Shafts: Definition, Types, And Application

What is a Shaft?

A shaft is a rotating machine element, usually circular in cross-section, which is used to transmit power from one part to another, or from a machine that produces power to a machine that absorbs power.

Shaft form an important element of machines. They support rotating parts like gears and pulleys and are themselves supported by bearings resting in the rigid machine housing.

The shafts perform the function of transmitting power from one rotating member to another supported by it or connected to it.

Thus, they are subjected to torque due to power transmission and bending moment due to the reactions of the members that are supported by them.

Shafts are to be distinguished from axles that also support rotating members but do not transmit power.

Shafts are always made of circular cross-sections and could be either solid or hollow. The shafts are classifieds as straight, cranked, flexible, or articulated. Straight shafts are the commonest to be used for power transmission.

Such shafts are commonly designed as stepped cylindrical bars, that is, they have various diameters along their length, although constant diameter shafts would be easy to produce. The stepped shafts correspond to the magnitude of stress which varies along the length.

Moreover, the uniform diameter shafts are not compatible with assembly, disassembly, and maintenance such shafts would complicate the fastening of the parts fitted to them, particularly the bearings, which have restricted against sliding in an axial direction.

While determining the form of the stepped shaft it is borne in mind that the diameter of each cross-section should be such that each part fitted onto the shaft has convenient access to its seat.

The Material Used for the Shafts

The material used for ordinary shafts is mild steel. When high strength is required, alloy steel such as nickel, nickel-chromium, or chromium-vanadium steel is used.

Shafts are generally formed by hot rolling and finished to size by cold drawing or turning and grinding.

The material used for the shafts must have the following properties:

• It should have high strength.
• It should have good mechanization.
• It should have a low-notch sensitivity factor.
• It should have good heat treatment properties.
• It should have high wear-resistant properties.

The materials used for regular shafts are carbon steel of grade 40 C8, 45 C8, 50 C4, and 50 C12.

Manufacturing of Shafts

Shafts are usually produced by hot rolling and are prepared for shape by cold drawing or turning and grinding. Cold-rolled shafts are stronger than hot-rolled shafts but with higher residual stresses.

Residual stress can cause deformation of the shafts when it is mechanized, especially when slots or keys are cut. Shafts of larger diameter are usually forged and shaped into a lathe.

Types of Shaft

Shafts are mainly classified into two types:

• Transmission shafts are used to transmit power between the source and the machine absorbing power. e.g., countershafts, line shafts, and all factory shafts.
• Machine shafts are an integral part of the machine itself. e.g., crankshaft
• Axle shafts are used in vehicles.
• A spindle shaft is a rotating shaft with a fixture for holding a tool or a workpiece.

Related Posts: 1. What is Crankshaft? 2. What is Axle in a Car?

The Standard size of shafts are:

The standard sizes of transmission shafts are:

• 25 mm to 60 mm with 5 mm steps
• 60 mm to 110 mm with 10 mm steps
• 110 mm to 140 mm with 15 mm steps and
• 140 mm to 500 mm with 20 mm steps
• The standard length of the shafts is 5 m, 6 m, and 7 m.

The standard sizes of Machine shafts are:

• Up to 25 mm steps of 0.5 mm

Advantages of Shafts:

• The shaft system is less likely to jam.
• Less maintenance than a chain system when a tube is attached to the drive shaft.
• A hollow shaft is a low weight than a solid shaft for the same torque transmission.
• In the hollow shaft, the internal shape is hollow so the materials required are less.
• The shaft is strong and it has a low failure chance.
• High polar moment of inertia
• High torsional strength

Disadvantages of Shafts:

• The power loss is due to loose coupling.
• Shafts can vibrate during rotation.
• Produced a constant noise
• Maintenance and manufacturing costs were high.
• The manufacturing process is difficult.
• The downtime was longer due to mechanical problems.
• The use of flexible couplings, such as a leaf spring coupling, can cause a loss of velocity between shafts.
• Changing the speed was not so easy.
• Oil dripping from overhead shafting.

FAQs.