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