Device for the uniform nitriding of a steel ball batch and its method
The device for uniform nitriding of steel balls addresses non-uniformity and surface burning issues by employing movable thermocouples and a tray design that ensures random movement and controlled temperature, resulting in consistent nitriding and improved surface quality.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2023-08-09
- Publication Date
- 2026-05-13
AI Technical Summary
Existing ion nitriding processes for steel balls result in non-uniform nitrided layers due to the hollow cathode effect, surface burning from arc discharge, and uneven temperature fields, leading to inconsistent surface quality and increased risk of bearing failure.
A device comprising a cylindrical vacuum chamber with movable thermocouples, wireless temperature monitoring, and a tray design that allows steel balls to move randomly, eliminating the cathode effect and ensuring uniform nitriding through controlled temperature and plasma exposure.
Achieves consistent nitriding across the entire surface of steel balls, preventing surface burning and ensuring uniform temperature distribution, thereby enhancing the reliability and efficiency of the nitriding process.
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Abstract
Description
Field of invention
[0001] The invention relates to a device for the uniform nitriding of a batch of steel balls and its method. State of the art
[0002] Nitriding is a typical process for increasing the surface hardness, surface wear resistance, and contact fatigue performance of steel parts. This process is particularly suitable for rolling contact components such as bearings and gears. After years of research, technologies such as gas nitriding and ion nitriding have been developed and applied to various parts.
[0003] Compared to gas nitriding, ion nitriding offers a high nitriding rate and simple parameter control, and is already being used for bearing components. Bearing components have a complex structure, and when nitriding steel balls, in particular, it is crucial to obtain a uniform nitrided layer on the surface of the steel ball to ensure the bearing's service life and reliability. In ion nitriding, the workpiece, including the support structure, is generally nitrided as the cathode. Although technologies such as double nitriding by inverting the steel ball exist, which improves the uniformity of the nitrided layer to some extent, achieving a completely uniform nitriding effect remains impossible due to the effect of the cathode coating in ion nitriding and the directed incidence of ions.The main problem is that when using a steel ball as the cathode in ion nitriding, the sheath layers between the steel ball, the support element, and the tray overlap, creating a hollow cathode effect that leads to a non-uniform surface temperature of the steel ball. Although nitrogen ions moving in the direction of an electric field can improve uniformity, the nitrogen ion density of the plasma, with which each part of the ball's surface comes into contact, is not uniform. These two factors result in inconsistencies in the depth of the nitrided layer on the steel ball's surface. Even performing the ion nitriding process twice by rotating the steel ball does not fundamentally solve the problem of nitriding uniformity.Furthermore, the steel ball, acting as the cathode, occasionally generates an arc discharge, known as arcing, which leads to localized burning on the surface. This significantly impairs the surface quality of the steel ball and increases the risk of bearing failure. Additionally, when processing steel balls in batches, the influence of the discharge's uniformity makes it difficult to achieve a uniform temperature field throughout the nitriding furnace, which also affects the consistency of the nitriding process.
[0004] DE 15 21 220 A, JP 2008-115 422 A, WO 2004 / 042 106 A1, DE 10 2017 131 047 A1 and JP 2010- 111 920 A concern devices for the nitriding of steel balls. Object of the invention
[0005] To solve the problems of an uneven nitriding layer, surface burning caused by the arc discharge of steel balls in the ion nitriding process, and poor conformity of steel ball nitriding caused by an uneven temperature field in the existing ion nitriding process for the surface of steel balls, the invention provides a device for uniform nitriding of a batch of steel balls according to claim 1 and a method for its use according to claim 10.
[0006] The device for uniform nitriding of a charge of steel balls according to the invention comprises a furnace body 1, an auxiliary heating device 4, a tray 7, several movable thermocouples 8, a hollow shaft 9, a wireless transmitter 10, an upper cathode disk 11 and a lower cathode disk 12.
