JP2014108997A - Grease composition and rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grease composition which allows for excellent oil film formation at extra-low speed and at high temperature; and a rolling bearing which exhibits excellent durability at extra-low speed and at high temperature.SOLUTION: A grease composition includes: a thickener including a mixture of an aromatic diurea compound represented by a general formula (1) and an aliphatic diurea compound represented by a general formula (2), and a base oil, i.e. a mixed oil of alkyl diphenyl ether oil and poly α-olefin oil with a mass ratio (alkyl diphenyl ether: poly α-olefin oil)=60:40 to 100:0. General formula (1): R1-NHCONH-R2-NHCONH-R1. General formula (2): R3-NHCONH-R4-NHCONH-R3. (In the formulae, R1 represents an aromatic hydrocarbon group having a carbon number of 6 to 12, R2 and R4 represents an aromatic hydrocarbon group having a carbon number of 6 to 15, and R3 represents an aliphatic hydrocarbon group having a carbon number 6 to 20.)

Description

  The present invention relates to a rolling bearing and a grease composition used for lubrication thereof.

  Among rolling bearings, rolling bearings used to support rolls in the steel equipment continuous casting process are extremely low speed, high load, high temperature, and use environment where cooling water and scale are externally applied. Used in extremely harsh conditions that are difficult. Rolling bearings used in such harsh conditions ensure that the oil film thickness is secured with a high-viscosity base oil and fluidity is increased by continuously supplying grease into the bearing by using a high consistency. New grease has always been supplied to the contact surface to suppress the occurrence of poor lubrication (see, for example, Patent Documents 1 and 2).

  However, even when the continuous greasing method is used, lubrication failure may occur particularly when water is mixed from the outside. When lubrication failure occurs, excessive wear occurs due to rotation under extremely low speed and high load conditions, and in some cases, the ring is damaged. In addition, rust was generated in the bearing stored outside the line during the roll maintenance period due to the influence of water, and when the operation was resumed after the maintenance was completed, the rust could be the starting point and the ring could be damaged.

JP 2008-298118 A JP 2002-61656 A

  As described above, conventionally, a method using a base oil having a high kinematic viscosity has been used as a means for improving oil film formation under extremely low speed and high temperature conditions, but excessive kinematic viscosity increase is exothermic due to increased stirring resistance, In some cases, the oil film thickness is lowered and a sufficient oil film forming effect cannot be obtained.

  Accordingly, an object of the present invention is to provide a grease composition capable of forming a good oil film even under extremely low speed / high temperature conditions, and a rolling bearing exhibiting excellent durability even under extremely low speed / high temperature conditions.

  It is known that the oil film thickness is proportional to the rolling speed of about 0.67. The lower the speed, the thinner the oil film thickness, and the more severe the lubrication conditions are such that the surfaces are in direct contact with each other. And as a result of earnestly examining the oil film forming method under extremely low speed, high temperature, and water mixing conditions, it is possible to increase the oil film thickness by using an aromatic diurea compound as a thickener, and by using an aliphatic diurea compound. It became clear that the inflow of grease to the contact surface was improved, and it was found that a thick oil film could be stably formed on the contact surface by mixing aromatic diurea and aliphatic diurea compound.

  In addition, when comparing aromatic diurea compounds with aliphatic diurea compounds, aromatic diurea compounds have a relatively thick and short fiber shape and require a large amount of thickener to obtain a certain consistency. On the other hand, the aliphatic diurea compound has a thin and long fiber shape, and the amount of the thickener for obtaining a certain consistency is small. And it is thought that an oil film becomes thick when a thick aromatic diurea compound enters into a contact surface, and forms an oil film sufficiently thicker than a base oil especially in a very low speed region. In addition, it is considered that the aliphatic diurea compound undergoes shearing in the vicinity of the contact surface to align the direction of the fibers, so that the stirring resistance is reduced and the grease fluidity is improved. Therefore, by adjusting the mixing ratio of the aromatic diurea compound and the aliphatic diurea compound, it is possible to improve the oil film thickness and the grease fluidity particularly under extremely low speed conditions.

  Furthermore, it has been clarified that the initial performance can be maintained for a long time without lubrication even in a high temperature environment where the bearing for continuous casting equipment is exposed by using an alkyldiphenyl ether oil as a main component in the base oil.

