Oxy-Acetylene Torch

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What I'm going to reveal here might come as a rewarding surprise: a wide variety of "thin metals" (those less than .090") can be joined to each other and to themselves in several ways: welding, brazing, hard soldering, silver soldering, and soft soldering.

The following are authentic, practical methods endorsed and used throughout American Industry today, and have been obtained through the American Welding Society, The Aluminum Association, Alcoa, Reynolds, old engineering texts, Navy aircraft training manuals, and rubbing elbows at the workbench with many old, highly-skilled master craftsmen.

The author's 30 years solving restoration joining problems for Harrah's Auto Collection, Nethercutt, and other private collections insures accurate appropriate technologies, free from myth and legend. First, some history: The oxy-acet torch was developed at the turn of the century, shortly after the discovery of acetylene, and subsequently the cutting torch revolutionized the shipbuilding industry to this extent: Where three men would take 18 hrs to drill and chisel a porthole in 6" plate for a common ship, the torch allowed one man to do it in 20 minutes!

By 1920, mild steel, stainless steel, cast iron, and aluminum were all being welded with the torch. Brazing steel and iron with brass alloys, and brazing stainless, copper, brass, and steel with silver alloys soon became popular.

By WWII, 4130 chromemoly, magnesium, monel, and inconel were being welded with oxy-acet, and aluminum brazing and soldering were commonly used in aircraft tank construction. Even with the discovery of the TIG welder (heliarc) in So. Cal. in 1942, the torch remained a mainstay until the mid-1950s, when the TIG finally became more widely accepted.

By the 1990s, aircraft and aerospace firms were still gas welding aluminum, and the markets for brazing aluminum heat exchangers, silver brazing copper and stainless, and soldering stainless and aluminum with the good old torch have never been better.Definitions: Soldering, or more accurately soft soldering occurs at temperatures from 250F to 650F. Copper, brass, stainless, aluminum, steel, and cast iron may be soft soldered, if the alloy of the solder and the flu x are correct.

Fluxes are important, because they clean the joining surfaces, prevent oxidation, and then "tin" the joint surfaces to allow the solder alloy to then flow into the joint. Lead/tin alloys like 30/70, 60/40, 50/50 are used for steel, cast iron, copper, and brass, while a 63/37 (Sn63 Latin-Stannum) is used for stainless. Because of lead hazards, new lead-free alloys are available using antimony Sb (Latin-Stibium).

SOLDERING: Soft soldering occurs from 150 Deg. F to 850F, because of those zinc diecast alloys.

However, if the parent metal melts, as in lead (Pb) welding, then it truly is welding at around 475F (although the old slang is "lead burning"). If we melt brass to join brass then we are welding, although it might also be referred to as "braze-welding". Aluminum has been soldered for many years, sometimes using a special flux or not, and soldering alloy, and the technique requires practice and finesse.

Zinc diecast parts may be soldered using a variety of fluxes and solders, many borrowed from other industries, but the soldering is a good way to restore for plating (unless the hardening matrix material is used). Tools for this may be the propane torch, a soldering iron, or a small oxy-acet torch.

The universal rule is: clean for grease and oil with a good solvent such as isopropyl, and then for both oxides and dirt with a stainless or bronze brush. Warm while adding flux, waiting for more dirt to free up. Scrub again, warm, and add flux again. The most difficult items will be tarnished brass and copper, stainless, and aluminum- hardest. Some filler rods appear to be bare and contain no flux. Be not deceived, as despite the cries of the flea-market hawkers, the techrep PhDs at the manufacturers assure me that fluxes are embedded in the filler material!

BRAZING: Commonly done with the oxy-acet torch at a temp over 850degF, other fuel gasses may be used as well: Propane, MAPP, propylene, natural gas, and hydrogen can be used with many torches, but check with the manufacturer for parts adjustments. Again, fluxes, procedure, and fillers save the day.

Silverbrazing is the same as hard soldering, where a silver alloy (5% to 45%) flows smoothly into fine joints to join carbide, steel, stainless, copper, brass, white brass, German Silver, bronze, and others. English bicycle, motorcycle, and race-car frames have been hard soldered for decades, as was the Crosley sheetmetal engine, made in Oakland, California (although far too complex for torch work, it was furnace-brazed). Aluminum aircraft tanks have had bungs (or fittings) brazed in since the 1930s, after having been gas welded.

Aluminum brazing materials are sometimes sold as welding materials, so caveat emptor, or let the buyer beware, as joints made in this fashion must be cut out completely if they fail, as it is hopeless to weld over braze.

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