Mechanical Aptitude Test | Jobs For Mechanical Engineers

1. Why are Head Gaskets blown?

Normally head gasket blows, when the engine overheats and they can also blow from incorrect installation or poor design. Head gaskets expand and contract according to engine temperature, these cycles may happen after a long period of time, causes the gasket to fail. If you’re replacing the gasket, check the engine block, and head for warping. Follow proper cleaning and torque specifications during assembly.

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2. What is the difference between a Fence and a Wall?

A fence is either more temporary or constructed from materials, other than concrete, stone or brick.

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3. What is the Difference between a Humidifier and Vaporizer?

The basic difference between humidifiers and vaporizers is that humidifiers disperse cool mist into the air, and vaporizers heat the water to disperse hot steam. Humidifiers are normally used in cooler climates, when due to the usage of heater, the air in the house becomes too dry for comfort and also, it becomes very difficult to breathe. Humidifiers release cool moisture droplets into the air.

Vaporizers also help in moistening the dry air in the house, but vaporizers release hot vapour into the air. There is a heating element in the vaporizers, which help in releasing steam. Vaporizers heat the water and then release vapours.

The basic difference between them is that one emits cold vapours, while the other one emits hot vapours.

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4. What is the Difference between a Generator and Inverter?

An inverter is only effective if there is already a source of electrical energy. It cannot generate its own. It can simply convert electrical energy that is already there. On the other hand, a traditional generator cannot make AC current into DC current.

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5. What is the Difference between Quantitative and Qualitative Research?

Quantitative research involves gathering data that is absolute, such as numerical data, so that it can be examined in as unbiased a manner as possible.

Qualitative research may yield stories, or pictures, or descriptions of feelings and emotions. The interpretations given by research subjects are given weight in qualitative research, so there is no seeking to limit their bias. At the same time, researchers tend to become more emotionally attached to qualitative research, and so their own bias may also play heavily into the results.

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6. Difference between Absorption and Adsorption

• In absorption, one substance (matter or energy) is taken into another substance. But in adsorption only the surface level interactions are taking place.

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7. Difference between Liquid and Aqueous

• Liquid is a state of matter, while aqueous is a special type of liquid formed by dissolving a compound in water

• All aqueous solutions are liquids, but not all liquids are aqueous solutions

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8. Difference between Gas and Vapour

· Vapour can turn back and forth into liquid and solid states but a gas cannot

· Gases cannot be see while vapours are visible

· Vapours settle down on ground while gases do not

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9. Difference between Boiling Point and Melting Point

- The melting point is a defined for solids when it transfers from solid state to liquid state.

- The boiling point is defined for liquids for a state change from liquid to gas.

- Boiling point is highly dependent on the external pressure whereas the melting point is independent of the external pressure.

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10. Why is sound faster in warm air?

The speed of sound in air c_air = 331.3 + (0.66 x T) m/s, where T is the temperature in °C.

The speed of sound is proportional to gas temperature and inversely proportional to its molar mass.

Sound is transferred by collisions of molecules. Therefore sound waves will travel faster on warm air because collisions of molecules of air in warm air is greater.

Shielded Metal Arc Welding Process | Shielded Metal Arc Welding Applications | Shielded Metal Arc Welding Coating

Shielded Metal Arc Welding: (SMAW)

It is also known as Manual metal arc welding; stick welding or electric arc welding. It is a fusion welding process. Welding is performed with the heat of an electric arc that is maintained between the ends of a coated metal electrode and the work piece.

The electric energy from the arc thus formed produces temperatures of 10000 degree Fahrenheit or higher. A pool of molten metal consisting of base metal and filler metal is formed near the tip of the electrode.

Both ferrous and non-ferrous metals and alloys can be welded by arc welding processes with proper electrodes. The arc and the weld metal pool are protected by the arc flame and slag produced and controlled by the electrode coating. The arc and the weld metal pool are protected by the arc flame and slag produced and controlled by the electrode coating.

