ME 6601 - DESIGN OF TRANSMISSION SYSTEMS WIRE ROPES AND SAMPLE PROBLEMS

1. DEPARTMENT OF MECHANICAL ENGINEERING
PROBLEMS ON DESIGN and selection wire
ropes using psg design data book
By
Mr. B.Balavairavan
Assistant Professor
Mechanical Engineering
Kamaraj College of Engineering and Technology
Virudhunagar

2. A history
• It evolved from the steel chains and wooden rods .
• As the wire ropes are made of strands of twisted metal wires it cant easily fail.
• Originally developed for hoisting in the 1830s, mining engineer Wilhelm Albert
twisted together several strands of metal wire around a hempen core, resulting
in a superior hoisting cable for use in vertical shafts.
• Later used for hoisting in cranes, elevators and for power transmission.
• Widely used for application like, Bowden cable, in suspension bridges, in
tramways and in spinning mills.

3. Wire Rope
Wire Ropes are made by twisting thin metal wires which increases the strength of
the rope.
Wire ropes have diameter larger than 9.52 mm.
If the diameter is less than 9.52 mm its called as cable or cords.
The common material used to make wire rope is steel.
It is used when large amount of power is to be transmitted from one pulley to
another pulley.

4. Advantages of wire ropes
• Ropes furnish smooth, continuous action.
• Rope Drives are low in cost of installation and high in efficiency.
• The ratio of revolutions can easily be changed by a new small pulley.
• Changes of pulley alignment which are so destructive to gears or chains do not
affect ropes.
• Freedom from shut downs by accidents is assured. The breaking of a tooth is
serious; a temporary overstraining of ropes does very little harm.
• Rope Drives are noiseless.
• The engine or motor may be located away from the grit and dust of the mill.
• Freedom from shocks is obtained, as ropes are elastic.
• Efficiency of Rope Drives varies from 87 % to 97%.

5. Wire Rope Construction

6. Strand and core
Strand is two or more wires wound
concentrically in a helix.
They are usually wound around a
centre wire called core.

7. Lay – 3 types
• The direction strands lay in the rope
right or left.
• The relationship between the direction
strands lay in the rope and the direction
wires lay in the strands.
 In regular lay, wires are laid in the
strand opposite the direction the
strands lay in the rope.
 In lang lay, the wires are laid the
same direction in the strand as the
strands lay in the rope.
• The length along the rope that a strand
makes one complete spiral around the
rope core

8. Code Number Composition

9. Choosing the right wire rope
To increase fatigue resistance by selecting a rope with more wires, the rope will
have less abrasion resistance because of its greater number of smaller outer
wires.
For a wire rope with greater abrasion resistance, one choice is a rope with fewer
(and larger) outer wires to reduce the effects of surface wear. But that means the
rope’s fatigue resistance will decrease.
You must consider all operating conditions and rope characteristics.

10. Basic characteristics of wire rope are,
Strength (Tensile strength)
Fatigue Resistance (a rope made of
many wires will have greater fatigue
resistance than a same-size rope
made of fewer, larger wires because
smaller wires have greater ability to
bend as the rope passes over
sheaves or around drums.)

11. Fatigue Resistance (a rope made of many
wires will have greater fatigue resistance
than a same-size rope made of fewer,
larger wires because smaller wires have
greater ability to bend as the rope passes
over sheaves or around drums.)

12. Crushing Resistance (Crushing is the
effect of external pressure on a rope,
which damages it by distorting the cross-
section shape of the rope, its strands or
core – or all three.)
Crushing resistance therefore is a rope’s
ability to withstand or resist external
forces, and is a term generally used to
express comparison between ropes.

