JP7625814B2 - Manufacturing method of bearing race - Google Patents

Description

The present invention relates to a method for manufacturing bearing rings.

The bearing ring, which is an annular component, needs to have a desired mechanical strength as a required function. In order to impart mechanical strength to the bearing ring, the manufacturing process for the bearing ring involves carrying out heat treatment, including quenching, on the annular component formed from bearing steel (SUJ2), for example.

For example, Patent Document 1 discloses a continuous heat treatment furnace that performs heat treatments such as carburizing and sintering on objects to be heated.

JP 2009-228116 A

Bearing raceways have low rigidity against elliptical deformation, and circular blanks machined from materials can become elliptical due to the effects of heat from the hardening process and phase transformation. In this way, elliptical deformation refers to the phenomenon in which circular steel parts become distorted into an elliptical shape.

The oval deformation of the bearing raceway is evaluated by measuring the roundness of the raceway surface of the bearing raceway after hardening. The oval deformation caused by this type of heat treatment is removed by subsequent grinding, but if the bearing raceway has a large oval deformation and poor roundness, the amount of grinding must be increased, which increases costs in the manufacturing process of the bearing raceway.

When heat treating the annular members that will become bearing races, for example, continuous or batch heat treatment can be used. The continuous type is a mass production method in which the annular members are placed on a belt conveyor or the like and heated as they pass through a furnace. The batch type is a method in which the annular members are placed in a basket and the basket is placed in a fixed furnace (batch heating furnace) for heat treatment (heating and cooling). A characteristic of batch heating furnaces is that the temperature and time can be freely adjusted each time depending on the type of bearing rolling element and heating conditions, etc.

However, when a ring-shaped component is heat-treated using a batch-type heating furnace, there has been a problem in the past where the ring-shaped component undergoes elliptical deformation and the roundness deteriorates. However, the cause of this elliptical deformation and the deterioration of the roundness was unclear.

The present invention was made in consideration of the above circumstances, and aims to provide a manufacturing method for bearing raceways that can suppress deformation due to heat treatment.

The above object of the present invention can be achieved by the following configuration.
(1) A method for manufacturing a bearing ring, comprising the steps of:
an annular member arrangement step of arranging a plurality of annular members that will become bearing races on a basket;
a basket placement step of placing the basket inside a heating furnace;
a heat treatment step of heat treating the plurality of annular members arranged on the basket;
Including,
In the annular member arrangement step, the plurality of annular members are arranged on the basket so as not to come into contact with each other;
In the heat treatment step, the plurality of annular members are quenched by performing heating and cooling while maintaining the arrangement of the plurality of annular members on the basket.
Manufacturing method of bearing races.
(2) A method for manufacturing a bearing ring as described in (1), in which, during the quenching in the heat treatment process, the basket is immersed in a cooling liquid stored in a liquid tank, and the cooling liquid is caused to flow in an upward and downward direction to come into contact with the multiple annular members, thereby cooling the multiple annular members.
(3) The method for manufacturing a bearing race according to (1) or (2), wherein the plurality of annular members are set at predetermined positions in the basket by a positioning member.
(4) The method for manufacturing a bearing ring according to any one of (1) to (3), wherein the heating furnace is a batch-type heating furnace.
(5) The method for manufacturing a bearing ring according to any one of (1) to (4), wherein in the annular member arranging step, the plurality of annular members are arranged in a staggered pattern.
(6) The method for manufacturing a bearing ring according to any one of (1) to (5), wherein the plurality of annular members are carburized in the heat treatment step.
(7) The method for manufacturing a bearing ring according to any one of (1) to (5), wherein the plurality of annular members are subjected to a nitriding treatment in the heat treatment step.
(8) The method for manufacturing a bearing ring according to any one of (1) to (5), wherein the plurality of annular members are carbonitrided in the heat treatment step.
(9) The method for manufacturing a bearing race as set forth in any one of (1) to (5), wherein the plurality of annular members are deep-hardened in the heat treatment step.
(10) In the heat treatment step, after the quenching is performed on the plurality of annular members, the plurality of annular members are further subjected to tempering.
A method for manufacturing a bearing race according to any one of (1) to (9).
(11) The method further includes a grinding step of grinding the annular member after the heat treatment step.
A method for manufacturing a bearing race according to any one of (1) to (10).

