A balanced nitriding method for controlling rack deformation during ion nitriding

Abstract

The present invention provides a balanced nitriding method for controlling the ion nitriding deformation of a rack, comprising the following steps: S1, performing stress relief treatment on the rack; S2, performing cleaning treatment on the surface of the rack; S3, brushing the back of the rack with ion nitriding anti-seepage paint at intervals; S4, and performing UV drying after brushing the ion nitriding anti-seepage paint; S5, ion nitriding process control; S6, cleaning the ion nitriding anti-seepage paint. The present invention uses the basic principle of residual stress balance to control the ion nitriding bending deformation of the rack, and uses the ion nitriding anti-seepage paint to brush the back of the rack at intervals in a rectangular shape to achieve a local anti-seepage effect, and controls the nitriding area of ​​the back of the rack to be the same as the nitriding area of ​​the tooth groove at the bottom of the open tooth surface, thereby achieving residual stress balance on both sides, thereby controlling the bending deformation of the rack, and having the effect of significantly improving the nitriding deformation of the rack under the effect of local anti-seepage.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial rack ion nitriding, and in particular to a balanced nitriding method for controlling rack ion nitriding deformation. Background Art

[0002] Racks are common, key components in industrial transmission systems, converting the rotational motion of gears into linear motion. Racks generally require surface hardening to improve their fatigue and wear resistance. Their asymmetric, slender structure is susceptible to heat-treatment deformation. Ion nitriding is a low-temperature surface heat treatment that undergoes no phase change in the matrix. It offers advantages such as high surface hardness, high fatigue strength, minimal deformation, and a low-carbon, environmentally friendly design. It is often used for surface hardening of precision racks to extend their service life. However, due to the complex and asymmetric shape of slender racks, deformations such as bending often occur during the ion nitriding process.

[0003] The deformation caused by nitriding can be divided into two categories: one is the physical strain caused by the expansion of the compound layer and the expansion of the iron lattice in the diffusion layer; the other is the material mechanical deformation based on the physical strain. Theoretical analysis shows that α-Fe forms γ'-Fe4N phase and ε-Fe 2-3 The strains in the N phase are 0.55 and 0.75, respectively. The microstructural transformation within the nitrided layer, due to differences in specific volume, results in microstructural stresses with compression at the surface and tension in the core. At the nitriding temperature, the material is essentially in an elastic-plastic state, with a lower yield strength in the core. The magnitude of this stress depends on the yield strength of the nitrided steel, the nitrogen concentration in the nitrided layer, and the depth of penetration. This stress, combined with the residual stress in the part before nitriding, constitutes the stress source that causes shape change. The basic principle of microstructural stress deformation is that, while enclosing the same volume, the surface area is increased, resulting in an expansion in the longitudinal dimension and a reduction in the transverse dimension, with sharp corners protruding and a concave surface. The magnitude of deformation caused by microstructural stress is primarily determined by the following factors: the difference in the workpiece dimensions in all directions; greater differences lead to more pronounced microstructural stress deformation caused by nitriding; the ratio of the nitrided layer area to the workpiece's longitudinal cross-section; a greater ratio leads to more pronounced microstructural stress deformation; and low material yield strength can increase deformation caused by microstructural stress.

[0004] Due to the complex and asymmetrical shape of the rack surface, a certain concentration of nitrogen atoms has penetrated into the rack surface, causing the structure to expand and generate a certain amount of compressive stress. The compressive stress on one side of the open tooth surface is parallel to the tooth surface and distributed along the tooth profile in different directions. Only the compressive stress at the bottom and top of the tooth is parallel to the back surface. The nitriding area on the back of the rack parallel to the center plane is larger, so the overall residual compressive stress on the open tooth surface parallel to the center plane is smaller than that on the back surface. Therefore, the deformation trend after nitriding is that one side of the tooth is concave, as shown in Figure 2. Figure 3 If the deformation is minor, the rack meshing accuracy will be reduced, and if it is serious, the rack will be scrapped. Summary of the Invention

[0005] To address the above shortcomings, the present invention provides an internal stress-balancing nitriding method for controlling rack deformation during ion nitriding. This method addresses the aforementioned problem: due to the complex and asymmetrical shape of the rack surface, a certain concentration of nitrogen atoms is infiltrated into the rack surface, causing the structure to expand and be constrained by the core matrix, resulting in a certain amount of compressive stress. The compressive stress on one side of the tooth surface is parallel to the tooth shape and distributed along the tooth profile in a different direction. Only the compressive stress at the tooth bottom is parallel to the back surface. The nitrided area on the back surface of the rack parallel to the center plane is larger, and the overall residual compressive stress on the open tooth surface parallel to the center plane is smaller than that on the back surface. As a result, the deformation trend after nitriding is concave on one side of the tooth. Minor deformation results in reduced rack meshing accuracy, while severe deformation can render the rack scrapped.

