JPH1137163A - Inner ring for rolling bearing and heat treatment method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a crack even in case of being used in a high temperature device or a high speed rotating device and facilitate manufacture by induction-hardening the raceway surface positioned on the outer peripheral surface side so as to be put in a compressive stress state. SOLUTION: The raceway surface positioned on the outer peripheral surface side of an inner ring is induction-hardened so as to be put in a compressive stress state. Because of being induction-hardened, texture near the raceway surface is transformed into martensite and is going to expand. A core part of the inner ring, on the other hand, is not transformed into martensite so as to suppress the expansion of the raceway surface. As a result, the raceway surface is put in a compressive stress state, and a crack of the inner ring can be prevented. It is desirable that the Rockwell C hardness difference between the raceway surface and the inner ring core part is 8 or more. With this constitution, the raceway surface and inner diameter surface of the inner ring formed of bearing steel, alloy steel or carbon steel have necessary strength, and the core part has low hardness so as to be able to obtain high crack fatigue strength equal to cemented steel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner ring of a rolling bearing and a heat treatment method thereof, and more particularly to an inner ring of a self-aligning roller bearing used under high fitting stress and a heat treatment method thereof.

[0002]

2. Description of the Related Art A self-aligning roller bearing in which a spherical roller is incorporated between an inner ring having two rows of races and an outer ring having a spherical race is a type of rolling bearing which has a radial load and a thrust load in both directions. It can be used for large machines such as paper machines because it has a large radial load capacity and is suitable for applications in which heavy loads and impact loads act.

[0003] Of these self-aligning roller bearings, those in which the inner diameter of the inner ring is a tapered hole are set by being pushed into a tapered shaft, and are used after adjusting the residual gap and interference by the pushing amount. The inner ring of the bearing expands due to the indentation and receives tensile stress. In large high-temperature equipment such as paper machine dryers, high-temperature steam and oil pass through the hollow shaft, so that during operation, the shaft expands due to the temperature difference with the inner ring, resulting in tensile stress, that is, the difference between the inner ring and the shaft. The fitting stress between them tends to further increase.

[0004]

An inner ring used under a large fitting stress receives repeated stress from rolling elements in a state where the inner ring raceway surface is subjected to a tensile stress. If there is a source (non-metallic inclusions, micro exfoliation, rust, etc.), fatigue cracks may propagate in the axial direction starting there, and the inner ring may crack in the axial direction.
This phenomenon is expected not only in high temperature equipment such as paper machine bearings, but also in spherical roller bearings rotating at high speed, the possibility of damage is increased because the raceway surface of the inner ring receives large tensile stress. Is done.

[0005] Even if there is such a source of stress concentration on the inner raceway surface, it is necessary to minimize the possibility of the above-mentioned damage from the viewpoint of improving the reliability of the machine.

As one of the countermeasures, it is conceivable to cool the shaft in a high-temperature device, but it is difficult to say that this is a general method because the structure of the device becomes complicated. Also, the generation of a tensile stress due to an increase in the centrifugal force is not realistic because it cannot be avoided unless the centrifugal force is reduced, that is, the rotational speed is reduced.

On the other hand, carburized steel can be used as a material for the inner ring to prevent cracking of the inner ring. However, the carburizing and quenching treatment requires a longer processing time than the normal soaking quenching treatment, and the bearing manufacturing cost increases. There is a problem.

There is also known a technique for manufacturing a bearing that is resistant to cracking by controlling the cooling rate during oil quenching of high carbon chromium bearing steel. However, it is difficult to control the cooling rate, and furthermore, the quenching of the material is difficult. There is a problem that it is difficult to adjust the input characteristics.

Therefore, the present invention has been made to solve the above-mentioned problems, and a rolling bearing which is hardly cracked even when used in a high-temperature device or a high-speed rotating device and which is easy to manufacture. An object of the present invention is to provide an inner ring and a heat treatment method therefor.

[0010]

Means for Solving the Problems As a result of detailed examination of the cause of the inner ring crack, the inventors have found the following.

The reason why the inner ring crack occurs is that the inner ring is used in a state where a large tensile stress is applied to the raceway surface. If the tensile stress is reduced, more preferably, if the compressive stress is reduced, the inner ring crack is generated. do not do.

In order to apply compressive stress to the raceway surface, it is effective to transform the raceway surface into martensite and not to transform the core of the inner ring into martensite.

