INDUSTRIAL AND ENGINEERING CHEMISTRY
1452
Vol. 23, No. 12
Improved Paraffin-Base Lubricating Oils’ G. H. B. Davis and A. J. Blackwood STANDARD OIL Co.
OF
LOUISIANA AND STANDARD OIL DEVELOPMENT Co., LINDEN,N. J.
A study of dewaxing paraffin-base oils indicates that, of oil to engine bearings is in order to obtain the advantages of low-pour oils years increasing presa well-established f a c t . (pumpability and quick distribution at low temperasure has been brought Lederer and Zublin point out ture) by this method, it is necessary to degrade the to bear upon the manufacthat channeling at the pump oil to some extent in most of its other characteristics: with paraffin-base oils occurs turers of petroleum products (1) Decrease the viscosity index of the oil with resultant for improved lubricants for at about 10’F.below the pour increase in difficulty of starting; (2) Increase the low-temperature operation. point. They also find that, a t carbon-forming tendency of the oil by removal of the The response of the oil industhe temperature correspondwax; (3) Increase the volatility of the oil, which causes try to t h e s e d e m a n d s has i n g t o t h e p o u r p o i n t or increased oil consumption in the engine; (4) Decrease been apparent in the advertisslightly above, the quantities the lubricating characteristics of the oil as indicated ingmaterial to be found in the pumped of various oils of the by lessened load-carrying ability and “oiliness;” press and radio programs of same viscosities a t 210’ F. are (5) Decrease oxidation stability with consequent sludgvarious manufacturers, emroughly proportional to their ing in the engine and other deleterious effects. phasizing totally d e w a x e d viscosity indices. It has been found that by the use of small quantities lubricants of low cold test. Becker (1) finds that exof Paraflow, a pure hydrocarbon lubricant, it is possible D e w a x i n g to low p o u r trapolated viscosity a t the to reduce the pour point of paraffin-base oils and to p o i n t h a s g e n e r a l l y been temperature of pumping and obtain the advantage of low-pour oils, without imt h o u g h t of as g i v i n g imthe pour point of the oil are of pairing the other desirable characteristics of the oils. proved lubricating oils. Deequal importance in getting Exhaustive tests show that the low-pour oil thus waxed oils have been adveran adequate supply of oil to produced is entirely stable, and has no unexpected or tised as s y n o n o m o u s with the bearings when starting a unusual effect upon the engine, and is somewhat high-quality oils so generally cold engine. M o u g e y (9) superior to the original oil with regard to lubricating that in many quarters the restates that high pour oils are characteristics. lationship is accepted as abresponsible for excessive wear It has been found possible by the use of Paraflow to solute fact. T h e r e has rein engines during cold startproduce oils of lower pour point than can be economimained, however, some doubt ing owing to the lubricant’s cally obtained by dewaxinp. as to the soundness of the connot reaching the wearing surelusion, and by careful invesfaces quickly enough. tigation it has been found that, with the exception of the lowered TAe data in Table I from files of the Standard OilDeveloppour, there is definite evidence that severe dewaxing lowers ment Company illustrate these points. The tests were rather than betters the quality of motor oils. It is the pur- made on a Cadillac pump submerged in the oil and delivering pose of this paper to clarify this situation and to introduce a to a simulated connecting-rod bearing. new method of producing improved paraffin-base oils of low Table I-Effect of Viscosity a n d Pour on Oil Pumpability pour point.
URING the past few
D
TIME FOR OIL
Effects of Dewaxing
The immediate effects of dewaxing upon the physical characteristics of a lubricant are as follows: POUR PorNT-The most significant facts in connection with low pour (other factors being the same) are: it has very little; if any, influence on ease of cold-weather starting, or cranking speed a t low temperatures; but it does aid the flow of oil to the bearings in cold weather, which tends to minimize engine wear during and immediately after starting has occurred. Actual tests on motor cars a t low temperatures have been reported by Blackwood and Rickles (2), and by Larson ( 5 ) , showing that cranking speed is not affected by pour point. That is to say, cranking speed is a function of the extrapolated temperature-viscosity curve rather than of the higher false viscosity of paraffin-base oils below their pour points. Lederer and Zublin (6) carried out tests on a laboratory set-up consisting of a cylinder moving up and down a t constant speed against a piston hanging on a balanced beam. The work corroborates the above in that hard starting does not follow the false viscosity of oils below their pour. They feel, however, that pour point has some bearing on cold shear resistance. That pour point plays an important part on the pumping Presented before the Annual Meeting 1 Received November 7, 1931. of the American Petroleum Institute, Chicago, Ill., November 10 to 12, 1931.