[0007] The furnace body 1 is a cylindrical vacuum chamber. The inner wall of the furnace body 1 is provided with a water-cooled wall. A gas inlet opening 3 and a gas outlet opening 2 are provided on opposite sides of the furnace body 1. The auxiliary heater 4 is arranged on the inner walls of the furnace body 1. The auxiliary heater 4 has a thermocouple for temperature monitoring. Heat shielding plates 5 are provided on the inner walls of the furnace body 1 to reduce heat loss in the furnace. In the uniform temperature zone in the furnace body 1, an upper cathode disk 11 and a lower cathode disk 12 are arranged parallel to each other. The upper cathode disk 11 and the lower cathode disk 12 are supported and connected by support rods 13. The support rods 13 are conductors. The upper cathode disk 11 and the lower cathode disk 12 are each provided with several gas holes for gas circulation.Several ceramic support feet 14 are provided between the lower cathode disk 12 and the base of the furnace body 1. The ceramic support feet 14 also provide insulation. A through-hole is provided in the center of the lower cathode disk 12. The lower cathode disk 12 is connected to the negative electrode of the power source for ion nitriding via an insertion electrode 15. An inclined tray 7 is arranged between the upper cathode disk 11 and the lower cathode disk 12. The center of the lower surface of the tray 7 is connected to the hollow shaft 9. The hollow shaft 9 passes through the through-hole in the center of the lower cathode disk 12, and its lower end protrudes from the furnace body 1. The upper surface of the tray 7 is conical, with the center of the tray 7 being lower than the outer ring.Tray 7 contains several steel balls 6 arranged so that they automatically fall back to the center. Several movable thermocouples 8 are embedded in the tray 7. The measuring ends of the movable thermocouples 8 in the tray 7 are equidistant from the upper surface of the tray 7. The lower ends of the movable thermocouples 8 are located in the hollow shaft 9. The movable thermocouples 8 are used to measure the surface temperature of the tray. The wireless transmitter 10 is attached to the lower end of the hollow shaft 9 by means of a bracket. The outputs of the movable thermocouples 8 are connected to the input of the wireless transmitter 10 via an aviation connector. The wireless transmitter 10 can rotate with the hollow shaft 9. The wireless transmitter 10 amplifies and converts the weak electrical signal from the movable thermocouples 8.The signals are received by a receiver connected to the computer to capture the temperature signals, thus enabling monitoring of the tray 7's temperature. The upper cathode disk 11, the lower cathode disk 12, and the support rods 13 form a cathode system. The furnace body 1, the steel balls 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding and form an anode system. The furnace body 1 is grounded. Sufficient distance is maintained between the cathode and anode systems within the furnace body 1 to prevent a collapse of the electric field during ion nitriding.
[0008] The process for ion nitriding of steel balls using the device for uniform nitriding of steel ball batches is carried out with the following steps: 1. Loading with steel balls
[0009] The steel balls 6 are placed in the tray 7 until the distance between the outermost steel balls 6 and the inner edge of the tray 7 is 2 to 5 times the diameter of the steel balls 6. 2. The furnace body 1 is vacuum-sealed down to the background vacuum. 3. The auxiliary heating device 4 is switched on to increase the temperature in the furnace body 1 to a predetermined temperature. 4. Supply of nitrating gas 5. Once the nitriding gas pressure has stabilized, the power source for the ion nitriding process is switched on. The rotational speed of the hollow shaft 9 is set to 0-50 rpm. The movable thermocouples 8 are rotated by the tray 7, causing the steel balls to move towards the edge of the tray 7 under the influence of centrifugal force and simultaneously rotate circumferentially. This position is held for 0-10 minutes. Then, the rotational speed of the hollow shaft 9 is reduced to zero. At the reduced speed, the steel balls 6 move towards the center of the tray 7 under the influence of friction and gravity and are held there for 0-10 minutes. 6. Step 5 is repeated until nitration is complete. 7. The power source for the ion nitriding process and the auxiliary heating device 4 are switched off after the nitriding process is complete. The supply of nitriding gas is stopped and the hollow shaft 9 continues to rotate. 8. After cooling, the hollow shaft 9 is stopped.