The inner ring for a rolling bearing according to the present invention, which has been made on the basis of the above study results, is obtained by induction hardening the raceway surface located on the outer peripheral surface side to bring the raceway surface into a compressive stress state.

In the inner race of the rolling bearing constructed as described above, since the raceway surface is induction hardened, the structure near the raceway surface is transformed into martensite and tends to expand. On the other hand, according to induction hardening, the core portion of the inner ring does not undergo martensitic transformation, and this core portion attempts to suppress the expansion of the raceway surface. As a result, the raceway surface becomes in a compressive stress state,
Cracking of the inner ring can be prevented.

Preferably, the difference between the HRC of the raceway surface (Rockwell hardness of C scale) and the HRC of the inner race core is 8 or more. Here, the “inner ring core portion” refers to a portion of the inside of the inner ring which is located at substantially the same distance from the raceway surface and the inner diameter surface.

Preferably, the difference between the HRC of the raceway surface and the HRC of the inner diameter surface is 5 or more.

Further, the HRC of the inner diameter surface and the HR of the inner race core portion are set.
The difference from C is preferably 8 or more.

Further, the H of the induction hardened raceway surface
Preferably, RC is 58 or more.

It is preferable that the inner diameter surface has an HRC of 48 to 55. The heat treatment method for the inner race of a rolling bearing according to the present invention is to induction harden the raceway surface so that the raceway surface located on the outer peripheral surface side of the inner race of the rolling bearing is in a compressive stress state.

According to this method, a compressive stress is applied to the raceway surface, so that it is possible to provide an inner ring that is less likely to crack.

According to another aspect of the present invention, there is provided a method for heat-treating an inner race of a rolling bearing, wherein the inner race and the raceway located on the outer periphery of the inner race of the rolling bearing are heated at a high frequency to cool the inner race. This is to cool the raceway surface at a faster cooling rate.

According to this method, the raceway surface is rapidly cooled, so that the raceway surface is transformed by martensitic expansion.
At this time, since the inner diameter surface is cooled slowly,
Since the inside of the inner ring is not heated very much, none of them undergoes martensitic transformation. As a result, the inner diameter surface and the core portion do not expand, the core portion suppresses the expansion of the raceway surface, and the raceway surface receives a compressive stress, so that it is possible to provide an inner ring that is less likely to crack.

Further, the heat treatment method for the inner race of a rolling bearing according to still another aspect of the present invention is characterized in that the inner race surface of the inner race of the rolling bearing and the raceway surface located on the outer peripheral surface side are heated at a high frequency, and This is to cool the raceway surface.

According to this method, since the raceway surface is heated at a high frequency and the core of the inner ring is not heated much, martensitic transformation occurs on the raceway surface and does not transform much on the core portion. As a result, the core portion suppresses the raceway surface to be expanded, and a compressive stress is applied to the raceway surface, so that it is possible to provide an inner race that is less likely to crack. Further, since the inner diameter surface is also induction hardened, the hardness of the inner diameter surface is increased, and the wear resistance of the inner diameter surface is improved.

A method for heat treating the inner ring of a rolling bearing according to still another aspect of the present invention is to heat the inner diameter surface of the inner ring of the rolling bearing at a high frequency and then cool the same, and thereafter to reduce the raceway surface located on the outer peripheral surface side to a high frequency. And then cool.

According to this method, first, the inner surface is hardened because the inner surface is quenched. However, when the outer surface is quenched, the inner surface is tempered under the influence of this heating. Optimum hardness. On the other hand, since the outer diameter surface is heated at a high frequency and then cooled, martensitic transformation occurs. Since the core is not heated so much, it does not cause martensitic transformation and acts to suppress the raceway surface which is about to expand. As a result, a compressive stress is applied to the raceway surface, and it is possible to provide an inner ring that is difficult to crack.

[0027]

EXAMPLES Sample preparation conditions 1 ( preparation of sample Nos. 1 to 4) JIS standard number NU2215 / 60 consisting of steel types shown in Table 1
Temperature of the entire inner ring of the cylindrical roller bearing of 860-88
After heating to 0 ° C., the outer peripheral surface on which the raceway surface was formed was quenched using water containing 5% of a water-soluble coolant (cooling rate: 40 ° C.).
/ S). On the other hand, the inner diameter surface was air-cooled. Next, set the inner ring to temperature 1
After tempering at 80 ° C. for 1 hour, sample No. 1 shown in Table 1 was obtained. 1
~ 4.

