US2005553A - Solid lubricating compound - Google Patents

Description

SQUID LRHCAYJTIING CQMUPQUNID Charles A. Miller and David A. Smith, lFra,

lP'a, assignors to Valvoline @il Company, a corporation of New Jersey No Drawing. Application August 20, 1932, Serial No. 629,743

Claims. (oi. 87-9) This invention relates to improvements in dency in the mass Of e t o O t o asolid lubricating compounds and particularly to tion of oil pockets, but on the contrary, a homothat class of hard, dense and dehydrated or pargeneous soap-like mass is produced. Furthertially dehydrated lubricating compounds primore, it was found that the use of stearic acid 5 marily employed for lubricating bearings carryas the saponifying acid enabled the introduction 5 ing heavy loads at high speeds, such as the drivof a relatively increased percentage of cylinder ing journals of railway locomotives, and com-- stock to be added to the lubricant than would be monly known as drivlng journal compounds or possible, for example, ,with other fatty oils. It eases. was also found that this grease had increased 110 Greases of this character have heretofore been efiiciency over other former greases in use in 1 manufactured by compounding a mineral oil the bearings of locomotive driving journals, parcomprising a viscous hydrocarbon oil such as ticularly under extraordinary conditions, as for cylinder stock with materials embodying the example, when there is such a mechanical irhigher fatty acids, such as tallow with the glyregularity in the mechanism lubricated as to cerol driven on, or a hard, higher member of cause excessive heat. We have observed, howthe fatty acids such as stearic acid; completely ever, that when such hard, dense grease, comsaponiiying the fatty acid by the use of an alkali posed as aforesaid, of mineral oil and sodium such as caustic soda, in an amount slightly in stear'ate with a slight or other excess of alkali excess of the quantity required for saponificais used under normal operating conditions, with an tlon and subjecting the mixture to a high temrelatively low temperatures for this class of perature to dehydrate the same, and to agitation grease, as well as under extraordinary operation to procure homogeneity. The resultant product conditions, as for example, when relatively high thus usually comprises an alkaline grease comtemperatures are reached, there is a loss of the pound containing the said mineral oil and a soda material fed through the perforated plate and soap, such as sodium stearate with a. low perthis results in a high consumption factor which 25 centage of free alkali, and a low percentage of was heretofore considered necessary because no water. It has thus been the practice to produce grease had been developed which met such opa finished grease in which the fatty-acid matecrating conditions without such loss. It is rial is completely saponified and the alkali is thought said loss is due to the excessive cohesiveto' present in a low degree, as for example, one-half ness of the grease or soap particles or to the exof one percent. When stearic acid is employed cessive adhesivesness of said grease to the metal in a grease of this type, a material may be proof the journal or to the excessive and unnecesduced which comprises a solid, relatively hard, sarily high melting point of said grease, or all of tough and compact grease of dense and fibrous said factors, so that while a grease of said type structure, which, when the cake is rubbed with will lubricate under high temperature conditions, as the fingers is somewhat sticky, butdoes not it will, under normal conditions of temperature granulate or permit fragmental particles to be obtaining in service as well as when used in rubbed oh, the particles having a' very high dejournal boxes that tend to heat, feed onto the gree of coherence, and thedensity and firmness bearings too rapidly, either in the form of a dill being substantially equal to the average hard paste or in the form of a softened grease. More no soap. This hard, dense and fibrous structure grease is thus passed through the perforated was considered to be desirable because greases plate of the journal boxes than is necessary to that are too soft or capable of being softened by lubricate the; bearings. The particles of pasty the temperature encountered in service will, in or softened grease thereafter drop off the beardtl such service, be squeezed out of the journal boxes ings and are lost on the roadway. We have an and lost on the roadway while the said hard, found, in many tests, that the amount of grease dense fibrous grease with its high melting point passing through the perforated plate and the of the order of 400 F. or over and its particles loss of such grease was very high. It is there with high degree of coherence will maintain its fore, an object of our invention to produce a h cake form without such excessive softening as new grease which will reduce both the quantity hill to permit the same to be squeezed out of the of'grease passing through the perforated plate, journai boxes. The high melting point of said and the loss of grease without reducing the efgrease resists excessive melting by the high temficiency of the lubricant at all temperatures peratures encountered in service, and it was which will be reached in service, and also to found that when compounded, there is no tenproduce a new grease, the use of which, in addition to reducing said quantity and loss, will at the same time efficiently lubricate the bearing surfaces and reduce the coefficient of friction and the temperature thereof.

