阅读说明：本技术 一种汽车活塞及其制造工艺 (Automobile piston and manufacturing process thereof ) 是由 潘松辉 潘菁 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种汽车活塞,包括活塞本体,在所述的活塞本体外覆有一层氮化层,在所述的氮化层外覆有一层盐浴氧化层。(The invention discloses an automobile piston which comprises a piston body, wherein a nitriding layer is coated outside the piston body, and a salt bath oxide layer is coated outside the nitriding layer.)

1. An automotive piston, comprising a piston body (100), characterized in that: the piston body (100) is externally coated with a nitrided layer (101), and the nitrided layer (101) is externally coated with a salt bath oxide layer (102).

2. The manufacturing process of the automobile piston as claimed in claim 1, wherein the manufacturing process of the automobile piston specifically comprises the following steps:

manufacturing a piston body (100), wherein the diameter size of the excircle of the piston body (100) is 36-60 mu m smaller than that of the finished product of the piston of the caliper;

secondly, preheating the piston body (100), putting the preheated piston body (100) into a salt bath nitriding furnace, filling clean and dry compressed air into the salt bath nitriding furnace for stirring, and ensuring that the part is fully contacted with the salt bath; the temperature of the salt bath is 540 +/-15 ℃, the time is 50-70 min, and the piston body (100) is cooled in the air after the salt bath is finished;

step three, taking the piston body (100) subjected to salt bath nitridation, cleaning the piston body in hot water at the temperature of 60-80 ℃ for 5-10 min, then transferring the piston body into clean normal-temperature water for rinsing for 10-30 min, and discharging the piston body out of the furnace;

step four, uniformly and regularly placing the cleaned piston bodies (100) in a material placing basket, placing the material placing basket in a gas nitriding furnace, and feeding at the temperature of room temperature to 150 ℃; opening an ammonia valve, wherein the flow of ammonia gas is 2.0-2.5 m 3/h; introducing ammonia gas and exhausting for 50-70 min;

nitriding the first stage, and heating the furnace to 530 +/-15 ℃; adjusting the ammonia constant to 0.2-1.0 m3/h, and keeping the temperature for 33-35 h when the ammonia decomposition rate is adjusted to 33% -43%;

nitriding the second section, and keeping the furnace temperature at 530 +/-15 ℃; adjusting the ammonia constant to 0.2-0.5 m3/h, adjusting the ammonia decomposition rate to 80% -90%, and keeping the temperature for 6.5-7.5 h;

nitriding the third section, and keeping the furnace temperature at 530 +/-15 ℃; closing ammonia gas, keeping the ammonia decomposition rate at 100%, and keeping the temperature for 2.5-3.5 h;

fifthly, introducing ammonia or nitrogen after the gas nitriding is finished to cool the parts in the nitriding furnace to below 150 ℃ and discharging the parts out of the furnace to obtain a nitrided piston body (100);

and step six, polishing the piston body (100) nitrided by the salt bath, and then performing salt bath oxidation treatment.

3. The manufacturing process of an automotive piston as claimed in claim 2, wherein: the piston body (100) before preheating is pretreated as follows: firstly, homogenizing at 1150 +/-15 ℃ for 80-120 min; then carrying out solid solution treatment at 1040 +/-15 ℃ for 60-100 min; finally, precipitation hardening treatment is carried out at 540 +/-10 ℃ for 100-120 min.

4. A process for manufacturing an automotive piston as claimed in claim 3, wherein: cleaning the piston body (100) with alkaline cleaning solution before salt bath until the surface of the part is free of stains; and (4) cleaning and polishing the piston body (100) before gas nitriding to ensure that the surface is clean, dry and scale-free.

5. The manufacturing process of an automotive piston as claimed in claim 4, wherein: the interval between the third step and the fourth step is 1-47 h.

6. The manufacturing process of an automotive piston as claimed in claim 5, wherein: and step four, when nitriding the gas, opening an ammonia valve to introduce ammonia, controlling the flow rate and the decomposition rate of the ammonia according to the requirements of each stage, controlling the heating temperature to be three-stage constant temperature, and performing constant temperature nitriding when heating to 530 +/-15 ℃.

