JP2000009597A - Method of evaluating cleanness of bearing steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the cleanness of a bearing steel, the factor of determining the bearing life, for a short time by the lift test of the rolling fatigue in a lubricant having a water content concn. in a specified range. SOLUTION: As a test piece the inner or outer lace of a flange-less type roll bearing or roll is made from a steel under test, the lift test of the rolling fatigue in a lubricant having a water concn. in a range of 1% to 80% is conducted to obtain a life value to be a cleanness index of the steel under test. About e.g. a life tester for thrust bearings, to avoid reducing the water content concn., a rubber seal 4 is used between a test bearing holder 2 supporting a test bearing 1 and inner race main shaft 3. In the lift test using a lubricant 5 immersing the test bearing 1, (steel) balls 11, outer race 12 and inner race 13, the test time is greatly reduced, compared with in the prior art, and a high correlation with the actual bearing rolling fatigue strength can be ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the cleanliness of bearing steel, which is performed for evaluating the life of rolling bearings.
In particular, the present invention relates to a method for evaluating the cleanliness of bearing steel, which regulates the conditions of a rolling fatigue test in a lubricant and can thereby ensure a high correlation with the rolling fatigue strength of the bearing.

[0002]

2. Description of the Related Art The rolling life of a bearing is determined by the "rolling" of steel constituting the bearing if the dimensions of the bearing, the applied load and the lubrication conditions are the same. Fatigue strength. " The failure form of rolling fatigue is "peeling", and even if the rolling bearing is used normally, it eventually "peels" and reaches the life of the bearing. The starting point of the delamination is non-metallic inclusions generally present as impurities in the steel. Therefore, the size and amount of the nonmetallic inclusions, in other words, the cleanliness of the steel, are important factors for determining the rolling fatigue strength. From such a viewpoint, various steel cleanliness measuring methods have been conventionally proposed and implemented.

[0003] In the following, the outline of these conventional steel cleanliness measurement methods will be described, and their problems will be described. 1) Optical microscopic measurement method The cut surface of the steel to be inspected is mirror-polished, the surface is observed with a metallographic microscope, and the cleanliness of the steel to be inspected is measured by quantifying the size and number of nonmetallic inclusions. How to However, since the size and number of nonmetallic inclusions scattered in the three-dimensional space are evaluated from a narrow two-dimensional inspection area, there is a problem that the accuracy or representativeness of the obtained result is extremely low. 2) Chemical component analysis method The concentrations of oxygen, a constituent element of oxide-based inclusions, sulfur, a constituent element of sulfide-based inclusions, and titanium, a constituent element of titanium-based inclusions, are measured by chemical analysis. , And their concentration values are used as the cleanliness of the steel to be inspected. However, since those concentration values do not include information on the size of the nonmetallic inclusions, there is a problem that the correlation with the rolling fatigue strength is weak. 3) Acid dissolving method This is a method of dissolving a steel to be inspected with an acid and measuring the particle diameter and the number of particles of nonmetallic inclusions remaining as residues. However, the non-metallic inclusions remaining as the residue were formed by crushing during the dissolution of the acid in the steel, so even if the size and number of the non-metallic inclusions in the residue were investigated, There is a problem that the cleanliness of the steel to be measured cannot be obtained. 4) Electron Beam Melting Method This is a method of electron beam melting a sample prepared from a steel material to be inspected in a vacuum and measuring the size and number of floating nonmetallic inclusions. However, Electron
Because non-metallic inclusions fuse during beam melting,
There is a problem that the size and the number of the raised nonmetallic inclusions do not become the cleanliness of the steel to be inspected. 5) Rolling fatigue test method A rolling bearing or a test piece having the function of a rolling bearing is manufactured from a steel material to be inspected, and a life value obtained by performing a rolling fatigue test on the test piece in a lubricant. Is a cleanliness index. However, in this case, since a long-time fatigue test must be performed, there is a problem that a large amount of time is required for evaluation. Therefore, there is a method of further increasing the test load in order to shorten the test time, but the life value obtained in this case is such that when the maximum contact surface pressure between the bearing ring and the rolling element exceeds 4000 MPa, plastic deformation occurs in the contact portion. Therefore, there is a limit that the life value of an actual rolling bearing that does not cause plastic deformation in the contact portion is not reflected. Another method to shorten the test time is to mix water in the lubricant.In this case, wear and corrosion pits occur on the rolling surface of the bearing ring, so the resulting life value is low. There is a problem that it cannot be determined only by the cleanliness of steel.