The present invention is based on such knowledge. That is, in order to solve the above problems, the present invention provides the following.
(1) A mixture of an aromatic diurea compound represented by the general formula (1) and an aliphatic diurea compound represented by the general formula (2) is used as a thickener, and the base oil is an alkyl diphenyl ether oil and a polyalphaolefin. A grease composition, wherein the oil is a mixed oil of alkyldiphenyl ether: polyalphaolefin oil = 60: 40 to 100: 0 in mass ratio.
General formula (1): R1-NHCONH-R2-NHCONH-R1
Formula (2): R3-NHCONH-R4-NHCONH-R3
(In the formula, R1 is an aromatic hydrocarbon group having 6 to 12 carbon atoms, R2 and R4 are aromatic hydrocarbon groups having 6 to 15 carbon atoms, and R3 is an aliphatic hydrocarbon group having 6 to 20 carbon atoms. .)
(2) The above (1), wherein the mixing ratio of the aromatic diurea compound and the aliphatic diurea compound is, by mass ratio, aromatic diurea compound: aliphatic diurea compound = 40: 60 to 95: 5 The grease composition as described.
(3) A rolling bearing characterized in that the grease composition according to (1) or (2) is enclosed.
(4) The rolling bearing according to (3) above, which is for a continuous casting machine.

  In the grease composition of the present invention, the base oil mainly composed of alkyldiphenyl ether oil can maintain the initial performance for a long period of time even in a high temperature environment, and also has an effect of improving the grease fluidity and the aromatic diurea compound excellent in the oil film thickness improving effect. By mixing with an excellent aliphatic diurea compound, an oil film can be stably formed even at extremely low speeds, high temperatures, and water mixing conditions where oil film formation is difficult, smooth lubrication without causing surface damage is possible, and water mixing conditions Excellent wear resistance even underneath. Therefore, the rolling bearing of the present invention also has excellent durability even under extremely low speed, high temperature, and water mixing conditions.

  Hereinafter, the present invention will be described in detail.

As the thickener of the grease composition of the present invention, a mixture of an aromatic diurea compound represented by the general formula (1) and an aliphatic diurea compound represented by the general formula (2) is used.
General formula (1): R1-NHCONH-R2-NHCONH-R1
Formula (2): R3-NHCONH-R4-NHCONH-R3
(In the formula, R1 is an aromatic hydrocarbon group having 6 to 12 carbon atoms, R2 and R4 are aromatic hydrocarbon groups having 6 to 15 carbon atoms, and R3 is an aliphatic hydrocarbon group having 6 to 20 carbon atoms. .)

  The mixing ratio of the aromatic diurea compound of the general formula (1) and the aliphatic diurea compound of the general formula (2) is, by mass ratio, aromatic diurea compound: aliphatic diurea compound = 40: 60 to 95: 5. Preferably, it is 68:32 to 95: 5. When the mixing ratio of the aliphatic diurea compound is less than 5%, the grease inflow property is lowered, and surface damage may easily occur due to occurrence of exhaustion lubrication. If the mixing ratio of the aromatic diurea compound is less than 40%, a sufficient oil film thickness increasing effect cannot be obtained, and surface damage may easily occur.

  The thickener is preferably prepared by separately preparing the aromatic diurea compound of the general formula (1) and the aliphatic diurea compound of the general formula (2), and mixing them so as to have the above mixing ratio.

  In addition, the diurea compound represented by General formula (1) and General formula (2) is obtained by making the diisocyanate which becomes R2 or R4 source, and the monoamine which becomes R1 or R3 source react in base oil. Diisocyanates that become R2 and R4 after the reaction include aromatic isocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane 4, 4'-diisocyanate, naphthylene-1,5-diisocyanate, and the like. It is a mixture of Examples of monoamines for R1 include aromatic amines such as aniline, benzylamine, toluidine, and chloroaniline. R3 monoamines include octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, nonyldecylamine, eicosylamine Linear amines such as

(Base oil)
As the base oil, an alkyl diphenyl ether oil is used as a main component. A poly α-olefin oil is used as an auxiliary component, and a mixing ratio of the alkyl diphenyl ether oil and the poly α-olefin oil is, by mass ratio, alkyl diphenyl ether oil: poly α-olefin oil = 60: 40 to 100: 0, preferably 85. 15 to 100: 0, more preferably 100: 0. ^{Further, 80mm 2 / s~150mm 2 / s} , in the base oil kinematic viscosity 40 ° C. and preferably from 80mm ² / s~100mm ² / s.

