US3129185A

US3129185A - Lubrication of refrigeration equipment

Info

Publication number: US3129185A
Application number: US161236A
Authority: US
Inventors: Carl J Rizzuti; Harold M Brewster
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1961-12-21
Filing date: 1961-12-21
Publication date: 1964-04-14
Anticipated expiration: 1981-04-14
Also published as: GB993641A

Description

United States Patent 3,129,185 LUBRIQATION 0F REFREGERATION EQUEPMENT Carl J. Rizzuti, Bronx, N.Y., and Harold M. Brewster,

Hillside, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Dec. 21, 1961, Ser. No. 161,236 11 Claims. (ill. 25268) This invention relates to the lubrication of refrigeration equipment, the compositions used in such lubrication and their preparation.

'In general, refrigeration equipment falls into two classes, that is, those which have: (a) compressors having a shaft seal with an external motor drive; and (b) hermetically sealed unit compressors with a direct shaft drive and having an internal motor operating directly in the oil and refrigerant mixture. In the hermetically sealed unit the motor heat is liberated within the compressor shell, whereas in the shaft seal type the motor heat is liberated externally. In the shaft seal type, oil temperatures rarely exceed 125 F.; in the hermetically sealed type, they can reach as much as 225 F. under severe operating conditions. Furthermore, in the shaft seal type of compressor it is relatively easy to remove the oil charge and replace with fresh oil.

In the hermetically sealed unit compressor it is so difficult to remove the refrigerant charge and the oil that it is conventional to consider the original oil charge as the lubricant for the operating life of the machine. This type of compressor has a long operating life, i.e., at least ten years. Therefore, the difliculty of removal, together with the high operating temperatures, has placed entirely new demands upon the chemical stability of the lubricant used.

Moreover, the design of some type of hermetically sealed units, such as the single vane rotary, requires the lubricant to be a very efficient sealing agent. In the reciprocating design, the lubricant film is spread over the entire area of contact between the piston and the cylinder wall, so that there is a very large sealing area to resist leakage of refrigerant from the high to the low pressure side. In the single vane rotary type, however, the only sealing area is a line contact between a vane and a roller. Yet, this oil film is expected to prevent leakage just as efliciently as in the older type of reciprocating compressors. Since the viscosity and sea-ling power of oil are diluted to some extent by solution of the refrigerant in the oil, it can readily be seen that these requirements are very stringent.

Recently there has been a pronounced trend towards the use of halo-hydrocarbon refrigerants. These halogensubstituted hydrocarbon refrigerants can be of the methyl chloride, methylene chloride or Freon type and they are characterized by the presence of carbon to-halogen bondings. These refrigerants are known largely by their trade names and include Carrene 7 (CCl F -l-c HrF Freon -11 (CCl F), Freon-12 (COI F Freon-13 (COIF Freon-21 (CHCl F), Freon-22 (CHClF Freon-113 (C Cl F and the like.

In actual service chemical bonds, particularly the chlorine-to-carbon bondings, tend to break, releasing free chlorine, free fluorine, or free radicals containing chlorine or fluorine into the mixture of refrigerant and lubricating oil. Free halogen or free radicals containing halogen tend to hydrolyze and attack the oil components, thus forming mineral and organic acidic products which further attack the oil and promote sludging as well as a phenomenon known as copper plating.

3,12%,l55 Patented Apr. 14, 1954 Every refrigeration system contains some copper. In ordinary reciprocating compressor systems, the quantity may be confined largely to the connecting lines. In sealed rotary compressors, for example, the motor windings are in direct contact with the oil and refrigerant in the system. A chemical reaction occurs. The copper in contact with the oil and refrigerant is dissolved and goes into solution. It then tends to plate out on the surfaces of other metals but most usually on steel surfaces. Since bearing surfaces are usually the brightest, cleanest, and most highly polished in the system, the deposition occurs preferentially at these points. Where tolerances are very close, the deposited copper may increase to such a thickness that binding and galling of such a surface may occur. This can lead to quite a serious situation. For instance, in certain types of rotary compressors, where tolerances are of the order of one ten-thousandth (0.0001) of an inch, this deposition may eventually result in the failure of the system.

