Description:
Field of the Invention
This invention relates to a system of a synthetic lubricant and a fluorocarbon refrigerant employed in centrifugal compressors for refrigeration air conditioning and allied uses.
BACKGROUND OF THE INVENTION
In providing air conditioning for office buildings, stores, apartments and motels, for example, it is desirable and important to provide quiet, low vibrationn compressors that are compact and occupying the smallest possible space for the power needed to provided the requisite heat removal under expected conditions. Many of these air conditioning units employ chilled water, produced by the heat exchanger associated with the compressor, to effect suitable conditioning of the air in the building.
Piston type units are not only relatively large for a given horsepower but they are noisy and vibrate. Centrifugal compressors driven by, for example, 50 to 600 horsepower electric motors have been found to be much more compact so that they occupy only a fraction of the space required for a piston type unit of the same horsepower. Furthermore considering the horsepower, the high speeds of up to 36,000 rpm of the centrifugal compressor, and large volumes of refrigerant handled per unit time, the compressor units are extremely quiet and are characterized by very little vibration.
However, a serious problem has been encountered in the starting of centrifugal compressors. The start-up of a centrifugal unit from a cold condition, nominally 60°-75°F, to a fully operational condition has often taken several hours. Under all conditions, a separate oil pump unit is first set in operation to deliver a flow of lubricating oil to the bearings, gears and oil-operated control mechanism, and only after an adequate flow of lubricant has been established, is the centrifugal compressor put into operation. Initial high thrust loads are encountered in the impeller bearings requiring good lubricant films to be present at all times when in operation.
This prolonged delay in a cold start occurs because of the high solubility of the fluorocarbon refrigerant, usually refrigerant 12, dichlorodifluoromethane, hereinafter referred to as R-12, in any of the otherwise satisfactory lubricating petroleum base oils used for lubricating the bearings and gearing of the centrifugal compressor. The fluorocarbon refrigerant comes into contact with the lubricant in the normal operation of the centrifugal compressor. Large volumes of fluorocarbon gas dissolve in cold oil because the solubility of the fluorocarbon gas increases as temperature drops, and when the oil is being pumped to the compressor rotor and bearings the dissolved fluorocarbon refrigerant readily boils out as a gas as a result of even small changes in pressure or temperature. Frequently, the oil or lubricant is flushed from the bearings during shutdown so that the bearing is dry and presents a highly undesirable dry metal to dry metal contact condition at the time start-up is required. On a cold start-up, oil in the oil sump is saturated with fluorocarbon which drastically dilutes the oil, and which fluorocarbon boils out of the oil lubricant to produce large volumes of foam both in the sump and in the oil lines, as well as in the bearings and at other places in the oil circuit when the oil pump is set into operation to convey oil or lubricant to the bearings, gears, and elsewhere. Unless the oil is still hot from previous use, insufficient oil will flow to the bearings and at most an initial fluorocarbon-oil foam is present which is inadequate to accomplish effective lubrication. Failure of the bearings will occur if the compressor motor is started under these poor lubricating conditions. Further, the viscosity of the oil is reduced seriously by the dissolved fluorocarbon so that the lubrication properties of the oil are deleteriously modified by this unwanted dilution. This is in addition to the danger that a sudden release of gas in the oil film on the bearing surfaces will cause a partial oil film failure which permits bare metal to bare metal contact with the potential for bearing damage.
At the present time, one involved procedure to mitigate this lubrication problem in centrifugal compressors is to provide a heater in or about the oil sump -- so that the oil will be heated up to and maintained at, for instance, 150°F to minimize the amount of the fluorocarbon refrigerant, such as R-12, in solution in the oil, which at this temperature comprises some 11%.
