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Mechanical Engineering Interview ques-ans

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  • 1. * What is bending moment?When a force is applied on a body far away from the fixed point, then the body will tends to bend with thesupport of the fixed end. this type of force is called bending moment.M=d*f (distance from the fixed end* force applied)* What is the difference between a Shaper machine and a Planner machine?In Shaper machine tool is having reciprocating motion and work piece is clamped on table which isstationary. It is mostly suitable for light duty operation. In Shaping large cutting force is transferred to tool.In Planer machine tool is having stationary and work piece is clamped on table which is reciprocatingmotion. It is mostly suitable for Heavy duty operation. In planner large cutting force is transferred to table.Shaper occupies smaller work area.Planner occupies larger work area.Initial cost of Shaper is cheap, whereas for Planner its costly.* What is the importance of the Thermodynamics in the field of Mechanical Engineering?Thermodynamics deals with relations between heat and work and heat and work are very important in thefield of Mechanical Engineering.* Explain the nomenclature of a 6203-ZZ bearing.6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means light, 03 is the bore,which is 17 mm and ZZ is the suffix meaning double shielded bearing.First two Digit from left indicates bore dia i.e. 03 - means 17 mm bore diameterthird digit indicates series like heavy, medium light & extra light duty - load carrying bearing here itsmedium capacity bearingLast or forth digit shows types of bearing here its Single row ball bearingZZ indicates double shielded bearing* What is the Expansion of SCADA, DCS & HMI?SCADA- Supervisory Control and Data AcquisitionDCS- Distribution Control System andHMI? Human Machine Interface* How failure of Knuckle Pin occurs?We know the knuckle pin is used in knuckle joint to join the two shafts together and mode of failure ofknuckle joint is failure due to crushing and failure due to shearing. When we exceed the designed load atthe ends of the shafts then failure occurs.Failure due to shearing:-P= 2X shearing stress X shearing areaFailure due to crushing:-P= crushing stress X crushing area* What is heat rate of a power plant?The cycle efficiency of power plant is expressed in terms of heat rate. Heat rate is define as the amount offlow of heat which generate one kilo watt power.Why Involutes Curve used in Gear?Involute curve is the path traced by a point on a line as the line rolls without slipping on the circumferenceof a circle. Involute curve has a contact angle between two gears when the tangents of two gears passthrough the contact point without friction.INVOLUTE:It is a locus of a free end of a string when it is woundround a circle or polygon.In an involute gear, the profiles of the teeth are involutes of a circle. (The involute of a circle is thespiraling curve traced by the end of an imaginary taut string unwinding itself from that stationary circlecalled the base circle.)In involute gear design contact between a pair of gear teeth occurs at a singleinstantaneous point (see figure at right). Rotation of the gears causes the location of this contact point tomove across the respective tooth surfaces. The path traced by this contact point is known as the Line ofAction (also called Pressure Line or Line of Contact). A property of the in volute tooth form is that if thegears are meshed properly, the line of action is straight and passes through the Pitch Point of the gears.When this is true, the gears obey the Fundamental Law of Gearing:[1]The angular velocity ratio betweentwo gears of a gear set must remain constant throughout the mesh.Which has more efficiency: Diesel engine or Petrol engines?diesel engine has the more efficiency because diesel engine has more compression ratio due to which
  • 2. the combustion and the power delivered is more. it is a compression ignition engine i.e. at high pressurethe ignition automatically takes place and the ignition is uniform thus giving more output.* What is operating pressure?The amount of pressure nearest the point of performing work at the output end of a pneumatic system.The system operating pressure is used to specify the capability of valves and actuators.* what is mean by viscosity?Viscosity is defined as the property of a fluid by which upper layer of fluid offers resistance to lower layerof a fluid is termed as viscosity.What are the points in the stress strain curve for steel?Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.Proportional limit, elastic limit, upper and lower yield point, ultimate point & breaking pointWhat are the safety valves? How many on each boiler?There are normally two to six safety valves provided in the drum depending upon the capacity.The super heater outlet will have one to three safety valves on either side of the boiler. There will be anelectrometric relief valve on the super heater pipe in addition. This valve will be set at lower pressure thanthe lowest set safety valve on the super heater. The reheated pipes both at the inlet and outlet side willalso have safety valves which can range from two to eight both in the inlet and outlet of the reheated puttogether. Safety valves are attached to the steam chest for preventing explosion due to excessivepressure of steam.