Arc time = (time arc is on)/ (Hours Worked)

Arc welding equipment:

1. Arc welding equipment (AC or DC)

2. Welding cables

3. Electrode holder

4. Ground clamp

5. Welding electrodes

6. Welding helmet and hand shield

7. Protective clothing including hand gloves

8. Chipping hammer, wire brush etc

Electrode Coatings:

Electrode coatings are generally electrical insulators and hence permit welding in narrow grooves and limited spaces without short circuiting. Electrode coatings provide an excellent means of introducing alloying elements in the weld metal.

Functions of the electrode coating:

Depending upon its composition the coating performs some or all of the following functions:

1. The coating is consumed at a slower rate than the electrode core wire forming a sheath of the un-burnt coating material over the arc. The length of this sheath depends upon the refractoriness of the coating material and its thickness. The existence of this sheath over the arc helps in directing the arc over the weld area making it more stable, reducing thermal losses, raising the temperature at the tip of the electrode and increasing the metal deposition rate.

2. The gas producing materials in the coating give out lot of gases due to dissociation and combustion. The gases so produced form a protective gaseous shield around the arc. This helps is shielding the arc and the welded metal from atmospheric oxygen, hydrogen and nitrogen. In addition to the shielding provided by the coating gases, shielding is also provided by the vapours of metallic oxides and silicates formed by the heat of the arc. The less volatile mineral ingredients in the coating help in the removal of oxides by forming a slag. The slag floats over the molten weld metal protecting it from atmospheric gases during welding and cooling. The removal of oxides by the slag improves the fluidity of the weld metal which in turn results in a sound, inclusion free joint.

3. The coating helps improve arc stability and makes possible a weld free from overlap, spattering and gas bubbles. Arc stability results from the sheath formation mentioned above and the addition of coating constituents like titanium dioxide, calcium carbonate and potassium silicates.

Advantages of Carbon electrodes:

1. Less expensive

2. Carry less current

3. Short life

4. Simple arc control

5. Soft material

6. Higher electrical resistance

Advantages of Graphite electrodes:

1. Comparatively costlier

2. Carry larger current

3. Long life

4. Arc control is comparatively difficult

5. Material is hard and brittle

6. Lesser electrical resistance

· The process is mostly manual and makes use of either a DC or an AC source.

· Current usually ranges from 50A to 300A

· Power requirements less than 10 KW

· Work piece thickness 3 to 19mm

Advantages of the SMAW process:

· The shielded metal arc welding process is simple, versatile and requires a smaller variety of electrodes.

. The equipment cost is low and it can be easily maintained. Welds by this process can be made in any position.

Limitation of the SMAW process:

· The process is slow

· Lot of electrode material is wasted in the form of unused ends, slag, arc gases

· If the slag is not removed properly, it remains in the bead leading to poor quality-welds.

Submerged Arc Welding SAW | Submerged Arc Welding Deposition Rates | Submerged Arc Welding Flux Composition

Submerged arc welding: (SAW)

In submerged arc welding also known as hidden arc welding, submerged melt welding, or sub-arc welding the arc is struck between a metal electrode and the work piece under a blanket of granular flux. The welding action takes place under the flux layer without any visible arc, spatter, smoke or flash.

Here the weld arc is shielded by granular flux, consisting of Lime, Silica, Manganese Oxide, Calcium Fluoride, and other elements.

The filler wire used may be bare or slightly copper coated. The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter.

Operation of Submerged Arc welding Process:

The welding action can be initiated by introducing a piece of high resistance conducting material like steel wool or carbon between the electrode and the work piece. Once the welding action has been initiated the intense heat produced by the flow of current in the high resistance path melts a path of the flux around the electrode forming a conducting pool. The molten filler displaces the liquid flux and fuses with the molten base metal forming the weld. The molten flux coating over the molten metal pool forms a blanket that eliminates spatter losses and protects the welded joint from oxidation. As welding proceeds, the molten weld metal and the liquid flux cool and solidify under a layer of unused flux. The molten flux on solidification forms a brittle slag layer which can be easily removed.

Unused granular flux material can be reclaimed and reused.