In order to avoid the continual use of the heaters for lengthy shutdown periods, at start-up the oil sump is initially heated for several hours (using for instance 5 KW heaters) in order to drive out as much fluorocarbon from the progressively heated oil as is reasonably possible before actual operation of the oil pump of the compressor. The oil pump is then energized to pump the hot oil with low fluorocarbon content through the oil lines and into the bearings. In these latter areas, the oil is cooled by contact with the cold metal and redissolves more fluorocarbon and the cooled oil with a large quantity of dissolved fluorocarbon flows through the oil lines, bearings and gear case and reenters the sump where it is reheated. Circulation of the hot oil continues for a period of time, often several hours, until all the oil lines, bearings and the like are sufficiently hot so that a reduced amount of fluorocarbon gas dissolves therein. When the bearings and gears are satisfactorily flooded with hot lubricant at the end of this time period, the centrifugal compressor motor may be started and the compressor safely put into operation. Of course, once the compressor is in full operational condition, the heaters on the oil sump must be turned off and the usual oil cooler be employed to cool the oil to some normal temperature of use. Unless these precautions are taken, and a precise start-up schedule is followed, failure of the bearings of the centrifugal compressor will occur.
These problems and requirements of centrifugal compressors are set forth in an American Society of Mechanical Engineers Paper No. 62-WA-179, entitled: "Internal Bearings in Centrifugal Gas Compressors" and presented sometime in Novemeber 25-30, 1962 before a meeting of this society.
The chemical stability of the lubricants for a centrifugal refrigeration compressor is an important factor since the systems are hermetically sealed and any reactions with the fluorocarbon refrigerant which cause deterioration of the lubricant so that it decomposes,, and fails to provide adequate lubrication or reacts to form solids which will plug up tubing and orifices, as well as lead to its failure to function effectively as a lubricant, is fatal to the compressor system. Metals such as iron, aluminum and copper used in compressors are commonly in contact with the lubricant, and the fluorocarbon, of course, dissolves in the lubricant. This combination of materials at elevated temperatures will react adversely to cause the oil to fail ultimately, the better lubricants, of course, lasting much longer. Alcohols, glycols, and triols, for example, exhibit considerable reactivity with these metals while associated with the fluorocarbons even at temperature of 80°C so that these hydroxy compounds react in a few weeks to produce solids. The chemical deterioration of these alcohols accelerates very rapidly upon exposure to higher temperatures. For example, tetraethylene glycol kept at 80°C in contact with iron, aluminum and copper in the presence of dichlorodifluoromethane completely solidified in three weeks. These hydroxy compounds would be completely unacceptable as lubricants for centrifugal compressors even if they were otherwise satisfactory.
Esters of castor oil and esters of ricinoleic acid have been prepared heretofore. In some of the prior art patents and publications, it has been indicated that some of these castor oil esters and ricinoleic acid esters are suitable for metal cutting or drawings lubricants. Thus, U.S. Pat. Nos. 3,634,245 and 3,720,695 discloses castor oil trans-esterified with polymeric alkylene oxide glycols which esters are water soluble compounds suitable for use as die lubricants. The indicated application for these esters is primarily for lubricating the surfaces of metal forming dies, such as are used for cold or hot reducing steel, hot metal cutting and grinding operations, as well as wire drawings. German patent 1,132,123 is directed to the preparation of lubricants by reacting ricinoleic acid with polyethylene glycols. British patents 573,202; 591,421; 590,386; and 657,750 are directed generally to the manufacture of ricinoleic esters as well as other esters for use as lubricants in automobile engines and the like. None of this art listed teaches the employment of any of these esters in refrigeration machinery where it would be in contact with a fluorocarbon.
