GAS WELDING

GAS WELDING 

    It is a type of fusion welding in which the heat for eldin is obtain by the combustion of fuel gas it joins metal using the heat of combustion of an oxygen and fuel gas, the gas fusion welding is particularly suitable for joining metal sheets and plates having thickness from 2 to 50mm in order to weld materials having thickness more thsn 15mm additional from the matter called filler metal fro the welded rod is melting into the gas between 2 parts to be joined

@ Types of flame :-

- neutral flame :-

        a neutral flame is obtain when equal amount of oxygen and acetylene are mixed and burn in a torch. the flame is recognised by two sharply define zine, the inner white cone flame and outer blue flame envelop . the reaction at the inner cone for the neutra flame where equal volume of cylinder oxygen and acetylene are used
C2H2 + O2 -----> 2CO + H2
  The reaction and the outer envelop are carbondioxide
H2 + 1/2O2 ----> H2O (vapour)

- Oxidising flame :-

      this type of flame is obtain where is an acces of exygen it is similar to neutral flame but the inner cone is flash less than shorter to obtain an oxidising flame the flame is passed said to the neutral condition than the acetylene condition than the acetylene value is turn the acetylene valve is turn down gradually to reduce the amount od acetylene giving an access of oxygen

- Carbarising flame :-

               the carbarising or reducing flame is obain when an acetylelne is supplied it is used for welding of many of the non -ferrous and hard surfacing

# Application :-

On the bases of  flame :-
*neutral flame :-
        the flame is widely used for the welding of steel, stainless steel, cast iron , copper and alumunium etc
* Oxidising flame :-
        it is mainly used when welding material are not oxidised readly ex:- brass, bronze and gold
* Carbarising flame :-
        it is suitable for welding low alloy steel, low carbon steel

@ Gas welding Hand equipments :-

- oxygen gas cylinder
- acetylene gas cylinder
- oxygen pressure regulator
- acetylene pressure regulator
- oxygen gas hose (blue)
- Acetylene gas hose (Red)
- Welding torch
- Trolley for the transportation of oxygen and acetylene oxygen and acetylene
- filler rod
- fluxes

@ Oxygen gas cylinder :-

             the standard colour is black . the oxygen is usually form from strong cylinder . the oxygen cylinder are usually by add a pressure of 12.5 to 14 m(square) and having capacity of 6.23 cubic metre

@ Acetylene gas cylinder :-

             the standard colour for the acetylene is mehroom, the acetylene is stored in cylinder under an initial pressure of 1.545 kilo newton/m(square) and having capacity of 7.6 cubic metre

@ Oxygen and acetylene pressure regulator :-

          the pressure of the gas obtain from the cylinder is considerable high than the gas pressure used to operate the welding torch . the purpose of using the gas pressure regulator is
- to reduce the high pressure of the gas cylinder to a stable working pressure . to produce a study flow of gas under varying cylinder pressure the desire pressure at the welding torch for oxygen is between 72 and 80 KN/m(square) and acetylene it is between 7 and 103 KN/m(square)

@ Blow pipe :-

          the blow pipe serves to max. the gases in proper proportional and to deliever the mixture to the nosel, where it is burn. the gasses from the cylinder are taken to the blow pipe through reducing valve
   depending upon the system of oxygen  acetylene welding there are 2 desigm of blow pipe which are low pressure type and high pressure type

@ Filter rod :-

        filter rod are used in gas welsing to provide exta metal to the weld by welding the end of the rod . the filler rod used in welding should have a chemical composition similar to that of the base metal, the dia. of the filler rod is selected to suite the thickness of the base metal
d= t/2+1 , where 't' is the thickness

@ Fluxes :-

           in gas welding when metal are heated the oxygen from the air combines with then and formed oxides. their oxideproduce poor quality and low strength  weld. sometime it makes the welding impossible so fluxes are used in order to prevent oxidation and other unwanted chemical reaction during weding, for alluminium the fluxes used are similar in composition to these fuse or magnesium alloy

  # Reversible PRocess :-

            the process which can be reversal in the direction and the system retraces the same path and the same equillibrium states is known as a reversible process

# Condition for reversible process :-

           - Process should be frictionless
- Process should proceed at infinity slow speed. the heat exchange only through infinity small temperature difference

@ Irreversible process :-

         a process should be irreversible if a system passes through a sequence of non- equillibrium states, when the process is carried out in such a manner that at  every instant deviation from the TD equillibrium is very small

# Internal energ :-

         it is the energy stored in a body or a system due to its moleculer arranement
- it depends on the initial and final state not upon the path
- The sum of internal energy and pressure volume product is known as enthalhy

@ Zeroth law of thermodynamic :-

             it states that if a body A in thermal equillibrium and body B in thermal equillibrium and also separately with a body C then the body B and C