[0028]

[Table 1]

In Table 1, a negative "residual stress on the raceway surface" indicates a residual compressive stress. The same applies to Tables 2 and 3.

In each of these samples, the hardness was smallest on the inner diameter surface, and increased as approaching the raceway surface.

Condition 2 (Preparation of Sample Nos. 5 to 8) JIS No. NU2215 / 60 consisting of steel types shown in Table 2
Temperature of the inner ring surface and raceway surface of the inner ring of cylindrical roller bearings
Heated to 880 ° C. and cooled both sides simultaneously (cooling rate 4
0 ° C / s). After tempering the inner ring at 180 ° C for 1 hour, Table 2
Were obtained.

[0032]

[Table 2]

The internal hardness of Samples 5 to 8 decreased as the distance from the inner diameter surface to the core decreased, became minimum at the core, and increased as the distance from the core to the track surface increased.

Condition 3 (Preparation of Sample Nos. 9 to 12) JIS No. NU2215 / 60 consisting of steel types shown in Table 3
The inner diameter surface of the inner ring of the cylindrical roller bearing was heated at a high frequency of 860 to 880 ° C., and the inner diameter surface was rapidly cooled (cooling speed 40
° C / s). When this inner ring was tempered at a temperature of 180 ° C. for 1 hour, the hardness of the inner diameter surface was similar to the value shown in Table 2. Next, the raceway surface is heated at a high frequency to a temperature of 860-88.
The temperature was set to 0 ° C. and quenched (cooling rate: 40 ° C./s). This inner ring was tempered at a temperature of 180 ° C. for 1 hour, and sample N shown in Table 3
o. 9-12 were obtained.

[0035]

[Table 3]

The sample No. About 9-12
The hardness of the inner diameter surface is smaller than the value shown in Table 2 because the hardness of the inner diameter surface is reduced by the influence of heat when heating the raceway surface. The hardness of the inner ring was smallest on the inner diameter surface, and increased as approaching the raceway surface.

(Preparation of Sample Nos. 13 to 15) As a comparative example, the inner ring of a cylindrical roller bearing of JIS No. NU2215 / 60 was processed under the following conditions, and the sample No. 13 was prepared. 13 ~
15 was obtained.

After maintaining SUJ2 at a temperature of 850 ° C. for 70 minutes, it was quenched with an oil at a temperature of 120 ° C. Next, this SU
J2 was kept at a temperature of 180 ° C. for 120 minutes and tempered to obtain a sample No. 13 was obtained.

After keeping SUJ3 at a temperature of 825 ° C. for 70 minutes, it was quenched with oil at a temperature of 120 ° C. Next, this SU
J3 was kept at a temperature of 180 ° C. for 120 minutes and tempered. 14 was obtained.

The SCR 420 was placed in a carburizing gas at a temperature of 890.
96 ° C, 72 minutes at 920 ° C, 2 minutes at 950 ° C
Carburizing was carried out for 40 minutes, at a temperature of 910 ° C. for 72 minutes, and at a temperature of 860 ° C. for 72 minutes, followed by quenching with oil at a temperature of 120 ° C. Next, this SCR420 was kept at a temperature of 180 ° C. for 120 minutes and tempered to obtain a sample no. 15 was obtained.

Crack fatigue life test sample no. Regarding 1 to 15, an artificial wound having a length of 5 mm, a width of 0.2 mm, and a depth of 0.25 mm was applied to the raceway surface of the inner ring by electric discharge machining. This inner ring was assembled into a bearing to form a test bearing, and it was examined whether or not the inner ring was cracked by rolling.
Table 4 shows the test conditions.

[0042]

[Table 4]

Since the calculated life of the bearing under the test conditions is 766 hours, 1100 hours which is longer than the calculated life was set as the test cutoff time.

Table 5 shows the test results.

[0045]

[Table 5]

"F / n" in Table 5 indicates that when n tests were performed, f damage occurred. Further, for the sample in which the breakage occurred, the 50% life was calculated by setting the time until the breakage to the Weibull distribution, and the 50% life was shown as “L50” in Table 5. In addition, if no damage occurred for all of the items,
The censoring time is indicated.

