace body 1, one hearth is preheated and heated, the other hearth is sintered for high-temperature nitriding reaction, the double-closed hearths 2 are connected by a heat pump and a heat exchanger 7, high-temperature hot air generated by nitriding exothermic reaction is replaced to the preheated and heated hearths for waste heat utilization, three groups of 54 silicon-molybdenum heating rod groups 4 are arranged in each hearth 2, four surfaces in the hearths are controlled to be heated uniformly, the temperature difference is less than or equal to 5 ℃, a trolley 6 is arranged in each closed hearth 2, an air inlet system is also arranged in each closed hearth 2, and a nitrogen air inlet control pipeline 5 is arranged on each closed hearth 2.
The double-closed hearth 2 shell adopts 18-20 mm Q345B high-temperature resistant steel plate double-sided argon arc welding, and the vacuum degree in the kiln reaches more than-0.05 MPa.
The air inlet system is an air chamber cavity consisting of 5000 multiplied by 300 multiplied by 1200 mm, which is formed by an outer layer heat-insulating light brick 8 and an inner layer sealing loading sagger 3, the heat-insulating light brick 8 and the sealing loading sagger 3 form a nitrogen air chamber 12, the upper end and the lower end of the sealing loading sagger 3 are respectively provided with a bottom air inlet 9 and a heat exchange bottom air inlet 10, and both sides of the heat-insulating light brick 8 are respectively provided with a side air inlet 11.
The sealed loading sagger 3 is an integral close-joint sagger made of a silicon nitride plate with the thickness of 30 mm, which is formed by high-temperature stable phase beta-Si 3N4 slurry and stainless steel short fibers through high-temperature firing at 1600 ℃.
The sealing loading sagger 3 is provided with micro air holes which are dispersed and uniformly distributed, so that nitrogen can be uniformly introduced.
Example 2
Referring to fig. 1-2, a method for manufacturing a high temperature vacuum nitriding furnace for efficiently producing nitrided materials includes the steps of:
a. the high-temperature vacuum nitriding furnace is designed for a double-closed hearth and a double-trolley. One hearth is preheated and heated, and the other hearth is sintered by high-temperature nitriding reaction. The double closed hearths are connected by adopting a heat pump and a heat exchanger, and high-temperature hot air generated by nitriding exothermic reaction can be replaced to the preheating and heating hearths to realize waste heat utilization so as to improve the heat utilization rate and the production efficiency.
b. The double-closed hearth shell adopts 18-20 mm Q345B high-temperature resistant steel plate double-sided argon arc welding, and the vacuum degree in the kiln can reach more than-0.05 MPa.
c. By adopting an electric heating mode controlled by a silicon controlled rectifier, three groups of 54 silicon-molybdenum heating rods are arranged in each hearth, four surfaces in the hearth can be controlled to be heated uniformly, and the temperature difference is less than or equal to 5 ℃.
d. The air inlet system is an air chamber cavity consisting of 5000 multiplied by 300 multiplied by 1200 mm and consisting of an outer layer heat-insulating light brick and an inner layer sealing loading sagger. The inner layer sealing loading sagger adopts high-temperature stable phase beta-Si 3N4 slurry and stainless steel short fibers, and is sintered at 1600 ℃ to form the integral close joint sagger made of the silicon nitride plate with the thickness of 30 mm. The sagger is provided with the micro air holes which are dispersed and uniformly distributed, which is beneficial to the uniform introduction of nitrogen and improves the nitriding efficiency and the product quality of nitrided products.
e. Starting an electric heating system, heating the furnace temperature to 900-1000 ℃ of the initial nitriding reaction temperature, stopping heating, and preserving the heat for 8 hours; nitrogen enters the air chamber, and enters the hearth through micro air holes uniformly dispersed on the sagger to perform gas-solid nitriding reaction with the materials; the pressure in the hearth is reduced due to the nitriding reaction, the opening of the unidirectional nitrogen inlet control electromagnetic valve is automatically increased, and the nitrogen flow is changed from 60m 3 The rate of the reaction per hour is increased to 80m 3 And/h, constantly keeping the pressure required by the nitriding reaction of the hearth at 0.02MPa;
f. stopping heating when the heat preservation is finished and the temperature is raised to 1250 ℃ again, and preserving the heat for 24 hours; when the temperature in the furnace is increased due to the fact that a great amount of heat is continuously generated in the gas-solid violent nitriding reaction process in the furnace, materials are possibly molten, and under the condition of preventing nitriding reaction, a heat pump is started to pump high-temperature hot gas in the furnace to a heat exchanger to be led into another furnace for preheating and heating the materials, and the pumping quantity of the high-temperature hot gas is controlled to stabilize that the nitriding reaction temperature in the furnace does not continuously rise to 1250 ℃; the nitrogen flow is changed from 80m 3 The height of the reactor/h is adjusted to 90m 3 And/h, controlling the pressure at 0.05MPa;
g. after the nitriding sintering reaction is finished, stopping heating to perform a heat preservation and cooling stage, switching the electric heating temperature control system to another preheating hearth, and heating to the nitriding reaction temperature to perform the nitriding sintering reaction;
h. when the nitriding sintering reaction in the first hearth is completed, after cooling to 600 ℃, opening a furnace door and pushing out the trolley; pushing the trolley with the newly loaded materials into a hearth again, sealing the furnace door, vacuumizing, filling nitrogen, and pumping high-temperature hot gas in the hearth with the second nitriding reaction to the charging hearth through a heat pump and a heat exchanger to preheat the materials; after the nitriding sintering reaction of the second hearth is finished, switching an electrothermal temperature control system to heat the preheated hearth material to the nitriding reaction temperature until the nitriding sintering reaction is finished; and (3) carrying out nitriding sintering reaction production in a circulating way in the two hearths.