7. The manufacturing process of an automotive piston as claimed in claim 6, wherein: the salt bath nitriding furnace used in the second step comprises a furnace wall (2), a furnace container arranged in an inner cavity of the furnace wall (2), and a furnace cover (1) arranged on the furnace wall (2), wherein the furnace cover (1) is controlled to be opened and closed by an air pump (13) connected with a furnace cover connecting part (14) of the furnace cover (1);

a salt adding opening (18) is formed in the middle of the furnace cover (1), a sleeve (19) is arranged in the middle of the salt adding opening (18), an annular gas channel is formed between the sleeve (19) and the salt adding opening (18), the lower portion of the sleeve (19) extends into the salt liquid (11) in the furnace liner, and an air inlet hole (20) is formed in the side wall of the sleeve (19); an air exhaust duct (8) is arranged on one side of the furnace cover (1) contacting with the furnace pipe, and the air exhaust duct (8) is communicated with the side wall of the salt adding port (18);

the furnace pipe comprises an outer furnace pipe (3) and an inner furnace pipe (4), a reaction layer (5) is arranged between the outer furnace pipe (3) and the inner furnace pipe (4), and a gap (6) is arranged between the reaction layer (5) and the inner furnace pipe (4);

the upper end of the outer furnace pipe (3) is clamped and embedded into the furnace wall (2) through a first sealing gasket (9), and a second sealing gasket (10) is further arranged between the furnace cover (1) and the first sealing gasket (9).

8. The process for manufacturing an automotive piston as claimed in claim 7, wherein: a heating element (7) is arranged between the furnace wall (2) and the outer furnace pipe (3); after the salt solution (11) in the inner furnace (4) overflows from the inner furnace (4), the reaction layer (5) can react with the salt solution (11).

9. The process for manufacturing an automotive piston as claimed in claim 8, wherein: a detachable slag dragging device (12) is arranged at a preset distance from the bottom of the inner furnace (4); the slag fishing device (12) comprises a first filter plate (15) and a second filter plate (16) arranged at the lower part of the first filter plate (15), and a slag fishing accommodating space (17) is reserved between the lower part of the second filter plate (16) and the inner furnace (4); the diameter of the filter hole of the first filter plate (15) is larger than the diameter of the impurity, and the diameter of the filter hole of the second filter plate (16) is smaller than the diameter of the impurity.

10. The process for manufacturing an automotive piston as claimed in claim 9, wherein: an exhaust duct (8) is arranged on one side of the furnace cover (1) which is in contact with the furnace pipe; when the salt solution (11) in the inner furnace (4) overflows from the inner furnace (4), the reaction layer (5) can react with the salt solution (11).

Technical Field

The invention belongs to the technical field of automobile pistons, and particularly relates to an automobile piston and a manufacturing process thereof.

Background

Brake calipers, which are widely used in vehicles to generate braking force through interaction between the brake caliper, which is generally fixed to a frame of the vehicle, and a brake disc, which is fixed to a wheel, are one of the core components of a brake system. The brake caliper includes a piston and brake pads that slide within a seat under the action of a pressurized fluid to urge the brake pads and brake disc to frictionally generate a braking force.

In actual production, after the surface of the piston body is plated with chrome, the required precision requirement is met by accurate grinding through a high-precision grinding machine, and the required wear resistance is achieved by using a hard chrome layer with high hardness. The hard chromium plating is a traditional surface electroplating technology, a chromic acid solution used in a chromium plating process can generate chromium-containing acid mist and waste water, the pollution problem of hexavalent chromium ions is larger than the harm of cyanide, and the pollution problem is difficult to eliminate, so that the serious environmental pollution problem is caused. The deposition speed of the chromium plating process is low, a plating layer with the thickness of 0.2-0.3 mm usually needs 16-24 hours, and the problems of long production period, low production efficiency, high production cost and the like exist. The chromium coating is easy to have microcracks, so that penetrating cracks are inevitably generated, a corrosive medium permeates from the surface to the interface to corrode the piston body, and rusty spots and even peeling are generated on the surface of the coating.

Although the prior art has produced protection of the piston body through a nitrided layer and an oxidized layer, the original gas nitriding treatment generally adopts methods such as sand blasting before nitriding or mixing of ammonium chloride and quartz sand and the like to activate the surface of the piston body

The surface passivation film Cr2O3, ammonium chloride decompose the back and easily crystallize in the nitridation process and cause the pipeline to block up and influence the quality stability of piston body nitriding treatment, adopt the sandblast to activate the surface because to the control requirement (be less than or equal to 2h) that has of stove time after the sandblast in the same time for there is quality fluctuation often in the gas nitriding treatment of piston body in batches, has the piston body hidden danger of inefficacy.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide an automobile piston with a simple structure and a manufacturing process which is simple and efficient to produce.

