couplings – general presentationm_ii_couplings_3spp.pdfcouplings – general presentation...

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May 2006 – T.Cicone 1/61 Couplings ME&M II

COUPLINGS – General presentation

• Connection.• Compensation (Positioning errors)• Disconnection (Automatic or manual)• Attenuation (Damping)

Couplings are used to connect two shafts.

Functions

Motor Working Machine

Couplings does not change operating parameters (Mt, n)


COUPLINGS – General presentation

Compensation (Misalignment)

Radial

Angular

Axial


PERMANENT

INTERMITTENT (CLUTCHES)

FIXED

MOBILE

AUTOMATED (Self-acting)

Rigid

Elastic

Hydraulic, pneumatic

Mechanical

Electrical

Speed (Centrifugal)

One-way (Overrunning)

Torque limiter (Slip Clutches

with elastomeric element

with metallic element

MECHANICALCOUPLINGS

COMMANDED

COUPLINGS – Classification

Electrical insulator

Connect/disconnect

During operation

2


Transmitting torque – by friction

Tapered bushing

Transmitting torque – by shape/form

Transverse pin

Key or splines

Axial compensation ??

COUPLINGS – Fixed (Ribbed, Sleeve) Coupling

Rigid


Key or spline transmitting torque

Ribbed Type Compression Coupling

COUPLINGS – Fixed (Ribbed) Coupling (Sleeve Type Couplings)


COUPLINGS – Fixed (Ribbed) Coupling(Sleeve Type Couplings)

3


Transmitting torque – by friction

Tapered bushing

COUPLINGS – Fixed (Ribbed) Coupling(Sleeve Type Couplings)


COUPLINGS – Flange Coupling

Widespread

Simple, rigid

Transmit forces by shape/friction


COUPLINGS – Flange Coupling

Screws in shearzD

MF tt

21 =

D

d

Safeguarding

4


COUPLINGS – Gear Coupling

Total compensation

•Radial

•Axial

•Angular

Modified tooth


COUPLINGS – Gear CouplingRequires Lubrication

SEAL – “O”-ringHigh load capacityNo damping

Simple or Double Gear Meshing


COUPLINGS – Gear Coupling

CrowningTip reliefBacklashDifferent width

Simple -Double -

ENGAGEMENT

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COUPLINGS – Gear CouplingSIMPLE ENGAGEMENT

DOUBLE ENGAGEMENT


COUPLINGS – Chain Coupling

Total compensation (Radial Axial Angular)


COUPLINGS – Jaw Type Rigid Coupling

Shear

Contact pressure

Bending (eventually)Axial compensation

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COUPLINGS – Elastic Coupling

Metallic elements Elastomeric elementsNegligible hysterezis Hysterezis – important DAMPING

Jaw type Couplings

Flange with elastomeric bolt

Tyre Couplings (PERIFLEX)

Bibby (Grid Type) Couplings

Beam Springs

Sleeve Type Elastic

With damping

Without damping

With damping

Without dampingElastic

Characteristic

Linear

Non-linear


COUPLINGS – Bibby (Grid Type) Coupling

1920 - BibbyElastic

Axial & Angular Compensation


Mt

θ

Total compensation•Radial (0.5 …3mm)

•Axial (4 …20mm)

•Angular (< 1°)

COUPLINGS – Bibby (Grid Type) Coupling

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COUPLINGS – Sleeve Type Elastic CouplingSlit Type Elastic Coupling

Bellow Coupling


COUPLINGS –Flexible Metallic CouplingsMembrane (Diaphragm) Coupling

Torque capacity 25,000 kW/1000 rpmSize 350 mm shaft diaSpeed 5,000 rpm

Facilitates mounting/dismountling

High torques due to metallicelastic elements used


COUPLINGS –Flexible Metallic CouplingsMembrane Coupling

ARCOFLEX COUPLING (LENZE Ltd.)

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COUPLINGS –Compensating Metallic CouplingsSchmidt Coupling – Offset compensator


COUPLINGS –Compensating Metallic CouplingsOldham Coupling – Offset compensator

Mechanical Efficiency < 1

Stresses ?Contact stressShearBending – very low


COUPLINGS –Flexible Nonmetallic Couplings

• Highly elastic (Excellent shock absorber / High damping characteristics)

• High torque (Up to 100kNm)

• Lubrication free (dry operation)

• Tolerate large amounts of misalignments in all plans (multidirectional flexibility)

• Simple installation (without disturbing the coupled machines)

• Easy inspection (without dismantling)

• Progressive torsional stiffness curve (not all the elastic couplings)

• Backlash free (only some of elastic couplings)

• Electrical insulator (No Metal-to-Metal Contact)

• Resistant to oil, dirt, sand, moisture and grease

Elastomeric intermediate element

Jaw-type couplings Tyre couplings Bolt type elastic couplings

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John Crane Inc.

COUPLINGS –Tyre Coupling

The highest torque rate and damping capabilities

Rubber disc or envelope vulcanized to a hub

Total compensation•Radial (0.5mm)

•Axial (1 …3mm)

•Angular (max. 1°)


COUPLINGS –Jaw Type CouplingsMt

θ

John Crane Inc.