[0006] The present invention is achieved in that:

[0007] A balanced nitriding method for controlling rack ion nitriding deformation includes the following steps:

[0008] S1. Stress relief treatment of the rack: The rack is subjected to multiple stress relief tempering treatments to eliminate the structural stress and processing stress existing after the rack is prepared, and multiple tempering treatments are used to eliminate the stress;

[0009] S2. Rack surface cleaning: Clean the rack surface after multi-stage tempering treatment, remove dust and oil on the rack surface, and dry the cleaned rack;

[0010] S3. Apply ion nitriding anti-seepage paint to the back of the rack at intervals: Apply ion nitriding anti-seepage paint to the back of the rack after drying at intervals in a rectangular shape, and control the nitriding area on the back of the rack to be the same as the nitriding area of ​​the tooth groove at the bottom of the tooth surface;

[0011] S4. After applying the ion nitriding anti-seepage paint, perform UV drying: After applying the ion nitriding anti-seepage paint on the back of the rack, use a UV dryer to quickly dry the ion nitriding anti-seepage paint to improve the adhesion of the metal particles in the ion nitriding anti-seepage paint;

[0012] S5. Ion nitriding process control: The rack coated with ion nitriding anti-seepage coating is hoisted in the ion nitriding furnace for ion nitriding treatment, and an array infrared thermometer is used to conduct a full range of temperature detection on the surface of the rack to facilitate the control of the ion nitriding temperature and timely regulation and control. The heating rate is controlled to be ≤2.5℃ / min, and the average temperature is 450℃ for 1.5 hours, which is conducive to the uniform temperature of the rack;

[0013] S6. Cleaning of ion nitriding anti-seepage coating: After the rack is ion nitrided, the rack is taken out and the ion nitriding anti-seepage coating on the back is cleaned by mechanical cleaning, and then the deformation and warping of the rack is tested.

[0014] In one embodiment of the present invention, the tempering temperature in S1 is lower than the quenching temperature of the rack, and the rack is tempered at a high temperature by tempering treatment, and the tempering temperature is controlled at 580-650°C, and the holding time is 120 minutes.

[0015] In one embodiment of the present invention, the cleaning in S2 is first performed by flushing the surface and tooth gaps of the rack with a high-pressure water flow, and after flushing, an ultrasonic cleaner is used to thoroughly clean the deep tooth gaps of the rack, and then a degreaser is used to degrease the surface of the rack, and then the degreaser is cleaned with clean water, and finally placed in hot air at 220~260℃ for drying.

[0016] In one embodiment of the present invention, the degreasing agent includes triethanolamine oleate soap, coconut oil fatty acid diethanolamide, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, sodium benzoate, sodium pyrophosphate, azelaic acid, myristic acid, ethanol, polyether-modified silicone, sodium hydroxide, and JFC. When used, it is mixed with 40°C warm water in a ratio of 1:5 and is convenient for use with an ultrasonic cleaner.

[0017] In one embodiment of the present invention, the interval at which the racks are coated with the ion nitriding anti-seepage coating in S3 is calculated as follows:

[0018] Assume the tooth groove width of the rack is A, and the tooth bottom width is B, then

[0019]

[0020]

[0021] Where: α is the rack pressure angle, m is the rack module

[0022] The coating-to-air ratio of the rack back ]Adjust according to the ratio of these two widths and distribute them at intervals along the length of the rack. The coating width is n*B+K and the spare width is n*A, where n is the coefficient, n=1~5, and is selected according to the size of the rack module. When the module is small, n is large, and when the module is large, n is small; K is the compensation constant, K=2.5~3.5.

[0023] In one embodiment of the present invention, the ion nitriding anti-seepage coating in S3 is applied by brushing with a soft brush. The thickness of the ion nitriding anti-seepage coating is 1.0-1.5 mm for the first time. After being placed at room temperature for 10 minutes, it is brushed for the second time, and the total thickness reaches 1.5~2.0 mm. After two brushings, it is quickly dried in a UV dryer.

[0024] In one embodiment of the present invention, the array infrared thermometer in S5 is used to detect the temperature of the rack surface during the ion nitriding process. When high-energy nitrogen ions bombard the workpiece surface at a very high speed and convert kinetic energy into thermal energy, the temperature distribution on the rack surface can be detected, which facilitates temperature adjustment so that the temperature of the rack surface can be maintained at 540~550℃, thereby improving the uniformity of nitriding.

[0025] In one embodiment of the present invention, the ion nitriding furnace in S5 is maintained in a vacuum state, and the glow discharge of the ion nitriding furnace is unevenly distributed from the cathode to the anode, and is divided into several regions from the cathode to the anode: Aston dark region, cathode glow region, cathode dark region, negative glow region, Faraday dark region, positive column region, anode dark region, and anode glow region;

[0026] The sum of the widths of the Aston dark area, cathode bright area, and cathode dark area is called the cathode drop area d k The voltage between the cathode and anode mainly falls within the cathode potential drop zone. k Inversely proportional to air pressure, P·d k =constant;

[0027] Cathode drop zone d k The length of the negative glow zone is called the cathode discharge length d glow. When the distance between the two cathodes is d1, d1<2dk, the glow is extinguished; when the distance between the two cathodes is d1, d1> 2d glow, the two cathode drop zones are independent of each other and do not affect each other, and the glow discharge proceeds normally; when the distance between the two cathodes is d1, d1=2d glow, the two negative glow zones merge, the current density increases, and the glow intensity increases, which is called the hollow cathode effect. During the ion nitriding process, the formation of the hollow cathode effect should be avoided.

