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FRICTION AND LUBRICATION 269 
will only move easily over.the paper in the direction of the edge. 
Instead of a drawing pencil, a piece of steel having a razor edge may 
be used. 
235. Tower’s Experiments on the Friction of Pivot and Collar 
Bearings. — The table below gives the results of the experiments 
on the friction of a pivot bearing carried out a 
by Mr. Beauchamp Tower, and described in the LTT TT 
fourth report of the Research Committee of : 
the Institution of Mechanical Engineers on fric- 
tion.*. The pivot experimented with was of steel Ff 
3 inches in diameter, and flat ended. The bear- §& ST 
ing, which was of manganese bronze, is shown = "= 
in Fig. 412. The oil was introduced, as shown, 
through a single central hole, and distributed over 
the bearing by a single diametrical groove, terminating at each end 
within ,',th of an inch of the circumference of the bearing. It was found 
that the oil circulated automatically, the pivot and bearing acting like 
a centrifugal pump. 
The coefficients of friction in the table below were calculated 
from the observed frictional moments, on the assumption that the mean 
leverage of the friction was two-thirds of the radius of the pivot, which 
would be correct if the pressure on the bearing was uniformly dis- 
tributed, and the friction was independent of the velocity. The circula- 
tion of the oil varied from 20 to 56 drops per minute at the lowest speed 
to a continuous stream at the higher speeds. 
Fia. 412. 
Load in Lbs. per Square Inch. 
per 20 | 40 | co | 8 | 100 | 120 | 140 | 160 
Coefficients of Friction. 
50 | 0°0196 | 00147 00167 | 00181 | 0-0219 | 00221 ee 2 
128 | 0°0080 | 00054 | 0:0053 | 0°0063 | 0°0077 | 0°0083 | 0-:0093 | 0°0113 
194 | 0°0102 070061 | 0-0051 | 0:0045 | 0:0044 | 00052 | 0°0062 | 0-0068 
290 | 0°0178 | 0°0107 | 0°0078 | 0:0064 | 0°:0056 | 0°0048 | 0:0046 | 0:0044 
353 | 00167 | 0°0096 | 0°0073 | 0°0063 | 0°0057 | 0°0053 | 0°0053 | 0°0054 
The results of Mr. Tower’s experiments on the friction of a collar 
bearing { showed that the friction in this type of bearing is practically 
independent of the speed. The adjoining table gives the mean values of 
the coefficient of friction () obtained with different intensities of 
pressure (py) on the ) 
bearing ring, in lbs. | » | 15 | 30 | 45 | 60 | 675 | 75 | 825 
per square inch. The 
mean leverage of the w =|0°054 | 0:046 | 0:037 | 0°036 | 0-035 | 0-035 | 0-034 
friction was taken 
as the mean radius of the ring. It was found in these experiments that 
the greatest load which the bearing would carry was 75 lbs. per square 
* Proceedings of the Institution of Mechanical Engineers, 1891. 
t Ibid., 1888. 
