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.
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.
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 hydro statically pressurized lubricated bearings: These
bearings are able to without any relative motion support steady loads.
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.
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 ).
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.
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.
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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