Welding MCQ Quiz in मल्याळम - Objective Question with Answer for Welding - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

• Joggle joints are used where a strong joint on the flat surface is needed to join two pieces of sheet metal.
• Generally, there are hand tools available to put the joggle into the sheet metal.
• Joggled welded joints are used where severe loading is encountered, and the upper surface of both pieces must be in the same plane.

Explanation:

• Grey Cast Iron is best Welded by Gas Welding (Oxy-Acetylene Gas Welding).
• Oxy Acetylene Gas Welding uses two types of Gas, one is Oxygen and the other is Acetylene. 
• Generally, Neutral Flame or Carburizing Flame is used for welding because Grey Cast Iron is already saturated with Carbon and It can not absorb carbon further if welded with Carburizing Flame.
• Sometimes slightly Oxidized Flame can also be used for Grey Cast Iron Welding.
• Grey Cast Iron is widely used for machine tool bodies, automotive cylinder blocks, flywheels, housing etc. 

Concept:

Flash butt welding

• In flash welding (FW), also called flash butt welding, heat is generated very rapidly from the arc as the ends of the two members begin to make contact and develop an electrical resistance at the joint.
• After the proper temperature is reached and the interface begins to soften, an axial force is applied at a controlled rate and a weld is formed by plastic deformation of the joint.
• The mechanism is called hot upsetting, and the term upset welding (UW) also is used for this process.
• Some molten metal is expelled from the joint as a shower of sparks during the process-hence the name flash welding. 
• It is used for joining of HSS drill bit to the carbon steel shank.

The advantages of flash butt welding are:

1) Less requirement of power

2) When the surfaces being joined, it requires only less attention.

3) Weld obtained is so clean and pure; due to the foreign metals appearing on the surfaces will burn due to flash or arc.

Soldering:

• Soldering is a non-fusion and non-pressure welding operation.
• The mechanism by which the joint formation taking place is wetting and surface alloying.
• The filler material used having a melting temperature less than 427°c
• Borax is used as Flux material.
• The filler material used is an alloy of lead and tin known as solder.
• Filler material entered into the workpiece by means of capillary action.

Brazing:

• It is also a non-fusion and non-pressure welding operation. 
• Filler material- Alloy of Cu and Zn, Cu and Ag, Cu and Al
• Flux material- Borax
• Filler material entered into the workpiece by means of capillary action.
• Filler material melting temperature greater than 427°c and less than the melting point of the base material

Braze welding:

• It is also a non-fusion and non-pressure welding operation.
• Filler material – an alloy of Cu and Tn (Bronze).
• The strength of the joint is more than brazing and soldering.
• Filler material entered into the workpiece by gravity force.

Explanation:

Thermit Welding:

It is a welding process utilizing heat generated by an exothermic chemical reaction between the components of the thermit (a mixture of metal oxide and aluminium powder). In this process, fine aluminium particles and metal oxide are mixed in and ignited by an external heat source.

The reaction will proceed according to the following equation:

Metal Oxide + Aluminum → Aluminum Oxide + Metal + Heat

Thermit Welding is mainly used for joining steel parts. It is used for repair of steel casings and forgings, for joining railroad rails, steel wires and steel pipes, for joining the large cast and forged parts. For which aluminium is mixed with the iron oxide in the ratio of 1 : 3 by weight. 

Due to the thermit chemical mixture reaction, 3 products are produced,

• Iron - Used as filler rod
• Al2O3 - Used as a slag
• Heat - Used for the melting of the parent material

Concept:  

Welding symbol:

A welding symbol has the following basic elements:

1. Reference line

2. Arrow

3. Basic weld symbols (like fillet, butt joints, etc.)

4. Dimensions

5. Supplementary symbols

6. Finish symbols

7. Tail 

Reference Line:

• It is used to apply weld symbols and other data.
• The reference line is always drawn horizontal to the bottom of the print. 
• Lower side of the reference line is termed as arrow side.
• Upper side of the reference line is termed as other side.

Arrow:

• The arrow is used to connect the reference line to the joint area to be welded.

Basic weld symbols:

• Basic symbol and type in mention in the given chart.

