METAL JOINING PROCESS,FLAMES AND SUBMERGED ARC WELDING

                          METAL JOINING PROCESS

                                         WELDING


Joining of two or more similar or dissimilar metal with or without application of heat or with or without application of pressure.

Type of welding
    1. pressure welding
    2. fusion welding
    PRESSURE WELDING- 

    Two piece of metal are joined with application of pressure. Sometimes in presence of heat and sometimes without heat.

    FUSION WELDING

    This is process in which heat is applied,the molten metal solidifies and weld is formed.
    •   EXAMPLES OF PRESSURE WELDING
    1. Forge welding
    2. Resistance welding
    3. Soldering
    4. Brazing
    5. cold pressure welding
    • EXAMPLES OF FUSION WELDING
    1. Gas welding
    2. Arc welding
    3. Thermit welding

    FLUX USED IN WELDING

    1. It absorbs gases produced in welding process
    2. It removes oxygen gas .
    Properties of flux are:-
      • Low melting point
      • Good absorbing power of oxygen
      • Low density
      • Example of flux--borax

      WELDING FLAMES

      1. Neutral flame
      2. Oxidizing flame
      3. Reducing flame

      Neutral flame:-

      When quantity of acetylene and oxygen is in equal volume proportionate then the flame is said to be balanced or neutral flame. It consists of two zones i.e. inner zone/envelope and outer zone. The inner zone is bluish-white and has cone, surrounding the inner cone is the outer cone. It is light blue surrounding. The temperature of the inner zone flame is nearly 3200 degree Celsius.


      Oxidizing flame:-


      When greater volume of oxygen by ratio is mixed with slightly less volume of acetylene then such flame is known as oxidizing flame. This also have two distinct flame regions i.e. inner flame and the outer flame. The inner flame is slightly purple in shade and outer flame surrounds it. The outer flame is small and narrow. The temperature of inner zone is around 3400 degree Celsius. 


      Reducing flame:-


      It is condition in which acetylene is in excess as compared to oxygen. Such flame has three zones i.e. inner zone, luminous zone and the outer zone. The inner cone is whitish in shade and luminous zone is twice the length of inner flame. The bluish outer zone surrounds the inner and intermediate zone. The temperature of inner zone is nearly 3100 degree Celsius.

       SUBMERGED ARC WELDING (SAW)



       CHARACTERISTICS

      This type of welding may be automatic or highly mechanized or semi automatic and can be operated with both alternating current or direct current. In submerged arc welding is propagated by continuously feeding the wire electrode towards work piece. The slag and protective gas formed is due to the flux when it burns. Initially flux powder is placed on the work piece. When arc is established and as the work piece melts, the protective layer is formed. The other advantage is that with the protective layer heat escape is minimum. Hence maintaining the temperature of the welding region high. There are various parameters that effect the weld. These are voltage, current, weld arc speed, penetration of weld. These parameters can be altered to obtain good quality weld.
      • FLUX USED- Bonded flux and fused flux.

      OPERATION ANALYSIS


      Submerged arc welding is quite similar to metal inert gas welding (MIG), but instead of inert gas here we use large amount of flux in powdered form. This powdered flux in supplied in weld pool. This may be automatic or semiautomatic system. The flux used may be oxide of manganese, silicon and aluminum.


      The flux used in process reacts highly with the weld pool and solidifies to strong weld. The arc produced between the tip of electrode and the specimen is submerged into the flux, hence the name implies submerged arc welding.


      DEMERITS

      • Not compatible for thick section.
      • Not economical as flux powder used in large quantity.
      APPLICATION
      • Used for butt and fillet weld.
      • Used for carbon-manganese steel, low alloy steels.
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