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 TWO
TOPIC: BELT AND CHAIN DRIVES
CONTENT
BELT DRIVES
A belt is a looped strip of flexible material used to mechanically link two or more rotating shafts. A belt drive offers smooth transmission of power between shafts at a considerable distance.Belt drives are used as the source of motion to efficiently transmit power or to track relative movement. When the belt is used for speed reduction, the smaller sheave is mounted on the highspeed shaft, like the shaft of an electric motor. The larger sheave is then put on the driven machine.
TYPES OF BELT DRIVES
The types of belt drives are diverse. The list of its kinds include the flat belts, synchronous timing belts, cog belts, vee-belts, round belts, multi-groove belts, ribbed belts, film belts, metal belts, endless round belts and speciality belts. Some of them are explained below:
- The Flat belt: The simplest type is often made from leather or rubber-coated fabric. The sheave surface is also flat and smooth, limiting the driving force by the pure fiction between the belt and the sheave.
- Synchronous Belts, or Timing belts: These ride onsprockets that have mating grooves that the teeth on the belt seat. It is a positive drive, limited only by the tensile strength of the belt and the shear strength of the teeth.
- Cog Belts: These are applied to standard V-grooved sheaves. The cogs give the belt greater flexibility and higher efficiency compared with standard belts.
- Vee-Belts: The V-shape causes the belt to wedge tightly into the groove, increasing friction and allowing high torques to be transmitted before slipping occurs.
BELT AND PULLEY ARRANGEMENT
There are various types of belt and pulley arrangement. These include:
- Open belt: An open belt connecting two pulleys makes them run in the same direction
- Crossed belt; this changes the direction of pulleys.
- V-belt: V-belts run on V-pulleys. A common use of the V-belt and V-pulley is the fan belt of an automobile.
EVALUATION
- What is a belt drive?
- State the types of belt drive
- Explain each type of belt drive
CHAIN DRIVES
A chain is a power transmission element made as a series of pin-connected links.The design provides for flexibility while enabling the chain to transmit large tensile forces.Chain drive is a way of transmitting mechanical power from one place to another. When transmitting power between rotating shafts, the chain engages mating toothed wheels, called sprockets.
TYPES OF CHAIN DRIVES
- Roller Chain Drives: The most common type of chain is the roller chain, in which the roller on each pin provides exceptionally low friction between the chain and the sprockets. Roller chain is classified by its pitch, the distance between corresponding parts of adjacent links. The pitch is usually illustrated as the distance between the centers of adjacent pins. Standard roller chain carries a size designation from 40 to 240.
- Conveyor Chain : Rollers sit proud of links and can roll along supporting surface It can be used for transporting materials, as rollers can support weight. Can also be used just to support weight of chain if transmitting power over long distances
- Inverted Tooth (or silent) Chain: Sprocket teeth mesh with shaped links instead of rollers on chain. Joints between links use rolling rather than sliding contact. Profiles of links are more like involute gear teeth. Overall effect is to reduce noise.
- Leaf (or lifting) Chain:It is designed for lifting rather (than power transmission). Do not have to mesh with sprockets, hence no rollers. Therefore can narrower than roller chain with equivalent strength. Example: fork-lift truck.
EVALUATION
- What is a chain drive?
- State the types of chain drive
- Explain each type of chain
GENERAL EVALUATION
- Differentiate between a belt drive and a chain drive
- State four(4) types each of belt and chain drives
READING ASSIGNMENT: Read more on belt and chain drives (NERDC Basic Tech. for JSS3 page 148-153)
WEEKEND ASSIGNMENT
- The most common type of chain is the ……… chain. (a) inverted tooth (b) roller (c) leaf (d) conveyor
- Which of these types of chains can be used for transporting materials?(a) roller chain (b) conveyor chain (c) inverted tooth chain (d) leaf chain
- ……….. is a power transmission element made as a series of pin-connected links. (a) Iron (b) Belt (c) Chain (d) magnet
- Which of the following offers smooth transmission of power between shafts at a considerable distance(a) Belt drives (b) Chain drives (c) Magnetic drives (d) Electrical drives
- Which of the following types of chain is used for lifting rather (than power transmission) (a) roller chain (b) conveyor chain (c) inverted tooth chain (d) leaf chain
THEORY
- (a) What is a belt? (b) State the types of belt we have?
- (a) State four (4) types of Chain drives (b) Explain any two
