Selecting the Right Gear Coupling for Your

Application

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Before We Start

Moderator Presenter

Miles Budimir Design World

Paul Konkol Altra Ameridrives Gear Couplings

Design World Webinar

Selecting the right gear coupling for your application

April 29, 2015

What is a Coupling ?

A Flexible Coupling is a machine part that transmits rotating power from one shaft to another while accommodating misalignment and axial displacement between the two shafts.

The basic functions of a flexible coupling:

•  Transmit power •  Accommodate misalignment •  Compensate for shaft end movement

Basic Coupling Functions

Transmit Torque

While allowing for:

Misalignment

Axial Movement

DRIVER DRIVEN

• Torque: The tendency of a force to cause or change rotational motion of a body, calculated by multiplying Force and distance. Defined more fully in the Torque section below.

• Misalignment: The state of being not in alignment. Alignment is generally defined as the state where opposing equipment shaft centerlines are coaxial. For machinery and couplings, it is the proper orientation of mechanical parts to obtain minimal wear and/or dynamic forces.

• Hub: The coupling component which is machined for mounting on a shaft.

• Spacer: A removable center member that provides a specified axial shaft separation.

• Distance Between Shaft Ends (DBSE): The distance from the face of one shaft to the face of the next shaft.

• Shaft: The revolving cylindrical bar, the centerline of which is also the center of rotation for the components to which it is attached, through which torsional power is transmitted or delivered.

• Bore: Cylindrical or conical holes in hubs of couplings with axes coincident with the rotational axis of the coupling.

• Flexible Element: The part of a coupling which provides flexibility. There are 3 main categories: Mechanical, Metallic, and Elastomeric.

• Sleeve: A gear coupling component with internal teeth.

• Hardware: The nuts, bolts, washers, etc., which are used to attach the various coupling components together.

• Clearance Fit: A condition where the hub bore diameter is equal to or larger than the shaft diameter.

• Interference Fit: A condition where the hub bore diameter is equal to or smaller than the shaft diameter.

• Pilots: A surface that positions a coupling component, subassembly or assembly.

• Key: A mating torsional load transmitting member placed in a groove in both shaft and hub.

• Keyway: The axial groove in the hub that holds the key

in the proper location.

Coupling Terminology

Basic Torque Calculation

Torque = Power x Unit Constant Speed •  in-lb. = HP x 63025 / RPM •  Nm = kW x 9554 / RPM

•  HP/100 RPM = HP x 100 / RPM

Torque

= HP transmitted x 63,025 x Service Factor RPM

Service  Factors  are  a  multiplier  to  the  calculated  torque  when  selecting  a  coupling.   •  Selection  Torque  =  Calculated  TQ  x  SF •  Note:    Different  coupling  types  and/or  manufacturers  recommend  different  service  factors  for  similar  operating  conditions.    Always  check  your  catalog

CLASS SMOOTH STEADY MODERATE MEDIUM HEAVY EXTRA HEAVY EXTREMELY HEAVY

DRIVER TYPE

MOTOR OR TURBINE

MOTOR OR TURBINE

MOTOR OR TURBINE

MOTOR OR TURBINE

HIGH STARTING TORQUE MOTOR OR ENGINE ENGINE ENGINE

LOAD TYPE

- SOFT START WITH STEADY LOAD

- CENTRIFUGAL EQUIPMENT

- NORMAL STARTING LOADS - SLIGHT TORQUE

VARIATIONS

- ABOVE AVERAGE STARTING LOADS

- MODERATE LOAD VARIATIONS

- HIGH STARTING TORQUE - MEDIUM TO HEAVY LOAD

VARIATIONS

- MILD SHOCK LOADING ENGINES WITH SMOOTH LOADING

- EXTREME RELIABILITY

- HEAVY SHOCK LOADING - LIGHT TO MODERATE

REVERSING

- EXTREME SHOCK LOADING

- HEAVY REVERSING WIDE TORQUE VARIATION

SERVICE FACTOR 1.0 1.5 2.0 2.5 3.0 3.25 4.0

Service Factors

Angular

Misalignment

Parallel Offset

Misalignment

Types of Misalignment

Misalignment

Parallel offset

Combination of both

Angular misalignment

Types of Misalignment

•  Axial Misalignment or End Float o  Some couplings will limit shaft movement, others will not o  Sometimes limited end float (LEF) devices may be added

to a coupling

A.  Small amount

•  Thermal growth

•  Bearing float

B.  Large amount

•  Axial adjustment

•  Operational shifting

Axial Movement

Coupling Categories and Types

Gear Chain Grid UJoint

Mechanical

Disc Diaphragm

Metallic

Shear Compression

Elastomeric

Pin & Bushing Spring Slider Block

Miscellaneous

Mechanical

UJoint

Gear

Chain

Grid

Elastomeric

Shear

Compression

Metallic

Disc

Diaphragm

Performance

L-jaw

Sure-Flex®

Dura-Flex®

Gear

Form-Flex®

Grid

Make to Stock

Modify/MTO

Price

Couplings Cover a Wide Range

So, which is the right coupling for my application?

