Gearbox Design

Gearbox Design (Layout only) Gearbox Design Issues: 1. Shafts 2. Rotating Elements (i.e., gears, sprockets, pulleys, etc.) 3. Bearings 4. Securing elements 5. Seals 6. Housing layout

Shafts: Functions •Locate and secure components in an appropriate manner and in their proper position. •Transmit all applied forces to their respective reaction point in the most efficient way.

Shaft Components To Consider

Shaft Components To Consider Internal Components, such as, gears.

Shaft Components To Consider Output Devices: Pulleys, Sprockets, Sheaves, etc.

Shaft Components To Consider Bearings: ball, roller, sliding.

For more about seals, visit www.skf.com

Methods of Securing Components 1. Welding Permanent assemblies 2. Machining from the solid shaft Not intended for 3. Interference or transitional fits replacement 4. Locating pins or dowels pins 5. Spacers and Sleeves 6. Keyways and keys 7. Splined Shafts 8. Steps and shoulders 9. Threaded fasteners 10. Clamping rings, collars, end caps 11. Friction fits (Taper Lock)

Secure the Components Circumferentially Splines External splines

Internal splines

Secure the Components Circumferentially Keys, pins, set screws, etc.

Pin hole in the shaft

Key

Pin hole in the hub

Pin

Secure bearing Circumferentially by press-fit Inner ring press fit to the shaft

Outer ring press fit to the housing

Secure the Components Axially by Shoulders, Snap rings (or retaining rings)

Secured by the snap rings

Secure the Components Axially by nuts Bearing Lock Nut:

Couplings - flexible couplings allow axial, radial, and angular misalignments - easy assembly and disassembly

For more information, please visit: www.ktr.com

Seals

Seals: labyrinth, O-rings, lips, etc.

For more info. about seals, visit www.trisunltd.com

Gearbox forces to be considered 1. Tangential Drive Force on Gear Teeth, Ft (torque transmitted to do work)

Ft

Torsion on shaft.

F Fr

Fa

Gearbox forces to be considered 2. Axial Force Due to Helix Angle, Fr (not to do work)

-Axial tension/compression on shaft. -Cyclical bending moment on shaft. Ft

Fa Fr

Gearbox forces to be considered 3. Radial Force on Gear Tooth, Fr (not do work)

-Cyclical bending force on shaft. Ft

Fa Fr

Gearbox forces to be considered 4. Weight of the Gear and Shaft -Radial Bearing reactions.

Gearbox forces to be considered 5. Externally Applied Loads -Overhung bending moment -Axial Thrust Load on the shaft. Overhung Bending due to belt or chain tension

Axial Thrust

Detailed Shaft Design Features Bearing Seats and Housings: Corner Details

General issues to be considered 1. What is the purpose of each device? 2. What must NOT occur (slippage of gear on shaft, …)? 3. Which parts must be fixed & which parts must be allowed to move? 4. What is the sequence of assembly? 5. What can fail and how will it happen? 6. How is the unit disassembled for repair? 7. What are maintenance requirements?

Detailed Shaft Design Features • Keyways • Steps & Shoulders • Fillets and Chamfers • Notches and Grooves • Thread Details • Bearing Seats and Housings • Gear Mounting Techniques • Spacers and Sleeves

Common practice in Shaft Design • Shafts get larger as speeds are reduced • Small pinions are often machined onto shafts • Larger gears generally use keys to transmit torque to shafts • Steps, Spacers and Retaining Rings are common ways to locate gears • Use Shims for adjustment and fine alignment of parts • Bearing Locking Nuts are a good way to secure Bearings • Consider stress risers due to grooves and sharp steps in shafts • Use chamfers to ease assembly and avoid interferences