SHAFTS

WHAT IS A SHAFT ?

The term shaft refers to a rotating machine element which is circular in cross-section and which supports transmission elements like gears, pulleys, and sprockets and transmits power. The power is transmitted from one part to another, or from a machine which produces power to another machine which absorbs power. The material used for ordinary shaft is a carbon steel of grades 30C8, 40C8, 45C8, 50C8. Standard lengths of the shaft are 5m, 6m, and 7m. A shaft is used in production control of camshafts and crankshafts for motor vehicle engines, Engine drive shaft, propeller shaft, differential, watch and clockmaking industry, etc.

MATERIALS OF SHAFTS :

Ordinary transmission shafts are made of medium carbon steels with carbon content from 0.15 to 0.40 percent such as 30C8 or 40C8. These steels are commonly called machinery steels. Where greater strength is required, high carbon steels such as 45C8 or 50C8 or alloy steels are employed. Alloy steels include nickel, nickel-chromium, and molybdenum steels. Common grades of alloy steels used for making transmission shafts are 16Mn5Cr4, 40Cr4Mo2, 16Ni3Cr2, 35Ni5Cr2, 40Ni6Cr4Mo2 and 40Ni10Cr3Mo6. Alloy steels have higher strength, hardness, and toughness. Commercial shafts are made of low carbon steels. They are produced by hot-rolling. They are finished to size either by cold-drawing or by turning and grinding.

TYPES OF SHAFTS :

There are 2 main types of shafts –

1.    Transmission Shafts : These shafts transmit power. The Counter shafts, Line shafts, Jackshaft, Axle, Spindle are all transmission shafts. Since these shafts carry pulleys, gears, etc., therefore they are subjected to bending in addition to twisting.  

    2.      Machine Shafts : It forms an integral part of the machine itself. The crankshaft is the best example of a machine shaft.

APPLICATION OF SHAFTS :

Shafts are given specific names in typical applications, although all applications involve the transmission of power, motion, and torque. Some of the specific categories of shafts are as follows:  

1.    Axle :-

The term ‘axle’ is used for a shaft that supports rotating elements like wheels, hoisting drums, or rope sheaves and which is fitted to the housing using bearings. In general, an axle is subjected to bending moment due to transverse loads like bearing reactions and does not transmit any useful torque, e.g., the rear axle of a railway wagon. Sometimes, the axle also transmits torque, e.g., automobile rear axle. An axle may rotate with the wheel or simply support a rotating wheel.

2.    Spindle :-

A spindle is a short rotating shaft. The term ‘spindle’ originates from the round tapering stick on a spinning wheel, on which the thread is twisted. Spindles are used in all machine tools, e.g., the small drive shaft of a lathe, the spindle of a drilling machine, etc

3.    Countershaft :-

It is used as a secondary shaft, which is driven by the main shaft. It supplies power to a machine component. Many times, the countershaft is driven from the main shaft using a pair of spur or helical gears. Thus, it rotates ‘counter’ to the direction of the main shaft. Countershafts are used in multi-stage gearboxes.

  

4.    Jackshaft :-

It is an auxiliary or intermediate shaft between two shafts that are used in the transmission of power. Its function is the same as that of the countershaft. A jackshaft is often just a short stub with supporting bearings at the ends. Also, two pulleys, gears, or cranks are attached to it.

5.    Line Shaft :-

A line shaft consists of several shafts. These shafts are connected in an axial direction using couplings. Line shafts were popular in workshops that were using group drive. In group drive construction, which was used in workshops, a single electric motor drives the line shaft. Several pulleys are mounted on the line shaft and power is transmitted to individual machines with help of different belts. Therefore, it is possible to drive several machines at a time by using a single electric motor. However, in recent times, individual drives have replaced the group drive, making the line shaft obsolete.

6.    Cranckshaft :-

A crankshaft is a rotating shaft. It converts the reciprocating motion of the pistons into rotational motion. Crankshafts are used in internal combustion engines. It consists of a series of cranks and crankpins to which the connecting rods are attached.

7.    Input Shaft :-

The initial part to receive the power is known as the input shaft. In RWD drive automobiles, input shafts are used to operate in conjunction with the output shaft. Together, these parts create a main shaft assembly.

8.    Output Shaft :-

The last part which transmits motion from the transmission into the wheels is the output shaft. This shaft is controlled by the countershafts and gearboxes. The precision gears are shifted manually by the driver.

9.     Flange Shaft :-

A flange shaft connects the transmission, differential, four-wheel drive (4WD), all-wheel drive (AWD) and the driveshaft to distribute the power coming from the engine and make the car move. The performance and quality of this component are essential.

10.  Propeller Shaft :-

The propeller shaft is incorporated for the transmission of power in the vehicle. They are exposed to heavy load and stress which results in gross misalignment of the wheels. In extreme cases of misalignment; the force generated can cause excessive wear and breaking of the shaft. The propeller shaft connects the gearbox to the final gear of a vehicle. The propeller shaft of vehicles is sufficiently long and operates at a very high speed.

REFERENCE :

          Design Of Machine Elements – Third Edition – V.B.Bhandari

 Writers : Pranav R. Badgujar, Krishna M. Malani, Srushti K. Rithe, Pranita D. Salunke