[0028] In one embodiment of the present invention, the mechanical cleaning in S6 is performed by sandblasting or wire wheel cleaning, and the sandblasting is performed by compressed air driving fine quartz sand to spray toward the back of the rack for cleaning, and the pressure of the compressed air is 0.5-0.6 MPa;

[0029] And the wire wheel cleaning uses the electric motor to drive the wire wheel transmission mechanism to clean the back of the rack evenly, thoroughly and safely.

[0030] The beneficial effects of the present invention are:

[0031] The present invention uses the basic principle of residual stress balance to control the ion nitriding bending deformation of the rack. The ion nitriding anti-seepage paint is used to brush the back of the rack at intervals. The brushing shape is rectangular to achieve a local anti-seepage effect. The nitriding area on the back of the rack is controlled to be the same as the nitriding area of ​​the tooth groove at the bottom of the open tooth surface, so as to achieve residual stress balance on both sides, thereby controlling the bending deformation of the rack. Specifically, most of the tissue stress and processing stress in the rack are eliminated through stress relief tempering, so that the stress of the rack can be released after the ion nitriding anti-seepage paint is applied. When a certain concentration of nitrogen atoms is infiltrated into the surface of the rack, the tissue expands and a certain compressive stress is generated. The rack is cleaned by multiple racks, so that the ion nitriding anti-seepage coating can be stably applied, and a UV dryer is used for drying to improve the rapid arrangement and adhesion of the metal particles in the ion nitriding anti-seepage coating. Array temperature measurement is used to facilitate the control of the temperature of the rack during the ion nitriding process, which is convenient for regulation. By setting the parameters of the ion nitriding furnace, the stability and speed of nitriding are improved. Under the action of local anti-seepage, the nitriding area on the back of the rack is controlled to be the same as the nitriding area of ​​the tooth groove at the bottom of the open tooth surface, so as to achieve residual internal stress balance on both sides, thereby controlling the bending deformation of the rack. The warping of the test rack is reduced from 0.16mm of conventional nitriding to 0.05mm, which has the effect of significantly improving the nitriding deformation of the rack. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 Schematic diagram of the steps of the present invention;

[0034] Figure 2 Schematic diagram of tooth groove width and tooth bottom width of the present invention;

[0035] Figure 3 Schematic diagram of the deformation trend of the rack after ion nitriding of the present invention;

[0036] Figure 4 Schematic diagram of the distribution of residual compressive stress along the surface of the rack nitriding layer according to the present invention;

[0037] Figure 5 Schematic diagram of the distribution of the anti-seepage coating on the back of the rack of the present invention. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, 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, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0039] See also Figure 1-5 , the present invention provides a technical solution:

[0040] A balanced nitriding method for controlling rack ion nitriding deformation includes the following steps:

[0041] S1. Stress relief treatment of the rack: The rack is subjected to multiple stress relief tempering treatments to eliminate the structural stress and processing stress existing after the rack is prepared, and multiple tempering treatments are used to eliminate the stress;

[0042] S2. Rack surface cleaning: Clean the rack surface after multi-stage tempering treatment, remove dust and oil on the rack surface, and dry the cleaned rack;

[0043] S3. Apply ion nitriding anti-seepage paint to the back of the rack at intervals: Apply ion nitriding anti-seepage paint to the back of the rack after drying at intervals in a rectangular shape, and control the nitriding area on the back of the rack to be the same as the nitriding area of ​​the tooth groove at the bottom of the tooth surface;

[0044] S4. After applying the ion nitriding anti-seepage paint, perform UV drying: After applying the ion nitriding anti-seepage paint on the back of the rack, use a UV dryer to quickly dry the ion nitriding anti-seepage paint to improve the adhesion of the metal particles in the ion nitriding anti-seepage paint;

[0045] S5. Ion nitriding process control: The rack coated with ion nitriding anti-seepage coating is hoisted in the ion nitriding furnace for ion nitriding treatment, and an array infrared thermometer is used to conduct a full range of temperature detection on the surface of the rack to facilitate the control of the ion nitriding temperature and timely regulation and control. The heating rate is controlled to be ≤2.5℃ / min, and the average temperature is 450℃ for 1.5 hours, which is conducive to the uniform temperature of the rack;

[0046] S6. Cleaning of ion nitriding anti-seepage coating: After the rack is ion nitrided, the rack is taken out and the ion nitriding anti-seepage coating on the back is cleaned by mechanical cleaning, and then the deformation and warping of the rack is tested.

