Which of the following ropes will be most flexible?
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.
It is usually preferable in chain drive to use
Number of pitches should be ‘even’ and number of teeth on sprocket should always be ‘odd’.
Which one of the following is positive drive
In chain drive slip is almost negligible. Hence it is positive drive.
The length of the belt in case of cross-belt drive is given in terms of centre distance between pulleys (C), diameter of the pulley D and d as:
The length of belt in case of open-belt drive
A 6 x 19 rope implies that there are
Wire rope designation
In case of belt drives, the effect of the centrifugal tension is to
Note that centrifugal tension reduces the power transmission capacity but it is provided to keep the belt on pulley.
In a belt drive the centrifugal tension is 1 kN. The ratio of tensions is 2 and runs at a linear speed of 10 m/s and has to transmits 20 kW. What should be the initial tension?
The creep in a belt drive is due to the
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.
Crowning of pulleys is generally done to
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.
In V-belt, belt should contact groove at
To increase the frictional resistance both the sides of the groove should be in contact with the belt.
Given that W = weight of load handled, Wr = weight of rope and f = acceleration, the additional load in ropes of a hoist during starting is given by:
= inertia force acting as additional load
In flat belt drive, if the slip between the driver and the belt is 1%, that between belt and follower is 3% and driver and flower pulley diameters are equal, then the velocity ratio of the drive will be:
Total slip will occur in a belt drive when
The ratio of tension on the tight side to that slack side in a flat belt drive is
A 50 KW motor using six V belts is used in a pulp mill. If one of the belts breaks after a month ofcontinuous running, then
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.
A 0.2 thick tape goes over a frictionless pulley of 25 mm diameter. If E of the material is 100 GPa, then the maximum stress induced in the tape is
From the equation
What diameter should the driving pulley have on which a rubber belt runs so that bending stress in belt is limited to 5 N/mm2 (the belt cross-section is a rectangle 15 mm thick x 110 mm wide, E for belt material is 100 N/mm2)
D = 300 mm
The following data refers to an open belt drive
Ratio of tensions may be calculated using relation
Since μB θB < μA θA
Hence we choose μB θB
In a cone pulley, if the sum of radii of the pulleys on the driving and driven shafts is constant, then
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.