A method for forging and heat treating a NN series double-row cylindrical roller bearing ring

Abstract

A forging and heat treatment method for NN series double-row cylindrical roller bearing rings, belonging to the field of bearing processing, includes the following steps: 1. After heating and forging a section of material to obtain a ring-shaped forging, if the temperature is too low, it is reheated and then rolled into a ring; 2. Atomized cooling is performed, with the forging reddening time on the conveyor belt being 2-5 seconds and the temperature ≤600℃, before unloading; 3. The forging is normalized, annealed, and quenched and tempered, then cold-treated, followed by low-temperature tempering, high-temperature tempering, rough grinding followed by stable tempering, and fine grinding followed by stable tempering. This invention avoids cracks caused by low rolling temperature; reheating treatment is performed on forgings with unqualified temperatures before rolling to prevent waste; spray cooling avoids temperature artifacts and ensures uniform internal structure of the ring; the unloading temperature is monitored to prevent the formation of network carbides; and the residual austenite content of the ring is effectively reduced to ensure the precision grade of the finished bearing. This invention is applicable to the forging and heat treatment of NN series double-row cylindrical roller bearing rings.

Description

Technical Field

[0001] This invention belongs to the field of bearing processing, specifically relating to a forging and heat treatment method for NN series double-row cylindrical roller bearing rings. Background Technology

[0002] The machining method for the NN series double-row cylindrical roller bearing rings is as follows: cutting, forging, annealing, turning, heat treatment, rough grinding, stabilizing tempering, fine grinding, precision grinding, cleaning and rust prevention. This series of bearings is mainly used in precision machine tool spindle bearings, with a bearing precision grade of P4 or P2, belonging to precision bearings.

[0003] The forging of bearing rings uses a forging press. Currently, the process only controls the initial and final forging temperatures, which cannot fully guarantee the quality of the forged rings. For example, cracks may occur due to low rolling temperatures, or the rings may develop unacceptable network carbides due to temperatures exceeding 700℃ after air cooling / atomization cooling. After quenching, the bearing rings undergo low-temperature tempering (160℃-185℃). X-ray residual austenite analysis revealed that the rings contain 10%-15% residual austenite. According to the national standard GB / T34891-2017 "Technical Conditions for Heat Treatment of High Carbon Chromium Bearing Steel Parts for Rolling Bearings," the residual austenite content of precision bearing parts after quenching and tempering should be ≤5%. Excessive residual austenite content can cause microstructural transformation in precision bearings during later use, leading to changes in product dimensional accuracy. Bearing ring grinding is divided into rough grinding and fine grinding. Rough grinding involves a single-sided grinding amount of 0.2-0.4 mm. Due to the large grinding amount, tensile stress exists on the bearing ring surface. Currently, a stabilizing tempering process is added after rough grinding to eliminate the tensile stress generated by grinding and ensure the dimensional accuracy of the bearing ring. Fine grinding involves a single-sided grinding amount of 0.05-0.10 mm. Although the grinding amount is smaller, tensile stress still exists. If not stabilized by tempering, this tensile stress will persist. After assembly and prolonged storage / use, the stress will release, leading to changes in bearing accuracy.

[0004] Currently, the forging and heat treatment methods for NN series double-row cylindrical roller bearing rings are prone to cracking due to the low temperature before ring rolling; after the forging is rolled, the ring is spray-cooled, resulting in a low surface temperature and a high core temperature, creating a temperature illusion, which easily produces network carbides, poor internal structure uniformity, thermal stress and structural stress generated by quenching, and low bearing precision. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems and to provide a forging and heat treatment method for NN series double-row cylindrical roller bearing rings.

[0006] A forging and heat treatment method for NN series double-row cylindrical roller bearing rings, which is implemented according to the following steps:

[0007] 1. After the material section is heated and forged, a ring-shaped forging is obtained. Then, the temperature of the ring-shaped forging is measured by an infrared thermometer. If the temperature is ≥850℃, a vertical ring rolling mill is used to roll the ring. If 800℃≤temperature<850℃, the ring-shaped forging is transferred to a high-temperature rotary furnace for reheating, and then rolled by a vertical ring rolling mill.

