Lead burning is a welding process used to join lead sheet. It is a manual process carried out by gas welding, usually oxy-acetylene.
Lead burning is a welding process used to join lead sheet. It is a manual process carried out by gas welding, usually oxy-acetylene.
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 leadworking 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 specialised, this work is still carried out today and not just for 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 plumber's solder (80% lead / 20% tin) and is carried out at 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. [1]
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. [2] Soldering, by contrast, uses a solder alloy that is some compatible alloy showing eutectic behaviour. 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 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 oxidising flame burns the lead and creates lead oxide dross, leading to poor welds with low malleability.
Lead burning requires a gas torch as autogenous processes require an intense, controllable flame that can be applied to a small area. It was first developed along with the early growth of the bulk chemical industry, as acid manufacture required leakproof lead vessels and flow process plumbing to be made. At the same time, coal gas was increasingly available for domestic lighting. By using a mouth-blown blowpipe, a gas flame could reach temperatures adequate for lead burning. Larger equipment could use mechanical fans.
Before this, leadworking used either manual bossing or wiped soldered joints to seal it.
Lead burning, and lead soldering, are some of the few building processes which still requires the on-site use of a naked flame. This has obvious safety hazards and lead working has been implicated in some fires during restoration work on historical buildings.
Metallic lead is relatively safe to work with, although lead oxide dross formed on the surface of lead is more easily absorbed by the body, thus much more of a hazard. As lead burning is a high temperature process, it creates a significant hazard from such dross. Safety precautions are relatively simple: goggles to protect the eyes from molten metal splash, overalls or dustcoat kept in the lead workshop to stop contamination spreading, and dedicated workbenches equipped with air extraction.
Regular lead burners should be screened for accumulated lead exposure. Industrially this is done by weekly checks for blue lines around the gums, a simple indicator for heavy metal poisoning, and by regular urine testing.
Acetylene is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.
Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent welding using chemicals to melt materials being bonded without heat, and solid-state welding processes which bond without melting, such as pressure, cold welding, and diffusion bonding.
Metalworking is the process of shaping and reshaping metals in order to create useful objects, parts, assemblies, and large scale structures. As a term, it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges, down to precise engine parts and delicate jewelry.
Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
MAPP gas was a trademarked name, belonging to The Linde Group, a division of the former global chemical giant Union Carbide, for a fuel gas based on a stabilized mixture of methylacetylene (propyne), propadiene and propane. The name comes from the original chemical composition, methylacetylene-propadiene propane. "MAPP gas" is also widely used as a generic name for UN 1060 stabilised methylacetylene-propadiene.
Gas tungsten arc welding is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas. A filler metal is normally used, though some welds, known as 'autogenous welds', or 'fusion welds' do not require it. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.
Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode and the workpiece. The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch, so the plasma arc is separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities and a temperature approaching 28,000 °C (50,000 °F) or higher.
In metalworking, a filler metal is a metal added in the making of a joint through welding, brazing, or soldering.
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches to process refractory materials and was the first gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
Atomic hydrogen welding is an arc welding process that uses an arc between two tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen. The electric arc efficiently breaks up the hydrogen molecules, which later recombine with tremendous release of heat, reaching temperatures from 3400 to 4000 °C. Without the arc, an oxyhydrogen torch can only reach 2800 °C. This is the third-hottest flame after dicyanoacetylene at 4987 °C and cyanogen at 4525 °C. An acetylene torch merely reaches 3300 °C. This device may be called an atomic hydrogen torch, nascent hydrogen torch or Langmuir torch. The process was also known as arc-atom welding.
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members.
A pipefitter or steamfitter is a tradesman who installs, assembles, fabricates, maintains, and repairs mechanical piping systems. Pipefitters usually begin as helpers or apprentices. Journeyman pipefitters deal with industrial/commercial/marine piping and heating/cooling systems. Typical industrial process pipe is under high pressure, which requires metals such as carbon steel, stainless steel, and many different alloy metals fused together through precise cutting, threading, grooving, bending, and welding. A plumber concentrates on lower pressure piping systems for sewage and potable tap water in the industrial, commercial, institutional, or residential atmosphere. Utility piping typically consists of copper, PVC, CPVC, polyethylene, and galvanized pipe, which is typically glued, soldered, or threaded. Other types of piping systems include steam, ventilation, hydraulics, chemicals, fuel, and oil.
Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld or cut metals. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903. Pure oxygen, instead of air, is used to increase the flame temperature to allow localized melting of the workpiece material in a room environment.
Soldering is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.
Fusion welding is a generic term for welding processes that rely on melting to join materials of similar compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created in the material.
Copper tubing is available in two basic types of tube—plumbing tube and air conditioning/refrigeration (ACR) tube, and in both drawn (hard) and annealed (soft) tempers. Because of its high level of corrosion resistance, it is used for water distribution systems, oil fuel transfer lines, non-flammable medical-gas systems, and as a refrigerant line in HVAC systems. Copper tubing is joined using flare connection, compression connection, pressed connection, or solder.
A blowtorch, also referred to as a blowlamp, is an ambient air fuel-burning tool used for applying flame and heat to various applications, usually in metalworking.
In metalworking, weld pool commonly refers to the dime-sized workable portion of a weld where the base metal has reached its melting point and is ready to be infused with filler material. The weld pool is central to the success of the welding process. It was first observed in oxy-fuel welding by Fouché & Picard in 1903, after the discovery of acetylene by Edmund Davy in 1836.
A wiped joint is a form of soldered joint used to join lead pipework.
Autogenous welding is a form of welding in which the filler material is either supplied by melting the base material or is of identical composition. The weld may be formed entirely by melting parts of the base metal, and no additional filler rod is used.