May, 1926
INDUSTRIAL AND ENGINEERING CHEMISTRY
out part of the film. In the case of the facts shown in Table I11 the reduction of the friction and the decrease in margin of error are possibly due to the building up of the brass spot on the steel contact area, smoothing over the irregularities. This same effect is manifested in bearings. It is well known that a bearing runs with less friction after it has l.)een worn in. If this assumption--namely, that there are interlocking projections-is correct, several conclusions that throw more light on the property of oiliness may be drawn: (1) The secret of good oiliness would be to have a tenaciously adsorbed film of such thickness t h a t the projecting asperities could not interlock. ( 2 ) The friction would be a function of the attractive forces of the metals, the tensile strength of the metals, and the internal friction of the lubricant. This may partly explain why soft bearing metals such as babbitts give lower resistance than the harder metals.
Conclusions
Accepting the property of oiliness as being important in the selection of lubricants for industrial lubrication, a method
467
of measuring this property has been developed and found t o give fairly reliable results. With brass and steel surfaces it is evident that there is an appreciable difference between various commonly used lubricants, although this difference is not shown in the tests usually made. The values obtained are in the same order of magnitude that experience in the field and other investigators, working with other materials for surfaces, have found them to be. A comparison of a Pennsylvania crude with a lubricating fraction of the same showed the process of refinement was not detrimental to the oiliness property of the oil. h study of the observations made on the static friction tests throws more light on the mechanism of the property of oiliness. Acknowledgment
The writer desires to express his appreciation to D. R. Kellogg and his associates for their constructive criticisms and helpful suggestions that aided in no small way in making this paper possible.
Some Little Understood Factors Affecting Lubrication By E. G. Gilson RESEARCH LABORATORY. GENERAL ELECTRIC Co., SCHENECTADY, N. T.
Changes in friction cannot always be satisfactorily explained by changes in viscosity of the oil due to a change of its temperature. Oil-film friction is shown to be influenced by change of one of the metals between which the film is working, and also by changing from an oxidizing to a nonoxidizing atmosphere. It is demonstrated by means of a complete bearing within an enclosure how the friction is affected by the atmosphere surrounding the bearing. In conclusion, it is pointed out that the facts shown cannot be explained by the viscosity-temperature changes of the oil, and it is suggested that efficient lubrication may be dependent upon a reaction between the metals of the bearing and the oil, the nature of this reaction being influenced by the atmosphere in which the bearing is operating.
N ALL bearing problems the viscosity of the lubricating oil receives great consideration. There is no doubt about the importance of viscosity in this connection, but there is some question as to the extent of our knowledge of the influence of this factor. In an effort made several years ago to obtain some definite information about oils, and incidentally bearing materials, great difficulty was experienced in getting results to check. It was finally established that differences found in friction were coincident with differences in room temperature, as shown by Figure 1, which contains typical friction curves taken on a standard machine. The only variable is the room temperature. Through an operating range up to 35 kg. per sq. cm. (500 pounds per square inch) there is a change in friction amounting to as much as 20 per cent. It is important to note that the ultimate temperature is practically the same in each case. The natural assumption from these curves is that the higher friction a t the lower temperature is due to the greater viscosity of the oil a t that lower temperature. However, a consideration of the method of the test will tend to weaken this conclusion. The test journal was 9.7 cm. (3.8195 inches) in diameter by 10.2 cm. (4inches) long. The test block was a comparatively
large piece of bronze in which were placed strips of the bearing material 1.27 cm. (0.5 inch) wide by 9.5 cm. (3.75 inches) long, spaced about 2.5 cm. (1 inch) apart. The long dimension was parallel to the axis of rotation. The oil was s u p plied to the under side of the journal by means of a wick extending its whole length. This wick fed the oil from a reservoir in which a constant level was maintained from a large supply tank. The speed of the journal was 500 r. p. m. The oil had a viscosity of 270 Saybolt seconds at 38" C. (100' F.). Fresh oil was supplied all the time, no oil being used over except that which stuck to the journal. Under these conditions it is hard to conceive of this very thin film of oil, supplied by the wick, not coming to the temperature of the journal during the approximate one-half revolution i t made before passing under the bearing surface. T h e tem-
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perature curves show that the ultimate temperature was approximately the same in each case; in other words, the viscosity of the oil, when it was effective as a lubricant, must have been approximately the same. Another factor, however, not recognized at 'the time, may have exerted considerable influence, and will be discussed later.
