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Shafts:
Shafts are a rotating element which is used to transmit power from one place to another. The power is delivered to the shaft by some tangential force and the resultant torque (or twisting moment) set up within the shaft permits the power to be transferred to various members such as pulleys, gears etc are mounted on it. These members along with the forces exerted upon them causes the shaft to bending. In other words, we may say that a shaft is used for the transmission of torque and bending moment. The various members are mounted on the shaft by means of key or spines.
Materials used for shafts:
The materials used for shafts should have the following properties:
1. It should have high strength.
2. It should have good mach inability.
3. It should have low notch sensitivity.
4. It should have good heat treatment properties.
5. It should have wear resistance.
Manufacturing of shafts:
Shafts are generally manufactured by hot rolling and finished to size by cold drawing or turning and grinding. The cold rolled shafts are stronger than hot rolled shafts but with higher residual stresses. The residual stresses may cause distortion of the shaft when it is machined. Especially when slots or keyways are cut. Shafts of larger diameter are usually forget and tuned to size in a lathe.
Types of shafts:
1. Transmission shafts: These shafts transmit power between the source and the machines absorbing power. The counter shafts, lines, over head and all factory shafts are transmission shafts. Since these shafts carry machine parts such as pulleys, gears etc, therefore they are subjected to bending in addition to twisting.
2. Machine shafts: These shafts from an integral part of the machine itself. The crank shaft an example shaft.
Stresses in shafts:
The following stresses are induced in the shafts:
1. Shear stresses due to the transmission of torque (i.e. due to torsional load).
2. Bending stresses (tensile or compressive) due to the forces acting upon machine elements like gears, pulleys etc as well as due to the weight of the shaft itself.
3. Stresses due to combined torsional and bending loads.
Design of shafts:
The shafts may be designed on the basis of
1. Strength 2.Rigidity and stiffness.
In designing shafts on the basis of strength, the following cases may be considered:
(a) Shafts subjected to twisting moment or torque only.
(b) Shafts subjected to bending moment only.
© Shafts subjected to combined twisting and bending moments, and.
(d) Shafts subjected to axial loads in addition to combined torsional and bending loads.
We shall now discuss the above cases, in detail in the following pages.