Electric arc welding

Introduction :

In electric arc welding, generation of heat by an electric arc is one of the most efficient methods. The electric arc welding process makes use of the heat produced by the electric arc to fusion-weld metallic pieces. This is one of the most widely used welding processes because of the ease of use and high production rates that can be achieved economically.

Principle of arc :

An arc is generated between two conductors of electricity, cathode and anode when they are touched to establish the flow of current and then separated by a small distance.
An arc is sustained electric discharge through the ionized gas column is called plasma between two electrodes.
The electrons liberated from the cathode move towards the anode and are accelerated in their movement. When they strike the anode at high velocity, a large amount of heat is generated.
In order to produce the arc, the potential difference between two electrodes should be sufficient to allow them to move across the air gap. 
For the convenience of explanation, we have chosen a direct current arc for the above description. But even with an arc of the alternating current ( AC ), it would be similar, with the main difference that the cathode and anode would change continuously and as a result, the temperature across the arc would be more uniform compared to a DC arc. 

How does it work?

The arc welding is a fusion welding process in which the heat required to fuse the metal is obtained from an electric arc between the base metal and an electrode.

First of all, metal pieces to be weld are thoroughly cleaned to remove the dirt, dust, grease, oil etc. After that, the workpiece should be firmly held in suitable fixtures. Insert a suitable electrode in the electrode in the electrode holder at the angle of 60 to 80 degree with the workpiece.

Select the proper current and polarity. The spot is marked by the arc at the places where welding is to be done. The welding is done by making contact of the electrode with the workpiece and then separating the electrode to a distance to produce an arc.

When the arc is obtained, heat is produced and melts the work below the arc, and forming a molten metal pool. A small amount of depression is formed in the work and the molten metal is deposited around the edge of this depression. After the completion of welding, the electrode holder should be taken out quickly to break the arc and the supply of current is switched off.

Arc welding equipment :

The main requirement in an electric arc welding is the source of electric power. They are essential for two types :

Alternating current ( AC ) machines 

• Transformer 
• Motor or engine-driven alternator

Direct current ( DC ) machines 

• Transformed with DC rectifier
• Motor or engine-driven alternator

The arc welding machines can also be divided into two types :
The first one is the constant current welding machines and the second one is droop curve machines.

Advantages of electric arc welding :

• low cost.
• Simplicity and portability of the tool.
• Versatile process.
• Wide choice of the electrode.
• Higher welding speed.
• No flux required.

Limitations of electric arc welding :

• Wastage of material.
• Less productive due to continuous wire process.
• Proper alignment and care of electrode required.
• Radiation impacts more extreme.

Difference between annealing and tempering

In this article you can check it out the difference between two manufacturing process annealing and tempering. First of all you should know about both of this process. 

What is annealing ?
Annealing is a hardening process, in which material is heated above the re-crystallization temperature and then is cooled in furnace / oil /water. 

What is tempering ?
Tempering is a stress removal process, in which material is heated below the re-crystallization temperature and then is cooled in air.

Annealing is used for :

• Soften a metal for cold working
• Improve machinability
• Enhance electrical conductivity

Tempering is used for:

• Hardness
• Ductility
• Toughness
• Strength
• Structural stability

Now we can check the difference between both the two process :

• Annealing is softening the metal after work hardening while tempering is reducing brittleness after quench hardening.
• Annealing increase ductility and toughness, stress relieving while tempering is the process of introducing toughness.

Difference between quenching and tempering

In this article you can check it out the difference between two manufacturing process quenching and tempering. First of all you should know about both of this process. 

What is quenching ?
Quench means rapid cooling so in this process rapid way of bringing metal to cool and back to room temperature after the heat treatment process.

What is tempering ?
Tempering is the process used to increase the toughness and is usually performed after hardening to reduce some of excess hardness.

Now we can check the difference between both the two process :

• Quenching is the process of heating the material above the re-crystallization temperature and cooling it suddenly while in tempering the material is heated to a temperature below the re-crystallization value and hold for few hours. 
• Quenched steels are brittle and tempering toughens them.
• The material becomes brittle, hard, ability to withstand wear and vibrations in quenching while tempering removes internal stress and improve a bit of ductility to the hard material.

Defects in welding

In view of the severe thermal regime through which the welding process proceeds the weldments are likely to be affected and if proper care is not taken they are likely to end up with certain defects.

Distortions have been discussed in greater detail earlier, and we will see the other defects here. The likely defects are :

• Undercut
• Incomplete fusion
• Porosity
• Slag inclusion 
• Hot cracking 
• Cold cracking 
• Lamellar tearing 
• Lack of penetration or Excess penetration

Now we can see the above defects in details :

• Undercut : 

The undercut is an extremely common welding defect it appears like a small notch in the weld surface.
It is generally attributed to the improper welding technique or excessive welding current.

