Types of Shafts : Operations, Working, Materials, Advantages and Disadvantage, Applications

In this article you will know about Types of Shafts Working Operations and Applications, Materials in details.

Shafts are an essential component of machines. They support rotating parts such as gears and pulleys and are supported by bearings that rest in the rigid machine housing.

Constructions of shaft

Shafts differ from axles, which also support rotating members but do not transmit power.

Shafts are always circular in cross-section and can be solid or hollow. Straight shafts, cranked shafts, flexible shafts, and articulated shafts are the four types of shafts. Straight shafts are the most common type of power transmission shaft.

Such shafts are commonly designed as stepped cylindrical bars, with varying diameters along their length, though constant diameter shafts would be simple to produce. The stepped shafts represent the magnitude of stress as it varies along the length.

Furthermore, uniform diameter shafts are incompatible with assembly, disassembly, and maintenance. Such shafts would complicate the fastening of the parts fitted to them, particularly the bearings, which are restricted against sliding in an axial direction.

When determining the shape of the stepped shaft, keep in mind that the diameter of each cross-section should be large enough so that each part fitted onto the shaft has easy access to its seat.

Material Used For The Shafts

Mild steel is the material which is used for ordinary shafts. When high strength is required, alloy steels such as nickel, nickel-chromium, or chromium-vanadium steel are used. Shafts are commonly formed by hot rolling and finished to size by cold drawing or turning and grinding.

The materials, which is used for the construction of the shafts must have the following properties:

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

Carbon steel of grades 40 C8, 45 C8, 50 C4, and 50 C12 are used for regular shafts.

Manufacturing of shafts

Shafts are generally produced by hot rolling and shaped by cold drawing or turning and grinding. Cold rolled shafts have higher residual stresses than hot rolled shafts.

When shafts are mechanized, residual stress can cause deformation, especially when slots or keys are cut. Larger diameter shafts are typically forged and shaped in a lathe.

After rolling, the shafts are subjected to an end working process in which one end of the shaft is loaded on check and the other end is supported by the turret of the lathe machine. To finish the shaft, the tool is held against the tool post, and when the power is turned on, the chuck begins rotating the shaft.

Dial gauges are used to check the concentricity of a shaft before machining it, and many operations such as turning, facing, grooving, taper turning, and so on are performed using them.

Applications such as high volume and CNC are best suited for the final working process. It can also be done with a CNC double end machine, in which the shaft is held between the rotating tool and the fixtures for machining. The rotating tools should be facing each other in the centerline to achieve concentricity and roundness. This process is commonly used to create transmission shafts and motors.

Types of shafts

Shafts are mainly classified into fou types:

1. Transmission shafts :-

These are stepped shafts, which is used for transmitting power between the source and absorbing machine. For transferring motion,gear, a hub or pulley is mounted on the stepped portion of the shaft.

Example :- Overhead shafts, line shafts, counter shafts, and all factory shafts.

2. Machine shafts

These shafts are an integral part of the machine and are located inside the assembly.

Example :- A crankshaft in a car engine is an example of a machine shaft.

3. Axle shafts

An axle shaft is a solid steel shaft that runs from the differential and gear set of an axle housing to the wheel.

These shafts can support rotating elements such as wheels and fit in housings with bearings, but the axle is a non-rotating element.

Example:- These are mostly found in automobiles. Axle in a car, for example.

4. Spindle

A spindle is a rotating shaft with a fixture for holding a tool (or workpiece in the case of a milling, grinding, or drilling spindle) (in the case of a turning spindle). The spindle shaft acts as a tool or workpiece support, positioner, and rotary drive.

These are the rotating parts of the machine that hold the tool or workspace. They are short shafts that are used in machines. A spindle in a lathe machine is an example.

Standards size of shafts

• Machine shaft standards size

Up to 25 mm with 0.5 mm steps.

The standard sizes of machine shafts are up to 25 mm with a 5 mm step. The standard lengths for shafts are 5m, 6m, and 7m, but they are usually taken as 1m to 2m.

• transmission shafts

Shafts standards size – Step sizes

25 mm to 60 mm – 5 mm step

60 mm to 100 mm – 10 mm step

110 mm to 140 mm – 15 mm step

140 mm to 500 mm – 20 mm step

Advantages of shafts

• The shaft system is less prone to jamming.
• When a tube is attached to the drive shaft, it requires less maintenance than a chain system.
• For the same torque transmission, a hollow shaft is lighter than a solid shaft.
• Because the internal shape of the hollow shaft is hollow, the materials required are reduced.
• The shaft is stronger and has a lower failure rate.
• The polar moment of inertia is very high.
• Torsional strength is very high.

Disadvantages of shafts

• The power loss caused by a loose coupling.
• Shafts can vibrate during rotation.
  It made a constant humming noise.
• Maintenance and manufacturing costs were high.
• The manufacturing process is difficult.
• Because of mechanical issues, the downtime was extended.
• The use of flexible couplings, such as a leaf spring coupling, can result in a loss of velocity between shafts.
• Changing the speed was not so simple.
• Oil dripping from the overhead shafting.

Designs stresses

The maximum permissible shear stresses are as follows:

1.56000 KN/m2 for the shafts with allowance provided for keyways.
2. 42000 KN/m2 for shafts with no allowance for keyways.

The maximum allowable bending stresses are as follows:

1. 112000 KN/m2 for the shafts with allowance provided for keyways.
2. 84000 KN/m2 for shafts with no allowance for keyways.

Power transmission by shafts

The power transmitted by a shaft is directly proportional to the shaft’s RPM and the torque applied to it, and it can be calculated using the below formula.

P = 2πNT/ 60 watt

Where, P is the power transmitted

N is the speed in revolution per minute (RPM).

T is the torque in Nm.

Speed of Shaft Used for Various Applications

Applications – Speed in RPM

1. Machinery – 100 – 200
2. Wood machinery – 250 – 700
3. Textile industry – 300 – 800
4. Light machine shop – 150 – 300
5. Countershaft – 200 – 600

Designs of shaft

Shafts can be designed using two distinct processes that are based on different loading considerations:

1. Design of Shaft on the Basis of Strength

Transmission shafts are commonly subject to bending moment, torsional moment, axial tensile force, and combinations of these forces. In general, shafts are subjected to a combination of torsional and bending stresses.

1. Shaft subjected to tensile stress

Tensile stress = P/ A

Where, A = (π/ 4) x D²

D is Diameter of the shaft in mm

Shaft subjected to the bending moment

Bending stress = (Mb x Y)/ I

Where, Mb = Bending Moment

Y = D/ 2 in which D is diameter

I = Moment of inertia = (π x D⁴)/ 64

Shaft subjected to the torsional moment

Torsional stress = Mt x R/ J

Where,

Mt = torsional moment

R = D/ 2 in which D is the diameter

J = Polar moment of inertia = (π x D⁴)/ 32

2. Design of Shaft on the Basis of Rigidity Basis

Transmission shaft are known as rigid on torsional rigidity basis if the shaft does not twist too much.

{Mt/ J} = {(G x ө)/ L}

Where,

Mt = Torsional moment in N – mm

J = Polar moment of inertia = (π x D⁴)/ 32

D = Diameter of shaft in mm

Ө = Angle of twist

G = Modulus of rigidity in N/ mm²

Frequently Asked Questions