May, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
to-solid adsorption. The writer has a specimen of a valve tappet which ran for some time in an engine lubricated with graphited oil, on the surface of which is a deposit of graphite rubbed and hammered in by the motion of the valve cam. The deposit is evidently not held by an oil film because it cannot be loosened by solvents for oil. A micrograph is shown in Figure 5 . Note that the graphite is in spots, usually not similar in shape to the scratches of the metal. For the purposes of comparative friction readings, the long mechanical method of establishing a graphite surface was impractical. The graphite surfaces used for the foregoing table were produced with the aid of a very slight residual oil film, the resulting frictional readings being lower than any which were obtained with that oil alone. The surface coated with Aquadag had a negligible amount of oil present. Graphite, Oil, and Water
If we shake a mixture of a little powdered graphite in water with an equal volume of oil, the oil will displace the water from the graphite surfaces and the graphite will all go into the oil phase (Figure 6). Des Condres has explained
499
this action as one of differential adsorption; in this case the graphite adsorbs oil to the practical exclusion of water. This experiment has more than theoretical interest in the case of bearing surfaces subjected to water. In steel rollingmill necks, for instance, a constant stream of water and a heavy scraping pressure tend to produce absolutely oil-free surfaces. These necks often rust within 10 minutes after the mill is shut down. If, however, a graphited surface has been established, the preferential adsorption of graphite for oil rather than water is very effective in maintaining an oily or greasy surface. Conclusion
Determinations of friction with and without graphite indicate that graphite is effective in prolonging the period of unbroken film lubrication, and in the ruptured film stage it reduces friction and minimizes metallic contact. This is probably because it deposits to a certain extent in the low places of the metal, thus making a smoother surface, and also because when solid-to-solid contact does take place, it abrades more readily and with less friction and damage than would plain metal surfaces.
Comparison of Lubricating Efficiencies of Oils and Some of Their Physical and Chemical Properties‘ By M. V. Dover ENGINEERING EXPERIMENTAL STATION, UNIVERSITY
The following properties of three mineral oils and one vegetable oil-olive oil-have been compared : iodine number, acid number, flash point, specific gravity, viscosity, surface tension, interfacial tension, and efficiency, as lubricants. A brief study has been made of the clogging effect of iron or steel capillaries by two of these oils, as suggested by previous work by Wilson and Barnard.
HE work upon lubrication for a number of years has been along two principal lines-namely , the nature and cause of lubrication, and the properties of oils that may affect their lubricating values. I n attempting to ascertain how ozonization affects the various properties of several oils, including their values as lubricants, various constants of these oils were determined and discussion of some of these constants of several oils when compared with their value as lubricants may be of interest.
T
Determination of Constants
The following properties have been determined : flash point, specific gravity, surface tension, interfacial tension (oil and water), viscosity, acid number, iodine number, and static coefficient of friction. From the static coefficient of friction the efficiencies of these oils have been calculated by Deeley’s formula. The oils tested are Velocite B, Renown engine oil, and turbine oil-all fairly light lubricants. For the sake of contrast, the foregoing properties of these three mineral paraffin-base oils have been compared with similar properties of a sample of olive oil, Maltese Cross brand. The static coeficient of friction was measured with a Deeley machine between steel surfaces. The friction surfaces were Meeting title, “-4 Comparison of Some Physical and Chemical Properties of Oils and of Their Efficiencies as Lubricants ”
OF
MISSOURI, COLUXBIA, Mo.
prepared as follows: After each run the disk and pegs were wiped comparatively free of the oil which had been tested and each was ground upon a steel lap with oil and flour of carborundum, until the track was ground out of the disk and the pegs were perfectly flat. The disk was then washed with ether until all of the oil was removed, as was shown by the fact that water adhered to the whole surface. After this treatment, the disk, while still wet, was sprinkled with flour of carborundum and carefully rubbed with a brass rubber provided with the machine, in order to remove completely any film that might have been left by the ether. The disk was then washed in cold water until all the carborundum was removed, dried with blotting paper, warmed very gently to remove the last traces of moisture, and a t once wetted with the oil to be tested. The pegs, after having been ground upon the lap with flour of carborundum and oil, were also washed in ether and then ground upon the carborundum disk provided with the machine, until a smooth bright surface was obtained. They were then rubbed with blotting paper to remove any particles of carborundum that might adhere to them and wetted, as in the case of the disk, with the oil to be tested. The machine was turned by a small motor a t the rate of approximately six revolutions per minute, the temperature of the room being kept a t about 22” C. Coefficients of friction shown on the graphs are in each case the average of several runs. The interfacial tension (oil and water) is reported in arbitrary units, measured by means of a Traube stalagmometer by dropping water into oil; the same capillary was, of course, used in each case. Surface tension was measured by the same instrument and is reported in dynes per square centimeter. Viscosity was measured with a Washburn viscometer and is reported as absolute viscosity.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
500
OIL ~-
Sp. gr.
