Final answer:
Liquid fluxes are applied to metal joints prior to heating with a torch, such as in residential plumbing and on larger scales like railroad construction. The flux cleans and deoxidizes the joint, ensuring proper solder flow and bond strength when heat is applied from tools like propane torches or through reactions such as thermite reactions.
Step-by-step explanation:
Liquid fluxes can be delivered to the joint through the torch when soldering or brazing metal components. In the context of residential plumbing, specifically when soldering copper pipes, a propane torch might be used as illustrated in Figure 4.3.4. The flux functions as a cleaner and deoxidizer, which helps the solder flow smoothly into the joint and create a strong bond.
One common method for flux delivery is applying the flux directly onto the pipe surfaces before heating. The torch, such as a propane torch, then heats the joint to the appropriate temperature for the solder to melt and flow into the joint, with the flux preventing oxidation and improving wetting characteristics.
In larger scale applications such as railroads, a thermite reaction might be utilized as shown in Figure 4.3.1. This reaction creates high heat and liquid metal (iron), which can be guided into a mold around rail gaps, where the flux can also be added to refine the metal and remove impurities.