Power Engineering 4A Welding Questions and Answers Rated A+

Power Engineering 4A Welding Questions and Answers Rated A+ Hardness Ability to resist wear, abrasion, cutting and indentation Brinell Tester Ball is forced by hydraulic pressure into the test specimen and the diameter of the indentation is measured Rockwell A 1.6 mm ball or diamond cone is forced onto the specimen and loaded with 100 kg. The ball or cone make an impression on the specimen which is measured to 0.002 mm and the indentation is converted to a hardness reading Brittleness - no permanent deformation before breaking - Usually breaks instantly - ie: glass, cast iron Ductility - can be drawn to a considerable length without rupture -soft copper, copper wires - can be permanently deformed without breaking -mild steel Plasticity -very soft and easily deformed and have little elasticity -wax, lead babbit -opposite of brittleness Elasticity -ability to return to original shape after force is removed Toughness -tough materials do not break easily under a sudden impact -also called impact strength -use izod and charpy test toughness Izod test -specimen held in vice -free end hit with a hammer -energy required to break specimen is measured and indicate toughness Charpy test -similar to izod test -supported at each end -struck at centre -measured in joules Pig iron - produced from iron ore, first stage in processing -iron ore is heated with coke and limestone -slag floats to top and is removed -molten iron is drawn off to form pig iron -useless bcuz hard, brittle and impossible to machine -further refined to produce steel or cast iron Strength -property that allows a material to resist deformation under load Yield Strength -load of material before plastic deformation Ultimate strength -maximum load material can withstand until breaking Impact strength -toughness How is cast iron made? -Melt pig iron and some scrap iron and get cast iron in a CUPOLA FURNACE Carbon Content of Cast Iron (2%-4% carbon content) Carbon Content of Steel less than 2% What is white cast iron and what is it used for? -Most of the carbon is chemically combined with the iron -Used for machinery parts that is subject to excessive wear -Crusher jaws, mill balls, liners -Very Hard and Brittle How is White cast iron made? -Made by cooling the molten cast iron rapidly in a mold, which prevents the carbon from precipitating out of the solution What is Grey cast Iron and what is it used for? -Made by allowing the molten cast iron to cool slowly -Used for machinery bases and internal combustion engine components How is Grey cast iron Made? - much of the carbon precipitates and becomes mechanically held in the iron -If most of the carbon precipitates as graphite flakes it is called Grey cast iron What is Malleable cast iron and what is it used for? -Made from annealing white cast iron (heating and cooling at a controlled rate) -Resulting material has increased toughness and ductility -used for farm implements, car parts, pipe fittings, tools What is Wrought Iron? What are some traits of Wrought iron? (long answer) -Formed from process called Puddling - pig iron is melted in a furnace and as it melts, the carbon and other impurities oxidize and leave the iron -as impurities pass off, the iron forms a plastic mass which is formed into a ball by manipulation and rolled to remove slag -Very ductile