Experiments With Needle Bearings Page: 4 of 29
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N.A.C.A. Technical Memorandum No. 707
ses, would seem to explain the brilliant results which
characterize this type of bearing. The experimental re-
sults constitute the best confirmation of our conclusions.
Let us consider a journal supported by a certain num-
ber of needles and the load p, which rests on the bear-,
ing, distributed between them in such manner that the wear
of the journal and of the bearing, in harmony with Reyoe's
hypothesis, is proportional to the work of friction. The
wear being necessarily the same at all points, the normal
pressure exerted by the journal on each needle (fig.. 2)
is represented by
- constant
cos cp
and, calling Pmax the value of which belongs to
cos c
the lower needle for 9 = O, we have
P = Pmax cos 9 (1)
We can consider the two components of p: namely, p/cos (p
which, according to formula (1), is equal to Pmax for
each needle and which acts on the bearing, and p tan cp
which tends to make each needle climb on the bearing till
it presses against the next needle.
Through the symmetry of the bearing and through the
clearance between the needles* it happens therefore that
all the needles on both sides of the lowest needle tend to
move away from the latter, as indicated in figure 3, with
increasing pressure on each side up to the two needles at
the ends of the horizontal diameter, and with uniform
pressure for all the needles of the upper half of the bear-
ing.
The value N of this pressure of the angle (p is
measured by the sum of the components of p tan C9 in the
direction of N (forming the angle cp1 with the hori-
zontal). These components (fig. 4) are represented by
*A radial clearance of not less than 0.02 to 0.04 mm (0.0008
to 0.0016 in.) is prescribed for the regular functioning of
the bearings.- --
3
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Ferretti, Pericle. Experiments With Needle Bearings, report, May 1933; (https://digital.library.unt.edu/ark:/67531/metadc63543/m1/4/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.