L3 Materials Topic 3

SUBJECT : MATERIALS LEVEL 3 TOPIC: 3 ITEMOHELENG CAMPUS DISTANCE LEARNING 2020-APRIL LECTURER: KHOSI MOHAPELOA Downloaded from hlayiso.com

TOPIC 3 : METALS LEARNING OUTCOMES: • HISTORY OF MAN KIND DISCOVERY • PHYSICAL PROPERTIES • RANKING METALS • DISTINGUISH BETWEEN PURE METALS AND ALLOYS • MANUFACTUTING OF STEEL AND ITS CONTENTS • STEEL IN CONSTRUCTION • METHODS OF CUTTING AND DRILLING METALS • ADVANTAGES AND DISADVANTAGES OF DITTO • CONCEPTUALIZE WORK-HARDENING, ANNEALING AND DRAWING • SELECT APPROPRIATE METALS FOR VARIOUS CONSTRUCTION ELEMENTS. • Downloaded MARK-OUT, from CUT, SHAPE hlayiso.com AND DRILL DIFFERENT METALS.

METALS Metal is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Downloaded from hlayiso.com

HISTORY OF METALS Stones discovered 2,5 million years ago as weapons Copper age begins = 3000 BCE Bronze age begins ( Molten tin and copper)= 2700 BCE Iron age begins = 1300 BCE BCE = BEFORE CHRIST ERA CE= CHRIST ERA Downloaded from hlayiso.com

PHYSICAL PROPERTIES Appearance or Lustre Downloaded from hlayiso.com

RANKING METALS Symbol Downloaded from hlayiso.com

DISTINGUISH BETWEEN PURE METALS AND ALLOYS An alloy is a metallic substance, but it is not a single chemical element. An alloy is formed by the union or mixture of two or more metals; in some cases, it may consist of one or more metals and a non- metal. Examples of alloys are iron , steel, and brass and bronze Downloaded from hlayiso.com

DISTINGUISH BETWEEN PURE METALS AND ALLOYS . Metals used as construction materials Pure metals Alloys Aluminium, iron, copper, lead, Brass, steel, stainless steel, zinc, tin. bronze, cast iron. Downloaded from hlayiso.com

STEEL There are three methods of manufacturing steel; • The Bessemer process • The Siemens-Martin process • Electric Arc Furnace method Downloaded from hlayiso.com

MANUFACTURING STEEL The Bessemer process was the first inexpensive industrial process for the mass- production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron Converts pig iron to steel Besser converter Downloaded from hlayiso.com

MANUFACTURING STEEL Siemens-Martin process Siemens-Martin open-hearth process is an obsolete process for making steel in which streams of air and fuel gas were fed alternately onto the furnace contents. It was used to make most of the steel during the twentieth century but was then superseded by the basic oxygen and electric-arc methods. The open-hearth process used the gases from the molten charge to pre-heat the air blast and so economize on fuel. An alkaline lining was used if the ore contained phosphorus. Downloaded from hlayiso.com

ELECTRIC ARC FURNACE METHOD Electric Arc Furnace (EAF) is a steel making furnace, in which steel scrap is heated and melted by heat of electric arcs striking between the furnace electrodes and the metal bath. Two kinds of electric current may be used in Electric Arc Furnaces: direct (DC) and alternating (AC). Downloaded from hlayiso.com

STEEL IN CONSTRUCTION Billet Mill a rolling mill designed for the rolling of blooms or ingots into b illets of square or round cross section. The billets are later processed in specialized rolling mills (section and tube rolli ng mills. Heavy Mill rollers: Blocks from the billet mill are rolled on the heavy mill rollers. These rollers produced rail way lines – structural steel industrial buildings Medium mill rollers: These rollers produce light channel iron, cocopan rails and angle iron. Light mill rollers: These rollers produce flat and round steel bars- Concrete reinforcement Fine rollers: These rollers produce frame sections, small angle iron and flat bar - Window frames Plate mill rollers: Flat sections are rolled on these rollers – Wire and plating in construction Downloaded from hlayiso.com

METHODS OF CUTTING AND DRILLING METALS Sawing: consist of blade, wire, or chain with a hard toothed edge. It is used to cut through material, such as metals or stone. The cut is made by placing the toothed edge against the material and moving it forcefully forth and less forcefully back or continuously forward (Slow)(Neat). Flame cutting: Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the United States) and oxy- fuel cutting are processes that use fuel gases (or liquid fuels such as gasoline) and oxygen to weld or cut metals (Cheap)(Heat Damages). Cropping: Cut the ends of metal that have defects in them ( Quick)(Simple)( Leaves cut ends)( Not neat results) Guillotining: Large machine with blades, cuts metal sheets to specified sizes (Quick)(Neat) ( Limited to cuttings) ( Only straight cuts). Downloaded from hlayiso.com

DRILLING THROUGH METALS Holes that fall into the “deep-hole drilling” category are three or more drill bit diameters in depth. When you are drilling this deep, you must adjust your speeds and feeds accordingly. The deeper the hole is, the more probable that chips might lodge in the flutes and clog the drill. When the flute clogs, the amount of friction and heat will increase. Heat build-up in the drill bit could cause failure and breakage. Lubricants always help the dissipation of heat from the tip of the drill bit, which prolongs the drill’s life. Removing the drill and evacuating the chips after drilling short distances, often called “step-drilling,” will also lessen the chance of heat build-up. Some good rules of thumb when deep-hole drilling are to reduce your rate of speed and feed, remove the bit more often from the material, and use lubricant whenever you can. Downloaded from hlayiso.com

WORK-HARDENING, ANNEALING AND DRAWING METALS Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. Drawing is a metalworking process which uses tensile forces to stretch metal or glass. As the metal is drawn (pulled), it stretches thinner, into a desired shape and thickness. Drawing is classified in two types: sheet metal drawing and wire, bar, and tube drawing. Downloaded from hlayiso.com

MARKING OUT METALS A scriber is a hand tool used in metal work to mark lines on work pieces, prior to machining. The process of using a scriber is called scribing and is just part of the process of marking out. Downloaded from hlayiso.com

SHAPING METALS • Forging • Rolling • Casting Downloaded from hlayiso.com

HOME ACTIVITY 1, State the characteristic of a non metal and metal under Electricity, Malleability, Lustre properties (3) 2. Distinguish pure metals and alloys (4) 3. Explain 3 processes of manufacturing steel (15) 4. List three methods of shaping steel (3) Total: (25) Downloaded from hlayiso.com

NEXT TOPIC: TOPIC 4; CORROSION OF METALS Downloaded from hlayiso.com

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