• Incomplete fusion :

It occurs when individual weld beads don't fuse together or don't fuse properly to the base metal that you are welding. This will be seen as a discontinuity in the weld zone. 

The main cause for this defect is improper penetration of the joint and wrong design of the joint or incorrect welding technique including the wrong choice of the welding parameters.

• Porosity :

It is caused by the presence of gases which get entrapped during the solidification process. The main gases that cause porosity are :

• Hydrogen
• Oxygen 
• Nitrogen 

There may be also some other gas that causes porosity like helium, argon and carbon dioxide that are also present in weld pool but in view of their insolubility, they do not cause porosity.

Porosity if present in large would reduce the strength of the joint.

Make sure all material are clean before start welding and try to using low hydrogen electrodes that may reduce the chances of porosity.

• Slag inclusion :

Slag is formed by the reaction with the fluxes. It is generally lighter. In view of its low density, it will float atop of the weld pool and would be chipped off after solidification.

Some of the factors that cause slag inclusion are :

• The high viscosity of weld metal 
• Rapid solidification 
• Insufficient welding heat
• Improper manipulation of the electrode
• Undercut on the previous pass

Also, in multi-pass welding the slag solidified in the previous pass is not cleaned before depositing the next bead, which may cause slag inclusion.

Slag inclusion is like porosity, weakens the metal by providing discontinuities.

• Hot cracking :

It generally occurs at high temperature and the size can be very small to visible.

The crack in most parts is intergranular and its magnitude depends upon the strains involved in solidification. 

It generally happens only in steels and its caused by deformities in the structure of the steel. They are more likely to form during the root pass when the mass of the base metal is very large compared to the weld metal deposited.

It can be prevented by preheating the base metal, increasing the cross-sectional area of the root bead, or by changing the contour or composition of the weld bead.

• Cold cracking :

Cold cracking occurs at room temperature after the weld is completely cooled. It can be seen in the heat-affected zone. 
Mainly cause for cold cracking is :

• Excessive restraint of the joint which induces very high residual stresses.
• Martensitic transformation making the metal very hard as a result of rapid cooling.

Pre and post-heating of the weldment help in reducing the cooling rates and the consequent locking of the stresses.

• Lamellar Tearing :

It is generally seen at the edge of the heat-affected zone. It appears as a long and continuous visual separation line between the base metal and heat-affected zone.

This is caused by the presence of the elongated inclusions such as Mn Fe and S in the base metal. 

Lamellar tearing can also be caused by the weld configuration which gives rise to high residual tensile stresses in the transverse direction.

• Lack of penetration :

In complete penetration happens when your filler metal and base metal are not joined properly and the result is a gap or crack appears.

Welds that suffer from incomplete penetration are weak at best, and they will likely fail if you apply much force on them.

Welding terms and definitions

In this article, you can learn the definitions of some of the welding terms that are generally in used.

• Baking :

It is the material support provided at the root side of a weld to aid in the control of penetration.

• Base metal :

The metal to be joined or cut is called the base metals.

• Bead or Weld bead :

Bead is the metal added during a single pass of welding. 

The weld bead appears as a separate material from the base metal.

• Crater :

In arc welding, a crater is a depression in the weld-metal pool at the point where the arc strikes the base metal plate.

• Deposition rate :

The rate at which weld metal is deposited per unit time is called deposition rate.

It is normally expressed as kg/h.

• Fillet weld :

The metal fused into the corner of a joint made of two pieces placed at approximately 90 degrees to each other is called fillet weld.

• Penetration :

It is a depth up to which the weld metal combines with the base metal as measured from the top surface of the joint.

• Puddle :

The portion of the weld joint that is melted by the heat of welding is called puddle.

• Root :

It is the point at which the two pieces to be joined by welding are nearest.

• Tack weld :

A small weld, generally used to temporarily hold the two pieces together during actual welding, is the tack weld.

• The toe of weld :

Toe of the world is the junction between the weld face and the base metal.

• Torch :

In gas welding, the torch mixes the fuel and oxygen and controls its delivery to get the desired flame.

• Weld's face :

It is the exposed surface of the weld.

• Weld metal :

Weld metal is the metal that is solidified in the joint. 

It may be only a base metal or a mixture of base metal and filler metal.

• Weld pass :

A single movement of the welding torch or electrode along the length of the joint which results in a bend is a weld pass.

Types of joints in welding

There are mainly five types of joints are used in welding for joining two parts of metal. 

