What is meant by welding ?
Welding is the process that allows the physical/chemical union of two joints by fusion of the same, or by means of filler metal. This material can be the component material of the parts themselves that are joined, but it can also involve material foreign to they, called filler material: in the first case we speak of autogenous welding (with or without filler material depending on the case) in the second of heterogeneous welding or brazing (in which the fusion affects only the filler material). Welding creates a permanent connection which differs from other permanent connections (for example nailing or gluing) which do not create the continuity of the material. With some autogenous welding processes, if performed correctly and according to certain principles,an almost total continuity is also guaranteed in the very characteristics of the material of the joined parts.
Types of welding
TIG welding
The process is based on a torch in which the tungsten electrode is inserted, around which the shielding gas flows which, through a ceramic material nozzle, is brought to the melting bath. The operator moves the torch along the joint to move the weld pool, positioning the infusible tungsten electrode at a maximum distance of a few millimeters and keeping this distance stable. It must absolutely be avoided that the electrode comes into direct contact with the piece to be welded otherwise the tungsten rod "sticks" to the joint and welding is interrupted. If filler material is required, the material rod is simultaneously moved so as to keep it constantly with the end within the arc and in any case under the protection of the gas.
Wire welding
Technically, "autogenous electric arc welding in a protective gas atmosphere (M.I.G. metal inert gas) more commonly called "continuous wire". The use of the MIG electric arc welding machine allows for welding even on relatively thin metal thicknesses and seams free from slag and porosity, characterized by a flawless appearance.
As for the electrode welding machine, here too there is the earth cable (to be connected to the object to be welded) and the torch (insulated pliers held by the operator). The electrode in this case consists of a coil of wire housed in the machine. Pressing the button on the torch activates three mechanisms:
1) The small electric motor that unwinds the coil and pushes the wire through a conduit to the torch.
2) The solenoid valve which opens the duct to let the protective gas reach the torch.
3) The closure of the electric circuit which allows welding.
All three mechanisms require calibration, wire speed, protective gas outlet pressure, current intensity. On the front panel of these machines there are at least two knobs, one for the wire speed and one for the current intensity (in the cheaper versions this regulation is limited to a switch with only two positions, minimum and maximum intensity).
The protective gas has its adjustments on the back of the welder or on the cylinder welder connection pipe.
SMAW - Shielded Metal Arc Welding
The coated electrode process derives from the first arc processes developed between the end of the 19th century and the beginning of the 20th century. In these processes initially the electrode (of the same type of material as that to be welded) was not protected, therefore it oxidized very rapidly and, what was much more serious, introduced oxides and other impurities into the weld pool. Soon it was seen that adding fluxes to the electrode material better results were obtained, initially these fluxes were inside the electrode (which was practically a tube containing the flux powder), but subsequent developments showed the usefulness of having a coating on the outside to the metallic material of which the interior is composed.
When the electrode is brought to a suitable distance from the piece, an electric arc is struck, which melts the metallic material of the electrode, the coating and the metal of the piece to be welded. The welder manually moves the gripper, thereby managing the weld pool. At the end of the operation, the welder must chisel away the crust (slag) that has formed over the weld, which has the function of protecting the metal during cooling.
at GIEFFE our welders are certified and equipped with a European license including all the qualifications for the above welding.