Vul. 18, No. 5 clianges ill friction is rlionn iii I&re 5. I f , during one of ilicpe riiiis i n liyrirogeii, air is nilowed to replace the hydrogen, tlre frictiini dropc off imnicdiately. &re n g d n if the s:riire
;irgtirnt:iit tibout blie tempenitiire-visi:osity relationship is
ere should be luw-er instead of higher friction. ir oil and slicrin oil show a lower friction and ternprniti~re wticn rim in the hydmgeii atmosphere --just thp of t,bc iiiincrd oils testid.
halnnced against, t l w calihratetl sgriiig, i o that the powrr ai)sorbed in tho oil filin pointer on tlie gradn a l e d SBIIIC. Tcmperittare is indicatt:(l bv a thcrmorouiilc of very fine wire projwting tlrrougli the ring sligSht,ly into tlir oil film. Effect of Different Metals
F i g n r e :i s h i i w s relircsottiirg two runs with this ~naohine---iiniler idenFieure 2 tical condit,ions except that iti inre case the ring was broiisc and in the other it was copper. The hroiize \vas morc theit XI) per (wit, copper. Tlir oil \vas orit of th T h e frirtirni corre for the than that for the copper, with a rarresponding higher curve for the temperat~nre. A s the saine oil mw wed in cacli riiii, the viscosiiy mist lie h e r with the higher t,emperatrir(! rvlien the I x w i a e ring i s used :ind we sti(jnlil, therefore, exprct, :I loxcr friction. Rnt on the c.iniI.riq, t,he friction is lrigiiei.. Renicnibering tirat there is maintained a n oil iiliri approxi3 cm. (0.013 inah) thick, i t seeins as if some factor osity i s rcsponsihle for bhis rest c,ilt, iiY a Rtllciv tilc surf:ioe t,ilc I~~~~ graph uf rrliieh is shoi\w in Figiirr 4. There results are typical of i~tnnyshowing 1:hunpr 0 1 friction in the oil oaused by cl~nngingi.he inotrd ring. .\ti attcinpt to explain tlie difference het,ivcmi these oil some change i n the oil due to the different metals the ring must take into account the fact, iliat. they star1 di w i t h a difference and innintniii it thronglroot,. 1: u r v e s
In g(::cneral, bhc oils do i,ot sludge o r change color, ~ierccptihly, in the Iiydrngeri atinosphere, wherem they do lilackrn and slndge very badly in air. Here also there is an esccptbin, where tlre friction increases in the hydrogen a t nmpltere although t,he nil blackens and sludges worse than in air. Ttrrse facts seem to indicate that for minimum friction :I roaction within t,hc oil itself is necessary and that this reaction is probably dependent on oxygen. In other words, the snrroiiniting atmosphere has an influence on the friction of tlie oil. This viewpoint has heen stn?ngtl~errodby nuiniiroiis other experiments. Experiments with
B Complete Bearing in Various Atmospheres
i'or further study a srnali hearing was set up iri siiclr B inannor that it could be run in any atmosphere or in a vacuum. The bearing sleeve was carried in a cradle, supported on knife edges, so that the torque reaotion could be weighed mitli a very considerahle degree of accuracy. This apparatns is sliomn in Figure 6. I t was difhorrlt t o get satisfactory results from this machine, usnally on account of variations iu teinperatnre in the room, and this ilr spite of the fact that t,he hcaring was operating in a n enrlosure. It was finally iieces-
Experiments Using Atmosphere of Hydrogen \Vtien this ~nsohineis run in an atmosphere of hydrogen. iustead of air, w e get entirely different mlues. The Frirtiiiii and temperature for all mineral oils t,ried are iintclr higher. with one exception, where tliero is sliglit.ly clei:reased f r i r t h t but rnuchhiglrer temlnmture. The inagnilude of snmcof t h e
Fipure 4
piit the whole tliiirg in another enclosure within teiiiperature could be kept constant. Even tiien i t \ m c iieemsary t,o use special roiist.riietion for tlie bearin:. .\ journal was made having a henting element imlie.ilrlcil just beluw its surface. A tlierinocoupie U'RS plmxI i / / t l i c lmiring sleeve just hclum its surface, and lo :i* i.Io.~ctis possible to the point of iiearest approach of j m r i i : i I ;id bearinp--in other n-nrds, where the oil filtri in. thinticst. Sinal1 supporting jnumnls were wed aiid thr xii?
tit
wltivli tlic
c n u 3 ~ ~ r ~ wsur,nq !