• Butt Joint
• Corner Joint
• Lap Joint
• Tee Joint
• Edge Joint 

Now let we discuss joints in details :

• Butt joint :

A butt joint is a technique in which two metal parts lie in the same plane and are jointed at their edges without any special shaping.

• Corner joint :

A cornet joint is a technique in which two metal parts located at right angles to one another in the form of the shape of L are joined at the centre of the angle.

It is used to connect two parts together and forming a corner.

• Lap joint :

A lap joint is a technique in which two metal parts are overlapped that are joined.

• Tee joint :

A tea joint is a technique in which two metal parts those surfaces are located approximately 90⁰ to each other that can be welded from both sides. 

• Edge joint :

An edge joint is a technique in which two metal parts joined by two edges and making a corner.

All these types of joints used when the thickness of the two metal parts to be joined is small so that heat of welding penetrates the full depth of the joint.

However, when the thickness increases, it becomes necessary to prepare the edge in such a way that the heat is able to penetrate the entire depth.

For very thick metal plates, the welding needs to be done from both sides. To provide necessary access into the joint, it could be made as to the following joints :

• V - Joint 
• U - Joint 
• J - Joint
• Bevel Joint 

In single joint welding is to be carried out only one side while in double joints the edge preparations are used when welding is to be carried out both sides.

Heat transfer

In this article, we will discuss the heat, heat transfer and different modes of heat transfer. Now, first of all, we check it out what is the heat ?

Heat is the quality of being hot OR Intensity of high temperature. 

Heat is defined as the form of energy that is transferred across a boundary by virtue of a temperature difference.  

The temperature difference is the potential or force and the heat transfer is called the flux.

The transfer of heat normally from a high-temperature object to a lower temperature object.

Heat transfer :

The heat is transferred between two bodies which are in direct contact is called conduction.

Heat may be transferred between two bodies separated by empty space or gases by the mechanism of radiation through electromagnetic waves.

The transfer of heat between the wall and a fluid system in motion is called convection. 

All the above are the modes of heat transfer. The direction of heat transfer is taken from high-temperature system to the low-temperature system.

Heat flow into the system is taken to be positive and heat flow out of a system is taken as negative.

For denote, heat transfer symbol is used is Q.

There is no heat crosses the boundary of the system this process is called adiabatic process.
Thus, an adiabatic process is one in which there is only work interaction between the system and its surrounding.

A wall which is impermeable to the flow of heat is called an adiabatic wall.
A wall which permits the flow of heat is called a diathermic wall.

The unit of heat is Joule in S.I Unit system.

The unit of heat transfer is kW or W.

Work transfer and Heat transfer

In this article, we will discuss the work transfer and heat transfer properties and also some similarities between both of them then the difference between them.

Points to remember regarding heat transfer and work transfer :

• Work and heat transfer both are energy interactions.
• The same effect in a closed system is about either by heat transfer or by work transfer. 
• Both heat transfer and work transfer are boundary phenomena.
• Heat transfer is one type of energy interaction and it is due to temperature difference. All other energy interactions may be termed as a work transfer.
• Heat or work is not a property of the system. It cannot be stored by the system. Both heat and work are energy in transit.
• Both heat and work are path functions and inexact differentials. 
• The magnitude of heat transfer or work transfer depends upon the path of the system that follows during the change of state.

Difference between heat transfer and work transfer :

Heat transfer is an interaction of energy between a system and its immediate surrounding due to temperature difference. 

Work transfer is the interaction of energy between a system and its immediate surrounding due to property difference other than temperature.

Work transfer in thermodynamics

A close system and its surroundings can interact in two ways :

• By work transfer 
• By heat transfer 

Both are those are called interactions and these bring about changes in the properties of the system. 

In thermodynamics mainly studies these energy interactions and the associated property changes of the system.

Work Transfer :

Work is one of the basic modes of energy transfer. In mechanics, the action of a force on a moving body is called work. A force is a means of transmitting an effect from one body to another. An effect of that certain distance can be performed by a body. The product of force and distance is the same to accomplish the same effect. 

What is work?

The work is done by a force as it acts upon a body moving in the direction of the force.

The action of a force through a distance is called mechanical work. The product of the force and distance moved parallel to the force is the magnitude of mechanical work.

W = F * d

In thermodynamics, work transfer is considered as occurring between the system and the surroundings.

Work is said to be done by a system if the sole effect on things external to the system can be reduced to the raising of a weight.

When work is done by a system, it is arbitrarily taken to be positive.

When work is done on a system, it is taken to be negative. 

The symbol used for work transfer is W.

The unit of work is N.m or Joule. 1 N.m = 1 Joule 

The rate at which work is done is called power.

There are various types of work transfer which can get involved between them. 