* What is ductile-brittle transition temperature?It is the temperature below which the tendency of a material to fracture increases rather than forming.Below this temperature the material loses its ductility. It is also called Nil Ductility Temperature. when thetemperature increase above the upper critical temperature then material behavior is changed and itdepends on rate of cooling if it will be fast rate of cooling then it make brittle.* What is the difference between Relay and Contactor?Purpose of a relay is to protect a device or a circuit. Whereas purpose of a contactor is to make and breakthe circuit thereby extracting the required signals from their auxiliary contact* What is Carnot engine?It was being designed by Carnot and let me tell you that Carnot engine is an imaginary engine whichfollows the Carnot cycle and provides maximum efficiency as compare to other cycles.* what is gear box and its application?Gear box is a box containing gears, which transmit the motion from one shaft to another shaft. there aremany application its used in automobile (i.e.Progreesive type,synchromesh, constant mesh, selectivetype, automatically).Gear box also used in Rolling mill(i.e. pinion gear box, reduction gear box, speedincreaser, reduction cum pinion.)* Which formula forms a link between the Thermodynamics and Electro chemistry?Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics andelectromagnetism.∆Hs/R = [∂ lnp /∂ (1/T)] xWhere: x ? mole fraction of CO2 in the liquid phasep ? CO2 partial pressure (kPa)T? Temperature (K)R? Universal gas constantα? Mole ratio in the liquid phase (mole CO2 per mole of amine)  How will you calculate the tonnage of Mechanical Press?F = S x L x T divided by 1000F = Force in kilo Newton’sS = shear stress of material in MPaL = the total length of peripheries being cut/sheared in mmT = thickness of material in mm  What is maximum continuous rating?It is defined as the maximum o/p a generating station can able to produce under normal conditions.
  • 3.  What is plant load factor?A plant load factor is a measure of average capacity utilizationThe ratio of the actual output of a power plant over a period of time and its output if it had operated at fullcapacity during that time period. The ratio between average load and maximum demand is known as loadfactor  What is the difference between Critical speed & Whirling speed?In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocitywhich excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed ofrotation approaches the objects natural frequency, the object begins to resonate which dramaticallyincreases system vibration. The resulting resonance occurs regardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft.  What is annealing?It is a process of heating a material above the re-crystallization temperature and cooling after a specifictime interval. This increases the hardness and strength if the material The process of putting material inits softest condition for further processing. This is normally done by heating material to a certaintemperature, then cooling it under controlled conditions.  Which is hard material Cast Iron or Mild Steel?Cast iron. Due to the excess carbon content than mild steel it is harder. The more carbon content, themore hardness will be. But it reduces the weld ability due to this hardness. It is brittle too.  How do you measure temperature in a wet bulb thermometer?Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick andwetting it with water. It corresponds to the dew point temperature and relative humidity.  How to find the amount of natural gas required producing 1 kwhr of energy?heat rate of power plant run by natural gas divided gross calorific value of the natural gas will give theamount of natural gas required to produce 1kwhr energy  What is the purpose of governor in automobile?Governors are used in automobiles to control the supply of fuel.  What is bearing stress?The stress which acts on the contact surface area between two members is known as bearing stress. Anexample for this is the stress between nut and the washer.  