As described above, in the conventional steel cleanliness measuring methods, it is difficult to purely determine the relationship between the bearing life and cleanliness due to various factors intervening. Cannot do it. The present invention has been made in view of such a problem of the conventional steel cleanliness measuring method, and it is possible to accurately measure the cleanliness of the bearing steel, which is a determinant of the bearing life, in a short time. It is an object to provide a possible cleanliness evaluation method.

[0005]

In order to achieve the above object, a method for measuring the cleanliness of a bearing steel according to the present invention according to the first aspect of the present invention provides a method of measuring the cleanliness of a rolling bearing having a flange less than the steel to be measured. An inner ring or a rolling element is prepared as a test piece, a rolling fatigue life test is performed in a lubricating oil having a water concentration of 1% or more and 80% or less, and the obtained life value is used as a cleanliness index of the steel material to be measured.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. If moisture is mixed into the lubricant,
The life of the rolling bearing is greatly reduced. The failure mode is either "wear" or "peeling" depending on lubrication conditions.
Since the wear resistance of steel does not depend on the cleanliness of the steel, "wear"
Is independent of the cleanliness of the steel. In contrast,
In the case of "peeling", the origin of the damage is a corrosion pit or a non-metallic inclusion, which is closely related to the cleanliness of the steel. Therefore, in order to determine the relationship between bearing life and steel cleanliness purely and perform appropriate cleanliness evaluation, test conditions should be such that the form of breakage should be exfoliated and the starting point should be a nonmetallic inclusion. is necessary.

[0007] The inventors of the present application have conducted research on the cleanliness evaluation test of the material steel which is directly involved in the peeling life of the rolling bearing. As a result, "wear" was eliminated, the lubricant used in the test was regulated, and water was mixed. The present inventors have found that a close correlation with the service life can be ensured by conducting a test, and have accomplished the present invention. The regulation of the test conditions in the method for evaluating the cleanliness of bearing steel according to the present invention will be described below.

[Lubricant and Moisture] In order to make the form of failure not peeling but abrasion, it is necessary to use oil as the lubricant. This is because it is difficult for a lubricant other than oil to uniformly mix with water, and local wear and corrosion pits are formed on the rolling surface. That is, the obtained life value cannot be determined only by the cleanliness of the steel. In order to uniformly mix the lubricating oil and water in order to prevent local abrasion and corrosion of the rolling surface, it is desirable that the lubricating oil used has a low viscosity of VG100 or less. VG is Visc
OsityGrade is referred to, and the numerical value represents the kinematic viscosity at 40 ° C. (cSt).

[0009] In order for the test piece to be "peeled" starting from non-metallic inclusions, the water concentration in the lubricating oil must be 1% or more and 80% or less (volume%, the same applies hereinafter). is necessary. If the water concentration exceeds 80%, peeling originating from the corrosion pits will be included, and if it exceeds 90%, the rolling surface will be significantly worn, and the corrosion pits will be scraped off and may not peel off. Become. That is, when the water concentration exceeds 80%, the life value of the test piece is not a function of only the cleanliness. Moisture concentration is 1
If it is less than%, the obtained life value is not only a function of the cleanliness of the steel but also a function of the moisture concentration, which is inappropriate as a condition.
When the water concentration is 1% or more, the service life is no longer shortened even if the water concentration further increases. Therefore, it is necessary to make the water concentration 1% or more and 80% or less.

