Patent Application
20120329687
The present disclosure relates generally to extreme pressure additives for lubricants and lubricants containing the extreme pressure additives.
Lubricants are used between contacting (sliding or rolling) surfaces of dynamic systems to reduce friction and wear therebetween. Lubricants are typically formulated by adding one or more additives to a base oil. The additives include, among others, antioxidants, corrosion inhibitors, defoamers, emulsifiers, lubricity additives, pour point depressants, viscosity index improvers, and extreme pressure additives (hereinafter “EP additive”). These additives provide desirable properties to the lubricant for a particular application. In addition to these additives, semisolid lubricants (called greases) also include a thickener that thickens the lubricant. Greases are typically used in areas where a continuous supply of a liquid lubricant cannot be retained, such as, for example, in an open bearing.
Lubrication occurs when the lubricated surfaces are separated by the lubricant and an applied load is carried by the lubricant, thereby reducing friction between the surfaces and the resulting wear. In general, four regimes of lubrication are broadly defined based upon the mechanism by which the lubricant operates to reduce friction between the parts. These four regimes are: hydrodynamic lubrication, mixed lubrication, boundary lubrication, and extreme pressure lubrication. In the hydrodynamic and mixed lubrication regimes, a film of lubricant (a thick film in the case of hydrodynamic and a thin film in the case of mixed lubrication) separates the moving surfaces. In boundary layer and extreme pressure lubrication regimes, an additive (boundary lubricity additive and extreme pressure additive) gets adsorbed on the metal surfaces to form a lubricant film that will reduce metal-to-metal contact. At high contact pressures and temperatures, a lubricant film formed by a boundary lubricity additive does not remain on the contacting parts, and therefore does not protect the parts from wear. Under these high contact pressure and temperature conditions, extreme pressure additives provide wear protection to the parts by enabling the lubricant film to survive these conditions.
The exact role of the EP additives in providing wear protection is the subject of some controversy. It is said that under extreme pressure conditions micro-welds are formed between the asperities of the metal parts in contact. Relative movement is thus only effected by breaking such micro-welds. Under high pressure conditions, friction and wear can therefore be considered as a function of the shear strength and temperature resistance of the lubricant film at the interface. It is said that the lubricant film formed in the presence of EP additives, has a lower shear strength than that of the metal itself. Therefore, the friction between the metals in sliding contact is reduced.
There are two main types of EP additives, those that are temperature-dependent (active), and those that are not (passive). The most common temperature-dependent types (active) of EP additives include chlorine, phosphorus and sulfur. They are activated by reacting with the metal surface when the temperature is elevated due to the heat produced from friction as a result of extreme pressure. The chemical reaction between the additive and metal surface creates metal salts that acts as a film to reduce friction and wear. The non-temperature dependent additives (passive), which include overbased sulfonates, operate by a different mechanism. These additives include a colloidal carbonate salt dispersed within the sulfonate which forms a film due to interaction with iron.
U.S. Pat. No. 4,923,625 issued to King ('625 patent) discloses an EP additive for a lubricant. The EP additive of the '625 patent is formed by mixing a metal thiosulphate and metal phosphate in a ratio from about 1:99 to about 99:1. The EP additive thus formed is added to a base oil to form a lubricant such that about 0.01 to about 30 weight percent of the lubricant consist of the EP additive. While the lubricant of the '625 patent may be suitable for some applications, it may not provide sufficient wear resistance for other applications.
The present disclosure is directed to EP additives and lubricants that decrease or overcome shortcomings in the '625 patent and/or other shortcomings in existing technology.
In one aspect, an extreme pressure additive for a lubricant is disclosed. The extreme pressure lubricant may include one or more phosphorous containing compounds and one or more boron containing compounds. The ratio of weight of phosphorous to boron in the extreme pressure additive may vary between about 1 to about 30.
In another aspect, a lubricant is disclosed. The liquid lubricant may include a base material, and one or more phosphorous containing compounds in a concentration of about 0% to about 15% in the base material. The lubricant may also include one or more boron containing compounds in a concentration of about 0.1% to about 10% in the base material.
In yet another aspect, a lubricant is disclosed. The lubricant may include a base material. The base material may be at least one of a base oil and a thickener. The lubricant may also include one or more phosphorous containing compounds in a concentration of about 0.25% to about 7% in the base material and one or more boron containing compounds in a concentration of about 0.1% to about 7% in the base material. The lubricant may also include molybdenum disulfide.
