Grade 9 Tech Gear Theory

GEARS

DESCRIPTION OF A GEAR

• Basically a wheel with teeth cut in the rim.
• A gearis a machine component used to

transmit motion or force.

TYPES of GEARS and their PURPOSE

Spur gears

Bevel gears

Spur gears are used transmit motion between two
parallel shafts. Used in bicycle bells, printing
machines,

Bevel gears used to change rotational movement
through 90 ⁰ movement. Used in handwisks , hand
drills, differentials of vehicles,

Rack and pinion

Rack and pinion gears are used to change
rotational movement to linear movement.
Used in safety gates, microscope, pillar,
drills, corkscrew.

TYPES of GEARS and their PURPOSE

Worm gears

Helical gears

Worm and spur gears are used to produce 90⁰
change in rotational movement and slows down
the speed of the movement.
Used in gearboxes, pumps and toy trains

Helical gears are used to transmit power between parallel shafts
Used in gearboxes of vehicles

Multiple Choice

The image represents a _______ gear.

• Spur

• Bevel

• Rack

• Worm

Multiple Choice

The image represents a _______ gear.

• Spur

• Bevel

• Rack

• Worm

Multiple Choice

The image represents a _______ gear.

• Spur

• Bevel

• Rack

• Worm

Multiple Choice

The image represents a _______ gear.

• Spur

• Bevel

• Rack

• Worm

Gear trains

Gear train

Planetary gear train

Gearbox - gear train

Gear train

Uses for gears

MOTORBIKE GEARBOX

MOTORCAR GEARBOX

WATER PUMPS

INDUSTRIAL EQUIPMENT

Why are lubricants(viz. gear oil) used in

gearboxes?

Provides three primary benefits:

• 1. to lubricate the gear teeth

• 2. to remove heat generated from the gear operation

• 3. to reduce noise created by gears

GEAR CALCULATIONS

• GEAR RATIO =NUMBER OF TEETH OF DRIVEN GEAR
NUMBER OF TEETH OF DRIVER GEAR

= 8/40
= 1/5
= 1:5

SPEED CALCULATIONS

IF THE INPUT SPEED OF THE DRIVER GEAR = 80RPM.
WHAT IS THE OUTPUT SPEED?

OUTPUT SPEED = INPUT SPEED
GEAR RATIO
= 80 / 1/5
= 400 RPM

COMPOUND GEAR CALCULATIONS

• IN COMPOUND GEAR CALCULATIONS THE NUMBER OF TEETH

OF THE IDLER GEAR (B) IS IGNORED.

• GEAR RATIO = NUMBER OF TEETH OF DRIVEN GEAR
NUMBER OF TEETH OF DRIVER GEAR
= 10/20
= 1:2