[Form of bearing] In a rolling bearing having a flange such as a tapered roller bearing or a cylindrical roller bearing, the frictional force of a sliding portion of the raceway against the head at the flange is particularly large under lubrication mixed with water. , Resulting in a reduced life value. In other words, the life value of a flanged rolling bearing is a function of not only the cleanliness of the steel constituting the bearing but also the frictional force of the sliding portion. The frictional force of the sliding part is proportional to the amount of carbide in the steel on the sliding surface and is also affected by the corrosion resistance of the base material. Are different. Therefore, it is necessary to use a flangeless type rolling bearing in order to make the resulting life value a function only of the cleanliness of the steel.

[Test Temperature] The test temperature must be 0 ° C. or higher, and preferably 100 ° C. or lower. The role of water in the lubricating oil under rolling contact is to allow water to enter gaps between the non-metallic inclusions present on the rolling surface and the surrounding matrix, thereby promoting stress corrosion cracking. Therefore, water must be liquid or vapor, and will not play its role below 0 ° C., where it becomes solid. On the other hand, if the test temperature exceeds 100 ° C., water evaporates and dissipates, making it difficult to maintain the water concentration in the lubricating oil.

[Effects of Materials of Test Bearing Components, Especially Carbides] When steel contacts at high surface pressure in the presence of water, contact corrosion occurs. That is, when steel comes into contact with water at a high surface pressure in the presence of water, the corrosion rate is significantly increased as compared with the case where the steel exists alone. As a result of the contact corrosion, the base portion of the rolling surface is melted, and carbides are present as protrusions in the rolling surface. In such a case, the true contact surface pressure between the rolling element and the bearing ring becomes larger than before the corrosion, and the life of the test piece is reduced. This contact corrosion phenomenon is particularly remarkable in the evaluation of high cleanliness steel in which the test time is long, and the obtained life value is not a function of only the cleanliness of the steel of the test piece, but the test piece and the mating member. Also becomes a function of the size and amount of the carbide, which is not preferable.
To prevent this contact corrosion, it is necessary to eliminate the effect of carbides in the steel, and when the outer or inner ring is a test piece,
It is desirable that the rolling elements be made of a ceramic material. When the rolling element is a test piece, it is desirable that the outer ring and the inner ring be made of a ceramic material. (Examples) Hereinafter, the present invention will be described more specifically with reference to examples. (A) Manufacture of Samples The steel types, smelting methods, cleanliness, and carbon concentrations shown in Table 1 were used for steel Nos. 1, 2, 3, and 4. Produced.

[0013]

[Table 1]

Oxygen concentration, sulfur concentration and titanium (Ti)
Judging from the concentration, the cleanliness of the steels of steel Nos. 1, 2 and 3 are the same, and the cleanliness of the steel of steel No. 4 having the sulfur concentration five times as high is the worst. Thrust ball bearing for life test 51305
Are 25 mm in inner diameter, 52 mm in outer diameter, and 20 mm in width. The retainer is made of 66 nylon to prevent corrosion wear with the rolling elements. The diameter of the rolling element is 9.
At 525 mm, the number of rolling elements is 4. Basic dynamic load rating C
Is 18 kN. Tapered roller bearing HR32017XJ
Dimensions are 85mm inner diameter, 130mm outer diameter, 29 assembly width
mm.

The basic dynamic load rating C is 143 kN. Turn
The moving body is made of SUJ2 of steel number 3 unless otherwise specified.
Was. SUJ2, which is a steel with a steel number of 1,3,4, is 840 ° C
Quenched with oil, tempered at 180 ° C for 2 hours, hardness HRC
62 was obtained. Case No.2 case hardened steel was dipped at 930 ° C for 6 hours.
Allow to cool after charcoal, oil quenching from 820 ° C, 2 hours at 180 ° C
Tempering and hardness HRC60 were obtained. Orbital surface carbon concentration
Is 0.8%. (B) Life test without water mixing 1) Test method Structure of main part of life test machine of thrust ball bearing 51305
Is shown in FIG. Testing to prevent loss of moisture concentration
Between the test bearing holder 2 that supports the bearing 1 and the inner ring main shaft 3
Used a rubber seal 4. 5 dipped test bearing 1
Lubricating oil, 11 is a ball (steel ball), 12 is an outer ring, 13 is an inner ring
It is. In the life test, one of the bearing rings peeled off
The time required to complete was defined as the life value. When the rolling element comes off
Was suspended. In the test, the number of peeling race rings was 10
Until 10% damage life L _Ten(P) was determined. Ma
In order to evaluate the cleanliness of bearing steel,
Thrust ball bearings are tested for life in pure oil without water injection.
Was. The test conditions were as follows: load P = 6.4 kN, rolling elements and races
Maximum contact surface pressure P_max= 2800Mpa, inner ring rotation speed =
1250 rpm, lubricating oil = VG10 (Nisseki Spinotox
S10) The water concentration in the lubricating oil is 0.01%. test
The temperature is about 60 ° C. Rated fatigue life (10% damage life
Is 297 hours.