SUMMARY OF THE INVENTION
In accordance with this invention centrifugal refrigeration compressors employing a fluorocarbon refrigerant are lubricated with certain synthetic diricinoleic acid esters of selected glycols, which avoid these prior art problems, so that the centrifugal compressors can be safely and satisfactorily started at any time with no appreciable delay. The synthetic esters employed in the system of this invention are excellent lubricants, having a suitable viscosity of from about 200 to 600 SUS at 100°F and from about 40 to 90 SUS at 212°F, and a low pour-point of from about -30° to -40°F, satisfactorily meeting the requirements for the centrifugal compressors, they also have excellent anti-wear properties enabling their eminently successful use for lubricating gears and the like in this application, and have sufficiently good thermal stability properties in the presence of the fluorocarbons and metals so that no chemical failure will occur in reasonably expected service for an acceptable lifetime of many years. These esters also have the prime characteristics of dissolving only small amounts of fluorocarbon refrigerants such as dichlorodifluoromethane (R-12), so that excessive foaming and other previously encountered difficulties are avoided.
The synthetic esters exhibiting this unique combination of properties are the diricinoleic esters of 2 to 5 carbon atom hydrocarbon glycols, and particularly, ethylene glycol, propylene glycol 1,4-butanediol, and 1,5-pentane-diol. Mixture of two or more of the glycols can be employed. Small quantities of lubricant additives may be incorporated in these esters -- examples being extreme pressure lubricating additives such as dodecylmonochlorodiphenyl oxide and other anti-wear agents, such as tricresyl phosphate.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical cross-section through a portion of an exemplary centrifugal refrigeration compressor; and
FIG. 2 is a schematic diagram with portions in cross-section of a centrifugal refrigeration compressor.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 of the drawings there is shown a vertical cross section through a portion of a typical centrifugal refrigeration compressor 10. The refrigeration compressor comprises a motor 12, for example from 50 to 600 horsepower, within a casing 14. The casing 14 includes bearings in which is mounted a motor drive shaft 18 extending through a bearing 16 into a gear compartment 20, with the right-hand end of the shaft being supported in a bearing 21. The portion of the shaft 18 in gear compartment 20 is provided with a large driven helical spur gear 22 driving smaller gear 24 affixed to a centrifugal impeller shaft 28. The ratio of the diameters of gears 24 and 22 is of the order to 10:1 so that when motor 12 is operating at 1800 rpm the compressor shaft will be rotating at a speed of 18,000 rpm, while a 3,600 rpm motor may drive the compressor at from 32,000 to 36,000 rpm. The ends of centrifugal impeller shaft 28 are mounted in bearings 32 and 34. Lubricant is supplied to the bearings 16, 32, 34 through channels 36, 38 and 40 from a main lubricant manifold 42. Bearing 21 is lubricated by a lubricant manifold 23. Because of the high speeds and high power being transmitted to the impeller it is mandatory that a large volume of lubricant be supplied to the bearings at all times during the operation of the compressor. An oil or lubricant mist escapes from bearings 16, 21, 32 and 34 by reason of shaft clearances into the gearing casing 20, the high speed of the shaft 28 in particular throwing out the oil as a mist which impinges on and lubricates the gear teeth of gears 22 and 24.
Upon the extreme right-hand end of the shaft 28 is mounted a centrifugal compressor impeller 44 having an inlet end 46 adjacent the right-hand end of the shaft hub and an exit portion 48 at which hot compressed refrigerant gases are expelled under pressure into a refrigerant gas mainifold 50 from where they flow to a suitable condenser (not shown). Refrigerant gas enters through a relatively large gas inlet conduit 52 at the extreme right-hand end of the compressor, as shown in FIG. 1. Admission of the fluorocarbon gas in conduit 52 to the inlet end 46 of the compressor is controlled by a series of circumferentially positioned inlet vanes 54 pivotally mounted in the conduit 52 in front of the inlet end of the centrifugal impeller. The vanes 54 are rotated to a desired gas flow control position by a piston member 56 having portions affixed to eccentrically placed pins on the vanes 54, which piston member moves in response to admission of lubricant under pressure to one or the other end thereof in response to amounts of refrigerant needed as determined by a vane control sensor mechanism (not shown) to move the vanes 54 to any position between fully open and a substantially closed position. Consequently flow of fluorocarbon refrigerant gas to the centrifugal impeller is controlled by this vane and piston mechanism.