COUPLINGS –Jaw Type Couplings

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• Standard Solid-Center Spider

• Open-Center Type

• Snap-Wrap

• Load Cushions

Spider designs

• Straight (US)

• Curved (Europe)


COUPLINGS –Jaw Type CouplingsSpider design: SNAP-WRAP

John Crane Inc.

• Spider in shear• Mounting without shaft displacement• Requires an outer collar/ring – reduced speed



Outer Collar

Snap-Wrap Spider

Spider in shear (Jaw-in-shear Coupling)

Compensation

•Radial (1 …4mm)

•Angular (up to 2°)

Max. Torque: 40kNm

for 360mm bore.

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COUPLINGS –Jaw Type CouplingsSpider in shear (Jaw-in-shear Coupling)

Compensation

•Radial (up to 3mm)

•Axial (limited)

•Angular (up to 1°)

•Torsional wind-up (15°)

• One-piece solid

• One-piece split

• Two-piece with retaining ring



Spider in shearSpider in compression

FAIL-SAFE !


COUPLINGS –Bolt Couplings

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COUPLINGS – Universal Joint

Hooke (Cardan ) articulation

spiderYoke

Intermediate splined shaft

bearing

Highly angular and axial compensation

No synchronism !

βωωβωω

coscos

1max2

1min2

==


COUPLINGS – Universal JointTandem mounting


COUPLINGS – Universal Joint

Syncronisms obtained ONLY for tandem mounting AND IF

•The axis of all shaft sections lie in the same plane

•The bearing bores of the inboard yokes of the center section lie in the same plane.

•The bend angles β1 and β2 are equal.

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BRAKE

CLUTCH

BRAKES & CLUTCHESProvide magnetic, hydraulic, mechanical connection between two elements


Internal Expanding Shoes External Contracting Shoes

BRAKES

RIM Types

Interruptible connections between a rotating element & a non-rotating ground plate or element


BRAKES

BAND TypeCONE Type

DISK Type

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RIM BRAKE (INTERNAL EXPANDING)

ShoeDrum


RIM BRAKE (INTERNAL EXPANDING)

=

app

θθ

sinsin

maxPressure distribution based on FEM modelling

Long shoe brake model

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(MULTIPLE) DISK BRAKE


CLUTCHES - Generalities

Connect & disconnect shafts at will (during rotation)

• to allow a high-inertia load to be started with a low-torque prime-mover than would be required if it were directly connected

• an emergency disconnect device to decouple in the case of a machine jam

• to maintain a constant torque on a shaft

Functions


• means of actuation

• means of energy transfer

• method of engagement

• Mechanical• Hydraulic/Pneumatic• Electrical• Automatic

CLUTCHES - Classification

• Positive mechanical contact• Friction• Hydraulic• Electromagnetic

• Synchronous• Non- synchronous

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CLUTCHES

POSITIVE CLUTCHES = Positive mechanical contact (toothed clutches)

Interlocked teeth Jaw type shape

Compact

(OLDHAM coupling)

No adjustment required Do not introduce important axial forces

No slipSynchronism required One element slides axially

(Hirth)


CLUTCHES - Positive

square-jaw (claw type)

spiral-jaw Short axial displacement(Hirth radial teeth)


One-directional

Reduced clashing

Bicycle – rear sprocket – rear wheel

CLUTCHES - Positive

Bi-directional

Clashing

Can be also trapezoidal

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CLUTCHES - FrictionMulti-disk friction clutch

Slip clutch


Constant Pressure Analysis (elastic plates)

( )22iomn rrpF −=π

mnio

ionmAf rF

rrrrFArpM µµµ =

−−

== ∫ 22

33

32d

Constant Wear Analysis (rigid plates) Vpwear ⋅≈

Vpconst=δdepth irppr max=ωrV =

( ) mnio

nioiAf rFrrFrrrpArpM µµπµµ =+

=−== ∫ 2d 22

max

Friction CLUTCHES - Pressure

ri

ro

r

dr


• high coefficient of friction• resistant to wear • sufficient compressive strength• temperature resistance (against

seizure)• thermal stability• good thermal conductivity• good elastic properties

Friction CLUTCHES - Materials

Characteristics

• Disks Lining– Molded

• Polymeric resin– Powder fillers– Fibrous material

– Woven– Sintered

• Higher temperature resistance• Compressive strength

– Greater than molded or woven

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Dynamics of Coupling

Ta

ωn ω1

ω2

ω

M

Mn

Mrez

Ma

t

t

Mω

t

Lf

La

aa T

IIM 2222ωε ==

( ) tta MMMM 1max −=−= β

ttcf MMMM β===max

( ) ta M

nIT130

2

−=

βπ

1) Engagement time

][3600

WzL

P ff =3) Power dissipated

][60

1 WTnML atf

πβ=2) Friction work

at

T

tf TMMLa

10

21d ωβθ

ω

== ∫


Disk Friction CLUTCHES


Automotive Clutch

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SLIP CLUTCH


OVERRUNING CLUTCHES

free-wheeling orone-way clutches

ratchet wheel


OVERRUNING CLUTCHES

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HYDRODYNAMIC CLUTCHES (inertia forces)

Start-up clutches Torque limiter Fottinger 1904


VISCO-COUPLINGS


VISCO-COUPLINGS

4+6 driving elements

2+3 driven elements

5 - fluid

21


CENTRIFUGAL CLUTCHES

Centrifugal Force used to:

(a) ENGAGE

(b) DISENGAGE

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