What is the Difference Between SCADA and BMS?SCADA is a control and data acquisition interface software, installed on computers (often PCs) and usedwith industrial automation controls (PLCs). They are generally developed by automation productmanufacturers, (Rockwell, Siemens, Invensys, by some independents) (often bought by larger automationindustries, look at wonder ware, Citect, In-touch), and sometimes by individuals who like their owninterfaces in Visual C, Delphi? Communications are carried out over specialized buses such as Modbus,Profibus, Fieldbus, and Industrial Ethernet? and the sensors, drives, motor controllers are designed toexchange with the PLCs over such links.Building Management Systems are a parallel industry; components are different, manufacturers areHVAC and lighting industrials (Carrier, Trane, and Honeywell) and standards are different. They usedifferent communication protocols (BACNET, EIB, and Lon Works) and different standards. Generally,industrial standards will use more power, control higher voltages, and use smaller gauge wire thanbuilding automation.  How many joules is 1 BTU?1 BTU is equal to 1055.056 joules.  Explain Otto cycle.Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle ofa four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to thecompression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejectedand the exhaust stroke. It was designed by Nicolas Otto, a German engineer.  What is the abbreviation of Welding rod 7018?7018=70=tensile strength 70000psi
  • 4. E7018E=electrode70=Tensile strength in KSI1=welding position8=type of flux coating on electrode  How many Laws of Thermodynamics are there?There are three laws of the thermodynamics.First Law: Energy can be neither created nor destroyed. It can only change forms. In any process in anisolated system, the total energy remains the same.Second Law: When two isolated systems in separate but nearby regions of space, each inthermodynamic equilibrium in itself, but not in equilibrium with each other at first, are at some timeallowed to interact, breaking the isolation that separates the two systems, and they exchange matter orenergy, they will eventually reach a mutual thermodynamic equilibrium. The sum of the entropies of theinitial, isolated systems is less than or equal to the entropy of the final exchanging systems. In theprocess of reaching a new thermodynamic equilibrium, entropy has increased, or at least has notdecreased.Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum.There is one more law Zero’th Law of thermodynamics.Statement: When body A is in thermal equilibrium with body B and body B is in thermal equilibrium withbody C, then body A is in thermal equilibrium with body C. This is basis for temperature measurement.  Is the boiler a closed system?Yes definitely the boiler is a closed system.Boilers can be the closed or open system. if we recycle the condensed water after condenser to boiler bypassing from cooling towers then we can say that the boiler is a closed system and when we doesnt usethe water after condenser then the boiler run on open system.  What is the consequence of not maintaining hydrogen (or air) pressure in generator casing at a value above atmospheric pressure when seal oil system is in service?Failure to do so will cause excessive seal oil to be drawn into the generator.  What is the function of EGR valve?EGR means Exhaust Gas Recirculation. The main function of EGR is to control NOx emission from theengine. At elevated temperature (during long run & full condition)if due to some reasons engine getsheated up beyond certain level? it produces NOx emission. In order to avoid this pollution, we have tocontrol the temperature rise inside the cylinder. This can be achieved by mixing some amount of exhaustgas with intake air. By doing this the temperature inside the combustion chamber is reduced. And NOx iscontrolled.  Explain the effect on which the cricket ball swings?Let us first look at some of the fundamental flow physics that will help to explain all three types of cricketball swing. As the ball is flying through the air, a thin layer of air called the "boundary layer" forms alongthe balls surface. The boundary layer cannot stay attached to the balls surface all the way around theball and it tends to leave or "separate" from the surface at some point. The location of this separationpoint determines the pressure, and a relatively late separation results in lower pressure on that side. Aside force or swing will only be generated if there is a pressure difference between the two sides of theball.Now the boundary layer can have two states: a smooth and steady "laminar" state, or a time-varying andchaotic "turbulent" state. The transition from a laminar to a turbulent state occurs at a critical speed that isdetermined by the surface roughness; the rougher the surface the lower the critical speed. However, on avery smooth surface and at nominal speeds, a laminar boundary layer can be forced to turn turbulent by"tripping" it with a disturbance. The disturbance can be in the form of a local protuberance or surfaceroughness which adds turbulent eddies to the laminar layer and forces it to become turbulent. It is similarto putting your finger into a smooth stream of water from a tap: note how small chaotic turbulent motionsare generated downstream of the finger location. Now it turns out that a turbulent boundary layer(because of its increased activity and energy) can stay attached to the balls surface for a longer distancecompared to a laminar layer.
