Abstract:
Extreme pressure additives may be added to greases to improve their lubricating properties, particularly to decrease friction and wear of parts that are exposed to very high pressures. Molybdenum disulfide is frequently used as an extreme pressure additive. However, molybdenum disulfide is expensive, has limited availability, and may have adverse environmental effects. This invention discloses an extreme pressure additive and grease formulation where the amount of molybdenum disulfide is reduced through the addition of calcium carbonate while the performance characteristics of the grease are maintained or improved. The extreme pressure additive may comprise about 20% molybdenum sulfide and about 80% calcium carbonate, by weight.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to an extreme pressure additive for greases. More specifically, the present invention relates to an extreme pressure additive comprised of molybdenum disulfide and calcium carbonate in a selected ratio. The present invention also relates to a grease formulation containing the extreme pressure additive. 
         [0003]    2. Description of the Problem and Related Art 
         [0004]    Lubricants are substances introduced between two moving surfaces to reduce the friction and wear between them. Greases are a category of lubricants that are used when a surface can only be lubricated infrequently or a lubricating oil would not stay in position. Greases also act as sealants to prevent ingress of water and dust. 
         [0005]    Greases are prepared by incorporating a lubricating oil in a thickener. Thickeners comprising soaps are generally preferred. The lubricating oil may be one of many different types of mineral oils, which are derived from petroleum. Alternatively, the lubricating oil may be one of many different types of synthetic fluids, which are generally produced by chemical reactions. 
         [0006]    Certain substances may be added to greases to modify their characteristics for specific situations or to improve their lubricating properties. For example, extreme pressure additives may be added in order to decrease friction and wear of surfaces that are exposed to high pressures. Extreme pressure additives may be activated at high temperatures. Alternatively, extreme pressure additives may be solid particles that form layers between the load-bearing surfaces and protect them from sliding against each other. 
         [0007]    Molybdenum disulfide is frequently used as a solid lubricant and an extreme pressure additive. However, molybdenum disulfide is relatively expensive, and its availability is sometimes limited. As a result, there is a need for a grease formulation where the amount of molybdenum disulfide is reduced while the performance characteristics of the grease are maintained or improved. 
         [0008]    Others have considered the use of various formulations of molybdenum disulfide and/or calcium carbonate as lubricants or extreme pressure additives. For background information relating to such uses, reference may be made to the following United States patents and patent publications: 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                   
                 Inventor 
                 Title 
               
               
                   
               
             
             
               
                 Pat. No. 
                   
                   
               
               
                 4,308,182 
                 Eckard et al. 
                 Dry wire drawing lubricants based on poly (3,5-dithio- 
               
               
                   
                   
                 1,2,4-thiadiazole) and poly (2,5-dithio-1,3,4-thiadiazole) 
               
               
                 4,411,804 
                 DeVries et al. 
                 Solid particles containing lubricating oil composition 
               
               
                 4,765,917 
                 Otaki et al. 
                 Water-base metal forming lubricant composition 
               
               
                 5,173,204 
                 Chiddick et al. 
                 Solid lubricant with high and positive friction 
               
               
                   
                   
                 characteristic 
               
               
                 5,308,516 
                 Chiddick 
                 Friction modifiers 
               
               
                 5,415,791 
                 Chou et al. 
                 Lubricating composition and a sliding member 
               
               
                   
                   
                 comprising the composition 
               
               
                 5,589,444 
                 Hatakeyama 
                 Grease composition for constant velocity joints 
               
               
                 5,952,273 
                 Suzuki et al. 
                 Grease composition for constant velocity joints 
               
               
                 6,432,889 
                 Kinoshita et al. 
                 Grease composition 
               
               
                 6,649,573 
                 Mitrovich 
                 Solid lubricant and composition 
               
               
                 7,053,028 
                 Kawamura et al. 
                 Grease and grease sealed bearing 
               
               
                 7,235,514 
                 Mack, Sr. et al. 
                 Tribological materials and structures and methods for 
               
               
                   
                   
                 making the same 
               
               
                 7,241,722 
                 Murase et al. 
                 Sliding component 
               
               
                 7,244,695 
                 Eadie 
                 Method for reducing wear of steel elements in sliding- 
               
               
                   
                   
                 rolling contact 
               
               
                 7,244,696 
                 Patel et al. 
                 Anti-seize composition in solid form 
               
               
                 7,256,163 
                 Akada et al. 
                 Grease composition 
               
               
                 7,291,581 
                 Levine et al. 
                 Borate ester lubricant additives 
               
               
                 7,307,047 
                 Ogawa et al. 
                 Lepidocrocite potassium magnesium titanate, method 
               
               
                   
                   
                 for manufacturing the same and friction material 
               
               
                 7,312,185 
                 Willey et al. 
                 Rock bit grease composition 
               
               
                 Pub. No. 
                   
