Heat treatment process method of cylindrical roller for bearing

Abstract

The invention discloses a heat treatment process method of a cylindrical roller for a bearing. The heat treatment process method comprises the following steps: performing pretreatment, quenching heating, salt bath cooling, air cooling, cleaning and rust prevention, tempering treatment and quenching and tempering on the cylindrical roller, and then inspecting. The cylindrical rollers are vertically placed in the heat treatment limiting tool frame, the rollers do not make contact with one another, heating and cooling are uniform, the product quality is guaranteed, and the loading efficiency is high and improved by 30%. According to the quenching mode, salt bath cooling is used for replacing rapid quenching oil cooling, due to the fact that salt bath cooling has the characteristics of rapid cooling in the high-temperature stage and slow cooling in the low-temperature stage, 1.2-1.3% of water is added into salt bath, the cooling performance of the salt bath is further improved, the salt bath cooling does not have a steam film stage, and product quenching cooling is more uniform.

Description

Technical Field

[0001] This invention relates to the field of heat treatment processing technology for bearing parts, and more specifically to a heat treatment process for cylindrical rollers used in bearings. Background Technology

[0002] Cylindrical rollers are one of the most commonly used rolling elements in bearings. Bearings using cylindrical rollers generally have line contact between the rollers and raceways, resulting in high radial load capacity and suitability for heavy and impact loads. Furthermore, the low coefficient of friction between the rollers and the inner and outer rings of the bearing makes them suitable for high speeds, with a limiting speed approaching that of deep groove ball bearings. Therefore, this type of rolling element is widely used.

[0003] With the updating of industry standards for heat treatment technology of rolling bearings, the control of key physical and chemical properties has become very strict. For example, for rollers with an effective diameter greater than 26mm, according to the technical requirements in Table 4 of JB / T1255-2001 Technical Conditions for Heat Treatment of Rolling Bearing Parts of High Carbon Chromium Bearing Steel, the troostite structure beyond 3mm from the working surface is not controlled. However, after the industry standard was updated, according to the technical requirements in Table 4 of GB / T34891-2016 Technical Conditions for Heat Treatment of Rolling Bearing Parts of High Carbon Chromium Bearing Steel, the troostite structure beyond 3mm from the working surface must be ≤ grade 2.

[0004] Therefore, for cylindrical rollers with an effective diameter of 30-40mm and made of GCr15 steel, the existing heat treatment process results in a martensite structure greater than grade 2 at a distance of more than 3mm from the working surface, which does not meet the requirements of current standards. In order to ensure the product quality of bearing parts and meet the requirements of current heat treatment technology, it is necessary to improve the existing heat treatment process. Summary of the Invention

[0005] In view of this, the present invention provides a heat treatment process for cylindrical rollers used in bearings. By changing the quenching medium of the rollers, adjusting the roller placement method, and modifying the mechanical structure at the bottom of the quenching salt bath, the present invention ensures that the quality of GCr15 steel cylindrical rollers with an effective diameter of 30-40 mm after heat treatment meets the standard requirements.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A heat treatment process for cylindrical rollers used in bearings. Cylindrical rollers are pretreated, quenched and heated, salt bath cooled, air cooled, cleaned and rust-proofed, tempered and then inspected after quenching and tempering. The preprocessing includes: roller placement; The rollers are arranged as follows: the machined cylindrical rollers are placed upright in the small grid of the roller heat treatment limiting loading frame inside the heat-resistant steel tooling, according to the process requirements; the number of heat treatment limiting loading frames with different small grids is selected according to the cylindrical rollers of different diameters being processed. The side length of the small mesh of the loading frame is 4~6mm larger than the effective diameter of the cylindrical roller, and the number of pieces is 196~324. The salt bath cooling includes: adjustment of the quenching salt tank, adjustment of the churning table, adjustment of the stirring motor, and setting of the quenching salt temperature; The quenching salt tank is adjusted as follows: the angle of the guide plate at the bottom of the salt outlet of the salt tank stirring motor is adjusted to 180°, and the mesh plate laid flat above the salt outlet is opened to 90°. The stirring motor is adjusted to run at 1200-1400 rpm. The quenching salt temperature is set to 170~190℃; the water content in the salt bath is 1.2~1.3%; the cooling time is 8~10min; and the salt rinsing time is 1~2min. The cleaning and rust prevention include: ultrasonic cleaning, foaming cleaning and rust prevention treatment. The parameters for ultrasonic cleaning are: frequency 28~30KHZ, water temperature 40~60℃, and time 8~10min; The parameters for the foaming cleaning are: water temperature 40~60℃, time 8~10min; The parameters for the rust prevention treatment are: water temperature at room temperature, and water containing a sodium nitrite aqueous solution with a concentration of 0.5-0.8%.