In order to secure a high output from the electrical motor 12, it is a common practice to spray condensed, liquid fluorocarbon refrigerant on the motor windings in order to absorb heat therefrom so that the motor will be cooled adequately to a safe operating temperature when high electrical power input is applied thereto. Because of this enhanced cooling an extremely small, in physical size, motor can be employed to deliver the necessary horsepower to the centrifugal compressor proper.
Referring to FIG. 2 of the drawings, there is illustrated schematically the distribution of lubricant to the centrifugal refrigeration compressor of FIG. 1. An enclosed oil sump and pump unit 60 encloses a motor 62 operating a pump 64 disposed within the lower portion thereof where it is immersed within a reservoir of lubricant 66 which will ordinarily be present at some level therein at all times. Lubricant escaping from the bearings, gears casing, and the vane control system, enters by way of a conduit 68 into the sump 60. The oil returning to the sump conduit 68 has been exposed to and has dissolved therein fluorocarbon refrigerant. The amount of dissolved fluorocarbon refrigerant for example, R-12, is related to the gas pressure and the temperature of the oil. The previously referred to article in the American Society of Mechanical Engineers publications contains a FIG. 3 which correlates the pressure and temperature of the oil to the solubility of R-12 refrigerant in petroleum base oils. Thus, when the oil is at 140°F and at a pressure of 70 psia, the amount of R-12 fluorocarbon dissolved therein will be approximately 12%. However, at 70°F and at a pressure of 70 psia the percentage of R-12 dissolved therein will be of the order of 50%.
When the pump 64 is energized, oil under pressure is conveyed through a pipe 70, passing first through a filter 72 to remove any solid particles therefrom and then through an oil cooler 74 to reduce the temperature of the oil. The cooled oil then is conveyed by a pipe 76 to manifold 23 and thence to the right-hand end bearing 21, supporting motor shaft 18, and also through a pipe 78 to the oil manifold 42 from where an abundant flow of oil is directed to the bearings 16, 32 and 34. In addition, oil is conveyed through conduit 80 to a vane control mechanism 81 operated by a suitable sensor (not shown), which feeds requisite amounts of oil through lines 82 and 84 to the vane control piston 56.
It has been found that if the oil in sump 60 is relatively cold and contains large amounts of dissolved fluorocarbon gas such as R-12, upon operation of the pump 64 and when the impeller 44 is started, the pressure in the sump will drop and immediately a large amount of oil fluorocarbon foam will be produced in the sump. Furthermore, as the cold oil still with substantial amounts of fluorocarbon dissolved therein passes into pipe 70 more fluorocarbon gas will evolve and the pipe, filter 72 and the oil cooler 74 will be filled with a foam. Some of the foam will pass through the oil separator where the oil is centrifugally spun off, and oil free fluorocarbon gas flows from connection 69 via a conduit to inlet 52 of FIG. 1. When a highly foamed oil containing substantial amounts of dissolved fluorocarbon is directed to the bearings, both its quantity and viscosity will have been reduced by reason of the foaming and the presence of the large volume of fluorocarbon liquid components therein so that the bearings will not have a sufficient amount of oil of a proper viscosity and load bearing film forming properties on the surface in a condition to provide effective lubrication. If the centrifugal compressor motor 12 were to be caused to operate under such conditions, bare metal to bare metal contact of the bearing surfaces is liable to occur, with excessive and rapid wear of the bearings taking place which could lead to catastrophic premature failure. Oil escaping from the shaft bearings enters gear casing 20 where it collects and absorbs more fluorocarbon gas and reenters oil drain line 68 (FIG. 2) and thus goes back to the sump 60.
