TYPES OF METAL

As a start to learning the skills of metalwork it is worth knowing something of the various metals available and their typical uses and properties. It is useful to know, for example, whether a metal is strong and if it can be easily bent, filed, soldered, drilled, welded and so on. A number of the metals you may be dealing with are described below to provide a guide to choosing the right material for the work you have in mind and to help you avoid wrong handling which could prevent a good result. MILD STEEL Consisting of iron with a small percentage of carbon, this is probably the metal most commonly used by the home worker. It is easy to file, saw, drill and join by welding. It can be soldered, but the strength of the joint relative to the strength of the steel is low and it is better joined by brazing, where an alloy of brass and zinc instead of normal solder is used. This is heated by means of a propane torch or similar device to a higher temperature than when soldering and forms a stronger bond.

A strong material in that it can carry a heavy load without failing, mild steel is also relatively soft and is therefore not very resistant to indentation. To combat this, it can be hardened on the outside by a process known as case-hardening, where the surface of the steel is hardened and the inside remains soft. Available as rods, strips, bars and sheets, it is either black in colour or brightly polished, depending on the method of manufacture. It is used industrially for structures such as girders. Around the home it can be used for repair and construction work where strength is required, for furniture making and for pot stands and other small-scale objects.

Because it rusts easily it should be protected by paint if it is to be used outdoors and by a coating of clear lacquer if used indoors. ALUMINIUM Another metal which is readily available and which can be put to good use in the home, aluminium is soft, lightweight and ductile and is therefore easy to bend, form, file and saw.,It is very resistant to corrosion and is a good conductor of electricity. In its pure form it is a low strength material; but it can be strengthened by alloying with other metals although this process may weaken its corrosion resistance.

Special solders are required for soldering aluminium, and special filler materials and fluxes which promote better fusion are needed when welding. Bending or other working makes it hard but it will soften again when heated to about 400°C. It comes as foil, sheet, rod, bar, plate, wire and tubing and is similar to silver in colour, but with a slight bluish tinge. Like mild steel it is widely used industrially; for domestic purposes, it is suitable for lightweight work including making kitchen utensils, light furniture, boxes and sculptures.

Aluminium alloy The one you are most likely to use for home metalwork has a six percent copper content. It is light, resistant to corrosion and nearly as strong as mild steel. In its original state it is hard to work; but after annealing it will bend, fold and work well. It can be hardened by a form of age-hardening, where it is heated then rapidly cooled or quenched by being plunged into cold water and then left to harden, which in the case of this particular metal is a relatively short period.

Available as sheet, rod and section, this alloy has endless uses in construction and is suitable for use on shelving systems, chair legs, claddings and other structures where lightweight but strong material is required. Cast iron An alloy of carbon and steel, cast iron has two main classes: grey and white – so called because of the metal’s appearance when it is fractured. Grey cast iron has a crystalline appearance at the fracture due to the presence of graphite flakes; the graphite gives cast iron its self-lubricating properties when it is being machined or used for sliding surfaces on machinery. Cast iron is cheap and, because it flows easily when molten, can be cast into very complicated shapes; but the temperature required to melt it is not readily attainable in domestic circumstances. The main disadvantage of cast iron is that it is not strong in tension, such as when subjected to pulling loads, and it does not resist shocks. The outer skin of cast iron is very hard and will damage files and saws; chip it away with a chisel to enable you to cut and drill the metal. Scrap cast iron is easy to obtain from old stoves and similar discarded objects and these could provide the raw material for making many useful and decorative items where weight is an asset, such as paperweights and ornamental bookends.

Processes have been developed to improve cast iron and these have led to the production of malleable cast iron by dispersing the carbon more widely; this makes the metal less brittle. It is used extensively in the car industry for the crankcases of engines and gear box casings. Neither cast iron nor malleable cast iron can be hardened, so they cannot be used in situations where they would be subjected to wear and bending, such as for rotating shafts. Copper Reddish-brown in colour, copper is a soft metal which can be easily bent, shaped, sawn, filed and joined. If it is worked repeatedly, however, it tends to harden and is likely to require annealing. Since it is a good conductor of heat and electricity, it is widely used in the electrical industry and also for plumbing in the form of tubing. It takes a good polish, but the colour darkens on exposure to air; to maintain the finish it should be protected by a coating of clear lacquer – if left unprotected for a prolonged period, it will acquire a green patina which protects the metal from further corrosion.