[0047] In order to control the quenching and tempering of the rack, eliminate the residual stress of the rack, improve the stability of the rack, and prevent excessive stress in the rack, which causes excessive stress in the local anti-seepage part after ion nitriding of the tooth groove at the bottom of the open tooth surface, resulting in bending, in this embodiment, preferably, the tempering temperature in S1 is lower than the quenching temperature of the rack, and the tempering temperature of the rack adopts high-temperature tempering treatment, and the tempering temperature is controlled at 580~650℃, and the holding time is 120min.

[0048] In order to process the dust and oil on the surface of the rack, clean the dust and oil in the rack gaps, and improve the cleanliness of the rack, in this embodiment, preferably, the cleaning in S2 is first performed by flushing the surface of the rack and the tooth gaps with a high-pressure water flow, and after flushing, an ultrasonic cleaner is used to thoroughly clean the deep parts of the tooth gaps of the rack, and then the surface of the rack is degreased with a degreaser, and the degreaser is then cleaned with clean water, and finally placed in hot air at 220~260℃ for drying.

[0049] In order to clean the oil stains on the surface of the rack and prevent the degreasing agent from having a large amount of foam, and to activate the oil stains to facilitate the removal of the oil stains, in this embodiment, preferably, the degreasing agent includes oleic acid triethanolamine soap, coconut oil fatty acid diethanolamide, sodium dodecylbenzenesulfonate, fatty alcohol polyoxyethylene ether, sodium benzoate, sodium pyrophosphate, azelaic acid, myristic acid, ethanol, polyether-modified silicone, sodium hydroxide, and JFC. When in use, it is mixed with 40°C warm water in a ratio of 1:5 and is convenient for use with an ultrasonic cleaner.

[0050] In order to calculate the size and proportion of local anti-seepage, the tooth groove width and tooth bottom width are calculated and obtained. In this embodiment, preferably, the interval of the rack coated with ion nitriding anti-seepage coating in S3 is calculated as follows:

[0051] Assume the tooth groove width of the rack is A, and the tooth bottom width is B, then

[0052]

[0053]

[0054] Where: α is the rack pressure angle, m is the rack module

[0055] The coating-to-air ratio of the rack back ] The two widths are adjusted according to the ratio and distributed at intervals along the length of the rack. The coating width is n*B+K and the spare width is n*A, where n is a coefficient, n=1~5, which is selected according to the size of the rack module. When the module is small, n is large, and when the module is large, n is small; K is a compensation constant, K=2.5~3.5, and considering that due to the superposition effect of the glow, the depth of the nitriding layer of the tooth groove will be slightly shallower than that of the back, and the residual stress amplitude will also be slightly smaller, which is compensated by K.

[0056] In order to achieve the precise application of ion nitriding anti-seepage coating on the back side of the rack, and to achieve multiple applications to a certain thickness, and to achieve rapid drying, in this embodiment, preferably, the ion nitriding anti-seepage coating in S3 is applied by brushing, with a soft-bristled brush. The thickness of the ion nitriding anti-seepage coating is 1.0~1.5mm for the first brushing. After standing at room temperature for 10 minutes, it is brushed for the second time. It is naturally allowed to stand at room temperature to prevent the first layer of ion nitriding anti-seepage coating from drying out, and the second layer cannot adhere to form a whole. It is naturally allowed to stand, which facilitates the application and stacking of the second layer of ion nitriding anti-seepage coating, and the total thickness reaches 1.5~2.0mm. After two brushings, a UV dryer is used for rapid drying.

[0057] In order to realize the overall temperature detection of the rack, facilitate the synchronous acquisition of temperature information, facilitate temperature control, and prevent large temperature differences during ion nitriding, which may cause inconsistent stress in the rack and bending deformation, in this embodiment, preferably, the array infrared thermometer in S5 is used to detect the temperature of the rack surface during ion nitriding. When high-energy nitrogen ions bombard the workpiece surface at a high speed and convert kinetic energy into thermal energy, the temperature distribution on the rack surface can be detected, which facilitates temperature adjustment so that the temperature of the rack surface can be maintained at 540~550℃, thereby improving the uniformity of nitriding.

[0058] In order to realize the control of the ion nitriding furnace, facilitate the ion nitriding of the rack, improve the effect of ion nitriding, and prevent the rack from bending, in this embodiment, preferably, the ion nitriding furnace in S5 is kept in a vacuum state, and the distribution of the glow discharge brightness of the ion nitriding furnace from the cathode to the anode is uneven, and is divided into several regions from the cathode to the anode, namely, Aston dark area, cathode glow area, cathode dark area, negative glow area, Faraday dark area, positive column area, anode dark area, and anode glow area;

[0059] The sum of the widths of the Aston dark area, cathode bright area, and cathode dark area is called the cathode drop area d k The voltage between the cathode and anode mainly falls within the cathode potential drop zone. k Inversely proportional to air pressure, P·d k =constant;

[0060] Cathode drop zone dk The length of the negative glow zone is called the cathode discharge length d glow. When the distance between the two cathodes is d1, d1<2dk, the glow is extinguished; when the distance between the two cathodes is d1, d1> 2d glow, the two cathode drop zones are independent of each other and do not affect each other, and the glow discharge proceeds normally; when the distance between the two cathodes is d1, d1=2d glow, the two negative glow zones merge, the current density increases, and the glow intensity increases, which is called the hollow cathode effect. During the ion nitriding process, the formation of the hollow cathode effect should be avoided.

