Law of gearing states that the common normal at the point of contact between a pair of teeth must always pass through the pitch point for all positions of mating gear. This law forms the basis for the gear profile design. This is a must condition for the two gears to perform properly.
Consider the portions of two gear teeth in mesh.o1 and o2 are centre points,
Let K= point of contact
TT = COmmon tangent at the point of contact K
Power transmission in belt drive depends on angle of lap and frictional grip between belt and pulley. As slack side is at upper side angle of lap and grip increases.
Flat belt speed = V = 600 m/min = 600/60 m/sec = 10 m/sec;
Power transmitted = P = 4 kW ;
Coefficient of friction =µ = 0.3;
Angle of lap = θ =1600
Belt tension ratio = T1/ T2 = eµθ = e 0.3(160x π/180) = 2.31; T1/ T2 = 2.31;
T1= T2 x 2.311--------------------------------(1)
P = ( T1 - T2) x V ; --------------------------------(2)
P = ( T2 x 2.31- T2)x 10; Putting value of power
P = 4 kW 4 x1000 = ( T2 x 2.31 - T2)x 10;
T2 = 305.34 N
T1 = 705.34N
Effect of centrifugal tension on power transmission:
As the belt passes over the pulley with high velocity, centrifugal force is produced on the belt, which tends to act on the belt. This force tries to move the belt away from the pulley.
This force is given by,
TC = m x V2
There is no effect of centrifugal tension on power transmitted.
Advantages of chain drive over belt drive
a) No slip takes place in chain drive as in belt drive there is slip.
b) Occupy less space as compare to belt drive.
c) High transmission efficiency.
d) More power transmission than belts drive.
e) Operated at adverse temperature and atmospheric conditions.
f) Higher velocity ratio. g) Used for both long as well as short distances
Slip --- Slip is defined as insufficient frictional grip between pulley (driver/driven) and belt. Slip is the difference between the linear velocities of pulley (driver/driven) and belt.
Creep ----- Uneven extensions and contractions of the belt when it passes from tight side to slack side. There is relative motion between belt and pulley surface, this phenomenon is called creep of belt.