[0007] Preferably, the pretreatment further includes: pre-roller cleaning; The pre-cleaning of the rollers includes cleaning with cleaning agent and cleaning with water. The cleaning temperature is 50~80℃ and the cleaning time for each cleaning is 8~12min. After cleaning, the rollers are dried at a temperature of 100~150℃ for 8~12min.

[0008] The cleaning agent is selected from KR-F400 water-based metal cleaning agent.

[0009] Preferably, the quenching heating is performed at 845~860℃ for 70~90 min; the protective atmosphere is: nitrogen + methanol dripping + propane; the furnace pressure is 150~200 MPa; and the furnace carbon potential CP% is 0.65~0.9.

[0010] Preferably, the air cooling is divided into 3 stations, with each station having an air cooling time of 8 to 10 minutes, and the surface temperature of the ring after air cooling is ≤50℃.

[0011] Preferably, the tempering process is performed using an air tempering furnace, with a tempering temperature of 180℃~200℃ and a tempering time of 210min~270min.

[0012] Preferably, the post-quenching and tempering inspection includes: Microstructure: Martensite grade 2-4; Bautism: >3mm from the working surface, ≤2 grade of bautism structure; Working surface hardness: 59-65HR.

[0013] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. Regarding the loading method, the existing process uses a single layer of loosely laid-out rollers. This method involves contact between the rollers, affecting heating and cooling efficiency and easily causing soft spots at the contact surfaces. Furthermore, this loading method reduces production efficiency. Therefore, this invention places the cylindrical rollers upright within the heat treatment limiting fixture, preventing contact between the rollers, ensuring uniform heating and cooling, guaranteeing product quality, and increasing loading efficiency by 30%.

[0014] 2. During physicochemical testing, it was found that the troostite content exceeding 3mm in the cylindrical rollers was substandard, and the troostite morphology was acicular troostite, indicating that the cooling rate was too slow during quenching. Regarding the quenching method, salt bath cooling was used instead of rapid quenching oil cooling because salt bath cooling has the characteristic of "rapid cooling at high temperatures and slow cooling at low temperatures." Adding 1.2~1.3% water to the salt bath further improves its cooling performance, and the absence of a vapor film stage in salt bath cooling results in more uniform quenching and cooling of the product.

[0015] 3. Adjust the mechanical structure inside the quenching salt tank, such as adjusting the angle of the guide plate and the angle of the mesh plate. Under the same speed of the stirring motor, the salt flows faster at the bottom salt outlet, which improves the cooling performance.

[0016] 4. Adjusting the upper limit of the churning platform can allow the product to move back and forth in the area with the highest flow velocity in the salt bath, further improving cooling performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 The image shows the microstructure of a 30×48 cylindrical roller with a troostite structure of >2 grade outside 3mm from the working surface during the heat treatment process of Comparative Example 1.

[0019] Figure 2 The image shows the microstructure of a 30×48 cylindrical roller with a troostite structure of grade <1 beyond 3mm from the working surface during the heat treatment process of Example 1. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0021] Heat treatment process for GCr15 steel cylindrical rollers 30×48 1. Heat treatment The 30×48 cylindrical rollers were heat-treated (quenched and tempered) using a 750 roller hearth furnace salt bath martensitic quenching production line with a protective atmosphere at Tangshan Yajie.

