Joining-lead-tin-zinc:

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Joining-lead-tin-zinc, lead flame welding, tinplate spotwelding, galvanized sheets resistance welding, coated steel for corrosion protection, low temp. melt metals, plumbing, storage batteries, lead poisoning, health and safety precautions. These and other subjects are detailed hereafter for providing answers to interested readers.

What is in here for me?

Basically we provide in this page important information on three common and economically useful metals and on their joining characteristics, which make them stand apart from other more known materials.

Joining-lead-tin-zinc is presented in this combined page with some of the most important characteristics of these three metals, Lead, Tin and Zinc, grouped together. They have quite important economic applications and they have a long history as they served the human kind for a long time.

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Although they all present quite low melting temperature, Joining-lead-tin-zinc is rarely performed as welding proper except for resistance welding used for coated steel sheets: other processes are usually preferred. Lead, Tin and Zinc are all known for their outstanding resistance to corrosion when exposed to atmosphere and other environmental agents. These metals are quite soft. Their low strength and hardness are not the important properties being exploited in their most common uses.

Table I
Melting Point and Density (at R.T.)

Metal	Symbol	Melting Point		Density
		oC	oF	g/cm3	lb./in.3
Lead	Pb	326	618	11.34	0.41
Tin	Sn	232	450	7.30	0.26
Zinc	Zn	420	787	7.13	0.26

Lead

Lead is a very corrosion-resistant, dense, ductile, and malleable blue-gray metal that has been used for at least 5,000 years. It was made in figures and ornamental items, in money coins and in structures. It was used by Romans for water pipes still visible in archaeological sites: the pipes were made by folding heavy sheets of cast lead and by fusing the seams together.

Lead has a low Coefficient of Thermal Expansion and is not a good conductor of heat and electricity. The metal is covered immediately by an oxide layer that prevents further oxidation. Lead is resistant to attack by many acids and therefore it is used in the chemical industry for lining acid containing tanks.

Lead high density is sometimes exploited when it is required to concentrate heavy weight in limited space. While considering Joining-lead-tin-zinc, Lead is the only one of the three that can be welded by the oxy acetylenic flame with a special low heat torch. The molten metal puddle is not glaring. It may run away by gravity however if not retained (as in lap joints).

Lead can be rolled into thin sheets ready to be stamped in useful forms that can be fabricated by welding or soldering. A singular type of Joining-lead-tin-zinc is performed as cold weld into a single mass of solid metal seal, by using a loose rope of fine lead fibers, called lead wool, forced (caulked) into crevices under pressure. This solution is useful for sealing where flame heating cannot be used.

Lead roof coverings of ancient buildings from centuries ago still stand in perfect condition. Lead is still widely used in pipes and accessories in the plumbing industry. (The name "plumbum" is lead in Latin). One of its largest uses is in lead storage batteries. Bearing alloys and soldering alloys of various compositions use up large quantities of this metal although there is a recent trend to try to limit lead use because of perceived risks to safety and wellbeing of workers and public in general. Shielding for radiography and isotope containers depend on lead for protection from ionizing radiation.

The "Lead Safe Housing Rule" was published in the Federal Register on September 15, 1999. The requirements apply to housing built before 1978, the year lead- based paint was banned nationwide in the USA for consumer use.

There is an increasing awareness of the dangers of Childhood Lead Poisoning, possibly originating from lead-based paints still available in old houses. Advisory help is provided by Centers for Disease Control and Prevention, at
http://www.cdc.gov/nceh/lead/lead.htm
Articles on the dangers of lead exposure can be found in
http://www.osha.gov/SLTC/lead/

Tin

Tin is one of the earliest metals known and used. Because of its hardening effect on copper, tin was used in bronze implements and decorative articles as early as 3,500 B.C.

A white soft metal melting at low temperature, tin is mostly used as a coating for steel. Once produced by the hot dip method, tinplate is now made by electrolytic deposition on continuous strips of rolled steel. Tinplate has long been used for food containers, being non toxic and corrosion resistant.

