Components Part 2

1. ComponentsPart 2 Mr P Mulholland AS Design and Technology St Joseph’s HS Crossmaglen

2. Rivets • Rivets are used to make simple permanent joints between two or more pieces of metal. • They can form rigid joints or hinged joints. • Snap Rivets are normally made out of soft iron which is ductile and can be easily deformed with a hammer to form the joint. They are available with three different head types: countersunk, flat, snap and round headed. • Pop Rivets are made from aluminium with a central steel pin. A special pop rivet gun is used to de-form the rivet. They are especially suited to joining thin sheet material or where access can only be gained from one side.

3. Gears • A gear is a basic mechanism that when coupled together with other gears can transmit rotary motion and force and change the direction of motion. • Gears can be used to: • Change direction of rotary motion • Change spindle speeds • Transmit motion through 90 degrees • Each gear has a shaft passing through its centre and the gear is fastened to the shaft by using cotter pins, splines or grub screws • When the gears are brought together their teeth mesh and they interlock. • The gear is a wheel onto which a number of teeth have been cut. • Gears should be designed to mesh together without jamming. This will allow force to be transmitted in an efficient way.

4. Spur Gears • Used in simple motors and gearboxes for children’s toys. • Speeds can be increased or reduced and direction of rotation can be changed. • Two spur gears together are termed a simple gear train. A crown wheel is another term for a single gear wheel.

5. Simple and Compound Gear Trains • A simple gear train consists of two gears meshing together. The input and output are in opposite directions • A compound gear train consists of two separate gear trains meshed together. This involves two gears mounted on the same shaft. In this arrangement, very large increases or decreases in speed can be achieved.

6. Rack and Pinion • A rack and pinion is used to change rotary motion into linear motion. • They are used on pillar drills to move the drill table up and down and also to move the drill down to the work piece. • The rack part of the system is a straight bar with teeth which mesh with the teeth on the pinion wheel. As the rack moves the pinion rotates. • Steering systems in cars are based on a rack and pinion with the track rods attached to each end of the steering rack and the pinion attached to the end of the steering column.

7. Worm and Wheel • Like bevel gears, worm gears are used to transmit force and linear motion through 90°. • The worm gear resembles a screw thread fixed to the driven shaft and is at right angles to the driver shaft and worm wheel. • Large reductions or increases in speed can be achieved because the worm wheel is considered to have only one tooth. • They are used in food mixers to turn the blending whisk. • Worm gears are widely used in industry as they can be used to achieve large reductions in speed in a relatively compact space.

8. Bevel and Mitre Gears • Bevel gears have their shafts at 90° to each other. This allows rotational direction/forces to be transmitted through 90°. • If different sized gears are used, the speed of rotation can be increased or decreased. • They are used in hand drills in school workshops.

9. Plain Bearings • Plain Bearing Video 1 • Plain Bearing Video 2

10. Plain Bearings • A plain bearing (bush) is a support that holds a rotating shaft. • Due to friction the moving parts will wear down and fail or become damaged. • A plain bearing or bush is placed between the support and the moving shaft. This bearing or bush has a low coefficient of friction. • The disadvantage of using a plain bearing or a bush is that they will wear away over a period of time and will need to be replace. • Plain Bearings or Bushes are made from: • Bronze • Nylon – self lubricating • Ceramics – porous and will soak up oil to provide lubrication

11. Journal Bearings Journal Bearing Video

12. Journal Bearings • A journal bearing is a simple bearing in which a shaft, or "journal", rotates in the bearing with a layer of oil or grease separating the two parts. • The shaft and bearing are generally both simple polished cylinders with lubricant filling the gap. Rather than the lubricant just "reducing friction" between the surfaces, letting one slide more easily against the other, the lubricant is thick enough that, once rotating, the surfaces do not come in contact at all. • To top up the oil or grease it is fed into a small hole under pressure. • The casing that houses the journal bearing is called the journal box.

13. Ball Bearings Ball Bearing Video 1 Ball Bearing Video 2

14. Ball Bearings • Most common type of bearing. • A ball bearing is an engineering term referring to a type of rolling-element bearing which uses balls to maintain the separation between the moving parts of the bearing. • The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. • It achieves this because when the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were rotating on each other.