Iodine number
0.8814
10.96 14.42 6.37 84.27
at.~~ 22 C. -
~
Velocite B Renown Turbine Olive
0.8925
0.87798 0.9150
T a b l e I-Constants of Oils Acid number Surface InterMg.KOH/l gram tension face oil Dvnedcrn. tension ~.
0.230 0.2380 0.166 1.37
30.85 30.805 44.04 33.08
All of these constants were measured a t 22" C., as was also the specific gravity. The $ash point was determined with a Pensky-Martin flash-point apparatus. Acid number was determined by hlethod D47-21 of the American Society for Testing Materials and is reported as Mg. KOH per 1 gram oil. Iodine number was determined by the Hub1 method.
?O
IO O
Z
7
'
40
30 l
\
l
50 n
;'
60
70
80
90
/00
+e
0 250
-
j
7urb;ne 017 Pmperafure ZZ'C Trsfinq SpeedI 6Rf I
Static Coeffclenfs on Dee/ey#achhe
1940.0 2593.0 2350.0 1061.54
Vol. 18, No. 5
Viscosity Abs.
Flash point
Index refraction
185 198 196.5 230
I. 4880
0.621
220 c. 0.6460
c.
0.5934 0.7937
1.4972 1.4855 1.4740
sion between oil and water does not necessarily lower the coefficient of friction, as measured by the Deeley machine. It may be seen from the curves showing the relation of load to static coefficient of friction, that Velocite B (Plate I), with an interfacial tension 1940.0, has a higher coefficient of friction for all loads than has turbine oil (Plate 11), with an interfacial tension of 2350, arbitrary units. True it is, however, that Renown engine oil (Plate 111) has a higher interfacial tension than turbine oil and it has also a higher average coefficient of friction. Assuming that adsorbed films are formed upon the surfaces of metals when in contact with lubricants, it might be supposed that an oil having a high iodine number would tend to be adsorbed more readily on the metal than one having a lower iodine number. This assumption is borne out by the fact that animal and vegetable oils (Plate IV), having a much higher iodine number than these mineral oils, are in general much better lubricants; but apparently this relation does not hold in the case of these oils when different mineral oils are compared inter se. It may be noted that turbine oil with an iodine number of 6.37 has a lower coefficient of friction than Renown engine oil with an iodine number of 14.42. Perhaps all of these iodine numbers are too small to exert any appreciable influence upon the lubricating value of these oils, or upon their ability to form adsorbed films upon the surfaces of metals. Velocite B is more readily acted upon by ozone than these oils having lower iodine numbers. Because the acid numbers of these mineral oils are so small, it is probable that the influence exerted by these very small amounts of acid upon the coefficients of friction is negligible. I ' P f a t e 'Z I I Coeff/nents on Dce/cyMach/nc-Renown fn9ine O// I I I iernperature -2Z'C Ps%ng Speed-6RPM
Effect on Lubricating Power
It is well known that olive oil, as an example of a vegetable oil, is a better lubricant than mineral oils. It is also common knowledge that the iodine and acid numbers of vegetable oil8 are much higher than those of mineral oils and that the interfacial tension (oil-water) of vegetable oils is lower. Low interfacial tension, high acid number, and high iodine number have each been considered to have some influence in rendering oils valuable as lubricants-in other words, in reducing friction. The addition of fatty acids to mineral oils has been shown by Hyde2 to improve the lubricating value of the oils-has reduced the static coefficient of friction as measured by the Deeley machine. It has also been shown by Southcomb and Wells3 that addition of a relatively small quantity of a fatty acid to a mineral oil lowers interfacial tension between the oil and water. These authors consider that interfacial tension between oil and water may be taken as some criterion of the interfacial tension between this oil and a metal surface, and they consider that the lowering of interfacial tension necessarily decreases the coefficient of friction. Wilson and Barnard4 take exception to this view. The work reported by Dover and Appleby6 seems to confirm the opinion of the last-named authors that lowering of interfacial ten:Engineering, 111, 708 (1921). a J . SOC.Chem. I n d . , 39, 51T (1920). 4 J . SOC. Aufomolioe Eng., 11, I50 (1922). CTms JOURNAL. 18, 63 (1926).