Lubricant 20 may also include several additives 26. These additives 26 may be added to the base oil 22 (and thickener 24 in the case of greases) to impart desirable properties to lubricant 20 for a particular application. The additives 26 may include, among others, antioxidants 26a, corrosion inhibitors 26b, defoamers 26c, emulsifiers, lubricity additives, pour point depressants, viscosity index improvers, and an EP additive 30. These additives 26 may impart desirable properties to the lubricant 20. The EP additive 30 may increase the ability of the lubricant 20 to operate in extreme pressure operating conditions. During operation, the EP additive 30 in the lubricant 20 may react with the mating surfaces of shaft 14 and bearing 18 (shown in
An EP additive 30 may include different concentrations of several chemical compounds. In general, EP additive 30 may include between about 0-15% of one or more phosphorous containing compounds mixed with between about 0.1-10% of one or more boron containing compounds in base oil 22. In some embodiments, between about 0.25-7% by weight of one or more phosphorous containing compounds may be mixed with between about 0.1-7% of one or more boron containing compounds in base oil 22. It is also contemplated that in some embodiments, between about 0.25-5% by weight of one or more phosphorous containing compounds may be mixed with about 0.1-5% of one or more boron containing compounds in base oil 22. Any phosphorous and boron containing compound may be used in EP additive 30. Exemplary phosphorous containing compounds that may be used in EP additive 30 include sodium tripolyphosphate (STTP), potassium tripolyphosphate (KTTP), dicalcium phosphate (DCP), monocalcium phosphate (MCP), tricalcium phosphate (TCP), and trilithium orthophosphate. Exemplary boron containing compounds that may used in EP additive 30 include lithium tetraborate, lithium metaborate, borax, colemanite, potassium pentaborate, potassium tetraborate, and calcium borate. In some embodiments, EP additive 30 may include the above-mentioned phosphorous containing compounds and boron containing compounds, and additionally include between about 0.1-5% by weight of molybdenum disulfide. In some embodiments of EP additives 30, the concentration of molybdenum disulfide may be between about 0.5-2% by weight. In addition to these compounds, EP additive 30 may also include commercially available additives (such as, for example, Oronite OLOA® 9750, etc.) to impart desirable properties to the lubricant 20. In some embodiments, EP additive 30 may include only one phosphorous containing and one boron containing compound, while in other embodiments, several phosphorous containing compounds may be mixed with several boron containing compounds to create EP additive 30. It should be noted that although EP additive 30 is described as having one or more phosphorus containing compounds mixed with one or more boron containing compounds, in embodiments of EP additives 30 that include about 0% phosphorous containing compounds, the EP additive may not include any substantial amount of phosphorous containing compounds. In these embodiments, the EP additive 30 may only include between about 0.1-10% of one or more boron containing compounds. Table I lists the ranges of concentration of phosphorous and boron containing compounds in base oil 22 (in weight percent) in some exemplary EP additives 30 of the current disclosure.
2 to 4.5
Table II lists the exemplary embodiments of EP additives 30 (EP1 to EP24) that are obtained by combining one or more of the compounds listed in Table I with base oil 22. It should be noted that the measurement accuracy of the data listed in Tables I and II is about ±20% of the listed value. For instance, although the concentration of sodium tripolyphosphate (STTP) in EP1 of Table II is listed as 4.18%, in reality the concentration of STTP in EP1 may vary from 3.34% (4.18−0.2×4.18) to 5.02% (4.18+0.2×4.18). It should further be noted that, in EP11 of Table II, a commercially available additive OLOA® 9750 is also added, and that EP23 of Table II does not include any phosphorous containing compound. Table II also includes the ratio of phosphorous to boron in the different embodiments of EP additives illustrated in Table II. In general, the ratio of the weight of phosphorous to boron in the EP additives 30 of Table II vary between about 0-30 (corresponding to a molar ratio of about 0-10.5). Please note that a weight ratio of “0” corresponds to the EP additive, EP23, that does not include any substantial amount of phosphorous containing compound therein. With the exception of EP23, the ratio of the weight of phosphorous to boron in EP additives 30 vary from between about 1-30 (corresponding to a molar ratio of about 0.3-10.5). As seen in Table II, when the boron containing compound includes calcium borate, the ratio of weight of phosphorous to boron varies from about 0-2.2 (molar ratio of 0-0.75), and when the boron containing compound does not include calcium borate, the ratio of weight of phosphorous to boron varies from about 9-30 (corresponding to a molar ratio of 3-10.5). Note that with the exception of EP23, the ratio of weight of phosphorous to boron in calcium borate containing EP additives vary from between about 1-2.2 (molar ratio of 0.3-0.75). An EP additive 30 that includes phosphorous and boron in the ratios discussed above may be added to a base oil 22 (and a thickener 24 if a semisolid lubricant 20 is being formulated) to formulate lubricants 20. In some embodiments, instead of mixing EP additive 30 to a base oil (and a thickener in semisolid lubricants), lubricant 20 may be formulated with the constituents of EP additive included therein.