Moreover, when the ratio of the alkyl diphenyl ether oil is less than 60% by mass, the oil film thickness may become thin. Furthermore, when the base oil kinematic viscosity is less than 80 mm ² / s (40 ° C.), the oil film thickness may become thin.

(Additive)
Various additives may be added to the grease composition of the present invention as necessary. For example, in steel continuous casting equipment, water is likely to enter from the outside, so rust may be generated in the bearings stored outside the line, especially during the roll maintenance period. In order to prevent the occurrence of such rust, it is preferable to add an antirust additive. As anti-rust additive,
・ Carboxylic acid and its derivatives; alkenyl succinic anhydride, alkenyl succinic acid ester, alkenyl succinic acid half ester, alkenyl succinimide, etc. ・ Carboxylic acid salt; fatty acid, dibasic acid, naphthenic acid, lanolin fatty acid, alkenyl succinic acid, etc. Amine salt / sulfonate salt; Ba salt, Zn salt, Na salt, etc. of sulfonic acid, passivating agent; Na nitrite, Na molybdate etc., ester; Sorbitan trioleate, sorbitan monooleate, etc .; Metal corrosion inhibitor; Benzotriazole or a derivative thereof, zinc oxide, or the like can be used. Particularly preferred are esters, carboxylic acids and their derivatives, and sulfonic acid metal salts.

Moreover, in order to maintain the grease performance for a long period of time, an antioxidant can be preferably used. Antioxidants include amines, phenols and quinolines, and typical ones are as follows. Antioxidants may be used alone or in admixture of two or more depending on their effects. Of these, amine-based antioxidants are preferred, and alkylated diphenylamine is particularly preferred.
・ Amine series: α-naphthylamine, phenyl α-naphthylamine, alkylated phenyl α-naphthylamine, alkylated diphenylamine, etc. ・ Phenols: 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis [3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and the like hindered phenols and quinoline series: 2 2,4-trimethyl-1,2-dihydroquinoline polymer, and the like. The necessary amount of the antioxidant is usually 0 to 10% by mass, preferably 0.5 to 10% by mass, more preferably 0, with respect to the total mass of the composition of the present invention, from the viewpoint of effect and economy. .8-7% by mass.

(Rolling bearing)
The present invention also provides a rolling bearing in which the above grease composition is enclosed. The type and structure of the bearing are not limited, but the grease composition described above can stably form an oil film even under extremely low speed, high temperature, and water mixing conditions. But it shows excellent durability. Therefore, the rolling bearing of the present invention is suitable for continuous casting machines.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

(Examples 1-6, Comparative Examples 1-7)
Test greases were prepared as shown in Table 1. At that time, Examples 1 to 6 were prepared by separately synthesizing an aromatic diurea grease as a thickener tA and an aliphatic diurea grease as a thickener tB, and then mixing them as indicated. Thickener mixing ratios in Table 1 are mass ratios. No additive was added. In the thickener tA, TDI was used as the isocyanate and p-toluidine was used as the monoamine. In the thickener tB, MDI was used as the isocyanate and octylamine was used as the monoamine.

  In addition, the thickener tC in Comparative Examples 2 to 3 was prepared by simultaneously reacting two types of monoamine with isocyanate in base oil using MDI as isocyanate and p-toluidine and octylamine as monoamine. Moreover, the same additive as the Example was added. MDI is an abbreviation for diphenylmethane 4,4'-diisocyanate, and TDI is an abbreviation for a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate.

  Each test grease was subjected to (1) oil film thickness measurement, (2) inflow evaluation, and (3) wear resistance evaluation shown below. The results are also shown in Table 1.

(1) Oil film thickness measurement The oil film thickness in the contact surface was measured by the optical interference method using a ball-on-disk tester. The ball material was SUJ2, and the disk used was a glass disk coated with chromium and silica on one side. The measurement conditions were an atmospheric temperature of 80 ° C., a rolling speed of 0.01 m / s, and a maximum surface pressure of 0.5 GPa. Further, 10% by mass of ion exchange water was previously added to the test grease, and measurement was performed in a state where the test grease was constantly supplied to the contact surface.

