Continuous furnace for acid mist treatment of MIM products

Abstract

The utility model relates to a kind of continuous furnace for MIM product acid mist treatment, including furnace body, material conveying belt, nitric acid supply system, acid mist generating device and gas circulating device. Its innovation point mainly is at: the acid mist generating device is independently set on the upper portion outside furnace body;The nitric acid supply system includes the nitric acid storage tank and metering pump for real-time monitoring liquid level by weighing device, nitric acid storage tank high position is set, liquid is supplied to the metering pump located below it by gravity, accurate metering and stable delivery are realized;The gas circulating device is provided with multiple along the extension direction of furnace body, ensure that acid mist is evenly distributed in furnace cavity.The utility model optimizes acid mist generation, conveying and distribution mode, effectively improves the stability and uniformity of acid mist treatment process, meets the high-precision, high-efficiency requirement of MIM product to acid treatment.

Description

Technical Field

[0001] This utility model relates to a continuous furnace for acid mist treatment of MIM products. Background Technology

[0002] During the production of metal injection molded (MIM) products, acid mist treatment is typically required to passivate, clean, or activate the surface, thereby improving the product's corrosion resistance, aesthetics, or adhesion to subsequent coatings. However, existing continuous furnace acid mist treatment systems for MIM products have significant technical defects, resulting in a product qualification rate generally below 90% and poor surface smoothness, which severely impacts the delivery and production capacity of high-end products.

[0003] Specifically, the shortcomings and deficiencies of existing technologies are mainly reflected in the following aspects: First, the acid treatment on parts is uneven. In traditional acid mist treatment processes, due to unreasonable acid mist distribution and equipment structure, the acid etching effect on parts inside the furnace is uneven. Especially in continuous furnaces, acid mist often enters from only one direction or lacks effective circulation, resulting in some areas of the parts being over-etched while others are under-etched, which seriously affects the consistency of the surface quality and performance of the parts.

[0004] Secondly, there is uneven acid density release. This stems directly from the inherent limitations of existing acid mist generation and delivery systems. Existing systems struggle to ensure uniform acid mist distribution throughout the processing space, resulting in excessively high acid density near the mist source and excessively low acid density in areas farther away. This leads to significant differences in the degree of acid treatment received by parts at different spatial locations, failing to meet the stringent uniformity requirements of high-precision MIM products.

[0005] Ultimately, these issues directly lead to poor surface uniformity of the parts. The combined effects of uneven acid distribution and acid density fluctuations make it impossible to guarantee the surface quality of the treated product. This not only affects the product's appearance but, in applications with extremely high surface performance requirements (such as medical devices and precision electronic components), it can severely impair the product's performance and reliability.

[0006] The root causes, besides the distribution problem, are that the existing system also has drawbacks in terms of stable acid mist generation and precise delivery: traditional acid supply systems have inaccurate metering, fluctuating delivery pressure, and untimely monitoring of nitric acid storage tank levels, which can easily lead to unstable acid mist concentration or even production interruption; at the same time, acid mist generation devices are mostly integrated inside the furnace, making maintenance inconvenient, and the high-temperature environment inside the furnace may also interfere with the stability of acid mist generation.

[0007] Therefore, there is an urgent need in this field for a continuous furnace that can fundamentally solve the problem of acid mist distribution uniformity and achieve stable acid mist generation and precise delivery, thereby significantly improving the pass rate and surface quality of MIM products. Utility Model Content

[0008] The purpose of this invention is to provide a continuous furnace for acid mist treatment of MIM products. By optimizing the generation, conveying and distribution of acid mist, it effectively improves the stability and uniformity of the acid mist treatment process, thus meeting the high precision and high efficiency requirements of MIM products for acid treatment.