As can be seen from Table 5, S as a comparative example
Standard heat-treated products of UJ2 and SUJ3 (Sample No.
In 13 and 14), cracks occurred from artificial wounds in all of the 12 inspection numbers. Carburized products of comparative examples (Sample No. 15), SUJ2, SUJ3 and SCM
Induction hardened sample consisting of No. 440 (sample No. 1)
In Nos. 3, 5, 7 and 9 to 11, no damage occurred in all the test pieces. No. S53C.
Samples Nos. 4, 8, and 12 were peeled off from an artificial wound. From these results, it can be seen that the inner ring crack of the bearing used under the fitting stress can be prevented by increasing the hardness of the raceway surface, lowering the hardness of the core or inner diameter portion, and making the raceway surface surface layer a compressive stress. Recognize. The sample No. The production costs of carburized products (sample N
o. 15) It was lower than the production cost.

In the heat treatment condition 3 of the embodiment, the hardness on the inner diameter side was reduced due to the influence of heating and quenching from the raceway surface, but in order to obtain excellent quality, the inner diameter surface was hardened. It is also possible to perform high-temperature tempering at a post-temperature of 300 to 400 ° C. for 1 hour, to set the hardness of the inner diameter surface to the value shown in Table 3, and then to harden the outer diameter surface to the hardness shown in Table 3. When the crack fatigue strength of the sample manufactured according to this method was measured under the same conditions as in Table 4, the sample No. The same results as in Nos. 9 to 12 were obtained. This method is more reliable for obtaining a predetermined hardness distribution.

Although the embodiment of the present invention has been described above, the embodiment shown here can be variously modified. First, as the steel constituting the rolling bearing, it is also possible to use other high-carbon chromium bearing steel, and it is also possible to use structural alloy steel or structural carbon steel other than the steel shown here. . The heating conditions and tempering conditions can be changed according to the type of steel. The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0050]

According to the present invention, by using induction hardening for heat treatment of the inner ring of a rolling bearing, the bearing steel (SUJ
(2, SUJ3), alloy steel (SCM440, etc.) or carbon steel (S53C, etc.) to make the raceway surface and inner diameter surface of the bearing inner ring necessary strength, make the core part low hardness and apply compressive stress to the raceway surface. Thereby, a bearing having high crack fatigue strength comparable to carburized steel can be realized. Further, even if the raceway surface is hardened and the inner diameter surface has a lower hardness, a bearing having high crack fatigue strength comparable to carburized steel can be realized.

Claims (10)

[Claims] 1. An inner race of a rolling bearing, wherein a raceway surface located on an outer peripheral surface side is induction hardened so that the raceway surface is in a compressive stress state. 2. The inner race of the rolling bearing according to claim 1, wherein a difference between HRC (Rockwell hardness of C scale) of the raceway surface and HRC of the inner race core is 8 or more. 3. The inner race of a rolling bearing according to claim 1, wherein a difference between the HRC of the raceway surface and the HRC of the inner diameter surface is 5 or more. 4. The inner race of a rolling bearing according to claim 1, wherein the difference between the HRC of the inner diameter surface and the HRC of the inner race core is 8 or more. 5. The inner race of a rolling bearing according to claim 1, wherein the HRC of the raceway surface that has been induction hardened is 58 or more. 6. The inner race of a rolling bearing according to claim 1, wherein the HRC of the inner diameter surface is 48 to 55. 7. A heat treatment method for an inner ring of a rolling bearing, wherein the raceway surface is induction hardened so that the raceway surface located on the outer peripheral surface side is in a compressive stress state. 8. A rolling bearing according to claim 1, wherein the raceway surface located on the inner diameter surface and the outer peripheral surface side of the inner race of the rolling bearing is heated at a high frequency, and the raceway surface is cooled at a cooling rate higher than the cooling speed of the inner diameter surface. Inner ring heat treatment method. 9. A heat treatment method for an inner ring of a rolling bearing, comprising heating an inner diameter surface of an inner ring of a rolling bearing and a raceway surface located on an outer peripheral surface side with high frequency, and cooling the inner diameter surface and the raceway surface. 10. A method for heat-treating an inner ring of a rolling bearing, wherein the inner surface of the inner ring of the rolling bearing is heated at a high frequency and then cooled, and then the raceway surface located on the outer peripheral surface is heated and cooled at a high frequency.