OIL
VIscosIrY A t 5’ F. POUR At 210’ F. (Saybolt) e
Pennsylvania motor oil Pennsylvania motor oil Mixed-base motor oil Coastal motor oil
F.
30 26 0 0
49 02 49 49
REACK BRARING AT 5’ F.
TO
Seconds
Seconds
10,000 55,000 32,000 50,000
30 120 10 42
These indicate that for oils of the same viscosity a t the temperature of test, a 25’ F. pour oil requires about three times as long to reach the bearing as does a zero pour oil. Similarly for oils of the same pour, the more viscous will require the greater time. It will be noted that channeling a t the pump did not occur with the high-pour oils in these tests. GRAvITY-The A. P. I. gravity is lowered in taking out wax, as shown by the inspection data given for typical samples later in the paper. The relation of the gravity (in and of itself) of lubricating oils to their performance in motor-car engines is not known. Secondary relationships, going to gravity as an index of other properties, are of course important and in part at least well understood. TEMPERATURE-VISCOSITY RELATIONSHIP-The temperature-viscosity relationship, which is hereafter referred to as viscosity index (S), is made less favorable by dewaxing. This change is important and is not always apparent from a casual inspection of the physical characteristics of commercial lubricants. Oil samples of known antecedent, all having approximately the same viscosity a t 210’ F. and in the same gravity class, are given in Table I1 and Figure 1, and illus-
December, 1931
INDUSTRI.4L A N D ENGINEERING CHEMISTRY
1453
oil-control rings. Mougey also says that the literature shows that, for easy starting a t 0" F., an oil of not over 50,000 seconds a t that temperature is essential; and that an oil meeting this requirement will have too low a viscosity under high-speed operating conditions, resulting in high oil consumption. Obviously it is undesirable to treat an oil in any way which may decrease its normal viscosity index. CONRADSON CARBON-Paraffin-base waxes containing oils have always been known to have high Conradson-carbon values, and often this has erroneously been associated with the wax content. Actually the Conradson carbon of paraffin wax is nil, and Ries (10) finds that increasing percentages of wax result in decreasing Conradson carbon. Data from the laboratory files bear out the statements of Ries (Table 111). The importance of Conradson carbon has been a subject of debate for years. In the last analysis, there seems little doubt that the work of Morley, Livingston, and Gruse (7), showing the correlation between carbon formation and Conradson carbon, holds true for oils of the same type and processing. Hence one may expect greater carbon formation from a dewaxed motor oil than from the same oil undewaxed. Table 111-Effect
of Wax on Conradson Carbon
OIL Naphthenic-base Naphthenic-base 4- 2% wax 5% wax Naphthenic-base Paraffin-base 5% wax Para5n-base
+
+
CONRADSON CARBON 0.241 0.184 0.128 0.79 0.72
VOLATILITY-The effect on volatility is somewhat difficult to demonstrate since, in dewaxing motor oils, the usual procedure is to dilute with naphtha and, after dewaxing, remove the naphtha by reducing to flash or viscosity. The picture of what happens may be found by examining the lower part of vacuum Engler-distillation data for oils before and after dewaxing. Table IV, showing distillation temperatures at 10 mm. pressure, illustrates the higher volatility and, by direct interpretation, the lower flash and fire points of the dewaxed motor oil. Table IV-Effect
of Dewaxing on Volatility of Lubricating Oils
PENN.MOTOROIL Waxy Dewaxed Gravity 29.4 28.5 Vis,at210°F. 56.2 55.5 Vis. Index 112 9s 420 395" Flash, O F. 110 5 Pour, O F.