Tail:

• Tail is added only when there is a need for including the specification process or other references.

Calculations:

Given:

Here the symbol is of fillet weld on lower side of the reference line that represents arrow side.

Here the symbol is of fillet weld on the upper side of the reference line that represents the other side.

∴ combining the two, 6 on the lower side represents the arrow side and 12 on the upper side represents the other side.

Concept:

The voltage supplied for welding is given by

,

where V_o = Open circuit voltage, I_s = Short circuit current.

Power supplied is given by

Now, For maximum arc power, 

∴ 

Calculation:

Given:

V_o = 80 V, I_s = 300 Ampere, I = ?

Now, we know that

∴ I = 150 Ampere

Explanation:

A fault/defect is an imperfection in the weld which may result in failure of the welded joint while in service.

The following defects occur commonly in gas welding.

1. Lack of fusion: If there is no melting of the edges of the base metal at the root face or on the side face or between the weld runs, then it is called lack of fusion.

Cause:

• It occurs because of the low heat input
• Incorrect electrode and torch angle
• Low welding current
• High welding speed

2. Undercut: A groove or channel formed in the parent metal at the toe of the weld is called an undercut.

Cause: 

• When the current setting is too high
• When welding speed is too fast
• By overheating of the job due to continuous heating
• Due to faulty electrode motion
• When the electrode angle is wrong

3. Incomplete Penetration: Failure of the weld metal to reach the root of the joint is known as incomplete penetration.

Cause:

• Too narrow edge penetration
• Excessive welding speed
• When the current setting is low
• When a larger diameter electrode is used
• Due to inadequate cleaning or gouging before depositing sealing run

4. Porosity or blow-hole:  A group of pin-holes in a weld (porosity) or a larger hole in the weld (blow-hole) are caused by the gas being entrapped.

Cause:

• Presence of contaminants on the job or electrode surface
• Presence of high sulphur in the job or electrode material
• Moisture trapped between joining surfaces
• Freezing of weld at a faster rate

5. Spatters: An unintentional deposit of weld metal, in the shape of small globules on the job surface along the weld is known as spatters.

Cause:

• A too high current setting
• Use of moisture affected electrode
• Wrong polarity
• Use of a long arc
• Arc-blows

6. Overlap: Metal flowing onto the surface of the base metal without fusing it.

Cause:

• Improper welding technique
• High welding current
• By using large electrodes

Explanation:

TIG Welding: 

• Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA) welding is the arc welding process in which arc is generated between a non-consumable tungsten electrode and a workpiece.
• The tungsten electrode and the weld pool are shielded by an inert gas normally argon and helium.
• The main application for TIG Welding of stainless steel, welding of light metals, such as Aluminium and Magnesium alloys, and the welding of Copper.
• It is also suitable for welding all weldable materials, apart from Lead and Zinc, with all types of joints and in all welding positions.
• However, TIG welding is best suited to thin materials, from about 0.5 mm to 3 mm thick.
• The thin sheets are manufactured by Aluminium, Copper like ductile material.
• Therefore, TIG welding is best suited for welding Aluminium

The principle of the tungsten inert gas welding process is shown below

Concept:

• In thermit welding, heating and coalescence is by superheated molten metal obtained from a chemical reaction between a metal oxide and a metallic reducing agent.
• Temperature around 2750°C produced in 30 seconds. Thus it involves highly exothermic chemical reaction for developing high temperature.
• In the mixture one part of aluminium and three parts of iron oxide are used and ignited by a magnesium fuse.
• The molten metal, produced by the reaction, acts as a filler material joining the work-pieces after Solidification.
• Thermit Welding is mainly used for joining steel parts.
• It is used for repair of steel casings and forgings, for joining railroad rails, steel wires and steel pipes, for joining the large cast and forged parts.

Concept:

Oxygen cylinders are seamless steel cylinders constructed by hand-forged steel; this is made seamless so that there is no possibility of gas leakage.

Cast iron is brittle in nature which is not recommended because during the transportation and loading-unloading chances of damage of cylinder.

Casting and welded structure are not used because in this there is a possibility of gas porosity.

• The Oxygen cylinder colour is Black
• The Acetylene cylinder colour is Maroon.