What Are They?
The slang in French for a bar or pub is “le zinc,” bar counters in France used to be clad in zinc – many still are – to protect them from the ravages of wine and beer. Bar surfaces have complex shapes – a flat top, curved profiles, rounded, or profiled edges. These two sentences say much about zinc: it is hygienic; it survives exposure to acids (wine), to alkalis (cleaning fluids), to misuse (drunk customers), and it is easy to shape. These remain among the reasons it is still used today. Another is the “castability” of zinc alloys – their low melting point and fluidity give them a leading place in die-casting. The molds are relatively cheap, and details are accurately reproduced.
Most zinc is used in galvanizing steel to improve corrosion resistance. Zinc die-casting alloys are strong enough for most consumer products; and the metal itself is cheap. They are the metallic answer to injection molded polymers. Zinc alloys offer higher strength than other die-casting alloys except those of copper. Die-cast parts can be held to close tolerances in thin sections and are easily machined. Wrought zinc is available as strip, sheet, foil, plate, rod, wire, and blanks for forging or extrusion. Bends in rolled zinc sheet should be at right angles to the grain or rolling direction and should have a radius no less than the sheet thickness.
Roofing, gutters, flashlight reflectors, fruit jar caps, radio shielding, gaskets, photoengraving plates, handles, gears, automotive components, kitchen countertops, protective plating.
Zinc vapor is toxic – if you inhale it you get the “spelter-shakes” – but adequate protection is now universal. In all other ways zinc is a star: it is non-toxic, has low energy content and – in bulk – can be recycled (not, of course, as plating).
Most zinc alloys are die-cast; for this, the prime alloys are AG40A and AC41A. Wrought zinc is made by hot rolling cast sheets, by extrusion, or by drawing. Zinc foil is made by electroplating zinc on an aluminum drum and then stripping it off. Superplastic zinc alloys can be formed by methods normally used for polymers – vacuum forming, compression molding – as well as traditional metal processes like deep drawing and impact extrusion. Extrusion and forging is done with zinc-manganese alloys. Wrought zinc alloys are easily soldered and spot welded. Zinc is frequently left uncoated. It can be polished, textured, plated, or painted.