Because it is easily worked, copper is suitable for DIY work, usually in the form of small-scale items such as bowls, name plates, trays and ornaments. Brass As an alloy of copper and zinc, the colour of brass varies from red-bronze to yellow-gold depending on the amount of zinc it contains. Brass is resistant to corrosion and available in various tempers ranging from soft to hard. It can be cut, etched, shaped and bent easily. but needs annealing for repeated working. Its uses in DIY work are similar to those for copper; it is extensively used in art metal work. Plated steel Tin plate is a mild steel sheet coated with tin; galvanized iron is a mild steel sheet coated with zinc. If the surface is scratched, the iron core will rust. These materials can be soldered and are easily bent into boxes, cylinders and tubing. Tin plate is used for tin cans, baking tins and other baking utensils and galvanized iron for water tanks, guttering and ventilation pipes. Tin This is a bright, soft, tarnish-free metal. It is rarely worked in its pure state, but is used for tin plate and for alloying with lead and zinc. Zinc A soft non-tarnishing metal which tends to clog files, zinc has a low melting point and can be soft-soldered. Its main uses are as an alloy with copper to make brass and in galvanizing mild steel. It can be used as a substitute for lead in flashings and linings and perforated zinc is extremely useful when used with epoxy resin fillers for repair work.

Lead A very heavy metal, lead has a high resistance to corrosion and chemical attack. It is soft and easily soldered and is used in plumbing, construction work, church roofs and nuclear fall-out shelters. Apart from plumbing and a few minor applications such as flashings and small items like paperweights and curtain weights, lead in its pure form is not often used for domestic purposes.

Bronze An alloy of copper and tin, bronze is particularly suited for casting where metal is shaped by being poured in a molten state into a mould. It is resistant to corrosion and easy to work and join. Not a common metal for everyday use, bronze can be used in DIY work for much the same items as brass.

Pewter An alloy of lead and tin, when polished pewter has a silvery sheen. It is easy to work but considerable skill is required for joining it. Uses include mugs, plates and other utensils for containing food and drink.

Wrought iron This is a very pure form of iron. although not readily available. It is an ideal material for forging, where it is shaped by heating in a fire, and hammering; this requires a forge. It is relatively soft and malleable and easily worked and joined. Since it tends to rust in exposed positions, it should be protected with paint outdoors and preserved indoors by waxing. Uses include chains and bolts and also decorative work such as gates and screens.

Stainless steel By definition, stainless steel is that which contains more than 10 percent chromium; the most commonly known is 18/8 stainless which contains about 18 percent chromium and 8 percent nickel. While stainless steel is resistant to corrosion it is not necessarily stainless. Used for items such as cutlery and furniture frames, it is a particularly difficult metal to work.

Cast steel This has a high carbon content and can be hardened and tempered for a wide variety of purposes including making cutting tools. It is expensive to buy and is generally available only in the form of discarded tools. Cast steel can be drilled. cut. filed and joined by normal methods but this work should be carried out while the material is in its soft state. Heat treatment consists of heating the steel to cherry red. quenching it and then tempering by a further heating and cooling process so the brittleness caused by quenching is eliminated. Silver steel Silvery in colour, this is really cast steel in its soft state, ground to accurate sizes and ready for immediate use in making workshop tools. It is readily available, usually in 330mm lengths and dimensionally accurate round and square shapes, from good tool shops. High speed steels Drills and similar tough tools are sometimes made from cast steel ; for extra hard tools high speed steels are used. These are very high grade materials containing a number of ingredients such as chromium. vanadium, tungsten, molybdenum, manganese and cobalt. High speed steels are much more expensive than cast steel; but while cast steel can be softened and rehardened. high speed steels. once hard, are always hard. When working with HSS tools there is no danger of their losing their hardness because, even at very high temperatures, they can still work quite satisfactorily without damage. When sharpening such tools, however. care must be taken not to cool them rapidly since there is a danger the shock of the quenching may cause them to crack.

Solders A variety of solders is available, to be used depending on the type of joint to be made and the metals being worked. Ordinary soft solder is a tin/ lead alloy made in different proportions to give different melting points. Eutectic solder consists of 63 percent tin and 37 percent lead and is used for work with electrical equipment. Plumber’s solder, used for joining lead pipes and cable joints, is a 30/70 tin, lead alloy which softens at 183 C but remains in a plastic state until 270°C. allowing a great deal of workability during this phase. Among the other types available are silver solders which are made of silver, tin and lead in varying proportions and silver, copper and zinc. Silver solder, also known as hard solder, produces a much stronger joint than soft solder.

Wire rods, thin steel sheets and tubing Steel for general workshop use Wires and high tensile tubing Springs, blades for scissors and shears. wood chisels Cold chisels, screw cutting taps and dies. axes, saws Razor blades, hand files, twist drills. metal cutting tools

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