[0009] The technical solution to achieve the purpose of this utility model is as follows: This utility model has a furnace body, a material conveyor belt, a nitric acid supply system, an acid mist generating device, and a gas circulation device; the furnace body includes a furnace cavity formed by enclosure; the material conveyor belt is used to continuously transport materials through the furnace cavity; the acid mist generating device is used to vaporize liquid nitric acid into acid mist; the gas circulation device is used to introduce the acid mist from the acid mist generating device into the furnace cavity and distribute the acid mist evenly; characterized in that: the acid mist generating device is located outside the furnace body and above the furnace body; the acid mist generating device is used to transport acid mist to the interlayer; the nitric acid supply system includes a nitric acid storage tank, a metering pump, and a weighing device; the nitric acid storage tank is set with... The weighing platform of the weighing device is located on the main control panel. The weighing device is used to monitor the weight change of nitric acid in the nitric acid storage tank in real time and transmit the data to the control unit on the main control panel. The nitric acid storage tank is connected to the suction end of the metering pump. The metering pump is located below the nitric acid storage tank, and the nitric acid in the nitric acid storage tank enters the suction end of the metering pump under the action of gravity. The pump outlet of the metering pump is connected to the inlet end of the acid mist generating device. The pump outlet of the metering pump is located on one side of the inlet end of the acid mist generating device. The metering pump is electrically connected to the control unit. Multiple gas circulation devices are provided along the extension direction of the furnace body. The gas circulation devices are electrically connected to the control unit.

[0010] Furthermore, the aforementioned main control panel is equipped with a nitric acid storage chamber that is higher than the ground; the nitric acid storage chamber is equipped with a safety door; a sliding frame is slidably mounted on the nitric acid storage chamber; the weighing platform is fixedly installed on the sliding frame; the nitric acid storage tank can slide out of the nitric acid storage chamber from the safety door along with the weighing platform via the sliding frame.

[0011] Furthermore, it also includes a protective gas input mechanism; the protective gas input mechanism includes a nitrogen heating chamber, a nitrogen heating device, a nitrogen inlet pipe, a nitrogen outlet pipe, and a nitrogen distribution pipe assembly; the nitrogen inlet pipe is connected to the inlet end of the nitrogen heating chamber; the nitrogen heating device is installed in the nitrogen heating chamber and is used to heat the nitrogen entering the nitrogen heating chamber; one end of the nitrogen outlet pipe is connected to the outlet end of the nitrogen heating chamber, and the other end is connected to the nitrogen distribution pipe assembly; the nitrogen distribution pipe assembly is arranged inside the furnace cavity; the nitrogen distribution pipe assembly consists of multiple parallel single pipes that converge to the nitrogen outlet pipe, or a coil arranged in a circuitous manner; nitrogen outlet holes are evenly distributed on the single pipes or coils; the nitrogen heating device is electrically connected to the control unit.

[0012] Furthermore, the aforementioned acid mist generating device includes a nitric acid vaporization chamber, a heating coil, a nitric acid nozzle, and an acid mist outlet; the heating coil is disposed within the nitric acid vaporization chamber and is used to heat liquid nitric acid to vaporize it; the nitric acid nozzle is fixedly disposed within the nitric acid vaporization chamber and is used to spray nitric acid into the nitric acid vaporization chamber; the nitric acid nozzle is connected to the pump outlet of the metering pump via a pipeline; the acid mist outlet is connected to the main insulation pipeline; the main insulation pipeline extends along the extension direction of the furnace body; multiple branch insulation pipelines are connected to the main insulation pipeline; the branch insulation pipelines are connected to the circulation pipeline of the gas exchanger.

[0013] Furthermore, the aforementioned gas circulation device includes an acid-resistant centrifugal fan, a first circulating insulation pipe, and a second circulating insulation pipe; the furnace body is divided into multiple processing zones along its extension direction; each processing zone is equipped with a corresponding gas circulation device; multiple interlayers are symmetrically arranged on both sides of each processing zone along the extension direction of the furnace body; the first circulating insulation pipe is located on one side of the furnace body along its extension direction; the second circulating insulation pipe is located on the other side of the furnace body along its extension direction; multiple circulating insulation branch pipes are connected to both the first and second circulating insulation pipes; each branch pipe on the first and second circulating insulation pipes is connected to a corresponding interlayer on the side of the corresponding processing zone; the interlayers are connected to the furnace cavity through a group of air distribution holes; the first circulating insulation pipe is connected to the outlet of the acid-resistant centrifugal fan; the second circulating insulation pipe is connected to the inlet of the acid-resistant centrifugal fan; the acid mist outlet of the acid mist generating device is connected to the second circulating insulation pipe of the gas circulation device in the processing zone closest to the feed end of the furnace body.

[0014] Furthermore, the aforementioned acid mist generating device is equipped with two independent nitric acid vaporization chambers; each of the two nitric acid vaporization chambers is equipped with a heating coil; each nitric acid vaporization chamber is equipped with a nitric acid nozzle; the two nitric acid nozzles are connected to the pump outlet of the metering pump via an acid inlet pipe; each acid inlet pipe is equipped with a control valve; each nitric acid vaporization chamber is equipped with an acid mist outlet, and each acid mist outlet is connected to the second circulating insulation pipe of the gas circulation device in the processing area closest to the furnace body.

[0015] Furthermore, the aforementioned nitric acid spray head is evenly distributed with multiple acid spray holes; the diameter of each acid spray hole is 0.5 mm, and 50 acid spray holes are distributed per square centimeter.

[0016] Furthermore, the aforementioned nitrogen gas distribution pipe assembly is arranged above the furnace cavity.

[0017] This utility model has the following positive effects: (1) This utility model raises the nitric acid storage tank and places it above the metering pump, using gravity to supply liquid to the pump, effectively preventing the "gas binding" phenomenon of the pump, ensuring stable and continuous liquid supply, and laying the foundation for accurate metering. At the same time, the consumption of nitric acid is monitored in real time by the weighing device, which can accurately determine the remaining liquid level, realize timely replenishment, avoid production interruption, and at the same time, the data is fed back to the control system, which helps to optimize the process and manage quality. Furthermore, this utility model sets up multiple gas circulation devices along the length of the furnace, which can independently control the circulation and distribution of acid mist for different processing sections, solve the concentration gradient problem that is easy to occur in the long furnace cavity, and ensure the uniformity of acid mist in the entire processing space.

[0018] (2) This utility model is equipped with a dedicated nitric acid storage chamber and a slide structure, which realizes the safe and sealed storage of nitric acid and allows the storage tank to be easily moved out for replacement or maintenance, thereby improving the safety and convenience of operation.

[0019] (3) This utility model introduces an independent protective gas (nitrogen) system and introduces heated nitrogen into the furnace cavity, which can form a protective atmosphere to prevent the workpiece from oxidizing, and can also use the airflow to promote the uniformity of the atmosphere in the furnace. At the same time, it avoids unnecessary side reactions between acid mist and oxygen, ensuring the purity and stability of the treatment effect.

[0020] (4) This utility model clarifies the specific structure of the acid mist generation device, which directly vaporizes nitric acid through a heating coil, resulting in high efficiency. The acid mist is transported to each gas circulation device by using insulated main pipes and branch pipes, which effectively prevents the acid mist from being lost due to condensation during long-distance transportation and ensures that the acid mist enters the treatment area in gaseous form.

[0021] (5) This utility model uses an acid-resistant centrifugal fan to force the acid mist to circulate between the two sides of the specific treatment area, and then it penetrates evenly into the furnace cavity through the air distribution holes, forming a highly efficient, forced circulation uniform distribution system, which greatly improves the utilization rate and treatment uniformity of acid mist.

[0022] (6) This utility model is equipped with two independent nitric acid vaporization chambers, forming a redundant backup system. When one chamber fails, it can be immediately switched to the other to ensure the continuity of production. It is especially suitable for continuous production lines that cannot be shut down, and greatly improves the reliability and availability of the equipment.

[0023] (7) This utility model specifies the nozzle size and distribution density of the nitric acid nozzle. The micron-sized pores and high density distribution can atomize nitric acid into extremely fine droplets, thereby greatly increasing the contact area between the nitric acid and the heating surface, achieving instantaneous and complete vaporization, and generating stable and fine acid mist.

