Lead is a waterproof metal that melts easily and is less prone to corrosion, making it an ideal choice for many welding projects. Although lead is often used for automobile parts and pipes, it is highly toxic when handled improperly.
Take precautions by ventilating the area and wearing safety gear before turning on your torch. Then, use an oxyacetylene torch and a rod of lead solder to complete the bond. Whether you work with old or new pieces of lead, weld them to create a strong, long-lasting bond.
What is Lead Welding?
Lead burning is a welding process used to join lead sheets. It is a manual process carried out by gas welding, usually oxy-acetylene.
The welding of lead is similar to welding of other metals except that no flux is required. Processes other than gas welding are not in general use.
Lead can be identified by the color of an unfinished surface (white to gray), the color and structure of a newly fractured surface (light gray, crystalline), the color of a freshly filed surface (white).
Three combinations of gases are commonly used for lead welding:
- Oxygen-natural gas
The oxyacetylene and oxyhydrogen processes are satisfactory for all positions. The oxygen-natural gas is not used for overhead welding. A low gas pressure ranging from 1-1/2 to 5 psi (10.3 to 34.5 kPa) is generally used, depending on the type of weld to be made.
Lead Welding Torch
The welding torch is relatively small in size. The oxygen and flammable gas valves are located at the forward end of the handle so that they may be conveniently adjusted by the thumb of the holding hand.
Torch tips range in drill size from 78 to 68. The small tips are for 6.0 lb (2.7 kg) lead (i.e., 6.0 lb per sq ft), the larger tips for heavier lead.
The filler rods should be of the same composition as the lead to be welded. They range in size from 1/8 to 3/4 in. (3.2 to 19.1 mm) in diameter. The smaller sizes are used for lightweight lead and the larger sizes for heavier lead.
Lead Welding Process
Lead burning is an autogenous welding process. Two sheets of lead are formed mechanically to lie close against each other. They are then heated with the torch flame and flow together. No filler rod is required, the sheets form their own filler (autogenous welding). Neither is a flux used.
Soldering, by contrast, uses a solder alloy that is some compatible alloy showing eutectic behavior. This gives a melting point lower than the base metal, allowing a soldering process rather than welding. A filler rod may be needed for some welds if there is no convenient way to form sufficient close overlap at a sheet edge.
Offcuts of the same lead sheet are used as this filler. Excessive use of a filler, rather than an initial close fit, is considered a sign of poor technique.
The torch used for lead burning is a small, hot, gas flame. Oxy-acetylene is most commonly used, as it is easily portable. A small size #0 nozzle is usually used, sometimes with a miniature torch body, but the torch is otherwise the same as that used for steel or copper work.
A variety of fuel gases may be used, but to achieve the high temperature needed, an oxygen supply is always used. Fuel gases may be acetylene, natural gas, or hydrogen. Oxy-hydrogen is considered to be the best but is not easily portable.
Oxy-natural gas is the cheapest and is often used on fixed workbenches. As it is less hot, it cannot be used for some awkward positional (overhead) welding. Oxy-acetylene is the most common, as much leadwork is carried out on-site and this is easily portable.
A neutral flame is used. A reducing flame (fuel-rich) gives trouble with soot deposits in the weld. An oxidizing flame burns the lead and creates lead oxide dross, leading to poor welds with low malleability.
Application of Lead Welding
Lead burning is carried out for roofing work in sheet lead, or for the formation of custom-made rainwater goods: gutters, downspouts, and decorative hoppers. Decorative lead working may also use lead burning, particularly where a waterproof joint is required as for planters.
Lead burning is thus part of traditional plumber’s work, in its original sense of a worker in lead (Latin: plumbum). Although rare and specialized, this work is still carried out today and not just for the restoration of historical buildings.
Most lead sheet work is formed and sealed by bossing, a mechanical fold, or crimp. This is adequate for roofing that sheds water but is insufficiently watertight when standing water sits upon it and so an impermeable burned joint is needed.
Lead burning is not used as part of plumbing work for installed pipework. Lead piping has long been considered obsolete, owing to the health aspects. Even where lead piping, or lead-sheathed cable, still needs to be jointed, this is carried out with a wiped joint, rather than a burned joint.
Wiping a lead joint is a soldering process, using a plumber’s solder (80% lead / 20% tin) and is carried out at a low temperature, with a natural-draught propane blowtorch. Today, even wiped joints are rare and where an existing lead pipe must be connected to, a proprietary mechanical joint is more likely to be used.
In some rare cases within the chemical industry, lead burning is used for pipework, where acid-resistant tanks and pipes are required to be made of lead rather than steel. Niche uses for lead burning include the manufacture of lead plates for lead-acid batteries and for electro-plating electrodes.