Rope Drive

A rope drive is a type of belt drive, used for mechanical power transmission. Rope drives use several circular section ropes, rather than a single flat or vee belt.

1. Wire Ropes

2. Introduction
•Whenalargeamountofpoweristobetransmittedoverlongdistances
fromonepulleytoanotherwireropesareused
•Whenthepulleysareupto150metresapart,thenwireropesareused.
•Thewireropesarewidelyusedinelevators,minehoists,cranes,
conveyors,haulingdevicesandsuspensionbridges.
•Thewireropesrunongroovedpulleysbuttheyrestonthebottomof
the*groovesandarenotwedgedbetweenthesidesofthegrooves.
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3. •The various materials used for wire ropes in order of increasing
strength are
•Wrought iron,
•Cast steel,
•Extra strong cast steel,
•Plough steel and alloy steel.
•For certain purposes, the wire ropes may also be made of
•Copper,
•Bronze,
•Aluminiumalloys and stainless steels.
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4. Advantages of Wire Ropes
These are lighter in weight
These offer silent operation
These can withstand shock loads
These are more reliable
These are more durable
They do not fail suddenly
The efficiency is high
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5. Cross-sections of wire rope.
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6. Classification of Wire Ropes
2. Parallel or langlay ropes 6

7. Designation of Wire Ropes
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Standard designation Application
6 ×7 rope
It is a standard coarse laid rope used as haulage rope in mines,
tramways, power transmission.
6 ×19 rope
It is a standard hoisting rope used for hoisting purposes in mines,
quarries, cranes, dredges, elevators, tramways, well drilling.
6 ×37 rope
It is an extra flexible hoisting rope used in steel mill laddles,
cranes, high speed elevators.
8 ×19 rope Itisalsoanextraflexiblehoistingrope.

8. Factor of Safety for Wire Ropes
Application of wire
rope
Factor of Safety Application of wire rope Factor of safety
Track cables 4.2 Derricks 6
Guys 3.5 Haulageropes 6
Mine hoists :
Depths
upto150 m
300 –600 m
600 –900 m
over 900 m
8
7
6
5
Small electric and air hoists 7
Over head and gantry
cranes
6
Jib and pillar cranes6
Hot ladle cranes 8
Miscellaneous hoists 5 Slings
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9. Stresses in Wire Ropes
•Direct stress due to axial load lifted and weight of the rope
•Bending stress when the rope winds round the sheave or drum.
•Stresses during starting and stopping.
•Stress due to change in speed
•Effective stress
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10. Direct Stress
�??????����??????�����(??????
�)=
??????+�
�
W = Load lifted,
w = Weight of the rope, and
A = Net cross-sectional area of the rope.
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11. Bending Stress
��??????�????????????????????????�����??????
�=
�
�∗�
�
�
E
r= Modulus of elasticity of the wire rope,
d
w= Diameter of the wire,
D = Diameter of the sheave or drum, and
A = Net cross-sectional area of the rope.
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12. Stresses during starting and stopping
•Additional load in the rope
??????
�=
??????+�
??????
∗�
And the corresponding stress
??????
�=
??????+�
??????
∗
�
�
where
a = Acceleration of the rope and load, and
g = Acceleration due to gravity.
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13. Stress due to change in speed.
•Theadditionalstressduetochangeinspeedmaybeobtained
•inthesimilarwayasdiscussedaboveinwhichtheaccelerationis
givenby
�=
(�
�–�
�)
�
•where(v
2–v
1)isthechangeinspeedinm/sandtisthetimein
seconds.
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14. Effective stress.
•Thesumofthedirectstress(
σd)andthebendingstress(σ
b)iscalledtheeffective
stressintheropeduringnormalworking.
•Mathematically,
•Effectivestressintheropeduringnormalworking
σ
d+ σ
b
•Effectivestressintheropeduringstarting
σ
st+ σ
b
•andeffectivestressintheropeduringaccelerationoftheload
σ
d+ σ
b+ σ
a
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15. Procedure for Designing a Wire Rope
•Firstofall,selectasuitabletypeofropeforthegivenapplication.
•Findthedesignloadbyassumingafactorofsafety2to2.5timesthefactorofsafety
(PSGDB9.1)
•Findthediameterofwirerope(d)byequatingthetensilestrengthoftherope
selectedtothedesignload.(PSGDB9.5&9.6)
•Findthediameterofthewire(dw)andareaoftherope(A)fromTable20.10.
•CalculationofSheavediameter(D)(PSGDB9.1)
•SelectionofareaforusefulcrossSection
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16. •CalculationofWireDiameter(d
w)=c(dw=d/1.5√I)I=Numberofwirein
therope
•Selectionofweightofrope(Wr)
•CalculationofVariousLoads
•CalculationofEffectiveLoads
•Nowfindtheactualfactorofsafetyandcomparewiththefactorofsafety(If
theactualfactorofsafetyiswithinpermissiblelimits,thenthedesignissafe.)
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17. Problems for Practice
•Selectawireropeforaverticalminehoisttoliftaloadof55kNfromadepth300metres.A
ropespeedof500metres/ministobeattainedin10seconds.
•Anextraflexible8×19ploughsteelwireropeof38mmdiameterisusedwitha2m
diameterhoistdrumtolift50kNofload.Findthefactorofsafety(ratioofthebreakingload
tothemaximumworkingload)underthefollowingconditionsofoperation:Thewirerope
isrequiredtoliftfromadepthof900metres.Themaximumspeedis3m/sandthe
accelerationis1.5m/s
2
,whenstartingundernoslackcondition.Thediameterofthewire
maybetakenas0.05d,wheredisthediameterofwirerope.Thebreakingstrengthof
ploughsteelis1880N/mm
2
andmodulusofelasticityoftheentireropeis84×103N/mm
2
.
Theweightoftheropeis53N/mlength.
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18. Reference
•Machine Design by RS Khurmiand GK Gupta
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19. B.Varun
9787608011
[email protected]
[email protected]
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