SUBJECT: BASIC TECHNOLOGY
CLASS: JSS2
DATE:
TERM: 3RD TERM
REFERENCE MATERIALS
- MELROSE, Basic Science and Technology Book 2
- NERDC, Basic Technology for JSS, Book 2
WEEK FOUR
TOPIC: GEARS
CONTENT
- Definition
- Types
- Lubrication of gears
- Uses
GEARS
A gear is a wheel with teeth around its rim that mesh with the teeth of another wheel to transmit motion.
OPERATION
When two gears mesh, one is the driver and the other becomes the driven. A gear is a driver gear because the power to drive the system is generated by it, while the other is the driven because it is only being driven, and does not produce the power/energy.
TYPES OF GEAR
There are various types of gears, namely: Spur gear, Bevel gear, Rack and Pinion gear, Helical gear and Worm gears
- Spur gears: They are used for transmitting drive between parallel shafts.
- Bevel gears: These are used for transmitting power/drive between shafts at angles.
- Rack and pinion gears: These gears are used for converting rotary motion of the pinion to linear motion of the rack.
- Helical gears: These gears can transmit motion and power between either parallel or right angle shafts.
- Worm gears: These gears operate silently and smoothly. They can be used for reducing speed and increasing torque.
LUBRICATION OF GEARS
Lubrication is the application of oily or greasy substance to machine parts in order to reduce friction. The substance applied (such as oil or grease) is called lubricant.
The purpose of lubricating gears is as follows:
- To promote sliding between teeth to reduce the coefficient of friction
- To limit the temperature rise caused by rolling and sliding friction.
Methods of Lubrication
There three gear lubrication in general use
- Grease lubrication
- Splash lubrication (oil bath method)
- Forced oil circulation lubrication
There is no single best method or lubricant. Choice depends upon tangential speed and rotating speed. At low speed, grease lubrication is a good choice. For medium and high speeds, splash lubrication and forced oil circulation are more appropriate, but there are exceptions. Sometimes, for maintenance reasons, a grease lubricant is used even with high speed.
USES OF GEAR
- Gears are used to transmit power from one shaft to another.
- They are used to change the speed of shafts to either high or low speed.
- They also change the running direction of a shaft.
EVALUATION
- Define (a) Gear (b) List three types of gear and the uses
- State the uses of gear
- State the methods of gear lubrication
GENERAL EVALUATION
- Mention three (3) types of gear and their applications.
- Sketch a spur gear.
READING ASSIGNMENT
Read about gear ratio and gear speed (NERDC Basic Tech. for JSS3 page 157-159)
WEEKEND ASSIGNMENT
- ………. are used for transmitting drive between parallel shafts (a) Bevel gears (b) Spur gears (c) Rack and pinion gears (d) Lift
- Which of the following is used for transmitting power/drive between shafts at angles (a) Spur gears (b) Leaf gears (c) Rack and pinion gears (d) Bevel gears
- In Rack and Pinion gears,……… generate rotary motion (a) rack (b) spur (c) lift (d) pinion
- A wheel with teeth around its rim that mesh with the teeth of another wheel to transmit motion is called (a) Belt (b) Chain (c) Gear (d) Clutch
- ……… are used to change the speed of shafts to either high or low speed(a) Chain (b) Belt (c) Clutch (d) Gear
THEORY
- What is a Gear? (b) State three uses of gears
- State three types of gears (b)Briefly describe the operation of gears