By our present invention, we have discovered that if, in compounding, we introduce into our new grease a quantity of fatty acid in excess of the quantity which will be saponified by a given amount of soap-making alkali, thus providing in the finished grease such a relatively low percentage of free acid that will not materially reduce the hardness of the grease or lower the melting point below the proper requirements, we are able, under similar service conditions to reduce the coefficient of friction of bearing surfaces lubricated with our improved grease to a degree materially lower than when said former grease is used, and also to greatly reduce both the quantity of grease so lost and the quantity of grease passing through the perforated plate of the journal box. In other words, by the use of our new grease composition, we procure efiicientlubrication while the quantity of grease passing through the said plate is greatly reduced, and ,we consequently ,save a large part of the quantity of grease which would be consumed if the aforesaid alkaline grease were used in the journal boxes and passed through said perforated plate.

It has been observed also that while the consumption of the aforesaid highly cohesive alkaline grease in service is excessive at all journal temperatures reached in service, the rise in such consumption up to approximately 270 F. is gradual and uniform, but when said temperature of the surface of the journal reaches 270 F., the rate of consumption of such highly c0- hesive alkaline grease increases very rapidly and abruptly with any further increase in tempera- .any higher temperatures of said bearing surface which may be reached in service. We believe, as above indicated, that this superior performance of our new grease is due to the difference in cohesiveness of the particles in relation to each other and/or to the reduced adhesiveness of our new grease to the metal of the bearings.-

It is-also our understanding that the use of our new grease causes the passage through said plate of a better and more efiicient lubricating film with a consequent great reduction of the percentage of loss of grease. We have been enabled to accomplish this result at varying speeds or revolutions per minute and with varying temperatures, including the relatively high temperatures accompanying high speeds and/or imperfect equipment. The percentage of free acid should preferably be between one-half of one percent and ten'percent by weight of our grease, depending on the characteristics of the grease it is desired to compound and upon the characteristics of thematerials used in this compound. We have found that when a grease of the character described is produced embodying free acid amounting to five percent (5%), the percentage of loss in use is reduced to a mini mum, and this, of course, will result in great economy. We have found that a grease such as described containing five percent (5%) offree acid will reduce such percentage of loss at speeds varying from 300 to 1000 R. P. M. to an extent which will result in saving of over fifty percentv of the quantity of grease heretofore used in lubricating a given bearing. Our invention, therefore, contemplates the preparation of a grease of the character described, which will not only be free from alkali, but which will contain a percentage of free fatty acid, suflicient to accomplish the purpose hereof, which may be on the order of one-half of one percent to ten percent by weight of the finished grease. We thus reduce the excessive coherence of the soap and/ or grease particles, also reduce the excessive and unnecessarily high melting point of the grease to the order of 360to 390 F., and also reduce the coeflicient of friction of bearings lubricated with said grease.

In order more fully to specify the ingredients Percent Stearic acid 48.00 Cylinder stock oil 44.

Sodium hydroxide (approximately 95%)- 7. 05

In preparing our preferred form of compound, these ingredients were compounded in an opentop steam-jacketed kettle of large enough capacity to prevent the mass. from overflowing the kettle. We preferably first introduce the stearic acid, then the mineral oil, in part or whole, heated to permit convenient handling, is run into the kettle, after which suflicient heat is applied to melt the stearic acid, such heat preferably being applied at approximately 200 F. during this period. Agitation is begun so soon as the stearic acid is partially melted to assist in the melting, and when the stearic acid is completely melted, the mixing is substantially completed at the same time. The alkali, preferably comprising the percentage indicated in the above formula of' sodium hydroxide which has been previously prepared by heating granular caustic soda with a small quantity of water to bring it into suitable form, is now added to the stearic acid and oil, agitation being continued during the introduction of this alkaline ingredient.