[0022] 1.1 Roller Placement: According to process requirements, the machined cylindrical rollers are placed upright in the small grid of the roller heat treatment limiting loading rack within the heat-resistant steel fixture; an 18×18 roller heat treatment limiting loading rack is selected; the small grid size of the loading rack is 35mm×35mm. The number of cylindrical rollers placed is 324.

[0023] 1.2 Pre-cleaning of the rollers: Pre-cleaning removes cutting fluid, dust, oil, and other impurities from the surface of the rollers, ensuring a consistent appearance and color after quenching and tempering. The pre-cleaning process involves both cleaning with a cleaning agent and rinsing with clean water. Cleaning temperature: 80℃, cleaning time per pass: 8 minutes; after cleaning, drying is performed at 130℃ for 8 minutes.

[0024] 1.3 Quenching heating: Heating temperature: 845℃, heating time: 70min.

[0025] 1.4 Protective atmosphere: nitrogen + methanol dripping + propane; furnace pressure: 200 MPa; furnace carbon potential CP%: 0.7; 1.5 Cooling: Quenching cooling method: Salt bath cooling.

[0026] 1.5.1 Adjustment of quenching salt tank: Adjust the angle of the guide plate at the bottom of the salt outlet of the salt tank stirring motor to 180°; open the mesh plate laid flat above the salt outlet to 90°.

[0027] 1.5.2 Adjustment of the moving platform: Adjust the upper limit position of the moving platform: The height of the top of the tooling on the moving platform from the salt surface is 230mm; the descent speed of the moving platform is 400mm / s; the moving platform moves up and down at a speed of 400mm / s. 1.5.3 Adjustment of stirring motor: Salt tank stirring motor speed: 1200 rpm; 1.5.4 Quenching salt temperature: 180℃; Water content in salt bath: 1.2%; Cooling time: 8 min; Salt rinsing time: 1 min.

[0028] 1.6 Air cooling: Air cooling is divided into 3 stations, with an air cooling time of 8 minutes for each station. After air cooling, the surface temperature of the ring is ≤50℃.

[0029] 1.7 Cleaning and Rust Prevention: Immersion cleaning, three stations in total, 8 minutes cleaning time per station: 1.7.1 Ultrasonic cleaning, frequency 28KHZ, water temperature 60℃; 1.7.2 Foaming cleaning, water temperature 60℃; 1.7.3 Rust prevention treatment, water temperature: room temperature, the rust prevention treatment station contains a 0.6% sodium nitrite aqueous solution for rust prevention.

[0030] 1.8 Tempering treatment: Tempering treatment was carried out using an air tempering furnace. Tempering temperature: 190℃, tempering time: 240min.

[0031] 2. Inspection after quenching and tempering Microstructure: Martensite grade 3 Troostite: Within 3mm of the working surface, the troostite structure is grade 1; beyond 3mm of the working surface, the troostite structure is grade 1.

[0032] Working surface hardness: 60.5, 60, 60 HRC. Example 2

[0033] Heat treatment process for GCr15 steel cylindrical rollers 40×40 1. Heat treatment The 40×40 cylindrical rollers were heat-treated (quenched and tempered) using a 750 roller hearth furnace salt bath martensitic quenching production line with a protective atmosphere at Tangshan Yajie.

[0034] 1.1 Roller Placement: According to process requirements, the machined cylindrical rollers are placed upright in the small grid of the roller heat treatment limiting loading rack within the heat-resistant steel fixture; a 14×14 roller heat treatment limiting loading rack is selected; the small grid size of the loading rack is 45mm×45mm. The number of cylindrical rollers placed is 196.

[0035] 1.2 Pre-cleaning of the rollers: Pre-cleaning removes cutting fluid, dust, oil, and other impurities from the surface of the rollers, ensuring a consistent appearance and color after quenching and tempering. The pre-cleaning process involves both cleaning with a cleaning agent and rinsing with clean water. Cleaning temperature: 80℃, cleaning time per pass: 8 minutes; after cleaning, drying is performed at 130℃ for 8 minutes.

