Shafts

NTRODUCTION


Shaft is a rotary bar or mechanical element, which transmit power from one place to another. It is usually of circular cross section. having mounted upon it such elements gears, pulleys, flywheels, cranks, sprockets and other power transmission elements, by means f keys or splines. Shafts my be subjected to bending, or torsional loads, acting singly or combination with one another. The word "shaft" covers numerous variations, such as AXLES AND SPINDLES.

AXLE

AXLE is a shaft either stationary or rotating, not subjected to a torsion load. It is used for the transmission of bending moment only. It simply acts as a support for some rotating body such as hoisting drum, car wheel or a rope pulley.

SPINDLE

            SPINDLE a short rotating shaft is often called a spindle. Spindle imparts motion either to a cutting tool ( e.g Drill Press Spindle) or to work piece (e.g. Lathe Spindle).

MATERIAL USE FOR SHAFTS: The material used for ordinary commercial shafting is mid steel. For high strength alloy steel such as, nickel,, nickel chromium or chrome- vanadium steel is used. Shafts are generally formed by hot rolling and finished to the required 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 shen slots or key ways are cut. Shafts of larger diameter are usually forged and turned to size in a lathe.

TYPES OF SHAFTS:

The following three types of shafts are important from the subject point of view.

  • · Prime mover Shafts
  • · Machine Shafts
  • · Transmission Shafts

PRIME MOVER SHAFTS: Prime mover shafts are those shafts by which power can be generated. The following are the three types of Prime mover Shafts.

· Engine shafts (crank shaft)

· Generator Shaft

· Turbine Shaft

MACHINE SHAFTS: These shafts form an integral part of the machine itself. The Cam Shaft is an example of machine shaft.

TRANSMISSION SHAFTS: These shafts transmit power between the source and the machine absorbing power. The following are transmission shafts.

· Line Shafts

· Jack Shafts

· Counter Shafts

· Line Shafts: Line shafts is a term used for specifying rather long of continues lines of shafting employs in mills, shops and factories for the distribution of power.

Jack Shafts: A Jack Shaft is a shaft that is directly connected to the source o power and from which other shafts are driven

Counter Shafts: A counter shafts is one placed between a line shaft and a machine. The power received by it from the line shaft is important to the driven shaft of the machine.

STANDARD SIZE OF THE SHAFTS

The standard size of transmission Shafts should always to used where possible. These size vary according to material specification and supplier. Typical sizes for solid shafts are

  • · Up to 25mm in 0.5mm increments
  • · 25 to 50mm in 1mm increments.
  • · 50 to 100mm in 2mm increments.
  • · 100 to 200mm in 5mm increments.

The standard length of shafts are 5m 6m, and 7m.

STRESSES IN SHAFTS

The following are the induced stresses in the Shafts.

  •                      Shear stresses due to the transmission of torque.
  •                      Bending stresses due to force acting upon mechanical elements like gears, pulleys, sprockets, flywheel, cranks etc.
  •                     Stresses due to combined torsional and bending loads.

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