Shortly after the addition of the alkaline ingredient, a very violent reaction takes place with a boiling and rising of vapors, and an autogenous generation of heat, the temperature of the mass being raised to approximately 320 F.

During this reaction, water in the form of steam is expelled from the mass. The heatis preferably turned off just prior to the addition of the off, as aforesaid, water in the form of steam.

formula hereinafter all So soon asthe reaction is complete, the bulk of the material begins to decrease and descend in the kettle and to pull away from the sides. At this time, the material is a relatively dry, spongy or gummy mass. Heat with agitation is now applied, a temperature of approximately 350 F. being preferred, for the purpose of softening the compound to bring it into a doughy form, in which form it may be caused to flow and be drawn from the kettle. Agitation is preferably continued throughout this period until the compound is removed from the kettle.

The quantity of sodium hydroxide is, in the above formula, measured in relation to the amount of stearic acid so as to provide in the product derived from said formula an excess of acid and in the preferred form of our invention, this excess of acid preferably amounts to, as aforesaid, approximately five (5%) percent of the finished grease and approximately ten percent of the sodium stearate soap content of said grease.

An average analysis represented by the examination of several samples of the above-mentioned lubricant with substantially the above formula gives the following composition:

Percent Free acidity as oleic 4.81 Soda soap 51. 88 Mineral oil 42. 71

Water 60 The above process may be carried out with a single or double pressed stearic acid of light or dark color or with refined stearic acid, but we preferably employ double pressed stearic acid in order to produce a hard grease of suitable melting point. The formula may contain the excess percentage of fatty acid either as stearic acid, oleic acid or other suitable fatty acid, and the free fatty acid in the finished product may consequently be present as oleic, stearic or other suitable acid. We are thus enabled to produce a grease which will have sufiicient hardness and density to meet all conditions of service to which it will be subjected, which will have a melting point of the order of 360 to 390 R, which we find, is sumciently high to take care of all requirements met under service conditions, and we are enabled to incorporate in such hard grease a percentage of mineral oil necessary in conjunction with the free fatty acid and sodium stearate soap to lubricate locomotive journals atall speeds and temperatures encountered in service, and at the same time the use of our improved grease avoids the loss-of greasewhich normally occurswhen an alkaline soda soap grease is employed.- It will be noted that we substitute for a portion of the mineral oil content of the former grease a percentage of fatty acid which in itself has lubricating value. The addition or substitution of this free fatty acid thus enables reduction of the mineral oil, and enables the feeding to the bearing of the quantities of grease which is necessary to lubricate the bearing with a minimum consumption of grease.

We find that our said preferred form of grease comprises at atmospheric temperatures a solid, greenish-brown, relatively hard and dry grease of fibrous structure, that when the cake is rubbed, rubbings, fragments or granular particles can be readily removed; that the structure of the grease appears to be partly fibrous and partly granular; that said dry fibrousstructure is shot or mottied throughout with a myriad of fine oi] globules or pockets composed 'of free fatty acid and cylinder stock, and which, when ruptured cause the release of the oils and the spread thereof, so as to form bands, streaks or areas in the mass saturated with free oil, and we believe that these more loosely held granules or particles and the occluded globules of cylinder stock and free acid, when the grease is used, reduce or assist in reducing the dryness and toughness of the fibrous mass or body; that the coherence of the particles of the grease for each other is greatly reduced with the result that instead of feeding through the perforated plate in a continuously flowing and fast-feeding paste or softened grease, the particles of grease on the surface adjacent to the perforated plate, having less coherence, feed more slowly therethrough and have time to be converted into an eflicient lubricating oil film, and we also believe furthermore, that these oil globules also furnish to the bearing a supply of free oil. We find that the average penetration of the said several samples above mentioned, unworked, approximated ASTM to that the melting points were approximately 384 F.; that the ingredients and qualities of said grease cause it to have greatly increased efliciency in service on bearings of locomotive driving journals, and the like; that the loss'of grease will, as hereinabove specified, be effectively reduced, and we have found that in many cases we are enabled by the use of our preferred compound to reduce the loss of grease more than 50%, thus resulting in great economy of grease and in a consequent reduction of the cost of lubrication per mile.