In order to achieve the purpose, the invention provides the following technical scheme: the utility model provides an automobile piston, includes the piston body, characterized by: the piston body is externally coated with a nitriding layer, and the nitriding layer is externally coated with a salt bath oxide layer.

The manufacturing process of the automobile piston specifically comprises the following steps:

manufacturing a piston body, wherein the diameter size of the excircle of the piston body is 36-60 mu m smaller than that of a finished caliper piston;

secondly, preheating the piston body, putting the preheated piston body into a salt bath nitriding furnace, filling clean and dry compressed air into the salt bath nitriding furnace, and stirring to ensure that the piston body is fully contacted with the salt bath; the temperature of the salt bath is 540 +/-15 ℃, the time is 50-70 min, and the piston body is cooled in the air after the salt bath is finished;

step three, taking the piston body subjected to salt bath nitridation, cleaning the piston body in hot water at the temperature of 60-80 ℃ for 5-10 min, then transferring the piston body into clean normal-temperature water, rinsing the piston body for 10-30 min, and discharging the piston body;

step four, uniformly and regularly placing the cleaned piston bodies in a charging basket, placing the charging basket in a gas nitriding furnace, and feeding at the temperature of between room temperature and 150 ℃; opening an ammonia valve, wherein the flow of ammonia gas is 2.0-2.5 m 3/h; introducing ammonia gas and exhausting for 50-70 min;

nitriding the first stage, and heating the furnace to 530 +/-15 ℃; adjusting the ammonia constant to 0.2-1.0 m3/h, and keeping the temperature for 33-35 h when the ammonia decomposition rate is adjusted to 33% -43%;

nitriding the second section, and keeping the furnace temperature at 530 +/-15 ℃; adjusting the ammonia constant to 0.2-0.5 m3/h, adjusting the ammonia decomposition rate to 80% -90%, and keeping the temperature for 6.5-7.5 h;

nitriding the third section, and keeping the furnace temperature at 530 +/-15 ℃; closing ammonia gas, keeping the ammonia decomposition rate at 100%, and keeping the temperature for 2.5-3.5 h;

fifthly, introducing ammonia or nitrogen after the gas nitriding is finished to cool the piston body in the nitriding furnace to below 150 ℃ and discharging the piston body out of the furnace to obtain the nitrided piston body;

and step six, polishing the piston body nitrided by the salt bath, and then performing salt bath oxidation treatment.

The piston body before preheating is pretreated as follows: firstly, homogenizing at 1150 +/-15 ℃ for 80-120 min; then carrying out solid solution treatment at 1040 +/-15 ℃ for 60-100 min; finally, precipitation hardening treatment is carried out at 540 +/-10 ℃ for 100-120 min.

Cleaning the piston body with alkaline cleaning solution before salt bath until the surface of the piston body is free of stains; and the salt bath in the second step refers to French sheffy basic salt plus adjusting salt or domestic common QPQ salt. And step four, cleaning and polishing the piston body before gas nitriding to ensure that the surface is clean, dry and scale-free.

The interval between the third step and the fourth step is 1-47 h.

And step four, when nitriding the gas, opening an ammonia valve to introduce ammonia, controlling the flow rate and the decomposition rate of the ammonia according to the requirements of each stage, controlling the heating temperature to be three-stage constant temperature, and performing constant temperature nitriding when heating to 530 +/-15 ℃.

Compared with the prior art, the investment cost and the energy consumption cost of the QPQ salt bath composite treatment technology are not half of those of the hard chromium plating technology; the QPQ salt bath composite treatment technology has the treatment cost of only 60 percent of that of the hard chromium plating technology. The corrosion resistance of the vehicle brake caliper piston after QPQ salt bath composite treatment is 70 times that of hard chromium plating. The QPQ salt bath composite treatment is pollution-free, pollution-free and free of heavy metals. Therefore, the automobile manufactured by the automobile manufacturing method has the advantages of energy conservation, environmental protection and low production cost.