To evaluate the wear protection of the EP additives 30 of the current disclosure, the EP additives of two commercially available greases (Cat® Advanced 3Moly grease (“3Moly”) and Cat® Ultra 5Moly grease (“5Moly”) were removed and replaced with the EP additives 30 listed in Table II. The modified greases thus obtained were subjected to an industry standard test used to evaluate extreme pressure properties of a lubricant. As known in the art, commercially available 3Moly grease includes about 3% of molybdenum disulfide as the EP additive in a lithium complex thickener, and commercially available 5Moly grease includes about 5% of molybdenum disulfide as the EP additive in calcium sulphonate thickener. Modified 5Moly greases were formulated by removing the existing EP additive (of 5% of molybdenum disulfide) from the grease, and replacing it with an EP additive 30 of Table II (namely, EP additives EP4, EP5, EP8-EP11, EP22, and EP23). Similarly, modified 3Moly greases were formulated by removing the existing EP additive (of about 3% of molybdenum disulfide) from the grease, and replacing it the other EP additives 30 of Table II (namely, EP1-EP3, EP6, EP7, EP12-EP21, and EP24). The modified 3Moly and 5Moly greases were then subjected to Four Ball EP test to evaluate their extreme pressure properties. Since the Four Ball EP test is well known and is commonly used to characterize lubricants in the art, only a brief description of the test will be provided herein.
The Four Ball EP test, described in ASTM D 2596, is performed using a Four-Ball Extreme Pressure (EP) Tester to measure the load carrying ability of the EP additive in a grease. In this test, four steel balls are arranged in the form of a tetrahedron. The lubricant to be tested is applied to the balls and the top ball is rotated under an applied compressive load while the bottom three balls are held stationary. A series of ten second runs are made at progressively higher loads until welding of the four balls occur. The weld point load is the load which the lubricant can bear without welding of the balls. A higher minimum weld point load indicates higher load carrying ability of the EP additive, and is therefore desirable. Table II shows the measured weld point loads (in kgf) for each modified grease.
The measured weld point load of commercially available 5Moly grease (with about 5% molybdenum disulfide as the EP additive) is about 620 kgf, and that of commercially available 3Moly grease (with about 3% molybdenum disulfide as the EP additive) is about 315 kgf. The higher weld point load of commercially available 5Moly grease (as compared to commercially available 3Moly grease) may be as a result of inherent load bearing properties of the calcium sulphonate thickener present in the grease. As evident from Table II, the measured weld point load of greases including exemplary EP additives 30 of the current disclosure were higher than the respective commercially available grease. Since the weld point load is a measure of the load carrying ability of the EP additive in the grease, the observed improvement in weld point load is believed to be due to the added EP additive 30.
The extreme pressure additives and lubricants of the current disclosure may be beneficial for any application where lubricants are used to reduce mechanical wear. An extreme pressure additive of the current disclosure may be created by mixing one or more phosphorous containing compounds with one or more boron containing compounds such that the ratio of the weight of phosphorous to boron varies between about 0-30. An extreme pressure lubricant of the current disclosure may be created by mixing between about 0-15% of one or more phosphorous containing compounds with between about 0.1-10% of one or more boron containing compounds in base oil and a thickener (if needed). These lubricants may be dispensed and applied in an application by any technique that is known in the art.
As described above, the extreme pressure lubricants of the current disclosure show improved load bearing characteristics. Further, based on the constituents in the EP additives, the cost and environmental impact of these lubricants will be low.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed extreme pressure additives and lubricants. Other embodiments will be apparent to those skilled in the art from consideration of the specification and known practice in the art. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
