Surface nitriding process and device for connecting rod die steel

Abstract

The invention discloses a surface nitriding process and device for connecting rod die steel, and the surface nitriding process comprises the following steps: firstly coating a layer of anti-seepage agent at a fillet of a through hole in the connecting rod die steel, and covering a layer of ceramic fiber blanket at the fillet; the connecting rod die steel is fed into a surface nitriding device to be nitrided, in the nitriding process, vacuumizing and first-time preheating are conducted, the connecting rod die steel is heated to 350 DEG C and subjected to heat preservation for 90-180 min during first-time preheating, then second-time preheating is conducted, the connecting rod die steel is heated to 480 DEG C and subjected to heat preservation for 120 min during second-time preheating, formal heating is conducted, the connecting rod die steel is heated to 550 DEG C and subjected to heat preservation for 660 min, and the connecting rod die steel is cooled to the room temperature; ammonia gas is introduced in the formal heating process, the flow of the ammonia gas is 2000 L / H, and the nitrogen potential Kn is kept to be 1.6; the connecting rod die steel is coated with the anti-seepage agent at the fillet of the through hole of the connecting rod die steel and then covered with the ceramic fiber blanket for anti-seepage treatment, the anti-seepage effect is improved, the fillet of the through hole in the nitrided connecting rod die steel is not prone to cracking, and the service life of the connecting rod die steel is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of nitriding of die steel, and in particular to a surface nitriding process and a device for connecting rod die steel. Background Art

[0002] The connecting rod mechanism of an automobile, also known as the lower pair mechanism, is a type of mechanical component. Because the connecting rod's metal volume is distributed along its axis, forming a large end, a shaft, and a small end, it is generally formed by blanking during forging. This process is typically performed through processes such as drawing and rolling to pre-divide the metal. Since the connecting rod's shaft often has an "I-shaped" cross-section, to avoid forging defects such as folding due to irrational metal flow, and to facilitate forging fill and die life, connecting rod forming typically involves two steps: pre-forging and final forging. Due to the high forging temperatures and prolonged contact time between the forging and die, the die steel must possess high thermal stability, high-temperature strength and hardness, thermal fatigue resistance, wear resistance, and ease of processing.

[0003] Nitrided mold steel exhibits excellent wear resistance, fatigue resistance, corrosion resistance, and high-temperature resistance. However, due to the high strength and hardness of the nitrided area, its plasticity and toughness are poor. In certain areas of mold steel prone to stress concentration, such as fillets and sharp corners, the presence of the nitrided layer can accelerate the onset and propagation of cracks in the mold. Therefore, these areas require anti-seepage treatment to prevent premature cracking, which can shorten the mold's lifespan.

[0004] Most connecting rod die steels are made of hot forming die steel materials, such as 4Cr5MoSiV1, etc. In order to obtain higher mold times, manufacturers usually choose die steel materials with better quality under the same conditions, such as German 1.2360 and 1.2367. However, after production verification, it was found that when using 1.2367 die steel materials, the connecting rod forging die will still have early cracks, causing the die to be scrapped. Early cracks appeared on the back of the die when the production reached 27,000 mold times (under normal circumstances, it can reach 50,000 mold times). The most serious crack has extended to the forming surface. After failure analysis of the scrapped die, it was found that the main reason for the cracks was that the nitriding anti-seepage effect of some parts of the die did not meet the design requirements, resulting in early cracks in the die and rapid expansion. Since there are two through holes on the back of the forging connecting rod die (see Figure 1 and Figure 2 As shown in the figure, stress concentration will occur at the rounded corners at the outer ends of the two through holes, causing cracks to occur first at these two locations during the production process. Summary of the Invention

[0005] In order to solve the above-mentioned deficiencies in the prior art, the present invention proposes a surface nitriding process and device for connecting rod die steel.

[0006] In order to achieve the above technical effects, the present invention adopts the following scheme: A surface nitriding process for connecting rod die steel comprises first coating a layer of impermeability agent on the fillets of two through holes on the connecting rod die steel, and covering the fillets with a layer of ceramic fiber blanket; then feeding the connecting rod die steel into a surface nitriding device for nitriding, first drawing a vacuum during the nitriding process, then performing a first preheating process, heating to 350°C and holding the temperature for 90-180 minutes, then performing a second preheating process, heating to 480°C and holding the temperature for 120 minutes, then performing a main heating process, heating to 550°C and holding the temperature for 660 minutes, charging ammonia gas during the main heating process, the ammonia flow rate being 2000 L / H, and maintaining the nitrogen potential Kn at 1.6; finally, cooling and removing the connecting rod die steel; The anti-seepage agent includes 40-50 parts of tin powder, 45-70 parts of aluminum oxide powder, 15-25 parts of quartz powder, 10-15 parts of kaolin, 10-15 parts of lithium bentonite, 4-7 parts of titanium dioxide, 3-6 parts of sodium hydroxide, 3-5 parts of cold-drawn polypropylene fiber and water.