Main nitride product technical index
The foregoing describes one embodiment of the present invention in detail, but the description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent changes and modifications within the scope of the present invention are intended to be covered by the present invention.
Claims (6)
1. The utility model provides a high temperature vacuum nitriding furnace of high efficiency production nitriding material, its characterized in that, including vacuum nitriding furnace body (1), the inside of vacuum nitriding furnace body (1) is provided with double containment furnace (2), and a furnace preheats and heaies up, and a furnace realizes high temperature nitriding reaction and burns, adopts heat pump and heat exchanger (7) to connect between double containment furnace (2), and the waste heat utilization is realized to the heat exchange of the high temperature hot gas that will nitridize exothermic reaction produced to preheating the heating furnace, sets up three group and total 54 silicon molybdenum heating rod group (4) in every furnace (2), four faces in the control furnace evenly heat, and the difference in temperature is less than or equal to 5 ℃, has all placed platform truck (6) in every confined furnace (2), still be provided with air intake system in the seal, all install nitrogen gas inlet control pipeline (5) on every confined furnace (2).
2. The high-temperature vacuum nitriding furnace for efficiently producing nitrided materials according to claim 1, wherein the outer shell of the double-closed hearth (2) is welded by adopting 18-20 mm Q345B high-temperature resistant steel plates through double-sided argon arc, and the vacuum degree in a furnace kiln reaches more than-0.05 MPa.
3. The high-temperature vacuum nitriding furnace for efficiently producing nitrided materials according to claim 1, wherein the air inlet system is an air chamber cavity consisting of 5000 x 300 x 1200 mm formed by an outer layer heat-insulating light brick (8) and an inner layer sealing loading sagger (3), the heat-insulating light brick (8) and the sealing loading sagger (3) form a nitrogen air chamber (12), the upper end and the lower end of the sealing loading sagger (3) are respectively provided with a bottom air inlet (9) and a heat exchange bottom air port (10), and both sides of the heat-insulating light brick (8) are respectively provided with side air inlets (11).
4. A high-temperature vacuum nitriding furnace for producing nitrided materials with high efficiency according to claim 3, characterized in that the sealing loading sagger (3) is an integral tight joint sagger made of a silicon nitride plate with thickness of 30 mm and formed by high-temperature firing at 1600 ℃ by adopting high-temperature stable phase beta-Si 3N4 slurry and stainless steel short fibers.
5. A high temperature vacuum nitriding furnace for producing nitrided materials with high efficiency according to claim 3, characterized in that said sealed loading sagger (3) is provided with micro ventilation holes distributed uniformly and dispersed, which is advantageous for the uniform introduction of nitrogen.
6. The manufacturing method of the high-temperature vacuum nitriding furnace for efficiently producing the nitriding material is characterized by comprising the following steps of:
e. starting an electric heating system, heating the furnace temperature to 900-1000 ℃ of the initial nitriding reaction temperature, stopping heating, and preserving the heat for 8 hours; nitrogen enters the air chamber, and enters the hearth through micro air holes uniformly dispersed on the sagger to perform gas-solid nitriding reaction with the materials; the pressure in the hearth is reduced due to the nitriding reaction, the opening of the unidirectional nitrogen inlet control electromagnetic valve is automatically increased, and the nitrogen flow is changed from 60m 3 The rate of the reaction per hour is increased to 80m 3 And/h, constantly keeping the pressure required by the nitriding reaction of the hearth at 0.02MPa;
f. stopping heating when the heat preservation is finished and the temperature is raised to 1250 ℃ again, and preserving the heat for 24 hours; when the temperature in the furnace is increased due to the fact that a great amount of heat is continuously generated in the gas-solid violent nitriding reaction process in the furnace, materials are possibly molten, and under the condition of preventing nitriding reaction, a heat pump is started to pump high-temperature hot gas in the furnace to a heat exchanger to be led into another furnace for preheating and heating the materials, and the pumping quantity of the high-temperature hot gas is controlled to stabilize that the nitriding reaction temperature in the furnace does not continuously rise to 1250 ℃; the nitrogen flow is changed from 80m 3 The height of the reactor/h is adjusted to 90m 3 And/h, controlling the pressure at 0.05MPa;
g. after the nitriding sintering reaction is finished, stopping heating to perform a heat preservation and cooling stage, switching the electric heating temperature control system to another preheating hearth, and heating to the nitriding reaction temperature to perform the nitriding sintering reaction;
h. when the nitriding sintering reaction in the first hearth is completed, after cooling to 600 ℃, opening a furnace door and pushing out the trolley; pushing the trolley with the newly loaded materials into a hearth again, sealing the furnace door, vacuumizing, filling nitrogen, and pumping high-temperature hot gas in the hearth with the second nitriding reaction to the charging hearth through a heat pump and a heat exchanger to preheat the materials; after the nitriding sintering reaction of the second hearth is finished, switching an electrothermal temperature control system to heat the preheated hearth material to the nitriding reaction temperature until the nitriding sintering reaction is finished; and (3) carrying out nitriding sintering reaction production in a circulating way in the two hearths.
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