GB2131828A - Lubricant film for preventing galling of sliding metal surfaces - Google Patents

Abstract

A lubricant film containing 60- 80 wt % of a solid lubricant which is MoS2 or MoS2+graphite; 10-30 wt % of a lubricant additive which is Sb2O3, Fe powder, Zn powder and/or Ag powder, and more than 3 wt % and less than 15 wt % of an organic binder which is an epoxy ester resin, acrylic resin and/or urea resin.

Description

SPECIFICATION Lubricantfilm for preventing galling of sliding metal surfaces This invention relates to a novel lubricant film to be formed on the surfaces of sliding metal parts under high surface pressure for preventing galling thereof.

Galling occurs to metal surfaces which are in sliding contact under high surface pressure, particularly where the metal has a low thermal conductivity and a large thermal expansion coefficient, such as stainless steel, often giving rise to problems in various industrial machines.

For example, if the phenomenon of galling occurs when connecting threaded ends of oil well pipes, the connecting and breaking operation has to be interrupted to lift up the pipe for cutting off the defective pipe end and tapping a fresh screw thread on the pipe end, wasting considerable time and labour. In addition to oil well pipes, the same applies to metallic sliding parts which are subjected to a high surface pressure.

Hitherto, various lubricants have been proposed for preventing galling of metallic sliding parts. In most cases these lubricants contain a solid lubricant, a lubricant additive and/or an organic resin. For example, a lubricant comprising an MoS2-resin system is proposed in U.S. Patent Nos. 3,051,586, 4,303,537,3,146,142 and 4,206,060 and Japanese Patent Publication No.51-43558, a lubricant comprising an MoS2-Sb203-resin system is disclosed in U.S. Patent Nos. 3,314,885 and 3,882,030, and Kirk-Othmer Encyclopedia of Chemical Technology, and a lubricant comprising a graphite-resin system is described in U.S. Patent No. 2,335,958.

In order to make the most of the functions of the component of a lubricant and to maintain satisfactory lubricative properties in severe conditions under a high surface pressure, the kinds and blending ratios based on the correlations of the respective ingredients are important factors which should be taken into consideration in this connection. The lubricants of the above-mentioned systems or compositions are not necessarily satisfactory as a lubricant for sliding metal parts under high surface pressure and cannot be expected to have a sufficient effect on the prevention of galling.

We have sought to eliminate the above-mentioned problem, and more particularly to provide a lubricant film which is capable of effectively preventing galling of sliding metallic parts under high surface pressures.

According to one aspect of the invention, there is provided a lubricant film containing: a solid lubricant containing 60~80 wt % of MoS2 or MoS2+graphite; a lubricant additive consisting of at least one component selected from 10-30 wt. % of Sb203, Fe powder, Zn powder and Ag powder; and an organic binder consisting of more than 3 wt. % and less than 1 5 wt. % of at least one component selected from epoxy-ester resin, acrylic resin and urea resin.

Reference is now made to the accompanying drawings, in which: Figure 1 is a graphic representation of the sliding time up to the occurrence of initial galling versus the Sb203 content; Figures 2 to 4 are schematic views of a plate-rider friction test apparatus; and Figure 5 is a diagram of the number of the sliding time versus the friction coefficient for various lubricants.

The lubricant film according to the present invention is constituted by a solid lubricant, an additive and an organic resin binder. The solid lubricant is selected, for example, from MoS2 and MoS2+graphite, the lubricant additive is selected, for example, from Sb203, Fe powder, Zn powder, Ag powder and any mixture thereof, and the organic resin is selected, for example, from an epoxy-ester resin, an acrylic resin, a urea resin and any mixture thereof.

With regard to the solid lubricant, the lubricant film according to the present invention contains MoS2 or MoS2+graphite, as mentioned hereinbefore, in an amount of 60-80 wt. %. The solid lubricant which plays the main role in lubrication lowers the friction coefficient and therefore reduces the amount of frictional heat in the sliding metal portions under high surface pressure to prevent galling, so that it should be contained in the range of 60-80 wt. %.

Solid lubricants such as WS2, (CF)n (carbon fluoride) PTFE (polytetrafluoroethylene) and the like have inadequate lubricating properties, so that the solid lubricant component in the present invention is restricted to MoS2 or MoS2+graphite in the above defined range. A solid lubricant content of less than 60 wt. % results in a deterioration in durability and a high friction coefficient, and the deterioration in durability will occur even with a solid lubricant content in excess of 80 wt. %. Thus, the content of the solid lubricant should be in the range of 60 to 80 wt. %.