[0008] 2. After the above-mentioned ring rolling is completed, the forging is dropped onto the conveyor belt for atomization cooling. The cooling time is 2-5 minutes. Then, the forging is reddened on the conveyor belt for 2-5 seconds and is detected by an infrared temperature measuring device. The temperature is ≤600℃. Then, it is dropped into the material basket at the material drop end of the conveyor belt to obtain the cooled forging.

[0009] 3. After cooling, the forgings are placed in a single layer in a special tooling and then placed in a protective atmosphere roller hearth normalizing furnace for normalizing. Then, the forgings are annealed and quenched and tempered. Then, they are cold treated at -75℃ to -85℃ for 120±2min. Then, they are subjected to low temperature tempering, high temperature tempering, rough grinding followed by stable tempering, and fine grinding followed by stable tempering in sequence. This completes the forging and heat treatment method of the NN series double row cylindrical roller bearing rings.

[0010] Furthermore, the process parameters for the reheating described in step one are: heating temperature of 945-955℃ and heating time of 10-15min.

[0011] Furthermore, the atomization cooling method used in step two is a fanless and spray device.

[0012] Furthermore, the process parameters for normalizing the forgings described in step three are as follows: heating temperature is 910-930℃, heating time is 4h±10min, and after removing the forgings from the furnace, they are quickly cooled to room temperature using a fan.

[0013] Furthermore, the process parameters for low-temperature tempering and high-temperature tempering in step three are as follows: the cold-treated forgings are placed in an air tempering furnace and tempered at 160-185℃ for 210-270 min, and then tempered at 220-240℃ for 210-270 min.

[0014] Furthermore, the process parameters for the stabilizing tempering after rough grinding in step three are as follows: after rough grinding, the forgings after high-temperature tempering are placed in a stabilizing tempering furnace and then tempered at 150-160℃ for 120-150 minutes.

[0015] Furthermore, the process parameters for the fine grinding and stable tempering described in step three are as follows: after rough grinding and stable tempering, the forgings are finely ground and then placed in a stable tempering furnace, and then tempered at 150-160℃ for 120-150 min.

[0016] Compared with existing processes, the present invention:

[0017] 1. The ring rolling process has added a temperature control process before ring rolling to prevent cracks caused by low ring rolling temperature; by adding a high-temperature rotary heating furnace, forgings with unqualified pre-ring rolling temperature can be reheated to prevent waste of forgings.

[0018] 2. After the ring rolling is completed, the cooling conveyor device used is changed from the original fan cooling to spray cooling, which improves the rapid cooling performance of the forgings in the temperature range of 700℃-900℃. A 1-meter length is left at the end of the conveyor belt without a fan or spray device to allow time for the forgings to reheat and prevent the surface temperature of the ring from being low while the core temperature is high, creating a false temperature reading. An infrared thermometer is added to the material dropping end of the conveyor belt to monitor the material dropping temperature and prevent the material dropping temperature from exceeding 700℃, which would cause the forgings to clump together and easily produce network carbides.

[0019] 3. The addition of a forging normalizing process can effectively eliminate the network carbides inherent in the raw materials and the network carbides generated due to insufficient atomization cooling in forgings with a wall thickness greater than 15mm, ensuring a uniform internal structure of the ring.

[0020] 4. After quenching and tempering, the forgings undergo a cold treatment process, which can effectively reduce the residual austenite content of the bearing rings to below 5%, in accordance with the provisions of the national standard GB / T34891-2017 "Technical Conditions for Heat Treatment of High Carbon Chromium Bearing Steel Parts for Rolling Bearings", thus meeting the precision requirements of precision bearings.