The manufacturing method of the bearing race of the present invention makes it possible to suppress deformation of the annular member due to heat treatment.

11 is a diagram showing a state in which a plurality of annular members are arranged on a basket in an embodiment (Example 1). FIG. FIG. 13 is a diagram showing a state in which a plurality of annular members are arranged on a basket in a comparative example. FIG. 2 is a schematic cross-sectional view of a heating furnace. FIG. FIG. 13 is a diagram showing a state in which a plurality of annular members are arranged on a basket in an embodiment (Example 2). 1A to 1C are diagrams showing the results of measurement of the roundness of a plurality of annular members after carbonitriding treatment, and (a) to (c) are the results of measurement of the roundness of a comparative example, an example 1, and an example 2, respectively. 1A to 1C are diagrams showing the results of measurement of the roundness of a plurality of annular members after secondary quenching, and (a) to (c) are the results of measurement of the roundness of a comparative example, an example 1, and an example 2, respectively.

The manufacturing method of the bearing race according to the embodiment of the present invention will be described below. In the following description, the bearing race will also be simply referred to as the "race".

The method for manufacturing the raceway includes an annular member preparation process for preparing an annular member 1 that will become the raceway, an annular member arrangement process for arranging a plurality of annular members 1 on a basket 10, a basket arrangement process for placing the basket 10 inside a heating furnace 20, a heat treatment process for heat treating the plurality of annular members 1 arranged on the basket 10, and a grinding process for grinding the annular members 1 after the heat treatment process.

(Annular member preparation process)
In the process of preparing the annular member 1 that will become the race (inner or outer race), the annular member 1 is prepared as a material that will become the race. Case-hardened steel is preferable as the material for the annular member 1, so that a surface hardened layer can be easily formed by carburizing, nitriding, carbonitriding, etc. Also, in order to improve hardenability, it is also preferable to add Cr, Mn, etc. to the annular member 1 as an alloy component.

(Annular member arrangement process)
After preparing the annular members 1, a plurality of the annular members 1 are placed on a basket 10 in an annular member placement step, as shown in Fig. 1. The basket 10 has a planar bottom surface 11 and a flange portion 13 standing up from the peripheral edge of the bottom surface 11. Therefore, the basket 10 has a tray-like shape without a top surface.

Although not shown, the bottom surface 11 and flange portion 13 of the basket 10 are mesh-like, which prevents the annular member 1 from falling out of the basket 10 and allows efficient heat treatment (heating and cooling) of the annular member 1.

In the present invention, multiple annular members 1 are arranged on the bottom surface 11 of the basket 10 so that they do not come into contact with each other. In other words, the minimum horizontal distance L between adjacent annular members 1 is set to be greater than 0 (L>0).

As shown in FIG. 1, it is preferable to arrange the multiple annular members 1 in a staggered pattern. Positioning members may be used to accurately place the multiple annular members 1 in predetermined positions on the basket. By adopting a staggered arrangement, it is possible to arrange more annular members 1 on the basket 10 while still ensuring gaps between adjacent annular members 1.

The arrangement of the multiple annular members 1 is not limited to a staggered pattern, but may be, for example, a checkerboard pattern (grid pattern), as long as a gap can be secured between adjacent annular members 1 (L>0).

When arranging multiple annular members 1 on the basket 10 with gaps between them, the multiple annular members 1 may be positioned using a jig that is separate from or integrated with the basket 10, or the multiple annular members 1 may be positioned by providing projections and recesses on the basket 10, and the positioning method is not particularly limited.

As shown in FIG. 2, in the conventional technology, multiple annular members 1 were packed tightly on a basket 10. Packing adjacent annular members 1 tightly so that they are in contact with each other is normal in terms of productivity. In other words, when multiple annular members 1 are packed tightly, the number of races that can be produced at one time can be increased, and the arrangement work is also very simple. In such conventional technology, elliptical deformation occurs in the annular member 1 after heat treatment, but the machining allowance is increased to ensure the roundness of the annular member 1 in the subsequent grinding process. Therefore, in the past, there was no tendency to be particularly concerned about elliptical deformation of the annular member 1. However, in reality, it took a lot of time and cost to ensure the roundness of the annular member 1 in the grinding process.