(2) Evaluation of inflow property The grease inflow property to the contact surface was evaluated by observing the grease flow behavior on the disk plane including the contact surface using the same apparatus as the oil film thickness measurement method. Apply test grease with 10% by mass ion-exchanged water added in advance to the surface of the disk coated with chromium and silica at a constant thickness until the test grease is removed from the rolling surface by the ball and does not flow into the contact surface. The inflowability was evaluated according to the time. The time until the gas-liquid interface between the test grease and the atmosphere touched the tip of the contact surface was measured, and the time until the inflow of Comparative Example 1 stopped flowing was set as 1, and a relative comparison of inflow properties was performed. A larger inflow value indicates that the inflow property is better because the contact surface continues to be filled with grease for a long time.

(3) Wear resistance evaluation The wear resistance was evaluated using a reciprocating tester. Using a test grease to which 10% by mass of ion-exchanged water is added, the center of the wear scar after a wear test under conditions of a plate / roller roller system, 80 ° C., maximum surface pressure 1 GPa, amplitude 2 mm, frequency 0.3 Hz, 7 hours. The wear volume per part width of 1 mm was measured. The wear volume of Comparative Example 1 was set to 1, and a relative comparison of wear resistance was performed. The smaller the value of the wear resistance, the less the wear and the better the wear resistance.

  Example 2 and Comparative Example 2 and Example 3 and Comparative Example 3 have the same thickener raw material, but the composition and structure of the thickener fiber differ depending on the preparation method. In Example 2 and Example 3 in which the aliphatic diurea compound and the aromatic diurea compound were separately synthesized and then mixed, the oil film was compared with Comparative Example 2 and Comparative Example 3 in which the three components of the diurea compound were mixed at the same time. It can be seen that the thickness is large, the inflow property is excellent, and the wear resistance is excellent. In addition, as shown in Examples 1 to 6, it can be seen that by mixing an aliphatic diurea compound and an aromatic diurea compound, excellent wear resistance can be obtained under extremely low speed conditions and water mixing conditions.

(Examples 7-8, Comparative Example 8)
As shown in Table 2, the base oil and the thickener were the same, and a test grease was prepared by replacing the rust preventive formulation. In Example 7, an antioxidant was further added. And about the test grease, rust prevention property was evaluated by the following (4) rust prevention property test.

(4) Rust prevention test Using an apparatus used in the bearing rust prevention test method of ASTM D 1743, a test grease containing 30% by mass of corrosive water was used as a sample, and 9.8 kN · A torque of cm was applied and left at a temperature of 80 ° C. for 48 hours, and then the rusting state of the bearing was confirmed according to the following evaluation criteria. The results are also shown in Table 2.
(Evaluation)
# 1: No rust on outer race surface # 2: Less than 3 rust on outer race surface # 3: Worse than # 2

  As shown in Example 7 and Example 8, by including sorbitan trioleate, succinic anhydride, Ca sulfonate, and alkenyl succinimide as a rust preventive agent, excellent prevention even in an environment where water is easily mixed from the outside. It turns out that rust property is acquired. In particular, as in Example 7, it can be seen that excellent rust resistance can be maintained even in a high temperature environment by using an alkylated diphenylamine as an antioxidant together.

Claims (4)

A mixture of an aromatic diurea compound represented by the general formula (1) and an aliphatic diurea compound represented by the general formula (2) is used as a thickener, and the base oil comprises an alkyl diphenyl ether oil and a poly α-olefin oil. A grease composition characterized by being a mixed oil of mass ratio of alkyldiphenyl ether: polyalphaolefin oil = 60: 40 to 100: 0.
General formula (1): R1-NHCONH-R2-NHCONH-R1
Formula (2): R3-NHCONH-R4-NHCONH-R3
(In the formula, R1 is an aromatic hydrocarbon group having 6 to 12 carbon atoms, R2 and R4 are aromatic hydrocarbon groups having 6 to 15 carbon atoms, and R3 is an aliphatic hydrocarbon group having 6 to 20 carbon atoms. .)   The grease composition according to claim 1, wherein the mixing ratio of the aromatic diurea compound and the aliphatic diurea compound is, by mass ratio, aromatic diurea compound: aliphatic diurea compound = 40: 60 to 95: 5. object.   A rolling bearing comprising the grease composition according to claim 1 or 2 enclosed therein. The rolling bearing according to claim 3, wherein the rolling bearing is for a continuous casting machine.