EXTRAHEAVY 200 PENN.NEUTRAL MOTOR OIL Waxy Dewaxed Waxy Dewaxed 29.9 29.8 29.0 27.2 45 45 73 73 ... 87 103 103 405 405 520 500 25 0 90 15
ENGLER DISTILLATION AT 10 MM. PRESSURE
B
i7 > 6
t
x5 54
E $3 L 2
w 0 ,
I . B . P . , F. 454 2% 463 478 106% 497 025
%
a
450 460 476 493 516
%
408 454 462 471 483 486 494
426 452 458 465 476 485 493
490 545 585 592 602 610 618
486 554 565 576 590 602 612
Probably in error.
The connection between volatility and flash-fire points is well recognized. Reference has already been made to the literature (9) showing that volatility affects oil consumption, being greater for the more volatile oils. The degree of vaporization occurring in the crankcase of an automobile is not always apparent to the operator. It frequently occurs that, with oils having low-boiling constituents, the oil level gage will indicate a rapid rate of consumption. However, after make-up is added, the consumption appears to settle down to a slower and more uniform rate. The reason is that the light fractions have volatilized off, leaving the heavier constituents in the crankcase. These of coume make for lower consumption. From an inspection of the data shown in Tables IV and V, it is clear that the dewaxed oil would show higher volatility ~ O S Bin an engine. RESISTANCE TO OXIDATION-TOstudy the effect of dewaxing upon the stability of oils toward oxidation, six oils were
INDUSTRIAL AND ENGINEERIhTG CHEiMISTRY
1454
subjected to a severe oxidation test. This test consists of measuring 300 cc. of oil into a flask and placing it in an oven for 12 hours. During this period, 5 cubic feet of air per hour are bubbled through the sample. The temperature is main-
SPEED
-
Figure 2-Special
El P.M
Oiliness Tests
tained a t 450" F. for the oils above S. A. E. 30, and 400" F. for lower-viscosity oils. At the end of 12 hours the samples are inspected for sludge formation, change in viscosity, development of acidity and volatility loss. Table V shows data for the original and oxidized oils, and clearly shows the inferiority of the dewaxed oil. These data show the disadvantage of dewaxing in three ways: Volatility loss is higher for dewaxed oil, forecasting higher engine consumption. Sludge is very much higher, forecasting more crankcase sludge and greater trouble from ring and valve sticking. Viscosity at 210" F. is increased, forecasting gumming of engine parts, faulty operation of filters, and increased frictional losses.
Vol. 23, No. 12
transition from liquids to solids. Some of Hardy's data are shown in Table VI. It is to be noted that some of the paraffins compare favorably with oleic and stearic acid, both commonlv used in lubricatine oils. T k t s on dynamic fricTion machines a t the Bayway laboratories show that the paraffin waxes have better friction-resistant qualities than the oils from which they are derived. Figures 2 and 3 show this point clearly. The characteristics of the particular oiliness machine from which the data in Figure 2 were taken are such that viscosity effect has very little influence on torque values, and consequently the low position of the curve for wax is very significant. These data were obtained when operating a t extremely high bearing pressures. The General Motors pin and bushing machine has been used extensively to determine load-carrying capacity of lubricants. The data from this machine, Figire 3, indicate that paraffin wax is superior to oil lubricants of the same viscosity a t 210" F. Table VI-Coefficient of Friction f r o m Hardy's Data ACIDS HYDROCARBONS Oleic 0.10 Octane 0 32 Stearic 0 . 1 5 B . p. paraffin. approx. 0.20 Paraffin 87' F. m p . ) , approx. 0.09 Paraffin 1115' F . m. p.), approx. 0 . 0 7 Benzene 0.34 Naphthalene 0.29 Anthracene 0 26
Table V-Resistance to Oxidation OIL DATAORIGINAL OIL DATA -OXIDIZED AcidTemp Vis. Vis. ity of Grav- at Grav- at Vol. OIL ity 210 F. Pour ity 21O'F. loss (K0H)Sludge test O F. 95 Me. Yo F . ," 80 2 7 . 4 58 8 . 7 0 . 6 5 0 . 7 4 400 Motor, medium 2 8 . 6 54 15 26.3 67 1 4 . 5 0 . 3 0 1 . 5 7 Same, dewaxed 2 7 . 4 53 67 2 . 4 0 . 3 5 0 . 7 6 450 85 27.2 Motor heavy 2 9 . 0 63 4 . 8 0.35 1.61 Same,hewaxed 2 7 . 3 6 2 . 8 15 2 6 . 0 73 Motor, extra heavy 29 0 73 90 2 6 . 8 114 7 7 0 30 1 23 450 Same,dewaxed 2 7 . 2 73 15 2 3 . 4 108 8 1 0 35 3 57
