Basic Metalworks Introduction PDF

BASIC METALWORKS Metalworking throughout history At the time Solomon's Temple was believed to be constructed (mid-10th century BCE), there lived a man named Tubal-Cain. He was said to be an instructor and artificer of bronze and iron and all other metals. Also written about that same time was this...

BASIC METALWORKS Metalworking throughout history At the time Solomon's Temple was believed to be constructed (mid-10th century BCE), there lived a man named Tubal-Cain. He was said to be an instructor and artificer of bronze and iron and all other metals. Also written about that same time was this statement: "They will beat their swords into plowshares." As old as I am, I was not there for those events, but it is evident that the Iron Age was not the beginning of metalworking. Sometime during the Middle Ages, the Iron Pillar of Delhi (Figure 1) was constructed. This is said to be the largest weldment made in this time period. The metalworking method of forging was becoming a common process used for all types of metal that could be forge-welded. This method was used in blacksmithing even in the 20th century. My grandfather made very strong fireplace tools in the 1940s by forging (Figure 2). Today it is us. The Davys' Discoveries The Davys are credited with two important discoveries in the early 1800s. Edmund Davy discovered acetylene, and Sir Humphry Davy discovered that two carbon sticks connected to a battery produced an electric arc. This became a usable welding process in the late 1800s and early 1900s that still is used today to weld galvanized sheet metal with cupro-bronze filler material. The arc between the two carbon electrodes places very little heat into the base material, barely affecting the galvanized material. Gas welding, brazing, and cutting with oxygen and coal gas (would be good for West Virginia) or hydrogen came into their own in the late 1800s. Because of its low flash point and its expansion in any conventional container, storing acetylene was a problem. At one time an attempt was made to store it in a glass bottle. This proved to be catastrophic. Then a steel container was used, and it also was a failure. The safest method at the time was to place the gas in a steel container filled with a concrete-like substance. The gas was absorbed in the porous material and became relatively stable. Later, a cylinder that contained a much lighter substance, similar to acoustic ceiling material, was found to be just as safe. This storage method continues to be used today. An additional stabilizer, acetone, is in the cylinder, which is stored at 250 PSI for safety. A gas regulator set at 15 PSI or less also is a safety requirement for cutting or welding. In the 1960s a fellow from Weston, W. Va., developed a torch that used gasoline and oxygen. He believed that it was safer than acetylene and much less expensive. It never really caught on because temperature variations caused liquid to be dispersed from the torch at times, which sparked fires adjacent to the operation mostly by artists at arts and crafts fairs. World War I Push World War I actually was the big push for the need for welding. The cost and efficiency of welding far outweighed those of the riveting process. Riveting required removing some material, and it was a two-person operation. Rosie the Riveter became Rosie the Welder. Ships were being built in the U.S. and Europe using arc welding. This activity called for definition and standardization of welding language and usage. In 1919 the American Welding Society was formed by the Wartime Welding Committee. A gentleman named Comfort Avery Adams led the effort and helped set the society's goals based on the criteria that it be "dedicated to the advancement of welding and allied processes." This mission statement remains broadly the same on the society's membership certificate. Metalwork Metalwork, useful and decorative objects fashioned of various metals, including copper, iron, silver, bronze, lead, gold, and brass. The earliest man-made objects were of stone, wood, bone, and earth. It was only later that humans learned to extract metals from the earth and to hammer them into objects. Metalwork includes vessels, utensils, ceremonial and ritualistic objects, decorative objects, architectural ornamentation, personal ornament, sculpture, and weapons. General Processes and Techniques Many of the technical processes in use today are essentially the same as those employed in ancient times. Hammering and Casting All decorative metalwork was originally executed with the hammer. The several parts of each article were hammered out separately and then were put together by means of rivets, or they were pinned on a solid core (for soldering had not yet been invented). In addition, plates of hammered copper could be shaped into statues, the separate pieces being joined together with copper rivets. A life-size Egyptian statue of the pharaoh Pepi I in the Egyptian museum, Cairo, is an outstanding example of such work. Embossing, or Repoussé Embossing (or repoussé) is the art of raising ornament in relief from the reverse side. The design is first drawn on the surface of the metal and the motifs outlined with a tracer, which transfers the essential parts of the drawing to the back of the plate. The plate is then embedded face down in an asphalt block and the portions to be raised are hammered down into the yielding asphalt. Next the plate is removed and re- embedded with the face uppermost. The hammering is continued, this time forcing the background of the design into the asphalt. By a series of these processes of hammering and re-embedding, followed finally by chasing, the metal attains its finished appearance. There are three essential types of tools—for tracing, for bossing, and for chasing—as well as a specialized tool, a snarling iron or spring bar, which is used to reach