THE WELDING PROCESS -
Welding is a process of connecting metal parts by fusion. Arc welding and ox-acetylene welding are the two usual methods adopted. Molten or fused metal is deposited between the metal parts which are to be connected. The metal parts are also fused to a speciﬁed depth. When the deposited fused metal is cooled, the metal parts get joined by new metal. The ends of metal parts to be connected and the tip of the weld rod are fused by arc which causes a high temperature of about 3300 degree Celsius. In the ox-acetylene method a jet of burning oxygen and acetylene is used as a source of heat. The weld rod has a coating which also melts during the welding process and forms a shield preventing combination of the heated metal with the freely available oxygen and nitrogen from the atmosphere.
|Fig. Gas metal arc welding (MIG welding)|
ADVANTAGES 0F WELDED CONNECTIONS
(I) Since the process does not involve driving holes, the gross sectional area of the welding members is effective. In the case of riveted tension member deductions have to be made for the area lost due to punching holes.
(ii) Welded structures are comparatively lighter than corresponding riveted structure.
(iii) A welded joint has a great strength. Often a welded joint has the strength of the parent metal itself.
(iv) Repairs and further new connections can be done more easily than in riveting.
(v) Welded joints provide rigidity. Hence welded members for the same loading, are n smaller bending moments than corresponding riveted members.
vi) Often welded joints are economical to riveted joints. For a welded structure maintenance and painting costs are lesser than for the riveted structure.
( Vii) Members of such shapes that afford difﬁculty for riveting can be more easily welded.
(viii) A welded structure has a better ﬁnish and appearance than the corresponding riveted structure
(ix) Connecting angles, gusset, plates, splicing plates can be minimized and in many cases, can be avoided in welded structures.
(x) Steel bars in reinforced concrete structures may be welded easily. Lapping of bars may be avoided if welding is resorted to.
(X!) It is possible to weld at any point at any part of a structure. But riveting will always require enough clearance.
(xii) The process of welding does not involve great noise compared to the noise produced in the riveting process.
DISADVANTAGES 0F WELDED CONNECTIONS
(1) Welding requires skilled labour and supervision.
(ii) Testing a welded joint is difﬁcult. An X-ray examination alone can enable us to study the quality of the connection.
(iii) Due to uneven heating and cooling, the welded members are likely to get warped at the welded surfaces.
(iv) Internal stresses in the weldedzones are likely to be set up.