2) Test Results The 10% failure life L ₁₀ (P) of the bearings made of steel Nos. 1, 2, 3 and 4 was 870 hours, 2430 hours, 8230 hours and 4820 hours, respectively. Therefore, the correct cleanliness indices of steel Nos. 1, 2, 3, and 4 are 870 hours, 2430 hours, 8230 hours, and 4820 hours, respectively.
It is a lifetime value of time. That is, the order of cleanliness is steel numbers 3, 4, 2, and 1 in descending order. From this result, it can be seen how inaccurate the cleanliness determined from the oxygen concentration, sulfur concentration and titanium concentration is. However, it took too much time to obtain these life values in a life test without water mixing. (C) Life test in water mixed oil 1) Test method and results Next, using a thrust ball bearing made of each of the above steels,
Life tests were performed in oil injected with water. The water concentration in the oil is 1
5%. Other test conditions are the same as the life test without the water mixing. As a result of the life test, steel numbers 1, 2,
10% failure life L ₁₀ (W) of bearings made of 3, 4 steel
Was 12 hours, 33 hours, 100 hours, and 66 hours, respectively.

2) Comparison of test results with and without water mixing FIG. 2 shows the above-mentioned bearing 10% failure life L ₁₀ (P) when water is not injected and the bearing life L when water is injected.
₁₀ (W) is shown. L ₁₀ (P) and L ₁₀ (W) have a direct proportional relationship, and the life value obtained in the lubricating oil mixed with water gives the cleanliness of the steel. Moreover, the life value (hour) obtained in the lubricating oil mixed with water is about one-half of the life without water injection.
It is 1/1000, which means that it is possible to evaluate the cleanliness of steel in a short time. (D) Relationship between Carbides in Steel and Bearing Life A tapered roller bearing made of steel Nos. 2 and 3 was subjected to a life test using a life tester shown in FIG. The test condition is radial load F
r = 35.8 kN, axial load Fa = 15.6 k
N, the inner ring rotation speed was 2500 rpm, and the lubricating oil was maintained at a water concentration of 15% with VG10 (Nisseki Spinox S10). In order to prevent the water concentration from decreasing, a rubber seal 4 is mounted between the main shaft 3 and the test bearing holder 2 as a housing. The test temperature is about 60 ° C. The rated fatigue life (calculated value of 10% failure life) is 674 hours.

The life values L10 (WT) of the tapered roller bearings made of steel Nos. 2 and 3 are 1608 hours and 720 hours. FIG. 4 shows the relationship between L ₁₀ (WT) and L ₁₀ (W). The magnitude relation of L ₁₀ (WT) is reversed in L ₁₀ (W). This is because the surface carbon concentration of SAE4320 steel is 0.8%, which is lower than that of SUJ2 steel, so that there is little carbide on the large flange surface which is the sliding shaft surface, and Ni is 1.7.
%, The corrosion resistance of the base material is high, and the carbides are unlikely to become projections, so that the sliding frictional force of the large flange and the head is low. As described above, the life value of the bearing having the flange is not only a function of the cleanliness of the steel but is also affected by the chemical composition of the steel. Therefore, the bearing having the flange cannot be used for the cleanliness measurement. (E) Relationship between Moisture Concentration in Lubricating Oil and Bearing Life Next, the relationship between the moisture concentration in lubricating oil and bearing life was confirmed using a thrust ball bearing 51305 made of steel No. 1. . FIG. 5 shows the relationship.