Types of Couplings & Application Requirements

Coupling Characteristics

Gear Spindle Grid U Joint Elastomeric Shear

Elastomeric Compression

Disc Diaphragm

Lubrication Yes Yes Yes Yes No No No No Backlash Med High Med None None Low None None Overhung Moment

Med High Med High High High Low Low

Unbalance Med High High High High High Med Low Bending Moment

High High Med High Low Med Med Med

Axial Force High High Med High Low Med Med Med

Torsional Stiffness

High High Med High Low Med High High

Damping Low Low Med Low High Med Low Low

Coupling selection based on application needs

Costs and Benefits Criteria

Coupling  Types

 

Elastomeric  -­‐‑  Shear Elastomeric  -­‐‑  Compress      

Tire Block Sleeve Jaw Curved-­‐‑Jaw Block   Gear Disc Grid

 

                   

   Lubrication N   N   N   N   N   N   Y   N   Y  

   Ease  of  Installation  ++ +++   +++   +++   +++   +++   +   +   +  

   Fail  Safe N   N   N   Y Y Y N N   N

   Misalignment  Rating  +++ +   ++   +   +   +   ++ +   +  

   Purchase  Cost  $$   $   $   $   $   $   $$$   $$$   $$  

   Maintenance  Cost N   N   N   N   N   N   Y   N   Y  

   Replacement  Cost  $$   $   $   $   $   $   $$$   $$$   $$  

   Installation  Cost/Time ++ +++ +++ +++ +++ ++ + + +

   Life    ++   +   ++ +   +   +   +++   +++   ++

   Torsional  Stiffness Low High Low High High High Highest Highest Low

+++ = BEST ++ = BETTER + = GOOD

$$$ = HIGHEST $$ = LOWER $ = LOWEST

Why Select a Gear Coupling? Coupling Characteristics

Gear Spindle Grid U Joint Elastomeric Shear

Elastomeric Compression

Disc Diaphragm

Lubrication Yes Yes Yes Yes No No No No Backlash Med High Med None None Low None None Overhung Moment

Med High Med High High High Low Low

Unbalance Med High High High High High Med Low Bending Moment

High High Med High Low Med Med Med

Axial Force High High Med High Low Med Med Med

Torsional Stiffness

High High Med High Low Med High High

Damping Low Low Med Low High Med Low Low

Gear Coupling is selected because it is torque dense, has axial capacity independent of angular misalignment, large bore capacity, and long life.

Why a Gear Coupling?

•  High torque

•  High misalignment

•  Axial capacity

Basic Gear Coupling Parts

Lube Plugs

Flange Nuts & Bolts Sleeve

O-ring Seal

Hub

How a Gear Coupling Transmits Torque

Torque is transmitted on the flank or face of the

gear tooth

Major Diameter Sleeve Piloting

•  Gear teeth are either straight or crowned

•  Clearance in gear mesh allows for misalignment

•  Crowned tooth allows for greater misalignment, higher torque capacity, less backlash

Gear Tooth Design

Crowned or Fully Crowned Gearing

A) Flank (Face)

B) Tip (and Root)

C) Chamfer

When everything is “perfectly” aligned all teeth share the

load equally

How a Gear Coupling Works

As you misalign, fewer and fewer teeth are in contact

Ratings are based on the torque that can be transmitted at a given

misalignment

Reduce your misalignment, increase your ratings

How a Gear Coupling Works

Fully Crowned Gearing Allows for Max Misalignment

Fully Crowned Gear Reduces Backlash and Vibration

Gear Couplings Require Lubrication

Original gear couplings 75+ years ago were filled with oil for

lubrication

A metal labyrinth seal and centrifugal force kept the gear

mesh lubricated

O-ring Seal

Buna-N O-ring seals keep contamination out, and lubricant in. Designed to accommodate temperatures up to 250°F. Viton seals are available for temperatures up to 550°F. O-ring Seal

Clean grease of the proper amount and type will give longest life

Recommended Grease

Suggested grease by manufacturer and operating conditions

Gear Coupling Standards

•  Flange Diameter is standard for manufactures •  Shrouded or Exposed bolt pattern is standard •  Allows for Identification & Half-to-Half Interchangeability

Standard AGMA Nomenclature Size 1 ½ to 7 Size Mfg.  K Mfg.  F Mfg.  A O.D. #  SB  Bolts #  EB  Bolts

1-­‐‑1/2 1-­‐‑1/2H 1015 201.5 6.00” 8 8 2 2H 1020 202 7.00” 10 6 2-­‐‑1/2 2-­‐‑1/2H 1025 202.5 8.38” 10 6 3 3H 1030 203 9.44” 12 8

7 7H 1070 207 20.75” n/a 16

O.D.