As a result of observations with respect to copper plating in the presence 'of refrigerants alone, it is now believed that the refrigerant is the dominant factor in the plating reaction. The theory is that small quantities of moisture present in the system produce a slow chemical hydrolysis of even the most stable halogenated refrigeranteven those of the well-known Freon type. In fact, microanalytical methods have demonstrated the presence of chloride and fluoride ions in corrosion deposits found in refrigeration systems. 7

It has now been discovered and forms the substance of this invention that the severe sludging and copper plating of refrigerator compressor lubricants caused by the highly acidic products formed during refrigerant breakdown can be overcome by the inclusion of certain oil soluble metal soaps in the lubricant. The preferred class of metal soaps are metal naphthenates although oil soluble salts of other organic acids, e.g. fatty acids such as metal octoates and the like, can also be used. The metals can be chosen from groups IA, IB, II, 1113, Ill-B, and VH1 of the periodic table. Specific suitable metals include sodium, copper, calcium, zinc, mercury, cadmium, aluminum, iron, cobalt, nickel. Zinc, cadmium and nickel are especially preferred.

Naphthenic acids are derived from petroleum stocks and should preferably be obtained from fractions having a boiling range at least as high as that of kerosene or lubricating oil cuts although, in some instances, naphthenic acids obtained from. lighter cuts, such as the naphtha fraction, can be used. The most desired naphthenic acids are those containing at least one cyclic nucleus and, preferably, containing more than 8 carbon atoms. They are usually, though not necessarily, monocarboxylic acids conforming to the general formula: Rnl-LpO where n is an integer between the limits of 7 and 23, x ranges between 2n2 and 2n4, and R is an aliphatic radical having from 1 to 25 carbon atoms and can contain aryl substituents. The preferred naphthenic acids have molecular weights of from about 250 to 350 and neutralization numbers of from about 150 to 225.

In the past, refrigeration grade lubricating oils were almost universally derived from naphthenic base crudes. They were Well refined pale oils characterized by good stability, low carbon residue, low floc test, low pour point, medium flash and fire points, and a low to medium viscosity index.

The lubricating oil base stocks which can be used in this invention are generally highly naphthenic type oils but can also be parafiinic base oils. They will generally have a viscosity of from 65 to 600 SUS at 100 F., e.g. to SOO'SUS at F., a specific gravity of from 0.80 to 0.95, e.g. 0.85 to 0.93, a pour point of from -45 to +15 F., e.g. 35 to +5 F., a floc point of 100 to F., e.g. 90 to -20 F., and a viscosity index of from 0 to 120, e.g. 5 to 100. Generally the oil will be chosen so that it will have the lowest viscosity which will give the necessary sealing and lubricating properties over the range of temperature and pressure likely to be experienced. The selection of the base oil stock for use as a refrigerator oil will be obvious to one skilled in the art.

Other conventional type additives such as antioxidants, e.g. 2,6 ditert. butyl-p-cresol, phenyl-u-naphthylamine, etc., anti-wear additives, e.g. zinc, dialkyl dithiophosphate, tricresylphosphate, etc., VI improvers, e.g. polybutenes, etc., and the like may be added to the compositions of the invention. In general, the compositions of the invention will comprise a major proportion of the base oil, 0.01 to 1.00, e.g. 0.1 to 0.8, wt. percent of metal soap, and 0.1 to wt. percent halogenated refrigerant.

The invention will be further understood by the following examples. In the description of these examples the weight percentages are based on the finished composition unless otherwise mentioned.

EXAMPLE I In order to evaluate lubricating compositions for refrigerant compressor performance, the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) has set forth a lubricant-refrigerant stability bench test which is called, in short, the ASHRAE stability test.

