what is Shielded Metal Arc welding?
Welding can be defined as “operation that produces coalescence of two or more members by applying heats or pressure or both, with or without the use of filler metal.” In fusion welding, members to be joined (base metals) are heated to melt with or without the use of ﬁller metal (e.g. covered electrode), and then the molten parts produce coalescence of the base metals, followed
by solidiﬁcation. In pressure welding, the joining parts are given the thermal energy by friction or gas ﬂame, and then mechanical pressure is applied to complete the welding process. In brazing or soldering, the brazing ﬁller metal or solder that has a lower melting point than the base
metal is fused, without melting the base metal, and then the fused ﬁller metal is distributed between the closely ﬁtted faying surfaces of the joint by capillary action. The brazing process uses a brazing ﬁller metal, and the soldering process uses a solder with a relatively lower melting point. Of these metallurgical joining processes, the fusion welding process, particularly the arc welding process that uses the arc discharge for the heat source, is most widely used.
The two types of manual arc welding that are most often found in the oil and gas industry are the SMAW and GTAW welding processes. Both processes are included in the arc welding category. Arc welding practitioners know 8 types of welding processes, namely:
- shielded metal arc welding
- TIG welding / GTAW
- plasma arc welding
- MIG / MAG welding
- self-shielded arc welding
- submerged arc welding
- electron gas arc welding
- stud welding
when two steel plates are arc-welded, the welded part can be categorized into 3 segments: metal weld, base metal, and heat affected zone.
Principles and characteristics of Shielded Metal Arc Welding
SMAW stand for Shielded Metal Arc Welding. SMAW is a process of connecting metals that use heat energy to melt workpieces and electrodes (filler material). The heat energy in the SMAW welding process is produced because of the electric jump (cathode and anode) that occurs at the electrode end and the material surface. In the SMAW welding process, the type of protector used is a membrane of flux found on the electrode. Flux on the SMAW electrode serves to protect the weld metal that melts during the welding process. This flux will become a slag when it is solid.
Shielded metal arc welding (SMAW) is generally called manual welding, which is broadly used for the
welding of steels such as carbon steels and alloy steels and nonferrous metals such as nickel alloys and copper alloys. In SMAW, an arc is generated by applying AC or DC currents across
the covered arc welding electrode (refer to as covered electrode hereinafter) which consists of a metallic cored rod and its covering (flux), and the metal to be welded (base metal). The heat of the arc (approx. 5000—6000K) melts the covered electrode and base metal, forming the weld metal for joining the base metal.
SMAW is easy to use because of simple equipment, and it can be used for wide applications. Therefore, SMAW has been used as the main welding process for a long time. Nevertheless, the usage ratio of SMAW has been reduced in tandem with the rapid expansion of the use of the CO2 gas arc welding process which is superior to SMAW in the cost performance.
The drooping characteristic power sources are used in SMAW. Power sources used in Japan are mostly AC power sources. DC power sources are used especially in cases where the arc stability is the primary concern as in the welding of carbon steel and low alloy steel sheet metals and pipes and the welding of stainless steels. By contrast, the usage ratio of DC power sources is high in Europe and the USA. A covered electrode is held by the electrode holder to manipulate along the welding line. The covering ﬂux plays important roles in workability and the weld joint properties in SMAW. The function of the covering ﬂux differs depending on the composition of the ﬂux. The covering flux is generally classiﬁed into low hydrogen type and non—low hydrogen type (ilmenite type, lime titanium type, high titanium oxide type, etc.).
In the SMAW welding process, there are three types or types of welding machines, namely AC, DC, and AC / DC machines. All types of welding machines have their own advantages and disadvantages, You can buy a type of AC / DC welding machine. For the SMAW engine with DC current, it is further divided into two polarities, namely DCEP polarity (Positive Direct Current Electrode) and DCEN (Negative Direct Current Electrode).
Positive Direct Current Electrodes – DCEP.
in DCEP, positive pole SMAW welding machine connected by a cable to the holder or electrode cable. While the negative pole is associated with a workpiece, this polarity is also called DCRP (Direct Current Reverse Polarity).
Direct Negative Current Electrodes – DCEN
in DCEN, a negative pole SMAW welding machine connected with an electrode cable, while a positive pole is connected to a workpiece, this Polarity is also called DCSP (Direct Current Straight Polarity).