It will be understood that instead of providing in the formula an excess percentage of stearic acid as hereinabove specified, a similar low percentage, such as five (5%) percent of any suitable vegetable or animal oil, fat, wax or any suitable organic or inorganic compound, as for example, chlorinated oil, hydrogenated fat, fish, vegetable stearins, and the like, may be introduced into the compound in such manner as to cause such material to be present in the final composition as free fatty acid, free oleic acid or similar fatty oil or in original form. It will also be understood that while we prefer to prepare our soap, from well-pressed stearic acid because of its high melting point, and the hardness of the soap produced therewith, various soaps having high melting points may be employed and various fatty oils and/ or fatty acids of high melting point may be used for the making of a suitable soap. For example, animal fatty oils, such as tallow and tallow oils, hydrogenated fats, fish and vegetable stearins having a relatively high melting point may be used or a sodium stearate soap may be prepared from tallow provided, however, that in such case the glycerol in the composition be driven ed to produce a relatively hard and solid grease. It will, furthermore, be understood that in the grease of our invention we employ a high boiling point and viscous hydrocarbon mineral oil having high flash point and fire test and that we prefer to use a parafiine base cylinder stock having a fire test of approximately 600 F. or over, a flash point of approximately 550 F., and a viscosity (Saybolt) at 210 of approximately 195 sec.

Having described our invention, we claim:-

1. A solid driving-journal lubricant of acid reaction comprising a substantially dehydrated, boiled, hard grease, the aggregate parts of which are loosely bound together and composed of substantially equal parts of a viscous'hydrocarbon mineral oil and a hard soap prepared from an alkali and a higher fatty acid in an amount suflicient to neutralize the alkali and to provide in said grease free fatty acid in a quantity amounting to approximately five (5%) percent of the lubricant.

2. A solid driving-journal lubricant comprising a substantially dehydrated, boiled, hard grease, the aggregate parts of which are loosely bound together and composed of substantially equal parts of a viscous hydrocarbon mineral oil and a hard soap prepared from an alkali and a higher fatty acid in an amount suflicient to neutralize the alkali and to provide in said grease free fatty acid in a quantity amounting to less than ten percent of the lubricant.

3. A solid driving-journal lubricant comprising a substantially dehydrated, boiled, hard grease, the aggregate parts of which are loosely bound together and composed of substantially equal parts of a hydrocarbon mineral oil and a hard soap prepared from caustic soda and stearic acid in an amount suflicient to neutralize the caustic soda and to provide in the grease free fatty acid in a quantity amounting to less than ten (10%) percent of the lubricant.

4. A solid driving-journal lubricant comprising a substantially dehydrated, boiled, hard grease, the aggregate parts of which are loosely bound together and composed of substantially equal parts of a viscous hydrocarbon mineral oil and a hard soap prepared from an alkali and a higher fatty acid in an amount sufilcient to neutralize the alkali, and to provide in said grease free fatty acid in a quantity amounting to less than ten (10%) percent of the lubricant, said lubricant also embodying free oil in the form of globules distributed throughout the mass.

5. A solid driving-journal lubricant comprising a substantially dehydrated, boiled, hard grease, the aggregate parts of which are loosely bound together and composed of substantially equal parts of hydrocarbon mineral oil and a hard soap prepared from caustic soda and stearic acid in an amount suflicient to neutralize the caustic soda and to provide in the grease free fatty acid in the form of oleic acid in a quantity amounting to less than ten (10%) percent of the lubricant.

CHARLES A. MILLER. DAVID A. SMITH.