# BELT DRIVE

The power is transmitted from one shaft to the another shaft by a belt, chain and gear drives. The belts and ropes are used where distance between the two shafts is large. The chains are used for intermediate distances. The gears are used for shorter distance between the shafts. Gear drive is a positive drive because there is no slip. Belts(or ropes) transmit power because of friction between the belt (or rope) and the pulley. Due to slip and creep in belts, this drive is not a positive drive. Thus it finds limited applications.

BELT DRIVE
Belt drive consists of
(i) Driver and driven pulleys
(ii) Motor and machine shafts
(iii) Two keys
(iv) One belt
TYPES OF BELT DRIVE
Open Belt Drive
Cross Belt Drive
Compound Belt Drive (3 shafts and two belts, four shafts and three belts)
Quarter turn belt drive

## Cross Belt Drive

In case of cross belt drive, both drive and driven shafts run in the opposite directions. But the more angle of contact (angle of wrap) increases power transmission. Chances of slip of belt are not there.

## Rope Belt Drive

Here a rope is used. But these not very common in industries.

## PRACTICAL APPLICATIONS OF A V- BELT DRIVE

#### (vii)  Cars

ANALYSIS OF FLAT BELT DRIVE

OPEN FLAT BELT DRIVE
When centrifugal tension is neglected
T1 / T2 = eµθ
T1 Tight side tension in Newton (N)
T2 Slack side tension in Newton (N)
µ = Coefficient of friction between the pulley and belt materials

θ = Angle of contact=angle of lap on the SMALLER PULLEY
Initial tension = Ti = (T1 + T2)/2
Power transmitted = (T1 –T2) v            Watts (W)
v is the linear velocity of the belt in meters
Hence v =πD N/60
Where N is RPM and D is the diameter of the pulley in meters

WHEN CENTRIFUGAL TENSION IS CONSIDERED
Tc = m v2
Where m is mass of belt PER UNIT LENGTH, kg/m
Initial tension = Ti = ((T1 + T2)/2 + Tc)
Firstly        Ttight = T1 + Tc
Secondly  Tslack = T2 + Tc
Thirdly      Ttight / Tslack = eµθ
Power transmitted = (Ttight — Tslack) v         Watt

CONDITION FOR MAXIMUM POWER WITH CENTRIFUGAL TENSION (Tc)
Firstly Tmax = 3 m v2

Secondly T1 = (2/3) Tmax

Thirdly T2 = (1/3) Tmax

V = (Tmax/3 m) 0.5

Max Power = (2/3) Tmax (1 — eµθ)( (Tmax/3 m)0.5)            Watts