What is a Shaft?
A shaft is defined as a rotating machine element, usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power.
Shaft form the important element of machines. They are element that support rotating parts like gears and pulleys and it turn 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 reactions on the members that are supported by them.
Shafts are to be distinguished from axles which also support rotating members but do not transmit power.
Shafts are always made to circular cross-sections and could be either solid or hollow. The shafts are classifieds as straight, cranked, flexible, or articulated. Straight shafts are 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 stepped shaft it is borne in mind that the diameter of each cross-section should be such that each part fitted on to 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, an 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 are 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.
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.
- More frequent performance. Dynamic bicycles claim that a drive shaft bicycle can deliver 94% efficiency, while a chain-driven bike can deliver anywhere from 75–97% efficiency depending on condition.
Disadvantages of Shafts:
- The power loss along the line shaft varies widely and was typically 25% and is often very high; However, the disadvantages can be reduced by using roller bearings and good quality lubrication. Roller and spherical bearings gained acceptance in the decade before factories began electrification.
- constant noise
- Maintenance costs were high.
- Systems were more dangerous.
- The downtime was longer due to mechanical problems.
- Changing the speed was not so easy.
- The factory layout was designed around access to the line shaft, not in the most efficient way for workflow.
- Line shafts and millwork took up a lot of space; Baldwin Locomotive Works estimated 40% higher than electric drives.
- Shafts and belting were in the way of lighting, overhead cranes, and ventilation ducts.
- The alignment of the system was critical and problematic for long shafts that were subject to expansion and contraction, settling, and vibration.
- The belting shed is constantly moving in the dust and air.
- Oil dripping from overhead shafting.
A shaft is a rotating machine element with a long handle of a spear or similar weapon, usually circular in cross-section, which is used to transmitting power from one rotating member to another supported by it or connected to it.
Types of shafts:
1. Transmission shafts are used to transmit power between the source and the machine absorbing power. e.g., countershafts, line shafts, and all factory shafts.
2. Machine shafts are an integral part of the machine itself. e.g., crankshaft
3. Axle shafts are used in vehicles.
4. A spindle shaft is a rotating shaft with a fixture for holding tool or workpiece.
A shaft is defined as 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.