The inventors of the present application noticed that when the annular member 1 is heat-treated using a batch-type heating furnace, the annular member 1 undergoes elliptical deformation and the roundness deteriorates when using the above-mentioned conventional method, and discovered that this elliptical deformation and the deterioration of roundness are caused by the fact that adjacent annular members 1 are heat-treated (especially when cooled during quenching) while in contact with each other. Therefore, as described above, they came up with the idea of arranging multiple annular members 1 so that they do not come into contact with each other.

(Basket placement process)
Next, a basket arrangement step for arranging the basket 10, on whose bottom surface 11 a plurality of annular members 1 are arranged, inside the heating furnace 20, will be described.

As shown in FIG. 3, the heating furnace 20 is a batch-type heating furnace, and includes an input section 30 into which the basket 10 is input, a heating section 40 for heating the multiple annular members 1, a cooling section 50 for cooling the multiple annular members 1, and a transport section 60 for transporting the basket 10 between the input section 30 and the heating section 40 and between the input section 30 and the cooling section 50. Note that the circulation device 55 provided in the cooling section 50 is omitted from FIG. 3. The circulation device 55 will be described later with reference to FIG. 4.

Each of the loading section 30, heating section 40, cooling section 50, and transport section 60 has a plurality of rollers 31, 41, 51, 61 for moving the basket 10, and a base 33, 43, 53, 63 for supporting the rollers 31, 41, 51, 61.

A first door 71 that can be opened and closed is provided between the loading section 30 and the transport section 60, and a second door 73 that can be opened and closed is provided between the transport section 60 and the heating section 40.

The heating section 40 is equipped with a burner 45 for heating the inside of the heating section 40 and a fan 47 for stirring the atmosphere inside the heating section 40.

The base 53 of the cooling section 50 and the base 63 of the transport section 60 are connected to each other and can be moved vertically together by a cylinder 65 provided above.

The cooling section 50 is a liquid tank in which a cooling liquid is stored, and in this example, it is an oil tank in which cooling oil O is stored. The cooling liquid is not limited to cooling oil, and may be water, an aqueous solution, or the like. The height of the liquid level of the cooling oil O is set so that all of the multiple baskets 10 arranged in the cooling section 50 are immersed in the cooling oil O.

As shown in Fig. 4, the cooling unit 50 includes a circulation device 55 that circulates the cooling oil in the oil tank. Fig. 4 is a view of the cooling unit 50 in Fig. 3 as viewed from the left and right direction.
The circulation device 55 is arranged on both sides of the base 53 and includes a pair of screws 56 that generate a flow of cooling oil O in the vertical direction, and a pair of guide members 57 that surround the pair of screws 56 from the outside and guide the flow of cooling liquid by the pair of screws 56.

Therefore, when a downward flow of cooling oil O is generated near the pair of screws 56, the cooling oil O passes upward through the basket 10 placed on the base 53 (see the dashed arrow in Figure 4). On the other hand, when an upward flow of cooling oil O is generated near the pair of screws 56, the cooling oil O passes downward through the basket 10 placed on the base 53.

When placing baskets 10 inside such a heating furnace 20, first, multiple baskets 10, each housing multiple annular members 1, are stacked vertically on the base 33 (rollers 31) of the loading section 30. In the illustrated example, ten stacked baskets 10 are placed in two rows on the base 33.

Next, the first door 71 is opened, the basket 10 is moved onto the base 63 of the transport section 60, and the first door 71 is closed. Then, the second door 73 is opened, the basket 10 is moved onto the base 43 of the heating section 40, and the second door 73 is closed. In this way, multiple baskets 10, each housing multiple annular members 1, are arranged in the heating section 40.

(Heat treatment process)
In the heat treatment process for heat treating the multiple annular members 1 housed in each basket 10, quenching (heating and cooling) is performed, and then tempering (heating and cooling) is performed.

