Table of Contents
GEAR –
Gears are toothed wheels used for transmitting motion and power from one shaft to another shaft when they are not too far apart and when a constant velocity ratio is desired.
A gear may be a quite machine element during which teeth are cut around cylindrical or cone shaped surfaces with equal spacing. By meshing a pair of those elements, they’re wont to transmit rotations and forces from the driving shaft to the driven shaft. Gears are often classified by shape as involute, cycloidal and trochoidal gears. Also, they will be classified by shaft positions as parallel shaft gears, intersecting shaft gears, and non-parallel and non-intersecting shaft gears.
Classification of gears –
Gears are classified as –
1) Gears with parallel axes
a) Spur gear
b) Helical gear
c) Rack and pinion gear
d) Double helical or herringbone gear
2) Gear in which the shaft axes intersects if prolonged
a) Bevel gear
b) Spiral bevel gear
3) Gears in which the axes are neither parallel nor intersecting
a) Worm gear
b) Hypoid gear
Spur gear –
Gears having cylindrical pitch surfaces are called cylindrical gears. Spur gears belong to the parallel shaft gear group and are cylindrical gears with a tooth line which is straight and parallel to the shaft. Spur gears are the foremost widely used gears which will achieve high accuracy with relatively easy production processes. They have the characteristic of getting no load within the axial direction (thrust load). The larger of the meshing pair is named the gear and smaller is named the pinion.
Helical gear –
Helical gears are used with parallel shafts almost like spur gears and are cylindrical gears with winding tooth lines. They have better teeth meshing than spur gears and have superior quietness and may transmit higher loads, making them suitable for top speed applications. When using helical gears, they create thrust force within the axial direction, necessitating the utilization of thrust bearings. Helical gears accompany right and left twist requiring opposite hand gears for a meshing pair.
Rack and pinion gear –
Same sized and shaped teeth cut at equal distances along a flat surface or a straight rod is named a rack and pinion gear. It is cylindrical gear with the radius of the pitch cylinder being infinite. By meshing with a cylindrical gear pinion, it converts rotational motion into linear motion. Gear racks are often broadly divided into straight tooth racks and helical tooth racks, but both have straight tooth lines. By machining the ends of drugs racks, it’s possible to attach gear racks end to finish .
Double helical or herringbone gear –
Herringbone gears are a special sort of helical gears.A double helical gear are often thought of as two mirrored helical gears mounted closely together on a standard axle. This arrangement cancels out the axial thrust, since each half the gear thrusts within the other way , leading to a net axial force of zero. This arrangement also can remove the necessity for thrust bearings. However, double helical gears are harder to manufacture due to their more complicated shape.
Bevel gear –
Bevel gears have a cone shaped appearance and are wont to transmit force between two shafts which intersect at one point (intersecting shafts). A pinion and crown wheel features a cone as its pitch surface and its teeth are cut along the cone.
Spiral bevel gear –
Spiral bevel gears are bevel gears with curved tooth lines. With higher tooth contact ratio, they’re superior to straight bevel gears in efficiency, strength, vibration and noise. On the opposite hand, they’re harder to supply . Also, because the teeth are curved, they cause thrust forces within the axial direction. Within the spiral bevel gears, the one with the zero twisting angle is named zerol pinion and crown wheel .
Worm gear –
A screw shape cut on a shaft is that the worm, the mating gear is that the gear , and together on non-intersecting shafts is named a gear . Worms and worm wheels aren’t limited to cylindrical shapes. there’s the hour-glass type which may increase the contact ratio, but production becomes harder . thanks to the sliding contact of the gear surfaces, it’s necessary to scale back friction. For this reason, generally a tough material is employed for the worm, and a soft material is employed for gear . albeit the efficiency is low thanks to the sliding contact, the rotation is smooth and quiet. When the lead angle of the worm is little , it creates a self-locking feature.
Hypoid gear –
Hypoid gears resemble spiral bevel gears except the shaft axes don’t intersect. The pitch surfaces appear conical but, to catch up on the offset shaft, are actually hyperboloids of revolution.Hypoid gears are nearly always designed to work with shafts at 90 degrees. counting on which side the shaft is offset to, relative to the angling of the teeth, contact between hypoid gear teeth could also be even smoother and more gradual than with spiral pinion and crown wheel teeth, but even have a sliding action along the meshing teeth because it rotates and thus usually require a number of the foremost viscous sorts of gear oil to avoid it being extruded from the mating tooth faces, the oil is generally designated HP (for hypoid) followed by variety denoting the viscosity. Also, the pinion are often designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and better are feasible employing a single set of hypoid gears.
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- Gears
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