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Sunday, 24 December 2017

Types of gears

          Before we start choosing a gear, we need to know that we are employing a metric gear, which is having metric gear module, or inch gear, that uses pitch, to conform proper gear sizing and compatibility. The gear module can be found by using a simple formula, by dividing the pitch diameter, or diameter of the pitch circle, by the quantity of the teeth the gear has. It is vital to make sure that gears we are using have an equivalent module, otherwise they will not work along. While choosing a gear two other important gear features has to be keep in mind they are gear ratio and backlash.

Types:

1. Spur Gear     
2. Helical Gear
3. Double Helical gear or Herringbone Gear
4. Bevel Gear or Miter gear
5. Worm gear 
6. Rack & Pinion
7. Internal and External Gear
8. Sprockets

According to the position of axis of shaft gears are also classified as :

1. Parallel Axis
          a. Spur Gear
          b. Helical Gear
          c. Rack and Pinion
2. Intersecting axis
          a. Bevel Gears
3. Non-interssecting and non-parallel
          a. Worm Gears


Below we can discuss them indetail

1. Spur Gear:

          Simplest and commonest kind of gear is Spur Gear and these are employed in series for large speed reductions. As discussed previously these gears are used to connect shafts which are Parallel and Co-Planar. This sort of arrangement is termed as Spur gearing.
          The teeth of spur gears are straight and parallel to the axis of the gear wheel. The benifits of spur gears are their simplicity in design, economy of manufacture and maintenance, and absence of end thrust. They impose solely radial loads on the bearings.
Spur gear
 Image Credits : http://www.gurukrupaeng.com/images/spur-2-big.jpg
          Spur gears are referred to as slow speed gears. Spur gears mate only one tooth at a time, leading to high stress on the pairing teeth and noisy operation. If noise isn't a significant design drawback, spur gear can be used at almost any speed. A normal gear ratio range is 1:1 to 6:1.
          Spur gears are used to this reasult in Laundry machines, Mechanical Clocks, Blenders, Kitchen aid beaters, Construction equipment, Fuel pumps and mills.

2. Helical Gear:

          The leading edges of the gear teeth are not parallel to the axis of rotation, but are set at an angle in the form of a helix, hence these gears got the name Helical gears. The usual array of helix angle ranges from 15 to 30 degrees. Helical gears are used to transmit the power between non-intersecting shafts. When the gear system interact, they first contact at tips of the tooth and the contact progressively spreads as the gears rotate, till complete engagement of tools teeth obtain. Because of this gradual engagement helical gears operation is more smooth and quiet compared to spur gears.
Helical Gear   !!!   Image courtesy : Google
          These gears are usually considered high speed gears. Helical gears can take higher loads than similarly sized spur gears. Both radial loads and thrust loads are imposed by single helical gears on their bearings. Thrust bearings we need to employ to counteract these thrust loads and also maintain gear allignment. When we enguage gears, they have same helix angle, pitch and pressure angle but the angle of the helix on both the gears must be same in magnitude but opposite in direction, i.e., a right hand pinion meshes with a left hand gear. Helical gears can be used to adjust the rotation angle by 90 deg. When mounted on perpendicular shafts. Helical gears normal gear ratio range is 3:2 to 10:1.
Advantages:
  • Large contact area
  • Quietness in operation
  • Less vibration
  • Able to transmit large force.

