Fundamentals of Mechanical Engineering [Part 1]

Lets begin with the basic question😄.......

What is Machine ?

• A machine is a device, consisting of various elements arranged together, so as to perform the prescribed task to satisfy the human needs. 
• Machine is capable of doing some useful work. It converts and transfers different forms of energy.
• Modern machines are complex systems that consist of structural elements, mechanisms and control components.
• INPUT ⟹ MACHINE ⟹  OUTPUT
• Ex. of Machine- I.C. Engine, Turbines, Compressors, C-clamp , Screw- Jack,etc. 

Machine Elements:-    

• Machine elements are basic mechanical parts 
• Machine elements are assembled together to form what we call as complete machine.
• Its function may be of holding the components together, to transmit power or to give supports.
• Ex. Elements of Screw Jack:-   Screw, Nut, Body, Handle    

  Some important Machine Elements:-

         1] Shaft :- To transmit the power

         2] Key :- To transmit the power from the shaft to other rotating elements

         3] Couplings :- To connect two shafts

         4] Bearings :- To support the shaft

         5] Nut and Bolt:- To connect two parts

        Lets see one by one...

  SHAFT:-

•  It’s rotating machine of circular cross section which is used to transfer power.
• Transmission of power from one shaft to another takes place by mounting ‘gears, pulleys, crank, sprockets etc. on it. 
• These members are mounted on the shaft by means of keys or splines.
• They are subjected to torque, bending moment, axial force. 
• Sometimes, hollow shafts are used to reduce the weight.

Types of Shafts:-

         A.    Transmission Shafts

         B.    Machine Shafts

A.    Transmission Shafts :- Shaft which is used to transmit the power from source to the machine absorbing power is called Transmission Shaft. Transmission shaft supports ‘ power transmission elements’ like pulleys, belts, sprockets, chains, gears, clutches.

      -  Examples of transmission shaft:

                Line Shaft and Counter Shaft 

B.     Machine Shafts:-   

It is a short rotating shaft which forms an integral part of the machine itself.

Ex.

Spindle Shaft :- A spindle is a rotating shaft with a fixture for holding a tool or a workpiece.

Crankshaft:-

      A crankshaft is a rotating shaft which converts reciprocating motion of the pistons into rotational motion.

Crankshafts are commonly used in internal combustion engines and consist of a series of cranks and crankpins to which the connecting rods are attached.

Axle:-

1. An axle looks a like shaft but it’s a non-rotating machine element which is used to support rotating elements.

2. The main purpose of axles is to transfer power to the rotating elements and to support the rotating machine elements.

3. Axle is subjected to bending moment and axial force but not torque as it’s not rotating

       

     Ex. Axle of car etc.

Car rear axle

Key:-

• Key is a machine element used on the shafts to secure rotating elements by inserting it between shaft and hub of element and prevents relative motion between them. Rotating elements like- gears, pulleys, sprockets.
• The secondary function of the keys is to prevent relative movements in the axial direction of the shaft.

•  Key is also used for transmitting the torque from shaft to rotating element or vice-versa.

• It’s having lower strength than shaft material to ensure that if at all there is failure the key should fail instead of shaft.

• Keyway is a slot or pocket in a shaft and hub of rotating element to insert a key.

Types of Keys:-

     A. Sunk keys :- Sunk Key is that kind of key that is mount half a side in hub of rotating element and half a side in shaft keyway. Most widely used keys are sunk keys.

Woodruff Key

Reactangular Key

Parallel Key

Gib- head key

Square Key

                                             

B.Saddle Keys:- 

• It’s tapered key fits only in hub of rotating element.
• Saddled key doesn’t sink inside the shaft , hence it’s not a sunk key.

They have low torque transmitting power. As it is outside the shaft, it doesn’t weaken the shaft.

    

          C.Tangent Keys:- 

• These are used in large heavy weight shafts.
•   It transmits the torque only in one direction by means of compressive force alone. Two tangent keys are separated by  90 degree.       

 D. Feather Keys:- Keys which allows some relative axial motion between hub and shaft but definitely prevents  relative rotational motion between them.

 

Feather key is used when the hub is required to slide along the shaft.

Feather Key which allows some axial motion.

E. Splines:-

• The splines are keys made integral with the shaft
• It prevents relative rotational motion but permits relative axial motion. 
•  Splined shaft is used when forces to be transmitted are large in magnitude. They are used in automobile gear boxes and machine tool gear boxes.                                                                                                                                 

         

Spline and Gear Shaft

                                       to be continued.............