[0010] The principles and effects of the invention are: 1. In the invention, the movable thermocouples 8 for temperature measurement are not in contact with the plasma, thereby avoiding the inaccurate temperature measurement caused by the change in the surface composition of the thermocouple in the nitriding atmosphere. 2. In the invention, the movable thermocouples 8 can rotate with the tray 7. The movable thermocouples 8 are not charged. Several movable thermocouples 8 can monitor the temperature of the tray of steel balls at multiple points. The auxiliary heater 4 heats the furnace to the nitriding temperature. Monitoring and control of the temperature of the tray 7 and the steel balls 6 are achieved by combining the movable thermocouples 8 and the nitriding power supply. Since the steel balls move during nitriding, their temperature stabilizes once the tray temperature has stabilized. The movement of the steel balls increases the consistency of their temperature. This movement prevents the steel balls from becoming fixed in specific positions. The movement is random.The energies received by the points on the spherical surface of the steel spheres are identical, thus achieving stable control of the steel sphere temperature. 3. The furnace body 1, the steel spheres 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding, forming an anode system. The furnace body 1 is grounded, meaning the steel spheres 6 are also grounded. The steel spheres 6 are not used as a cathode. The steel spheres 6 are immersed in the plasma generated by glow discharge. The active nitrogen in the plasma forms a nitriding layer by adsorbing onto the surface of the steel spheres. The surfaces of the steel spheres 6 are neither discharged nor bombarded by high-energy ions, which reduces the impact on the surface roughness of the steel spheres and ensures that the steel spheres are not burned. 4. The acceleration and deceleration exerted on the steel balls during the accelerated rotation and the stopping of the rotation of the tray 7 in the invention cause the steel balls to move randomly. The steel balls can appear anywhere on the entire tray. The inclined surface of the tray 7 prevents the steel balls from rotating around a fixed axis. The inner and outer steel balls can be completely interchanged to achieve this random movement. Simultaneously, the uniform discharge generated by the upper cathode disk 11 and the lower cathode disk 12, as well as the rotation of the tray 7, ensure that the surface temperature of the tray 7 is uniform. Under the influence of the two factors mentioned above, the steel balls 6 in the tray 7 can reduce the difference in energy received by the steel balls, thus ensuring a uniform temperature among them.Due to the random movement of the steel balls, their surfaces have an equal probability of coming into contact with the plasma. Combined with temperature control, this ensures that the nitriding conditions at every point on the surface of the steel balls are uniform over an extended period. Simultaneously, the design and installation of the tray guarantee the random positioning of the steel balls, thus ensuring consistent nitriding of the same batch. The steel balls do not serve as the cathode, thereby eliminating the problem of uneven surface temperature due to the hollow cathode effect. 5. In the invention, no distance needs to be maintained between the steel balls in the tray 7, which can significantly increase production efficiency. 6. In the device of the invention, several spaced sets of cathode disks and trays can be arranged, which can significantly increase production efficiency. 7. The auxiliary heating device 4 serves to increase the oven temperature to a set temperature in order to assist the heating during the glow discharge during nitriding and to reduce the heating effect of the glow discharge power source, thus facilitating the adjustment of the plasma density in the oven. 8. The invention employs wireless temperature measurement. The wireless transmitter and the movable thermocouples rotate together with the tray, thus avoiding the problem of the temperature of the moving mechanism not being directly measured. Simultaneously, electrical isolation between the movable thermocouples and the computer acquisition system is achieved. This structure can also be directly applied to measuring the cathode temperature of ion nitriding, thereby overcoming the problem that, in the prior art, the stationary thermocouple cannot directly measure the temperature. Brief description of the drawings Fig. 1 a schematic representation of the device for uniform nitriding of a charge of steel balls of embodiment 1 of the invention, Fig. 2 a macroscopic photograph of steel spheres of embodiment 1 of the invention obtained by nitriding, Fig. 3 a metallographic photograph of any cross-section of the steel sphere of embodiment 1 of the invention obtained by nitriding, Fig. 4 an enlarged photograph of the nitrided layer at the 0° position of the steel ball in Fig. 3, Fig. 5 an enlarged photograph of the nitrided layer at the 45° position of the steel ball in Fig. 3, Fig. 6 an enlarged photograph of the nitrided layer at the 90° position of the steel ball in Fig. 3, Fig. 7 an enlarged photograph of the nitrided layer at the 135° position of the steel ball in Fig. 3, Fig. 8 an enlarged photograph of the nitrided layer at the 180° position of the steel ball in Fig. 3, Fig. 9 an enlarged photograph of the nitrided layer at the 225° position of the steel ball in Fig. 3, Fig. 10 an enlarged photograph of the nitrided layer at the 270° position of the steel ball in Fig. 3. Fig. 11 an enlarged photograph of the nitrided layer at the 315° position of the steel ball in Fig. 3. Description of preferred embodiments
[0011] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any meaningful combination between the specific embodiments.
[0012] Embodiment 1: The device for uniformly nitriding a batch of steel balls of this embodiment comprises a furnace body 1, an auxiliary heating device 4, a tray 7, several movable thermocouples 8, a hollow shaft 9, a wireless transmitter 10, an upper cathode disk 11 and a lower cathode disk 12.