[0061] In order to clean the ion nitriding anti-seepage coating on the back of the rack after ion nitriding and prevent the rack from being affected by chemical agents, in this embodiment, preferably, the mechanical cleaning in S6 adopts sandblasting cleaning or wire wheel cleaning, and the sandblasting cleaning is carried out by compressed air driving fine quartz sand to spray the back of the rack for cleaning, and the pressure of the compressed air is 0.5~0.6MPa;

[0062] And the wire wheel cleaning uses the electric motor to drive the wire wheel transmission mechanism to clean the back of the rack evenly, thoroughly and safely.

[0063] Production operating procedures

[0064] (1) Preparation and furnace loading.

[0065] (2) Use gasoline to carefully clean the rack to remove oil, rust, mud, and burrs. The surface must be free of oil, paint, and other contaminants. Threaded holes, blind holes, and other areas must be thoroughly cleaned with tools. Do not wipe the surface of the workpiece with a lint-prone cloth. Do not touch the cleaned rack with oily gloves. Bake the rack for 3 to 5 hours after cleaning.

[0066] (3) Match the model and type of the rack with the drawing, and clarify which parts require local waterproofing.

[0067] (4) Install fixtures: When hoisting the racks, ensure a reasonable spacing between the racks. Add a cover plate on the top and necessary auxiliary cathodes and auxiliary anodes to improve temperature uniformity. When loading the furnace, the distance between the racks and the furnace shell must not be less than 30mm. Pay attention to improving the furnace atmosphere and the uniformity of the rack temperature to avoid arcing and glow concentration caused by improper installation, poor contact, and small gaps.

[0068] (5) The end of the temperature measuring thermocouple should be located at a suitable position to reflect the rack temperature.

[0069] Furnace treatment

[0070] (1) Before loading the rack into the furnace, open the vent valve and fill the vacuum furnace chamber with air to reach atmospheric pressure. Then, lift the furnace bell cover and use coarse sandpaper to clean the cathode disk and other dirt. Check the insulation of the cathode support. If necessary, remove it for cleaning. Check whether the cathode connection screws are loose. When loading the furnace, pay attention to the placement of the workpieces. Try to be as symmetrical as possible and the heat dissipation conditions should be as similar as possible. If necessary, set up auxiliary cathodes or auxiliary anodes to facilitate temperature uniformity. Finally, place the metallographic specimens and check the loading of the furnace. Do not use oily gloves during the loading process. Use a gasoline cloth to wipe the furnace bottom sealing ring, furnace tube and bell cover flanges. Cover the furnace cover. When it is almost in place, use a slow crane to slowly lower it to prevent the furnace body from being greatly impacted, damaging the equipment and causing the workpiece to tip or shift. Then tighten the vent valve and connect the anode quick connector on the furnace cover.

[0071] (2) Turn on the cooling water of the vacuum pump, close the main power switch, turn on the main control switch on the electric control cabinet, then the relevant indicator light will be displayed, start the vacuum pump, and during pre-vacuuming, two vacuum pumps can be started at the same time to speed up the pumping speed. During nitriding and cooling, turn on one vacuum pump to maintain the vacuum. At the beginning of the pumping, give the electric butterfly valve on the 1# vacuum pump a smaller angle to prevent the vacuum pump from spraying oil. After a certain period of time, gradually open the butterfly valve angle until it reaches 90°. Open the electric butterfly valve on the 2# vacuum pump to 90°. After a certain period of time, the pressure value displayed on the vacuum instrument should drop.

[0072] (3) When the pressure in the furnace is pumped down to 50-6.7 Pa, prepare to connect the high voltage. Before this, the "voltage setting" and "duty cycle setting" potentiometers on the "pulse controller" should be in the low position, and the function selection switch should be in the "manual" position. Turn on the "high voltage" button, slowly adjust the "voltage setting" potentiometer, and observe the "peak voltage" meter. When it reaches about 500V, turn on the "pulse" button and connect the power chopper. At this time, a glow should appear in the furnace, bombarding the oil and oxides on the surface of the workpiece, accompanied by arc flashes. The "arc display" indicator on the "pulse controller" flashes continuously. Use a small current to break up the arc and clean the rack surface, and slowly increase the temperature. At the same time, pass a small amount of cooling water into the furnace shell.