[0007] A surface nitriding device for connecting rod die steel includes a furnace body and a nitrogen supply system, a vacuum system, a temperature control system, and an atmosphere detection system connected to the furnace body. A take-in and put-out port is provided on one side of the furnace body, and a furnace door is matched with the take-in and put-out port. A support platform is provided at the bottom of the furnace body, and a rotating turntable is provided on the support platform. The turntable is driven to rotate by a first motor. A discharge tray is placed on the turntable, and a support leg is provided at the lower end of the discharge tray. A plurality of vertically penetrating hollow holes are arranged in an array on the discharge tray, and a plurality of jacks are arranged in an array on the upper end of the discharge tray. Vertical support rods are inserted into the jacks.

[0008] According to a preferred technical solution, the furnace door is driven to open and close vertically by a lifting mechanism, and the two sides of the furnace door are slidably installed on the furnace body. The lifting mechanism includes telescopic frames located on both sides of the furnace door, the telescopic frames are vertically arranged, and the lower ends of the telescopic frames are installed on the furnace body, and the upper ends of the telescopic frames are fixedly connected to the furnace door. The two sets of telescopic frames are driven to extend and retract by the same driving mechanism.

[0009] The preferred technical solution is that the telescopic frame includes at least three sleeves that are slidably connected in sequence in the vertical direction, the lower end of the sleeve located at the top is matched and inserted into the sleeve located at the bottom for sliding arrangement, wherein the lower end of the sleeve located at the bottom is fixedly installed on the furnace body, and the upper end of the sleeve located at the top is fixedly connected to the furnace door, a rotating screw rod is provided in each of the sleeves, the lower end of the sleeve is fixedly provided with a bottom plate, the lower end of the screw rod in the sleeve is rotatably installed on the bottom plate, and a through hole is opened in the center of the bottom plate. The upper end of the screw rod in the lower sleeve passes through the through hole, and the through hole is provided with an external thread adapted to the corresponding screw rod. The bottom of the screw rod in the upper sleeve extends upward and is provided with an inner hole adapted to the lower screw rod. After the upper end of the screw rod in the lower sleeve passes through the corresponding through hole, it is inserted into the inner hole of the screw rod in the upper sleeve. A vertically extending limiting ridge is protruded on the inner wall of the inner hole, and a limiting groove adapted to the limiting ridge is provided on the outer wall of the screw rod inserted into the inner hole. The driving mechanism includes a transmission rod, a worm wheel, a worm and a second motor. There are two transmission rods, both of which are rotatably mounted on the furnace body, and the two transmission rods are respectively located below the two sets of telescopic frames. The upper ends of the transmission rods are fixedly connected to the lower ends of the screw rods in the lowest sleeves in the corresponding telescopic frames. The lower ends of the transmission rods are fixedly provided with a worm wheel. The worm is horizontally and rotatably arranged on the furnace body. The worm is matched with the worm wheels at the lower ends of the two transmission rods, and one end of the worm is connected to the second motor.

[0010] According to a preferred technical solution, an airbag arranged in a circle is fixed on the inner side of the furnace door, and the airbag is correspondingly arranged around the outer side of the loading and unloading port. An air inlet connected to the airbag is provided on the furnace door, and the air inlet is used to connect to an external high-pressure air supply system.

[0011] According to a preferred technical solution, the vacuum system includes an exhaust pipe connected to the furnace body, an exhaust pump is connected to the exhaust pipe, a vacuum gauge is provided on the exhaust pipe, and the vacuum gauge is located between the exhaust pump and the furnace body.

[0012] A preferred technical solution, the temperature control system includes a heating system and a water cooling system; the heating system includes a heating tube, a display panel and a temperature sensor, the number of the heating tubes is several, the heating tubes are vertically arranged and installed on the inner wall of the furnace body through a bracket, the temperature sensor is inserted into the furnace body, and the temperature sensor is electrically connected to the display panel; the water cooling system includes a water cooling tube, the water cooling tube is spirally wound on the inner wall of the furnace body, and the outer wall of the furnace body is provided with a water inlet and a water outlet connected to both ends of the water cooling tube, and the water inlet is located below the water outlet.

[0013] The preferred technical solution is that the water inlet and the water outlet are connected to a water circulation system, and the water circulation system includes a water outlet pipe, a cooling device, a water supply pipe, a water tank, a submersible pump and a water inlet pipe, the two ends of the water outlet pipe are respectively connected to the water outlet and the cooling device, the two ends of the water supply pipe are respectively connected to the cooling device and the water tank, the submersible pump is arranged in the water tank, and the two ends of the water inlet pipe are respectively connected to the submersible pump and the water inlet; the cooling device includes at least one heat exchange box, the heat exchange box includes a box body, the upper and lower ends of the box body are respectively provided with an air outlet cavity and an air inlet cavity, the upper end of the air outlet cavity is provided with an air outlet, the lower end of the air inlet cavity is provided with an air inlet, a fan assembly is provided in the air inlet, a plurality of heat exchange pipes connecting the air inlet cavity and the air outlet cavity are densely distributed in the box body, an inlet and an outlet are respectively provided on two sides of the box body, and the inlet and outlet are respectively connected to the water outlet pipe and the water supply pipe. When there are multiple heat exchange boxes, the multiple heat exchange boxes are detachably spliced ​​in a continuously bent "Z" shaped path.