[0036] 1.3 Quenching heating: Heating temperature: 860℃, heating time: 90min.

[0037] 1.4 Protective atmosphere: nitrogen + methanol dripping + propane; furnace pressure: 200 MPa; furnace carbon potential CP%: 0.7; 1.5 Cooling: Quenching cooling method: Salt bath cooling.

[0038] 1.5.1 Adjustment of quenching salt tank: Adjust the angle of the guide plate at the bottom of the salt outlet of the salt tank stirring motor to 180°; open the mesh plate laid flat above the salt outlet to 90°.

[0039] 1.5.2 Adjustment of the moving platform: Adjust the upper limit position of the moving platform: The height of the top of the tooling on the moving platform from the salt surface is 250mm; the descent speed of the moving platform is 400mm / s; the moving platform moves up and down at a speed of 400mm / s. 1.5.3 Adjustment of stirring motor: Salt tank stirring motor speed: 1400 rpm; 1.5.4 Quenching salt temperature: 180℃; Water content in salt bath: 1.3%; Cooling time: 8 min; Salt rinsing time: 1 min.

[0040] 1.6 Air cooling: Air cooling is divided into 3 stations, with an air cooling time of 8 minutes for each station. After air cooling, the surface temperature of the ring is ≤50℃.

[0041] 1.7 Cleaning and Rust Prevention: Immersion cleaning, with three stations, each station requiring 8 minutes of cleaning time. 1.7.1 Ultrasonic cleaning, frequency 28KHZ, water temperature 60℃; 1.7.2 Foaming cleaning, water temperature 60℃; 1.7.3 Rust prevention treatment, water temperature: room temperature, the rust prevention treatment station contains a 0.6% sodium nitrite aqueous solution for rust prevention.

[0042] 1.8 Tempering treatment: Tempering treatment was carried out using an air tempering furnace. Tempering temperature: 180℃, tempering time: 240min.

[0043] 2. Inspection after quenching and tempering Microstructure: Martensite grade 3 Troostite: Within 3mm of the working surface, the troostite structure is grade 1; beyond 3mm of the working surface, the troostite structure is grade 2.

[0044] Working surface hardness: 59.5, 59, 59.5 HRC. Comparative Example 1

[0045] (Existing process) Heat treatment process for 30×48 cylindrical rollers made of GCr15 steel 1. Heat treatment 30×48 cylindrical rollers are heat-treated (quenched and tempered) using a roller hearth furnace martensitic quenching production line with a protective atmosphere.

[0046] 1.1 Roller placement: The machined cylindrical rollers are scattered and laid flat (1 layer) in the heat-resistant steel fixture according to the process requirements; quantity: 249 pieces.

[0047] 1.2 Pre-cleaning of the rollers: Pre-cleaning removes cutting fluid, dust, oil, and other impurities from the surface of the rollers, ensuring a consistent appearance and color after quenching and tempering. The pre-cleaning process involves both cleaning with a cleaning agent and rinsing with clean water. Cleaning temperature: 80℃, cleaning time per pass: 8 minutes; after cleaning, drying is performed at 130℃ for 8 minutes.

[0048] 1.3 Quenching heating: Heating temperature: 845℃, heating time: 70min.

[0049] 1.4 Protective atmosphere: nitrogen + methanol dripping + propane; furnace pressure: 200 MPa; furnace carbon potential CP%: 0.7; 1.5 Cooling: Quenching cooling method: Nanjing Kerun KR118H rapid quenching oil was used for cooling. The churning table moved up and down at a speed of 400 mm / s; the oil tank stirring motor was started at a speed of 1400 rpm. To improve cooling performance, both the churning speed and the stirring motor speed were at maximum. Quenching oil temperature: 80℃, cooling time: 6 min; oil spraying time: 1 min.

[0050] 1.6 Degreasing and cleaning: Cleaning temperature: 60℃, cleaning time: 6min, cleaning agent: 5% sodium bicarbonate aqueous solution.

