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              d  Basic or hydrogen-controlled electrodes: (Low hydrogen electrode e.g. E7018)
                 Basic or hydrogen controlled electrode coatings are based on calcium fluoride or calcium carbonate. This
                 type of electrode is suitable for welding high-strength steels without weld cracks and the coating have
                 to be dried. This drying is achieved by backing at 450°C holding at 300°C and storing at 150°C until
                 the time of use. By maintaining these conditions it is possible to achieve high strength weld deposits on
                 carbon, carbon manganese and low alloyed steels. Most electrodes in this group deposit welds with easily
                 removable slags, producing acceptable weld shape in all positions. Fumes given off by this electrode are
                 greater than with other types of electrodes.
           Types of electrodes: Electric arc welding electrodes are of three general types. They are
           a  Carbon electrodes
           b  Bare electrodes
           c  Flux coated electrodes
              a  Carbon electrodes
                 Carbon electrodes are used in the carbon arc welding process (Fig 3). The arc is created between the
                 carbon electrode and the job. The arc melts a small pool in the job and filler metal is added by using a
                 separate rod. Normally the carbon arc has very little use of welding. Its main application is in cutting and
                 gouging operations.
              b  Bare electrodes
                 Bare electrodes are also used in some arc welding processes (Fig 4). An inert gas is used to shield the
                 molten weld metal and prevent it from absorbing oxygen and nitrogen. Filler metal is separately added
                 through  a  filler  rod.  Usually  tungsten  is  used  as  one  of  the  bare  wire  electrode.  In  Co2  welding  and
                 submerged arc welding processes the mild steel bare wire electrode is also used as a filler wire.

              Fig 3                                              Fig 4
















           c  Flux coated electrodes
           Flux coated electrodes are used in the manual metal arc welding process for welding ferrous and non-ferrous
           metals. (Fig 5)
           The composition of the coating provides the flux, the protective shield around the arc and a protective slag which
           forms over the deposited weld metal during cooling.


             Fig 5





















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                                          CITS : CG & M - Welder -  Lesson 27 - 30
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