Flexible Mechanical Elements

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FLEXIBLE MECHANICAL ELEMENTS

BeltsChainsRopes

Advantages. Simplifies the design. Reduces the cost. Obsorb shocks (since elastic and quite). Isolate vibration. Improve machine life

DisadvantagesMost flexible elements do not have an infinite life.Inspection requires to guard against wear, aging, and loss of elastisity

Belt Drives:

*

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*

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maximize small angle of wrap to increase transmitted load

Flat and Round Belt Drives:

2

2

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2

2

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*

< *

(Smaller sheave)

0

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Tight side

Loose side

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V Belt Drives:Main Features:- High spped ratio- Belt Speeds 5m/s < V < 50m/s (~20-25m/s)- Long lives- Quiet- Absorb Shocks- 500 < T < 800C

Narrow V-Belts (T.S. 198/4 – DIN7753)

Classic V-Belts (T.S. 198/1 - DIN 2215)

. small cross section, size advantage in designs

. high bending capability: bending frequency

. because of the sections;have small deformation;fits sheave;good heat transfer

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Defines Belt Profile

. Cross Section Gets larger

. Heavy duty stronger belts

. Minimum sheave sizes get larger

. Power rating increases



Lw is the effective V-Belt length which is measured at effective width bwbw is the width measured in the plane where the length of the

V_Belt is not changing due to the bending

Li : Inside LengthLa : Outside LengthLw : Effective (pitch Length)

Classic V-Belts(Table 45)

Narrow V-Belts(Table 18)

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Used in preliminary selection – (approximation)

Used in exact calculations,after belt selection is fialized

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Angle of wrapon dwk

Tension adjustment

Belt seating adjustment

Tension adjustment (x) and Belt seating adjustment (y)

Angle of wrap

Constraint: (The distance between the sheave centers)

Reduction ratio

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Power ratings (PN) listed in tables as functions of dwk, i, nk.

Belt selection is based on power ratings (PN) listed in tables as functions of dwk, i, nk.

Tables are prepared for a certain life under certain conditionsfor and for a certain length, Lw.

To take into account variations in these adjustment factors are used.

0180=β

Nominal driving machine powerDesign power

# of belts required

Rated power per belt Correction factor for

angle of contact

Belt length correction factor

Overload service factor

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Correction factor for angle of contact

Nominal driving machine powerDesign power

# of belts required

Rated power per beltBelt length correction factor

Overload service factor

N:Table 6Table 8Table10Table12

C:Table24Table26Table28Table30Table32Table34Table36Table38Table40

N:Table 3

C:Table 22

N:Table 7 (SPZ)Table 9(SPA)Table 11(SPB)Table 13(SPC)

C:Table 25 (Profil 8)Table 27 (Profile 10/z)Table 29 (Profile 13/A)Table 31 (Profile 17/B)Table 33 (Profile 20)Table 35 (Profile 22/C)Table 37 (Profile 25)Table 39 (Profile 32/D)Table 41 (Profile 40E)Table 25 (Profile 8)Table 25 (Profile 8)

N:Table 2

C:Table 21

Driving machineDriven machineHours of operation per day

V-Belt (Profile) Selection: Decide c2 based on what’s given in the problem

Pdesign = c2 x Power to be transmitted N:Table 2

C:Table 21

*

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Correction factor for angle of contactN:Table 3

C:Table 22

Belt length correction factorN:Table 7 (SPZ)Table 9(SPA)Table 11(SPB)Table 13(SPC)

C:Table 25 (Profil 8)Table 27 (Profile 10/z)Table 29 (Profile 13/A)Table 31 (Profile 17/B)Table 33 (Profile 20)Table 35 (Profile 22/C)Table 37 (Profile 25)Table 39 (Profile 32/D)Table 41 (Profile 40E)Table 25 (Profile 8)Table 25 (Profile 8)

C1

Rated power per beltN:Table 6Table 8Table10Table12

C:Table24Table26Table28Table30Table32Table34Table36Table38Table40

PN C3

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Power ratings (PN) listed in tables as functions of dwk, i, nk.

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If z > 6, too many belts; use a stronger belt profile(if we use many belts dw’s are low)

* Belt profile selectioni) If we are not trying to minimize # of belts (z), we can follow the recommendation of the catalog

ii) If a single belt drive is desired or if we want to minimize z we can begin with a stronger belt type.

(using stronger belt causes larger dwk, hence increases e)

N:Figure 3

C:Figure 10

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* Sheave diameter selection:- Depend on belt profile- Selection is based on i- We usually chose minimum dwk and dwb which satisfies desired i so that “e” and overall size of the drive is minimized- On the other hand we may choose larger dwk and dwb to improve belt life.(Peripheral Velocity should be less than 40 m/s)N:Table 17

C:Table 44

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* Belt length selection:After choosing dw’s and deciding e, calculate (Lw) (approximate), considering the limitations.

N:Table 14

C:Table 42

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* Bending frequency

1

1

40

100−

−

≤

≤

sf:C

sf:N

maxb

maxb

(Peripheral Velocity should be less than 40 m/s)

mm rpmmm

m/s belt speed

* x, y adjustments

Tension adjustment (x) and Belt seating adjustment (y)

* Minimum axial force for pre-tension (preloading):

* Minimum static belt tension:

belt speedm/s

Design Power kW # of belts

N:Table 5

C:Table 23

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* Belt deflection:In order to control the initial tension belt deflection is measuredunder a certain load N: Figure 5 C: Figure 12 Deflections/100 mm

between sheave depends on T & belt profile

Deflections under control load

Standart V-Belt Length

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Roller Chains:

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Large impact wear liferoller-sprocket chain joint

tooth

d

N effects velocity ratioChordal action: chain moves up and down

)(CosDd 2γ=

Dd =

)N180(Sin

p60n

60DnVmax π

=π

=

60Npn

60DnV:velocityChain

NpD:nceCircumfere

≈π

=

≈π

)N180(C

)N180(Sin60

n)2(C60n

60DnVmin os p os D π

=γπ=

π=

)N180()2(

0=γ

represent

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Wire Rope Drives:

strand

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Strength reductiondue to sheave bending

Applied load

Flexible Mechanical Elements

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