NSSCO Metalwork and Welding 6188 flashcards
NSSCO Metalwork and Welding 6188 · Build recall with a focused review session.
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- Arc welding helmet shade
- A filter lens numbered 10 to 13 for arc welding; choose a higher shade for higher current, and use shade 3 to 6 for gas welding.
- Acetylene cylinder pressure limit
- Acetylene delivery pressure must not exceed about 1 bar (15 psi); higher pressure can decompose the gas and cause a cylinder explosion.
- Welding galvanised steel hazard
- Zinc oxide fume from the coating causes metal fume fever; grind the coating back at least 25 mm and use local exhaust ventilation.
- Mild steel carbon range
- Mild steel contains about 0.15 to 0.30 percent carbon; it is ductile, weldable and has a tensile strength near 400 to 500 MPa.
- Stainless steel chromium minimum
- Stainless steel contains at least 10.5 percent chromium, which forms a passive oxide layer that resists corrosion.
- Aluminium density compared with steel
- Aluminium has a density of about 2.7 g/cm3, roughly one-third that of steel, and forms a tough oxide layer.
- Spark test for high carbon
- High-carbon steel gives short, bright, bushy sparks with many bursts, while mild steel gives longer white sparks with fewer bursts.
- Vernier caliper least count
- A standard vernier caliper reads to 0.02 mm; the reading is the main scale value plus the coinciding vernier division times 0.02 mm.
- Micrometer least count
- An outside micrometer reads to 0.01 mm; the reading is the barrel value plus the thimble division times 0.01 mm.
- Try square purpose
- A try square checks a 90-degree angle and straightness; a combination square also gives 45 degrees and can be used as a depth gauge.
- Datum in marking out
- A datum is a reference face or line from which all dimensions are measured, so errors do not accumulate across the workpiece.
- Tap drill size rule
- For metric threads, tap drill diameter equals major diameter minus pitch; M10 x 1.5 therefore needs an 8.5 mm drill.
- Hacksaw blade pitch
- Use 18 TPI for general mild steel, 24 to 32 TPI for thin tube and sheet, and keep at least three teeth in contact.
- File card use
- A file card is a stiff brush used to clean metal chips from file teeth; clogged teeth cause scratching and reduce cutting efficiency.
- Drill speed formula
- N equals 1000 times cutting speed divided by pi times diameter; N is rpm, speed is m/min and diameter is mm.
- Twist drill point angle
- A general-purpose twist drill has a 118-degree point angle; 135-degree points are used for hard materials and sheet metal.
- Countersink versus counterbore
- A countersink cuts a conical seat for a flat-head screw, while a counterbore cuts a flat-bottomed recess for a cap screw head.
- Bend allowance formula
- BA equals pi times (R plus K times T) times theta divided by 180, where R is inside radius, T thickness and K about 0.33 to 0.5.
- Rivet pitch rule
- Rivet pitch is about three to four times rivet diameter, and edge distance is about 1.5 to 2 times diameter.
- Parallel line development
- Parallel line development is used for prisms and cylinders; radial line development is used for cones and pyramids.
- Annealing purpose
- Annealing heats steel above the critical temperature and cools it slowly, softening the metal, refining grain and relieving internal stress.
- Tempering temperature range
- Tempering reheats hardened steel below the lower critical temperature, usually 150 to 650 degrees Celsius, to reduce brittleness while keeping hardness.
- Case hardening process
- Case hardening adds carbon to the surface of low-carbon steel at about 900 to 950 degrees Celsius, then quenches it to harden the case.
- Soft soldering temperature
- Soft soldering uses filler that melts below 450 degrees Celsius; brazing uses filler above 450 degrees Celsius and does not melt the parent metal.
- Brazing capillary gap
- Brazing relies on capillary action, which fills a joint gap of about 0.05 to 0.2 mm; wider gaps weaken the joint.
- Bolt grade meaning
- In bolt grade 8.8, the first number is one hundredth of tensile strength in MPa and the second is ten times the yield ratio.
- MMA current rule
- For manual metal arc welding, set about 30 to 40 amps per millimetre of electrode diameter; a 3.2 mm electrode needs roughly 100 to 130 amps.
- E7018 electrode storage
- E7018 is a low-hydrogen electrode that must be kept dry and baked at about 250 to 300 degrees Celsius before use.
- TIG current for aluminium
- Aluminium is TIG welded with alternating current, which breaks the oxide layer during the positive half cycle and gives penetration during the negative half.
- First-angle projection
- In first-angle projection the view from the front is placed behind the object, so the top view appears below the front view.
- Welding symbol arrow side
- A welding symbol with the fillet triangle on the reference line above the arrow side means the weld is made on the arrow side of the joint.
- ISO clearance fit H7/h6
- H7/h6 is a clearance fit: H7 is the hole tolerance and h6 is the shaft tolerance, leaving a small gap between them.