The solubility of an R-12 fluorocarbon refrigerant in good grade petroleum base lubricants employed in centrifugal refrigeration compressors is high. Thus, in commercial naphthenic base petroleum oils used widely for such centrifugal compressors, and sold on the market under the Trade Mark Suniso 5GS and Suniso 4GS, the solubility of fluorocarbons is as follows: At 26°C (78°F) the solubility of R-12 gas (96 psia) in both 5GS and 4GS lubricants is about 60% by weight or 43% by liquid volume. R-12 liquid in contact with these two lubricants is infinitely soluble. Furthermore, at lower temperatures, the solubility of R-12 gas in these lubricants is even greater. In a cold start with the oil sump 60, FIG. 2, at say 60°F, the volume of absorbed gas in the oil would be so great that it may take several hours or more of heating of the oil sump to bring its temperature up to, for example, 140°F to drive out most of the R-12 gas. Then the pump such as 62-64 in FIG. 2 must be set in operation and the oil caused to flow through the pipes and through the compressor bearings for a considerable period of time in order to heat up the metals to a temperature approaching that of the oil before it would be safe to rely upon the oil to lubricate the compressor bearings and gears adequately so that the high speed rotor impeller 44 may be started and the compressor rendered effective for its refrigeration use proper.
In accordance with the present invention, it has been discovered that a unique combination of properties not heretofore known, are possessed by the diricinoleate esters of 2 to 5 carbon atom hydrocarbon diols, and particularly ethylene glycol, polypropylene glycol, 4-butanediol and 1,5-pentanediol. Tests were performed by exposing each of these ricinoleic diesters to R-12 gas at the indicated pressure for a period of time to determine the solubility of the gas therein. The following table sets forth these data along with data for the Sunisoc 5GS and 4GS lubricants:
TABLE I ____________________________________________________________
______________ Tests of Solubility of R-12 in Various Organic Fluids at 23°C Fluid Class and Species Pressure - PSIG Mineral Oils: Initial 3 hrs. (ΔP) 24 hours (ΔP) ____________________________________________________________
______________ Suniso 5GS 54 34.5 (19.5) 29 (25)* Suniso 4GS 57 34. (23.) 28.25 (28.75)* Ricinoleates Castor Oil 55 49 (6) 37 (18) Ethylene Glycol Diricinoleate 58.75 47.5 (11.25) 34 (24.75) Propylene Glycol Diricinoleate 55.25 43. (12.25) -- 1,4-Butanediol Diricinoleate 57. 41.5 (15.5) -- 1,5-Pentanediol Diricinoleate 57.25 43. (14.25) -- Propylene Glycol monoricinoleate 56. 47.5 (8.5) -- ____________________________________________________________
______________ *These values are attained in 8-10 hours and remainded essentially unchanged to 24 hours.
The Δp is indicative of the amount of R-12 gas dissolved in the respective fluid.
Table II sets forth solubility properties of R-12 computed from both liquid and gas absorption weight measurements.
TABLE II ______________________________________ Solubility of R-12 at 26°C in Selected Fluids at 96 psia R-12 Introduced R-12 Introduced as Gas as Liquid Fluid wt. % Vol. % wt. % Vol. % ______________________________________ Suniso 5GS 60 43 Infinite Infinite Suniso 4GS 60 43 Infinite Infinite Castor Oil 21 16.5 22 16 Ethylene Glycol 34 25 41.5 29. Diricinoleate Propylene Glycol 26 20 26 18 Monoricinoleate ______________________________________
It is also necessary that lubricants suitable for centrifugal refrigeration compressors possess certain viscosity-temperature characteristics, and low pour points, in order to function satisfactorily over the expected range of conditions to be met in service. Table III sets forth these viscosity characteristics of the several lubricants of the present invention and others for comparison.