[0073] (4) During the arcing process, adjust the "voltage setting" and "duty cycle setting" potentiometers according to the situation, and pay attention to their coordinated use, so that the glow current should gradually increase. After the arcing in the furnace has been basically stable for a certain period of time, open the hydrogen bottle valve, adjust the hydrogen pressure reducing valve to adjust the output pressure to 0.1~0.2 MPa, set the temperature to open the hydrogen flow meter, and introduce a small amount of gas medium into the furnace to speed up the arcing process. When the "arc display" indicator light changes from constantly on to intermittently on and off, you can rotate the "voltage setting" potentiometer clockwise to increase the voltage. When the voltage rises to 600~800V, the "arc display" light flashes sparsely, indicating that the arc cleaning stage is over. Adjust the "conduction ratio setting" potentiometer to 20~30% and start heating.

[0074] (5) After the glow in the furnace stabilizes and the temperature rises to a certain stage (300-350°C), increase the flow of atmosphere into the furnace, adjust the opening angle of the small butterfly valve, and adjust the gas pressure in the furnace to the process requirement. At this time, the glow thickness on the workpiece surface is about 3-5mm. As the gas pressure increases, the current increases accordingly. Adjust the voltage and duty cycle to appropriate values ​​to provide the corresponding heating power and heating speed.

[0075] (6) Air supply and water supply: After the glow becomes stable, the voltage and current can be increased appropriately, and the heating rate can be controlled to be 200~250℃ / h. After the gear is heated to about 300℃, an appropriate amount of hydrogen is introduced to maintain high voltage and low pressure to enhance sputtering (Note: During the entire ventilation process, the pressure at the inlet end of the nitrogen and hydrogen flowmeters, that is, the pressure at the outlet end of the gas cylinder pressure reducing valve, shall not exceed 19.8N / cm 2 , the outlet pressure is maintained at 1atm.

[0076] (7) During the heating or holding process, if there is a strong arc discharge concentrated in a certain place and it cannot be extinguished automatically, measures should be taken to extinguish the arc as soon as possible, such as reducing the voltage and conduction ratio. If the arc is caused by improper furnace installation or small holes or slits, the power should be turned off, the furnace cover should be opened after the temperature has dropped, and the furnace should be reinstalled. Do not force the operation.

[0077] (8) Temperature uniformity: When the gear temperature approaches 450°C, the furnace pressure and other parameters should be adjusted according to the temperature uniformity in the furnace, and the temperature should be uniformed for 1 to 2 hours.

[0078] (9) Perform the first stage of nitriding process: When the rack temperature rises to 520~530℃, bombard the rack again with uniform temperature for one hour. Then, introduce nitrogen, hydrogen and argon gas at a nitrogen supply ratio of 4~10% (the total flow rate of the mixture is generally 800~1100ml / min). Adjust the butterfly valve opening and voltage and current values, adjust the furnace pressure, maintain a certain furnace pressure, the recommended voltage is 650~750V, and the recommended furnace pressure is not less than 350Pa. Stabilize the temperature and start timing. Turn the temperature control selector switch to the "automatic" position. The temperature controller will output a PID control signal to control the "duty cycle".

[0079] (10) Because the heating method of the ion nitriding furnace is to heat the workpiece by bombarding it with ions, the workpiece generates heat by itself and then radiates heat outward. The temperature difference between the furnace and the workpiece is large, and there is a certain difference between the thermocouple and the actual workpiece. Therefore, the temperature measured by the thermocouple is lower than the actual temperature of the workpiece. The corresponding instrument indicates a temperature difference from the actual workpiece temperature. During the furnace opening process, the glow voltage should be turned off frequently and the actual temperature of the workpiece in the furnace should be visually observed. At the nitriding temperature, the workpiece should be slightly red. When the heat transfer reaches equilibrium, the temperature difference between the workpiece and the thermocouple is basically constant, and the furnace temperature can be controlled by the instrument.

[0080] (11) Execute the second stage nitriding process: After completing the first stage process for 10 to 15 hours, increase the voltage and current values ​​and raise the temperature to 550 to 560 ° C. Nitrogen and hydrogen mixed gas are introduced at a nitrogen supply ratio of 10 to 15% in the second stage, and a certain furnace pressure and temperature are maintained.

[0081] (12) Execute the third stage of nitriding process: After the second stage is carried out for 30 to 50 hours, reduce the voltage, current and nitrogen supply ratio to keep them basically the same as the parameters of the first stage for insulation.

[0082] (13) Cooling down and stopping the furnace: When the total process time of the "three-stage method" ion nitriding treatment is up, turn off the nitrogen and argon gases, reduce the amount of hydrogen gas entering the furnace, open the large butterfly valve and the furnace cooling water, reduce the glow current, and allow the workpiece to cool down under weak glow protection. When the instrument temperature drops below 200°C, adjust the "peak voltage" to zero, adjust the "duty cycle setting" to the minimum, disconnect the "pulse" switch and the "high voltage" switch, and turn off the corresponding gas cylinder valve, pressure reducing valve, and flow meter. Evacuate the furnace to below 50Pa, close the butterfly valve and vacuum pump. When the instrument temperature reaches about 150°C, the furnace can be stopped and the main power supply turned off. At this time, the cooling water of the furnace body cannot be completely turned off, and a small amount of cooling water should be maintained.

