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In practice we must cater for various torque
conditions.
Time
Transient torques
Time
Cyclic torques
Peak Torques – Cyclic Stresses
H P Coupling – Membrane Design
2
Steady Stress
Cyclic
Str
ess
Safe working stress
Material Failure
MEAN TORQUE
(MAX)
SPEED
(MAX) (MAX) AXIAL
DEFLECTION
Angular
Deflection
plus
Cyclic Torque
ANGULAR LIMIT Rated
Operating
Point
> 2
Goodman Diagram
H P Coupling – Membrane Design
3
Potential for
failure at the
Edge of
Washer
H P Coupling - Fatigue Failure Mode
Clamping
Washer Area
4
Fatigue crack propagation area
H P Coupling - Fatigue Failure Mode
5 Washer Radius
Lif
e
Optimum Radius
Maximum
Life
Washer Radius
H P Coupling – Profiled Washers
Life Enhanced by Profiled Washers
6
H P Coupling - Bolting System Design
Hub
Stripper Bolt
Drive Bolt
Membrane
Overload Sleeve
Lock Nut
Spacer Washer
Guard Ring Spacer
7
Hubs High Alloy steel
Spacer High Alloy steel
Guard Ring High Alloy steel
Membranes AISI 301 Stainless steel
Drive Bolts High Alloy steel (Forged & plated)
Nuts High Alloy steel
Sleeves High Alloy steel
Overload Collars High Alloy steel (Monel Option)
Stripper Bolts High Alloy steel (Forged & plated)
Excluding stripper bolts and membranes all parts are
phosphate and oil protected
H P Coupling – Materials
8
Factors Affecting Performance
Rotor- dynamic behavior / natural vibration
frequencies (coupling & machine) Lateral
Axial
Torsional
High speeds - dynamic balance is critical
- windage effects
Shaft interface requirements/assembly
Peak torque - short circuit effects
Electrical insulation and other features
H P Coupling – Engineering Considerations
9
Machinery Natural Vibrations
SYSTEM LATERAL VIBRATION
BEARING
DRIVER COUPLING DRIVEN MACHINE
MASS MASS
BEARING BEARING BEARING
H P Coupling – Engineering Considerations
10
Coupling Natural Vibrations
MEMBRANES PIVOT MEMBRANES PIVOT
COUPLING WHIRLING
SPACER BENDS
H P Coupling – Engineering Considerations
11
SYSTEM AXIAL VIBRATIONS
Ka
MEMBRANES
SPACER Mass
Ka
MEMBRANES
Machinery Axial Vibrations
H P Coupling – Engineering Considerations
12
Machinery Natural
Torsional Vibrations
Node
SYSTEM TORSIONAL
VIBRATIONS
H P Coupling – Engineering Considerations
13
Electrical short circuits
High start and re-acceleration effects
5 + times normal torque for 100,000 cycles
Changes in torsional stiffness needed
No yield and/or no fracture, no shaft hub slip
H P Coupling – Engineering Considerations
Peak Torques
14
Contributors To Unbalance
Balance tolerance limits
Balance fixture/mandrel unbalance
Balance machine error
Balancing set up eccentricity
Pilot clearances & eccentricities
Hardware unbalance (match weight bolts)
Effect of keyways
Shaft run-out
Fit of hub on shaft
H P Coupling – Balancing Considerations
15
Dynamic Balance to API 671
Formula proportional to Weight
Speed
At 10,000rpm eccentricity of mass < .001 mm
Repeatability is critical
Dynamic balancing techniques are critical
H P Coupling – Balancing Considerations
16
Dynamic Balance to API 671 There are 3 options dependent on Weight & Speed
0
1
2
3
4
5
6
7
0 5000 10000 15000 20000
Speed in RPM
Ec
ce
ntr
icit
y i
n 0
,00
1 m
m
ISO 1940 G=0,63
API 671 [4W/N]
In practice 5000 rpm is the critical
speed, where formula 2 takes over,
and for couplings weighing less
than 5.7Kg formula 3 takes
precedent
1. U = 6350 W/N g mm
(4 W/N)
2. U = 1.25 W g mm
3. U = 7.2 g mm
H P Coupling – Balancing Considerations
17
Factory Assembled Membrane Packs
Balance to G0.66 (API 671 limits)
Spigotted Design
High Alloy materials
Profiled Spacer Washers
O/Load Collars
Tight controls on manufacturing process
Improves balance retention and reliability
Can operate up to very high speeds
To retain balance Integrity and repeatability
Light weight and high torque & speed
capability
High reliability
Over torque protection with Spark resistant
option
Ensure reliable and high integrity product
Feature Benefit
H P Coupling - Features & Benefits
Recommended