• pdV work
• Electrical work 
• Shaft work 
• Paddle-wheel work or Stirring work 
• Flow work 
• Work was done in stretching a wire
• Work was done in changing the area of a surface film
• The magnetization of a para-magnetic solid

TDI full form

What is the full form of TDI?

Answer :

• Turbocharged Direct Injection 

What does TDI mean?

It uses direct injection where a fuel injector sprays atomized fuel directly into the main combustion chamber of each cylinder and are also fitted with turbochargers to boost power output.

It is a very popular latest technology nowadays are used in many automobile companies like Tata Mahindra, Toyota, or Volkswagen.

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CRDI full form

What is the full form of CRDI?

Answer :

• Common Rail Direct Injection 

What does CRDI mean?

CRDI is the direct fuel injection system for petrol and diesel engine. 

Direct injection of the fuel into the cylinders of a diesel engine via a single or common line called common rail which is connected with all fuel injectors.

The common rail system accumulates high-pressure fuel in the common rail so that the fuel to be atomized and injects the fuel into the cylinder at a timing controlled by the Electronic Control Unit alloying high-pressure injection independent from the engine speed. 


Explore more information: 

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• VMC full form

• SFC full form

• TDI full form

• PDI full form

• ESC full form

• LASER full form

• ARAI full form

• VTVT full form

• DFI full form

• GVWR full form

• HVAC full form

• IHP full form

• ISFC full form

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Emissions norms in India

Emission norms are statutory requirements that set specific limits to the amount of pollutants that can be released into the environment. Norms focus on regulating pollutants released by automobiles and from industries and power plants. The pollutants in general that are regulated are NO_x, sulfur oxides, CO or volatile hydrocarbons.

In USA, emission standards are managed by the Environmental Protection Agency ( EPA ).
The state of California has special dispensation to promulgate more stringent vehicle emissions standard.

The European Union has its own set of emissions standards that all new vehicles must meet. The European Union is to introduce Euro 4 effective from January 1, 2008. Euro 5 effective from January 1, 2010 and Euro 6 effective from January 1, 2014.

The first Indian emission regulations were ideal emission limits which became effective in 1989. Indian started adopting European Union norms and fuel regulations for four-wheeled light-duty and for heavy-duty vehicles. 

History of emissions norms in India :

• 1991 

Ideal CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission for Gasoline Vehicles.

• 1992 

Mass Emission Norms for Diesel Vehicles.

• 1996 

Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.

• 2000

India 2000 ( equivalent to Euro I ) Norms, Modified IDC ( Indian Driving Cycle ), Bharat Stage II Norms for Delhi.

• 2001 

Bharat Stage II ( equivalent to Euro II ) Norms for All Metros, Emission Norms for CNG and LPG vehicles.

• 2003

Bharat Stage II ( equivalent to Euro II ) Norms for 11 major cities.

• 2005 

From 1st April Bharat Stage III ( equivalent to Euro III ) Norms for 11 major cities.

• 2010 

Bharat Stage III Emission Norms for 4-wheelers for entire country whereas Bharat Stage - IV ( equivalent to Euro IV ) for 11 major cities.

Disadvantages of liquid cooling system

The liquid cooling system takes away the excessive heat generated in the engine and saves it from overheating. It also keeps the engine at working temperature for efficient and economical working. Let us have a deep insight into the disadvantages provided by using this liquid cooling system. 

Disadvantages of a liquid cooling system :

• This is a dependent system in which water circulation in the jackets is to be ensured by additional means.
• Power absorbed by the pump is considered for water circulation and this affects the engine's power output.
• Cost of this system is considerably high.
• System requires considerable maintenance of its various parts.
• In the event of cooling system failure, serious damage to the engine may occur.

Advantages of liquid cooling system

The liquid cooling system takes away the excessive heat generated in the engine and saves it from overheating. It also keeps the engine at working temperature for efficient and economical working. Let us have a deep insight into the advantages provided by using this liquid cooling system. 

Advantages of the liquid cooling system :

• The compact design of engines with an appreciably smaller frontal area is possible.
• The fuel consumption of the high compression liquid-cooled engine is lower than that of the air-cooled engine.
• Because of even cooling of cylinder barrel and head due to jacketing makes it possible to reduce the cylinder head and valve seat temperature.
• Installation is not necessarily at the front of the mobile vehicles, aircraft as the cooling system can be conveniently located wherever required. This is not the case in the air-cooled engine.
• The size of engines does not involve serious problems as far as the design of a cooling system is concerned.
• In case of air-cooled engines particularly in high horsepower, range difficulty is encountered in the circulation of requisite quantity of air for cooling purposes.