350
IXDUSTRIAL AhTDENGINEERISG CHEMISTRY
*
of tests were made in which the clearance was purposely varied by the use of journals of different diameters. The results of one such series are given in Fig. 8, in which the value of z n / p at the transition point is plotted against the ratio d/c. It will be noted that the slope of the curve is
FIG.6-EFFECT
O F OILINESS ON VALUE O F 2
n/P
AT
TRANSITION POINT
Journal. . . . . .Steel Bearing.. .Bronze Diameter .I150 Clearance .71 pounds per square inch Load.. T . . ........ ..Velocite B spindle oil (Run 2 2 ) 0. . L a r d oil (Run 23) A.. ..Velocite B+2'% oleic acid (Run 24)
... -. ... ...... ..........
.........
very small for a considerable range either side of the value of d / c = 1000. As this figure represents approximately the clearance a t which the tests on oiliness were conducted, it seems improbable that the very small amount of wear occurring could have produced any appreciable variation in the position of the transition point. The tendency of the observed curve to rise a t values of d / c greater than 1000 (for the 1-inch diameter bearing this corresponds to a clearance of 0.001 inch) indicates clearly the reason for seldom fitting continuously loaded bearings tighter than this figure. In fact, the large majority of complete bearings carrying uni-directional loads are fitted so that d / c is rarely greater than 500. These figures do not, of course, apply to bearings in which the direction and magnitude of the load are constantly changing, as in the crankshaft and connecting rod bearings of reciprocating engines.
Vol. 16, No. 4
stable lubrication for a complete cylindrical bearing is altered by variations in oiliness of the lubricant. 2-The transition point occurs a t a lower value of the modulus, z n / p , when oiliness, as indicated by the coefficient of static friction, is increased.
FIG
7-EFFECT
O F O I L I N E S S ON VALUE O F 8
% / aA T TRANSITION POINT
Journal.. . . . . ,Steel Bearing. .Bronze Diameter ,1110 Clearance .Velocite B spindle oil (Run 12) 0.. .Lard oil ( R u n 13)
..... .... + ......... ........
.I
3-The variation of the transition point to be expected with commercial lubricants is small, certainly not over 10 per cent. 4-While it is possible to detect changes in oiliness by means of a suitable journal-testing machine, the experimental difficulties are such as to preclude the use of such a machine for measurement of this property. It is believed that the coefficient of static friction offers the most convenient single measurement of oiliness. 5-The position of the transition point is strongly affected by variations in clearance.
ACKNOWLEDGMENT The writers wish to express their indebtedness to the General Motors Research Corporation and the Standard Oil Company of New Jersey for permission to publish this paper; to the Godfred Cabot Fund a t the Massachusetts Institute of Technology for funds from which to construct the machine; to Charles Mills, of the Saco-Lowell Shops, for his coijperation and advice in planning the experimental procedure; to F. W. Perkins, of the Mechanical Engineering Department of the Institute, and to H. Van Keuren, of the Van Keuren Instrument Company, for the care and precision with which they constructed, respectively, the testing machine and the test parts and gages.
Gasoline Statistics
F I O . 8-EFFECT
OF CHANGING C L E A R A N C E ON V A L U E OF Z ? t / P AT
TRANSITION POINT
CONCLUSIONS The results of the foregoing work justify the following conclusions : 1-The position of the transition point from stable to un-
Gasoline production in the United States in January amounted to 695,322,500 gallons, and established a new high record of monthly production, according to figures compiled by the Bureau of Mines. The month of December had also established a new high record production mark. The daily average of gasoline production in January amounted to an increase of 5.5 per cent over the December daily average and an increase of 11.5 per cent over the rate for January a year ago. Imports of gasoline during January were 19,309,197gallons, a decrease of approximately 6,000,000 gallons from the December imports. The new gasoline supply (production plus imports) was 714,631,697 gallons, an increase of 12.1 per cent over last year's figures. In comparison with the gasoline statistics for January, 1923, the figures for January, 1924, show an increase of 12.1 per cent in the new supply, of 13.2 per cent in the total demand, and of 19.9 per cent in refinery stocks.
