WELDING
The terms welding is define the joining of two or more surface (usually metals, but not always) under the influence of heat, so the product shall be nearly homogeneous union as possible. This is the main definition of welding.                

Technical Background of Welding:

In all welding joint processes heat is applied to or produced at the joint and heated surfaces are brought into close contact, as result the joint surfaces to grow together into single body.

Now we will see what happen during this growing up together process. It is we all known that the matter is made of molecules which in turn into atom. The atoms of molecules are become active when the temperature of material reaches absolute zero (-2730C). At that time the molecules are moves with vibratory motion. In the higher temperature the vibratory motions of atoms is greater. During welding temperature it is sufficient to allow the atoms to make a bridge for the closely contacting surfaces. Thus there is an exchange of atoms among the molecules of the surfaces to be joined. Through this exchange of molecules of one surface interlock with adjacent other surface and this process we get weld joint

         GAS WELDING                                      ARC WELDING

       1)  AIR ACETYLENE WELDING                         1)  CARBON ARC WELDING

      2)  OXY-ACETYLENE WELDING                         2)  TIG WELDING

      3)  OXY-HYDROGEN WELDING                          3)  MIG WELDING

      4)  PRESSURE GAS WELDING                           4)  SUBMERGED ARC WELDING

                                                                                5)  SHIELD METAL ARC WELDING

        RESISTANCE WELDING                           6)  PLASMA ARC WELDING

      1)  SPOT WELDING                                            7)  FLUXED CORED ARC WELDING

      2)  SEAM WELDING                                           8)  STUD ARC WELDING

      3)  PERCUSSION WELDING                               9)  ELECTRO SLAG WELDING

      4)  HIGH FREQUENCY WELDING

      5)  PROJECTION WELDING                              SOLID STATE WELDING

      6)  RESISTANCE WELDING                                 1)  FRICTION WELDING

      7)  FLASH BUTT WELDING                                 2)  COLD WELDING

                                                                                  3)  ULTRASONIC WELDING

        RADIANT ENERGY WELDING                 4)  HOT PRESSURE WELDING

       1)  LASER BEAM WELDING                               5)  DIFFUSION WELDING

       2)  ELECTRO BEAM WELDING                           6)  FORGE WELDING

                                                                                  7)  EXPLOSIVE WELDING

       THERMO CHEMICAL WELDING
            

       1)  THERMIT WELDING                                          
       2)  ATOMIC WELDING       

         SOLDERING

        BRAZING

                      AIR ACETYLENE WELDING                                                Air acetylene welding is one type of gas welding process, where unit body is produced by the heating work piece. The heat is produced from mixture of acetylene and air. Weld joint is made without the application of pressure and with or without use of filler metal.                                                                                         Air acetylene welding working principle                                                                                                                  Bunsen burner working principle is followed in air acetylene welding torch. A certain amount of pressure acetylene gas is flowing through Bunsen jet torch and same time a suitable amount of air included. Such this a weld-able flame is produced.                                                                                                                                            First acetylene gas is flown through a proper hose and it is regulated by a valve system. Acetylene gas is mixed with automatic included air for combustion. During combustion required amount of oxygen is obtained from air. There a special designed torch is used.

    APPLICATION OF AIR ACETYLENE WELDING

    The flame temperature is lower than the other kind of fuel acetylene and oxygen welding. The following application-

Where soft solder is required for copper plumbing.

Lead welding purposes (of course small cross section).

Small thickness copper sheet welding.

Refrigerant copper tube joining.

       
       

       
            

                                       OXY ACETYLENE WELDING  

            Oxy-acetylene welding is one of the flame welding or gas weld process, because the flame is produced of mixture of gasses in a combustion chamber for heat provided to the job. Oxy-acetylene mixture of gasses most commonly used for producing high temperature 32600C.

It is oldest development fusion welding process. No pressure is required on the job to be welded, the heat is drive to welding the pieces. The acetylene is obtained by the action of oxygen and calcium carbide.

CaC2 + 2H2O = Ca(OH)2 + C2H2

(Acetylene)

The gas acetylene( C2H2 )is play the most important role in Oxy-acetylene welding because it has the highest calorific value.

Advantages-

In gas welding the heating and cooling rate is slow, so it is advantage in some material welding from welding failure.

The flame can be controlled easily where need low and high temperature for welding or brazing or soldering.

Filler metal deposit rate can be controlled easily, because source of heat and filler metals are separate.

Preheating facility is in welder’s hand. So where required it can be applied.

In comparison of other welding process, it is low cost and low maintenance.

Nozzle sizes for various metal thickness-

Nozzle size 1 2 3 5 7 10

Plate thickness 1/32 3/64 1/16 3/32 1/8 5/32

Gas welding temperature for various common material.

Aluminium —–––- 6500C Bronze —–––––9000C Brass —––––-8900C

Copper —–––––– 10650C Lead —–––––––3300C Steel(C 0.2%) 15500C

Grey cas-tiron–––12000C Zink —–––––––4250C Tin —–––––––2300C