TABLE III ______________________________________ Viscosity (SUS) Pour Fluid 100°F 210°F Point °F ______________________________________ Suniso 5GS 500 52 -35 Suniso 4GS 285 46 -40 Castor Oil 1555 103 -10 Ethylene Glycol Diricinoleate 600 80 -40 Propylene Glycol Monoricinoleate 545 57 -15 Propylene Glycol Diricinoleate 520 69 -30 1,4-Butanediol Diricinoleate 530 72 -30 1,5-Pentanediol Diricinoleate 510 75 -30 ______________________________________
It will be evident from the above data in Table III that the viscosity and pour point characteristics of each of the diricinoleate esters of the present invention are satisfactory and adequate for the conditions. Both castor oil and the monoricinoleate have a poor pour point. Moreover the viscosity at 100°F, of castor oil, is entirely too high to be considered.
As mentioned previously, the thermal and chemical stability of a selected lubricant with respect to the metals with which it will come in contact while associated with a refrigerant such as R-12, are critical factors. While the compressor does not heat the refrigerant gas at its outlet end to a temperature much above 70°C, in order to complete tests within a reasonably short time, accelerated aging tests which were conducted at higher temperatures are set forth in the attached Table IV.
With regard to thermal and chemical stability, the standard "sealed tube test" has been utilized. This test is described in detail by H. Elsey in "Small Sealed Tube Procedure for Quality Control of Refrigeration Oils", 71 ASHRAE Transactions, Pt. 1, p. 143 (1965). Generally, this test involves introducing equal amounts of lubricant and refrigerant and samples of the compressor metals employed with which the lubricant and refrigerant come in contact, into a clean, dry glass tube which is sealed and heated to the requisite temperatures and held for a long period of time. These tubes are visually inspected from time to time for changes in color and appearance of the lubricant, the metals and any reaction products or solid deposits.
TABLE IV ______________________________________ Chemical and Thermal Stability Tests Toward R-12 In Presence of Fe, Al and Cu - Sealed Tube Tests Weeks to Failure Fluid 80°C 100°C 125°C ______________________________________ Suniso 5GS -- -- 50-55 Suniso 4GS -- -- 45-50 Tetraethyleneglycol 3 -- -- Castor Oil -- -- 44 (Still on Test) Ethylene Glycol Diricinoleate -- -- 40-48 Propylene Glycol Diricinoleate -- -- 36 Propylene Glycol Monoricinoleate 37 37 13 ______________________________________
Experience has shown that most of the chemical reactivity reactions involved follow the 10°C rule, namely that a reaction rate doubles for each 10°C increase in temperature, or conversely, halved for each 10°C drop in temperature. For this reason, tests were conducted at 125°C on most of the compositions, to accelerate any deleterious reactions which occur. Some of these endured nearly a whole year. Tests were conducted at 80°C and 100°C on the poorest material, the monoricinoleate ester.
The ethylene and propylene diricinoleate are shown to have the same order to chemical stability toward R-12 at 125°C, as the currently used naphthenic base refrigerator oils, Suniso 4GS and 5GS.
Clearly, the propylene glycol monoricinoleate is inferior to the other fluids tested, and is not considered therefore, like a satisfactory candidate.
A number of tests are customarily employed in the art in order to determine the wear characteristics and load carrying capacities of lubricants. Tests made show that the lubricant diricinoleic acid -- glycol compositions of the present invention have satisfactory properties in these areas. A standard test known as the Falex lubricant test is well recognized in the art. Briefly, two test blocks having V grooves are disposed on either side of a rotatable pin driven by a motor at 290 rpm and a pressure is applied to the V blocks up to a maximum of 4500 lbs. The V blocks and rotating shaft are immersed in the lubricant being tested which is heated to a predetermined standard temperature and the motor operated over a period of several hours. The wear of the pins in this instance, when operated at 250 lb. gauge pressure is expressed in standard units per hour. The lower the wear units per hour, the better the lubricant. The pin and blocks are prepared from standard steels which have been found to be readily correlated with many bearing steels. The following Table V sets forth Falex wear tests and Falex seizure tests performed on the lubricants of the present invention together with that obtained on several other prior art lubricants, for comparative purposes. It will be observed that the lubricants of the present invention exhibit wear rates substantially less than the best prior art hydrocarbon oils used previously. For comparison purposes, there are also included in the Table Falex extreme pressure (EP) tests which gives data on the lubricating ability of the lubricants in terms of maximum load carrying ability to the point of failure.
