Lightweight and durable, aluminium tubing forms the skeleton for items such as performance bicycles and commercial airliners. It also forms the vacuum lines in some cars and industrial equipment. It accepts and dissipates heat quickly, making it a good electrical conductor. Tubing is joined through a welding process known as soldering. Most aluminium tubing is rated to 13608 Kilogram per square inch (psi) of pressure, which makes it ideal for high-pressure or high-flow applications when copper won't do. It also resists corrosion better than copper, making it more suitable for transfer of chemicals.
Measure and cut the tubes to the desired length using a chop or hacksaw. Be sure to account for depth in joints that will be welded later.
Drag the metal file over cut ends or rub them with emery cloth to remove any burs and dull the edges.
Press the joints onto tubing by hand, then strike them with a rubber mallet until you have a snug fit.
Ignite the propane torch and turn it to the highest setting. Note that depending on the torch, this may require a source of spark--a flint or match will do.
Place the inner tip of the flame over centre of the joint. Drag the flame back and forth and side to side over the joint for about 15 seconds.
Dip the aluminium solder rod into flux, then rub it over the seam. Apply liberally: Extra flux will not affect the quality of the weld. Continue to wave the torch over the joint with one hand while applying the flux.
Observe the behaviour of the flux: Once it starts to wick into seam, the joint is the proper temperature to accept solder.
Drag the tip of the solder rod over the seam and observe its behaviour. If the solder bubbles up, the tubing has cooled and needs more heat. If the solder draws into the joint, turn the tubing over and repeat. Note that tubing will be hot. Use pliers or heat-resistant gloves.
Monitoring the behaviour of flux and solder is the key to a successful weld. Watch closely. Also, when completing solder on the underside of tubing, it is important to act quickly: Overheating tubing can undo the work already completed on the top half.
The flame of a propane torch can reach temperatures exceeding 2,760 degrees C. Use extreme caution and never point toward the face or body. Even several inches away from flame, temperatures remain high enough to inflict third-degree burns.