otherwise inaccessible areas. Ornament in relief is also produced by mechanical means. A thin, pliable sheet of metal may be pressed into molds, between dies, or over stamps. All of these methods have been known from antiquity. Chasing Chasing is accomplished with hammer and punches on the face of the metal. These punches are so shaped that they are capable of producing any effect—either in intaglio (incising beneath the surface of the metal) or in relief—that the metalworker may require. The design is traced on the surface, and the relief may be obtained by beating down the adjacent areas to form the background. Such chased relief work sometimes simulates embossed work, but in the latter process the design is bossed up from the back. The detailed finish of embossed work is accomplished by chasing; the term is applied also to the touching up and finishing of cast work with hand-held punches. Engraving To engrave is to cut or incise a line. Engraving is always done with a cutting tool, generally by pressure from the hand. It detaches material in cutting. When pressure is applied with a hammer, the process is called carving. Inlaying The system of ornamentation known as damascening is Oriental in origin and was much practiced by the early goldsmiths of Damascus; hence the name. It is the art of encrusting gold wire (sometimes silver or copper) on the surface of iron, steel, or bronze. The surface upon which the pattern is to be traced is finely undercut with a sharp instrument. The gold thread is forced into the minute furrows of the cut surface by hammering and is securely held. Niello is the process of inlaying engraved ornamental designs with niello, a silver sulfide or mixture of sulfides. The first authors to write on the preparation of niello and its application to silver were Eraclius and Theophilus, in or about the 12th century, and Benvenuto Cellini, during the 16th. According to each of these authors, niello is made by fusing together silver, copper, and lead and then mixing the molten alloy with sulfur. The black product (a mixture of the sulfides of silver, copper, and lead) is powdered; and after the engraved metal, usually silver, has been moistened with a flux (a substance used to promote fusion), some of the powder is spread on it and the metal strongly heated; the niello melts and runs into the engraved channels. The excess niello is removed by scraping until the filled channels are visible, and finally the surface is polished. Enameling There are two methods of applying enamel to metal: champlevé, in which hollows made in the metal are filled with enamel; and cloisonné, in which strips of metal are applied to the metal surface, forming cells, which are then filled with enamel. Gilding Gilding is the art of decorating wood, metal, plaster, glass, or other objects with a covering or design of gold in leaf or powder form. The term also embraces the similar application of silver, palladium, aluminum, and copper alloys. Ferrous and Non-ferrous Metal The word “ferrous” comes from the Latin term “ferrum,” which Choice of to translates materials for a machine “containing element iron.” Thus, depends ferrous metals very aremuch thoseon its properties, that contain cost, availability iron, while and such non-ferrous other are metals factors. thoseIt that is therefore do not. important Both ferrousto and havenon-ferrous some idea of the common metals may beengineering raw metals,materials purified metals, or properties and their alloys. Thebefore presence or lack learning the of iron of details affects the design physical, procedure. mechanical, This topic isand chemical in the domain properties of the of material metal. science or These metallurgy but properties in turn some relevant determine discussions arewhich applications necessary they are best at this stage. suited for. Ferrous Metals Ferrous metals include all forms of iron and iron-base alloys, with small percentages of carbon (steel, for example), and/or other elements added to achieve desirable properties. Wrought iron, cast iron, carbon steels, alloy steels, and tool steels are just a few examples. Ferrous metals are typically magnetic. Iron Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. Iron ore is the raw material used to make pig iron, which is one of the main raw materials used to make steel. Ninety-eight percent of the mined iron ore is used to make steel. Iron is produced by converting iron ore to pig iron using a blast furnace. Pig iron is the intermediate product of smelting iron ore with coke, usually with limestone as a flux. Pig iron has very high carbon content, typically 3.5–4.5%, which makes it very brittle and not useful directly as a material except for limited applications. From pig iron, many other types of iron and steel are produced by the addition or deletion of carbon and alloys. The following briefly presents different types of iron and steel made from iron. Steelworker Advanced will present additional information about their properties. Pig Iron — comparatively weak and brittle with limited use. Approximately ninety percent is used to produce steel, although cast-iron pipe and some fittings and valves are manufactured from pig iron. Wrought Iron — made from pig iron with some slag mixed in during manufacture, it is almost pure iron. Wrought iron usage diminished with the increasing availability of mild steel in the late 19th century. Some items traditionally produced from wrought iron included rivets, nails, chains, railway couplings, water and steam pipes, nuts, bolts, handrails, and ornamental ironworks. Many products still described as wrought iron, such as guardrails and gates, are made of mild steel. Cast Iron — any iron containing greater than 2% carbon alloy. It tends to be brittle, except for malleable cast irons. Cast irons have a wide range of applications, including pipes, machine and automotive industry