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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Long service life, free from wear problems depends on lubrication system; its ability to keep gear cool, and to deliver lubricant free from hard particles filter with 5 micron rating.

To design gear, we need to estimate W n Fig.

Chapter 1. Introduction to Mechanisms

But sometime failure of lubrication pump failure, filter chocking, excessive leakage occurs and gear materials must be able to handle such extreme situations. Higher entraining velocity increase traims losses”. Therefore, contact stress is. It is interesting to note that oil sample collected after 3 hours of operating gear at rpm no load conition show wear Fig.

Lack of lubricant, may initiate scuffing failure. The limit on velocity ratio depends on gear pair for example:.

Epicyclic gear train nptel pdf merge

It is interseting to note that npttel spur gears experience sliding ,as depicted in Fig. Q v vs geometric tolerance. It is interesting to note that coefficient of friction is variable and it depends on operating conditions. The lower pressure angle has the advantage of smoother and quieter tooth action because of larger profile contact ratio.


An efficient method of achieving high reduction ratios in minimum gaer is the use of planetary gearing.

Friction between gear pair occurs due to sliding between meshed teeth and churning of lubricant. Maximum contact stress is equal to p max. In absence of lubricant additives and antifriction coating, gears will be subjected to direct friction.

By adding teeth of the proper shape on disk, power can be transmitted without slip at uniform rate. For high speed reduction, two stage or three stage construction are preferred, otherwise gear wheel size increases, which increases the gearbox size.

Typical values of gear efficiencies are listed in Table 6. Most gears are in the hardness range of approximately Rc 30 to Rc 38 or Rc 55 to Rc If sufficient backlash has not been provided to take care of the differential thermal expansion, the teeth will bind, with disastrous results.

Tooth curves of the mating teeth need to be tangent to each other as shown in Fig. In simple gear mesh, a maximum ratio in order of 7: Normal load on tooth. In normal atmospheric conditions, all engineering metallic surfaces are primarily coated with some adsorbed gas Fig.

These types of geometrics are known as external gears. 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. The sliding friction losses are related to the coefficient of friction, normal load and sliding velocity on the contact surfaces, while the rolling friction nptfl occur due to the formation of an elastohydrodynamic EHL film.

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NPTEL :: Textile Engineering – Mechanics of Textile Machinery

Internal gears are generally more efficient since the sliding velocity along the profile is lower than equivalent external gears. Surface failure of gear tooth occurs due to very high local contact stresses.

Gear surfaces coated with boundary additive or antifriction coating. Typical gear pair having high sliding is shown in Fig. In case of heavily loaded gears, however, more viscous lubricant will be recommended.

Usually, following two types of lubrication mechanisms are commonly used for gear lubrication. These dimensions are determined on the basis of tooth stresses, which are imposed npte, the transmitted tooth load. In this regime, friction and wear are influenced by the ability of lubricant to create protective boundary films on gear tooth with chemical and physical reactions, and by its viscous characteristics. By using parameters shown in Table 6.

Using AGMA pitting equation formula, determine the maximum contact stress.