In addition, the temperature uniformity of equipment adopting salt bath nitriding pretreatment is good, semi-automatic production is realized, and the quality state of the surface of the piston body is consistent and controlled during the salt bath nitriding pretreatment; after the salt bath nitriding pretreatment is adopted for activation, the superficial layer is nitrided, so that the influence of a Cr2O3 passive film generated secondarily on the gas nitriding speed is avoided; after the salt bath nitriding pretreatment activation is adopted and a shallow nitriding layer is formed, the interval time from the turning to the gas nitriding is greatly prolonged, and the sand blasting activation is generally controlled to be prolonged to 47 hours from about 1 hour; after the salt bath nitriding pretreatment is adopted, the strong permeation time of gas nitriding is saved (shortened from about 50 hours of the original general strong permeation to 33-35 hours), and the production period and the cost are reduced.

The invention is further configured to: the salt bath nitriding furnace used in the second step comprises a furnace wall, a furnace pipe arranged in an inner cavity of the furnace wall and a furnace cover arranged on the furnace wall, wherein the furnace cover is controlled to be opened and closed by an air pump connected with a furnace cover connecting part of the furnace cover;

a salt adding port is formed in the middle of the furnace cover, a sleeve is arranged in the middle of the salt adding port, an annular gas channel is formed between the sleeve and the salt adding port, the lower portion of the sleeve extends into the salt liquid in the furnace liner, and an air inlet hole is formed in the side wall of the sleeve; an air exhaust duct is arranged on one side of the furnace cover, which is in contact with the furnace pipe, and the air exhaust duct is communicated with the side wall of the salt adding port;

the furnace pipe comprises an outer furnace pipe and an inner furnace pipe, a reaction layer is arranged between the outer furnace pipe and the inner furnace pipe, and a gap is formed between the reaction layer and the inner furnace pipe;

the upper end of the outer furnace pipe is clamped and embedded into the furnace wall through a first sealing gasket, and a second sealing gasket is arranged between the furnace cover and the first sealing gasket.

The invention is further configured to: a heating element is arranged between the furnace wall and the outer furnace pipe; after the salt solution in the inner furnace pipe overflows from the inner furnace pipe, the reaction layer can react with the salt solution.

The invention is further configured to: a detachable slag dragging device is arranged at a position which is a preset distance away from the bottom of the inner furnace; the slag fishing device comprises a first filter plate and a second filter plate arranged at the lower part of the first filter plate, and a slag fishing accommodating space is reserved between the lower part of the second filter plate and the inner furnace; the diameter of the filter hole of the first filter plate is larger than the diameter of the impurity, and the diameter of the filter hole of the second filter plate is smaller than the diameter of the impurity.

The invention is further configured to: an exhaust duct is arranged on one side of the furnace cover, which is in contact with the furnace pipe; when the salt solution in the inner furnace pipe overflows from the inner furnace pipe, the reaction layer can react with the salt solution. By adopting the technical scheme of the method, the device can be used,

the salt bath nitriding furnace adopts a double-layer furnace pipe structure, when the salt bath nitriding furnace is used, if the salt solution leaks outwards, the salt bath nitriding furnace can perform chemical reaction with a reaction layer through the reaction layer, and the dangerous case can be controlled in the inner layer of the outer furnace pipe, so that the salt solution is prevented from contacting with a heating element outside the outer furnace pipe, the damage of the heating element is avoided, the reaction layer can be replaced at any time, and the maintenance cost of the salt bath furnace is saved; the gap between the inner furnace and the outer furnace is used for preventing the heating element from expanding when heating the outer furnace to cause extrusion; the slag dragging device arranged at the bottom of the inner furnace pipe locks impurities between two layers of filter plates through different filter plate apertures, and only needs to be replaced and maintained regularly. And the salt bath nitriding furnace with the structure has the advantages of convenient maintenance and replacement, effective prolonging of the service life of equipment and the like, and can be widely popularized in the fields of heat treatment and the like for the reasons.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is an enlarged view of a portion of FIG. 1 at I;

FIG. 3 is a schematic structural view of a salt bath nitriding furnace used in step two of the present invention;

FIG. 4 is a schematic view of a partial structure of a salt bath nitriding furnace used in step two of the present invention;

FIG. 5 is a schematic structural diagram of a slag dragging device in the salt bath nitriding furnace used in the second step of the invention;

reference numbers in the drawings and corresponding part names: 1-furnace cover, 2-furnace wall, 3-outer furnace liner, 4-inner furnace liner, 5-reaction layer, 6-gap, 7-heating element, 8-exhaust duct, 9-first sealing gasket, 10-second sealing gasket, 11-salt solution, 12-slag removing device, 13-air pump, 14-furnace cover connecting part, 15-first filter plate, 16-second filter plate, 17-slag removing containing space, 18-salt adding port, 19-sleeve, 20-air inlet hole, 100-piston body, 101-nitriding layer and 102-salt bath oxidation layer.