[0013] The furnace body 1 is a cylindrical vacuum chamber. The inner wall of the furnace body 1 is provided with a water-cooled wall. A gas inlet opening 3 and a gas outlet opening 2 are provided on opposite sides of the furnace body 1. The auxiliary heater 4 is arranged on the inner walls of the furnace body 1. The auxiliary heater 4 has a thermocouple for temperature monitoring. Heat shielding plates 5 are provided on the inner walls of the furnace body 1 to reduce heat loss in the furnace. In the uniform temperature zone in the furnace body 1, an upper cathode disk 11 and a lower cathode disk 12 are arranged parallel to each other. The upper cathode disk 11 and the lower cathode disk 12 are supported and connected by support rods 13. The support rods 13 are conductors. The upper cathode disk 11 and the lower cathode disk 12 are each provided with several gas holes for gas circulation.Several ceramic support feet 14 are provided between the lower cathode disk 12 and the base of the furnace body 1. The ceramic support feet 14 also provide insulation. A through-hole is provided in the center of the lower cathode disk 12. The lower cathode disk 12 is connected to the negative electrode of the power source for ion nitriding via an insertion electrode 15. An inclined tray 7 is arranged between the upper cathode disk 11 and the lower cathode disk 12. The center of the lower surface of the tray 7 is connected to the hollow shaft 9. The hollow shaft 9 passes through the through-hole in the center of the lower cathode disk 12, and its lower end protrudes from the furnace body 1. The upper surface of the tray 7 is conical, with the center of the tray 7 being lower than the outer ring.Tray 7 contains several steel balls 6 arranged so that they automatically fall back to the center. Several movable thermocouples 8 are embedded in the tray 7. The measuring ends of the movable thermocouples 8 in the tray 7 are equidistant from the upper surface of the tray 7. The lower ends of the movable thermocouples 8 are located in the hollow shaft 9. The movable thermocouples 8 are used to measure the surface temperature of the tray. The wireless transmitter 10 is attached to the lower end of the hollow shaft 9 by means of a bracket. The outputs of the movable thermocouples 8 are connected to the input of the wireless transmitter 10 via an aviation connector. The wireless transmitter 10 can rotate with the hollow shaft 9. The wireless transmitter 10 amplifies and converts the weak electrical signal from the movable thermocouples 8.The signals are received by a receiver connected to the computer to capture the temperature signals, thus enabling monitoring of the tray 7's temperature. The upper cathode disk 11, the lower cathode disk 12, and the support rods 13 form a cathode system. The furnace body 1, the steel balls 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding and form an anode system. The furnace body 1 is grounded. Sufficient distance is maintained between the cathode and anode systems within the furnace body 1 to prevent a collapse of the electric field during ion nitriding.
[0014] The principles and effects of this embodiment are: 1. In this embodiment, the movable thermocouples 8 for temperature measurement are not in contact with the plasma, thus avoiding the inaccurate temperature measurement caused by the change in the surface composition of the thermocouple in the nitriding atmosphere. 2. In this embodiment, the movable thermocouples 8 can rotate with the tray 7. The movable thermocouples 8 are not charged. Several movable thermocouples 8 can monitor the temperature of the tray of steel balls at multiple points. The auxiliary heater 4 heats the furnace to the nitriding temperature. Monitoring and control of the temperature of the tray 7 and the steel balls 6 are achieved through the combination of the movable thermocouples 8 and the nitriding power supply. Since the steel balls move during nitriding, their temperature stabilizes once the tray temperature has stabilized. The movement of the steel balls increases the consistency of their temperature. This movement prevents the steel balls from becoming fixed in specific positions. The movement is random.The energies received by the points on the spherical surface of the steel spheres are identical, thus achieving stable control of the steel sphere temperature. 3. The furnace body 1, the steel spheres 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding, forming an anode system. The furnace body 1 is grounded, meaning the steel spheres 6 are also grounded. The steel spheres 6 are not used as a cathode. The steel spheres 6 are immersed in the plasma generated by glow discharge. The active nitrogen in the plasma forms a nitriding layer by adsorbing onto the surface of the steel spheres. The surfaces of the steel spheres 6 are neither discharged nor bombarded by high-energy ions, which reduces the impact on the surface roughness of the steel spheres and ensures that the steel spheres are not burned. 4. The acceleration and deceleration exerted on the steel balls during the accelerated rotation and the stopping of the rotation of the tray 7 in this embodiment cause the steel balls to move randomly. The steel balls can appear anywhere on the entire tray. The inclined surface of the tray 7 prevents the steel balls from rotating around a fixed axis. The inner and outer steel balls can be completely interchanged to achieve this random movement. Simultaneously, the uniform discharge generated by the upper cathode disk 11 and the lower cathode disk 12, as well as the rotation of the tray 7, ensure that the surface temperature of the tray 7 is uniform. Under the influence of the two factors mentioned above, the steel balls 6 in the tray 7 can reduce the difference in energy received by the steel balls, thus ensuring a uniform temperature.Due to the random movement of the steel balls, their surfaces have an equal probability of coming into contact with the plasma. Combined with temperature control, this ensures that the nitriding conditions at every point on the surface of the steel balls are uniform over an extended period. Simultaneously, the design and installation of the tray guarantee the random positioning of the steel balls, thus ensuring consistent nitriding of the same batch. The steel balls do not serve as the cathode, thereby eliminating the problem of uneven surface temperature due to the hollow cathode effect. 5. In this embodiment, no distance needs to be maintained between the steel balls in the tray 7, which can significantly increase production efficiency. 6. In the device of this embodiment, several spaced sets of cathode disks and trays can be arranged, which can significantly increase production efficiency. 7. The auxiliary heating device 4 serves to increase the oven temperature to a set temperature in order to assist the heating during the glow discharge during nitriding and to reduce the heating effect of the glow discharge power source, thus facilitating the adjustment of the plasma density in the oven. 8. This embodiment uses wireless temperature measurement. The wireless transmitter and the movable thermocouples rotate together with the tray, thus avoiding the problem of the temperature of the moving mechanism not being directly measured. Simultaneously, electrical isolation between the movable thermocouples and the computer acquisition system is achieved. This structure can also be directly applied to measuring the cathode temperature of ion nitriding, overcoming the problem that, in the prior art, the stationary thermocouple cannot directly measure the temperature.