[0014] A preferred technical solution, the nitrogen supply system includes an ammonia tank, an air supply pipe, an air supply pump and a gas flow meter, the air supply pipe connects the ammonia tank and the furnace body, the air supply pump and the gas flow meter are connected to the air supply pipe, and the gas flow meter is located between the air supply pump and the furnace body; an air inlet pipe is provided at the upper end of the furnace body, the air inlet pipe is connected to the air supply pipe, an air outlet pipe is provided at the upper part of the furnace body, the air outlet pipe is coiled into a circular shape, one end of the air outlet pipe is connected to the air inlet pipe, the other end of the air outlet pipe is sealed, and a plurality of air holes are opened at the lower end of the air outlet pipe along the length direction of the air outlet pipe.

[0015] According to a preferred technical solution, a vent is provided on the side wall of the furnace body, a one-way guide valve with the gas flow direction inward is provided in the vent, and a gas valve is provided at the outer end of the vent.

[0016] Compared with the prior art, the beneficial effects are: The present invention has a simple structure and is easy to use. After the anti-seepage agent of the present invention is coated on the rounded corners of the through hole of the connecting rod mold steel, it is covered with a ceramic fiber blanket to perform anti-seepage treatment, thereby improving the anti-seepage effect, making the rounded corners of the through hole on the nitrided connecting rod mold steel less likely to crack, and extending the service life of the connecting rod mold steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a perspective structural diagram of the connecting rod die steel in the prior art; Figure 2 This is another perspective structural diagram of the connecting rod die steel in the prior art; Figure 3 Schematic diagram of covering the fillet of the connecting rod die steel with a ceramic fiber blanket in the process of the present invention; Figure 4It is a schematic diagram of the device structure of the present invention; Figure 5 It is a schematic cross-sectional view of the furnace body in the present invention; Figure 6 It is a schematic structural diagram of the discharge tray in the present invention; Figure 7 is a schematic cross-sectional view of the telescopic frame of the present invention; Figure 8 yes Figure 7 A schematic diagram of the enlarged structure of part A; Figure 9 It is a schematic diagram of the inner structure of the furnace door in the present invention; Figure 10 It is a schematic structural diagram of the cooling device in the present invention; Figure 11 It is a schematic diagram of the top view of the cooling device in the present invention; Figure 12 It is a cross-sectional schematic diagram of the heat exchange box in the present invention.

[0018] Figure 1: 1. furnace body; 2. access port; 3. furnace door; 4. air inlet; 5. rotary table; 6. discharge tray; 7. first motor; 8. telescopic frame; 9. sleeve; 10. worm; 11. second motor; 12. exhaust pipe; 13. vacuum pump; 14. ammonia tank; 15. air supply pipe; 16. air supply pump; 17. gas flow meter; 18. temperature sensor; 19. atmosphere detection system; 20. water outlet pipe; 21. water pipe; 22. water tank; 23. water inlet pipe; 24. box; 25. air inlet chamber; 26. air outlet chamber; 27. exhaust end expansion cover; 28. support platform; 29. Turbine; 30. Inlet pipe; 31. Connecting pipe; 32. Outlet pipe; 33. Air hole; 34. Water-cooling pipe; 35. Heating pipe; 36. Bracket; 37. Support leg; 38. Hollow hole; 39. Support rod; 40. Bottom plate; 41. Through hole; 42. Screw rod; 43. Inner hole; 44. Transmission rod; 45. Airbag; 46. Air inlet; 47. Air outlet; 48. Connecting part; 49. Entry end expansion cover; 50. Heat exchange tube; 51. Inlet; 52. Outlet; 53. Water inlet connection port; 54. Water outlet connection port; 55. Connecting rod mold steel; 56. Through hole; 58. Ceramic fiber blanket. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0020] A surface nitriding process and device for connecting rod die steel, such as Figure 3As shown, the surface nitriding process includes first coating a layer of anti-seepage agent on the rounded corners of the two through holes 56 on the connecting rod mold steel 55, and covering the rounded corners with a layer of ceramic fiber blanket 58. Specifically, a ball of ceramic fiber blanket 58 is partially stuffed into the through hole 56 of the connecting rod mold steel 55 and plugged tightly, so that the ceramic fiber blanket 58 is fixed to the connecting rod mold steel 55 and is not easy to fall off. The part of the ceramic fiber blanket 58 located outside the through hole 56 is fluffy because it is not plugged tightly, so it can cover the rounded corner of the through hole 56.

[0021] Then the connecting rod die steel 55 is sent to the surface nitriding device for nitriding. During the nitriding process, vacuum is first drawn, and then the first preheating is carried out. During the first preheating, it is heated to 350° and kept warm for 90~180 minutes. Then the second preheating is carried out. During the second preheating, it is heated to 480° and kept warm for 120 minutes. Then, formal heating is carried out, heated to 550° and kept warm for 660 minutes. Ammonia is filled in during the formal heating process. The ammonia flow rate is 2000L / H, and the nitrogen potential Kn is maintained at 1.6; finally, the connecting rod die steel 55 is cooled and taken out.

[0022] The anti-seepage agent includes 40-50 parts of tin powder, 45-70 parts of aluminum oxide powder, 15-25 parts of quartz powder, 10-15 parts of kaolin, 10-15 parts of lithium bentonite, 4-7 parts of titanium dioxide, 3-6 parts of sodium hydroxide, 3-5 parts of cold-drawn polypropylene fiber and water.

