|Solders, which are tin-lead alloys in different proportions depending on the purpose, consume one third of the produces tin. Alloy with 62% Tin and 38% Lead, is called eutectic of Sn-Pb system with minimal melting temperature. It is used in electronics. Other lead-tin alloys such as 30% Sn + 70% Pb, which have a broad solidifying zone, are used in pipelines welding as welding filler. Solders without lead are also used. Tin-copper (-antimony) materials are used as antifriction alloys (babbit, bronze) as bearing alloys. Contemporary tin-lead alloys contain 90-97% Sn with slight antimony and copper dopant for strengthening. Today's tin articles are quite safe. |
Tin is used for protective and decorative coating immersing the article into the molten metal; however most articles are coated by tin alloys with lead, copper, nickel, zinc and cobalt are coated by electroplating.
Old Tin applications
|Because it resists the action of air, water and vegetable acids, and so keeps a bright surface, tin is a very useful metal for household and technical purposes. It is employed alone in place of lead for making pipes used for condensation in distilling industries, and also in the form of tin-foil, now so widely used for wrapping purposes. Its chief use, however, is as a coating for other metals, i.e. for tin-plate; it is also a constituent of a number of important alloys shortly to be described. |
The manufacture of tin-foil depends on the property of tin, which it shares with other metals, of becoming malleable at an elevated temperature. Thus at 100° C. tin is sufficiently malleable to be rolled into thin sheet and foil. Tin-foil was formerly much used in an amalgamated state for making mirrors, but it has now been largely replaced by silver.
The art of tinning brass and copper was known to the Romans, and so thin was the coating obtained by them that Pliny states that copper when tinned does not increase in weight. The tinning of iron, which is the most important part of the modern industry, probably originated in Bohemia early in the seventeenth century. An English tin-plate company was formed in 1670; and the industry flourishes now chiefly in South Wales.
Formerly wrought-iron formed the basis of tin-plate, but now Siemens' mild steel is chiefly employed. Bars of mild steel are rolled into plates of suitable thickness, which are " pickled " in dilute sulphuric or hydrochloric acid, annealed, cold-rolled, reannealed at lower temperature, pickled again in weaker acid, washed with water, and introduced, wet, into the tinning machine. This consists of a box containing molten tin and divided by a partition extending into the metal. On one half of the molten metal a flux of zinc chloride floats, on the other half is a layer of hot grease. The plate is passed through the flux into the molten metal and under the partition, so as to emerge through the grease. It is then passed through rollers which remove rurplus tin and induce a smooth and bright surface on the plate.
Formerly the plate was treated in a series of pots, in which it was first dried in hot grease, then coated with tin, and afterwards brushed with oil to cause an alloy of tin and iron to be formed; then it was immersed in a pot of purest tin, covered with oil, to give it a second coating, and passed through rollers immersed in hot oil; it was next cooled in oil, and finally cleansed by being scrubbed with bran and chalk. Copper, brass, or iron wire is tinned by being wound off a drum through cleaning and rinsing vats and a drying medium, and then through molten tin. A vessel is tinned on its interior by means of molten tin poured into it whilst it is hot; the tin is then rubbed over the surface by rags, a little rosin or sal ammoniac being employed to prevent oxidation.