Detailed Description

One embodiment of the present invention is further explained with reference to fig. 1 to 5.

An automobile piston comprises a piston body 100 and is characterized in that: the piston body 100 is coated with a nitrided layer 101, and the nitrided layer 101 is coated with a salt bath oxide layer 102.

The manufacturing process of the automobile piston specifically comprises the following steps:

step one, manufacturing a piston body 100, wherein the diameter size of the excircle of the piston body 100 is 36-60 mu m smaller than that of the finished product of the piston of the caliper;

secondly, preheating the piston body 100, then placing the preheated piston body 100 into a salt bath nitriding furnace, filling clean and dry compressed air into the salt bath nitriding furnace for stirring, and ensuring that the piston body 100 is fully contacted with the salt bath; the temperature of the salt bath is 540 +/-15 ℃, the time is 50-70 min, and the piston body 100 is cooled in the air after the salt bath is finished;

step three, taking the piston body 100 subjected to salt bath nitridation, cleaning the piston body in hot water at the temperature of 60-80 ℃ for 5-10 min, then transferring the piston body into clean normal-temperature water for rinsing for 10-30 min, and discharging the piston body out of the furnace;

step four, uniformly and regularly placing the cleaned piston bodies 100 in a charging basket, placing the charging basket in a gas nitriding furnace, and feeding at the temperature of between room temperature and 150 ℃; opening an ammonia valve, wherein the flow of ammonia gas is 2.0-2.5 m 3/h; introducing ammonia gas and exhausting for 50-70 min;

nitriding the first stage, and heating the furnace to 530 +/-15 ℃; adjusting the ammonia constant to 0.2-1.0 m3/h, and keeping the temperature for 33-35 h when the ammonia decomposition rate is adjusted to 33% -43%;

nitriding the second section, and keeping the furnace temperature at 530 +/-15 ℃; adjusting the ammonia constant to 0.2-0.5 m3/h, adjusting the ammonia decomposition rate to 80% -90%, and keeping the temperature for 6.5-7.5 h;

nitriding the third section, and keeping the furnace temperature at 530 +/-15 ℃; closing ammonia gas, keeping the ammonia decomposition rate at 100%, and keeping the temperature for 2.5-3.5 h;

fifthly, introducing ammonia or nitrogen after the gas nitriding is finished to cool the piston body 100 in the nitriding furnace to below 150 ℃ and discharging the piston body 100 out of the furnace to obtain the nitrided piston body 100;

and step six, polishing the piston body 100 nitrided by the salt bath, and then performing salt bath oxidation treatment.

The piston body 100 before preheating is pretreated as follows: firstly, homogenizing at 1150 +/-15 ℃ for 80-120 min; then carrying out solid solution treatment at 1040 +/-15 ℃ for 60-100 min; finally, precipitation hardening treatment is carried out at 540 +/-10 ℃ for 100-120 min.

Cleaning the piston body 100 with alkaline cleaning solution before salt bath of the piston body 100 in the second step until the surface of the piston body 100 is free of stains; and the salt bath in the second step refers to French sheffy basic salt plus adjusting salt or domestic common QPQ salt. And step four, before the gas nitriding is carried out on the piston body 100, the surface is cleaned and polished to ensure that the surface is clean, dry and free of scale.

The interval between the third step and the fourth step is 1-47 h.

And step four, when nitriding the gas, opening an ammonia valve to introduce ammonia, controlling the flow rate and the decomposition rate of the ammonia according to the requirements of each stage, controlling the heating temperature to be three-stage constant temperature, and performing constant temperature nitriding when heating to 530 +/-15 ℃.

Compared with the prior art, the investment cost and the energy consumption cost of the QPQ salt bath composite treatment technology are not half of those of the hard chromium plating technology; the QPQ salt bath composite treatment technology has the treatment cost of only 60 percent of that of the hard chromium plating technology. The corrosion resistance of the vehicle brake caliper piston after QPQ salt bath composite treatment is 70 times that of hard chromium plating. The QPQ salt bath composite treatment is pollution-free, pollution-free and free of heavy metals. Therefore, the automobile manufactured by the automobile manufacturing method has the advantages of energy conservation, environmental protection and low production cost.

