Selecting the Right Gear Coupling for Your
Application
q This webinar will be available afterwards at www.designworldonline.com & email
q Q&A at the end of the presentation q Hashtag for this webinar: #DWwebinar
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 [email protected] Twitter: @DW_Motion
Paul Konkol Altra Ameridrives Gear Couplings [email protected]
Thank You q This webinar will be available at
designworldonline.com & email
q Tweet with hashtag #DWwebinar
q Connect with Design World
q Discuss this on EngineeringExchange.com
Top Related