The ASHRAE stability test is carried out by filling special thick walled pyrex glass tubes (9" long, 1617 mm. outer diameter, 2.5 mm. Wall thickness) with equal volumes (2 cc.s) of oil and Freon-12 (CCI F along with a set of connected copper and steel strips (each 2.375 x 0.25 x 0.0625") sealing the tubes under a pressure of 5-15 microns of mercury and heating them at 347 F. for specified periods of time. Four tubes are sealed for each oil sample, with one being held as a control, and the other three being heated. The tubes are inspected visually after 4, 8, l6, and 32 days for darkening of the liquid and copper plating and corrosion on the metal strips. The ASHRAE test is designed to simulate the environmental conditions encountered by a refrigeration lubricant in actual service to such an extent that it can be used to reliably predict the relative stabilities of various oils to break down under those conditions. After In order to demonstrate the superiority of the lubricants of the invention containing mtal soaps, a series of compositions was prepared utilizing a commercial refrigeration lubricant as a base stock. This commercial refrigeration lubricant has the following specific properties and will be referred to herein as the 155 SUS lubricant.

Viscosity, SUS 100 F 155 Specific gravity 0.89 Flash pt., F 350 Wax precipitation (fioc) pt., F 45 Four pt., F Dielectric strength, kv./cm Color, ASTM 1/2 Conradson carbon, wt. percent 0.00

A sample of the SUS lubricant itself was used as a control and labeled composition A. To another sample of the 155 SUS lubricant was added 0.05 wt. percent of a zinc naphthenate which was prepared from naphthenic acids having a molecular weight of about 250, a neutralization number of about 170, said acids being obtained from a petroleum diesel oil fraction. This Was labeled composition B. Compositions C, D, and E were prepared by adding 010, 0.25 and 0.50 wt. percent, respectively, of the same zinc naphthenate to the 155 SUS lubricant. These compositions were then tested in the ASHRAE stability test. The results are summarized in Table I following with the rating scheme as explained above. Also several samples were analyzed to determine the total free chloride ion formed. These results are also summarized in Table I.

Table I .--ASHRAE Test Results With Zinc Naphthenate Days at 347 F 4 8 16 32 Total Total Total Visual Visual Chloride Visual Chloride Visual Chloride Formed, Formed, Formed, mg. mg. mg.

OIL Comp.

155 SUS Lubricant: A L 2 S 3 C 3 155 SUS Lubricant, 0.05% Zn Naphthenate: B L 0 1-2 G 1 155 SUS Lubricant, 0.10% Zn Naphtheuate: C L 0 S l C- 0-1 155 SUS Lubricant, 0.25% Zn Naphthcnatc: D L 0 S 1 C 1 155 SUS Lubricant, 0.50% Zn Naphthenate: E L 0 0-1 0-1 NorE.-L-Liquid, S-Steel, C-Copper.

The data in Table I show that there is a gradual discoloration and sludging of the oil-refrigerant solution, and copper plating and corrosion of the metal catalysts with increasing time of heating. The above data illustrate the increase in stability of the oil to this degradation as inhibitor content is increased.

EXAMPLE II In order to further illustrate the invention another series of compositions was prepared. Composition F which was the 155 SUS lubricant was used again as a control. Composition G was prepared by adding 0.25 Wt. percent of zinc naphthenate to the 155 SUS lubricant. Composition H was used as a control and represented another commercial type base oil of refrigerator lubricant which will be referred to herein as the 300 SUS lubricant and has the following typical properties:

Blend I was prepared by adding 0.25 wt. percent of the zinc naphthenate of Example I to the 300 SUS lubricant. Blend J was prepared by adding 0.31 wt. percent of a zinc naphthenate having a lower zinc content than that of Example I to the 155 SUS lubricant and composition K was prepared by adding 031 wt. percent zinc octoate to the 155 SUS lubricant. These compositions were evaluated for 32 days in the ASHRAE stability test. Some of the compositions were also evaluated in the four-ball wear test in order to demonstrate the improved wear properties of the refrigerating lubricant obtained by the use of the metal soaps of the invention.

The four-ball wear test (see Clinton, W. C., A Study of the Four-Ball Wear Machine, Naval Research Laboratory Report 3709 (1950)) is designed to measure the relative tendencies of various lubricants to enable metal parts to resist wear under conditions of sliding friction where seizure does not occur, i.e. at relatively low loadings. Such conditions would be found in the bearings and cylinders of modern hermetic refrigeration compressors. In general, the apparatus consists of three balls held fixed in a pot containing the test lubricant. A fourth ball, held in a chuck, is pressed :down against the lower threeand rotated. At the conclusion of the test, a circular scar is worn on each of the three lower balls and a circular track is worn on the upper ball. The average scar diameter of the three lower balls is then used as an indication of the tendency of a lubricant to resist wear relative to another lubricant under the same test conditions; the larger the scar diameter, the worse the lubricant.