With regard to the lubricant additive which improves the thermal stability of the solid lubricant containing film, Sb203, Fe powder, Zn powder, Ag powder or any mixture thereof is added in an amount of 10-30 wt. %. This lubricant additive serves to suppress the oxidation of MoS2 of the solid lubricant (MoS2 being oxidized to MoO3 which has lower lubricating properties). The content of the lubricant additive should be in the range of 10-30 wt. % since the above-mentioned effect cannot be expected if its content is less than 10 wt. % and the lubricating property of the solid lubricant containing film is instead lowered if its content is greater than 30 wt. %.

Figure 1 shows the results of sliding tests of lubricant films containing an epoxy-ester resin and MoS2+Sb203 in a constant weight ratio of 8:92 but with variations in the content of Sb203. As is clear therefrom, the durability of the lubricant film is improved conspicuously when the Sb203 content is in the range of 10-30 wt. %, enduring more than 500 cycles of sliding motions before initiation of galling.

Examples of other lubricant additives include PbO, MnCI2 ~ 4H2O, As203 and the like. However, it will be clear from Table 1 below that, except in the case of the lubricant additives according to the invention, galling occurs at a relatively early time due to an unsatisfactory effect of the lubricant additive.

With regard to the organic binder, it consists of an epoxy ester resin, an acrylic resin, a urea resin or a mixture thereof is added in the range of 3-1 5 wt. %. More particularly, the organic binder, which plays an important role in binding the particles of the solid lubricant powder and the lubricant additive powder to each other as well as to the base metal surface, should be present in an amount of more than 3 wt. % in order to secure that effect in a sufficient degree but its content should not exceed 1 5% in view of the low lubricating property of the binder itself under high surface pressure, a preferred range being 3.5 to 12 wit. %.

Table 1

Sample Solid Organic Lubricant Sliding Sliding No. lubricant lubricant additive time (A) time {B) 1 MoS2 Epoxy-ester ZnS04 ~ 7H2O 153 387 resin 2 ,, ,, Fe203 160 > 500 3 ,, ,, MnCi2 4H2O 370 > 500 4 ,, ,, NaHCO3 320 405 5 ,, ,, As203 201 305 6 ,, ,, Bi203 280 > 500 7 ,, ,, SiO2 305 > 500 8 ,, ,, PbO 380 420 9 ,, ,, TiO2 345 > 500 10 " ,, Cu powder 374 > 500 11 ,, " Pb powder 374 > 500 12 ,, ,, CaO 418 > 500 13 ,, ,, Ag powder 500 > 500 14 ,, ,, Zn powder 2500 > 500 15 ,, ,, Fe powder > 500 > 500 16 ,, ,, Sb203 > 500 > 500 Note: The sliding times A and B represent an average number of sliding motions before initiation of galling and an average number of sliding motions up to a time when an abrupt increase in friction coefficient occurs, respectively, in a sliding test which was repeated three times under the same conditions.

In consideration of the above-mentioned function of the resin binder, its nature is regarded as an important factor which governs the durability of the lubricant film. The organic binders which are generally known in the art include phenol resins, epoxy resins+phenol resins or alkyd resins, urethane resins and the like. In this regard, the present invention restricts the binder to epoxy ester resins, acrylic resins urea resins and mixtures thereof for the following reasons.

Table 2 below shows the sliding time up to the time point at which galling initially takes place, with regard to lubricant films of an MoS2-Sb203-organic resin system formed on sliding metal portions under high surface pressure and containing different kinds of organic binders. It will be understood therefrom that acrylic resins, epoxy ester resins and urea resins which are employed in the present invention have excellent properties with regard to the durability of the lubricant film as compared with other organic binders.

Examples of acrylic resins, epoxy ester resins and urea resins useful in the present invention include, but are not limited to, acrylic resins such as copolymers of methyl methacrylate, ethyl methacrylate, propyl methacrylate and the like, epoxy ester resins such as epichlorohydrinbisphenol Atype epoxy resins esterified with an unsaturated fatty acid of, for instance, linseed oil, castor oil and the like, and urea resins such as condensation polymers of urea and formaldehyde.

Table 2

Sample Solid Lubricant Sliding Sliding No. lubricant additive Organic resin time (1) time 121 1 MoS2 Sb203 Urethane resin 190 > 500 2 ,, ,, Epoxy-ester resin 195 310 +phenol resin 3 ,, ,, Phenol resin 250 90 4 ,, ,, Alkyd resin 325 470 5 ,, ,, Silicon resin 210 320 6 ,, ,, Epoxy resin 450 > 500 7 ,, ,, Acrylic resin > 500 > 500 8 ,, ,, Epoxy-ester resin > 500 > 500 9 ,, ,, Urea resin > 500 > 500 The lubricant film according to the present invention is formed on sliding metallic parts in the following manner.

