1) How do you identify a planetary gear? A gear whose axis itself is revolving is called a planetary gear. In some epicyclic gear trains, we may find two or more. described a number of gear applications, typical ones are shown in Figs. used in high speed and high load application in all types of trains and a wide range. The velocity ratio of an epicyclic gear train is determined by the following methods: (a) Tabulation method; (b) Formula method; and (c) Instant centre method or.
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Generally, a gear pair acts as a speed reducer aiming torque amplification at output shaft.
But sometime failure of lubrication pump failure, filter chocking, excessive leakage occurs and gear materials must be able to handle such extreme situations. Following empirical formulae are availiable for splash lubrication system to minimize churning losses.
Torque is calculated from the horsepower transmitted and the speed of npteel component in question. In this topic, we shall discuss about the geometry of gears and then consider three different aspects of gearing namely elastohydrodynamic lubrication, tooth contact phenomena, and wear of gears.
Q v vs geometric tolerance.
NPTEL Phase II :: Tribology
Gear surfaces coated with boundary additive or antifriction coating. Helical crossed axes Fig. Recommended oil viscosity .
The lower pressure angle has the advantage of smoother and quieter tooth action because of larger profile contact ratio. Worm gears have crossed axes Fig. Too much or too less lubricant is harmful for gear operation. Friction between gear pair occurs due to sliding between meshed teeth and churning of lubricant. In such trains as shown in Fig. It prevents jamming of teeth and compensates for thermal expansion of teeth.
Trainw case of heavily loaded gears, however, more viscous lubricant will be recommended.
The limit on velocity ratio depends on gear pair for example:. Insufficient backlash is sometimes the cause of excessive heat and wear.
But for home applications, we use N-N gear pair, where rate of heat generation is relatively low. These types of geometrics are known as external gears. The total mechanical loss is then given as the sum of losses from all gear meshes and bearings. Inadequate lubrication may also be a source of excessive heat and wear.
It is interseting to note that even spur gears experience sliding ,as depicted in Fig. Helical gearing, in which the teeth are cut at an angle with the axis of rotation, was developed after spur gearing and has the advantages that has the smoother action and tends to be quieter Fig. Maximum contact pressure at the contact point between two cylinders is given by:. Sliding at point I. Properly designed gear-sets should never fail but must be expected to eventually fail by wear of one of surface.
Typical values of gear efficiencies are listed in Table 6.
In high speed units, the churning losses may exceed the friction losses; therefore, the type and amount of lubricant are critical. In absence of lubricant additives and antifriction coating, gears will trsins subjected to direct friction. If sufficient backlash has not been provided to take care of the differential thermal expansion, the teeth will bind, with disastrous results.
Gears are machine elements, which are required to transmit power between shafts rotating at different rotational speeds. Using AGMA pitting equation formula, determine the maximum contact stress. As contact moves towards or away from pitch point, sliding occurs.
Epicyclic gear train nptel pdf merge
Difference between tooth space and tooth thickness is known as backlash. By adding teeth of the proper shape on disk, power can be transmitted without slip at uniform rate. Bore diameter of pinion is 17 mm, and bore dia of gear is 20 mm.
Gear surface with adsorbed gases. Effect of Brinell hardness on allowable contact stress for through-hardness steel . To estimate the working life of gears, it is essential to analyze the destructive forces at work, and knowledge of the ability of chosen gear materials to withstand those forces.