parts such as cylinder heads, cylinder blocks, and gearbox cases. A malleable cast iron is produced through a prolonged annealing process. Ingot Iron a commercially pure iron (99.85% iron). It is easily formed, with properties practically the same as the lowest carbon steel. In iron, the carbon content is considered an impurity; in steel, the carbon content is considered an alloying element. The primary use for ingot iron is for galvanized and enameled sheet. Steel Of all the different metals and materials that Steelworkers use, steel and steel alloys are by far the most used and therefore the most important to study. The development of the economical Bessemer process for manufacturing steel revolutionized the American iron industry. Figure 1-1 shows the container vessel used for the process. With economical steel came skyscrapers, stronger and longer bridges, and railroad tracks that did not collapse. Steel is manufactured from pig iron by decreasing the amount of carbon and other impurities and adding specific and controlled amounts of alloying elements during the molten stage to produce the desired composition Figure 1-1 — Example of a Bessemer Converter. The composition of a particular steel is determined by its application and the specifications developed by the following: American Society for Testing and Materials (ASTM) American Society of Mechanical Engineers (ASME) Society of Automotive Engineers (SAE) American Iron and Steel Institute (AISI) Carbon steel is a term applied to a broad range of steel that falls between the commercially pure ingot iron and the cast irons. This range of carbon steel may be classified into four groups: Low-Carbon Steel — tough and ductile, easily machined, formed, and welded, but does not respond to any form of heat-treating except case hardening. Medium-Carbon Steel — strong and hard but cannot be welded or worked as easily as the low- carbon steels. They are used for crane hooks, axels, shafts, setscrews and so on. High-Carbon Steel — responds well to heat treatment and can be welded with special electrodes, but the process must include preheating and stress-relieving procedures to prevent cracks in the weld areas. Very High-Carbon Steel — similar to high-carbon, it responds well to heat treatment and can be welded with special electrodes, but the process must include preheating and stress-relieving procedures to prevent cracks in the weld areas. Both steels are used for dies, cutting tools, mill tools, railroad car wheels, chisels, knives, and so on. High-strength steels are covered by American Society for Testing and Materials (ASTM) specifications. Low-Alloy, High-Strength, Tempered Structural Steel — special low carbon steel that contains specific, small amounts of alloying elements. Structural members made from these high-strength steels may have smaller cross-sectional areas than common structural steels and still have equal or greater strength. This type of steel is much tougher than low-carbon steels, so the shearing machines must have twice the capacity required for low-carbon steels. Stainless steels are classified by the American Iron and Steel Institute (AISI) and classified into two general series: Stainless Steel 200-300 series — known as Austenitic [aw-stuh-nit-ik]. This type of steel is very tough and ductile in the as-welded condition; therefore, it is ideal for welding and requires no annealing under normal atmospheric conditions. The most widely used are the normally nonmagnetic chromium nickel steels. Stainless Steel 400 series — further subdivided according to their crystalline structure into two general groups: Ferritic [fer-rit-ik]. Chromium — non-hardenable by heat treatment and normally used in the annealed or soft condition, they are magnetic and frequently used for decorative trim and equipment subjected to high pressures and temperatures. Martensitic [mahr-tn-zit-ik] Chromium — readily hardened by heat treatment, they are magnetic and used where high strength, corrosion resistance, and ductility are required. Nickel Steels — used in the manufacture of aircraft parts such as propellers and airframe support members. Chromium Steels — used for the races and balls in antifriction bearings; highly resistant to corrosion and to scale. Chrome Vanadium Steel — used for crankshafts, gears, axles, and other items that require high strength; also used in the manufacture of high-quality hand tools such as wrenches and sockets. Tungsten Steel — expensive to produce, its use is largely restricted to the manufacture of drills, lathe tools, milling cutters, and similar cutting tools. Molybdenum — used in place of tungsten to make the cheaper grades of highspeed steel and in carbon molybdenum high-pressure tubing. Manganese Steels — use depends upon the properties desired: Small amounts produce strong, free-machining steels. o Larger amounts produce a somewhat brittle steel. o Still larger amounts produce a steel that is tough and very resistant to wear after proper heat treatment. Nonferrous Metals Nonferrous metals contain either no iron or only insignificant amounts used as an alloy, and are nonmagnetic. The following list will introduce you to some of the common nonferrous metals that SWs may encounter and/or work with. Additional information about their properties and usage is available in Steelworker Advanced. Copper one of the most popular commercial metals; used with many alloys; frequently used to give a protective coating to sheets and rods and to make ball floats, containers, and soldering coppers. True Brass an alloy of copper and zinc, sometimes with additional alloys for specific properties; sheets and strips are available in several grades. Bronze a combination of 84% copper and 16% tin, and the best metal available before steel-making techniques were developed; the name bronze is currently applied to any copper-based alloy that looks like