When the water concentration is less than 1%, the life value greatly depends on the water concentration, but when the water concentration is 1% or more, the life value becomes stable. However, when the water concentration exceeds 80%, the nasal life starts to decrease again, and the shortest life is reached at 90%. The reason why the life is shortened when the water concentration is more than 80% and 90% or less is that corrosion pits are formed on the rolling surface and serve as a starting point of peeling. When the water concentration exceeds 90%, the entire rolling surface is corroded and worn, and the peeling at the starting point of the corrosion pit is reduced, and only the abrasion proceeds, and the number of cases where the peeling is not performed increases.
In this moisture concentration range, the cleanliness of the steel is not related to the service life. As described above, the water concentration in the lubricating oil is 1% or more and 8% or more.
It is necessary to keep it below 0%. The characteristic is that any water concentration within the range does not affect the life value.

In the above-described embodiment using the life tester shown in FIGS. 1 and 3, a rubber seal is mounted between the rotating shaft and the housing or the holder in order to keep the water concentration in the lubricating oil constant. Since the allowable range of the water concentration is wide, a method may be adopted in which the amount of evaporation loss of the water is appropriately injected so that the water concentration falls within the above-mentioned concentration range. For example, FIG.
FIG. 6 shows a testing machine in which the rubber seal of the testing machine is removed and water is supplied from the outside. (F) Relationship between Viscosity of Lubricating Oil and Life of Bearing Using a tester shown in FIG. 6, a life test was performed on the thrust ball bearing of Steel No. 4 in oils of various viscosities. The water concentration is
Controlled between 1% and 80%. FIG. 7 shows the relationship between the life value L ₁₀ (W) obtained in this test and the lubricating oil viscosity.

For lubricating oil of VG 100 or less, the same level
Lifetime value, but exceeds VG100
And the life value decreases. This is due to poor mixing of oil and water
The lower limit of the lubricating oil concentration increases,
When corrosion pits are formed on the (outer ring), causing peeling
Because there is. From this, the viscosity of VG100 or less
It may be desirable to use a grade grade oil. (G) Relationship between bearing life when grease is used as lubricant
In connection with the tester shown in FIG.
Life test of each steel thrust ball bearing in grease
Tested. Grease used increased lithium (Li) soap
A grease that uses a base oil of viscosity VG64
is there. The concentration of the injected water is 15%. Other tests
The conditions are the same as in the previous test. Steel numbers 1, 2, 3, 4
10% failure life L of bearing made of steel_Ten(WG)
325 hours, 268 hours, 331 hours, 319 respectively
It was time. Failure modes originate from wear and corrosion pits
It was peeling. FIG._Ten(WG) and the L
_Ten(P). From this result, L_Ten(WG)
Is L_TenIt can be seen that there is no correlation with (P). Sand
The life value obtained under water-containing grease lubrication is
Not relevant to the cleanliness of the piece steel. Therefore, the form of damage
Non-metallic, not wear or corrosion pit origin delamination
In order to remove the inclusion starting point, use lubricant as oil.
Is necessary. (H) Relationship between bearing component materials and bearing life In the description of FIG. 2, thrust in lubricating oil without water contamination
10% failure life L of ball bearing_Ten(P) and in water-mixed lubricating oil
Thrust ball bearing life L_Ten(W) is in direct proportion
Strictly speaking, the longest life shaft of steel number 3
Life ratio [L _Ten(W) / L_Ten(P)] x 100 is other
Slightly lower than that of bearings. This is illustrated in FIG.
You. This is due to the contact between the rolling element (steel) and the raceway (steel).
Causes corrosion and long test times cause carbides on the rolling surface
Is projected into a protruding shape, so that the true contact surface between the rolling element and raceway
Pressure increases compared to before corrosion, shortening bearing life
That's why.