Unalloyed tin is the best lining material for handling high-purity water in distillation plants because it is chemically inert to pure water and will not contaminate it.

Tin has long been used as an alloying element of copper, for bronze cast in bells and statues. Bearing alloys called babbitts present low coefficient of friction and sufficient wear resistance to be used for demanding applications.

Alloyed with Lead and other elements, and possibly accounting for the largest use of Tin, it is an essential component of many solders. Solders used for food containers should be lead free. Whenever practical, soldering of tinplate is the preferred method for Joining-lead-tin-zinc, performed with a suitable solder. For reading the page on this site dealing with Soldering, click here.

Joining-lead-tin-zinc by Projection welding of tinplate is sometimes preferred to spot welding because of less contamination (electrode pickup) being produced on the electrodes faces. This can be controlled by taking care that the current density at the electrodes face be low, by paying special attention to their size and shape.

The joint for Joining-lead-tin-zinc should be so designed that the metal coating (tin or zinc) can be expelled or extruded from between the surfaces to allow formation of a nugget in the base metal. The hold time including cooling time under pressure should be long enough to permit the molten coating metal to solidify at the interface near the weld nugget.

Zinc

Centuries before zinc was recognized as a distinct element, zinc ores were used for making brass (an alloy of copper and zinc). Unalloyed zinc is a white metal that can be readily cast or fabricated in wrought form.

Its most known and useful property is its good resistance to atmospheric corrosion, making zinc the most effective of the common sacrificial coatings for steel. Hot dip galvanizing is used for complex steel fabricated structural elements. Continuous electroplating is now preferred for zinc plated steel sheet production.

Conventional strip galvanizing makes use of an alloy with a nominal content of 0.20% Al and a balance of zinc. The coating is known for excellent adhesion and formability. This and the good weldability for Joining-lead-tin-zinc by conventional welding techniques, make strip galvanizing particularly attractive for automobile manufacturing.

Galvanized strip is also used in the building industry, where significant quantities are used in prepainted condition. The appliance industry is also a large consumer of both painted and unpainted galvanized strip.

Some galvanized strip is subjected to a heat treatment known as galvannealing that converts the coating to an iron-zinc alloy. New strip coatings, designated by commercial names, and containing also some aluminum together with zinc were adopted because of improved corrosion resistance.

Besides for steel coating, zinc is used for producing die castings, it is an important alloying element in copper (for brass), aluminum, magnesium and other alloys, it is employed in wrought form as rolled sheet and extrusions, and for the manufacturing of chemicals like zinc oxide.

An interesting Joining-lead-tin-zinc method used for zinc castings consists in die casting a joint upon properly aligned zinc alloy cast parts. Zinc alloy die cast parts can have fasteners economically stud welded to them instead of integrally cast.

Stud welding is an arc welding process using a special gun holding the fastener to be welded very near to the base metal. An electric arc is struck between the two and melts the two surfaces. As soon as the heat generated is sufficient, the fastener is forced under pressure against the base and let solidify in place.

See our page on Stud Welding.

The Joining-lead-tin-zinc by stud welding does not destroy the decorative coating that may be previously applied to the castings. Other Joining-lead-tin-zinc processes for galvanized (zinc coated) steel include soldering and resistance welding.

Zinc coated steel, dip galvanized or electroplated are usually spot welded, except that the current must be higher than that normal for uncoated steel. The buildup of zinc on the electrode face must be controlled by regularly cleaning or replacing the electrodes.

Comparing Joining-lead-tin-zinc with spot welding of uncoated steel, shorter weld times and higher currents (by as much as 50%) are required, depending on thickness. Thinner sheets require proportionately higher currents than thicker sheets.

See the Welding Handbook Ninth Edition Volume 3 at page 41.
AWS WHB-3.9
Welding Handbook, 9th Edition, Volume 3, Welding Processes, Part 2
American Welding Society , 01-Jan-2007, 669 pages
Click to Order.

Also the electrode force used must be higher by 10 to 25% than that for uncoated steel, because the coating reduces considerably the surface resistance which is an important parameter in the following formula establishing the weld heat: