GKN Land Systems Identifying Damage To Elastic Couplings: Failure Modes & Photo ExamplesCornell Pump Company, November 2014

2

PLUG-IN STYLE COUPLING GENERAL FORM

3

Visual Failure Mode Identification: PVN, PVA, PS Models

Plug-In Style Coupling Models PVN & PVAWith Rubber Bonded to Center Ring

PS Model With Bushings and Clamping Ring

4

Visual Failure Mode Identification – Mode Interrelation

Event Strings and Interrelation of Multiple Visual Cues:

The next slides will highlight examples of visual cues which are indicators of events that have occurred in a flexible coupling’s rubber element due to environmental conditions and system related forces exerted on the coupling such as:

Applied torque

Shock torque

Torsional vibration levels

Oscillation (reversing torques)

High ambient temperature

Heat conduction though shafting

Oil contamination

Exposure to solvents and cleaning agents

5

Visual Failure Mode Identification – Mode Interrelation

Event Strings and Interrelation of Multiple Visual Cues:

Visually identifiable features related to coupling failures can provide an indication of the types of events that have occurred prior to the rubber element failing – normally this means the working area of the rubber that was stressed and stretched while transmitting system torque has in some way separated/sheared with a mechanical fuse effect thus stopping further transmission of torque in the driveline.

NOTE: In the majority of cases these visual indicators are highly interrelated in a string of events such that one event which gives a certain visual cue leads to second or third events producing other visual cues (domino effect). It is uncommon to have only a single effect produce a singular visual indicator.

For these reasons it is suggested you consult GKN Stromag for further analysis. This includes possible dissection and chemical testing to determine more conclusively what chain of events has most likely caused the rubber element to fail/shear.

6

Visual Failure Mode Identification – Force Break

Torque Overload: system torque exceeds the coupling’s maximum torque capacity TKmax (typically > 300% of

nominal torque rating) Shock torques – momentary load spikes Driveline system lockup – rubber element shears as planned design of

mechanical fuse effect to protect driveline components (examples: pump stoppage from debris intrusion, seized bearings)

Visual Cue: 45° tears all in one direction, distributed around the face of the shear plane (surface where the two sections of rubber have separated or sheared)

High Shock Torque Visual Cue: separation/removal if drive teeth on plug-in style couplings (PVN, PVA, PS)

7

Visual Failure Mode Identification – Vibration Break

Vibratory Torque Overload: high alternating torque (system oscillation) exceeds the

coupling’s admissible alternating torque capacity TKW (in units of Nm or lb-ft)

Visual Cue: 45° tears in both directions from high amplitude oscillations forming “X” shaped tear patterns distributed around the face of the shear plane (surface where the two sections of rubber have separated or sheared)

8

Visual Failure Mode Identification – Vibration Break

Excessive Power Loss: vibration energy in the system exceeds the

coupling’s permissible power loss PkV (admissible damping power in Watts)

Damping in the rubber absorbs vibration energy and converts it to heat energy, and this heat must be dissipated by cooling (also linked to high ambient temperatures that restrict cooling)

If more vibration energy is absorbed by the rubber than can be released by cooling, the rubber melts from the inside out at the working zone (shear area) of the rubber element where it is most stretched under load

Visual Cue: face of shear plane without repeating tear patterns and few 45° tears in one direction at random locations; inside of shear plane area melted from the inside out with voids in the rubber from gasification (essentially a melted ring where the rubber has been vaporized)

Example Causes: engine issues such a cylinder misfire, governor hunting on older engines, trouble maintaining load (sensor faults, fuel rail supply issues, water contamination in the fuel, air feed restriction, etc...) and therefore the engine cycles its speed repeatedly when loaded

9

Visual Failure Mode Identification – Misalignment Effects

Angular Misalignment:

Visual Cue: ramped tooth wear uniformly angled toward front or rear on plug-in style couplings (PVN, PVA, PS models)

Radial Misalignment:

Visual Cue: tooth base cracks, outer/radial edge of rubber element teeth abraded from offset compression pressure within cast aluminum flywheel ring on plug-style couplings (PVN, PVA, PS models)

Axial Misalignments:

Visual Cue: pump side protruding rubber teeth cut by inside edge of cast aluminum flywheel ring on plug-style couplings (PVN, PVA, PS)

Visual Cue: flywheel side face of rubber element discolored by heat conduction from contact with engine flywheel on plug-in style couplings (PVN, PVA, PS)

Visual Cue: bolt-though steel bushings torn out of rubber where hub flange and clamp ring attach to rubber element (PS model)

10

Visual Failure Mode Identification – Environment/Chemical

High Ambient Temperature – Heat Induced Power Loss Failure:

Damping in the rubber converts vibration energy to heat energy, and this heat must be dissipated by cooling. If the ambient temperure is so high that heat cannot be removed by cooling, the rubber melts from the inside out at the working zone of the rubber element (similar to excessive power loss failure)

Maximum Allowable Ambient Temperature for Natural Rubber: 80°C or 176°F

Visual Cue: shear plane edges without repeating pattern and few 45° tears in one direction at random locations

Oil Impregnation/Contamination:

Visual Cue: swollen rubber at surface from oil contamination (example: engine crankshaft seal

failure)

Chemical Contamination:

Visual Cue: rubber surface shows features such as blisters, pitting, white dust, or extensive surface cracking

(example: excessive use of cleaning agents entering vent holes)

11

Load Induced Failure: Shock Torque

Reasons: TS,reg (t) > TKmax

or TS,irreg (t) > 1.5 TKmax

the machine locks up sudden overload

Picture: plain surfaces no heating cracking at 45° angle hardening

12

VA 421.65 W

Crack is located near the hub (inner ring)

Damage at the surface shows numerous 45° cracks in the same direction

Wavy shear surface

Force Break: Torque Overload

12

13

PS 42.70 W

Damage to the highly stressed bushing holes(Angle approximately 45°)

Flat shear surface with no indication of melting

No signs of heat input like embrittlement or smearing of the rubber

Force Break

13

14

V 42.80 W

Cracked near mounting points

Further cracks pass under 45° in the rubber element

No signs of heat input like embrittlement or smearing of the rubber

Force Break

14

15

Vibration BreakReasons: Tw(n) > TKW

high alternating torque

Picture: slowly cracking – lifetime reduction zig-zag cracking edges cracking at 45° angle no heating

Vibration Break

1616

Common symptom during vibration break:Shearing is located in the zone which is most stretched during loads.

Vibration Break

17

VN 35031

Shearing is located in the working zone which is most stretched during loading

Melting has occured from the inside out (voids from gasification)

Rubber is very tender and slimy in the shear zone

No visible 45° tears

Vibration Break

17

18

Temperature

Ozone, Oxygen

Moisture

Oil, Solvents, Cleaning Agents

External Influences

18

19

Vibration Break: Heat Induced Power Loss Failure

Reasons: Pv(n) > PKV

hot environment low air flow internal rubber friction result: heating

Picture: internal melt down because of heat cracking is clean and uniform surface feels oily

20

VN 43351

Increased Shore hardness of the material due high ambient temperature

Embrittled surface with 45° cracks due to vibratory torque load

Temperature Influence, High Ambient Temperature

20

21

VN 43331

Failure of the rubber-metal bonding due to high temperature of the connected gear shaft transfering heat to center ring

T ≥ 110°C or 230°F

Heat Conduction

21

22[DOCUMENT NAME]

23[DOCUMENT NAME]