Transactions

642 TRANSACTIONS OF THE A.S.M.E. OCTOBER, 1941films,” and the dimensions of the test capillaries used in thiswork would correspond to thick-film conditions in bearings.The effect of orientation of molecules is thought to be pronouncedonly in the case of thin films, but it is possible thatorientation as well as plasticity affects the flow curves as Messrs.Schlesman and Bulkley point out.Further work was carried on during the summer of 1940 usingtwo capillaries in series. The principal results are given in theform of rate-of-shear versus shear-stress curves for Veedolmedium at 0 C in Fig. 20 of this closure, and for castor oil atMr. Hersey asks for a statement concerning check observations,using a smaller-diameter test capillary. An attempt wasmade toward the end of the summer to check the flow curves forsperm oil at 20 C, Fig. 11, since it was felt that these curveswere the best defined. For this work a test capillary was chosenwith an internal diameter approximately 0.6 that previouslyused, the length being such as to give approximately the sameflow for a given pressure difference as occurred in the previouswork. Such a capillary made the taking of observations easier,since it was possible to predict the value of pi necessary togive the desired average pressure for a given resistance capillary.The lowest measurable shear stresses were much higher thanthose of the previous work, and the observations were, therefore,not conclusive. Mr. Mooney mentions a method of determiningthe existence of slip described in bibliography reference(13), based upon flow observations from differently dimensionedtest capillaries when equal shear stresses are used. The methodassumes that the material studied does not have thixotropicbehavior, but it is interesting to note that, if data from severalcapillaries coincide when plotted as Q/irr3 against S, freedomfrom both slip and thixotropy is indicated.Fig. 20 S h e a r C h a r a c t e r i s t i c s o f P a r t i a l l y W o r k e d V e e d o lM e d i u m a t 0 C(Average pressures indicated along curves, in psi.)F ig . 2 2F low C u rves for C astor Oil at 2 0 C U n d er 2 5 ,0 0 0 P siAv erage P r essu reF i g . 2 1 S h e a r C h a r a c t e r i s t i c s o f P a r t i a l l y W o r k e d C a s t o rO i l a t 20 C(Average pressures indicated along curves, in psi.)20 C in Fig. 21. The test capillary used for the Veedol mediumhad an internal diameter of 0.0456 cm and a length of 6.08cm; the test capillary used for the castor oil had an internaldiameter of 0.0456 cm and a length of 16.1 cm. These curvesmerely extend the data given in the paper and are subject to thelimitations hitherto discussed.Tests were made upon Veedol medium at 40 C, using pressuredifferences appreciably smaller than in the previous work. Theobservations were erratic due to insufficient accuracy in determiningthe pressure difference. For example, on the 10,000-psiaverage-pressure curve, several negative pressure differences wererecorded even after using a calibration curve for the Bourdontubes. The curves, therefore, were ill defined, and the dataare not given.26 These observations emphasized the limitationsof the present apparatus.26 A complete record of the data obtained, during the summer of1940, has been filed with the Special Research Com mittee on Lubricationof T h e A m e r i c a n S o c i e t y o f M e c h a n i c a l E n g i n e e r s .An investigation of the temperature rise in the oil was made,using an iron-alumel thermocouple in place of p2 of Fig. 9 ofthe paper. Readings so obtained were ambiguous in view of thevery small diameters of the test capillaries, but they indicatedthat the temperature rises were not excessive. The thermocouplejunction was placed in the bore of a connecting block,having a cross-sectional area approximately 12 times that ofthe test capillary. The bore had a volume of approximately0.05 cm3 while an average-flow sample might contain 0.5 cm3.In other words, approximately 10 times the volume of the borewas swept out during the taking of a test. Neglecting the conductionof heat by the thermocouple, some sort of mean exittemperature was measured. The limit of sensitivity of the thermocouplewas y 3 C, and the highest observed temperature risewas 3V3 C, while the majority of the tests showed no perceptibletemperature rise.It is instructive to recall the test procedure when discussingtemperature variations. A given pressure po was applied for10 min while the outlet valve remained closed. Upon openingthe valve, pi was kept at pa while p2 adjusted itself to flowconditions. When p%became steady, a flow sample was taken,the whole procedure being limited to a relatively short time bythe capacity of the intensifier. When the thermocouple wasused, the opening of the valve was followed by a sudden tem­