[0023] After the anti-seepage agent of the present invention is applied to the rounded corners of the through-hole on the connecting rod mold steel 55, it is covered with a ceramic fiber blanket 58 for anti-seepage treatment, thereby improving the anti-seepage effect, making the rounded corners of the through-hole on the nitrided connecting rod mold steel 55 less likely to crack, and extending the service life of the connecting rod mold steel 55.

[0024] like Figure 4 As shown, the surface nitriding device includes a furnace body 1 and a nitrogen supply system, a vacuum system, a temperature control system, and an atmosphere detection system 19 connected to the furnace body 1. The vacuum system is used to draw a vacuum into the furnace body 1, the temperature control system is used to adjust the temperature inside the furnace body 1, the nitrogen supply system is used to transport a nitrogen source into the furnace body 1, which is ammonia in the present invention, and the atmosphere detection system 19 is used to detect the gas atmosphere in the furnace body 1. The atmosphere detection system 19 adopts existing technology, such as a gas detector.

[0025] like Figure 5As shown, a take-in / out port 2 is provided on one side of the furnace body 1, through which the connecting rod mold steel 55 is fed into or taken out of the furnace body 1. The take-in / out port 2 is matched with a furnace door 3. A support platform 28 is provided at the bottom of the furnace body 1, and a rotating turntable 5 is provided on the support platform 28. The turntable 5 is driven to rotate by a first motor 7. Specifically, a plurality of legs are provided at the lower end of the furnace body 1 to suspend the lower end of the furnace body 1. A rotating hole is vertically penetrated in the support platform 28, and a rotating shaft is installed in the rotating hole. The first motor 7 is installed at the lower end of the furnace body 1. The lower end of the rotating shaft extends out of the furnace body 1 and is connected to the output end of the first motor 7. The upper end of the rotating shaft extends upward from the rotating hole and is connected to the rotation center of the turntable 5. A discharge tray 6 is placed on the turntable 5, and the discharge tray 6 is used to place the connecting rod mold steel 55.

[0026] like Figure 6 As shown, the lower end of the discharge tray 6 is provided with a support leg 37, which allows the lower end of the discharge tray 6 to be suspended in the air, facilitating the insertion of a forklift's forks. The upper end of the discharge tray 6 is provided with a plurality of vertically extending hollow holes 38, and the upper end of the discharge tray 6 is provided with a plurality of insertion holes, into which vertical support rods 39 are inserted. The support rods 39 are inserted into the insertion holes to form a support for the connecting rod mold steel 55. The connecting rod mold steel 55 is then placed on the discharge tray 6 and tilted so that one edge of the connecting rod mold steel 55 is supported on the discharge tray 6 and the other edge of the connecting rod mold steel 55 rests on the support rods 39, thereby exposing the surface of the connecting rod mold steel 55 as much as possible for nitriding. After placement, the forklift's fork is inserted under the discharge tray 6 to pick up the discharge tray 6 and place it on the rotating table 5 within the furnace body 1.

[0027] like Figure 4 As shown, further, the furnace door 3 is driven by a lifting mechanism to open and close vertically, and the two sides of the furnace door 3 are slidably installed on the furnace body 1. The furnace body 1 is provided with vertical slide rails on both sides of the loading and unloading port 2. The two sides of the furnace door 3 are matched and installed on the two slide rails to slide. The lifting mechanism includes a telescopic frame 8 located on both sides of the furnace door 3, the telescopic frame 8 is vertically arranged, and the lower end of the telescopic frame 8 is installed on the furnace body 1, and a support frame is fixed on the outer wall of the furnace body 1. The lower end of the telescopic frame 8 is installed on the support frame, and the upper end of the telescopic frame 8 is fixedly connected to the side of the furnace door 3. The two sets of telescopic frames 8 are driven to extend and retract by the same driving mechanism, and the driving mechanism is installed on the support frame.

[0028] like Figure 7-Figure 8As shown, further, the telescopic frame 8 includes at least three sleeves 9 that are slidably connected in sequence in the vertical direction, the sleeves 9 are through-set up and down, the lower end of the sleeve 9 located at the top is matched and inserted into the sleeve 9 located at the bottom for sliding arrangement, the lower end of the lowest one of the at least three sleeves 9 is fixedly mounted on the support frame, the upper end of the highest one of the at least three sleeves 9 is fixedly connected to the side of the furnace door 3, each sleeve 9 is provided with a rotating screw rod 42, the lower end of each sleeve 9 is fixedly provided with a bottom plate 40, the lower end of the screw rod 42 in the sleeve 9 is rotatably mounted on the corresponding bottom plate 40 through a bearing, and a through hole is opened in the center of the bottom plate 40 Hole 41, the upper end of the screw rod 42 located in the lower sleeve 9 passes through the through hole 41 and enters the upper sleeve 9, and the through hole 41 is provided with an external thread adapted to the corresponding screw rod 42, and the bottom of the screw rod 42 located in the upper sleeve 9 extends upward and is provided with an inner hole 43 matching the lower screw rod 42. After the upper end of the screw rod 42 located in the lower sleeve 9 passes through the corresponding through hole 41, it is inserted into the inner hole 43 of the screw rod 42 located in the upper sleeve 9, and a vertically extending limiting ridge is protruded on the inner wall of the inner hole 43, and a limiting groove adapted to the limiting ridge is provided on the outer wall of the screw rod 42 inserted into the inner hole 43.