Aside from the lubricant, the scar diameter is influenced by the metals used, load (kgrn.), speed (r.p.m.), temperature C.), and time (hours). Although any metal can be used, steel on steel is the most common combination and was used in these tests. Other conditions were: loadkgrn, speedl800 r.p.m., temperature100 C., and time-l hour, and were the same for all experimental samples tested.

The results of the tests are summarized below in Table Table II ASHRAE Stability, 32 Days at 347 F.

Comp. Oil

Total Four-Ball Visual Chloride Wear, Scar Formed, Diarn.,

mg. mm.

155 SUS Lubricant: F Liquid 3+ Steel 4+ 7. 06 0. 563

Copper 4+ 155 SUS Lubricant +0.25%

Zinc Naphthenate: 2 G L 0 1-2 300 SUS Lubricant H 3+ C- 4+ 300 SUS Lubricant+0.25%

Zinc Naphthenate: 2 I L 1 O 1 r J' 155 SUS Lubricant+0.31% 0.404

Zinc Naphthenate. K 155 SUS Lubricant+0.3l% 0. 311

Zinc Octoate.

1 Conditions: 10 kgms, 1800 r.p.m., C., 1 hour. 2 Additive contains -10% zinc. B Additive contains -8% zinc.

EXAMPLE III In another series of tests, the zinc naphthenate of Example I was added to two other lubricants. These are experimental oils similar in type to the SUS lubricant and the 300 SUS lubricant but having viscosities of 100 and SUS 100 F. These lubricants will be referred to herein as the 100 SUS lubricant and the 190 SUS lubricant. The typical properties of these lubricants are listed below.

100 SUS at 190 SUS at F. 100 F. Oil

Viscosity, SUS at 100 F 100 190 Specific Gravity 0. 88 0. 89 Pour Pt., F -30 30 Wax Precipitation Pt., F... 45 -40 Flash 1%., COO, F 360 355 Dielectric Strength, kv./cm 40 40 Color, ASTM 1/2 1/2 Oonradson Carbon, wt. Percent..- 0.00 0.00

In this example, composition L is the 100 SUS lubricant, composition M is composition L containing 0.25 Wt. percent of the zinc naphthenate of Example I, composition N is the 190 SUS lubricant and composition 0 is composition N containing 0.25 wt. percent of the same zinc naphthenate. The results shown in Table IH following, further substantiate the remarkable reduction in sludge formation, corrosion, and refrigerant breakdown resulting from the addition of zinc naphthenate.

Table III Days at 347 F 4 8 14 32 Total Total Visual Visual Visual Chloride Visual Chloride Formed, Formed, mg. mg.

on. Comp.:

100 SUS Lubricant Base Oil: 11-..- L 1 l-2 2 3+ 1 3 3-4 1. 22 4+ 4.17 C 1 2-3 3 4+ Abve+0.25% Zn N aphthenate: M 0 0 0 0 3 34 4 2. 29 4+ 11.13 C- 2-3 3 4 4+ Above+0.25% Zn N aph theuate: O L 0 0 0 1 EXAMPLE IV thenate and Zinc octoate both rmpart lmproved wear prop- In addition to improving the refrigerant-oil stability, as measured by the ASHRAE stability test, and the wear properties, as measured by the four-ball wear test, of the base oils as discussed above, the additive also improves the oxidation stability of the base oils as measured by the Sligh oxidation test.

The Sligh oxidation test measures the tendency of an oil to form sludge under oxidative conditions. This test is carried out as follows: Ten grams of sample are sealed in a long necked Ehrlenmeyer-type flask in an atmosphere of oxygen. The sealed flask containing the oil and oxygen are then heated for 24 hours at 200 C. At the end of the test, the flask contents are dissolved in a certain amount of petroleum naphtha and insoluble matter is quantitatively filtered and weighed. Results are reported as milligrams of naphtha-insoluble sludge per 10 grams of oil oxidized, referred to as Sligh oxidation number. The Sligh oxidation number is taken as the relative resistance of an oil to oxidation. I

Uninhibited compositions A, H, L, and N and inhibited compositions D, I, M, and 0 were evaluated in the Sligh oxidation test. The test results, as summarized in Table IV following, show that the inhibitor markedly reduces the sludge-forming, and therefore oxidative, tendencies of the base oils.

