HomeJSS 3BASIC TECHNOLOGYSECOND LEARNING NOTES JS 3 (BASIC 9) BASIC TECHNOLOGY

SECOND LEARNING NOTES JS 3 (BASIC 9) BASIC TECHNOLOGY

SECOND TERM: E-LEARNING NOTES

JS 3 (BASIC 9)

SUBJECT: BASIC TECHNOLOGY

JSS 3

 

WEEK: 3

TOPIC: GEAR DRIVE

CONTENT:

  • Gear drive
  • Seizure
  • Types of gears
  • Use of gear drive
  • Gear ratio
  • Speed ratio
  • Changing direction of drive

Gear drive

This isa device used to transmit motion between parallel or inclined shafts that are close to each other (such that the tooth on the wheel mounted on the shafts mesh together). When two gears are in mesh, they are called GEAR TRAIN. Friction always occurs between the meshed teeth of the gear train. Constant lubrication is therefore necessary to prevent wearing. The teeth on each gears in mesh must be uniformly spaced around the gear (that is symmetrical) for them to mesh properly and to prevent damage of the tooth. Improperly meshed gears can also lead to seizure of the gear train.

Seizure is the total movement stoppage of the gear train.

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Unlike the belt and the chain drive, the driver and the driven gear move in different direction. To make the driver and the driven gear move in the same direction, another gear (called the IDLER) is inserted between the two (driver and the driven gear).

 

Types of gears

  1. Spur gear: this has teeth parallel to the shaft of the gear.
  2. Helical gear: this has teeth inclined to the shaft of the gear.
  3. Worm gears: these are gears formed when a spur gear mesh with a screw.
  4. Rack and pinion: these are gears that run on a flat toothed rack.
  5. Planetary gears: these consist of a number of spur gear meshed with one another and another gear with internal gear.
  6. Bevel gears: these are gears used when power is to be transmitted between inclined shafts

   

Helical gear

Spur gear

Uses of gear drive

  1. To transmit motion between two inclined or parallel shafts.
  2. To change direction of motion.
  3. For speed selection.

Gear ratio

This can be defined as the ratio of the number of teeth on the driver gear to that on the driven gear

T1is number of teeth on driver gear

T2is number of teeth on driven gear

Speed ratio

This can be defined as the ratio of the speed of the driven gear to the speed of the driver gear.

S1 speed of the driver gear

S2is speed of the driven gear

The gear ratio and the speed ratio of a gear train are equal. The speed of rotation of the driven gear depends on the number of teeth on the driven and the driver gear.Where a large increase in speed is desired (like in the case of motor car), a compound gear train is used.

 Compound gear

The speed of the driven gear S2 is given as

Where each symbols has it usual meaning.

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Changing the direction of drive,

Chain drives cannot be used for changing the direction of rotationof drives. Belt drive cannot be used to change direction of rotation of drive except when belt is crossed. Gears can be used for changing the direction of motion. The bevelled gear is often used for changing direction of motion between two perpendicular/inclined shafts.

 

EVALUATION

  1. Which of these drives can be used to change the direction of rotation? (a) straight lap belt (b) chain drive (c) gear drive (d) none of the above
  2. A gear with tooth parallel to the shaft is called —(a) helical gear (b) planetary gear (c) worm gear (d) spur gear
  3. The ratio of the speed of driver gear to the speed of the driven gear is — (a) gear ratio (b) speed ratio (c) velocity ratio (d) none of the above

Answers

  1. (c) 2. (d) 3. (d)

PERIOD TWO

CONTENT

CALCULATIONS ON GEAR AND SPEED RATIO

Question 1: the number of teeth on the driver and the driven gear is 12 and 16 respectively. If the speed of the driver gear is 100rev/min, calculate (i) the gear ratio (ii) speed of the driven gear

Solution

Number of teeth on the driver gear T1 = 12

Number of teeth on the driven gear T2 = 16

  1. Gear ratio G = ?

Gear ratio G =

  1. Speed of the driver gear S1 = 100rpm

Speed of the driven gear S2= ?

Speed of the driven gear S2 = 75 rpm

Question 2: A gear train is such that the number of teeth on the driver gear is 20 while that on the driven is 8. If the speed of the driver gear is 150rev/min. calculate the speed of the driven gear.

Solution

Number of teeth of the driver gear T1 = 20

Number of teeth on the driven gear T2 = 8

Speed of the driver gear S1 = 150rpm

Speed of the driven gear S2= ?

Speed of the driven gear S2 = 375rpm

Question 3: in a compound gear train, the effective gear ratio is . if the speed of the driver gear is 100rev/min, calculate the speed of the driven gear.

Solution

Speed of the driver gear S1 = 100rpm

Gear ratio

Speed of driven gear S2= ?

Speed of the driven gear S2= 320rpm

Question 4: A gear train has a gear ratio of and a driven gear rotating at a speed of 180revolution per minute. What would have been the speed of the driver gear?

Solution

Speed of the driven gear S2 = 180rpm

Gear ratio

Speed of the driver gear S1= ?

Speed f the driver gear S1 = 72rpm

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Practical

The teacher should guide the students on how to use a hard cardboard to construct gear with uniform tooth with the aid of the construction tools.

Using hard cardboard gear of different radii and their centres with nail at different portion on a wood, the students should demonstrate the operation of compound gear.

Evaluation question

  1. Which of these gears is a combination of a spur gear and a screw? (a) bevel gears (b) helical gear (c) spur gear (d) worm gear
  2. A condition in which the movement of a gear system is halted due to a spoil is known as —- (a) slip (b) seizure (c) reverse (d) bevel
  3. The friction between the teeth of meshed gears can be reduced BY (a) avoiding the use of gear (b) exposing gear to air (c)Lubrication (d)aeration
  4. The major use of drive is to (a) transmit motion (b) change direction of motion (c) reduce speed (d) avoid friction
  5. The ratio of the number of teeth on the driven gear to the number of teeth on the driver gear is called (a) speed ratio (b) gear proportion (c) gear ratio (d) none of the above
  6. The gear ratio of a gear train is and the speed of the driver gear is 80rpm. What is the speed of the driven gear? (a) 70rpm (b) 140rpm (c) 150rpm (d) 210rpm

ASSIGNMENT

  1. Consult your textbook and make a list of ten types of gear.
  2. List five applications of the gear drives

READING ASSIGNMENT: Read your Basic Technology textbook by Olawehinmi, pages 160 – 169 and answer the following questions.

  1. Define motion.
  2. Write a short note on the following (i) linear motion (ii) rotary motion.

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