Full resolution (JPEG) - On this page / på denna sida - Belts - To find the arc of contact of a belt - Pressure on the bearings caused by the belt
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
BELTS. 333
Solution
:
16 feet = 192 inches.
60 inches diameter = 30 inches radius.
20 inches diameter = 10 inches radius.
Cos. of half the angle = (
30 ~ 10) = .104
192
In tables of natural cosine (page 158), the corresponding-
angle is found to be 84 degrees, very nearly ; thus, the angle
for arc of contact will be 2 X 84 = 168 degrees on the small
pulley. On the large pulley the arc of contact will be 360 —
108 = 192 degrees.
For a crossed belt the arc of contact is always the same on
both pulleys, and it may be calculated by the formula:
Cos. of half the angle = — —~,
—
R = Radius of large pulley.
;• = Radius of small pulley.
/ = Distance between centers.
Example.
What will be the arc of contact for the belt on the pulleys
in the previous examples if belt is run crossed instead of open?
Solution :
Cosine of half the angle = — 30 + 10
= — 0.208 : the
192
corresponding angle will be 180 — 77 = 108 degrees, and the
arc of contact will be 103 X2 = 206 degrees.
Pressure on the Bearings Caused by the Belt.
Approximately, the pressure on the bearings caused by the
belt may be considered to be three times the force which the
belt is transmitting. Therefore, the pressure may be calculated
by the formula :
p _ 3 X 33000 X H
v
P = Pressure on the bearings due to pull of belt.
H= Number of horse-power transmitted by the belt.
v = Velocity of belt in feet per minute.
Example 1.
A belt is transmitting 60 horse-power and its velocity is 900
feet per minute. What is the pressure in the bearings due to
the belt ?
<< prev. page << föreg. sida << >> nästa sida >> next page >>