[0029] The screw rod 42 located in the lower sleeve 9 rotates, and since it is threadedly connected to the through hole 41 of the upper sleeve 9, it can drive the upper sleeve 9 to slide up and down in the lower sleeve 9, and due to the cooperation between the limiting protrusion and the limiting groove, the lower screw rod 42 rotates, which can drive the upper screw rod 42 to rotate synchronously, thereby realizing the extension and retraction of the telescopic frame 8.

[0030] like Figure 4 and Figure 7 As shown, the driving mechanism includes a transmission rod 44, a worm wheel, a worm 10 and a second motor 11. There are two transmission rods 44, and the two transmission rods 44 are rotatably mounted on the support frame of the side wall of the furnace body 1, and the two transmission rods 44 are respectively located below the two groups of telescopic frames 8. The upper end of the transmission rod 44 is fixedly connected to the lower end of the screw rod 42 in the lowest sleeve 9 in the corresponding telescopic frame 8, and the lower end of the transmission rod 44 is fixedly provided with a worm wheel. The worm 10 is horizontally and rotatably arranged on the furnace body 1. The worm 10 is cooperated with the worm wheels at the lower ends of the two transmission rods 44, and one end of the worm 10 is connected to the second motor 11.

[0031] The worm 10 has two sections of threads that respectively cooperate with the two turbines 29 , so that only one second motor 11 is required to drive it. The cooperation between the worm 10 and the turbine 29 can drive the two sets of telescopic frames 8 to extend and retract synchronously.

[0032] like Figure 9As shown, further, an air bag 45 is fixedly provided on the inner side of the furnace door 3 in a circle, and the air bag 45 is correspondingly surrounded on the outer side of the taking and placing port 2. An air inlet 4 connecting to the air bag 45 is provided on the furnace door 3, and the air inlet 4 is used to connect to an external high-pressure air supply system.

[0033] The high-pressure air supply system utilizes existing technology to inflate air into the airbag 45 through the air inlet 4. For example, it includes an air pump and an air pipe, which connects the air inlet 4 on the furnace door 3 to the air pump. After the furnace door 3 is closed, the high-pressure air supply system inflates the airbag 45, causing it to swell and press against the perimeter of the access opening 2, thereby improving the sealing around the access opening 2.

[0034] like Figure 4 As shown, further, the vacuum system includes an exhaust pipe 12 connected to the furnace body 1, and an exhaust pump 13 is connected to the exhaust pipe 12. A vacuum gauge is provided on the exhaust pipe 12, and the vacuum gauge is located between the exhaust pump 13 and the furnace body 1. The exhaust pump 13 extracts the gas in the furnace body 1 to form a vacuum, and the vacuum gauge adopts existing technology to detect the vacuum degree in the furnace body 1.

[0035] Furthermore, the temperature control system includes a heating system and a water cooling system. The heating system is used to heat the furnace body 1, and the water cooling system is used to take away heat to cool the furnace body 1. Through the cooperation of the heating system and the water cooling system, the temperature inside the furnace body 1 is balanced, and after the nitriding is completed, the furnace body 1 can be quickly cooled by the water cooling system, so that the connecting rod mold steel 55 can be taken out as soon as possible.

[0036] like Figure 4~Figure 5 As shown, the heating system includes a heating tube 35, a display panel and a temperature sensor 18. The number of the heating tubes 35 is several. The heating tubes 35 are vertically arranged and installed on the inner wall of the furnace body 1 through a bracket 36. The material of the bracket 36 is high-temperature resistant ceramic. The setting of the bracket 36 allows the heating tube 35 to be close to the inner wall of the furnace body 1, thereby avoiding the heat of the heating tube 35 being directly transferred to the furnace body 1, which causes the side wall temperature of the furnace body 1 to be high and causes heat waste. The temperature sensor 18 is inserted into the furnace body 1 to detect the temperature inside the furnace body 1, and the temperature sensor 18 is electrically connected to the display panel.

[0037] The water cooling system includes a water cooling pipe 34, which is spirally wound on the inner wall of the furnace body 1. At the position of the access port 2, the water cooling pipe 34 bypasses the edge of the access port 2. The outer wall of the furnace body 1 is provided with a water inlet and a water outlet connected to both ends of the water cooling pipe 34. The water inlet is located below the water outlet. Cold water is sent from the water inlet into the water cooling pipe 34 to take away the heat in the furnace body 1, and then discharged from the water outlet.

[0038] like Figure 4As shown, further, the water inlet and the water outlet are connected to a water circulation system, which includes a water outlet pipe 20, a cooling device, a water delivery pipe 21, a water tank 22, a submersible pump, and a water inlet pipe 23. The two ends of the water outlet pipe 20 are respectively connected to the water outlet and the cooling device, the two ends of the water delivery pipe 21 are respectively connected to the cooling device and the water tank 22, the submersible pump is arranged in the water tank 22, and the two ends of the water inlet pipe 23 are respectively connected to the submersible pump and the water inlet. The hot water discharged from the water outlet is sent to the cooling device through the water outlet pipe 20 for cooling. The cooled cold water is sent to the water tank 22 through the water delivery pipe 21 and is pumped by the submersible pump through the water inlet pipe 23 and enters the water cooling pipe 34 again to cool the furnace body 1, thereby realizing water recycling. The water tank 22 is provided with a water exchange port, which can replenish the water in the water circulation system and replace the water after a long time.