                   
               
               
                 2004/0043908 
                 Mitrovich 
                 Solid lubricant and composition 
               
               
                 2006/0128570 
                 Mitrovich 
                 Environmentally friendly solid lubricant sticks 
               
               
                 2008/0011776 
                 Patel et al. 
                 Anti-seize composition in solid form 
               
               
                   
               
             
          
         
       
     
         [0009]    For example, U.S. Pat. No. 4,411,804, to DeVries et al., discloses a lubricating oil composition containing 0.1% to 2% by weight of molybdenum disulfide. However, molybdenum disulfide is classified as a lubricant and not an extreme pressure agent. In addition, the composition does not contain calcium carbonate. 
         [0010]    U.S. Pat. No. 5,173,204, to Chiddick et al., discloses a solid lubricant containing at least 5% by weight of solid lubricant (which may be molybdenum disulfide) and 5% by weight of powderized solid mineral friction modifier (which may be calcium carbonate). 
         [0011]    U.S. Pat. No. 5,589,444, to Hatakeyama, discloses a grease composition for constant velocity joints containing 0.5% to 5.0% of molybdenum disulfide by weight. However, the composition does not contain calcium carbonate. 
         [0012]    U.S. Pat. No. 6,649,573, to Mitrovich, discloses a solid lubricant composed of 5% to 75% by volume extreme pressure additives, which may include molybdenum disulfide and calcium carbonate. 
         [0013]    U.S. Pat. No. 7,244,695, to Eadie, discloses a high-positive frictional grease that includes about 0.02% to about 40% by weight of a lubricant (which may be molybdenum disulfide) and about 0.5% to about 30% by weight of a friction modifier (which may be calcium carbonate). However, the disclosure does not specify a ratio of molybdenum disulfide to calcium carbonate. 
         [0014]    U.S. Pat. No. 7,256,163, to Akada et al., discloses a grease composition containing 0.1% to 20% by mass of a sulfur-type extreme pressure agent and 0.01% to 10% by mass of carbonate. However, molybdenum disulfide is classified as a lubricant and not an extreme pressure agent. Although calcium carbonate is used in the formulation process, the disclosure does not specify a ratio of molybdenum disulfide to calcium carbonate. 
         [0015]    U.S. Pub. No. 2004/0043908, to Mitrovich, discloses a solid lubricant composed of 5% to 75% by volume extreme pressure additives, which may include molybdenum disulfide and calcium carbonate. 
         [0016]    U.S. Pub. No. 2008/0011776, to Patel et al., describes an anti-seize composition in solid form containing 10% to 60% by weight of lubricants. Lubricants may include molybdenum disulfide, calcium carbonate, and calcium stearate. 
         [0017]    None of these references specifically discloses an extreme pressure additive or a grease formulation where the amount of molybdenum disulfide is reduced through the addition of calcium carbonate while the performance characteristics of the grease are maintained or improved. As discussed above, there is a need for such an extreme pressure additive and grease formulation due to the cost, and limited availability. 
       SUMMARY OF THE INVENTION 
       [0018]    The invention provides an extreme pressure additive composition for a base grease, where the additive comprises a first amount of molybdenum disulfide and a second amount of calcium carbonate, the first amount and the second amount being related according to a selected ratio. In one embodiment, the selected ratio may be about 20% by weight of molybdenum disulfide and about 80% by weight of calcium carbonate. 
         [0019]    A grease composition is also provided, where the grease comprises a first amount of finished grease which may optionally contain a performance additive package and a second amount of an extreme pressure additive composition that is comprised of molybdenum disulfide and calcium carbonate in a selected ratio. 
         [0020]    A method is also provided for formulating a reduced molybdenum grease, the method comprising the steps of providing a base grease which may optionally include a performance additive package (additized); providing an extreme pressure additive composition, where the extreme pressure additive is comprised of molybdenum disulfide and calcium carbonate in a selected ratio; and mixing the finished grease with a selected amount of the extreme pressure additive composition. 
         [0021]    These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and claims. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0023]    Broadly, the current invention may include an extreme pressure additive for a finished grease, a composition for an extreme pressure grease, and methods for formulating a reduced molybdenum grease. The amount of molybdenum disulfide may be reduced while the performance characteristics of the grease may be maintained or improved. For example, when compared to commercially available greases containing 3 or 5% molybdenum disulfide by weight, the invention may provide similar extreme pressure, stability, and pumpability (flow) performance. In addition, the invention may provide improved fretting wear protection, water resistance, oxidation resistance, and extreme pressure protection as measured by the Timken OK load rating. Finally, the amount of molybdenum disulfide contained in the grease may be reduced, resulting in lower costs. 
