 ———— Se er 
“—=—_——. ~~ T = i —— 
4 BELT, ROPE, AND CHAIN GEARING 373 
_ 200 revolutions per minute. The stepped pulleys are to be designed so that the 
B may be driven at 600, 300, or 100 revolutions per minute as required. 
DP, =30 inches, e=50 inches, Find the other diameters and /, the length of the 
. which is an open one. 
10. Find the answers to the preceding exercise when a crossed belt is used, 
11. A cone pulley AE (Fig. 574) drives the cone pulley ae by means of an 
open belt. Diameter at A=diameter at ¢=16 
inches. Diameter at a= diameter at E=8 inches. 
The slant side of AE is straight. Find the 
diameters at b, c, and d, so that the belt may 
be equally tight in each position. Draw the 
ae to scale, half size for diameters, and 
ze for widths. 
12. Taking the dimensions given in Fig. 574, 
and in the ype exercise, except that the 
slant side of AE is no longer straight, determine 
the diameters at B, 6, C, c, D, and d for an open 
belt, so that the speed ratios when the belt is Fia. 574. 
at Aa, Bb, Ce, Dd, and Ee in turn may be in 
geometrical progression. Draw the pulley ae to scale, balf size for diameters, 
and 4th size for widths. : 
13. A belt drives a pulley 4 feet in diameter at 100 revolutions per minute, 
and transmits 34 horse-power. Assuming that the tension on the tight side is 
twice that on the slack side, find these tensions. 
15-20. In the exer- 
cises given in the an- 
nexed table H=horse- | Exercise | 15 16 17 18 19 20 
wer transmitted by a 
t. W=speed of belt 
in feet per minute. H — re 25 100 
20 50 
T, = tension on tight Vv 3000 | 2800 | 2500 | 3000 | 3500] ... 
side. T,=tension on | T,+T, 2 2 1Z 2 2 2 
slack side. b= breadth of b 5 9 i AY 5 10 
belt in inches, ¢=thick- t es Lox 3 ve } g 
ness of belt in inches. St 300 | 350 | 400 | 300 | ... | 350 
f=working stress in lbs. 
per square inch. w the 
weight of 12 cubic inches of belt is to be taken at 0-4 lb. Find the unknown 
quantities in each case, (1) neglecting centrifugal tension, (2) taking centrifugal 
tension into account. 
21. Taking the data of Exercise 16, with the exception of V, determine the 
maximum horse-power which may be transmitted, taking into account the 
centrifugal tension. 
22. Given T,=2T,, f=350, and w=0°4, calculate the horse-power H, per 
square inch of belt section, taking into account the centrifugal tension, at 
intervals of 10 feet per second, between the values of v which make H=0. Plot 
the results on squared paper. Scales.—1 inch=5 horse-power, and 1 inch=20 
feet per second. Determine H and # for the highest point of the curve. 
23. Show that when a belt is transmitting the maximum power, the centri- 
fugal stress is one-third of the greatest stress, 
24. A countershaft, which runs at 300 revolutions per minute, is required to 
transmit 10 horse-power from a main line shaft to a machine. The driving 
pulley of the machine shaft is 12 inches in diameter. The main shaft runs at 
100 revolutions per minute, and the machine shaft at 900 revolutions per minute. 
The diameter of the main shaft pulley is 3 feet. Assuming the coefficient of 
friction between the belt and its pulley to be 0°3 in each case, and the belt § inch 
thick, determine the width of each belt, taking account of the centrifugal 
tensions, The weight of a cubic inch of belt may be taken as 0035 Ib., and the 
tension per square inch as 350 Ibs. Prove the formule you use. (U.L.] 
25. Find the maximum horse-power whieh can be transmitted by a hemp 
rope l inch in diameter at a of 70 feet per second if the rope is broken 
with a pull of 5700 1bs., and it is desired to have a factor of safety of 30. The 