[0039] like Figures 10 to 12 As shown, the cooling device includes at least one heat exchange box, which takes away the heat of the hot water through the heat exchange box to cool the hot water into cold water. The heat exchange box includes a box body 24, which is rectangular. The upper and lower ends of the box body 24 are respectively provided with an air outlet cavity 26 and an air inlet cavity 25. The upper end of the air outlet cavity 26 is provided with an air outlet 47, and the lower end of the air inlet cavity 25 is provided with an air inlet 46. A fan assembly is provided in the air inlet 46. The box body 24 is densely provided with a number of heat exchange tubes 50 connecting the air inlet cavity 25 and the air outlet cavity 26. Driven by the fan assembly, an air flow is formed to enter the air inlet cavity 25 from the air inlet 46, and then enter the air outlet cavity 26 after passing through the box body 24 through the number of heat exchange tubes 50, and is blown out from the air outlet 47.

[0040] The housing 24 is provided with an inlet 51 and an outlet 52 on either side thereof. These inlet 51 and outlet 52 are connected to the water outlet pipe 20 and the water supply pipe 21, respectively. When multiple heat exchanger boxes are provided, the boxes are arranged in a continuously curved "Z"-shaped path for removable connection. For a housing 24 located on a straight path, the inlet 51 and outlet 52 are located on opposite sides of the housing 24. For a housing 24 located on a corner path, the inlet 51 and outlet 52 are located on adjacent sides of the housing 24. The dimensions of the inlet 51 and outlet 52 are consistent with the cross-section of the interior space of the housing 24, and the cross-section is parallel to the side of the housing 24 where the inlet 51 or outlet 52 is located, ensuring that the water flowing through the housing 24 passes through as thoroughly as possible. Connecting portions 48 are provided at both the upper and lower ends of the inlet 51 and outlet 52 of the box 24. When two adjacent boxes 24 are joined, the corresponding connecting portions 48 are fastened by bolts to securely connect the two boxes 24. During connection, the inlet 51 of the rear box 24 connects to the outlet 52 of the front box 24. Preferably, a sealing ring is interposed between the two adjacent boxes 24 to enhance the sealing performance of the connection. Furthermore, preferably, a mounting bracket is connected to the lower end of each heat exchange box, and the lower end of the mounting bracket is equipped with a universal wheel with a brake.

[0041] When there is only one heat exchange box, the inlet 51 and the outlet 52 of the box body 24 are connected to the outlet pipe 20 and the water supply pipe 21 respectively through the inlet end expansion cover 49 and the discharge end expansion cover 27. The upper and lower ends of the larger ends of the inlet end expansion cover 49 and the discharge end expansion cover 27 are provided with connecting edges corresponding to the connecting part 48 of the box body 24. The connecting part 48 and the connecting edge are fastened with bolts to connect the inlet end expansion cover 49 and the discharge end expansion cover 27 to the box body 24. Preferably, a sealing ring is provided between the inlet end expansion cover 49 and the box body 24 and between the discharge end expansion cover 27 and the box body 24 to improve the sealing performance of the connection.

[0042] A water inlet connection port 53 connected to the water outlet pipe 20 is provided at the smaller end of the inlet end expansion cover 49, and a water outlet connection port 54 connected to the water supply pipe 21 is provided at the smaller end of the discharge end expansion cover 27, wherein the lower end of the water outlet connection port 54 is not higher than the lower end of the outlet 52 of the box body 24, so that the water in the box body 24 can be completely discharged from the water outlet connection port 54.

[0043] When multiple heat exchange boxes are spliced ​​together, the inlet 51 of the box body 24 located at the front is connected to the inlet end expansion cover 49, and the outlet 52 of the box body 24 located at the rear is connected to the outlet end expansion cover 27.

[0044] Hot water in outlet pipe 20 is delivered to tank 24 through inlet end expansion housing 49 and inlet 51. Air flowing through heat exchange tubes 50 within tank 24 exchanges heat with the hot water, removing the heat from the hot water. The hot water is then delivered through outlet 52 of tank 24 and outlet end expansion housing 27 into water pipe 21 and into water tank 22. The number of heat exchange tanks can be selected based on needs. A greater number of heat exchange tanks allows for greater heat exchange and lowers the water temperature within water tank 22.

[0045] In addition, multiple heat exchange boxes are spliced ​​in a continuously bent "Z"-shaped path, which can reduce the length and space occupied.