bronze. Copper-Nickel Alloys nickel adds resistance to wear and corrosion; some alloys used for saltwater piping systems; other sheet forms used to construct small storage tanks and hot-water reservoirs. Lead a heavy metal, but soft and malleable; surface is grayish in color, but after scratching or scraping it, the actual color of the metal appears white. Zinc — used on iron or steel in the form of a protective coating called galvanizing. Tin — used as an important alloy adding resistance to corrosion. Aluminum — easy to work with; good appearance; light in weight; needs alloys added to increase strength. Duralumin — one of the first strong structural aluminum alloys; now classified in the metal working industries as 2017-T; “T” indicates heat-treated. Alclad — a protective covering of a thin sheet of pure aluminum rolled onto the surface of an aluminum alloy during manufacture. Monel — an alloy in which nickel is the major element; harder and stronger than either nickel or copper; acceptable substitute for steel in systems where corrosion resistance is the primary concern K-Monel — developed for greater strength and hardness than Monel; comparable to heat-treated steel; used for instrument parts that must resist corrosion. Inconel — provides good resistance to corrosion and retains its strength at high-operating temperatures; often used in the exhaust systems of aircraft engines Non-metals Non-metallic materials are also used in engineering practice due to principally their low cost, flexibility and resistance to heat and electricity. Though there are many suitable non-metals, the following are important few from design point of view: Timber This is a relatively low cost material and a bad conductor of heat and electricity. It has also good elastic and frictional properties and is widely used in foundry patterns and as water lubricated bearings. Leather This is widely used in engineering for its flexibility and wear resistance. It is widely used for belt drives, washers and such other applications. Rubber It has high bulk modulus and is used for drive elements, sealing, vibration isolation and similar applications. Plastics These are synthetic materials which can be moulded into desired shapes under pressure with or without application of heat. These are now extensively used in various industrial applications for their corrosion resistance, dimensional stability and relatively low cost. There are two main types of plastics: a. Thermosetting plastics- Thermosetting plastics are formed under heat and pressure. It initially softens and with increasing heat and pressure, polymerisation takes place. This results in hardening of the material. These plastics cannot be deformed or remoulded again under heat and pressure. Some examples of thermosetting plastics are phenol formaldehyde (Bakelite), phenol-furfural (Durite), epoxy resins, phenolic resins etc. b. Thermoplastics- Thermoplastics do not become hard with the application of heat and pressure and no chemical change takes place. They remain soft at elevated temperatures until they are hardened by cooling. These can be re-melted and remoulded by application of heat and pressure. Some examples of thermoplastics are cellulose nitrate (celluloid), polythene, polyvinyl acetate, polyvinyl chloride ( PVC) etc.  Mechanical properties of common engineering materials Elasticity This is the property of a material to regain its original shape after deformation when the external forces are removed. All materials are plastic to some extent but the degree varies, for example, both mild steel and rubber are elastic materials but steel is more elastic than rubber. Plasticity This is associated with the permanent deformation of material when the stress level exceeds the yield point. Under plastic conditions materials ideally deform without any increase in stress. Hardness Property of the material that enables it to resist permanent deformation, penetration, indentation etc. Size of indentations by various types of indenters are the measure of hardness e.g. Brinnel hardness test, Rockwell hardness test, Vickers hardness (diamond pyramid) test. These tests give hardness numbers which are related to yield pressure (MPa). Ductility This is the property of the material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs. The percentage elongation or percentage reduction in area before rupture of a test specimen is the measure of ductility. Normally if percentage elongation exceeds 15% the material is ductile and if it is less than 5% the material is brittle. Lead, copper, aluminium, mild steel are typical ductile materials. Malleability It is a special case of ductility where it can be rolled into thin sheets but it is not necessary to be so strong. Lead, soft steel, wrought iron, copper and aluminium are some materials in order of diminishing malleability. Brittleness This is opposite to ductility. Brittle materials show little deformation before fracture and failure occur suddenly without any warning. Normally if the elongation is less than 5% the material is considered to be brittle. E.g. cast iron, glass, ceramics are typical brittle materials. Resilience This is the property of the material that enables it to resist shock and impact by storing energy. The measure of resilience is the strain energy absorbed per unit volume. Toughness This is the property which enables a material to be twisted, bent or stretched under impact load or high stress before rupture. It may be considered to be the ability of the material to absorb energy in the plastic zone. The measure of toughness is the amount of energy absorbed after being stressed upto the point of fracture. Creep When a member is subjected to a constant load over a long period of time it undergoes a slow permanent deformation and this is termed as “creep”. This is dependent on temperature. Usually at elevated temperatures creep is high.