TABLE V ______________________________________ Falex Wear Tests and EP Data on Lubricants Lubricant Weat Test* EP Test** ______________________________________ Suniso 5GS 9 units/hr. 1000 lbs. Suniso 4GS 9 units/hr. 1000 lbs. Castor Oil 2 units/hr. 1600 lbs. Ethylene Glycol Diricinoleate 2 units/hr. 1700 lbs. Propylene Glycol Diricinoleate 4 units/hr. 1600 lbs. ______________________________________ *250 lb. gauge, SAE 3135 Pin, and SAE 1137 Block, 290 rpm **Gauge pressure at seizure.
These data indicate that the diricinoleate esters of the present invention are superior to the commercial hydrocarbon oils widely used for centrifugal compressors.
A recently devised test known as the Ryder 4-square gear test is frequently used to evaluate the load carrying capacity of lubricants involved in the lubrication of gears. This test is outlined in Federal Standards Number 791, Method 650.8, as required in ASTM D-1947 Specification. Briefly, in this test, an oil is evaluated in a standard 4-square gear machine at increasing loads under controlled conditions. The amount of tooth face scuffing occurring at each load increment is measured. The percentage of tooth face scuffing is plotted against the load to determine the load carrying capacity of the oil under these tests. The test gears used in this test are special spur gears made of case hardened and ground SAE 9310 steel. This steel is the same composition as that which is used commercially for producing the gearing in the compressor of FIG. 1. Test data comparing Suniso 4GS and ethylene glycol diricinoleate using the Ryder test results are set forth in the Table VI.
TABLE VI ______________________________________ Ryder 4-Square Gear Tests Fluid Gear Side Load Carrying Capacity ______________________________________ Suniso 4GS A 1675 in. lbs. Suniso 4GS B 1268 in. lbs. Average 1472 in. lbs. Ethylene Glycol A 3936 in. lbs. Diricinoleate Ethylene Glycol B 3446 in. lbs. Diricinoleate Average 3691 in. lbs. ______________________________________
The totality of the above tests clearly indicate not only the superiority of the diricinoleate esters of the present invention in terms of excellent thermal stability improved wear, load bearing capacity and other properties in standard lubrication tests, but also the outstanding freedom from adverse effects due to the relatively low solubility therein of such refrigerant fluorocarbons as R-12.
The diricinoleic acid-glycol esters may be prepared in accordance with the prior art esterification practices. It is desirable to remove any unreacted glycols and mono-ricinoleates therefrom by appropriate vacuum stripping. Esterification catalysts also should be removed in order to avoid any undesired reactions when the esters are used as disclosed herein. Minor proportions of other lubricants may be added to the glycol diricinoleate esters of this invention. Low viscosity ricinoleates such as methyl ricinoleate may be added in amounts of, for example, 2 to 10%.
A number of commercial type centrifugal compressor units were tested with (1) the best available petroleum base oil lubricants and (2) with ethyleneglycol diricinoleate esters of the present invention.
The first unit extensively tested was a 500 horsepower (480 Ton) unit which required about 12 gallons of a lubricant-either Suniso 4GS petroleum base oil or the ethyleneglycol-diricinoleate ester of this invention. The unit employed several hundred pounds of R-12 refrigerant. With the petroleum base oil, after the unit had stood for 4 to 6 hours at 70° to 80°F, with a sump refrigerant pressure due to the R-12 gas of from 60 to 70 psi, considerable difficulty was experienced in attempting a start-up. Foaming was so extensive after the oil pump in the sump was started that an automatic trip operating upon excessive oil pressure drop in the oil line, made it impossible to start the centrifugal compressor motor and have it keep running.
