Spur gear and helical gear

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Guided by;Prof. HRTSpur Gear and Helical Gear

G.H Patel College of Engineering and TechnologyBy:150110119124 ( Mitul )150110119125 ( Deep )150110119126 ( Sharvil )150110119127 ( Vishvak )150110119128 ( Festus ) (2C19)Mechanical Engineering

SPUR GEAR

Characteristics of Spur GearSpur gears have straight teeth parallel to the axes and thus are not subjected to axial thrust due to tooth load.At the time engagement of the to gear of the two gears, the contact extends across the entire width on line parallel to the axes of rotation.This result is sudden application of the load, high impact stresses and excessive noise at a high speed. The gears have external teeth on the out surface of the cylinders, the shafts rotates in the opposite direction.

In an internal spur gear, the teeth are formed on the inner surface of an annulus ring.An internal gear can mesh with an internal pinion ( small gear ) only and the two shafts rotates in the direction

External Spur GearInternal Spur Gear

Force on spur gear teethF = Transmitted forceF = Normal force or separating force F =Resultant force = Pressure angle F = F tanF = F/cos

Power = T n / 63000Torque, T = F r and r= D / 2Combining the above we can write

F = 2T / D

Metal cutting machinesPower plantsMarine enginesMechanical clocks and watchesFuel pumpsWashing MachinesGear motors and gear pumpsRack and pinion mechanismsMaterial handling equipmentsAutomobile gear boxesSteel millsRolling millsApplication of Spur Gear

HELICAL GEARS

HELICAL GEARS CONT.... In HELICAL GEARS the teeth are inclined to the axis of a gear. They can be left-handed or right-handed depending on the direction in which helix slopes.

In HELICAL GEARS the teeth gears, the teeth are curved, each being helical in shape. 2 mating gears have the same helix angle, but teeth of opposite hands.Are used in transmitting torques between parallel or non parallel shafts, they are not as noisy as spur gears.

Terms related to helical gearsHelix Angle- It is the angle at which the teeth are inclined to the axis of gear. It is also known as Spiral Angle.Circular Pitch- It is the distance between the corresponding points on adjacent teeth measured on the pitch circle. It is also known as Transverse Circular Pitch.Normal Circular Pitch(Normal Pitch)- It is the shortest distance measured along the normal to the to the helix between corresponding points on the adjacent teeth. The normal circular pitch of two mating gears must be same.

Why Helical Gears???The angled teeth more gradually than the Spur Gear teeth, causing them to run more Smoothly and Quietly. With the parallel Helical Gears, each pair of teeth first make contact at a single point at one side of the Gear wheel.A moving curve of contact than grows gradually across the tooth face to a maximum than recedes until the teeth break contact at a single point on the opposite side.Also Spur Gears WHINE at high speeds. So Helical Gears are preferred instead of Spur Gears in high speed applications.

ApplicationsHelical Gears are used in high speed applications. Speed is considered high when the Pitch Line Velocity exceeds 25m/s.Large Power TransmissionAlso recommended for very high Load as in Automobile Gear boxes, etc.

DisadvantagesThe disadvantage of Helical Gears is that they induce axial thrust in one direction on the Bearings.The thrust is usually an end thrust due to action of a force component along the Gear Axis. The bearings and the assemblies mounting the Helical Gears must be able to withstand the thrust load.As stated the thrust is along the axis of the Gear, so it is often accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth often addressed with the additives in the lubricant.

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