[0015] Embodiment 2: The difference between this embodiment and embodiment 1 is that the outer wall of the hollow shaft 9 and the furnace body 1 are sealed by a rotary sealing mechanism.
[0016] Embodiment 3: The difference between this embodiment and embodiment 1 or 2 is that each movable thermocouple 8 in the tray 7 is connected to a wireless transmitter 10.
[0017] Embodiment 4: The difference between this embodiment and embodiments 1 to 3 is that the lower end of the hollow shaft 9 is connected to a central drive shaft 16.
[0018] Embodiment 5: The difference between this embodiment and embodiment 4 is that the central drive shaft 16 is connected to the power output shaft of the motor to achieve the rotation of the hollow shaft 9 and the tray 7.
[0019] Embodiment 6: The difference between this embodiment and embodiments 1 to 5 is that the distance between the measuring ends of the movable thermocouples 8 and the upper surface of the tray 7 is 1-5 mm.
[0020] Embodiment 7: The difference between this embodiment and embodiments 1 to 6 is that the aviation connector is arranged at the lower end of the hollow shaft 9 and a static seal is provided between the aviation connector and the hollow shaft 9.
[0021] Embodiment 8: The difference between this embodiment and embodiments 1 to 7 is that the angle between the generating line of the conical surface of the tray 7 and the horizontal direction is 0.1-5°.
[0022] Embodiment 9: The difference between this embodiment and embodiments 1 to 8 is that the lower surface of the tray 7 is a flat surface and forms an angle of 0-5° with the horizontal plane.
[0023] Embodiment 10: the method for ion nitriding of steel balls using the device for uniform nitriding of steel ball batch is carried out with the following steps: 1. Loading with steel balls
[0024] The steel balls 6 are placed in the tray 7 until the distance between the outermost steel balls 6 and the inner edge of the tray 7 is 2 to 5 times the diameter of the steel balls 6. 2. The furnace body 1 is vacuum-sealed down to the background vacuum. 3. The auxiliary heating device 4 is switched on to increase the temperature in the furnace body 1 to a predetermined temperature. 4. Supply of nitrating gas 5. Once the nitriding gas pressure has stabilized, the power source for the ion nitriding process is switched on. The rotational speed of the hollow shaft 9 is set to 0-50 rpm and maintained for 0-10 minutes. The movable thermocouples 8 are rotated by the tray 7, causing the steel balls 6 to move towards the edge of the tray 7 under the influence of centrifugal force while simultaneously rotating circumferentially. The rotational speed of the hollow shaft 9 is then reduced to zero and maintained for 0-10 minutes. At the reduced speed, the steel balls 6 move towards the center of the tray 7 under the influence of friction and gravity. 6. Step 5 is repeated until nitration is complete. 7. The power source for the ion nitriding process and the auxiliary heating device 4 are switched off after the nitriding process is complete. The supply of nitriding gas is stopped and the hollow shaft 9 continues to rotate. 8. After cooling, the hollow shaft 9 is stopped.