'
'F,
j$
0.2/0
10
20
30
1
7
Load- /bx per sqm. 40 50 60 70
Plate 'T
80 I
Static Cocfficlents o n Dee/ey Muchme - O h e 0 7 0 200
90
/00
I
-
-
Temperature 72'C Teshnq Jpeed - 6 RfM
Clogging of Capillaries
Though it seems to be generally assumed that adsorbed films are formed upon surface of metals which are in contact w-ith lubricants, there is apparently very little known as to properties or thickness of these films. Wilson and Barnard*
I N D U S T R l A L A N D ENGINEERIA*Q CHESlIXTRY
May, 1926
conceived the idea that some light might be thrown upon this rather illusive subject by causing oils with what they call ‘‘film-forming tendencies” to flow through fine metal capillaries. These investigators consider the results of their experiments t o be “satisfactory confirmation of previous experiments.” However, because they saw no way of makI20 io0
501
a steel capillary. The results (Plate VI) are similar, though they do not check quantitatively. It is, of course, a very common experience in oil work to find that results cannot be repeated. Because the Velocit,e B used in this experiment had been standing in glass containers for about a year since the constants recorded above had been determined, and before the clogging effect was tried, it was thought that aging might have caused some changes in its properties. To determine whether or not this was the case, some of the oil was heated for 2 hours a t from 50” to 60” C. The Engler viscosity and acid
80
CLOGGING EFFECT OF V€lOCITE 5 OIL f - Cast-Iron Cupl’llary
100
I\l
I
1-
00
60
:
ing quantitative comparisons between oils, they discontinued this line of work. It occurred to the writer that, although the comparisons might be qualitative, this method of testing oils might throw some light upon their oiliness or upon their tendency to form these films. Accordingly an apparatus similar to the one used by Wilson and Barnard4 was procured and turbine oil, after having been filtered through 200-mesh copper gauze, was run through a cast-iron capillary of 0.018 inch diameter and 0.197 inch long. Very erratic results were obtained from this experiment, as is indicated by the curves. Plate V shows data in terms of percentage of the weight flowing in the first 10-minute period, before appreciable clogging could have taken place. This is the method of plotting used by Wilson and Barnard. Because these results were so very erratic, it was decided to try the same experiment using the same kind of oil (Velocite B) as that used by Wilson and Barnard and, like them, using
I
1
2
3
Hours 4
5
6
7
8
number showed no appreciable change, which would seem to indicate t,hat standing was not responsible for variation in results. Note-The turbine oil used in the last experiment was obtained a t a n earlier date than the sample, constants of which have already been mentioned. The acid number of these samples was considerably higher than t h a t of the one whose properties have been described, perhaps partly b y the fact t h a t a different method of determination of acid number was used in these two cases. The static coe5cient of friction was somewhat higher in this sample than in the one which has just been described. The iodine number checked very well in both samples.
Patent Protection of Chemical Products Protection of chemical products by resort to patent laws of the various countries is a matter pertinent to every manufacturer and is complicated by unexpected changes in the laws and the many technical phases of formulas and processes. According t o the January 8, 1926, issue of Engineering (London), patent protection in Great Britain has materially changed since the Act of 1919 was enacted. Before t h a t law became effective there was no restriction on patenting a chemical product, providing it was something new and was capable of being regarded an invention. The Act of 1919, however, limited available protection and provided that “in the case of inventions relating t o substances prepared or produced by chemical processes* * * * the specification shall not include claims for the substance itself, except when prepared or produced by the special methods or processes of manufacture described and claimed or by their obvious chemical equivalents.” Continuing its explanation of the British law, the periodical quoted states: T o some extent where a patent is obtained for a process, i t is unnecessary for any specific protection to be sought for the product, because i t has long been held a s axiomatic in British patent law t h a t the most effective way in which an infringer can damage the owner of a patent for a process is b y selling the product of the process in competition with the inventor. For this reason, British process patents may be regarded a s covering the products of their processes, even though they may not specifically indicate this, In the application of the section of the Act of 1919 referred to above, the Patent Office deals with the matter very broadly in the sense t h a t if a chemical substance is treated b y a process which is not a chemical process, b u t may be, say, a physical process, the Patent Office will not permit t h e product resulting
from this physical process to be protected specifically, except in so far a s protection is sought for a product made by the process described and claimed and not a product made by other processes. The ground on which the Patent Officeacts is t h a t the substance treated was in fact originally prepared by a chemical process and, therefore, must be regarded a s coming withi n the act. It is true t h a t the act permits the claim to extend to products made b y obvious chemical equivalents of the process claimed, b u t British patent law has always conceded t h a t the claim may be infringed b y the obvious equivalents thereof, if they were known t o be obvious equivalents a t the date of the patent.
Laws of other countries differ widely from that adopted by Great Britain, there being, broadly speaking, three other types of laws dealing with t h e patenting of chemical products. According to Engineering the German law provides definitely that “the products resulting from a process are automatically protected by the patent for a process.” The law in Holland is understood to be substantially the same. The Swiss law provides that patents for inventions relating to the manufacture of chemical substances can be granted only when a single process results in a single substance. This is a serious handicap for a manufacturer who is able to turn out a product by various processes, and means that he must take out a series of patents each dealing with the conversion of a single substance into a definite product. For the benefit of its British readers, the publication also refers to the American law by which “specific patents are allowed for products broadly independent of their method of manufacture, and in t h a t country (the United States) a process patent is not infringed by the sale of the product of the process.”
