Chap 7: belt drives

Question 1

5 types of belts

Answer 1

flat, vee, ribbed, timing, link belts

Question 2

perks of flat belts

Answer 2

simple and cheap

high speed and low power usage

Question 3

perks of vee belts

Answer 3

high power
speed ratio 7:1
normal range of power requirements

Question 4

perks of ribbed belts

Answer 4

light duty
high speed ratio 30:1
better grip (wedging)

Question 5

perks of timing belts

Answer 5

constant angular velocity

do not creep or slip

Question 6

perks of link belts

Answer 6

centre distance is not crucial (can be changed by number of links added or removed)
belt replacement is easy

Question 7

types of chains and its applications

Answer 7

power transmission chains: transmit power through mechanical interlocking of drive and driven sprockets

hoisting chains: lift heavy loads (engines/machines from their mounting)

conveying chains: move parts by pulling

Question 8

advantages of belt drives over chain drives

Answer 8

absorb shock and vibration
simple maintenance cost (no lubrication needed)
low cost (initial & replacement costs are low)
design flexibility (allows power transmission over non-parallel shafts (flat belts only))

Question 9

advantages of chain drives over belt drives

Answer 9

high efficiency (allows smooth & efficient flow of power), efficiency can be as high as 98%

positive drive (no slip): greater power capacity

can be operated in oil-surrounded or high temp environment

single chain can drive many shafts at different speeds

can be driven on both sides

Question 10

what are belts subjected to?

Answer 10

tension, bending, centrifugal forces

Question 11

belt properties needed

Answer 11

strong in tension
light weight
flexible for bending
elasticity (absorb shock)
sufficient friction

Question 12

vee belt drive speed ratio, best & ideal operating speeds

Answer 12

speed ratio 7:1
operates best between 8 - 30 m/s
ideal speed (23 m/s)

Question 13

4 components on a vee belt drive

Answer 13

flexible top section (tensile layer)
cover (rubberised woven jacket)
load carrying section (main tension carrying cord)
compression section (resilient compression material)

Question 14

types of pully and sheave for vee belt drive and its properties

Answer 14

formed steel, light duty (sheave with integrated hub)
spoked cast sheave (integrated hub)
disk type cast sheave (removable hub)

Question 15

conversion from Hp to kW

Answer 15

1 Hp = 0.746 kW

Question 16

steps for selection of v belts

Answer 16

1) find design power
2) find the v belt section (A, B, C or D)
3) determine PCD of small and big pulley ( & speed ratio)
3a) find actual output speed if needed
4) find pitch length of belt (formula)
5) find actual centre distance (formula)

6) find number of belts needed
6a) power rating per belt (from table)
6b) arc of contact CF (choose smaller value)
6c) belt length correction factor
6d) actual power rating of belt
6e) number of belts = design power / actual power rating of belts (round up)