3. Herringbone Gear:

          Herringbone gears also referred as "Double Helical Gears". Herringbone gears is a special variety of gear they looks like two helical gears placed side by side in opposite helix pattern. When we see from the top every groove looks like the letter "V". In herringbone gears there is no thrust loading on the bearings. In the double helical gears arrangement, the side thrust of on half is balanced by the counter half by this the thrusts are counter-balanced.
Herringbone Gear   !!!   Image Courtesy: Google 
4. Bevel Gear/Miter Gear:

          Bevel gears are used to connect intersecting but co-planar shafts. This arrangement is known as Bevel Gearing. Whenever we want to alter the direction of shaft rotation we use bevel gearing. Straight bevel gears are most common type. Straight bevel gears is used on shafts at any angle, but right angle is the most common. Bevel gears have conical blanks. The teeth of straight bevel gears are tapered in each thickness and tooth height. This slight curvature in teeth of straight bevel gears is called crowning.
Straight bevel gear    !!!    Image Courtesy: Google

Spiral Bevel Gears:

Spiral Bevel Gear
Image Courtesy : Google
          In spiral bevel gears the teeth are oblique. As we are well know about straight bevel gear, there is one problem similar to spur gear i.e., the mating gears teeth engagement is not be gradual and hence the operation of straight bevel gear is so noisy. Now solution of this problem will be to cut and prepare the teeth oblique (Curved) so that the mating gears teeth engagement will be gradual and higher tooth to tooth contact as compared to straight bevel gearing. Because of this reason spiral bevel gear will provide quieter operation and also take up more load as compared to straight bevel gearing.

Zero Bevel Gears:
Straight Bevel gear  !!!  Image Courtesy: Google
          Zero Bevel gears are just like straight bevel gears, but their teeth are curved lengthise. These curved teeth of zero bevel gears are arranged in a manner that the effective spiral angle is zero.

5. Worm Gear:

          These gears consists two elements called the worm screw (Driving element) and  worm wheel (Driven element). Worm gears are used to transmit power beteen two non-parallel and non-intersecting shafts (shafts at 90° generally) and where high reductions are required. Worm gears have reduction ratio 20:1 and even up to 300:1 or greater. The reduction ratio depends on two things they are number of starts of the worm and number of teeth on the worm gear. The shafts of worm gears lie in parallel planes and can be slashed at any angle between zero and a right angle. Worm and worm gear have sliding contact so they form a lower pair. In worm gears, one gear has screw threads. Due to this, working of worm gears is quiet, vibration free and also gives a smooth output.
Image Courtesy: Google
Advantages:
1. They operate silently and smoothly.
2. they are self-locking. (Worm can easily turn the gear, but the gear can't turn the worm. This will act as a break in conveyor when the motor is not working).
3. They occupy less space.
4. They have good meshing effectiveness.
5. High velocity ratio can be obtained in a single step.

Disadvantages:
1. Worm gear material are expensive.
2. High power losses and low transmission efficiency.
3. They produce a lot of heat.

Applications:
1. Gate control mechanism
2. Hoisting machine
3. Automobile stearing mechanism
4. Lifts
5. Conveyors

6. Rack and Pinion:

Image Courtesy: Google
          A rack is a flat, toothed bar or rod which is taken into account as a sector gear with an infenitely large radius of curvature. Torque can be converted to linear force by meshing a rack with a pinion: the pinion rotates; the rack moves in a straight line. Such a mechanism is employed in vehicles to alter the rotation of the steering wheel into the left-to-right motion of the tie rod(s). Rack also feature in the theory of gear geometry, where, as an example, the tooth shape of an interchangeable set of gears may be pecified for the rack (infinite radius) and the tooth shapes for gears of perticular actual radii then derived from that. The rack and pinion gear type is employed in a rack railway.
Rack and pinion -- stearing mechanism
Image Courtesy : Google

7. Internal & External Gears:

An Internal Gear is a cylindrical shaped gear, one with the teeth on the inner surface of cylinder (or Cone). Conversly an external gear is the one with the tooth fashioned on the outer surface of cylinder.
Image Courtesy: Google
    
8. Sprocket:

Sprocket is a profiled wheel with teeth, or cogs. Sprockets are used to run chains or belts. They are typically used in conveyor systems. Based on the transmission and reception sprockets are classified in many ways like Simplex Duplex, Half duplex, Full duplex etc.,
Image Courtesy : Google


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