[0046] like Figure 4 As shown, further, the nitrogen supply system includes an ammonia tank 14, an air supply pipe 15, an air supply pump 16 and a gas flow meter 17, the air supply pipe 15 connects the ammonia tank 14 and the furnace body 1, the air supply pump 16 and the gas flow meter 17 are connected to the air supply pipe 15, and the gas flow meter 17 is located between the air supply pump 16 and the furnace body 1; an air inlet pipe 30 is provided at the upper end of the furnace body 1, the air inlet pipe 30 is connected to the air supply pipe 15, and an air outlet pipe 32 is provided at the upper part of the furnace body 1, the air outlet pipe 32 is coiled into a circular shape, one end of the air outlet pipe 32 is connected to the air inlet pipe 30 through a connecting pipe 31, the other end of the air outlet pipe 32 is sealed, and a plurality of air holes 33 are opened at the lower end of the air outlet pipe 32 along the length direction of the air outlet pipe 32.

[0047] The ammonia gas in the ammonia tank 14 is driven by the gas supply pump 16 to enter the furnace body 1 through the gas supply pipe 15 , the gas inlet pipe 30 , the gas outlet pipe 32 and the gas hole 33 .

[0048] Furthermore, a vent is provided on the side wall of the furnace body 1. A one-way valve for inward gas flow is provided within the vent, and a gas valve is provided at the outer end of the vent. The one-way gas valve utilizes existing technology to prevent gas from entering the furnace body 1 from outside. During vacuuming, the gas valve is closed. After nitriding is completed, the gas valve is opened, and a vacuum pump 13 is used to extract the remaining ammonia and hot air within the furnace body 1, thereby accelerating the cooling of the furnace body 1.

[0049] Furthermore, an insulation layer is provided on the outer wall of the furnace body 1 to prevent burns to personnel caused by excessive temperature of the furnace body 1. The insulation layer adopts existing technology, for example, including an insulation paint layer and a ceramic fiber cotton layer arranged from the inside to the outside.

[0050] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0052] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A surface nitriding process for connecting rod die steel, characterized in that: The method comprises first coating a layer of an impermeability-proofing agent on the fillet of the through hole (56) on the connecting rod mold steel (55), and covering the fillet with a layer of a ceramic fiber blanket (58); then sending the connecting rod mold steel (55) into a surface nitriding device for nitriding, first drawing a vacuum during the nitriding process, then performing a first preheating, heating to 350° and keeping the temperature for 90 to 180 minutes, then performing a second preheating, heating to 480° and keeping the temperature for 120 minutes, then performing formal heating, heating to 550° and keeping the temperature for 660 minutes, charging ammonia gas during the formal heating process, the flow rate of ammonia gas is 2000L / H, and the nitrogen potential Kn is maintained at 1.6; finally cooling the connecting rod mold steel (55) and taking it out; The anti-seepage agent includes 40-50 parts of tin powder, 45-70 parts of aluminum oxide powder, 15-25 parts of quartz powder, 10-15 parts of kaolin, 10-15 parts of lithium bentonite, 4-7 parts of titanium dioxide, 3-6 parts of sodium hydroxide, 3-5 parts of cold-drawn polypropylene fiber and water.

2. A surface nitriding device as claimed in claim 1, characterized in that: The invention comprises a furnace body (1) and a nitrogen supply system, a vacuum system, a temperature control system, and an atmosphere detection system (19) connected to the furnace body (1). A loading and unloading port (2) is provided on one side of the furnace body (1), and a furnace door (3) is matched with the loading and unloading port (2). A support platform (28) is provided at the bottom of the furnace body (1), and a rotating table (5) is provided on the support platform (28). The rotating table (5) is driven to rotate by a first motor (7). A material discharge tray (6) is placed on the rotating table (5), and a support foot (37) is provided at the lower end of the material discharge tray (6). A plurality of vertically penetrating hollow holes (38) are arranged in an array on the material discharge tray (6). A plurality of plug holes are arranged in an array on the upper end of the material discharge tray (6), and vertical support rods (39) are inserted into the plug holes.

3. The surface nitriding device according to claim 2, characterized in that: The furnace door (3) is driven by a lifting mechanism to open and close vertically. The furnace door (3) is slidably mounted on the furnace body (1) on both sides. The lifting mechanism comprises telescopic frames (8) located on both sides of the furnace door (3). The telescopic frames (8) are vertically arranged, and the lower ends of the telescopic frames (8) are mounted on the furnace body (1). The upper ends of the telescopic frames (8) are fixedly connected to the furnace door (3). The two sets of telescopic frames (8) are driven to extend and retract by the same driving mechanism.

