Question Set 3

14. During the design of a friction clutch what are the considerations that should be made?

In order to design a friction clutch the following points must be kept in mind:
> The material for the contact surfaces must be carefully selected.
> For high speed devices to minimize the inertia load of the clutch, low weight moving parts must be selected.
> The contact of the friction surfaces must be maintained at all the times without the application of any external forces.
> Provisions for the facilitation of repairs must be there.
> In order to increase safety the projecting parts of a clutch must be covered.
> A provision to take up the wearing of the contact surfaces must be present.
> Heat dissipaters to take away the heat from the point of contacting surfaces must be there.

15. What are the different types of brakes and explain them briefly?

Brakes can be classified on the basis of their medium used to brake, they are as follows:
> Hydraulic Brakes: These brakes as their name suggest use a fluid medium to push or repel the brake pads for braking.
> Electric Brakes: These brakes use electrical energy to deplete or create a braking force.
Both the above types of breaks are used primarily for applications where a large amount of energy is to be transformed.
> Mechanical Brakes: They can be further classified on the basis of the direction of their acting force: Radial Brakes: As their names suggests the force that acts on the brakes is of radial direction. They can further be classified into internal and external blades. Axial Brakes: In these types of brakes the braking force is acting in an axial direction as compared to radial brakes.

16. On what basis can sliding contact bearings be classified? Explain?

Sliding contact bearings can be classified on the basis of the thickness of the lubricating agent layer between the bearing and the journal. They can be classified as follows:
> Thick film bearings: These type of bearings have their working surface separated by a layer of the lubricant. They are also known as hydrodynamic lubricated bearings.
> Thin film bearings: In this type of bearings the surfaces are partially in direct contact with each other even after the presence of a lubricant. The other name for such type of bearings is boundary lubricated bearings.
> Zero Film Bearings: These type of bearings as their name suggests have no lubricant present between the contact layers.
> Externally or hydrostatically pressurized lubricated bearings: These bearings are able to without any relative motion support steady loads.

17. What are the basis on which the best material for Sliding Contact Bearings manufacturing?

Some of the important properties to lookout for in the material for sliding contact bearings are as follows:
> Compressive Strength: In order to prevent the permanent deformation and intrusion of the bearing the material selected should be possess a high compressive strength to bear the max bearing pressure.
> Fatigue Strength: the material selected for the bearing should be able to withstand loads without any surface fatigue cracks getting created. This is only possible if the material has a high level of fatigue strength.
> Comfortability: The material should be able to adjust or accommodate bearing inaccuracies and deflections without much wear and heating.
> Embeddability: The material should allow the embedding of small particles without effecting the material of the journal.
> Bondability: The bearings may be created by bringing together ( bonding ) multiple layers of the material. Due to the above reason the bondability of the material should be sufficiently high.
> Thermal conductivity and corrosion resistance: Thermal conductivity is an essential property for bearing materials as it can help in quickly dissipating the generated heat. Also the material should have a level of corrosion resistance against the lubricant.

18. Briefly explain the advantages of Cycloidal and Involute gears?

The advantages of the Cycloidal gears are as follows: 
> Having a wider flank as compared to Involute gears they are considered to have more strength and hence can withstand further load and stress.
> The contact in case of cycloidal gears is between the concave surface and the convex flank. This results in less wear and tear.
> No interference occurs in these types of gears. 
The advantages of Involute gears are as follows:
> The primary advantage of involute gears is that it allows the changing of the centre distance of a pair without changing the velocity ratio. 
> The pressure angle remains constant from start to end teeth, this results in less wear and smooth running of the gears.
> The involute gears are easier to manufacture as they can be generated in a single curve ( the face and flank ).

19. How can the reaction of support of a frame be evaluated?

Generally roller or hinged support are used to support the frames. The conditions of equilibrium are used to determine the reaction support of a frame. The condition of equilibrium takes place when the sum of the horizontal and vertical forces sum equal to zero. The system must form a state of equilibrium even after considering the external loads and the reactions at the supports. For equilibrium to be prevalent in the system the following conditions are required to be in occurrence:
> Summation of V = 0. This implies that the summation of all the forces in the vertical direction results to zero.
> Summation of H = 0 . This implies that the total of all the forces acting in horizontal direction is also zero.
> Summation of M = 0. The sum of all the moment of forces around a point must be zero.

20. Explain in an orderly manner how the force in the member of a truss be detected using the method of joint.

The steps required to calculate the force are as follows:
> The reaction at the support has to be first calculated.
> Once the reaction is calculated the direction of force of the member is made to make it tensile. On getting the result to be negative the direction assumed is wrong and this implies the force being compressive in nature.
> A joint needs to be selected whose 2 members are not known. The lami`s theorem is used on the joint on which less than three forces are acting.
> After the above process is complete the free body diagrams of the joint needs to be made. Since the system is in equilibrium the condition of Summation of V and H must result in zero. 
> After the above step the resolution of forces method needs to be used on the joint on which more than 4 forces are acting.

21. In order to derive the torsional formulas what are the assumptions taken?

The torsion equation is derived on the basis of following assumptions:
> The shaft material is uniform, throughout the shaft.
> Even after loading the shaft circular remains circular.
> After the application of torques the plain section of a shaft remains plain.
> Any twist that occurs in the shaft remains uniform and constant.
> After the application of torque the distance between any two cross-sectional references remains constant.
> The elastic limit value of a shaft is never exceeded even after the shear stress induced because of torque application.

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