Objective type questions for mechanical engineering

 Theory of mechanics 

Simple mechanisms:

 1)In a reciprocating steam engine, which of the following forms a kinamatic link crank shaft and flywheel

2)The motion of a piston in the cylinder of steam engine is an example of completely constrained motion

3)The motion transmitted between the teeth of gear in mesh is partly sliding and partly rolling

4)The cam and follower without a spring forms a self closed pair

5)A ball and a socket joint forms a spherical pair

6)The lead screw of lathe with nut forms a screw pair

7)When the elements of the pair are kept in contact by the action of external forces, the pair is said to be force closed pair

Objective type questions for mechanical engineering theory of machines

Theory of machines

 1) The unit of linear acceleration is m/s2

2) The angular velocity of a body rotating at N r.p.m is 2πN/60

3) The liner velocity of a body rotating at w rad/s along a circular path of radius r is given by w.r

4) When a particle moved along a straight path, then the particle has tangential acceleration only

5) When a particle moves with a uniform velocity along a circular path,then the particle has centripetal acceleration only

 6) The force which acts along the radius of a circle and directed towards the centre of the circle is known as centripetal force 

7) The unit of mass moment of inertia in S.I unit is kg-m2

8) Joule is a unit of work

9) The bodies which rebound after impact are called elastic bodies

10) The coefficient of restitution for inelastic bodies is  zero

Electron Beam Welding

  Electron Beam Welding

Introduction:

                       ⚓️ Electron Beam Welding (EBW) is fusion welding process in which a beam of high velocity electrons is used for producing high temprature and melting the workpiece to be welded. The electrons strikes the workpiece and there Kinetic energy is converted into thermal energy by releasing heat which is used to heat the metal so that the edges of workpiece are fused and joined together forming a weld.

Diagram:

Working principle:

                                   ⚓️  If a filament of tungsten or tantalum is heated to high temperature in a vacuum either directly by means of electric current or indirectly by means of an adjacent heater, a great number of electrons are given off from the filament. These electrons carry a negative charge which is passed through the anode hole. The greater is the filament current, the higher will be the temperature and greater will be the electron emission.

Atomic Hydrogen Welding

  Atomic Hydrogen Welding 

Introduction:

                       👉 Atomic Hydrogen Welding (AHW) is a combination of electric arc and gas Welding technique. It is a thermo-chemical arc welding process in which the workpiece are joined by heat obtained on passing a stream of hydrogen through an electric arc stuck between two tungsten electrodes.

Diagram:

working:

              👉 The equipment consist of a Welding torch with two tungsten electrodes inclined and adjusted to maintain a stable arc. Annular nozzles around the tungsten electrodes carry the Hydrogen gas supplied from gas cylinders.

              👉 AC power source is suitable as compared to DC because equal amount of heat will be available at both electrodes. A transformer with an open circuit voltage 300 V is required to strike and maintain the arc

             👉  The workpieces are cleaned to remove dirt, oxides and other impurities to obtain a sound weld. Hydrogen gas supply and Welding current are switched ON. An arc is struck by bringing two tungsten electrodes in contact with each other and instantaneously separated by a small distance of 1.5 mm. Therefore, the arc still remains between two electrodes.

             👉 As the jet of hydrogen gas is passed through the electric arc, it disassociate into atomic Hydrogen by absorbing large amount of heat supplied by the electric arc

THERMIT WELDING

                        THERMIT WELDING

Introduction:

                      *Thermit welding is fusion welding process. In this process, neither arc is produced to heat parts nor flames are used.

                      *For getting high temprature, the exothermic reaction is used

              Fe3O4 + Al. ------------>Al2O3 + Fe

                      *it requires no external source of heat or current. The intense heat is released because of the chemical action not only melt the iron but also it raises the molten metal to a temprature of about 2800°C

Diagram:

Various stages:

               ∆ Thermit ignited

               ∆ Crucible is tapped, and super                               heated metal flows in to mould 

         

              ∆ Metal solidifies to produce weld                          joint.          

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