[0051] 1.7 Rust prevention: Rust inhibitor temperature: room temperature; Rust prevention method: spray rust prevention; Spraying time: 6 min; Rust inhibitor: 0.6% sodium nitrite aqueous solution.

[0052] 1.8 Tempering treatment: Tempering was performed using an air tempering furnace. Tempering temperature: 190℃, tempering time: 240min.

[0053] 2. Inspection after quenching and tempering Microstructure: Martensite grade 3 Troostite: Within 3mm of the working surface, the troostite structure is grade 2; beyond 3mm of the working surface, the troostite structure is grade > 2.

[0054] Working surface hardness: 59, 59.5, 59.5 HRC.

[0055] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat treatment process for cylindrical rollers used in bearings, characterized in that, Cylindrical rollers are pretreated, quenched and heated, salt bath cooled, air cooled, cleaned and rust-proofed, tempered and then inspected after quenching and tempering. The preprocessing includes: roller placement; The rollers are arranged as follows: the machined cylindrical rollers are placed upright in the small grid of the roller heat treatment limiting loading frame inside the heat-resistant steel tooling, according to the process requirements; the number of heat treatment limiting loading frames with different small grids is selected according to the cylindrical rollers of different diameters being processed. The side length of the small mesh of the loading frame is 4~6mm larger than the effective diameter of the cylindrical roller, and the number of pieces is 196~324. The salt bath cooling includes: adjustment of the quenching salt tank, adjustment of the churning table, adjustment of the stirring motor, and setting of the quenching salt temperature; The quenching salt tank is adjusted as follows: the angle of the guide plate at the bottom of the salt outlet of the salt tank stirring motor is adjusted to 180°, and the mesh plate laid flat above the salt outlet is opened to 90°. The stirring motor is adjusted to run at 1200-1400 rpm. The quenching salt temperature is set to 170~190℃; the water content in the salt bath is 1.2~1.3%; the cooling time is 8~10min; and the salt rinsing time is 1~2min. The cleaning and rust prevention include: ultrasonic cleaning, foaming cleaning and rust prevention treatment. The parameters for ultrasonic cleaning are: frequency 28~30KHZ, water temperature 40~60℃, and time 8~10min; The parameters for the foaming cleaning are: water temperature 40~60℃, time 8~10min; The parameters for the rust prevention treatment are: the water temperature is room temperature, and the water contains a sodium nitrite aqueous solution with a volume concentration of 0.5-0.8%.

2. The heat treatment process for cylindrical rollers for bearings according to claim 1, characterized in that, The pretreatment also includes: pre-roller cleaning; The pre-cleaning of the rollers includes cleaning with cleaning agent and cleaning with water. The cleaning temperature is 50~80℃ and the cleaning time for each cleaning is 8~12min. After cleaning, the rollers are dried at a temperature of 100~150℃ for 8~12min.

3. The heat treatment process for cylindrical rollers for bearings according to claim 1, characterized in that, The quenching heating is carried out at 845~860℃ for 70~90 minutes; the protective atmosphere is: nitrogen + methanol dripping + propane; Furnace pressure: 150~200Mpa; Furnace carbon potential CP%: 0.65~0.

9.

4. The heat treatment process for cylindrical rollers for bearings according to claim 1, characterized in that, The air cooling is divided into 3 stations, with each station having an air cooling time of 8 to 10 minutes. After air cooling, the surface temperature of the ring is ≤50℃.

5. The heat treatment process for cylindrical rollers for bearings according to claim 1, characterized in that, The tempering process is carried out using an air tempering furnace, with a tempering temperature of 180℃~200℃ and a tempering time of 210min~270min.

6. The heat treatment process for cylindrical rollers for bearings according to claim 1, characterized in that, The post-quenching and tempering inspection includes: Microstructure: Martensite grade 2-4; Bautism: within 3mm of the working surface, the bautism structure is ≤ grade 2; beyond 3mm of the working surface, the bautism structure is ≤ grade 2. Working surface hardness: 59-65HR.

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