# * SLIP AND CREEP

SLIP AND CREEP
Slip is there when belt does not grip pulley fully and perfectly i.e. there is not full friction between the pulley and the belt.

SLIP BETWEEN DRIVER PULLEY AND BELT
This slip is the difference between the linear velocities of driver pulley and belt. It is expressed in terms of driver linear velocity.
Linear velocity of driver pulley = [(πd1N1)/60)]
Linear velocity of belt = v
S1 = % slip between driver pulley and the belt
∴[(πd1N1)/60)] (S1/100) = [(πd1N1)/60)]-v

∴v = [(πd1N1)/60)] [1 — S1/100] (i)

SLIP BETWEEN BELT AND DRIVEN PULLEY
This slip is the difference between the linear velocities of belt and the driven pulley. It is expressed in terms of linear velocity of belt.
S2 = % slip between the belt and driven pulley
Slip = = v — πd2N2/60
v x S2/100 = v — πd2N2/60
v(1 — S2/100 ) = πd2N2/60
Substituting the value of v from equation (i), we get
[(πd1N1)/60)] [1 — S1/100] (1 — S2/100) = πd2N2/60
Multiply brackets containing S1 and S2
[(πd1N1)/60)] [1 — S1/100 — S2/100 + S¬1S2/10000 )= πd2N2/60
Neglecting S¬1S2/10000, we get
[(πd1N1)/60)] [1 — S1/100 — S2/100)= πd2N2/60
[(πd1N1)/60)] [1 – (S1+S2)/100)= πd2N2/60
Let Total % slip = S = S1+S2, then
[(πd1N1)/60)] [1 – S/100)= π d2 N2/60

DIFFERENCE BETWEEN SLIP AND CREEP IN A BELT DRIVE
SLIP
Slip Is due to incorrect tensions in the belt such that driver pulley moves and the driven pulley does not move. It is more prominent in a V-belt drive than a flat belt drive.

CREEP
Belt is made of material of low modulus. Thus there will be significant change in length of the belt in moving from tight side tension to slack side tension and hence creep occurs. It can also occur because of pulleys not being parallel to each other. It is more prominent in a flat belt drive. To avoid creep, pulleys are crowned in the center so that there is no relative motion between the pulley and the belt. Both slip and creep cause relative motion between the pulley and belt. These also reduce power transmission.These should be reduced to the minimum.