Table IV Sligh oxidation Composition: 31335333 greet A--155 SUS lubricant 10.6 Dl55 SUS lubricant+0;25 wt. percent zinc naphthenate 3.5 H-300 SUS lubricant 10.9 I300 SUS lubricant-+0.25 wt. percent zinc naphthenate 4.1 L100 SUS lubricant 3.5 M-100 SUS lubricant+0.25 wt. percent zinc naphthenate 2.8 N190 SUS lubricant 9.2 O190 lubricant+0.25 wt. percent zinc naphthenate 4.3

As can be seen by the data in the above examples, the use of metal soaps has a pronounced effect in preventing refrigerant breakdown (as indicated by chloride formation), oil sludging', and copper plating under conditions existing in hermetic refrigeration units using halogenated refrigerants, and in improving the oxidation stability of the oil. Moreover, it can be seen that the zinc napherties to the refrigerator lubricants.

Although the aboveexamples have been described with a certain degree of particularity it will be understood that modifications can occur without departing from thespirit of the invention as hereinafter claimed.

What is claimed is:

1. In the operation of refrigerator equipment employing a halohydrocarbon refrigerant and lubricant, the improvement which comprises the use of a lubricant comprising a major amount of a lubricating oil having a viscosity of from 65 to 600 SUS at F. and 0.01 to 1.00 wt. percent of an oil-soluble metal soap selected from the class consisting of metal naphthenates and metal octoates wherein said metal is selected from the class consisting of sodium, copper, calcium, zinc, mercury, cadmium, aluminum, iron, cobalt and nickel.

2. A method according to claim 1 in which said metal soap is a metal naphthenate.

3. A method according to claim 1 wherein said metal soap is Zinc naphthenate.

4. A method according to claim 1 wherein said metal soap is a zinc octoate.

5. A compression refrigeration lubricant comprising a halogen-substituted hydrocarbon refrigerant, a major proportion of a mineral oil and from 0.01 to 1.00 wt. percent of an oil soluble metal soap selected from the class consisting of metal naphthenates and metal octoates wherein said metal is selected from the class consisting of sodium, copper, calcium, zinc, mercury, cadmium, aluminum, iron, cobalt and nickel.

6. A composition according to claim 5 wherein said metal soap is a metal naphthenate.

7. A composition according to claim 5 wherein said metal soap is a zinc naphthenate.

8. A composition according to claim 5 wherein said soap is a zinc octoate.

9. A method of lubricating refrigerator compression equipment comprising contacting the relatively moving surfaces of said compressor with the composition of claim 5.

10. A method of lubricating refrigerator compression equipment comprising contacting the relatively moving surfaces of said compressor with the composition of claim 6.

11. A method of lubricating refrigerator compression equipment comprising contacting the relatively moving surfaces of said compressor with the composition of claim 7.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Doell et a1 Nov. 11, 1930 Parker May 14, 1935 Bergstrom Ian. 14, 1941 Toussaint et a1 Mar. 25, 1941

Claims

1. IN THE OPERATION OF REFRIGERATOR EQUIPMENT EMPLOYING A HALOHYDROCARBON REFRIGERANT AND LUBRICANT, THE IMPROVEMENT WHICH COMPRISES THE USE OF A LUBRICANT COMPRISING A MAJOR AMOUNT OF A LUBRICATING OIL HAVING A VISCOSITY OF FROM 65 TO 600 SUS AT 100*F. AND 0.01 TO 1.00 WT. PERCENT OF AN OIL-SOLUBLE METAL SOAP SELECTED FROM THE CLASS CONSISTING OF METAL NAPHTHENATES AND METAL OCTOATES WHEREIN SAID METAL IS SELECTED FROM THE CLASS CONSISTING OF SODIUM, COPPER, CALCIUM, ZINC, MERCURY, CADMIUM, ALUMINUM, IRON, COBALT AND NICKEL.