NATIONAL CERTIFICATE (VOCATIONAL) NQF LEVEL 3 NOVEMBER

Transcription

1 MARKING GUIDELINE NATIONAL CERTIFICATE (VOCATIONAL) NQF LEVEL 3 NOVEMBER 2009 This memorandum consists of 5 pages.

2 MARKING GUIDELINE -2- NC1520(E)(N3)/V QUESTION 1: GENERAL True True True False False False B B C C A B Malleable Plastic Refractory bricks High quality steel Impurities Temperature % Sheet materials QUESTION 2: METALS 2.1 High carbon steel Medium carbon steel Low carbon steel 2.2 Connecting rods Axles Gears High tensile wire 2.3 Is the ability of a metal to be hammered, rolled or pressed into various shapes without cracking or breaking.

3 MARKING GUIDELINE -3- NC1520(E)(N3)/V 2.4 Lead has low strength Resists corrosion Is malleable and ductile Is bright and shiny Makes it easy to work Can also be cold worked, welded and machined Does not form useful alloys 2.5 Motor vehicle parts Aluminium foil Gears Door and window frames 2.6 Bullets Battery plates ANY TWO ANY ONE ANY ONE 2.7 Gives steel the property of retaining its hardness at high speeds and temperatures. 2.8 They are relatively cheap and easy to grind Cutting speeds are moderate Tool life is good with most brasses, coppers and coppers alloys Have good wear resistance 2.9 Is hard and brittle Is similar to iron in general chemical activity Is unstable and reacts easily with other chemicals QUESTION 3: NON-METALS 3.1 Brake and clutch linings Roofing sheets Heater panels Insulating materials Fire-resistant materials 3.2 Forms more compounds than all the other elements combined Exists in three forms Diamond and graphite are crystalline in structure Carbon black includes charcoal,lampblack.coal and coke Both diamond and graphite are chemically inert Pure diamond is the hardest naturally occurring substance known Graphite is a soft, slippery solid that is a good conductor of both heat and electricity ANY THREE

4 MARKING GUIDELINE -4- NC1520(E)(N3)/V 3.3 Clear and colourless Lightweight Highly adhesive Shock resistant 3.4 White phosphorus Red phosphorus Black phosphorus 3.5 Is used in photoelectric cells and photographic exposure meters Can convert alternating current to direct current Selenium in small quantities is used as a decolouriser in the manufacture of glass It is also used to make red enamels for ceramics and steel ware It is used for the vulcanisation of rubber QUESTION 4: METAL PROCESSING 4.1 The bottom of the furnace is covered with lime and then charged with scrap of a known quality The three carbon electrodes are lowered to the surface of the metal and melting begins The furnace is tilted slightly and the slag is manually raked off into a ladle Temperatures is checked and if correct the steel is tapped into the ladle and ingot moulds are filled from the ladle 4.2 Bessemer converter Steel casing Tyeres Blast box Blast pipe Basic lining 4.3 High cost Ageing temperature and time critical Steel work pieces are placed in a box containing a charcoal mixture The box is then sealed and gradually heated to about 925ºC, and maintained at that temperatures for 8 hours It produces a hard skin on the steel by heating it to about 900º C and allowing it to come into contact with carbon It results in a hard outer skin with a soft inner core

5 MARKING GUIDELINE -5- NC1520(E)(N3)/V 4.5 Is one of the few methods of continous melting It has a high melt rate Relative low operating costs ( cheap ) Ease of operation The bottom of can drop away at the end of melting to aid cleaning and repairs Can be operated intermittently to suit casting requirements ANY FOUR QUESTION 5: MATERIAL TESTING Cylindrical Spot Shallow Plane 5.2 Modulus of elasticity in shear Yield shear strength Ultimate shear strength Modulus of rupture in shear Ductility Solid ductile material Solid brittle material Thin walled tube of length greater than diameter, failed by buckling Thin walled tube of length smaller than diameter, failed in torsion across the reduced section 5.4 Note the original cross-sectional area of the specimen Place a standardised specimen in the heads or jaws of the testing machine Apply a load on the sample with the hydraulic or mechanical lever loading system The force is indicated on the calibrated dial Use the formulas to calculate the ultimate tensile strength, yield point, percentage elongation and percentage reduction of area Tensile strength is the ability of a material to resist being pulled apart. Tensile strength ( MPa ) = 3,4 x B (2) TOTAL 100