Wire ropes are constructed by twisting individual steel wires into strands and then twisting the strands around a core. Common constructions include 6x7, 6x19, and 6x37, indicating the number of strands and wires per strand. Regular lay ropes, where the wire twist is opposite the strand twist, provide more stability and are more commonly used. Ropes experience both tensile and bending stresses that can lead to fatigue failure over time. Proper selection of rope construction, flexibility, and safety factors is necessary depending on the application. Grooved drums are generally preferred over plain drums to reduce rope wear.

1. Wire Ropes
© Dr.V.R Deulgaonkar 2018

2. Construction of wire ropes
Prof.Deulgaonkar V.R University of Pune

3. • Wire rope consists of number of “Strands”.
• Each strand comprises several steel wires.
• The no. Of wires in each strand is 7,19,37
while the number of strands is usually six
• Individual wires are twisted into the strand
and then strands are twisted around fibre or
steel core.
Prof.Deulgaonkar V.R University of Pune

4. • Specification of wire rope includes two
numbers as 6X7 or 6X19.
• First number indicates the number of strands
while the second number gives the number of
steel wires in each strand.
• Popular constructions of steel wire ropes are
6X7 (6/1) , 6X19 (12/6/1), 6X37 (18/12/6/1)
Prof.Deulgaonkar V.R University of Pune

5. • Central portion of the wire rope is called core
• Cores are of three types : fibre, wire and
synthetic material .
• Fibre Core : it includes natural fibers like sisal,
hemp, jute or cotton. It is flexible & suitable
for all normal working conditions, except
under high load.
• Wire core is used for severe heat or crushing
conditions.
Prof.Deulgaonkar V.R University of Pune

6. • Rope Lay : It refers to the manner in which the
wires are helically laid into strands and the
strands into the rope.
• If the wires in the strand are twisted in the
same direction as the strands, then the rope is
called Lang’s Lay rope.
• When the wires in the strand are twisted in a
direction opposite to that of strands, then the
rope is said to be “regular or ordinary lay”
Prof.Deulgaonkar V.R University of Pune

7. Prof.Deulgaonkar V.R University of Pune

8. • Regular lay ropes are more popular than the
other one as it offers following advantages:
1) More structural stability.
2) More resistance to crushing and distortion.
3) Less tendency to rotate under load.
4) Less possibility of kinking.
5) Easy handling during installation.
Prof.Deulgaonkar V.R University of Pune

9. Stresses in wire ropes
• The individual wires are subjected to direct
tensile stress & bending stresses due to load
being raised.
• The bending stress in one individual wire is
given by
σb = Mb y/I ; y = dw/2
dw = wire diameter in (mm)
σb = Mb dw/2I ----------- (a)
Prof.Deulgaonkar V.R University of Pune

10. • The elastic curve equation is Mb/EI = 1/r.
• Radius of curvature in the above equation =
radius of sheave.
Mb/EI = 2/D -------- (b)
D is dia of sheave
From (a) & (b)
σb = Edw/D -------- (c)
Prof.Deulgaonkar V.R University of Pune

11. • The modulus of elasticity is replaced by
effective modulus of elasticity of wire rope Er
• So equation (c) becomes
σb = Erdw/D ----------- (d)
To design wire ropes, it is convenient to bending
stress into equivalent bending load, that
would induce the same bending stress.
Prof.Deulgaonkar V.R University of Pune

12. • The equivalent bending load is Pb is
Pb = σb A = A {Erdw/D} --------- (e)
A is the area of metallic cross-section in the wire
rope. (refer table 23.7 :Bhandari V.B)
Failure of wire rope is mainly due to fatigue or
wear. Bending and straightening of wire as it
passes over the sheave results in fluctuating
stresses.
Prof.Deulgaonkar V.R University of Pune

13. • Amount of wear depends upon the pressure
between the rope and sheaves. The force per
unit length is pdr
• Considering the equilibrium of forces in
vertical direction we have
2P = D p dr : p = 2P/D dr
Prof.Deulgaonkar V.R University of Pune

14. Selection of wire ropes
• Guidelines for selection of wire ropes are
1) Referring to table 23.4 {Design of machine
elements by V B Bhandari} wire ropes of
designation 1960 have higher load capacity
than those with designation 1570. Use of steel
cores in place of fibre cores increases the
strength of wire ropes to some extent.
Prof.Deulgaonkar V.R University of Pune

15. 2) Flexibility of wire rope is one of the important
consideration. The wire rope of 6X7
construction consists of a few wires of
relatively large size. It is too stiff for hoisting
purposes. It is suitable for haulage and guy
ropes.
The 6X19 or 6X37 constructions are flexible wire
ropes and are commonly used in hoists.
Prof.Deulgaonkar V.R University of Pune

16. 3) Where wire rope is likely to drag through
gritty material or across stationery object
abrasion resistance is of concern. Large
diameter wires with 6X7 gives better wear
resistance.
Factors of safety for wire ropes for different
applications are given in tables as
Prof.Deulgaonkar V.R University of Pune

17. F.O.S in wire ropes for general applications
Application Class 1 Class 2
& 3
Class
4
Fixed guys, jib cranes , ancillary
applications as lifting beams .
3.5 4.0 4.5
Hoisting and luffing systems of
flexible cranes as mobile
derrick(Shock absorbing devices
are incorporated in the system)
4.0 4.5 5.5
Cranes and hoists 4.5 5.0 6.0
Prof.Deulgaonkar V.R University of Pune

18. FOS for wire ropes in mining applications
Application Factor of
safety
a) Mining ropes
For shafts of varying depths
Upto 300 mm 10
300-500 9
500-700 8
700-1000 7
b) Haulages ropes 7
Prof.Deulgaonkar V.R University of Pune

19. Rope drum construction and design
• Two types of constructions for rope drum are
available viz.
a) Drums with helical grooves
b) Plain cylindrical drums without grooves
Preference is given to grooved drums rather
than plain drums for most hoisting
installations.
Prof.Deulgaonkar V.R University of Pune

20. • The machined grooves increase the bearing
surface of the drum and prevent friction
between adjacent turns of rope. This reduces
wear and increases the life of rope.
• Drums are made of grey cast iron of Grade
FG200. Sometimes steel is used.
Prof.Deulgaonkar V.R University of Pune

21. Prof.Deulgaonkar V.R University of Pune

22. • A grooved drum and the grove profile are
shown in fig. below . Drum is provided with
helical grooves so that the rope winds up
uniformly on the drum.
• Radius of the helical groove should be
selected so as to prevent jamming of the rope.
• Drums designed for two rope members are
provided with two helical grooves. R.H & L.H
Prof.Deulgaonkar V.R University of Pune

23. • The pitch of the groove is given by
t = dr + (2 to 3 mm)
The shell thickness of the cast iron drum is given
by t1 = 0.02D +(6 to 10 mm)
where dr = nominal dia of rope (mm)
D = drum dia (mm)
Prof.Deulgaonkar V.R University of Pune

24. Prof.Deulgaonkar V.R University of Pune