It is preferable to form a surface-hardened layer on the annular member 1 by carburizing, nitriding, or carbonitriding. This is because, when elliptical deformation is suppressed as in the case of the annular member 1 of this embodiment, the surface-hardened layer can be ground evenly in the circumferential direction, so that a hardened layer with little unevenness can be formed on the surface of the annular member 1. The carburizing, nitriding, or carbonitriding process is carried out by holding the annular member 1 in a carbon or nitrogen gas atmosphere at 900 to 1000°C for several to several tens of hours. This allows the desired surface-hardened layer to be obtained.

The multiple annular members 1 arranged in the heating section 40 are hardened (heated). It is preferable to subject the multiple annular members 1 to deep hardening. The deep hardening conditions are oil cooling at a hardening temperature of 800 to 850°C.

Next, the cylinder 65 is driven to raise the base 53 of the cooling section 50 and the integrated base 63, and position them at the same height as the base 33 of the loading section 30 and the base 43 of the heating section 40. Then, after hardening (heating) of the multiple annular members 1 is completed, the second door 73 is opened and the baskets 10 are moved to the base 53 of the cooling section 50. Then, the base 53 of the cooling section 50 is lowered so that all the baskets 10 are immersed in the cooling oil O.

As described above, the pair of screws 56 causes the cooling oil O to pass upward or downward through the mesh basket 10 placed on the base 53. Quenching (cooling) is performed by stirring the cooling oil O at 60 to 100°C.

Here, the heating furnace 20 is a batch-type heating furnace and has the above-mentioned configuration, so that quenching (heating) and quenching (cooling) are performed while maintaining the arrangement of the multiple ring-shaped members 1 on the basket 10. That is, the multiple ring-shaped members 1 are arranged on the basket 10 in a staggered pattern so as not to come into contact with each other as shown in FIG. 1, and move between the loading section 30, heating section 40, cooling section 50, and transport section 60 while maintaining this arrangement (without the multiple ring-shaped members 1 moving).

Therefore, even when the multiple annular members 1 are quenched (cooled) in the cooling section 50, the multiple annular members 1 are arranged on the basket 10 so that they do not come into contact with each other. As a result, the cooling oil O flows vertically between adjacent annular members 1, so that the cooling of the annular members 1 is uniform. On the other hand, if the cooling oil O flows horizontally (both sides, one side), the cooling will be different due to the difference in the flow speed of the cooling oil depending on where the annular members 1 are placed, and all the annular members in the same basket will not be cooled uniformly, resulting in large deformation of the annular members 1. When the cooling oil O flows vertically as in this embodiment, problems such as only part of the annular member 1 being cooled and other parts not being cooled do not occur, and the entire annular member 1 is cooled uniformly.

The inventors of the present application have discovered that whether or not the annular member 1 can be cooled uniformly during this quenching (cooling) is related to the elliptical deformation (deterioration of roundness) of the annular member after heat treatment. In other words, they discovered that the cause of the elliptical deformation of the annular member 1 after heat treatment is uneven cooling, whereby the parts of the annular members 1 that are in contact with each other are not cooled sufficiently during quenching (cooling), while the parts of the annular members 1 that are not in contact with each other are cooled. They then came up with a configuration in which multiple annular members 1 are arranged on a basket 10 so that they do not come into contact with each other, in order to cool the annular members 1 uniformly.

The above-described arrangement of the multiple annular members 1 is particularly suitable when quenching (heating) and quenching (cooling) are performed while maintaining the arrangement of the multiple annular members 1 on the basket 10, i.e., when using a batch-type heating furnace 20. In the batch-type heating furnace 20, the arrangement of the multiple annular members 1 on the basket 10 is maintained from the annular member arrangement step before the annular members 1 are loaded into the heating furnace 20, through the basket arrangement step and the heat treatment step, so the arrangement of the multiple annular members 1 during the annular member arrangement step is very important.

In contrast, in a continuous heating furnace, the arrangement of the multiple annular members 1 may differ between quenching (heating) and quenching (cooling). That is, during quenching (cooling), the multiple annular members 1 are individually placed into an oil tank that stores cooling oil. In this case, the arrangement of the multiple annular members 1 is not maintained. In such a case, even if the multiple annular members 1 are arranged so that they do not come into contact with each other and quenched (heated), the annular members 1 may come into contact with each other during quenching (cooling), causing elliptical deformation of the annular members 1.