[0021] 5. The tempering process has been changed from one low-temperature tempering to one low-temperature tempering plus one high-temperature tempering. The process method of this invention can effectively eliminate the thermal stress and structural stress generated by quenching of forgings; the high-temperature tempering can further reduce the residual austenite content in the ring to less than 3%, meeting the precision requirements of precision bearings.

[0022] 6. The addition of stable tempering after fine grinding can eliminate the grinding stress caused by fine grinding and ensure the precision grade of the finished bearing.

[0023] This invention is applicable to forged and heat-treated NN series double-row cylindrical roller bearing rings. Attached Figure Description

[0024] Figure 1 This is a 500x microscopic tissue image of the ring after processing with the existing method in the embodiment;

[0025] Figure 2 This is a 500x microstructure image of the NN series double-row cylindrical roller bearing rings obtained through forging and heat treatment in the embodiment. Detailed Implementation

[0026] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0027] Specific Implementation Method 1: This implementation method describes a forging and heat treatment method for NN series double-row cylindrical roller bearing rings, which is achieved through the following steps:

[0028] 1. After the material section is heated and forged, a ring-shaped forging is obtained. Then, the temperature of the ring-shaped forging is measured by an infrared thermometer. If the temperature is ≥850℃, a vertical ring rolling mill is used to roll the ring. If 800℃≤temperature<850℃, the ring-shaped forging is transferred to a high-temperature rotary furnace for reheating, and then rolled by a vertical ring rolling mill.

[0029] 2. After the above-mentioned ring rolling is completed, the forging is dropped onto the conveyor belt for atomization cooling. The cooling time is 2-5 minutes. Then, the forging is reddened on the conveyor belt for 2-5 seconds and is detected by an infrared temperature measuring device. The temperature is ≤600℃. Then, it is dropped into the material basket at the material drop end of the conveyor belt to obtain the cooled forging.

[0030] 3. After cooling, the forgings are placed in a single layer in a special tooling and then placed in a protective atmosphere roller hearth normalizing furnace for normalizing. Then, the forgings are annealed and quenched and tempered. Then, they are cold treated at -75℃ to -85℃ for 120±2min. Then, they are subjected to low temperature tempering, high temperature tempering, rough grinding followed by stable tempering, and fine grinding followed by stable tempering in sequence. This completes the forging and heat treatment method of the NN series double row cylindrical roller bearing rings.

[0031] In step one of this embodiment, the material segment is heated and forged to obtain a ring-shaped forging: the material segment is heated using a medium-frequency induction heating furnace, the initial forging temperature is controlled, and the temperature of the bar exiting the furnace is controlled at 1050℃-1150℃, and the temperature is measured using an infrared thermometer; then, forging is performed using a forging press. Before forging, the forging die of the press needs to be preheated at 150-250℃, and then upsetting, forming and punching are performed in sequence to obtain a ring-shaped forging. The final forging temperature is 900-950℃, and the final forging temperature is measured using an infrared thermometer.

[0032] In step two of this embodiment, a 1-meter length is left at the end of the conveyor belt, without a fan or spray device, for the rings to return to their red color.

[0033] The forging annealing described in step three of this embodiment: The normalized forging is placed in a special tooling and then placed in a continuous spheroidizing annealing furnace for forging annealing; the process parameters for forging annealing are: annealing heating temperature is 780±10℃, heating time is 240±10min, furnace cooling to 720℃, isothermal temperature is 720±10℃, isothermal time is 240±10min, furnace cooling to 550℃, and then air cooling to room temperature.

[0034] The quenching and tempering described in step three of this embodiment: After annealing, the forgings are machined and then quenched and tempered in a protective atmosphere roller hearth furnace salt bath martensitic quenching production line; the process parameters for quenching and tempering are: heating temperature of 830-860℃, heating time of 40-70min, cooling in a salt bath at 170-185℃ with a water content of 0.6%-1.2% for 3-6min, then air cooling until the surface temperature of the forgings is ≤50℃, and then cleaning and rust prevention are performed;

[0035] The cleaning and rust prevention process involves three stages: immersion cleaning.