[0025] The principles and effects of this embodiment are: 1. In this embodiment, the movable thermocouples 8 for temperature measurement are not in contact with the plasma, thus avoiding the inaccurate temperature measurement caused by the change in the surface composition of the thermocouple in the nitriding atmosphere. 2. In this embodiment, the movable thermocouples 8 can rotate with the tray 7. The movable thermocouples 8 are not charged. Several movable thermocouples 8 can monitor the temperature of the tray of steel balls at multiple points. The auxiliary heater 4 heats the furnace to the nitriding temperature. Monitoring and control of the temperature of the tray 7 and the steel balls 6 are achieved through the combination of the movable thermocouples 8 and the nitriding power supply. Since the steel balls move during nitriding, their temperature stabilizes once the tray temperature has stabilized. The movement of the steel balls increases the temperature consistency of the steel balls 6. This movement prevents the steel balls from becoming fixed in specific positions. The movement is random.The energies received by the points on the spherical surface of the steel spheres are consistent, thus achieving stable control of the steel sphere temperature. 3. The furnace body 1, the steel spheres 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding, forming an anode system. The furnace body 1 is grounded, meaning the steel spheres 6 are also grounded. The steel spheres 6 are not used as a cathode. The steel spheres 6 are immersed in the plasma generated by glow discharge. The active nitrogen in the plasma forms a nitriding layer by adsorbing onto the surface of the steel spheres. The surfaces of the steel spheres 6 are neither discharged nor bombarded by high-energy ions, which reduces the impact on the surface roughness of the steel spheres and ensures that the steel spheres are not burned. 4. The acceleration and deceleration exerted on the steel balls during the accelerated rotation and the stopping of the rotation of the tray 7 in this embodiment cause the steel balls to move randomly. The steel balls can appear anywhere on the entire tray. The inclined surface of the tray 7 prevents the steel balls from rotating around a fixed axis. The inner and outer steel balls can be completely interchanged to achieve this random movement. Simultaneously, the uniform discharge generated by the upper cathode disk 11 and the lower cathode disk 12, as well as the rotation of the tray 7, ensure that the surface temperature of the tray 7 is uniform. Under the influence of the two factors mentioned above, the steel balls 6 in the tray 7 can reduce the difference in energy received by the steel balls, thus ensuring a uniform temperature.Due to the random movement of the steel balls, their surfaces have an equal probability of coming into contact with the plasma. Combined with temperature control, this ensures that the nitriding conditions at every point on the surface of the steel balls are uniform over an extended period. Simultaneously, the design and installation of the tray guarantee the random positioning of the steel balls, thus ensuring consistent nitriding of the same batch. The steel balls do not serve as the cathode, thereby eliminating the problem of uneven surface temperature due to the hollow cathode effect. 5. In this embodiment, no distance needs to be maintained between the steel balls in the tray 7, which can significantly increase production efficiency. 6. In the device of this embodiment, several spaced sets of cathode disks and trays can be arranged, which can significantly increase production efficiency. 7. The auxiliary heating device 4 serves to increase the oven temperature to a set temperature in order to assist the heating during the glow discharge during nitriding and to reduce the heating effect of the glow discharge power source, thus facilitating the adjustment of the plasma density in the oven. 8. This embodiment uses wireless temperature measurement. The wireless transmitter and the movable thermocouples rotate together with the tray, thus avoiding the problem of the temperature of the moving mechanism not being directly measured. Simultaneously, electrical isolation between the movable thermocouples and the computer acquisition system is achieved. This structure can also be directly applied to measuring the cathode temperature of ion nitriding, overcoming the problem that, in the prior art, the stationary thermocouple cannot directly measure the temperature. Example 1:
[0026] In this embodiment, nitriding is carried out according to the conventional ion nitriding process, with the plasma generated by the glow discharge forming the anode nitriding layer. The process is as follows: 1. Loading with steel balls
[0027] The steel balls 6 are placed in the tray 7 until the distance between the outermost steel balls 6 and the inner edge of the tray 7 is 4 times the diameter of the steel balls 6. 2. The furnace body 1 is vacuum-sealed down to the background vacuum. 3. The auxiliary heating device 4 is switched on to increase the temperature in the furnace body 1 to a predetermined temperature. 4. Supply of nitrating gas 5. Once the nitriding gas pressure has stabilized, the power source for the ion nitriding process is switched on. The rotational speed of the hollow shaft 9 is set to 40 rpm and maintained for 1 minute. The movable thermocouples 8 are rotated by the tray 7, causing the steel balls 6 to move towards the edge of the tray 7 under the influence of centrifugal force while simultaneously rotating circumferentially. The rotational speed of the hollow shaft 9 is then reduced to zero and maintained for 1 minute. At the reduced speed, the steel balls 6 move towards the center of the tray 7 under the influence of friction and gravity. 6. Step 5 is repeated until nitration is complete. 7. The power source for the ion nitriding process and the auxiliary heating device 4 are switched off after the nitriding process is complete. The supply of nitriding gas is stopped and the hollow shaft 9 continues to rotate. 8. After cooling, the hollow shaft 9 is stopped and gas supply and delivery are carried out.
