JPS6228323B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a self-lubricating rolling bearing that obtains lubricity by utilizing surface chemical reactions between solids. Grease and oil are widely used as lubricants for rolling bearings, but they cannot be used at high temperatures or under vacuum due to the risk of combustion or evaporation.
Furthermore, solid lubricants such as powder are also difficult to use in environments where cleanliness is required. For this reason, in the past, instead of injecting and adding lubricant to the bearing as described above, Mo (molybdenum) and W (tungsten) were added to the friction surface of the bearing in advance.
Or, the compound is attached and the bearing is used in a gas atmosphere such as H ₂ S (hydrogen sulfide) that reacts with these substances on the friction surface, so that a solid lubricant film is generated during friction, or The friction surfaces of bearings are directly coated with a solid lubricant film made of soft metals such as gold, silver, or lead, or MoS ₂ (molybdenum disulfide), WS (tungsten sulfide), etc. However, the former method requires atmospheric gas, making it difficult to use in a vacuum, and the latter method suffers from severe abrasion and peeling of the solid friction film, resulting in a short service life. The present invention has been made in view of the above circumstances, and its purpose is to
Mo or its compound is present on the other side, and S (sulfur) or its compound is present on the other side, and by utilizing the surface chemical reaction between both friction surfaces, a solid lubricant film made of MoS ₂ etc. is formed in the necessary places and in the necessary amount during friction. To provide a self-lubricating rolling bearing that can withstand long-term use by being continuously produced, has accurate lubricity even under vacuum and high temperatures, and can be used even under conditions where cleanliness is required. It is in. Hereinafter, a case where the present invention is applied to a ball bearing will be explained based on the drawings. FIG. 1 is a schematic half-cut diagram of a ball bearing according to the present invention. In the figure, 1 is a ball, 2 is an outer ring, and 3 is an inner ring. 3 between the respective raceway surfaces 2a and 3a, the holding surface 4
is rotatably supported by the
During relative rotational movement between the outer ring 2 and the inner ring 3, the balls 1 are supported by the retainer 4 and rotate against the raceway surface 2 of the outer ring 2.
a and the raceway surface 3a of the inner ring 3 to rotate. The ball 1, the outer ring 2, the inner ring 3, and the cage 4 are all made of heat-resistant steel, and the ball 1 is made of steel that contains Mo or its compound in a higher amount than normal bearing steel, or By forming a layer of Mo or its compound on the entire outer circumference by sputtering or other methods, it is possible to
In addition, a thin layer of MoS ₂ is applied to one or both of the raceway surfaces 2a and 3a of the outer ring 2 and inner ring 3 by a method such as sputtering. S or a compound thereof, such as FeS (iron sulfide) or Ag ₂ S (silver sulfide), is present on the ball receiving surface. Of course, S or a compound thereof may be present on the outer peripheral surface of the ball 1, and Mo or a compound thereof may be present on the ball receiving surface of the cage 4, and Mo or a compound thereof may be present on one of the friction surfaces that slide against each other, and Mo or a compound thereof may be present on the other side. S or a compound thereof may be present. Also,
Regarding the method of making the above-mentioned Mo or its compound, S or its compound present on the surface of the friction surface, conventionally known methods other than those described above may be adopted as appropriate. Therefore, although the product of the present invention configured in this manner is not limited to any atmosphere, when used in a high vacuum and high temperature atmosphere, first of all, in the initial stage of use, the Mo on the outer circumferential surface of the ball 1 and the retainer are 4 is in an unreacted state with FeS, etc. on the ball receiving surface, and a solid lubricant film such as MoS ₂ , which will be described later, is not formed, although it is thin on each raceway surface 2a, 3a of the outer ring 2 and inner ring 3. MoS ₂ , which is a solid lubricant film, is initially made to exist, and this MoS ₂ has a lubricating function between the balls 1 and the raceway surfaces 2a and 3a of the outer ring 2 and inner ring 3, as well as between the balls 1 and the cage 4. and the bearing functions smoothly. During this time, the load stress and frictional force that act between the outer circumferential surface of the balls 1 and the ball holding surface of the cage 4, the temperature rise of the balls 1 and cage 4 themselves due to use under high temperatures, and the microscopic effects due to friction. In order to increase the target temperature, Mo on the outer peripheral surface of the ball 1 and S or sulfide on the retaining surface of the cage 4 are mixed as shown below (1), (2), (3)
It becomes a solid lubricant by causing a chemical reaction as shown in the formula
A film of MoS ₂ is formed. That is, first, FeS or Ag ₂ S on the holding surface of the cage 4 decomposes to generate S. FeS→Fe+S ……(1) Ag ₂ S→2Ag+S ……(2) Next, this S is interposed on the outer peripheral surface of ball 1
Reacts with Mo to produce _MoS2 . Mo+2S→MoS ₂ ...(3) Therefore, each raceway surface 2a, 3a of outer ring 2 and inner ring 3
Even if the MoS ₂ formed in the bearing wears out early after the bearing starts to be used, it will be replaced by a chemical reaction between the balls 1 and the cage 4.
MoS ₂ is generated, and it continuously performs a lubricating function not only between the balls 1 and the retainer 4 but also between the balls 1 and the raceway surfaces 2a and 3a of the outer ring and the inner ring 3. Moreover, the above chemical reaction is promoted in proportion to the degree of applied stress and frictional force, so MoS ₂ is generated in areas with large applied stress and frictional force, in other words, in areas that require more lubricity. This means that the reactive materials can be used effectively. By the way, the chemical reactions shown in equations (1) and (2) above are as follows.
It is reversible to the chemical reactions shown in equations (4) and (5). Fe+S→FeS...(4) 2Ag+S→Ag ₂ S...(5) Therefore, the S decomposed and produced in equations (1) and (2) returns to FeS again through the reactions in equations (4) and (5). There was some doubt as to whether MoS ₂ could be produced by combining with Mo in equation (3), but we calculated the production energies of FeS, MoS ₂ , and Ag ₂ S, and determined the priority of the reaction. As a result of the investigation, it was confirmed that the production of MoS ₂ , that is, the reaction of formula (3) takes precedence over the production of FeS and Ag ₂ S, that is, the reaction of formula (4) or (5). Next, the process of determining the priority of the reaction will be explained. Judgment was made by determining the Gibbs energy of formation at room temperature (25°C) and high temperature (527°C), and determining that the formation with a lower value occurs preferentially over the others. The standard Gibbs energy of formation ΔGf (298〓) for each substance at 25℃ (298〓) is given in Table 1 [Refer to the Basics of Chemistry Handbook (hereinafter referred to as reference book), edited by the Chemical Society of Japan, published by Maruzen in 1966]