[0083] (14) When the actual temperature of the workpiece drops below 150°C, stop the water supply, release the air, and remove the workpiece from the furnace. Excessive temperature in the furnace can easily cause the workpiece to oxidize. After removing the workpiece from the furnace, the fixtures should be properly stored and kept clean for future use. After removing the rack from the furnace, lay it flat with sleepers under it, remove the mechanical shielding, and use fine sandpaper to grind off the anti-seepage coating.

[0084] (15) During the entire processing process, parameters such as time, voltage, current, conduction ratio, furnace pressure, furnace temperature and other related conditions should be recorded in a timely manner for reference.

[0085] Nitriding quality inspection

[0086] The samples accompanying the furnace are bagged and their serial numbers and other information are recorded. The samples are then cut, clamped, or mounted, and tested. The Vickers hardness of the surface is measured, the brittleness of the nitrided surface is assessed, and metallographic specimens are prepared, with the thickness of the nitrided layer determined by corrosion or microhardness testing. An Inspection Report is issued, and the goods and samples are packed together for shipment.

[0087] Working principle of the balanced nitriding method to control the deformation of the rack ion nitriding:

[0088] The first step is to perform stress relief treatment on the rack: the rack is subjected to multiple tempering treatments to eliminate the structural stress and processing stress existing after the rack is prepared, and multiple tempering is used to eliminate the stress relief tempering temperature. The rack is subjected to high temperature tempering treatment, and the tempering temperature is controlled at 580-650℃, and the holding time is 120min.

[0089] The second step is to clean the rack surface: clean the rack surface after multi-stage tempering treatment, remove dust and oil on the rack surface, and dry the cleaned rack. Rinse the rack surface and tooth gaps with high-pressure water flow, and after rinsing, use an ultrasonic cleaner to thoroughly clean the deep tooth gaps of the rack. Then use a degreasing agent to degrease the back of the rack, and then clean the degreasing agent with clean water. Finally, dry it in hot air at 220~260℃.

[0090] Step 3: Apply ion nitriding anti-seepage paint to the back of the rack at intervals: Apply ion nitriding anti-seepage paint to the back of the rack after drying at intervals. The paint should be applied in a rectangular shape. The nitriding area on the back of the rack should be the same as the nitriding area of ​​the tooth groove at the bottom of the tooth surface. The intervals for applying ion nitriding anti-seepage paint to the rack are calculated as follows:

[0091] Assume the tooth groove width of the rack is A, and the tooth bottom width is B, then

[0092]

[0093]

[0094] Where: α is the rack pressure angle, m is the rack module;

[0095] The coating-to-air ratio of the rack back ] According to the ratio of these two widths, they are distributed at intervals along the length of the rack. The coating width is n*B+K, and the spare width is n*A, where n is a coefficient, n=1~5, selected according to the size of the rack module. When the module is small, n is large, and when the module is large, n is small; K is a compensation constant, K=2.5~3.5;

[0096] Step 4: UV drying after applying the ion nitriding anti-seepage paint: After applying the ion nitriding anti-seepage paint on the back of the rack, use a UV dryer to quickly dry the ion nitriding anti-seepage paint to improve the adhesion of the metal particles in the ion nitriding anti-seepage paint;

[0097] Step 5: Ion nitriding process control: The rack coated with ion nitriding anti-seepage coating is hoisted in the ion nitriding furnace for ion nitriding treatment, and an array infrared thermometer is used to conduct a full range of temperature detection on the surface of the rack to facilitate the control of the ion nitriding temperature and timely regulation. The heating rate is controlled to be ≤2.5℃ / min and the average temperature is 450℃ for 1.5h, which is conducive to the uniform temperature of the rack.

[0098] Step 6. Cleaning of ion nitriding anti-seepage coating: After the rack is ion nitrided, take out the rack, clean the ion nitriding anti-seepage coating on the back, and use mechanical cleaning, and then detect the deformation and warping of the rack.