[0024] (8) The present invention arranges the nitrogen gas distribution pipe above the furnace cavity, which conforms to the physical characteristics of hot nitrogen rising, which is conducive to the protection gas quickly filling the entire upper space of the furnace cavity and replacing it from top to bottom, forming a more effective protective atmosphere. Attached Figure Description

[0025] To make the content of this utility model easier to understand, the present utility model will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 This is a schematic diagram of the installation of the main control console in this utility model; Figure 3 This is a schematic diagram of the nitric acid supply system in this utility model; Figure 4 This is a schematic diagram of the acid mist generating device in this utility model; Figure 5 This is a schematic diagram of the protective gas input mechanism in this utility model; Figure 6 This is a schematic diagram of the nitrogen gas distribution pipe assembly in this utility model; Figure 7 This is a schematic diagram of the gas circulation device in this utility model.

[0026] In the diagram, the components are: furnace body 1, material conveyor belt 2, nitric acid supply system 3, acid mist generating device 4, gas circulation device 5, protective gas input mechanism 6, main control console 7, furnace cavity 101, interlayer 102, nitric acid storage tank 301, metering pump 302, weighing device 303, nitric acid vaporization chamber 401, heating coil 402, acid mist outlet 403, acid-resistant centrifugal fan 501, first circulating insulation pipe 502, second circulating insulation pipe 503, circulating insulation branch pipe 504, nitrogen heating chamber 601, nitrogen heating device 602, nitrogen inlet pipe 603, nitrogen outlet main pipe 604, nitrogen distribution pipe assembly 605, control unit 701, nitric acid storage chamber 702, safety door 703, and carriage 704. Detailed Implementation

[0027] See Figures 1 to 7 This utility model includes a furnace body 1, a material conveyor belt 2, a nitric acid supply system 3, an acid mist generating device 4, a gas circulation device 5, and a protective gas input mechanism 6.

[0028] The furnace body 1 has an internal enclosure forming a furnace cavity 101 for acid mist treatment. The material conveyor belt 2 passes through the furnace cavity 101 and carries and continuously transports MIM materials through the entire treatment area.

[0029] The nitric acid supply system 3 is one of the key components of this invention to achieve a stable liquid supply. The system includes a nitric acid storage tank 301, a metering pump 302, and a weighing device 303.

[0030] The nitric acid storage tank 301 is placed on a weighing platform, which is fixed to the main control console 7. A weighing device 303 (such as a high-precision load cell) monitors the total weight of the nitric acid storage tank 301 and its contents in real time and transmits the data to the control unit 701 within the main control console 7. Through weight changes, the system can accurately monitor the rate of nitric acid consumption and the remaining amount, enabling low-level warnings and automatic replenishment prompts, ensuring continuous production.

[0031] To ensure safe and convenient operation, the main control panel 7 is equipped with a nitric acid storage chamber 702 raised above the ground, which features a safety door 703. A slide 704 is installed inside the nitric acid storage chamber 702, and a weighing platform is fixed to the slide 704. When it is necessary to replace or maintain the nitric acid storage tank 301, the operator can open the safety door 703 and easily pull out the entire nitric acid storage tank 301 via the slide 704, greatly improving operational safety and efficiency. In this embodiment, the height of the nitric acid storage tank is raised from the ground to a height of 2 meters.

[0032] The metering pump 302 (preferably a corrosion-resistant mechanical diaphragm pump) is located below the nitric acid storage tank 301. The outlet of the nitric acid storage tank 301 is connected to the suction end of the metering pump 302 via a pipe. This "high-level tank + low-level pump" layout allows nitric acid to flow naturally into the pump body under its own gravity, effectively avoiding the "air binding" phenomenon of the pump and ensuring absolute stability of the liquid supply. The pump outlet of the metering pump 302 is connected to the acid mist generating device 4 via a pipeline, and its pumping flow rate is precisely controlled by the control unit 701. At the same time, the length of the pipeline connecting the pump outlet of the metering pump 302 to the acid mist generating device is greatly reduced. In this embodiment, the original 2-meter pipeline is shortened to 0.3 meters. This can effectively reduce the pressure loss of acid liquid and the diffusion loss of acid mist during the transportation process, so that the acid liquid can reach the nozzle position more quickly and stably, improving the efficiency and stability of acid mist generation.