7,rr.e
round~nqAhoibhere
-rln,ilb>
journal was mrried on a qi&x so timt most. US t h e beat H o w was from the heating eleniciit out through the journal i x e tlrrougli the oil filin to the hearing sleeve froin which it !\-:is radiated. The temperature indicat,cd hy the therinocouple mas then taken as the operating temperature. Sucli :in rrrrangernent, although far from perfect, gives the most cnmistent results yet obtained. The bearing was 5 . 8 em. E inches) in diiinieter by 7.6 cm. (3 inches) long, the journal liciiig 3 per cent nickel steel and the sleeve of bronze. The iliarnetrical clearance was 0.1 mm. (0.OOA inch). The speed in all Cases was 2000 r. p. m. The load was about 0.7 Icg. i ~ e sq, r em. (10 pounds per square inch) gross projected area. A preliminary run was made in vacuum and then repeated in air. The friction in vacuum was found to be higher than in air, rrs is shown in Figure 7, coiitaining curves innde by pluitiiig tis ordinates the scale reading on tlre t,orque arm as
suii was continued in vaeuiiiii Errm day to day, readings being t,akcn a t %how intervals. The frictioii was found to he progressively higher arid higher, but. tlie run was not continued until the inanirnurn was reached. The bearing \vas then run in air for another 8-Iioiir intervnl, a t tlie end of which the friction wits rioivii nliiiost to tlie original ruii in oxygeli r l lhcsc preiiiiiinnry runs seemed to iiidicatc that tlie presciice of oxygen is necessary in order to ohtaiii t.he minimum iuiciion and, that whatever the react,ion may be after running iri oxygen, th$ results are overcornc quite slowly when tlre oxygen is replaced by a nonoxidizing atmosphere, Ixit reproduced quite rapidly wlien it is again present,. The vacuum mentioned here (:orresponds t,o a prcssure of 100 riricrons of mercury or less. TIILLusual working pressure miis 10 lo 20 iiiicroiiz. A ri o t h e r riin was made in vacuu m for a total of IS lioiirs' running time. The bearing ~ v i ~ i i hbe l run coiitirruously for 8 hoors, stand idle for 16, and theti run another 8
twt.
iifter eich 8-hour r u n n i n g period showed a progressiveincreasein friction. The hearing was then run in air for another %hour p e r i o d . a n d tlie friet,ion emir hack alrnost to that :it the start. The air was then replaced by hydrogen, and at t,he end of ano t 11e r 8 - h 0 u r period the friction h a d g o i i e 1111. Aft,er anot,ht!r 8hour interval in hydrogen tlre Eriet,ion was down below that at the start, but during t,liis p e r i o d the soom teniperntwc )vas 7' or X" C. above noriiial o w irte to v e r y h o t weather. I'revioiis to t,his tlic rooiii tcmrwatiire had been quite constant at about 21" C. I$giire S sI&s t,hcse two curves in hydrogen, the oiic at. rooiii trinperat,ure of 24" C., and the other at room temFigure 6 perature of 3 1 " 6. All through this hot spell t,his TUII was iiiriicnting tlie frii&ii, m d for hwissa Lhc tcirrper:tt,urc a t continued, bot the results, althougli uiiiforrnly low, were very which tlie rending was taken. crratie. Even though tire run was continued in air for 20 A run made in an at.tnosphereof oxygen gnve a I o r n x friction hours after the hot spell had passed, the results could not be iliiiii \\-hen run in air. After a subsequent run in a vacuum for made to check with That had been previously obtained. 8 hours, the frictioii was highrr than after the run in oxygen, Figtire 9 s l i o ~ ~ the s comparison of the frict,ion curves at the hiit, not so high as after the original rim iii vacuum. TIIF start, after 48 running hours in vacuum, and then at the end
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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of 8 hours in air, after the 48 hours in vacuum. Figure 10 shows the percentage change in the friction after each interval as described above. To attribute the difference in friction, as shown in Figure 8, to change of viscosity due to temperature (of room) is not satisfactory because of the care taken to maintain constant temperature a t the bearing when friction was measured. Evidently something had caused a change of condition, for with a return to normal temperatures the friction did not return to the former values, but went much higher. Another similar test run was made in which hydrogen was used all the time. The hydrogen was very carefully dried and oxygen and carbon dioxide were removed. The bearing enclosure was thoroughly evacuated and the oil well agitated while under vacuum so that all traces of air were removed as far as possible. The run in dry hydrogen covered a period of 220 hours with the bearing running practically all of the time. The oil was changed once on account of an accident which it was feared had contaminated it. This change did not make any radical difference in the general trend of the curve, except for a small dip, due probably to exposing the parts to the atmosphere.
