Automotive Materials and Measurement
This domain tests the metals, alloys and non-metals used in vehicle construction, and the measuring instruments used to check them to a hundredth of a millimetre.
Materials
Mild steel for frames and brackets; high-carbon steel for springs, chisels and files; alloy steel for gears and crankshafts; cast iron for cylinder blocks and brake drums because it damps vibration and resists wear; aluminium alloys for pistons and cylinder heads because they are light and conduct heat well; copper for wiring, brass for radiator cores, white metal (babbit) for bearings; cork, rubber and multi-layer steel for gaskets. Heat treatment: annealing softens and relieves stress, hardening followed by tempering restores toughness, and case hardening gives a hard skin on a tough core.
Measurement
Steel rule 1 mm; vernier calliper 0.02 mm; micrometer 0.01 mm; dial bore gauge 0.01 mm; feeler gauge for gaps and clearances; torque wrench for bolt preload; plastigauge for bearing clearance. Clean the jaws, check for zero error, and never spring the jaws on a hot part.
Worked example
Vernier calliper: the main scale reads 12 mm and the 8th vernier division coincides, with least count 0.02 mm. Reading = 12 + (8 × 0.02) = 12.16 mm. If the instrument had a +0.02 mm zero error, the true size would be 12.14 mm - always subtract a positive zero error.
Traps
Confusing least count with accuracy; measuring a bore with a vernier when a bore gauge is specified; closing a micrometer hard on the workpiece; forgetting to correct zero error; using a torque wrench to undo a bolt.