[0033] Under the influence of gravity, liquid nitric acid typically flows through a Y-type coarse filter and enters the suction end of metering pump 302. Metering pump 302 is the core component, usually employing a mechanical or hydraulic diaphragm type. Its working principle involves a motor converting rotary motion into the reciprocating linear motion of a plunger via a worm gear or eccentric mechanism. The plunger pushes hydraulic oil, which in turn pushes a metal or PTFE diaphragm, causing elastic deformation. The reciprocating motion of the diaphragm periodically changes the volume of the pump head cavity, thus achieving liquid suction and discharge. The diaphragm completely isolates the corrosive nitric acid from the pump's mechanical transmission components, which is crucial for the delivery of nitric acid.

[0034] The acid mist generating device 4 is independently installed on the outside of the furnace body 1. This independent external design facilitates inspection and maintenance, while also preventing the high temperature of the furnace body from interfering with the precision vaporization process.

[0035] The acid mist generating device 4 includes at least one nitric acid vaporization chamber 401, inside which a heating coil 402 (which can be electrically or steam-heated) is installed. A nitric acid nozzle is fixed to the top of the vaporization chamber, and this nozzle is connected to the outlet of a metering pump 302 via a pipe. The nitric acid nozzle has a large number of micropores evenly distributed on it. In a preferred embodiment, the diameter of the spray holes is 0.5 mm, and the distribution density is 50 holes per square centimeter. This fine design atomizes nitric acid into extremely fine droplets, allowing them to fully and rapidly contact the heating coil 402 after falling into the nitric acid vaporization chamber 401, thus achieving instantaneous and complete vaporization. Although the specific structure of the nitric acid nozzle is not shown in the accompanying drawings, it is essentially a modification of an existing nitric acid nozzle (with a single hole on a single plate, which is the spray nozzle) to one with multiple spray holes on a single plate. Those skilled in the art can clearly understand its structure from the above description.

[0036] The vaporized nitric acid vapor is discharged from the acid mist outlet 403 at the top of the nitric acid vaporization chamber 401. To ensure that the acid mist does not condense during transportation, the acid mist outlet 403 is connected to an insulated main pipe 8. The main insulated main pipe 8 is arranged along the extension direction of the furnace body 1 and is connected to multiple insulated branch pipes 801 to distribute the acid mist to each gas circulation device 5.

[0037] To further improve system reliability, as a preferred embodiment, the acid mist generating device 4 can be equipped with two independent nitric acid vaporization chambers 401. Each nitric acid vaporization chamber 401 is equipped with an independent heating coil 402, nitric acid nozzle, and acid mist outlet 403. The inlet pipes of the two nitric acid nozzles are connected to the metering pump 302 after merging, and a control valve is installed on each branch. Both acid mist outlets 403 are connected to the downstream system. This dual-system design constitutes a redundant mode of one in use and one on standby or alternating use. When one system needs maintenance or fails, it can be immediately switched to the other, ensuring seamless and continuous production operation.

[0038] To achieve the most uniform distribution of acid mist within the furnace cavity, this invention employs a zoned circulation design.

[0039] Along the extension direction of the furnace body 1, the furnace cavity 101 is divided into multiple processing zones. Each processing zone is equipped with an independent gas circulation device 5.

[0040] Each gas circulation device 5 includes an acid-resistant centrifugal fan 501, a first circulation insulated pipe 502, and a second circulation insulated pipe 503. Multiple interlayers 102 are symmetrically arranged inside the furnace wall on both sides along the furnace body direction in each processing zone. The interlayers 102 are connected to the furnace cavity 101 through a uniformly distributed group of gas distribution holes.

[0041] The first circulating insulation pipe 502 is located on one side of the furnace body 1 and is connected to the air outlet of the acid-resistant centrifugal fan 501; the second circulating insulation pipe 503 is located on the other side of the furnace body 1 and is connected to the air inlet of the acid-resistant centrifugal fan 501. Multiple circulating insulation branch pipes 504 are connected to both the first circulating insulation pipe 502 and the second circulating insulation pipe 503, and each circulating insulation branch pipe 504 is connected to a corresponding interlayer 102 on its side.