[Table] As is clear from Table 1, the standard production Gibbs energy of MoS ₂ is the lowest, and therefore it can be seen that the production reaction of MoS ₂ occurs preferentially over other reactions. Next, find the Gibbs energy generated ΔGf at 527°C (800〓). Generally, the generated Gibbs energy ΔGf(T) at T is given by the following equation (5). ΔGf(T〓)=ΔHf(T〓)−T・ΔSf(T〓) ……(5) However, ΔHf(T〓): Heat of formation at T〓 ΔSf(T〓): Entropy at T〓 By the way, the above The heat of formation ΔHf (T〓) is as follows (6)
In addition, the entropy ΔSf(T〓) is given by the following equation (7). ΔHf(T〓)=ΔHf(298〓)+ ^T ₂₉₈ ΔCpdT...(6) However, ΔHf(298〓): Standard heat of formation ΔCp: Change in molecular heat Cp, given by equation (6') below. It will be done. ΔCp _AaBb − (aCp _A + bCp _B ) ... (6') However, Cp _AaBb : Molecular heat of chemical substance AaBb consisting of A molecule with number of atoms a and B molecule with number of atoms b Cp _A : Molecular heat of A molecule Cp _B : Molecular heat of B molecule ΔSf(T〓)=ΔSf(298〓)+ ^T ₂₉₈ ΔCpdlnT...(7) However, ΔSf(298〓): Standard entropy, given by equation (7') below . ΔSf (298〓) = 1/T {ΔHf (298〓) − ΔGf (298〓)} ... (7') In the above equation, ΔSf (298〓), ΔHf (298〓),
As for ΔGf (298〓), first, Cp and ΔCp are used as mentioned in the reference book.
seek. Cp is Cp quoted from the above reference book
The values were plotted on a coordinate system with absolute temperature T on the horizontal axis and Cp molecular heat (atomic heat) on the vertical axis as shown in FIG. 2, and were approximately determined as a function of T from this graph. In Figure 2, A, B...E are respectively
Molecular heat (atomic heat) of MoS ₂ , FeS, Fe, Mo, S
It shows the value. In addition, ΔCp is the Cp value obtained in the above procedure as (6′) for the chemical reaction shown by equation (3).
formula, i.e. below for e.g. MoS ₂ (6″)
It was obtained by substituting into the formula. ΔCp=Cp _MO1S2 −(1・Cp _MO +2・Cp _S ) …(6″) Table 2 shows these Cp and ΔCp values converted into kcal units. FeS was also found in the same way. Ta.