         [0024]    Generally in the prior art, the term “base grease” is used to designate a pure grease compound which may contain thickeners, whereas the term “finished grease” is used to designate a base grease to which performance additives have been added. The performance additive composition may contain such components as corrosion inhibitors, rust inhibitors, oxidation inhibitors, copper corrosion passivators, and other similar performance additives. A base grease that contains such a performance additive composition or performance additives is said to be a “finished grease”, or optionally, a base grease that has been “additized.” An extreme pressure additive composition may contain components that enable the grease to perform with acceptable characteristics under extreme pressures without breaking down or otherwise decomposing. While some grease descriptions may not make a distinction between a performance additive composition and a high pressure additive composition, such a distinction will be made for purposes of this disclosure, so that the terms “performance additive composition” and “extreme pressure additive composition” are considered to be mutually exclusive in terms of the components contained in each composition. 
         [0025]    The extreme pressure additive composition may contain as components both molybdenum disulfide and calcium carbonate in a selected ratio. In one embodiment of the invention, the selected ratio may be about 20% by weight molybdenum disulfide to about 80% by weight calcium carbonate. The calcium carbonate may be either uncoated or coated with a coating agent. Different coating agents may be used without departing from the scope of the invention, but stearic acid may be preferable, when a coating agent is used. 
         [0026]    The composition for an extreme pressure grease may comprise a finished grease mixed with a selected amount of the extreme pressure additive. In one embodiment, the selected amount of the extreme pressure additive may be in a range from about 3% by weight to about 5% by weight of the total grease composition, with values of 3% and 5% being preferable. The remaining portion of the grease may be comprised of the base grease, a performance additive composition, or a combination of the base grease and the performance additive composition in some selected ratio. 
         [0027]    The base grease used in the present invention may be generic and not restricted to a specific grease. Instead, the extreme pressure additive composition may be used with any suitable commercially available grease without departing from the scope of the invention. The extreme pressure additive composition may be incorporated into the base grease or finished grease after the thickener system or soap has been formed. Alternatively, the extreme pressure additive composition may be incorporated during the soap or thickener manufacturing process. Enhanced performance may be obtained by incorporating the molybdenum disulfide or calcium carbonate or both during the thickener manufacturing process. 
         [0028]    The invention may also include a method for formulating reduced molybdenum grease, where method may consist of providing a finished grease; preparing an extreme pressure additive composition comprised of about 20% molybdenum disulfide and about 80% calcium carbonate, by weight; and mixing the finished grease and the extreme pressure additive composition in selected amounts. In one embodiment of the invention, the selected amounts may be about 95% by weight of the finished grease and about 5% by weight of the extreme pressure additive composition. In another embodiment of the invention, the selected amounts may be about 97% by weight of the finished grease and about 3% by weight of the extreme pressure additive composition. 
         [0029]    The extreme pressure additive composition may be combined with the base grease and optional performance additives either as the composition or as individual components without departing from the scope of the invention. Furthermore, the calcium carbonate and the molybdenum disulfide may be added to the base grease during a stage when reactions are taking place to form the thickener system or they may be added to the grease after the thickener has been formed. Enhanced performance may be obtained by incorporating the solid calcium carbonate and the molybdenum disulfide additives during the stage when the soap or thickener system is being formed. 
         [0030]    Alternative embodiments of the invention may include, but are not limited to, coating the calcium carbonate with coating agents other than stearic acid, varying the particle sizes of the calcium carbonate or the molybdenum disulfide or both, varying the ratio of molybdenum disulfide to calcium carbonate, and changing the way in which the extreme pressure additive is incorporated into the grease composition. The particle size of the calcium carbonate may range from about 0.025 micrometers to about 1.75 micrometers without departing from the scope of the invention, with an optimal particle size of 0.07 micrometers to 0.5 micrometers being preferred. The calcium carbonate may be in either a ground or a precipitated form, with precipitated calcium carbonate being preferred. 
       EXAMPLES 
       [0031]    The present invention may be further illustrated in the following examples. However, it is to be understood that these examples are for illustrative purposes only and should not be used to limit the scope of the present invention in any manner. 
         [0032]    Physical properties of a grease containing the inventive extreme pressure additive were evaluated according to the evaluation methods identified below. In a first example, the invention was compared against a commercially available grease containing 3% molybdenum disulfide. The 3% molybdenum disulfide was, in essence, replaced by the inventive extreme pressure additive so that the inventive extreme pressure addition represented 3% of the grease formulation. Table 1 tabulates the different characteristics measured for each of the two formulations. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Test 
                 3% Formula 
                 Invention 
               