[0036] 1. Ultrasonic cleaning, frequency 26-32KHZ, water temperature 50±5℃;

[0037] 2. Foaming cleaning, water temperature 50±5℃;

[0038] 3. Cold water cleaning, water temperature 10±2℃, the cold water station contains a sodium nitrite solution with a concentration of 0.5-0.8% for rust prevention of the rings.

[0039] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the material segment mentioned in step one is made from NN series double-row cylindrical roller bearing rings machined from high-carbon chromium bearing steel GCr15 or GCr15SiMn. Everything else is the same as in Specific Implementation Method One.

[0040] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the process parameters for the reheating in step one are: heating temperature of 945-955℃ and heating time of 10-15 minutes. Everything else is the same as in Specific Implementation Method One or Two.

[0041] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the atomization cooling in step two uses a fanless and spray-free device. Other steps and parameters are the same as in Specific Implementation Methods One to Three.

[0042] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the process parameters for normalizing the forgings in step three are as follows: heating temperature is 910-930℃, heating time is 4h±10min, and after removal from the furnace, the forgings are rapidly cooled to room temperature using a fan. Other steps and parameters are the same as in Specific Implementation Methods One to Four.

[0043] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the cooling time in step two is 3 minutes, and the reddening time of the forging on the conveyor belt is 4 seconds. Other steps and parameters are the same as in Specific Implementation Methods One to Five.

[0044] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that, in step three, the device is cold-treated at -80°C for 120 minutes. All other steps and parameters are the same as in Specific Implementation Methods One to Six.

[0045] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the process parameters for the low-temperature tempering and high-temperature tempering in step three are as follows: the cold-treated forgings are placed in an air tempering furnace and tempered at 160-185℃ for 210-270 minutes, and then tempered at 220-240℃ for 210-270 minutes. Other steps and parameters are the same as in Specific Implementation Methods One to Seven.

[0046] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the process parameters for the stable tempering after rough grinding in step three are as follows: After high-temperature tempering, the forging is placed in a stable tempering furnace after rough grinding, and then tempered at 150-160℃ for 120-150 minutes. Other steps and parameters are the same as in Specific Implementation Methods One to Eight.

[0047] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the process parameters for stabilizing tempering after fine grinding in step three are as follows: After rough grinding and stabilizing tempering, the forging is finely ground and then placed in a stabilizing tempering furnace, and then tempered at 150-160℃ for 120-150 minutes. Other steps and parameters are the same as in Specific Implementation Methods One to Nine.

[0048] The beneficial effects of the present invention are verified through the following embodiments:

[0049] Example:

[0050] A forging and heat treatment method for NN series double-row cylindrical roller bearing rings, which is implemented according to the following steps:

[0051] 1. After the material section is heated and forged, a ring-shaped forging is obtained. Then, the temperature of the ring-shaped forging is measured by an infrared thermometer. The temperature is 850℃≤Temperature<900℃. The ring is rolled using a D51Q-250E vertical ring rolling mill.

[0052] 2. After the above-mentioned ring rolling is completed, the forging is dropped onto the conveyor belt for atomization cooling. The cooling time is 3 minutes. Then the forging is reddened on the conveyor belt for 4 seconds and is detected by an infrared temperature measuring device. The temperature is 550℃≤600℃. Then it is dropped into the material basket at the material drop end of the conveyor belt to obtain the cooled forging.

[0053] 3. After cooling, the forgings are placed in a single layer in a special tooling and then placed in a Jinzhou protective atmosphere roller hearth normalizing furnace for normalizing. Then, the forgings are annealed and quenched and tempered. Then, they are cold treated at -80℃ for 120±2min. Then, they are subjected to low temperature tempering, high temperature tempering, rough grinding followed by stable tempering, and fine grinding followed by stable tempering in sequence. This completes the forging and heat treatment method of the NN series double row cylindrical roller bearing rings.