Under the conditions of normal operation in internal-combustion engines, the variation in frictional coefficient (aside from viscosity effect) is negligible. Mougey (8) finds this socalled oiliness effectof minor importance in normal operation. However, under unusual situations, such as reduction in lubricant supply, unusually tight-fitted bearings, and unreasonable dilution of the oil, and during the starting and stopping periods, it may be argued that the high oiliness of certain oils will carry over the temporary deficiency without undue wear on the parts. To the extent that this conclusion (so difficult to weigh experimentally) is sound, the extra factor of safety in a wax-containing oil, may be of value in
The relation between oxidation characteristics of lubricants and their performance in an internalcombustion engine is too uncertain to warrant definite claims. Undoubtedly the oils most resistant t o oxidation will maintain their lubricating value longer than the unstable oils. But contributing factors, such as moisture in the crankcase, dilution, acidity from the combustion products, effect of metals on different oils, and others, all tend t o make good correlation difficult. It has been observed that piston-ring sticking, s t o p p i n g of d r a i n holes i n t h e scraper-ring groove, and clogging of oil ring slots are usually attributed to poor high-temperature s t a b i l i t y rather than to carbon-forming tendency alone. The reason for this is that the oil collects around the rings and is cooked a t high temperature under oxidizing conditions. In the combustion chamber the oil is actually burned, whereas around the rings it is simply heated to high temperature without ignition. COEFFICIEKT OF FRICTION-In 1918 Hardy (4) reported data pertaining to the coefficient of state friction of paraffin. His data show the paraffin waxes to be slightly superior to other hydrocarbons of equivalent molecular weight. He also concludes that for a given chemical series the coefficient of friction falls off with increasing molecular m-eight, and that the relation is not affected by melting point continuing in the
running in new motors and during the initial operating period in cold weather. The foregoing discussion has shown that dewaxing an oil while improving the pour point has resulted in giving a product inferior with regard to viscosity index, Conradson carbon, volatility (including flash and fire points), oxidation stability, and lubricating value as compared to the undewaxed oil of the same viscosity. Individually the changes in most of these items is small but collectively they are of sufficient
I
I _
importance to require serious consideration when producing oils of the highest quality. For this reason tlie sigriificarice of each item as relat.ed to performance in a motor car has been analyzed. Considering the trend in automotive design towards units requiring better lubricants, it appears that tlie corresponding trend in part of the oil industry in the direction of higher degrees of dewaxing is progress of doubtful value since low-pour oils are produced only at t.he expense of other essential lohricating-oil properties. Properties of Paraflow
The Standard Oil Development Company has worked out a method of obtaining oils which flow freely at low temperatures and has attained this end withoiit the dcgradativn ind e n t to dewaxiiig. I t has been found possible to supply a
Plant of Srandsrd 011 Company of New Jersey
Flbure 4-New
pruduct (United States Patent 1,815,022) which has all the desirable properties of a wax-containing oil plus the low pour of the dewaxed oil. The mcthod involves the addition of a very sniall quantity of a specially prepared pure-hydrocarbon lubricating oil, capahle of reducing the pour point of paraffin base oils without the necessity for severe dewaxing. An inspection of this product (called "Paraflow") is given in Table VfI. Table VII-Typical
craVity,0 a. r'.
I.
100~ F. viscosity ai 210P. ViSCOillY rt
viscosity imier Pour point, 0 1'. Flesh ""in%. " F. Conradson carbo" Color (Robinson)
Inspection of P*raflow 23.8 36LP 214 106 5
1 99
'h
Green
cast
T a b i e v i ~ I - - T y p i c a i ~ n s p e c t i ~ P~ ~a ~f ~ R O W - B I~~t~~ ~ M ~oilr ~ SA?.%=
< iovity,
e
A . P. I.
viscosity si 100- F. V i ~ r n i ilnder t y ~ i 2 1F.0 ~ viscosily Pour p.,i.t, 0 1'. Flash point. P. Conrrdson carbon Color (Robinson) Ci0"d. 13. Deinulsiliiliiy at l3US F. steam emu1i;on NO.
Snme
+
+
S*lI