               
                   
               
             
             
               
                 Color 
                 Gray 
                 Gray 
               
               
                 Texture 
                 Smooth,  
                 Smooth,  
               
               
                   
                 adhesive 
                 adhesive 
               
               
                 Un-Wk Pen 
                 288 
                 290 
               
               
                 Wk-60 
                 294 
                 295 
               
               
                 Wk-1000 
                 300 
                 303 
               
               
                 D 1831 Roll Stability 
                 4.97% 
                 4.97% 
               
               
                 Drop Point (° F.) 
                 ND @ 277° C./ 
                 ND @ 277° C./ 
               
               
                   
                 530° F. 
                 530° F. 
               
             
          
           
               
                 Weld (kgf) 
                 400  
                 kg 
                 400  
                 kg 
               
               
                 Wear Scar (mm) 
                 0.44  
                 mm 
                 0.43  
                 mm 
               
               
                 Timken 
                 50  
                 lbs 
                 55  
                 lbs 
               
               
                 Fretting Wear 
                 3.10  
                 mg 
                 2.75  
                 mg 
               
             
          
           
               
                 D 1743 Corrosion 
                 Pass 
                 Pass 
               
               
                 D 6138 Emcor 
                 0 
                 0 
               
               
                 D 4048 Copper Cor. 
                 1A 
                 1A 
               
               
                 D 942 Oxidation 
                 6.5 PSI Loss 
                 4.5 PSI Loss 
               
               
                 D 1264 Water Washout 
                 3.00% 
                 2.73% 
               
               
                 USS Mobility @ 40° F. gpm 
                 242 
                 243 
               
               
                 USS Mobility @ 20° F. gpm 
                 144 
                 135 
               
               
                 USS Mobility @ 0° F. gpm 
                 57 
                 51 
               
               
                   
               
             
          
         
       
     
         [0033]    As shown in Table 1, the invention may provide similar wear protection, stability, and pumpability (flow) performance while at the same time requiring much less molybdenum disulfide than the present formulation. However, in addition, the grease formulation containing the inventive extreme pressure composition may provide significantly improved fretting wear protection, water resistance, oxidation resistance, and Timken OK load rating. 
         [0034]    In a second example, the invention was compared against a commercially available grease containing 5% molybdenum disulfide. As in the first example, the 5% molybdenum disulfide was, in essence, replaced by the inventive extreme pressure additive so that the inventive extreme pressure addition represented 5% of the grease formulation. Table 2 tabulates the different characteristics measured for each of the two formulations. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Test 
                 5% Formula 
                 Invention 
               
               
                   
               
             
             
               
                 Color 
                 Gray 
                 Gray 
               
               
                 Texture 
                 Smooth,  
                 Smooth,  
               
               
                   
                 adhesive 
                 adhesive 
               
               
                 Un-Wk Pen 
                 286 
                 290 
               
               
                 Wk-60 
                 291 
                 293 
               
               
                 Wk-1000 
                 299 
                 299 
               
               
                 Drop Point (° F.) 
                 ND @ 277° C./ 
                 ND @ 277° C./ 
               
               
                   
                 530° F. 
                 530° F. 
               
             
          
           
               
                 LNSL 
                 100  
                 kg 
                 100  
                 kg 
               
               
                 Wear Scar (mm) 
                 0.43  
                 mm 
                 0.44  
                 mm 
               
               
                 Timken 
                 45  
                 lbs 
                 50  
                 lbs 
               
               
                 Fretting Wear 
                 3.50  
                 mg 
                 2.25  
                 mg 
               
             
          
           
               
                 D 1743 Corrosion 
                 Pass 
                 Pass 
               
               
                 D 6138 Emcor 
                 0 
                 0 
               
               
                 D 4048 Copper Cor. 
                 1A 
                 1A 
               
               
                 D 942 Oxidation 
                 8 PSI Loss 
                 6 PSI Loss 
               
               
                 D 1264 Water Washout 
                 3.02% 
                 2.93% 
               
               
                 USS Mobility @ 40° F. gpm 
                 230 
                 212 
               
               
                 USS Mobility @ 20° F. gpm 
                 124 
                 119 
               
               
                 USS Mobility @ 0° F. gpm  
                 57 
                 46 
               
               
                   
               
             
          
         
       
     
         [0035]    The test results are similar to the results in the first example. Once again, the invention may provide similar wear protection, stability, and pumpability (flow) performance as well as significantly improved fretting wear protection, water resistance, oxidation resistance, and Timken OK load rating. 
         [0036]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.