•  Measure flange O.D. •  Count the bolts •  Step in ½ sizes

Special Coupling Functions Many couplings today are special made to order

and incorporate other special features. §  Allow for axial travel §  Maintain sleeve bearing motor

rotor position (Limited End Float or LEF)

§  Allow for extended DBSE §  Protect Equipment from overload §  Dampen vibration and reduce

peak or shock loads §  Electrically insulate the driver

from the driven equipment §  Incorporate a brake disc or drum

§  Tune a system out of a torsional critical

§  Support the rotor of a generator or other radial load (single flex)

§  Electrically insulate the driver from the driven equipment

§  Measure output torque of driven equipment

§  Support axial loads on vertical installation

§  Support other PT Components §  V-Belt Drive, Fluid Drive, Clutch, etc.

Special Coupling Functions Application Data Form to gather all information

important to the installation §  HP, speed, DBSE, shaft sizes,

SF, temperature, etc. §  What is currently being used? §  Drawings of existing

application §  What changes have been

made since original installation?

§  What operational problems are there?

§  Special documentation

BORES, FITS AND HUB MOUNTING

Hub to Shaft Fits

•  Slip or Clearance Fits o  Hub bore is always larger than shaft OD

•  Press or Interference Fits o  Hub bore is always smaller than shaft OD

Clearance Fits

•  Use for Low Speeds o  1800 to 3600 RPM max

•  Requires set screws and keyway o  Worse for balance

•  Low HP ranges o  Generally 250 HP and under

•  Smaller Shaft Diameters o  Generally 3 3/8” or less

•  Risk of Fretting

Interference Fits •  Light: under .0005 in/in

o  Must use a key – minimal interference will slip under heavy load

o  AGMA Standard A86

o  Hub mounting: Heating necessary

o  Stresses are usually not an issue

•  Medium: ~.0005 - .0015 in/in

o  Usually tapered shaft and some keyless fits

o  AGMA standards A86 & A91

o  Hub mounting: Must be heated or hydraulically mounted

o  Stresses may need to be checked

•  Heavy: ~over .0015 in/in

o  Keyless fits

o  AGMA Standard A91

o  Hub mounting: Heating necessary

o  Stresses need to be checked

AGMA Fit Tables

Interference Fit Calculations

•  Steel expands .0006”/inch of diameter per 100°F temp rise •  Heat the hub to expand bore by 150%+ of the interference •  Example: 5” dia. shaft with .004” interference

•  5” dia. x .0006” = .003” expansion per 100°F temp rise •  .004” x 150% = minimum .006” growth •  .003”/100°F x 2 = .006” bore growth = min 200°F temp rise •  At 70°F temp, need to heat hub to at least 270°F

Ø  350°F is recommended, even heat distribution, less that 600°F

Interference Fit Hub Installation

•  Calculate the correct temperature rise •  Make sure bore and shaft are clean and free

of burrs •  Plan how you will handle the heated hub •  Heat hub thoroughly – if not heated through,

hub may cool, shrink and bind before completely on the shaft

•  Shield shaft and seals from over-heating when you install the hub

•  Quickly and safely position the hub on the shaft and allow it to cool

Metric vs. English Shaft Specification

Inch Shafts •  Standard AGMA tolerances •  Square keys

•  Half in hub / half in shaft

Metric Shafts •  Various Metric standards DIN Standards •  Rectangular keys

•  Keyway depth per metric standards •  Overkey dimension for keyway depth

Inch Keyways

Metric Keyways

Fitting of Keys

1.  Tight Fit in Shaft Keyway 2.  Sliding Fit in Hub Keyway 3.  Clearance over Top of Key 4.  Chamfered Key Corners

Interference Fit with Key

The proper gear coupling selection and design will give

you the maximum misalignment capacity &

maximum torque capacity for the longest life in your

application.

Questions? Miles Budimir Design World mbudimir@wtwhmedia.com Twitter: @DW_Motion

Paul Konkol Altra Ameridrives Gear Couplings Paul.konkol@ameridrives.com

Thank You q  This webinar will be available at

designworldonline.com & email

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