Therefore, the outer ring and the inner ring are made of steel numbers 1, 2, 3,
4 made of steel and the rolling element is made of ceramic material (Si
_The life test was performed on the thrust ball bearing made of 3N ₄ ) in a water-mixed lubricating oil using the tester shown in FIG. The water concentration in the oil is 15%. Other test conditions are the same as when the above-mentioned steel balls were used. However, since the Young's modulus of silicon nitride is higher than that of steel, the maximum contact surface pressure _Pmax between the rolling element and the bearing ring is 3100 MPa. Steel numbers 1, 2, 3, 4
The 10% failure life L ₁₀ (WC) of a bearing made of
4.3 hours, 12.2 hours, 41.2 hours, 2 respectively
It was 4.1 hours.

The life ratio of each bearing [L ₁₀ (WC) / L
₁₀ (P)] × 100 is compared with FIG. The life ratio [L ₁₀ (WC) / L ₁₀ (P)] × 100 of each bearing was a constant value, and no carbide protrusion was found on the raceway surface.
By eliminating the contact corrosion between the bearing ring and the rolling element in this way, it is possible to measure the cleanliness of the steel extremely accurately and in a short time.

[0024]

As described above, according to the first aspect of the present invention, when the cleanliness of the bearing steel is evaluated by using the raceway of the rolling bearing or the rolling element as a test piece, the raceway is rolled. To eliminate the contact corrosion with the moving body, and to perform the life test of rolling fatigue in lubricating oil in which the water concentration is regulated and the water concentration is regulated and evenly dispersed, the test time is greatly shortened compared to before, It is possible to secure a high correlation with the actual rolling fatigue strength of the bearing, and to obtain an effect that excellent efficiency and accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a main part of a life tester of a thrust ball bearing 51305.

FIG. 2 shows thrust ball bearings in lubricating oil without water contamination.
5 is a graph showing the relationship between% failure life L ₁₀ (P) and 10% failure life L ₁₀ (W) of thrust ball bearings in lubricating oil mixed with water.

FIG. 3 is a cross-sectional view showing the structure of a main part of a life tester for a tapered roller bearing using water-mixed lubricating oil.

4 shows a relationship between steel Nos. 2 and 3 10% damage life in water contaminated lubricating oil of the thrust ball bearings produced in L ₁₀ (W) 10% of the tapered roller bearing damage life L ₁₀ (WT) Graph.

FIG. 5 is a graph showing a relationship between a water concentration in oil and a 10% failure life L ₁₀ (W) of a thrust ball bearing.

FIG. 6 is a cross-sectional view showing a structure of a main part of a life tester provided with a water supply device with a rubber seal of FIG. 1 removed.

FIG. 7 is a graph showing a relationship between a 10% failure life L ₁₀ (W) of a thrust ball bearing in lubricating oil mixed with water and a viscosity of the lubricating oil at 40 ° C.

[8] and 10% of the thrust ball bearing of water mixed in the grease damaged life L ₁₀ (WG), the relationship between the 10% 10% breakage life of the thrust ball bearing in the free lubricant of water contaminated L ₁₀ (P) A graph showing.

FIG. 9: Water between each thrust ball bearing using steel balls
10% failure life L in mixed lubricating oil_Ten(W) and no water contamination
10% failure life of thrust ball bearings in lubricating oil 10% L
_TenThe graph which shows the relationship with (P).

FIG. 10: 10% failure life L ₁₀ (WC) in lubricating oil mixed with water between thrust ball bearings using ceramic balls
And 10% failure life in lubricating oil without water contamination 10% L ₁₀
Graph comparing the ratio _{[L 10 (WC) / L} 10 (P)] of the (P).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ryo Gono No. 12, Kirihara-cho, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 2G024 AC01 AC06 BA12 BA19 DA09 DA26 FA03 3J101 AA01 AA32 EA03 EA41 EA52 FA31 FA60

Claims (1)

[Claims] 1. A life test of rolling fatigue in a lubricating oil having a water concentration of 1% or more and 80% or less, wherein an outer ring or an inner ring or a rolling element of a rolling bearing having a flange less than a steel material to be measured is prepared as a test piece. And the obtained life value is used as the cleanliness index of the steel to be measured.