[Table] Also, ΔSf (298〓) for FeS and MoS ₂
In equation (7'), T = 800 and ΔHf(298
〓) and ΔGf(298〓) are given as shown in Table 3 below by quoting the number of reference books.

[Table] According to Table 3, the first term on the right-hand side of equation (7) and the second term on the right-hand side
The term is ⁸⁰⁰ ₂₉₈ ΔCp1/Td _T , and this ΔCp
are calculated from Table 2, so ΔSf of FeS and MoS ₂
(800〓) is given as shown in Table 4.

[Table] In equation (6), the first term on the right side is 800 298 ΔCpdT, and the second term on the right side is ⁸⁰⁰ ₂₉₈ ΔCpdT, which can be calculated based on Table ₂ .
〓) is given as shown in Table 5.

[Table] From the above, the first term on the right side of equation (5) is shown in Table 5.
Therefore, since the second term on the right side is obtained from Table 4 with T=800, ΔGf (800〓) is given as shown in Table 6.

[Table] In addition, the ΔGf (800〓) of Ag ₂ S is −14.4 kcal·mol ⁻¹ when only the results are shown. From the above, the ΔGf (800〓) of MoS ₂ is clearly lower than that of FeS or Ag ₂ S, and therefore 527℃
Also, the production reaction of MoS ₂ , that is, the reaction shown in equation (3), is the production reaction of FeS, that is, the reaction shown in equation (4) or (5).
It can be seen that this reaction occurs more preferentially than the reaction shown in the formula. As described above, in the bearing of the present invention, since Mo or its compound is present on one of the solid friction surfaces and S or its compound is present on the other, the surface chemical reaction between the two friction surfaces is utilized to solidify the solid during friction. A lubricating film is generated, and it is possible to continuously generate a solid lubricating film in the necessary amount in the necessary places, and it can withstand long-term use and provide accurate lubricity even under vacuum and high temperatures. In addition, the present invention has excellent effects such as being usable even under conditions where cleanliness is required.

[Brief explanation of the drawing]

FIG. 1 is a schematic half-cut diagram of the product of the present invention, and FIG. 2 is a graph showing the relationship between molecular heat (or atomic heat) and absolute temperature. 1...Ball, 2...Outer ring, 3...Inner ring, 4...
...Retainer.

Claims (1)

[Scope of Claims] 1. A self-lubricating rolling bearing characterized in that molybdenum or a compound thereof is present on one of the friction surfaces of the solid parts that are in sliding contact with each other, and sulfide is present on the other. 2. The solid portion according to claim 1, wherein each of the solid portions is made of heat-resistant steel, one of which is made of molybdenum or a compound thereof, and the other of which is made of a material containing sulfide. Self-lubricating rolling bearing. 3. The self-lubricating rolling bearing according to claim 1, wherein the molybdenum or its compound and sulfide are attached to a friction surface of a solid portion.