Characteristics of Submerged Arc welding Process:

• Electric current is 300 to 2000A.
• Power supply is 440 V.
• Velocity is 5m / Min
• The SAW process provides very high welding productivity, depositing 4 – 10 times the amount of weld metal per hour.

Advantages of Submerged Arc welding Process:

• Thin plates can be easily welded in one pass without any edge preparation while only a slight bevelling is necessary in most other cases.
• The quality of welds produced in submerged arc welding is very high with good toughness, ductility and uniformity of properties.
• Submerged arc welding is most suitable for welding in the down hand or flat position although welds can be made on a straight slope.
• Materials successfully welded by the process include low carbon steel, medium carbon steel, heat resistant steel, corrosion resistant steel, high strength steels and non ferrous metals like Monel metal, nickel and others.
• High  speed of execution due to the use of high currents in one or more electrode wires
• No smoke
• The arc is concealed, enabling the operator to work without a mask and without disturbing others nearby

Limitations of Submerged Arc welding Process:

• Solid flux submerged arc welding can be used only on alloy and non-alloy carbon steel, stainless and refractory steel
• The use of a powder flux means that welds must be executed horizontally, unless special measures are taken
• The process cannot weld plate less than 1.8 mm thick (due to its high penetration)
• It is not possible to butt joint work pieces more than 16 mm thick ; thicknesses greater than 16 mm require special preparation (bevelling).

Application of Submerged Arc welding Process:

• Shipbuilding
• Heavy Duty Pressure vessels
• Off shore engineering

Frequently Asked Interview Questions | 10 Job Interview Questions | Mechanical Engineering Test Questions

1. A hollow shaft of same cross-section area as solid shaft transmits

A. Same torque

B. Less torque

C. More torque

D. Unpredictable

Answer:

B. Less torque

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2. In a cantilever beam, maximum deflection occurs at where

A. Bending moment is zero

B. Bending moment is maximum

C. Shear force is zero

D. Slope is zero

Answer:

A. Bending moment is zero

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3. In a rectangular beam, when width, depth and length are doubled, the bending stress will be

A. Shall remain unchanged

B. Shall be doubled

C. Shall become ¼ th

D. Shall be halved

Answer:

C. Shall become ¼ th

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4. In an I –section beam, the bending moment is resisted mainly by

A. Flanges only

B. Web only

C. Both by flanges and web

D. None of the above

Answer:

B. Web only

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5. In internal combustion (I.C.) engines, combustion of fuel takes place in

A. Outside the cylinder

B. Inside the cylinder

C. Not in the cylinder

D. None of the above

Answer:

B. Inside the cylinder

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6. Power available at the shaft of an I.C engine is known is

A. Brake horse power

B. Indicated horse power

C. Net indicated horse power

D. Pumping power

Answer:

A. Brake horse power

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7. In internal combustion engine piston the maximum temperature occurs at

A. Ring section

B. Gungeon pin

C. Bottom centre

D. Top centre

Answer:

A. Ring section

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8. A two-stroke engine is generally preferred to a four-stroke engine because

A. It offers low fuel consumption

B. It gives lesser shocks and vibrations

C. It can be easily started

D. It has smaller size for the same output.

Answer:

D. It has smaller size for the same output.

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9. During idling process, a petrol engine requires

A. Lean mixture

B. Rich mixture

C. Variable mixture

D. None of above

Answer:

A. Lean mixture

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10. Cavitation in a pipe will begin when

A. Pressure at any location reaches pressure equal to the saturated vapour pressure of liquid

B. Pressure becomes more than critical pressure

C. Flow is increased

D. Pressure is increased

Answer:

A. Pressure at any location reaches pressure equal to the saturated vapour pressure of liquid

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11. Capillary action of liquid is due to the

A. Viscosity of liquid

B. Cohesion of liquid particles

C. Surface tension

D. Adhesion of liquid particles on the surface

Answer:

B. Cohesion of liquid particles

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12. In one ton refrigeration machine, the term “one ton” implies

A. One ton refrigerant is used

B. One ton water can be converted into ice

C. One ton ice when melts from and at 0^oC in 24 hours, the refrigerating effects is equivalent to 3000 kcal/hour

D. None of the above

Answer:

