PROCESSING MATERIALS

Conditioning Processes  Magnetic Conditioning –Magnetizing force lines up the steel molecules in one direction  Thermal Conditioning –Hardening: Heating steel red hot and cooling quickly –Tempering: Heating the steel again not quite as hot, and cooling it quickly --- it becomes less brittle –Annealing: Heating steel ret hot and allowing it to cool very slowly --- steel becomes softer  Mechanical Conditioning –Hammering a piece of metal --- crystal structure gets longer and thinner  Chemical Conditioning –Heating a mixture of plaster and water --- the plaster hardens –Examples on page 230

Use of Computers –Microwave Oven –Rolling Mill --- Reheating Furnaces –Computer-numerical-controlled (CNC) machines and robots –Using a wire-cut machine to cut the profile of a die –A robot can be taught to move through the movements needed to do a job --- use of teach pendant (remote controller)

Properties of Materials –Materials are chosen for their characteristics or properties –Examples: copper, glass, nylon, steel etc  Mechanical Properties –Drawing wire: Making wire from a thick rod –Ductility: A material can be bent, twisted or pressed to shape –Ductile materials are either elastic or plastic –Elasticity: A material comes back to its original shape after deformation –Plasticity: A material remains deformed after deformation –Brittleness: A material does not deform without breaking --- window glass –Strength: A material’s ability to keep its own shape when a force is applied –Tension: A force that pulls on a piece of material –Compression: A force that pushes on or squeezes a material –Torsion: Twisting of a material --- twisting force itself is called torque

Properties of Materials  Mechanical Properties –Shear force: Acts on a material like a pair of scissor –Toughness: Ability of material to absorb energy without breaking –Hardness: Ability to resist being scratched or dented --- diamond is the hardest material known –The teeth of circular saw blades are often made of tungsten carbide  Electrical & Magnetic Properties –Conductors and insulators –Silver is the best conductor of electricity –People make a trade-off by choosing copper instead of silver –Magnetic materials: those that can be attracted to magnets –An electromagnet can be made by wrapping wire around a piece of iron

Properties of Materials  Thermal Properties –Material’s ability to conduct heat –Copper and aluminum are the two best conductors of heat –Insulation --- a layer of material that does not conduct heat  Optical Properties –Scientific tools like telescopes use glass that transmits light well enough –Plastic is used in contact lenses and eyeglasses –Very pure glass is used in glass fibers in communication –Some metals are used as reflectors for headlights and flashlights

Disposal of Resources –We live in a “throw-away” society –Burning --- polluting the air –Landfills --- polluting the groundwater –Toxic materials like Lead and Mercury and radioactive wastes should be disposed properly –Materials that do not decompose should be recycled –Material decomposition time --- page 238