[0099] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A balanced nitriding method for controlling rack ion nitriding deformation, characterized in that: The following steps are included: S1. Stress relief treatment of the rack: The rack is subjected to multiple stress relief tempering treatments to eliminate the structural stress and processing stress existing after the rack is prepared, and multiple tempering treatments are used to eliminate the stress; S2. Rack surface cleaning: Clean the rack surface after multi-stage tempering treatment, remove dust and oil on the rack surface, and dry the cleaned rack; S3. Apply ion nitriding anti-seepage paint to the back of the rack at intervals: Apply ion nitriding anti-seepage paint to the back of the rack after drying at intervals in a rectangular shape, and control the nitriding area on the back of the rack to be the same as the nitriding area of ​​the tooth groove at the bottom of the tooth surface; The interval for applying ion nitriding anti-seepage coating to the rack is calculated as follows: Assume the tooth groove width of the rack is A, and the tooth bottom width is B, then ； ； Where: α is the rack pressure angle, m is the rack module; The coating-to-air ratio of the rack back ] According to the ratio of these two widths, they are distributed at intervals along the length of the rack. The coating width is n*B+K, and the spare width is n*A, where n is a coefficient, n=1~5, selected according to the size of the rack module. When the module is small, n is large, and when the module is large, n is small; K is a compensation constant, K=2.5~3.5; S4. After applying the ion nitriding anti-seepage paint, perform UV drying: After applying the ion nitriding anti-seepage paint on the back of the rack, use a UV dryer to quickly dry the ion nitriding anti-seepage paint to improve the adhesion of the metal particles in the ion nitriding anti-seepage paint; S5. Ion nitriding process control: The rack coated with ion nitriding anti-seepage coating is hoisted in the ion nitriding furnace for ion nitriding treatment, and an array infrared thermometer is used to conduct a full range of temperature detection on the surface of the rack to facilitate the control of the ion nitriding temperature and timely regulation and control. The heating rate is controlled to be ≤2.5℃ / min, and the average temperature is 450℃ for 1.5 hours, which is conducive to the uniform temperature of the rack; S6. Cleaning of ion nitriding anti-seepage coating: After the rack is ion nitrided, the rack is taken out and the ion nitriding anti-seepage coating on the back is cleaned by mechanical cleaning, and then the deformation and warping of the rack is tested.

2. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The tempering temperature in S1 is lower than the quenching temperature of the rack, and the rack is tempered at a high temperature and the tempering temperature is controlled at 580-650° C., and the holding time is 120 minutes.

3. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The cleaning in S2 is first performed by flushing the surface and tooth gaps of the rack with a high-pressure water flow, and after flushing, an ultrasonic cleaner is used to thoroughly clean the deep tooth gaps of the rack, and then a degreaser is used to degrease the surface of the rack, and then the degreaser is cleaned with clean water, and finally placed in hot air at 220~260℃ for drying.

4. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 3, characterized in that: The degreasing agent includes triethanolamine oleate soap, coconut oil fatty acid diethanolamide, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, sodium benzoate, sodium pyrophosphate, azelaic acid, myristic acid, ethanol, polyether-modified silicone, sodium hydroxide, and JFC. When in use, it is mixed with 40°C warm water in a ratio of 1:5 and is convenient for use with an ultrasonic cleaner.

5. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The ion nitriding anti-seepage coating in S3 is applied by brushing with a soft brush. The thickness of the ion nitriding anti-seepage coating is 1.0-1.5 mm for the first application. After being placed at room temperature for 10 minutes, the coating is applied for the second application, and the total thickness reaches 1.5-2.0 mm. After the two applications, a UV dryer is used for rapid drying.

6. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The array infrared thermometer in S5 is used to detect the temperature of the rack surface during the ion nitriding process. When high-energy nitrogen ions bombard the workpiece surface at a very high speed and convert kinetic energy into thermal energy, the temperature distribution on the rack surface can be detected, which facilitates temperature adjustment so that the temperature of the rack surface can be maintained at 540~550℃, thereby improving the uniformity of nitriding.

7. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The ion nitriding furnace in S5 is kept in a vacuum state, and the distribution of the glow discharge of the ion nitriding furnace from the cathode to the anode is uneven, and is divided into several regions from the cathode to the anode: Aston dark area, cathode glow area, cathode dark area, negative glow area, Faraday dark area, positive column area, anode dark area, and anode glow area; The sum of the widths of the Aston dark area, cathode bright area, and cathode dark area is called the cathode drop area d k The voltage between the cathode and anode mainly falls within the cathode potential drop zone. k Inversely proportional to air pressure, P·d k =constant; Cathode drop zone d k The length of the negative glow zone is called the cathode discharge length d glow. When the distance between the two cathodes is d1, d1<2dk, the glow is extinguished; when the distance between the two cathodes is d1, d1> 2d glow, the two cathode drop zones are independent of each other and do not affect each other, and the glow discharge proceeds normally; when the distance between the two cathodes is d1, d1=2d glow, the two negative glow zones merge, the current density increases, and the glow intensity increases, which is called the hollow cathode effect. During the ion nitriding process, the formation of the hollow cathode effect should be avoided.

8. The balanced nitriding method for controlling rack ion nitriding deformation according to claim 1, characterized in that: The mechanical cleaning in S6 is performed by sandblasting or wire wheel cleaning, and the sandblasting is performed by compressed air driving fine quartz sand to spray the back of the rack for cleaning, and the pressure of the compressed air is 0.5~0.6MPa; And the wire wheel cleaning uses the electric motor to drive the wire wheel transmission mechanism to clean the back of the rack evenly, thoroughly and safely.

Images