Joining Metals: notes

Soldering and brazing

• Soft soldering: uses a tin and lead alloy that melts at about 180 to 250 degrees C. It makes weak joints for electrical work and tin plate.
• Flux: cleans the surface and stops oxide forming so the filler flows. Use resin on electrical work and a zinc chloride flux on steel.
• Brazing: uses brass filler melted above 450 degrees C. The joint is much stronger than solder. The parent metal does not melt.

Welding

• Gas welding: oxy-acetylene flame melts the edges and a filler rod. Flame temperature is about 3 200 degrees C. The neutral flame is used for most steel.
• Arc welding: an electric arc between electrode and work melts the metal. The flux coating on the electrode makes a gas shield and slag that protects the weld.
• Defects: porosity (gas holes), undercut (a groove at the toe) and lack of fusion.
• Safety: wear a helmet, gloves and leather apron. Keep the gas cylinders upright and chained.

Mechanical fastening

• Rivets: permanent joints. Snap head and countersunk heads are common.
• Bolts, nuts and screws: removable joints. A washer spreads the load.
• Adhesives: epoxy resin glues metal to metal where heat is not wanted.

Choosing

• Permanent and strong: welding. Removable: bolts. Thin and leak proof: soldering.