4. The surface nitriding device according to claim 3, characterized in that: The telescopic frame (8) comprises at least three sleeves (9) which are slidably connected in sequence in the vertical direction, wherein the lower end of a sleeve (9) located at the top is matched and inserted into a sleeve (9) located at the bottom for sliding arrangement, wherein the lower end of a sleeve (9) located at the bottom is fixedly mounted on the furnace body (1), and the upper end of a sleeve (9) located at the top is fixedly connected to the furnace door (3), and a rotatable screw rod (42) is provided in each of the sleeves (9), and a bottom plate (40) is fixedly provided at the lower end of the sleeve (9), and the lower end of the screw rod (42) in the sleeve (9) is rotatably mounted on the bottom plate (40), and a through hole (41) is opened at the center of the bottom plate (40), and the sleeve (9) located at the bottom is fixedly mounted on the bottom plate (40). ) passes through a through hole (41), the through hole (41) is provided with an external thread matching the corresponding screw rod (42), the bottom of the screw rod (42) located in the upper sleeve (9) extends upward and is provided with an inner hole (43) matching the lower screw rod (42), the upper end of the screw rod (42) located in the lower sleeve (9) passes through the corresponding through hole (41), and is inserted into the inner hole (43) of the screw rod (42) located in the upper sleeve (9), the inner wall of the inner hole (43) is provided with a vertically extending limiting convex edge, and the outer wall of the screw rod (42) inserted into the inner hole (43) is provided with a limiting groove matching the limiting convex edge; The driving mechanism comprises a transmission rod (44), a worm wheel, a worm (10) and a second motor (11). Two transmission rods (44) are provided. Both transmission rods (44) are rotatably mounted on the furnace body (1). The two transmission rods (44) are respectively located below two sets of telescopic frames (8). The upper ends of the transmission rods (44) are fixedly connected to the lower ends of the screw rods (42) in the lowermost sleeves (9) of the corresponding telescopic frames (8). The lower ends of the transmission rods (44) are fixedly provided with worm wheels. The worm (10) is horizontally and rotatably arranged on the furnace body (1). The worm (10) is cooperatively connected to the worm wheels at the lower ends of the two transmission rods (44). One end of the worm (10) is connected to the second motor (11).

5. The surface nitriding device according to claim 3, characterized in that: An air bag (45) is fixedly provided on the inner side of the furnace door (3) and surrounds the outer side of the access opening (2). An air inlet (4) communicating with the air bag (45) is provided on the furnace door (3). The air inlet (4) is used to connect to an external high-pressure air supply system.

6. The surface nitriding device according to claim 2, characterized in that: The vacuum system comprises an exhaust pipe (12) in communication with the furnace body (1), the exhaust pipe (12) being connected to an exhaust pump (13), the exhaust pipe (12) being provided with a vacuum gauge, and the vacuum gauge being located between the exhaust pump (13) and the furnace body (1).

7. The surface nitriding device according to claim 2, characterized in that: The temperature control system comprises a heating system and a water cooling system; the heating system comprises a heating tube (35), a display panel and a temperature sensor (18); the number of the heating tubes (35) is several; the heating tubes (35) are vertically arranged and mounted on the inner wall of the furnace body (1) through a bracket (36); the temperature sensor (18) is inserted into the furnace body (1); the temperature sensor (18) is electrically connected to the display panel; the water cooling system comprises a water cooling tube (34); the water cooling tube (34) is spirally wound on the inner wall of the furnace body (1); a water inlet and a water outlet connected to two ends of the water cooling tube (34) are provided on the outer wall of the furnace body (1); the water inlet is located below the water outlet.

8. The surface nitriding device according to claim 7, characterized in that: The water inlet and the water outlet are connected to a water circulation system, the water circulation system comprising a water outlet pipe (20), a cooling device, a water delivery pipe (21), a water tank (22), a submersible pump and a water inlet pipe (23), the two ends of the water outlet pipe (20) being respectively connected to the water outlet and the cooling device, the two ends of the water delivery pipe (21) being respectively connected to the cooling device and the water tank (22), the submersible pump being arranged in the water tank (22), and the two ends of the water inlet pipe (23) being respectively connected to the submersible pump and the water inlet; the cooling device comprising at least one heat exchange box, the heat exchange box comprising a box body (24), the upper end and the lower end of the box body (24) being respectively provided with an air outlet cavity (26) ) and an air inlet chamber (25), the air outlet chamber (26) is provided with an air outlet (47) at the upper end, the air inlet chamber (25) is provided with an air inlet (46) at the lower end, a fan assembly is provided in the air inlet (46), a plurality of heat exchange tubes (50) connecting the air inlet chamber (25) and the air outlet chamber (26) are densely distributed in the box body (24), an inlet (51) and an outlet (52) are provided on two sides of the box body (24), the inlet (51) and the outlet (52) are respectively connected to the water outlet pipe (20) and the water supply pipe (21), and when there are multiple heat exchange boxes, the multiple heat exchange boxes are detachably spliced ​​in a continuously bent "Z" shaped path.

9. The surface nitriding device according to claim 2, characterized in that: The nitrogen supply system comprises an ammonia tank (14), an air supply pipe (15), an air supply pump (16) and a gas flow meter (17); the air supply pipe (15) connects the ammonia tank (14) and the furnace body (1); the air supply pump (16) and the gas flow meter (17) are connected to the air supply pipe (15); and the gas flow meter (17) is located between the air supply pump (16) and the furnace body (1); an air inlet pipe (30) is provided at the upper end of the furnace body (1); the air inlet pipe (30) is connected to the air supply pipe (15); an air outlet pipe (32) is provided at the upper part of the furnace body (1); the air outlet pipe (32) is coiled into a ring shape; one end of the air outlet pipe (32) is connected to the air inlet pipe (30); the other end of the air outlet pipe (32) is sealed; and a plurality of air holes (33) are provided at the lower end of the air outlet pipe (32) along the length direction of the air outlet pipe (32).

10. The surface nitriding device according to claim 2, characterized in that: A vent is provided on the side wall of the furnace body (1), a one-way guide valve with the gas flow direction facing inward is provided in the vent, and a gas valve is provided at the outer end of the vent.

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