Basic propane torches are one example of the class "air-fuel" torches. There are also high-temperature examples called "oxygen-fuel" torches, such as the "Oxy-propane" torch. Fuel flowing through the torch body ignites with air or oxygen and produces a clean, steady flame which can then be used to heat an object, such as a metal sheet, ready for welding. Temperatures of Oxy-propane torches can reach 3,500 degrees Celsius, according to welding procedures.
Purchase a quality high temperature Oxy-propane cylinder torch to enable you to perform welding, rather than simple, low temperature soldering or light brazing. Look for a torch with two hoses, one red (for the fuel supply) and one green (for the oxygen supply). Purchase a cylinder of propane and a cylinder of oxygen. Propane cylinders for domestic applications range from 46 inches to 287 inches in length, according to leading supplier American Welding and Tank.
Link the torch hoses to the correct cylinders. Tighten the connectors using an adjustable wrench. Check the position of all the valves. Adjust the fuel flow valve first. Work slowly and steadily to achieve the best flame. Make sure the fuel valve is open as you begin to light the torch. Use a spark lighter (not a butane lighter) to light the fuel. Turn the adjustment knob down when the torch is lit to control the flame. Aim for a steady flame.
Adjust the oxygen flow to maintain the flame. Look at the flame itself. Increase the oxygen input very slowly. Aim to create a deep centrally-located blue cone inside the flame because this means you have got the level of oxygen right. If the flame burns yellow, there is too much fuel compared to oxygen, so adjust the fuel knob down and the oxygen knob up.
Begin to heat your metal workpiece slowly. Keep the torch moving rather than holding still in one location because that way you will avoid burning holes in your work. Apply a base metal or flux (can be found at your local hardware store) if you are welding anything other than carbon-based steel to form the joint filler. Heat the base metal slowly with the torch as you go along. Let it run into the joint and fix the two edges of the workpiece together.
Adjust the tip size when the torch is cool and switched off if you need to tackle different sized welding projects. For a smaller weld, try a smaller tip and vice versa. Use a trial-and-error technique to get the exact size of tip that suits your purposes. Clean the tips regularly with a damp cloth to remove old filler.
Perform regular propane leak tests, required by law, to ensure your system is safe. Turn the system off. Open and close all valves to check they work effectively. Replace loose or broken valves immediately. Check all seals in the system, particularly in the fuel and oxygen tanks and hoses. Replace damaged seals or purchase new components. Check threads and fixings are in good condition. Replace if any threads are burred.
Do not try torch welding with stainless steel because it does not work. You need to perform steel brazing on stainless steel surfaces.
Oxygen cylinders are highly explosive if heated or broken, so keep them cool, out of the sun and away from naked flames. Replace a torch with faulty valves because if fuel and oxygen are allowed to blow backwards from the hot torch, an explosion will occur causing damage to property, injury to you and in the worst cases, death. Do not touch the tip of the propane torch or attempt to replace the tip when the device is on or still hot from previous use as you will burn your hands. Never use butane lighters with molten metal as a metal drip entering the lighter will cause it to explode and this can lead to serious facial and arm injuries. Wear protective clothing, gloves and head and eye protection at all times.