ELECTRIC ARC WELDING

 Electric arc welding -:                                    In welding generation of heat by an electric arc is one of the most efficient method. Approximately 50 % of the energy is libera-ted in the form of heat produced by the electric arc to fusion matelic peices. This is one of the most widely used method mainly because of the edge of use and high produc-tion rate that can be achieved economically. 

          The main requirement in electric arc welding set-up is the source of the electric power. They are two types-: 

1. A.C. machine-:  

( a ) Transformer   

( b ) Motor or engine drive alternater 

2. D.C. machine -: 

( a ) Transformer with D.C. rectifier 

( b ) Generater 

The transformer does not have any moving part and as a result, oprate with less maintaness cost.

In A.C. welding normally only transformer are used. And in D.C. welding a rectifier or generator can be used to supply the required D.C. power. 

A tipical A.C. arc welding set-up using the transformer is show in fig.  The work peice is kept on a machine table to which the ground lit of the secondary winding of the welding transformer is connected. The other lit of the secondary winding is connected to an elect-rod holder into which electrod is crriped.  When electrod is brought into connecte with the path welding takes place. 

TUNGSTEN - INERT GAS WELDING

 Tungsten-inert gas welding -: It is also known as " gas tungsten arc welding ". It is an inert gas shielded arc welding process using a non- comsumerabl electrod. The electrod may also contain 1 to 2 % of " thorium oxide " mixed along with the core tungsten or tungsten with 0.15 to 0.04 % " zirconium oxide ".

                       

The pure tungsten electrod are less-expansive but will carry less current. The zirconium added in tungsten electrod are better than the pure tungsten. A tipical tungsten inert gas welding set-up in figure. It consist of welding torch at the center of which is the tungsten electrod . The inert gas supply to the welding zone through the annular path surrounding the tungsten electrod to the effectively displayed the atmosphere around the weld puddle. The smaller weld torch may not be provided with any polling devices for the electrod.

             The tungsten inert gas arc welding process can be use for joining of number of material through the most common welding arc aluminium, magnesium and stainless steel.            

S.No.   MATERIAL              ELECTROD

 1.        Stainless steel          De-oxidize Tungsten  

 2.        Aluminium                 All types of tungsten 

 3.       Magnesium                Tungsten 

 4.       De-oxidizing copper  Toriated tungsten 

 5.      High carbon steel       Toriated tungsten 

 6.      Cast iron                       toriated tungsten 

FLUX CORED ARC WELDING

FLUX CORED ARC WELDING -: Flux cored arc welding is the modification of gas metal arc welding.  Where the solid electrod wire is replaced by the tubular electrod containing a flux of the center of electrod through out it's length.  Because of availability of flux in the welding zone the weld metal of any required composition can be slowly controlled and a smooth weld heat can be obtain. Flux cored arc welding are normally used for the welding of structural steel or alloy steel.

                        

METAL INERT GAS WELDING

METAL INERT GAS WELDING -: Metal inert gas welding is also known as " gas metal arc welding " . In this welding utilies a comsumerabl electrod enhance the term metal appear in the title.  There are other gas shielded arc welding process utilising comsumerabl electrods such as flux coat arc welding or of which can be termed under metal inert gas welding. When thicker sheets are to be welded the filler metal requirement the gas metal welding. 

                   

 

 The tipical set-up for MIG show in fig. The comsumerabl electrod is the form of a wire rill,  which is fed at a constant rate . The welding torch is connected to the gas supply cylinder which provide the necessary inert gas . The electrod and workpiece are connected to the welding power supply. The current from the welding machine is change by the rate of feeding of the electrod wire. Normally D.C. arc welding machine are used for metal inert gas welding with electrod positive.

              The shielding gases that can be used for metal inert gas welding are helium, argen , nitrogen, oxygen and carbon dioxide and mixture of the above gases in various propositions. Each of this have that the fact on the formation of heat. The electrod wire comes generally in the form of coils . Various wire composition are available depending on the base metal composition.  The diameter of wire may be of order of 0.5 to 3.2 mm. 

SUBMERGED ARC WELDING

SUBMERGED ARC WELDING-: It is generally used for faster doing welding jobs. It is possible to use larger welding electrod 12 mm as well as very high current 4000 ampier so that very high metal disposition rate of the order of 20 kg/hr or more can be achive with process also very high welding speeds 5 meter/minute are possible in submerged arc welding. Some saw machine are able to well plated of thickness as high as 75 mm in butt joints in a single pass .

                 

 The arc is produced by the comsumerable electrod wire is continuously fed into the wild zone. The welding zone is completely covered by a measure amount of granulated flux which is delivert at a rate of the welding electrod by means suffer welding flux fed tube. The arc offering between electrod and workpiece us completely submerged under the flux and is not visible from outside. The power source are used with submerged arc welding can be either A.C. or D.C. . The electrod wire is normally used are sizes 1.6 to 2.5 , 3.15 , 4 ,5 , 6.3 and 8 mm .

CARBON ARC WELDING

CARBON ARC welding-: Carbon arc welding is the earliest arc welding process. In this process the electrod is made of ideal carbon or graphide. In contrast to graphide electrod , carbon electrod are soft and therefore they can't taken up very high current capasities. The arc with the carbon electrod is more controllable. Lower current act's to the higher electrod life.

                         

  

                       Through the carbon or graphide electrod arc not expected To made as the consumeabl electrod. They do get it to a rate for temperature because of the heat from the arc which causes a slow disintegration of the electrod take as also it's oxidation this means that electrod is slowly consumed.  In the carbon arc welding the required filler material is supply through a sale are filler rod. The arc can be obtain between the carbon electrod and workpiece or between the carbon electrod. 

Cooling tower MCQ

Q.1 Open cooling system is also called as _____ system .  
A. Once through 

B. Air based

C. Reversible 

D. Non-reversible 

Ans-: A

Q.2 What are used in the direct flow system to transverse the pond before uniting at intake?

a) Separators
b) Filters
c) Baffle walls
d) Porous pipes

Ans-: C

Q.3 The type of cooling towers with maximum heat transfer from air to water is ___.

A. Natural draft

B. Mechanical draft

C. A + B

D. None of the above 

Ans -:  B

Q.4 Natural draft cooling towers mostly used in the ______ .

A. Power station

B. Steel industry 

C. Aluminium industries 

D. All of the above 

Ans -: A

Q.5 Normally the guaranteed best approach a cooling tower achived is _____ .

A. 10 ° C

B. 15 ° C

C. 2.8 ° C

D. 8.2 ° C

Ans -: C

Q.6  A cooling tower reduces the water temperature close to _____.

A. Dry bulb temperature 

B. Wet bulb temperature 

C. Atmospheric temperature 

D. Dew point temperature 

Ans -: D

Q.7 The principle of work of the mostly cooling towers is ___.

A. Evaporative cooling 

B. Condensation 

C. Compression 

D. None of the above 

Ans -: A

Q.8  Approximately about _____ of cooling in cooling tower is through the sensible cooling. 

A. 50 %

B. 30 %

C. 20 %

D. 25 %

Ans -: C

Q.9  In cooling towers, higher temperature ______ corrosion potential. 

A. Decrease 

B. Increase 

C. Not affect 

D. Increase at 100 ° C

Q.10 The size of the cooling tower varies ______ with the temperature range .

A. Directly 

B. Inversely 

C. Proportionaly 

D. None of the above 

Ans -: B