14 Define a spur gears involute\" 15. What is an advantage and a disadvantage of

Question

14 Define a spur gears involute" 15. What is an advantage and a disadvantage of a pin bearing? 16. Define a "thrust load" on a bearing, What is one type of bearing that is good if you have thrust loads on your bearings. 17. Define the load life relationship as it pertains to bearing design 18. Give 2 reasons why some clearance is necessary between bearings and races 19. Describe a bearing materials "pv value" 20. Define the following types of shear stresses: a. Direct b. Beam or vertical c. Torsional 21. Why is the analysis of a member more difficult if it is subjected to bending and torsional shear than if it is subjected to bending and tensile stresses? 22. Describe a hydrodynamic bearing. 23. What are the two types of stresses that are induced into spur gear teeth? 24. Why does deflection often control shaft design rather than bending or torsional stresses? 25. Describe the difference between a tolerance and an allowance when detailing machine parts

Explanation / Answer

14) Involute:

Involute is a teeth profile on spur gear. It is defined as "An Involute of a gear profile is a plane curve generated by a point on a circle which rolls with out slipping". normal at any point of an involute is a tangent to the base circle. It is most widely used gear profile.

15)

the advantage of pin bearing:

Pin bearing is capable of transferring or supporting a large amount of load along any direction in the horizontal plane. It also allows rotation along any of the desired axes in a horizontal plane.

Disadvantage:

Pin bearings cannot take up any vertical load. they are poor at handling any vertical load.

16)

the bearing is meant to support rotating shafts. thrust load or axial load on the bearing is the load which acts parallel to the axis of rotation.

thrust bearings support thrust loads effectively. They use tapered rollers in it.

17)

bearing life in terms of a design point of view is defined as the total number of revolutions, or the number or hours at a given constant speed, of bearing operation required for failure criteria to develop such as cracks initiation and crack propagation or yielding failure of bearing.

18)

1) It impacts on bearing life.

2) for effective lubrication.

3)For effective temperature dissipation.

4) To avoid misalignment and avoid wear outs.

19)

While choosing any bearing material along with conditions like temperature working range, lubrication etc, one of the important parameters is PV value which is the product of pressure “P” and sliding velocity“V ”, is often used as the criteria to determine if the operating condition is allowable for the sliding material or not. Every sliding material hs got its own "PV" value.

20)

a) Direct shear stress is the stress which is generated in the material due to the application of the force which is parallel to the cross-section of the body.

b)

the force in the beam which is acting perpendicular to its longitudinal axis. It is called as a beam or vertical shear stress.

c)

Shear stress which is developed due to the twisting moment in shafts. Pretty much we encounter in rotating shafts or automobile axles.

21)

Here we need to account for both axial and bending moments and shear. this is combined effect. Whereas if the beam is subjected to only bending or tensile, the analysis is simple. we no need to account for torsion.

22)

Hydrodynamic bearing is a fluid film bearing, where the fluid is oil or some kind of lubricant which reduce friction and bring cooling effect. In hydrodynamic bearing the pressure is developed by the high-speed journal at higher rpm, this helps the movement of a thin film of lubricant between shaft and journal. This is the basic difference between hydrostatic and hydrodynamic bearings.

23)

In most of the machine components like shafts, failure criterion is based on deflection because the shafts are meant to carry or transmit high loads. For example, if we look at a shaft supporting a gear is deflected, the meshing of gear teeth would not be proper which results in interference or entire gear system failure which is more dangerous.

If we look at bearings and a shaft, the misalignment or deflection of shaft results in increasing the load on bearing results in early wear at the shaft and bearing surfaces.

25)

tolerance is a limit of a dimension from anyone nominal value. It is individual. Whereas the allowance is the deviation between two mating part dimensions in a fit.

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