Therefore, 5 to 6 KW of immersion heaters were applied to the oil sump to heat the oil to about 130°F so as to reduce very substantially the amount of R-12 refrigerant dissolved in the oil. After several hours of heating and operating of the oil pump, the main 500 horsepower motor was turned on. It usually tripped out several times because of inadequate oil pressure, in the line, due to foaming, to the bearings before the compressor began to operate steadily. Once the centrifugal compressor ran for a short period and the entire batch of oil in the sump because hot enough to reduce sharply the volume of dissolved R-12 refrigerant, the unit was very effective.
When the ethyleneglycol diricinoleate was substituted for the petroleum oil, in the same unit, the centrifugal compressor started and ran without any trip outs within a minute after the oil pump was started.
In another test, in an 83 ton unit, after many hours of standstill, the temperature of the diricinoleate ester in the sump was 80°F. The oil pump was started and the viscosity of the cold diricinoleate ester lubricant was relatively high so that the oil pump was pulling a high current of from 5.5 to 5.9 amperes in order to cope with the thick lubricant: this is a roughly 40% overload since under normal load conditions the oil pump motor pulls from about 4.4 to 4.6 amperes. The Table VII sets forth the lubricant pressure in the oil line, R-12 gas pressure at the suction end adjacent vanes 54, (FIG. 1) the compressed gas pressure in manifold 50, the R-12 gas pressure in the lubricant sump, the amperage to the oil pump, and the temperature of the ethyleneglycol diricinoleate ester in the lubricant sump.
TABLE VII ____________________________________________________________
______________ Data Obtained on Start of 83 Ton Unit Lubricated With Ethyleneglycol Diricinoleate Time - Minutes 0 1 2 4 6 8 10 30 50 75 105 ____________________________________________________________
______________ Main Rotor Oil Pressure psig -- On 225 205 203 202 200 -- -- -- -- Gas Suction Pres.-psig 78 " -- -- 37 36 36 30 34 54 33 Gas Discharge Pres.-psig 78 " -- -- 90 91 93 -- 107 128 82 Gas Sump Pres.-psig 78 " 51 34 34 31 30 30 34 40 27 Oil Pump - Amperes average -- " 5.5 5.9 5.0 5.0 4.8 4.6 4.55 4.42 4.6 Sump Temp. °F 80 " 84 86 89 93 100 108 117 124 121 (No record made of suction or discharge pressure during initial phase) ____________________________________________________________
______________ Note: No excess foam evident in any of the above test observations.
A number of starts were made with hot ethyleneglycol diricinoleate lubricant in the centrifugal compressor oil sump. Within 30 seconds of starting of both the oil pump and the centrifugal compressor motor, the machine was in full operation with very little foam evident and ran successfully for a full half hour until the tests were ended. With petroleum oil lubricant under the same conditions of temperature pressure, the start of the oil pump tended to generate a large volume of foam and several trip outs, due to automatic safety controls responsive to low oil pressure, were sometimes encountered before the main centrifugal compressor ran properly.
Tests were also made comparing Suniso 4GS petroleum oil lubricant with ethyleneglycol diricinoleate ester lubricant in a 83 ton centrifugal compressor unit. As far as bearing temperatures, lubricant pressure and sump conditions were concerned, the tests indicated that the properties were comparable in lubrication over the centrifugal compressor range of speeds of from 10,000 to 31,800 rpm.
These tests confirm that the diricinoleate ester lubricants of this invention have the necessary properties overcoming the major problem of re-starting centrifugal refrigeration compressors.
The term "fluorocarbon refrigerant" denotes hydrocarbons, usually from one to three carbon atoms compounds, wherein fluorine and chlorine have replaced all or nearly all of the hydrogen atoms. Mixtures of fluorocarbon compounds may be employed.