[0028] The device for the uniform nitriding of a batch of steel balls in this embodiment comprises a furnace body 1, an auxiliary heater 4, a tray 7, several movable thermocouples 8, a hollow shaft 9, a wireless transmitter 10, an upper cathode disk 11, and a lower cathode disk 12. The furnace body 1 is a cylindrical vacuum chamber. The inner wall of the furnace body 1 is provided with a water-cooled wall. A gas inlet opening 3 and a gas outlet opening 2 are provided on opposite sides of the furnace body 1. The auxiliary heater 4 is arranged on the inner walls of the furnace body 1. The auxiliary heater 4 has a thermocouple for temperature monitoring. Heat shielding plates 5 are provided on the inner walls of the furnace body 1 to reduce heat loss in the furnace.In the uniform temperature zone within the furnace body 1, an upper cathode disk 11 and a lower cathode disk 12 are arranged parallel to each other. The upper cathode disk 11 and the lower cathode disk 12 are supported and connected by support rods 13. The support rods 13 are conductors. The upper cathode disk 11 and the lower cathode disk 12 are each provided with several gas holes for gas circulation. Several ceramic support feet 14 are provided between the lower cathode disk 12 and the bottom surface of the furnace body 1. The ceramic support feet 14 also provide insulation. A through-hole is provided in the center of the lower cathode disk 12. The lower cathode disk 12 is connected to the negative electrode of the power source for ion nitriding via an insertion electrode 15. An inclined tray 7 is arranged between the upper cathode disk 11 and the lower cathode disk 12.The lower surface of the tray 7 is a flat surface and forms an angle of 0-5° with the horizontal plane. The center of the lower surface of the tray 7 is connected to the hollow shaft 9. The hollow shaft 9 passes through the through-hole in the center of the lower cathode disk 12, and its lower end protrudes from the furnace body 1. The outer wall of the hollow shaft 9 and the furnace body 1 are sealed by a rotary sealing mechanism. The upper surface of the tray 7 is conical, with the center of the tray 7 being lower than the outer ring. Several steel balls 6 are arranged in the tray 7 so that they automatically return to the center. Several movable thermocouples 8 are embedded in the tray 7. The measuring ends of the movable thermocouples 8 in the tray 7 are equidistant from the upper surface of the tray 7.The lower ends of the movable thermocouples 8 are located inside the hollow shaft 9. The movable thermocouples 8 are used to measure the surface temperature of the tray. The wireless transmitter 10 is attached to the lower end of the hollow shaft 9 via a bracket. The outputs of the movable thermocouples 8 are connected to the input of the wireless transmitter 10 via an aviation-grade connector. The aviation connector is located at the lower end of the hollow shaft 9, and a static seal is provided between the aviation connector and the hollow shaft 9. The wireless transmitter 10 can rotate with the hollow shaft 9. The wireless transmitter 10 amplifies and converts the weak electrical signal from the movable thermocouples 8. The signals are received by a receiver connected to the computer to capture the temperature signals, thus enabling monitoring of the tray 7's temperature.Each movable thermocouple 8 in the tray 7 is connected to a wireless transmitter 10. The upper cathode disk 11, the lower cathode disk 12, and the support rods 13 form a cathode system. The furnace body 1, the steel balls 6, the tray 7, and the hollow shaft 9 are connected to the positive electrode of the power source for ion nitriding and form an anode system. The furnace body 1 is grounded. Sufficient distance is maintained between the cathode and anode systems in the furnace body 1 to prevent a collapse of the electric field during ion nitriding. The lower end of the hollow shaft 9 is connected to a central drive shaft 16. The central drive shaft 16 is connected to the power output shaft of the motor to rotate the hollow shaft 9 and the tray 7. The distance between the measuring ends of the movable thermocouples 8 and the upper surface of the tray 7 is 2 mm.The angle between the generating line of the conical surface of the tray 7 and the horizontal direction is 3°.
[0029] In this embodiment, the movable thermocouples 8 are of the K-type model. The receiver is a ZigBee to RS485 wireless serial server (CC2530) and the wireless transmitter 10 is a wireless-to-serial transparent multi-node transmission module of the LRF215A model.
[0030] Fig. Figure 2 shows a macroscopic photograph of steel spheres obtained by nitriding. It can be seen that the surface color is uniform and no arc traces are present. Fig. Figure 3 shows a metallographic photograph of an arbitrary cross-section of the steel sphere obtained by nitriding. It can be seen that the nitrided layer on the steel sphere surface is uniform. Fig. 4 to Fig. Figure 11 shows the enlarged photos of the nitriding layer at 8 positions of the steel ball in Fig.3 (angle with the positive x-axis). It can be seen that the depth of the nitriding layer is consistent.
