The Oxy-Fuel process is considered old-school. It’s popular with artists who work with metal and also used for soldering or brazing dissimilar or non-ferrous metals. In most shops, acetylene gas is combined with oxygen to produce the torch flame. Acetylene produces more heat than other fuels, but some welders use propane, propylene or another gas in its place. None of the alternatives generate as much heat as acetylene, but are typically cost a lot less.
If you’re unfamiliar with Oxy-Fuel welding, take a moment to watch this video:
As the narrator explains, gas rods are typically sold in three-foot lengths. The rods come in a 1-pound tube or 50-pound box, with a minimum tensile strength of either 45,000 or 60,000 PSI. They usually have a thin protective sheath of copper to prevent oxidation (i.e. rust) and come in six different diameters (1/16, 3/32, 1/8, 5/32, 3/16 and 1/4 inch). These roughly correspond to the six welding tips available for use on Oxy torches. (FYI — Most kits for sale only include one or two tips.)
Here’s a table that matches up welding tips to the thickness of the base metal you’re working with:
Metal Thickness – Tip Size
1/4 – 1/2 = 5
3/16 – 1/4 = 4
1/8 – 3/16 = 3
1/16 – 1/8 = 2
5/64 – 3/32 = 1
3/64 – 5/64 = 0 (The zero tip is called an “ought”)
1/32 – 3/64 = 00 (“double ought”)
1/64 – 1/32 = 000 (“triple ought”)
Of course, it’s not an exact science. If you only have one or two tips, or one size of rod to work with, you can often complete the job by increasing or decreasing your torch flame, or laying down multiple passes. In addition, when purchasing new sheet metal, you may need to convert the gauge of the material to its fractional equivalent so you can figure out the right tip.
Remember, the higher the gauge, the thinner the sheet. (With wire gauges, it’s just the opposite.) Gauge 3 sheet metal, for example, represents a meaty 1/4 inch, whereas Gauge 16 is just 1/16 inch.
Carbon steel welding rods have a copper coating to prevent rusting and oxide build-up. The AWS classification for these products is pretty straightforward. Most welders use RG-45 or RG-60 rods. Here’s what the designation means:
RG – Rod Gas
45 – tensile strength times 10,000 = 45,000 PSI
RG-65 is a less commonly used, low-alloy rod designed for high speed fusion welding of pressure vessels, tanks and piping.
Brazing aluminum and other metals with the Oxy-Fuel process is also possible. In brazing, the filler rod’s melting point is much lower than that of the base metal, which is why the process is used primarily for non-ferrous metals. Brazing doesn’t fuse metal like welding. It just bonds the two sides together. Soldering does exactly the same thing, only the heat generated must be less than 88 degrees Fahrenheit.
By turning down the torch flame, you can use the Oxy-Fuel process to perform either process. While steel melts at around 2700 degrees farenheit, for copper and gold it’s 2000, brass 1700, aluminum 1200, silver 960, lead at 650 and tin at 450. Thus, lead, and tin are used as solder metals. (For more temperatures of different metals, here’s the full list.)
Meanwhile, the two sides of the joint must be coated with a flux before brazing or soldering. The flux helps create the bond by cleaning the metal and preventing oxides from forming that will obstruct the braze. With that protection in place, it’s the chemistry of capillary action that causes the molten filler to bond with both sides of the base metal, leaving behind a solid joint.
Aluminum rod comes in two varieties, according to Airgas, which sells a lot of it – bare and flux-cored. Bare is recommended for brazing thin sheets, extruded shapes and corner joints. The flux-cored version has a non-corrosive, non-hygroscopic flux inside a tubular rod, which in plain English means you don’t need to apply a separate flux. (Hygroscopic refers to a material that readily absorbs air moisture.)
Next: Compressed Gases