[0042] Acid mist from acid mist generating device 4 is introduced into the second circulating insulated pipe 503 of the processing zone closest to the furnace feed end through insulated branch pipe 801. During operation, acid-resistant centrifugal fan 501 starts, "drawing" gas (containing newly replenished acid mist) from the furnace cavity through the second circulating pipe 503 and jacket 102 on one side, then "pressing" it into the first circulating pipe 502 and jacket 102 on the other side, and then spraying it into the furnace cavity 101 at a uniform speed through the air distribution hole group. In this way, a circulating airflow loop is formed within each processing zone, allowing the acid mist to fully and uniformly contact the workpiece, completely eliminating the concentration gradient caused by traditional unidirectional air supply.

[0043] To create an inert atmosphere environment, prevent workpiece oxidation, and help the atmosphere to be uniform, this utility model is equipped with a protective gas input mechanism 6.

[0044] The mechanism includes a nitrogen heating chamber 601, which houses a nitrogen heating device 602 (such as an electric heater). A nitrogen inlet pipe 603 connects to the nitrogen heating chamber 601, heating the nitrogen before it is delivered through a nitrogen outlet pipe 604 to a nitrogen distribution pipe assembly 605 positioned above the furnace cavity 101. The nitrogen distribution pipe assembly 605 can consist of multiple parallel single pipes or a winding coil, with nitrogen outlet holes evenly distributed along its length. The heated nitrogen is evenly blown downwards from the top of the furnace cavity, creating a protective atmosphere and promoting uniform airflow throughout the furnace. The nitrogen heating device 602 is also controlled by a control unit 701.

[0045] The working principle of this invention is as follows: MIM products are carried by conveyor belt 2 and continuously pass through furnace chamber 101. Nitric acid is precisely delivered by metering pump 302 and vaporized into uniform acid mist in external acid mist generating device 4. The acid mist is sent to the gas circulation system of the first processing zone and is forced to circulate in each independent processing zone by acid-resistant centrifugal fan 501, and evenly penetrates to the surface of the workpiece through the air distribution holes of jacket 102. At the same time, hot nitrogen is introduced into the upper part of the furnace chamber for protection. This system ensures that all workpieces can be processed in a stable and uniform acid mist atmosphere from the feeding end to the discharging end, thereby achieving extremely high consistency and pass rate.

[0046] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above descriptions are merely specific embodiments of this utility model and are not intended to limit this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A continuous furnace for acid mist treatment of MIM products, comprising a furnace body, a material conveyor belt, a nitric acid supply system, an acid mist generating device, and a gas circulation device; the furnace body includes a furnace cavity formed therein; the material conveyor belt is used to continuously transport material through the furnace cavity; the acid mist generating device is used to vaporize liquid nitric acid into acid mist; the gas circulation device is used to introduce the acid mist from the acid mist generating device into the furnace cavity and distribute the acid mist evenly; characterized in that: The acid mist generating device is located outside and above the furnace body; it is used to deliver acid mist to the interlayer; the nitric acid supply system includes a nitric acid storage tank, a metering pump, and a weighing device; the nitric acid storage tank is mounted on the weighing platform of the weighing device; the weighing platform is mounted on the main control panel; the weighing device is used to monitor the weight change of nitric acid in the nitric acid storage tank in real time and transmit the data to the control unit on the main control panel; the nitric acid storage tank is connected to the suction end of the metering pump; the metering pump is located below the nitric acid storage tank, and the nitric acid in the storage tank enters the suction end of the metering pump under gravity; the pump outlet of the metering pump is connected to the inlet end of the acid mist generating device; the pump outlet of the metering pump is located on one side of the inlet end of the acid mist generating device; the metering pump is electrically connected to the control unit; multiple gas circulation devices are provided along the extension direction of the furnace body; these gas circulation devices are electrically connected to the control unit.

2. The continuous furnace for acid mist treatment of MIM products according to claim 1, characterized in that: The main control panel is equipped with a nitric acid storage chamber that is higher than the ground. The nitric acid storage chamber is equipped with a safety door. A sliding frame is mounted on the nitric acid storage chamber. The weighing platform is fixedly installed on the sliding frame. The nitric acid storage tank can slide out of the nitric acid storage chamber from the safety door along with the weighing platform via the sliding frame.