Claims
Device for the uniform nitriding of a batch of steel balls, comprising a furnace body (1), an auxiliary heating device (4), a tray (7), several movable thermocouples (8), a hollow shaft (9), a wireless transmitter (10), an upper cathode disk (11) and a lower cathode disk (12), wherein the furnace body (1) is a cylindrical vacuum chamber, the inner wall of the furnace body (1) is provided with a water-cooled wall, and a gas inlet opening (3) and a gas outlet opening (2) are provided on opposite sides of the furnace body (1), wherein the auxiliary heating device (4) is arranged on the inner sides of the furnace body (1), the auxiliary heating device (4) has a thermocouple for temperature monitoring, and heat shielding plates (5) are provided on the inner walls of the furnace body (1), wherein an upper cathode disk (11) and a lower cathode disk (12) are arranged in the uniform temperature zone in the furnace body (1), which are parallel run towards each otherthe upper cathode disk (11) and the lower cathode disk (12) are supported and connected by support rods (13), the support rods (13) being conductors, and the upper cathode disk (11) and the lower cathode disk (12) are each provided with several gas holes, wherein several ceramic support feet (14) are provided between the lower cathode disk (12) and the bottom surface of the furnace body (1), a through-hole is provided in the center of the lower cathode disk (12), and the lower cathode disk (12) is connected to the negative electrode of the power source for the ion nitriding via an insertion electrode (15), wherein an inclined tray (7) is arranged between the upper cathode disk (11) and the lower cathode disk (12), the center of the lower surface of the tray (7) being connected to the hollow shaft (9),and the hollow shaft (9) passes through the through-hole in the center of the lower cathode disk (12) and the lower end of the hollow shaft (9) protrudes from the furnace body (1), wherein the upper surface of the tray (7) is a conical surface, the center of the tray (7) is deeper than the outer ring, and several steel balls (6) are arranged in the tray (7), wherein several movable thermocouples (8) are embedded in the tray (7), the measuring ends of the movable thermocouples (8) in the tray (7) are equidistant from the upper surface of the tray (7), and the lower ends of the movable thermocouples (8) are located in the hollow shaft (9), wherein the wireless transmitter (10) is attached to the lower end of the hollow shaft (9) via a bracket, and the outputs of the movable thermocouples (8) are connected to the input of the wireless transmitter (10) via an aviation connector, wherein the upper cathode disk (11),the lower cathode disk (12) and the support rods (13) form a cathode system, the furnace body (1), the steel balls (6), the tray (7) and the hollow shaft (9) are connected to the positive electrode of the power source for the ion nitriding and form an anode system, and the furnace body (1) is grounded. Device for uniform nitriding of a charge of steel balls according to claim 1, characterized in that the outer wall of the hollow shaft (9) and the furnace body (1) are sealed by a rotary sealing mechanism. Device for uniform nitriding of a charge of steel balls according to claim 1, characterized in that each movable thermocouple (8) in the tray (7) is connected to a wireless transmitter (10). Device for uniform nitriding of a charge of steel balls according to claim 1, characterized in that the lower end of the hollow shaft (9) is connected to a central drive shaft (16). Device for uniform nitriding of a charge of steel balls according to claim 4, characterized in that the central drive shaft (16) is connected to the power output shaft of the motor to achieve the rotation of the hollow shaft (9) and the tray (7). Device for uniform nitriding of a batch of steel balls according to claim 1, characterized in that the distance between the measuring ends of the movable thermocouples (8) and the upper surface of the tray (7) is 1-5 mm. Device for uniform nitriding of a charge of steel balls according to claim 1, characterized in that the aviation connector is arranged at the lower end of the hollow shaft (9) and a static seal is provided between the aviation connector and the hollow shaft (9). Device for uniform nitriding of a charge of steel balls according to claim 1, characterized in that the angle between the generating point of the conical surface of the tray (7) and the horizontal direction is 0.1-5°. Device for uniform nitriding of a batch of steel balls according to claim 8, characterized in that the lower surface of the tray (7) is a flat surface and forms an angle of 0-5° with the horizontal plane. A method for ion nitriding steel balls using the apparatus for uniform nitriding of a batch of steel balls according to claim 1, carried out in the following steps:
1. Loading of steel balls: The steel balls (6) are placed in the tray (7) until the distance between the outermost steel balls (6) and the inner edge of the tray (7) is 2 to 5 times the diameter of the steel balls (6); 2. The furnace body (1) is evacuated to a background vacuum; 3. The auxiliary heating device (4) is switched on to raise the temperature in the furnace body (1) to a predetermined temperature; 4. Supply of nitriding gas; 5.Once the nitriding gas pressure is stable, the power source for ion nitriding is switched on; the rotational speed of the hollow shaft (9) is set to 1-50 rpm and maintained for 1-10 minutes; the movable thermocouples (8) are rotated by the tray (7), causing the steel balls (6) to move towards the edge of the tray (7) under the influence of centrifugal force while simultaneously rotating circumferentially; then the rotational speed of the hollow shaft (9) is reduced to zero and maintained for 1-10 minutes; at the reduced speed, the steel balls (6) move towards the center of the tray (7) under the influence of friction and gravity; Step 6 (5) is repeated until the nitriding is complete; the power source for ion nitriding and the auxiliary heater (4) are switched off after the nitriding is complete; the supply of nitriding gas is stopped, and the hollow shaft (9) continues to rotate; and 8.After cooling, the hollow shaft (9) is stopped.