Figure 12 shows the percentage c h a n g e , calling the friction a t the start 100 per cent.
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Conclusion
These experiments indicate that for efficient lubrication some kind of a reaction is necessary which is dep e n d e n t upon the presence of moisture and of oxygen. It is I fiQure / Z I possible that dry oxygen is not very effective in this reaction, although this has not yet been determined. The reaction seems to be accelerated when b o t h o x y g e n and RUN moisture are present. 90. .*Y-. IN DRY HYOROGFN ZZOURS h'ET% Just what is happen- 80. 38 ms 2 70 . ing is not known, but B the fact seems to be 8 E well established that , TIME-HOURS , the surrounding atmosphere has a very decided effect upon the friction obtained. Surely temperature control was sufficiently accurate so that differences of friction cannot be accounted for by differences of viscosity due to changes of temperature. At the time the curves in Figure 1 were made nothing was known about the effect of the surrounding atmosphere upon friction. While attempts to explain them by viscosity differences due to temperature did not fully satisfy, this seemed the most logical explanation. However, perhaps if humidity determinations had been made at the time, data might have been available which in view of later experience would have given a more satisfactory explanation. A close study of the friction curves will show that all tend to come together in the region around 100' C. A checking over of other data and replotting on a friction temperature basis seems to show the same characteristic. Whether or not there is any significance attached to this is not yet known. I
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At the end of 220 hours the hydrogen was passed through a bubble bottle containing tap water and the run continued in this moist hydrogen for 38 hours longer. The readings taken from day to day show a progressive increase in the friction over the period of 220 hours' run in dry hydrogen, and a sharp falling off in the friction as soon as the moist hydrogen is admitted to the bearing. Figure 11 shows the friction curve a t the start, then after the 220 hours in dry hydrogen, and one a t the end of 38 hours in moist hydrogen.
The New Japanese Tariff and American Trade The recent adoption by the Japanese Diet of a bill embodying a complete revision of the import tariff has removed the feeling of uncertainty which has long been prevalent in the minds of those having trade connections in Japan, according t o information received from the Department of Commerce. The new tariff law was promulgated and made effective March 29, 1926, and goods arriving in Japan on or after t h a t date will be subject t o the new tariff schedules. No period of grace was allowed goods already ordered or en route t o Japan. In introducing the bill the Japanese Minister of Finance stated t h a t the principal objects of the measure were: first, t o adjust existing specific rates of duty so as to bring them into conformity with current prices; second, t o reduce or abolish the duties on raw materials needed by Japanese industries; and third, to afford protection t o important industries which are developing in Japan or which show promise of development. The first of these purposes was considered the most urgent. The previous tariff had been in operation since 1911, and except for partial revisions a t different times on selected articles, mainly iron and steel products, copper, dyes, and articles considered as luxuries, the rates of duty had remained practically unchanged. I n the interim, and particularly since the war, the prices of
commodities have increased considerably, so t h a t the old specific duties amounted to a smaller percentage of the value of the goods than when originally established. Moreover, there had been growing a n insistent demand for protection t o domestic industries, especially those born or expanded during the abnormal war and post-war period, against the importation of rival foreign products. Also, in a number of lines, such as dyestuffs, the government has been aiming a t national self-sufficiency, with tariff protection as a n important aid t o t h a t end. The commercial relations between the United States and Japan are governed by a treaty of commerce and navigation signed on February 21, 1911, whereby both countries assure to the products of the other most-favored-nation treatment in tariff matters. Thus, the tariff concessions at present accorded certain French and Italian products are likewise granted t o similar products of the United States, and should any further tariff concessions be granted to products of these or any other powers, such concessions would automatically apply t o similar goods from the United States. I n order t o receive the benefit of the conventional duties, it will still be necessary for products of the United States to be accompanied by a certificate of origin certified by the Japanese consul a t the place of production or shipment.
