Test: Belt, Rope & Chain Drives - 3 - Mechanical Engineering MCQ

The wire rope of 6 x 7 construction consists of a few wires of relatively large size. It is too stiff for hoisting purposes. The 6 x 19 or 6x 37 constructions are flexible wire ropes, and are commonly used in hoists.

Number of pitches should be ‘even’ and number of teeth on sprocket should always be ‘odd’.

In chain drive slip is almost negligible. Hence it is positive drive.

Wire rope designation

Note that centrifugal tension reduces the power transmission capacity but it is provided to keep the belt on pulley.

In Belt drives when the belt passes from the slack side to the tight side, a certain portion of the belt extends. Similarly, when the belt passes from the tight side to the slack side it contracts. Hence creep in belt drive is due to uneven extensions and contractions of the belt when it passes from tight side to slack side.
This phenomenon of alternative stretching and contraction of the belt results in relative motion between the belt and the pulley surface. This relative motion is called creep.

There is a specific term crowning of pulley in flat-belt drive. The objective of providing crowining are as follows:
1. The crown on pulley helps to hold the belt on pulley in running condition.
2. The crown on pulley prevents the belt from running off the pulley.
3. The crown on pulley brings the belt to running equilibrium position near the midplane of the pulley.

To increase the frictional resistance both the sides of the groove should be in contact with the belt.

= inertia force acting as additional load

If one of the belt in multi-belt drive is breaks then all the belts should be replaced by new set of belt to ensure uniform stress in all the belt.

From the equation

D = 300 mm

Since μ_B θ_B < μ_A θ_A
Hence we choose μ_B θ_B 

In a cross belt drive, both the pulleys rotate in opposite directions. If sum of the radii of the two pulleys be constant, then length of the belt required will also remain constant, provided the distance between centres of the pulleys remain unchanged.