Welding, Brazing and Soldering Processes
This domain tests joining processes, their temperature ranges, electrode coding, flame types and common weld defects.
Welding processes
- Manual metal arc (SMAW) uses a coated consumable electrode; the coating gives shielding gas and slag. In E6013, 60 means 60,000 psi minimum tensile strength, 1 means all positions, and 3 indicates a rutile coating. E7018 means 70,000 psi, all position, low-hydrogen iron powder coating, which must be stored in a heated drying oven.
- Gas welding uses an oxy-acetylene flame at about 3200 C. Neutral flame is roughly 1:1; carburising has excess acetylene and suits high-carbon steel and hard facing; oxidising has excess oxygen and suits brass.
- Resistance welding (spot, seam, projection) uses pressure plus current and no filler.
- TIG uses a non-consumable tungsten electrode with separate filler; MIG uses a continuous wire feed.
Joints and defects
Butt, lap, tee, corner and edge joints. Defects include porosity from gas, slag inclusion from poor cleaning, undercut from excessive current or a long arc, incomplete penetration from low current or wrong root gap, spatter, distortion and cracks.
Brazing and soldering
Brazing uses a filler melting above 450 C, typically 600-900 C, with borax flux. Soldering uses filler melting below 450 C, with rosin flux for electronics. Neither melts the parent metal; both rely on capillary action.
Worked example
Identify E7018: 70,000 psi tensile strength, all-position work, low-hydrogen coating usable on AC or DC electrode positive. Reasoning: the digits are read in order as strength, position, coating and current type, so the electrode suits restrained joints where hydrogen cracking is a risk.
Traps that cost marks
- Calling brazing a process that melts the parent metal.
- Using an oxidising flame on steel.
- Storing low-hydrogen electrodes in the open.
- Quenching a hot weld and causing cracks.