Components Part 2

1
ComponentsPart 2

• Mr P Mulholland
• AS Design and Technology
• St Josephs HS Crossmaglen

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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.

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Spur Gears

• Used in simple motors and gearboxes for
  childrens 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.

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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.

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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.

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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.

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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.

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Plain Bearings

• Plain Bearing Video 1
• Plain Bearing Video 2

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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

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Journal Bearings
Journal Bearing Video
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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.

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Ball Bearings
Ball Bearing Video 1 Ball Bearing Video 2
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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.