In addition, the equipment adopting the salt bath nitriding pretreatment has good temperature uniformity and semi-automatic production, and the quality state of the surface of the piston body 100 is consistently controlled during the salt bath nitriding pretreatment; after the salt bath nitriding pretreatment is adopted for activation, the superficial layer is nitrided, so that the influence of a Cr2O3 passive film generated secondarily on the gas nitriding speed is avoided; after the salt bath nitriding pretreatment activation is adopted and the shallow nitrided layer 101 is formed, the interval time from the transition to the gas nitriding is greatly prolonged, and the sand blasting activation is generally controlled to be prolonged to 47 hours from about 1 hour; after the salt bath nitriding pretreatment is adopted, the strong permeation time of gas nitriding is saved (shortened from about 50 hours of the original general strong permeation to 33-35 hours), and the production period and the cost are reduced.

The invention is further configured to: the salt bath nitriding furnace used in the second step comprises a furnace wall 2, a furnace container arranged in the inner cavity of the furnace wall 2 and a furnace cover 1 arranged on the furnace wall 2, wherein the furnace cover 1 is controlled to be opened and closed by an air pump 13 connected with a furnace cover connecting part 14 of the furnace cover 1;

a salt adding port 18 is arranged in the middle of the furnace cover 1, a sleeve 19 is arranged in the middle of the salt adding port 18, an annular gas channel is formed between the sleeve 19 and the salt adding port 18, the lower part of the sleeve 19 extends into the salt solution 11 in the furnace pipe, and an air inlet 20 is arranged on the side wall of the sleeve 19; an air exhaust duct 8 is arranged on one side of the furnace cover 1, which is in contact with the furnace pipe, and the air exhaust duct 8 is communicated with the side wall of the salt adding port 18;

the furnace pipe comprises an outer furnace pipe 3 and an inner furnace pipe 4, a reaction layer 5 is arranged between the outer furnace pipe 3 and the inner furnace pipe 4, and a gap 6 is arranged between the reaction layer 5 and the inner furnace pipe 4;

the upper end of the outer furnace pipe 3 is clamped and embedded into the furnace wall 2 through a first sealing gasket 9, and a second sealing gasket 10 is further arranged between the furnace cover 1 and the first sealing gasket 9.

The invention is further configured to: a heating element 7 is arranged between the furnace wall 2 and the outer furnace pipe 3; after the salt solution 11 in the inner furnace pipe 4 overflows from the inner furnace pipe 4, the reaction layer 5 can react with the salt solution 11.

The invention is further configured to: a detachable slag dragging device 12 is arranged at a preset distance from the bottom of the inner furnace 4; the slag fishing device 12 comprises a first filter plate 15 and a second filter plate 16 arranged at the lower part of the first filter plate 15, and a slag fishing accommodating space 17 is reserved between the lower part of the second filter plate 16 and the inner furnace 4; the diameter of the filter hole of the first filter plate 15 is larger than the diameter of the impurity, and the diameter of the filter hole of the second filter plate 16 is smaller than the diameter of the impurity.

The invention is further configured to: an exhaust duct 8 is arranged on one side of the furnace cover 1, which is in contact with the furnace pipe; when the salt solution 11 in the inner furnace pipe 4 overflows from the inner furnace pipe 4, the reaction layer 5 can react with the salt solution 11. By adopting the technical scheme of the method, the device can be used,

the salt bath nitriding furnace adopts a double-layer furnace pipe structure, when the salt bath nitriding furnace is used, if the salt bath 11 leaks outwards, the reaction layer 5 can perform chemical reaction with the salt bath nitriding furnace, the inner layer of the outer furnace pipe 3 can be controlled in a dangerous situation, the salt bath 11 is prevented from contacting with the heating element 7 on the outer side of the outer furnace pipe 3, the damage of the heating element is avoided, the reaction layer 5 can be replaced at any time, and the maintenance cost of the salt bath furnace is saved; the gap 6 between the inner furnace pipe 4 and the outer furnace pipe 3 is used for preventing the outer furnace pipe 3 from being extruded due to thermal expansion when the heating element 7 heats the outer furnace pipe; the slag dragging device 12 arranged at the bottom of the inner furnace 4 locks impurities between two layers of filter plates through different filter plate aperture, and only needs to be replaced and maintained regularly. And the salt bath nitriding furnace with the structure has the advantages of convenient maintenance and replacement, effective prolonging of the service life of equipment and the like, and can be widely popularized in the fields of heat treatment and the like for the reasons.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, so: all equivalent changes made according to the structure, shape and principle of the invention are covered by the protection scope of the invention.