Welding Technology Questions and Answers

Answer: B

The commonly used brazing flux is borax.

Brazing is done at higher temperatures than soldering (above about 450 °C), and borax melts into a glassy layer at those temperatures that dissolves oxides and keeps air off the joint, letting the filler metal wet and flow into it.

Rosin and zinc chloride are soldering fluxes: rosin for electrical work and zinc chloride for general sheet-metal soldering; both work at soldering temperatures, not brazing ones. Lead sulphide is not a flux.

Answer: C

The principal materials of solder are tin and lead.

Traditional soft solder is a tin-lead alloy, typically 60/40 or 63/37 tin to lead, which melts at about 183 °C to 190 °C, low enough to join electrical connections and sheet metal without melting the parts. Lead-free solders now replace the lead with small amounts of copper, silver or bismuth, but tin remains the main metal.

Copper is the metal usually being soldered, not the solder, and zinc-lead and tin-copper pairs are not the classic soldering alloy.

Answer: A

Flux in soldering is used to prevent formation of oxide.

Solder will not wet a surface covered with oxide. The flux cleans away the thin oxide film and shields the joint from air while it is hot, so fresh oxide cannot form and the solder can flow and bond to the clean metal.

Flux does not lower the melting point of the solder, which is set by the alloy's composition, and it does not wash away surplus solder. Since those two are false, 'All of the above' is wrong.

Answer: D

Copper is used because it is a good conductor of heat.

The bit of a soldering iron must take heat from the heater (or flame) and pass it quickly to the joint, so that the solder melts and flows. Copper is one of the best thermal conductors among common metals, and solder wets it easily, which is why the bit is made of copper.

Weight and thermal expansion are not reasons for choosing it, and a bad conductor of heat would be useless for a soldering bit.