3. The continuous furnace for acid mist treatment of MIM products according to claim 1, characterized in that: It also includes a protective gas input mechanism; the protective gas input mechanism includes a nitrogen heating chamber, a nitrogen heating device, a nitrogen inlet pipe, a nitrogen outlet pipe, and a nitrogen distribution pipe assembly; the nitrogen inlet pipe is connected to the inlet end of the nitrogen heating chamber; the nitrogen heating device is installed in the nitrogen heating chamber and is used to heat the nitrogen entering the nitrogen heating chamber; one end of the nitrogen outlet pipe is connected to the outlet end of the nitrogen heating chamber, and the other end is connected to the nitrogen distribution pipe assembly; the nitrogen distribution pipe assembly is arranged inside the furnace cavity; the nitrogen distribution pipe assembly consists of multiple parallel single pipes that converge to the nitrogen outlet pipe, or a coil arranged in a circuitous manner; nitrogen outlet holes are evenly distributed on the single pipes or coils; the nitrogen heating device is electrically connected to the control unit.

4. The continuous furnace for acid mist treatment of MIM products according to claim 1, characterized in that: The acid mist generating device includes a nitric acid vaporization chamber, a heating coil, a nitric acid nozzle, and an acid mist outlet. The heating coil is installed in the nitric acid vaporization chamber and is used to heat liquid nitric acid to vaporize it. The nitric acid nozzle is fixedly installed in the nitric acid vaporization chamber and is used to spray nitric acid into the nitric acid vaporization chamber. The nitric acid nozzle is connected to the pump outlet of the metering pump through a pipeline. The acid mist outlet is connected to the main insulation pipeline. The main insulation pipeline extends along the extension direction of the furnace body. Multiple branch insulation pipelines are connected to the main insulation pipeline. The branch insulation pipelines are connected to the circulation pipeline of the gas exchanger.

5. The continuous furnace for acid mist treatment of MIM products according to claim 4, characterized in that: The gas circulation device includes an acid-resistant centrifugal fan, a first circulating insulated pipe, and a second circulating insulated pipe. The furnace body is divided into multiple processing zones along its extension direction. Each processing zone is equipped with a corresponding gas circulation device. Multiple interlayers are symmetrically arranged on both sides of each processing zone along the extension direction of the furnace body. The first circulating insulated pipe is located on one side of the furnace body along its extension direction. The second circulating insulated pipe is located on the other side of the furnace body along its extension direction. Multiple circulating insulated branch pipes are connected to both the first and second circulating insulated pipes. Each branch pipe on the first and second circulating insulated pipes is connected to an interlayer on the corresponding side of the corresponding processing zone. The interlayers are connected to the furnace cavity through a group of air distribution holes. The first circulating insulated pipe is connected to the outlet of the acid-resistant centrifugal fan. The second circulating insulated pipe is connected to the inlet of the acid-resistant centrifugal fan. The acid mist outlet of the acid mist generating device is connected to the second circulating insulated pipe of the gas circulation device in the processing zone closest to the feed end of the furnace body.

6. The continuous furnace for acid mist treatment of MIM products according to claim 5, characterized in that: The acid mist generating device has two independent nitric acid vaporization chambers; each of the two nitric acid vaporization chambers is equipped with a heating coil; each nitric acid vaporization chamber is equipped with a nitric acid nozzle; the two nitric acid nozzles are connected to each other through an acid inlet pipe and then connected to the pump outlet of a metering pump; each acid inlet pipe is equipped with a control valve; each nitric acid vaporization chamber is equipped with an acid mist outlet, and each acid mist outlet is connected to the second circulating insulation pipe of the gas circulation device in the processing area closest to the furnace body.

7. The continuous furnace for acid mist treatment of MIM products according to claim 4, characterized in that: The nitric acid spray head is evenly distributed with multiple acid spray holes; the diameter of each acid spray hole is 0.5 mm, and there are 50 acid spray holes per square centimeter.

8. The continuous furnace for acid mist treatment of MIM products according to claim 3, characterized in that: The nitrogen gas distribution pipe assembly is arranged above the furnace cavity.

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