After quenching (cooling), the basket 10 is again moved to the base 33 of the loading section 30 and then moved to a tempering furnace (not shown), where the multiple annular members 1 are tempered (heated and cooled). The tempering is performed at 150 to 300°C for 1 to 2 hours.

(Grinding process)
After the heat treatment step, a grinding step is performed to grind the annular member 1. In the grinding step, the inner and outer diameter surfaces of the annular member 1 are ground to produce a bearing ring. According to the manufacturing method of the present application, elliptical deformation of the annular member 1 due to heat treatment is suppressed and the circularity of the annular member 1 is good, so that the amount of grinding required in the grinding step can be reduced, and the number of grinding steps can be reduced.

The bearing races completed by the above method can then be assembled with rolling elements and a cage to form a bearing.

(Example)
Next, the effect of the arrangement of the multiple annular members 1 on the basket 10 on the elliptical deformation (roundness) of the annular members 1 after heat treatment was examined.

In Example 1, as shown in FIG. 1, multiple annular members 1 are housed in a basket 10 so that they do not come into contact with each other. The number of annular members 1 placed in one basket 10 is 42, and these baskets 10 are stacked in 16 layers, which are arranged in two rows as shown in FIG. 3 and subjected to heat treatment. Therefore, 1,344 annular members 1 (42 x 16 x 2) are heat treated at the same time.

In Example 2, as shown in FIG. 5, multiple annular members 1 are housed in a basket 10 so as not to come into contact with each other. In Example 2, compared to Example 1, the number of annular members 1 arranged on the basket 10 is reduced in order to further increase the distance between adjacent annular members 1. Nine annular members 1 are arranged in one basket 10, and 12 of these baskets 10 are stacked in two rows as shown in FIG. 3 and subjected to heat treatment. Therefore, 216 (9 x 12 x 2) annular members 1 are heat treated at the same time.

In the comparative example (L=0), as shown in FIG. 2, multiple annular members 1 are packed tightly on a basket 10. The number of annular members 1 arranged in one basket 10 is 54, and these baskets 10 are stacked in 12 layers, which are arranged in two rows as shown in FIG. 3 and subjected to heat treatment. Therefore, 1296 (54 x 12 x 2) annular members 1 are heat treated at the same time.

The material of the annular member 1 used in Example 1, Example 2, and Comparative Example is steel with a carbon concentration of 0.4 wt%, to which appropriate amounts of alloy elements such as Cr and Mn are added to ensure hardenability with oil cooling. This steel was used as the material and formed into a specified size by machining, and various effects were evaluated. It was confirmed that when annular members made from the above material were hardened under the heat treatment conditions described in this application, they were sufficiently hardened for all annular members 1 and all heat treatment conditions.

The outer diameter of the annular member 1 was approximately φ75 mm. In the heat treatment process, the annular member 1 was subjected to carbonitriding treatment for 3.5 hours in a batch heating furnace, and then secondary heating was performed, followed by quenching in oil at approximately 100°C (secondary quenching), and tempering treatment. The roundness of multiple annular members 1 that had undergone this heat treatment was measured.

The results of measuring the roundness of multiple annular members 1 after carbonitriding are shown in Figures 6(a) to (c). In Figures 6(a) to (c), the horizontal axis is the roundness (μm) and the vertical axis is the number of annular members 1 having a roundness within the corresponding range. Figures 6(a) to (c) show the roundness measurement results for the comparative example, Example 1, and Example 2, respectively. The results of Figures 6(a) to (c) are summarized in Table 1 below.

In the comparative example, among the multiple annular members 1, the maximum circularity was 200 μm, the minimum circularity was 20 μm, and the average circularity was 85 μm. In the first example, among the multiple annular members 1, the maximum circularity was 160 μm, the minimum circularity was 10 μm, and the average circularity was 58 μm. In the second example, the maximum circularity was 120 μm, the minimum circularity was 10 μm, and the average circularity was 43 μm. Thus, it can be seen that the circularity of the first and second examples is better than that of the comparative example. In particular, the circularity of the second example, in which the gap between adjacent annular members 1 is set to be large, is even better than that of the first example.