[0054] In step one of this embodiment, the material segment is heated and forged to obtain a ring-shaped forging: the material segment is heated using a medium-frequency induction heating furnace, the initial forging temperature is controlled, and the temperature of the bar exiting the furnace is controlled at 1100℃-1120℃, and the temperature is measured using an infrared thermometer; then, forging is performed using a forging press. Before forging, the forging die of the press needs to be preheated at 150-250℃, and then upsetting, forming and punching are performed in sequence to obtain a ring-shaped forging. The final forging temperature is 920-945℃, and the final forging temperature is measured using an infrared thermometer.

[0055] In step three of this embodiment, the forging annealing is performed as follows: the normalized forging is placed in a special tooling and then placed in a continuous spheroidizing annealing furnace for forging annealing; the process parameters for forging annealing are: annealing heating temperature is 780±10℃, heating time is 240±10min, furnace cooling is 720℃, isothermal temperature is 720±10℃, isothermal time is 240±10min, furnace cooling is 550℃, and then the forging is removed from the furnace and air-cooled to room temperature; the network carbides are tested to be <2 grade.

[0056] In step three of this embodiment, the quenching and tempering process is as follows: After annealing, the forging is machined and then quenched and tempered on the Tangshan Yajie 750 salt bath martensitic quenching production line. The quenching and tempering process parameters are: heating temperature of 845±5℃, heating time of 50±2min, cooling in a salt bath at 180℃ with a water content of 0.8% for 5min, and then air cooling until the surface temperature of the forging is close to room temperature, and then cleaning and rust prevention are performed.

[0057] The cleaning and rust prevention process involves three stages: immersion cleaning.

[0058] 1. Ultrasonic cleaning, frequency 26-32KHZ, water temperature 50±5℃;

[0059] 2. Foaming cleaning, water temperature 50±5℃;

[0060] 3. Cold water cleaning, water temperature 10±2℃, the cold water station contains a sodium nitrite solution with a concentration of 0.5-0.8% for rust prevention of the rings.

[0061] In step one of this embodiment, the material segment is made of NN3024K double-row cylindrical roller bearing rings machined from high-carbon chromium bearing steel GCr15.

[0062] The atomization cooling method described in step two of this embodiment uses a fanless and spray device.

[0063] The process parameters for normalizing the forgings described in step three of this embodiment are: heating temperature of 910-930℃, heating time of 4h±10min, and rapid cooling to room temperature using a fan after removal from the furnace.

[0064] The process parameters for low-temperature tempering and high-temperature tempering in step three of this embodiment are as follows: the cold-treated forgings are placed in an air tempering furnace and tempered at 180±5℃ for 240±2min, and then tempered at 220±5℃ for 240±2min; the residual austenite content is 2.5% after testing.

[0065] The process parameters for the stable tempering after rough grinding in step three of this embodiment are as follows: After high-temperature tempering, the forging is placed in a stable tempering furnace and then tempered at 150±5℃ for 120±2min.

[0066] The process parameters for the fine grinding and stable tempering described in step three of this embodiment are as follows: After rough grinding and stable tempering, the forging is finely ground and then placed in a stable tempering furnace for use, and then tempered at 150±5℃ for 120±2min.

[0067] The microstructure of the ring after processing with existing technology is as follows: Figure 1 As shown, the carbide distribution is uneven; while the NN3024K double-row cylindrical roller bearing rings obtained by forging and heat treatment in this embodiment have the following microstructure: Figure 2 As shown, the carbides are evenly distributed, avoiding cracks caused by low rolling ring temperature, and no network carbides are produced. The internal structure of the ring is uniform and consistent, resulting in high bearing precision.

