RRB ALP Welder (Gas & Electric) Trade — Complete CBT-2 Study Guide

• Arc welding (SMAW — Shielded Metal Arc Welding, "stick welding") uses a flux-coated electrode; the arc melts both the electrode and base metal, while the burning flux coating produces a shielding gas and slag layer that protects the molten weld pool from atmospheric contamination. • Gas welding (oxy-acetylene) burns a mixture of oxygen and acetylene gas to produce a high-temperature flame (~3200°C) that melts base metal and filler rod — offers good control for thin sheet metal and pipe work, though generally slower than arc welding. • Flame types in gas welding: Neutral flame (balanced oxygen-acetylene ratio, used for most general welding), Carburizing flame (excess acetylene, used for hard-facing), Oxidizing flame (excess oxygen, used mainly for brazing/braze-welding, NOT for regular steel welding as it causes oxidation of the weld). • Arc welding current type: AC (Alternating Current) or DC (Direct Current) — DC gives a smoother, more stable arc and is generally preferred for critical/precision work; DC polarity (DCEP/DCEN) affects heat distribution between electrode and workpiece.

• TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode with an inert shielding gas (typically argon); filler metal (if needed) is added separately by hand — produces the cleanest, highest-quality, most precise welds, well suited for thin materials and critical joints (aerospace, pipe welding), but slower and requires more operator skill. • MIG (Metal Inert Gas, also called GMAW) welding uses a continuously fed consumable wire electrode with a shielding gas (inert like argon, or active like CO2 mixtures) — faster than TIG, easier to learn, and well suited to production-line welding of thicker materials. • Shielding gas protects the molten weld pool from atmospheric oxygen and nitrogen, which would otherwise cause porosity and weakened welds — argon and CO2 (or their mixtures) are the most common shielding gases. • TIG generally produces a superior finish/quality weld but at lower speed; MIG is faster/more productive but with a slightly less refined finish — the choice depends on the application's quality requirement versus production speed needs.

• Brazing joins metals using a filler metal with a melting point ABOVE 450°C but below the base metal's melting point — the base metal itself is never melted, only the filler flows into the joint by capillary action, giving a strong joint with less thermal distortion than welding. • Soldering is similar to brazing but uses a filler metal (solder) melting BELOW 450°C — generally used for electrical connections and light-duty joints (e.g. plumbing pipe joints, electronic components), producing a weaker joint than brazing or welding. • Flux is used in both brazing and soldering to remove oxide films from the metal surfaces and improve filler-metal flow/wetting — without proper flux, the filler metal will not bond properly to an oxidized surface. • Braze-welding uses a brazing filler metal but applies it similarly to gas welding technique (fillet/groove build-up rather than capillary flow into a close-fitting joint) — useful for repair work and joining dissimilar metals.

• Arc welding produces intense ultraviolet and infrared radiation — a welding helmet with an appropriately rated dark filter lens is mandatory to protect eyes from "arc eye" (photokeratitis, a painful UV burn of the cornea) and skin from radiation burns. • Welding fumes contain metal oxides and gases that can be harmful if inhaled in enclosed/poorly ventilated spaces — adequate ventilation or fume extraction is essential, especially when welding galvanized/coated metals (zinc fumes can cause "metal fume fever"). • Fire hazards: welding sparks/spatter can travel several meters and ignite nearby combustible materials — the work area must be cleared of flammables, and a fire extinguisher should be kept accessible. • Personal protective equipment (PPE) for welding includes flame-resistant clothing/apron, welding gloves, safety boots, and the welding helmet — bare skin exposure to arc radiation or hot spatter/slag risks burns even from a short exposure.