C. One ton ice when melts from and at 0^oC in 24 hours, the refrigerating effects is equivalent to 3000 kcal/hour

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13. In a refrigeration cycle, the moisture content is to be removed before it enters into which system

A. Cold side of system

B. Evaporator

C. compressor

D. condenser

Answer:

B. Evaporator

TIG Welding | GTAW Welding | Arc Welding Equipment’s

Tungsten Inert Gas (TIG) or Gas Tungsten Arc welding (GTAW):

It is an arc welding process wherein coalescence is produced by heating the job with an electric arc struck between a tungsten electrode and the job. The electrodes used in this process are made of either Tungsten or Thoriated Tungsten. Thoriated Tungsten electrodes run cooler than plain tungsten electrodes and maintain square arcing ends but it is more expensive.

Shielding gas:

A Shielding gas (Argon, Helium, Nitrogen, Carbon dioxide or a mixture of gases etc.) is used to avoid atmospheric contamination of the molten weld pool. The inert gas blanket shields the entire weld area from the atmospheric attack eliminating the need for any flux. General inert gas used is Argon though Helium or a mixture of the two may also be used. A filler metal may be added if required.

Commercial grades (Shielding gas) used for welding are 99.9% pure. Argon is 0.38% heavier than air and about 10 times heavier than Helium. Both gases ionize when present in an electric arc. This means that the gas atoms lose some of their electrons that have a negative charge. These unbalanced gas atoms, properly called positive ions, now have a positive charge and are attracted to the negative pole in the arc.

When the arc is positive and the work is negative, these positive ions impinge upon the work and remove surface oxides or scale in the weld area. Argon is most commonly used of the shielding gases. So Argon is suitable for welding thinner material.

Whereas Helium produces a higher arc voltage than Argon. This makes it more suitable for welding heavy sections of metal that have high heat conductivity or for automatic welding operations where higher welding speeds required.

TIG Welding Polarity:

The current source may be either DC or AC depending upon application. DC straight polarity arc is used in metals other than aluminium and magnesium including copper alloys, cast iron, steel and stainless steel. It gives good heat concentration and produces welds that are deep and narrow. Welding rates are high and there is less distortion of base metal. DC reverse polarity is not generally used because it produces shallow and wide welds. AC arc is used for welding aluminium, magnesium, cast iron and a number of other metals. Penetration with AC arc is midway between the penetration produced by DC direct polarity and DC reverse polarity.

The process is most suitable for low gauge sheet metal welding and cannot compete with conventional shielded metal electrode welding for welding of heavier gauges due to the cost of inert gas.

TIG Welding Process:

A high frequency, high voltage (100 kHz to 2 MHz, 2000 volts) low amperage current supply is often used in TIG welding to initiate the arc. This is to avoid the contamination of the electrode caused when the arc is initiated by short circuiting with the work piece. When electrode tip reaches within a distance of 3 to 2 mm from the job, a spark jumps across the air gap between the electrode and the job. The air path gets ionized and arc is established.

The superimposed high frequency current causes a spark to jump the gap between the electrode and the work piece. If a high frequency source is not available the arc can be initiated by scratch starting using copper striker plate to limit electrode contamination. Tungsten inert gas welding can be done in any position. Welding speeds of the order of 400 to 1000 mm per minute have been attained by manual process. The process can also be adapted to mechanized and automatic operation.

Advantages:

1. No flux is used, hence there is no danger of flux entrapment when welding refrigerator and air conditioner components.

2. Because of clear visibility of the arc and the job, the operator can exercise a better control on the welding process

3. This process can weld in all positions and produces smooth and sound welds with less spatter.

4. TIG welding is very much suitable for high quality welding of thin materials (0.125mm)

5. It is a very good process for welding Nonferrous metals (Aluminum etc.) and Ferrous metals.

Disadvantages:

1. Tungsten if it transfers to molten weld pool can contaminate. It is Hard and Brittle.

2. Filler rod end can cause weld metal contamination

3. Equipment costs are higher than that for flux shielded metal arc welding.