In the first place, the respective components of the lubricant film are blended in the abovedefined proportions and then mixed with an organic solvent such as toluene or the like. The resulting suspension is applied uniformly and thinly, for example, on threaded joint portions of stainless steel pipes by a brush or a sprayer, and then the organic solvent is removed by air seasoning to form a film of the above-mentioned constituents. Although natural seasoning is sufficient, it is preferred that the film which has been formed in this manner be thermally treated for a time period of several minutes to 5 hrs in a temperature range of 200-3000 C.

The above-described lubricant film according to the present invention exhibits good durability when applied to sliding metal parts under high surface pressure, eliminating the problem of galling which occurs with conventional lubricants.

The lubricant film of the present invention can be applied to various sliding metal parts which are subjected to a high surface pressure for diverse purposes, for example, to stainless steel pipes to be used as oil well pipes. Although grease (thread compounds) is usually applied to the threaded ends of such pipes before joining them end to end, some parts of the threaded end portions are subjected upon tightening to a surface pressure close to the yield stress of stainless steel (e.g. 70 kg/mm2) with the problem of galling as mentioned hereinbefore. However, tightening and breaking of the threaded joint portions with the lubricant film of the present invention can be effected smoothly and without galling problems.Furthermore, the above-mentioned grease which is applied to the threaded joint portions of stainless pipes in the conventional pipe joining operations may possibly become contaminated with muddy water or sea water depending upon the environment in which it is to be used. The lubricant film of the present invention can maintain good lubricant properties and exhibits high durability even in such severe environments.

The invention is now illustrated more particularly by way of an example.

Example There were prepared lubricant compositions containing MoS2, Sb203 and an epoxy-ester resin in the ratios of 52 wt. %: 13 wt. %: 35 wt. % (No. 1), 72 wt. %: 18 wt. %: 10 wt. % (No. 2) respectively, and after mixing with an organic solvent, each suspension was applied on plate 1 of the testing apparatus as shown in Figures 2 to 4. After natural seasoning, the resulting film was subjected to the plate-rider friction tests, in which an apparent contact load of 100 kg/mm2 was imposed on the plate 1, a test piece of SUS 410, by a rider 2.

In the test shown in Figure 2, the sliding duration was measured by counting the number of oneway sliding movements of the plate 1 in the leftward or rightward direction from one to the other end (over a distance of 60 mm) at a sliding speed of 30 mm/sec.

As seen in Figure 5 which shows the test results, the lubricant film No. 1, outside the range of the present invention, endured only about 30 sliding motions before initiation of galling, showing an abrupt increase in friction coefficient thereafter. On the other hand, the test pieces with the lubricant film No.

2 according to the present invention were completely free of galling even after 500 sliding motions, proving good durability of the films.

Claims (9)

Claims

1. A lubricant comprising: 60-80 wt. % of a solid lubricant which is MoS2 or MoS2+graphite; 10-30 wt. % of a lubricant additive selected from Sb203, Fe powder, Zn powder and Ag powder, and mixtures thereof; and 3 wt. % to 15 wt. % of an organic binder selected from epoxy-ester resin, acrylic resin and urea resin, and mixtures thereof.

2. A lubricant as claimed in claim 1, wherein said organic binder is contained in an amount of 3.5-12 wt. %.

3. A lubricant as claimed in claim 1 or 2, in the form of a film for preventing galling of sliding metal parts under high surface pressure.

4. A lubricant as claimed in claim 1, substantially as hereinbefore described with reference to the Example and/or the accompanying drawings.

5. A method for preventing galling of a sliding metal part under high surface pressure, said method comprising the steps of: preparing a suspension by mixing with an organic solvent a lubricant film composition containing 60-80 wt. % of a solid lubricant consisting of MoS2 or MoS2+graphite, 10-30 wt. % of a lubricant additive consisting of at least one component selected from Sb203, Fe powder, Zn powder, Ag powder and mixtures thereof, and more than 3 to 15 wt. % of an organic binder consisting of at least one component selected from epoxy-ester resins, acrylic resins, urea resins and mixtures thereof; applying said suspension on the surface of said sliding metal part; and drying the applied suspension to remove said organic solvent and to form a lubricant film on said sliding metal part.

6. A method as claimed in claim 5, wherein the suspension is dried by natural seasoning.

7. A method as claimed in claim 5, wherein said lubricant film formed on said sliding metal part is thermally treated for a time period of several minutes to 5 hrs in a temperature range of 200-3500 C.

8. A method as claimed in claim 5, substantially as hereinbefore described with reference to the Example and/or the accompanying drawings.

9. A stainless steel oil well pipe having threaded joint portions thereof coated with a lubricant film constituted by 60-80 wt. % of solid lubricant consisting of MoS2 or MoS2+graphite, 10-30 wt. % of a lubricant additive consisting of Sb203, Fe powder, Zn powder, Ag powder or a mixture thereof, and 3-1 5 wt. % of an organic binder consisting of an epoxy-ester resin, an urea resin, an acrylic resin or a mixture thereof.