Claims

1. A forging and heat treatment method for NN series double-row cylindrical roller bearing rings, characterized in that... It is implemented in the following steps:

1. After the material section is heated and forged, a ring-shaped forging is obtained. Then, the temperature of the ring-shaped forging is measured by an infrared thermometer. If the temperature is ≥850℃, a vertical ring rolling mill is used to roll the ring. If 800℃≤temperature<850℃, the ring-shaped forging is transferred to a high-temperature rotary furnace for reheating, and then rolled by a vertical ring rolling mill.

2. After the above-mentioned ring rolling is completed, the forging is dropped onto the conveyor belt for atomization cooling. The cooling time is 2-5 minutes. Then, the forging is reddened on the conveyor belt for 2-5 seconds and is detected by an infrared temperature measuring device. The temperature is ≤600℃. Then, it is dropped into the material basket at the material drop end of the conveyor belt to obtain the cooled forging.

3. After cooling, the forgings are placed in a single layer in a special tooling and then placed in a protective atmosphere roller hearth normalizing furnace for normalizing. Then, the forgings are annealed and quenched and tempered. Then, they are cold treated at -75℃~-85℃ for 120±2min. Then, they are subjected to low temperature tempering, high temperature tempering, rough grinding followed by stable tempering, and fine grinding followed by stable tempering in sequence. This completes the forging and heat treatment method of NN series double row cylindrical roller bearing rings. The material segment mentioned in step one is made of NN series double row cylindrical roller bearing rings processed from high carbon chromium bearing steel GCr15 or GCr15SiMn. The process parameters for normalizing the forgings in step three are: heating temperature of 910-930℃, heating time of 4h±10min, and rapid cooling to room temperature using a fan after removal from the furnace. The process parameters for low-temperature tempering and high-temperature tempering in step three are as follows: the cold-treated forgings are placed in an air tempering furnace and tempered at 160-185℃ for 210-270 min, and then tempered at 220-240℃ for 210-270 min. The process parameters for the stabilizing tempering after rough grinding in step three are as follows: After rough grinding, the forgings after high-temperature tempering are placed in a stabilizing tempering furnace and then tempered at 150-160℃ for 120-150 min. The process parameters for fine grinding followed by stable tempering in step three are as follows: After fine grinding and stable tempering, the forgings are placed in a stable tempering furnace and then tempered at 150-160℃ for 120-150 min. The forging annealing described in step three: The normalized forging is placed in a special tooling and then placed in a continuous spheroidizing annealing furnace for forging annealing; the process parameters for forging annealing are: annealing heating temperature is 780±10℃, heating time is 240±10min, furnace cooling to 720℃, isothermal temperature is 720±10℃, isothermal time is 240±10min, furnace cooling to 550℃, and then air cooling to room temperature after removal from the furnace. The quenching and tempering process described in step three: After annealing, the forgings are machined and then quenched and tempered in a protective atmosphere roller hearth furnace salt bath martensitic quenching production line. The process parameters for quenching and tempering are: heating temperature of 830-860℃, heating time of 40-70min, cooling in a salt bath at 170-185℃ with a water content of 0.6%-1.2% for 3-6min, followed by air cooling until the surface temperature of the forgings is ≤50℃, and then cleaning and rust prevention.

2. The forging and heat treatment method for an NN series double-row cylindrical roller bearing ring according to claim 1, characterized in that... The process parameters for reheating in step one are: heating temperature of 945-955℃ and heating time of 10-15min.

3. The forging and heat treatment method for an NN series double-row cylindrical roller bearing ring according to claim 1, characterized in that... The atomization cooling method used in step two is a fanless spray device.

4. The forging and heat treatment method for an NN series double-row cylindrical roller bearing ring according to claim 1, characterized in that... The cooling time in step two is 3 minutes, and the reddening time of the forging on the conveyor belt is 4 seconds.

5. The forging and heat treatment method for an NN series double-row cylindrical roller bearing ring according to claim 1, characterized in that... In step three, the sample is cooled at -80℃ for 120 minutes.

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