416
MOLESWORTH'S POCKET-BOOK,
Hekp Kofe Gearing.
(Duiee, * Trans. Inst. Mech. Eng.,’ 1876.)
Ropes 5i to 6; circumference; 4} for small power.
Velocity of rope from 3000 to 6000 feet per minute.
Circumference of pulley not less than 30 times the circum-
ference of the rope. A good proportion for the diameter of
the driving pulley first motion is 600 times the diameter
of the rope; second motion, 50 times.
The distance of the two pulleys apart, from 30 to 60 feet.
The ropes should not rest on the bottom of the groove,
which should be V-shaped, the sides bong at an angle of
40°.
The length of the eplice should be about 15 times the
circumference of the rope.
The rope should never be strained bo as to draw it to a
near approach to straight, even in short spans.
Weight of ropes in lbs. per foot = -04 C2.
Working tension of the rope from 110 to 120 lbs. per square
inch of its section.
Formula for Hemp Rope Gearing.
V = Velocity of rope in feet per minute.
n — Number of ropes.
C = Circumference of rope in inches.
I’ — Indicated horse-power.
O V (n - 1)
~ 4000 "
l< — A / ^(TF
~ V(n - 1) ’
This formula is under the supposition that the number of
ropes is one in excess of the number actually required, so as to
provide for changing and repairs.
Some ropes have run for 10 f years, but as a rule the life of
a rope is from 3 to 5 years.