The results of measuring the roundness of multiple annular members 1 after secondary hardening are shown in Figures 7(a) to (c). In Figures 7(a) to (c), the horizontal axis is the roundness (μm) and the vertical axis is the number of annular members 1 having a roundness within the corresponding range. Figures 7(a) to (c) show the roundness measurement results for the comparative example, Example 1, and Example 2, respectively. The results of Figures 7(a) to (c) are summarized in Table 2 below.

In the comparative example, the maximum circularity of the multiple annular members 1 was 260 μm, the minimum circularity was 20 μm, and the average circularity was 108 μm. In example 1, the maximum circularity was 220 μm, the minimum circularity was 10 μm, and the average circularity was 68 μm. In example 2, the maximum circularity was 140 μm, the minimum circularity was 10 μm, and the average circularity was 52 μm. As with the circularity measurement after carbonitriding, it can be seen that examples 1 and 2 have better circularity than the comparative example in the circularity measurement after secondary quenching as well. In particular, example 2, in which the gap between adjacent annular members 1 is set large, has even better circularity than example 1.

As described above, it has become clear that elliptical deformation can be suppressed when the annular members 1 are placed at a fixed distance from each other and subjected to heat treatment. In Examples 1 and 2, the elliptical deformation of the annular members 1 after heat treatment is suppressed and the circularity is good, so that the amount of grinding can be reduced in the grinding process after heat treatment, resulting in significant cost reduction effects.

1 Annular member 10 Basket 11 Bottom surface 13 Flange portion 20 Heating furnace (batch type heating furnace)
30 Carry-in section 31 Roller 33 Base 40 Heating section 41 Roller 43 Base 45 Burner 47 Fan 50 Cooling section 51 Roller 53 Base 55 Circulation device 56 Screw 57 Guide member 60 Conveying section 61 Roller 63 Base 65 Cylinder 71 First door 73 Second door O Cooling oil (cooling liquid)

Claims (10)

A method for manufacturing a bearing ring, comprising the steps of:
an annular member arrangement step of arranging a plurality of annular members that will become bearing races on a basket such that the central axes of the annular members face in the vertical direction ;
a basket placement step of placing the basket inside a heating furnace;
a heat treatment step of heat treating the plurality of annular members arranged on the basket;
Including,
In the annular member arrangement step, the plurality of annular members are arranged on the basket so as not to come into contact with each other;
In the heat treatment step, the plurality of annular members are quenched by performing heating and cooling while maintaining the arrangement of the plurality of annular members on the basket ;
During the quenching in the heat treatment step, the basket is immersed in a cooling liquid stored in a liquid tank, and the cooling liquid is caused to flow in an up-down direction to contact the plurality of annular members, thereby cooling the plurality of annular members;
The cooling liquid passes through the mesh-like basket in the vertical direction, flows through the central hole of the annular member in the vertical direction, and flows between adjacent annular members in the vertical direction.
Manufacturing method of bearing races. The method for manufacturing a bearing race according to claim 1 , wherein the plurality of annular members are set at predetermined positions in the basket by a positioning member. 3. The method for manufacturing a bearing ring according to claim 1 , wherein the heating furnace is a batch type heating furnace. The method for manufacturing a bearing race according to any one of claims 1 to 3 , wherein in the annular member arranging step, the plurality of annular members are arranged in a staggered pattern. 5. The method for manufacturing a bearing ring according to claim 1, wherein the plurality of annular members are carburized in the heat treatment step. 5. The method for manufacturing a bearing race according to claim 1 , wherein the plurality of annular members are subjected to a nitriding treatment in the heat treatment step. 5. The method for manufacturing a bearing race according to claim 1 , wherein the plurality of annular members are carbonitrided in the heat treatment step. 5. The method for manufacturing a bearing race according to claim 1 , wherein the plurality of annular members are deep-hardened in the heat treatment step. In the heat treatment step, after the quenching is performed on the plurality of annular members, the plurality of annular members are further subjected to tempering.
A method for manufacturing a bearing ring according to any one of claims 1 to 8 . The method further includes a grinding step of grinding the annular member after the heat treatment step.
A method for manufacturing a bearing ring according to any one of claims 1 to 9 .

Images