  • 5.  What is PS?PS is Pferdestarke, the German unit for Horsepower.ps is a German unit of a horse power(hp or bhp)ps and bhp are same but both are used in automobiles( car , bike etc )  What is gear ratio?It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear. It is ratio ofnumber of revolutions of the driving gear to the number of revolutions of the driven gear.  Define torque.Torque is defined as a force applied to an object those results in rotational motion.  What is Hess Law?According to the Hess law the energy transfer is simply independent of the path being followed. If thereactant and the product of the whole process are the same then same amount of energy will bedissipated or absorbed.  How to control Temperature (Electronics way)?We can use 1 RTD (Resistance Temperature Detector) for temperature detection. When temperaturechange, resistance also changes in RTD. This RTD input can be given to a PLC and from the output ofthe PLC a valve can be controlled based on RTD input. This valve can in turn control the temperature of acontainer by the valve ON/OFF operation.  What is a Newtonian fluid?A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. Thefluid properties of a Newtonian fluid do not change when any force acts upon it.a real fluid(fluids which possess viscosity.....generally all fluids)in which shear stress is directlyproportional to the rate of shear strain is known as Newtonian fluid.  What is the mechanical advantage of a double pulley?It only takes half the effort to move an object but twice the distance.  What is the significance of Torque (in N-m) given in the engine specification?It gives the moment about any point or simple rotation. As we know that unit of torque is Nm, here Newtonstands for force which tends to revolve or produce torque with respect to distance, in meter. so both theproduct of force and distance provides torque in engine shaft, which helps in power generation.It gives the moment about any point or simple rotation.As we know that unit of torque is Nm, here Newton stands for force which tends to revolve or producetorque with respect to distance, in meter. So both the product of force and distance provides torque inengine shaft, which helps in power generation.  How to make various operations by Pressing a single push button (at least for 2 operations)?It is simple by using contactors and auxiliary relays to do the operation. BMS (Building ManagementSystem) and PLC (Programmable Logic Controller) are the latest versions but comparatively expensive.  Explain the second law of thermodynamics.The entropy of the universe increases over time and moves towards a maximum value. It is impossible toconstruct a derive that operates in cycle to produce a net amount of work by transferring heat from asingle reservoir.  What are the materials used for Sliding Wear pad?Urethane-Coated Base Material Provides Optimum Sliding Surfaces for Maximum Wear AbilityGalvanized Steel for Backing on Head and Side PadsFor crane services, we use Velcro Nylon wearing pad  What are the differences between gas turbine and a steam turbine?Gas turbine works on Briton cycle where as steam turbine works Rankin cycle. Construction, operation ofa gas turbine is entirely different to steam turbine. Gas turbine has a compressor to compress thecombustion air, a combustion chamber to burn the fuel and a turbine section to extract the work forburning fuel. Steam turbine is just has a turbine section to extract the work from steam.  What is OEE?OEE means Overall Equipment Effectiveness. This terminology widely used in Total productivemaintenance, which is used to calculate the effectiveness of machines in manufacturing. Basically itcaptures the losses of machines in production and try to improve defects on machines. Higher the OEE,
  • 6. more capable is the machine.  Define Reynolds number.Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless number. Itdetermines the type of fluid flow.  What is knurling?It is a machining process to enhance grip on object.  What is extruding aluminum?Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/orgive it a final shape.Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varietiesof small non-structural, decorative pieces.  What is a sentinel valve?Sentinel valves are simply small relief valves installed in some systems to warn of impending overpressurization. Sentinel valves do not relieve the pressure of the system. If the situation causing thesentinel valve to lift is not corrected, a relief valve (if installed) will lift to protect the system or component.If a relief valve is not installed, action must be taken quickly to secure the piece of equipment or system toreduce the pressure.  What is principal work of? O ring??O rings are fitted to form leak proof joints between two mating surfaces. O ring is like a Gasket which ismade by rubber to protect the leakage of gas or vapor in-between two metal products.  What is the difference between blower and fan?A fan can turn air, but a blower forces the air faster.A blower can able to increase the pressure of the air with a small rate but fan increases the pressure ofthe air with a very small rate when compared to blower.  What is the function of Hydrogen seals work on a generator?Provide a seal between the generator housings and rotor shaft to maintain the pressurized hydrogen gasinside the generator. Also, provides a trap-vent system to prevent the release of hydrogen into the turbinegenerator lube oil system and building atmosphere.  How is the excess discharge pressure prevented?Pressure relief valves on the discharge side of each seal oil pump relieve back to seal oil system. Pleaseexplain it, Pressure relief valves on the discharge side of each seal oil pump relieves back to seal oilsystem.  Which two seal oil pumps are driven from the same motor?Main seal oil pump and re-circular seal oil pump; both are driven by Main seal oil pump motor.  When does Emergency Seal Oil Pump automatically start?When its pressure switch senses Main Seal Oil Pump discharge pressure reduced to 78 PSI.When supplyoil header pressure falls below the predefined pressure value initiated by pressure sensing device.