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MODULE 12 MATERIAL AND MATERIAL PROCESS LO : Explain and understand the difference between ferrous and non- ferrous metals, iron and alloy and discuss the general behaviour of specific materials during specific workshop process. ITEMOHELENG CAMPUS METALS • The property that separates the metals is whether they contain iron or not. • We have two groups, ferrous and non-ferrous metals. FERROUS METALS NON FERROUS METALS Contain iron, and the common used are cast iron and Contains no iron as a basic metal, and most common plain carbon steel. used are copper, aluminum, lead, tin and zinc. Iron is alloyed with carbon or other elements like They are non magnetic and corrosion resistance. tungsten, nickel, silicon, sulphur and manganese. These elements in various portions give metal Have electrical conductivity and they mechanical specific properties like heat resistance, elasticity strength is low. plasticity and toughness. Iron is called ferrite, a soft grey metal and obtained We can improve their mechanical properties by from a mined ore. alloying them together. Steel is an alloy of iron and carbon which gives steel certain properties that makes it useful for certain applications. Alloy can be defined as a combination of iron and carbon. ITEMOHELENG CAMPUS PROPERTIES OF METALS Toughness • It is the ability of a metal to withstand resistance force impact or hammering load. • It has the ability to resist fracture when subjected to continuous bending forces in opposite directions. Tensile strength • Is a measure of the ability of a metal to resist force acting to pull it apart and withstand stretching load without breaking. Elasticity • Is a measure of the ability a metal to be deformed under load and yet return to its original shape when load is removed. Plasticity • Is a measure of a metal to be deformed under load and then retain the new shape when load is removed. Ductility • Is the property that permits a metal to withstand considerable elongation under tension before breaking apart. Malleability • Metals having the ability of being permanently extended in all directions by hammering , bending , twisting or rolling without cracking or breaking. Hardness • Is a measure of the ability of a metal to withstand starching, cutting or rubbing by other body or hard material. ITEMOHELENG CAMPUS HEAT TREATMENT PROCESSES HARDENING TEMPERING ANNEALLING • Heat treatment is the process whereby the physical properties of a metal usually steel are changed by heating it up to a certain temperature and then cooling it down. Toughness , hardness and wear are some of the Steel is heated at a predetermined Steel is heated in its harden state to Is done by slowly heating steel to a properties that can be improved by various heat treatment processes. temperature and then quenched rapidly in a a tempering temperature and then certain temperature and then • Below is processes and purposes of each. quenching medium such water. quench it in water or oil. allowing it to cool down very slowly. The purpose of tempering is Its purpose is soften steel so that it removes the stresses and strains can be machined easily and to The purpose of hardening is to harden steel. induced by hardening. reduce grain structure. To release internal stresses that The other purpose is to enable steel to resist The other purpose is to reduce have been set up during previous wear and to cut other metals. brittleness and increase toughness. working of metals. NORMALISING CASE HARDENING Low carbon steel is heated in a furnace to weaken steel and Steel is heated slowly to a normalizing temperature and refine grain. This produces hard surface skin with a thickness then allow it to cool in air. of 1 to 2 mm. The purpose for normalizing is to refine steel structure Results of case hardening are the hard out layer that present and obtain uniform structure. a good wearing surface. To remove strains and stresses caused by cold working The strong and tough inner core which is hardened but can ITEMOHELENG CAMPUS and to improve steel strength. resist all the shock loads to be carried by the work-piece. COLOUR CODING OF METALS METAL COLOUR Low carbon steel Orange High carbon steel Brown Case hardened steel Orange Low alloy steel Light purple Structural steel Red Steel for pressure containers White Stainless steel Black Carbon and alloy spring steel Black Silicon chrome steel Black Cast steel Blue Pipeline steel Grey Steel for lifting machines Green ITEMOHELENG CAMPUS
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