13. Resistance to metal loss and deformation/Abrasion
resistance (ability to withstand metal being worn away
along its exterior).
Resistance to rotation (In rotation resistant ropes, the lay of the outer
strands is in the opposite direction to the lay of the inner strands)

14. Lubrication

15. Other types of ropes used for power transmission
Torque Wire Rope Torque coil

16. Wire Rope
Selection using PSG design
data book

17. Procedure
1. Selection of wire rope type
2. Calculation of design load
3. Selection of wire rope diameter
4. Calculation of sheave or drum diameter
5. Selection of useful cross sectional area
6. Calculation of wire diameter
7. Selection of weight of rope
8. Calculation of Effective Load
9. Calculation of factor of safety
10.Calculation of number of wires
11.Sheave dimensions

18. Problem 1
Problem Statement:
Design a wire rope for an elevator in
a bulding 60 m high and for a total
load of 20 kN. The speed of the
elevator is 4 m/sec and the full speed
is reached in 10 seconds.
Given Data:
Load (W) = 20 kN
Velocity (v) = 4 m/s
Time (t) = 10 s
Height (H) = 60 m

19. Step 1 “Selection of wire rope”
Given that a wire rope has to designed
for a elevator, from Page No. 9.1 for the
given application,
Wire rope 6 x 19 Class 3 is selected

20. Step 2 “Calculation of Design Load”
Design Load = 2.5 x Load to be lifted x Assumed factor of safety
Considering the given application and the
selected wire rope 6 x 19 Class 3, from
Page No. 9.1,
Design Load = 2.5 x (20 x103 ) x 5
Design Load = 250 x 103 N
Factor of safety = 5

21. Step 3 “Selection of wire rope diameter (d)”
Assuming the design load
as breaking load select
the wire rope diameter
from PSG Design Data
Book P. No: 9.4 to 9.5
Design Load = 250 x 103 N
Design Load = 25.48 Tonnes
Rope dia (d) = 22 mm

22. Step 4 “Calculation of sheave or Drum Diameter (D)”
Using the selected type of wire rope select D/d ratio from PSG Design Data Book
P. No: 9.1 and using the ratio D (Drum diameter) is calculated.
For the selected wire rope 6 x 19 Class 3,
D
d
= 23
D
22
= 23
D = 506 mm

23. Step 5 “Selection of useful cross sectional area (A)”
Using the formula for "A" in PSG Design
Data Book P. No: 9.1 cross sectional
area is calculated,
π
4
d 2A = 0.4 x
π
4
22 2A = 0.4 x
A = 152.05 mm 2

24. Step 6 “Calculation of wire diameter (dw)”
d w =
d
1.5
d w = 1.373 mm
d w =
22
1.5
i = Number of strands x number of wires in each strand

25. Step 7 “Selection of weight of rope (Wr)”
For the selected
diameter of wire rope
in PSG Design Data
Book P. No: 9.4 to 9.5
select the weight of
rope.
W r = 1.84 kgf/m
=18.05 N/m
For 60 m height, Wr x 60
=1083 NW r

26. Step 8 “Calculation of Effective load”
Wea - Effective Load
Wd - Direct Load (load to be handled)
Wb - Bending Load
Wa - Acceleration Load
E' - Take it from PSG Design Data Book P. No: 9.1
v1 = 0 (initial velocity)

27. Wea - Effective Load
Wd - Direct Load (load to be handled)
Wb - Bending Load
Wa - Acceleration Load
E' - Take it from PSG Design Data Book P. No: 9.1
v1 = 0 (initial velocity)

28. Wea - Effective Load
Wd - Direct Load (load to be handled)
Wb - Bending Load
Wa - Acceleration Load
E' - Take it from PSG Design Data Book P. No: 9.1
v1 = 0 (initial velocity)

29. Wea - Effective Load
Wd - Direct Load (load to be handled)
Wb - Bending Load
Wa - Acceleration Load
E' - Take it from PSG Design Data Book P. No: 9.1
v1 = 0 (initial velocity)

30. Step 9 “Calculation of factor of safety”
Working factor of safety =
Working factor of safety =
250 x 103
56129
The working factor of safety is not greater than the
recommended factor of safety hence the design is not
safe. Hence number of wire ropes is calculated as in next
step.
4.454

31. Step 10 “Calculation of number of wires”
Number of wires = 1.122 = 2 wires
Number of wires=
5
4.454

32. Step 10 “Sheave Dimensions”
From Page No. 9.2 and 9.3