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34° WIRE ROPE TRANSMISSION.
Transmission Capacity of Wire Ropes.
A one-inch rope running 5000 feet per minute is capable of
transmitting 200 horse-power. The transmitting capacity of the
rope is in proportion to the square of its diameter, and the power
transmitted by the rope when the velocity is less than 5000 feet
per minute is practically in proportion to its velocity* Hence
the formula:
H= d*
X VX 200
which reduces to H = 0.04 X d* X V
5000
H= Horse-power transmitted.
<-/= Diameter of rope in inches,
JS= Velocity of rope in feet per minute.
Example.
How many horse-power may be transmitted by a wire rope
]/
2 inch in diameter running over proper pulleys at a velocity of
2500 feet per minute ?
Solution :
H’= 0.04 X ]/
2 X y
z X 2500 = 25 horse-power.
The pressure on the bearings will not be less than three
times the force transmitted, and may be calculated thus :
Pressure on bearings = g X horse-power X 38000
V elocity in feet per min.
Example.
What will be the least pressure in bearings for a wire rope
transmitting 150 horse-power at a velocity of 5000 feet per
minute ?
Pressure on bearings = 3 X 150 X 33000 _ 29TQ d
5000
F
If there is one bearing on each side at an equal distance
from the pulley, the pressure on each bearing will be 29
2
yo =
1485 pounds. This is the calculated pressure, and represents
what the pressure should be, but it is not certain that this is the
actual pressure. It may be greatly increased by having the rope
too tioht.f
* When the velocity of the rope exceeds 6000 feet per minute the stress caused
by centrifugal force when the rope is bending around the pulley considerably
reduces its transmitting capacity. This loss increases very fast above this speed,
because the centrifugal force increases as the square of the velocity. It is very
doubtful if there is practically any gain to run wire ropes at a speed exceeding 6000
feet per minute when wear and tear, loss due to centrifugal force, etc., are
considered.
t Sometimes a pulley is put on the free end of a line of shafting projecting
through the wall and drawn by a wire rope outside the shop; this will do only
when a comparatively small amount of power is to be transmitted.
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