(a) General. Zinc is a medium low strength metal having a very low melting point. It is easy to machine, but coarse grain zinc should be heated to approximately 180°F (82°C) to avoid cleavage of crystals. Zinc can be soldered or welded, if it is properly cleaned and the heat input closely controlled.

(b) Zinc Uses. 1. Galvanizing metal is the largest use of zinc and is done by dipping the part in molten zinc or by electroplating it. Examples of items made in this way are galvanized pipe, tubing, sheet metal, wire, nails, and bolts. Zinc is also used as an alloying element in producing alloys such as brass and bronze. Those alloys that are made up primarily of zinc itself. 2. Typical parts made with zinc alloy are die castings, toys, ornaments, building equipment, carburetor and fuel pump bodies, instrument panels, wet and dry batteries, fuse plugs, pipe organ pipes, munitions, cooking utensils, and flux. Other forms of zinc include zinc oxide and zinc sulfide, widely used in paint and rubber, and zinc dust, which is used in the manufacture of explosives and chemical agents.

(c) Zinc Capabilities. Zinc can be cast, cold worked (extruded), machined, and welded.

(d) Zinc Limitations. Do not use zinc die castings in continuous contact with steam.

(e) Zinc Properties. Zinc has a tensile strength of 12,000 psi (82,740 kPa) (cast) and 27,000 psi (186,165 kPa) (rolled); a specific gravity of 7.1; a melting point of 790°F (421°C); is corrosion resistant; and is brittle at 220°F (104°C).

(f) Zinc Appearance. Both zinc and zinc alloys are blue-white in color when polished, and oxidize to gray.

(g) Zinc Fracture test. Zinc fractures appear somewhat granular.

(h) Zinc Spark test. Zinc and zinc alloys give off no sparks in a spark test.

(i) Zinc die castings. 1. Appearance test. Die castings are usually alloys of zinc, aluminum, magnesium, lead, and tin. They are light in weight, generally silvery white in color (like aluminum), and sometimes of intricate design. A die-cast surface is much smoother than that of a casting made in sand, and is almost as smooth as a machined surface. Sometimes, die castings darkened by use may be mistaken for malleable iron when judged simply by looks, but the die casting is lighter in weight and softer.
2. Fracture test. The surface of a zinc die casting is white and has a slight granular structure.

3. Spark test. Zinc die castings give off no sparks.

4. Torch test. Zinc die castings can be recognized by their low melting temperatures. The metal boils when heated with the oxyacetylene flame. A die casting, after thorough cleaning, can be welded with a carburizing flame using tin or aluminum solders as filler metal. If necessary, the die-cast part can be used as a pattern to make a new brass casting.

Comments

No comments yet.

Only registered users can comment.