Karnataka SSLC Elements of Mechanical Engineering IV - JTS (KSEAB) cheat sheet

Mechanical properties: strength (stress at failure), stiffness (Young's modulus E = stress/strain in elastic range), ductility (% elongation or % reduction in area), hardness (resistance to indentation - Brinell HB, Vickers HV, Rockwell HRC), toughness (energy absorbed before fracture, measured by Izod/Charpy impact test), brittleness (little plastic deformation before fracture).

Ferrous metals: plain carbon steel (0.05–2.0% C), cast iron (2–4% C, brittle, good compressive strength and damping), wrought iron (slag fibres, ductile, now obsolete), alloy steels (Cr, Ni, Mo, V improve hardenability and wear resistance).

Non-ferrous metals: aluminium (light, 2.7 g/cm³, good conductivity, corrosion-resistant oxide layer), copper (excellent electrical/thermal conductivity), brass (Cu-Zn), bronze (Cu-Sn), zinc (galvanising), lead (dense, soft, radiation shielding).

Non-metals: polymers (thermoplastics soften on reheating, thermosets do not), ceramics (hard, brittle, heat-resistant), composites (fibre-reinforced - high strength-to-weight ratio), wood, rubber.

Heat treatment: annealing (soften, relieve stress, slow furnace cooling), normalising (refine grain, air cooling), hardening (heat above critical temperature then quench), tempering (reheat hardened steel to reduce brittleness and relieve internal stress).

Case hardening and surface hardening (carburising, nitriding, induction hardening) harden only the outer skin while keeping a tough core.

Hooke's law applies within the elastic limit: stress σ = F/A, strain ε = ΔL/L, and E = σ/ε. Yield point marks the onset of permanent deformation; the ultimate tensile strength is the maximum stress on the stress-strain curve.

Material selection criteria: strength-to-weight ratio, machinability, weldability, corrosion resistance, thermal and electrical conductivity, cost, and availability in standard sections.

Marking and measuring hand tools: steel rule, try square (90° checking), scriber (marks metal), centre punch (locates drill points, 90° point), dot punch, dividers, calipers (inside/outside/odd-leg), surface plate and V-block.

Hacksaw: blade teeth per inch (14 TPI coarse for soft thick sections, 18–24 TPI for thin/tube), set of teeth provides clearance, cut on forward stroke, blade mounted with teeth pointing forward.

Files: cut by pressure on forward stroke only; single-cut (lathe work, sharpening), double-cut (rapid metal removal), rasp (wood); grades rough, bastard, second-cut, smooth; file card cleans the teeth.

Chisels: flat cold chisel (chip metal), cross-cut chisel (keyways/grooves), diamond-point chisel (corner grooves); cutting angle for general steel about 60°, softer metal smaller angle.

Drilling and thread tools: twist drill (point angle 118° for general steel, 135° for hard materials), taps (taper, second, plug) cut internal threads, dies cut external threads, tap wrench and die stock hold them.

Striking and holding tools: ball-peen hammer (peen for riveting), mallet (soft-faced for sheet/wood), bench vice, pliers (combination, long-nose), spanners (open-end, ring, box, adjustable) sized to nut flats.

Scraping and finishing: scrapers (bearing fitting, surface finishing), hand reamers (accurate hole sizing), abrasive paper and lapping for fine finish.

Safety rules for hand tools: never use a file without a handle, never strike a hardened tool with a hardened hammer, keep cutting edges sharp, and never carry tools in a pocket.

Least count (LC) = smallest value an instrument can read. Vernier caliper LC = 1 main scale division − 1 vernier scale division; typical metric LC = 0.02 mm. Reading = main scale reading + (vernier coincidence × LC).

Micrometer (screw gauge): pitch = axial advance per revolution (commonly 0.5 mm); LC = pitch / number of circular scale divisions (commonly 0.01 mm). Reading = barrel reading + (thimble division × LC); zero error must be added or subtracted.

Other instruments: dial indicator (runout, 0.01 mm), depth gauge, height gauge, feeler gauge (gap thickness), sine bar (angle measurement), spirit level, surface roughness comparator, go/no-go gauges.

Fits and tolerances: clearance fit (hole always larger than shaft), interference fit (shaft larger), transition fit (either). Hole basis is preferred in industry; fundamental deviation fixes the nearest limit, IT grades fix tolerance size.

Limits: upper and lower limits define the tolerance zone; tolerance = upper limit − lower limit; allowance = minimum clearance (can be negative for interference).

Workshop layout: marking-off table, bench work, fitting, turning, milling, drilling, grinding, welding, and inspection sections; 5S (sort, set in order, shine, standardise, sustain) supports housekeeping.

Marking practice: datum surfaces, centre lines, witness marks; use layout dye or chalk for visibility; punch-mark after scribing so the line survives handling.

Measurement errors: parallax, zero error, temperature effect (standard reference 20 °C), wear of instrument, and Abbe error; calibrate instruments periodically against standards.

Thread terminology: major (crest) diameter, minor (root) diameter, pitch (distance between corresponding points), lead (axial advance per revolution), pitch = lead for single-start threads, lead = n × pitch for multi-start.

Thread forms: V-thread (BSW, UNC/UNF, metric) for general fastening; square and Acme threads for power transmission (low friction, high efficiency); buttress thread for one-directional loading; knuckle thread for rough castings.

Metric thread designation: M12 × 1.75 means nominal major diameter 12 mm and pitch 1.75 mm; coarse pitch is default, fine pitch is used where vibration or thin walls demand it.

Right-hand thread tightens clockwise; left-hand thread is used on rotating parts (e.g. one side of a bicycle pedal, grinder spindle) so rotation tends to tighten it.

Temporary fasteners: bolts, screws, studs, nuts, washers, circlips, keys, pins, and split pins. Permanent fasteners: rivets (snap, pan, countersunk heads), welding, brazing, soldering, and adhesives.

Bolted joint design: preload stretches the bolt; thread engagement should be at least one bolt diameter in steel; a washer spreads load; locking devices include spring washer, nylon insert nut, castle nut with split pin, and thread-locking compound.

Riveted joints: lap joint and butt joint (single or double strap); pitch, margin, and diagonal pitch define the layout; efficiency = strength of joint / strength of solid plate.

Thread production and repair: taps for internal threads, dies for external, thread rolling gives stronger continuous grain; stripped threads are repaired with helicoil inserts or by oversize tapping.

Sliding (plain) bearings: journal rotates in a sleeve with a lubricant film; types are hydrodynamic (full fluid film, self-generated by rotation), hydrostatic (external pressure supply), and boundary (thin film, start-up).

Bearing materials: white metal (babbitt), bronze, gunmetal, cast iron, and polymer/PTFE composites; required properties are low friction, embeddability, conformability, and fatigue resistance.

Rolling-element bearings: ball bearings (radial and thrust), cylindrical roller (high radial load), taper roller (combined radial and axial load), spherical roller (misalignment), needle roller (limited space).

Bearing designation: the last two digits of a basic designation give the bore in mm × 5 (e.g. 6205 → 25 mm bore); the 6 prefix indicates a single-row deep-groove ball bearing.

Lubrication: grease for sealed, maintenance-free, low-speed duty; oil for high speed and heat removal; viscosity must suit speed and load; over-greasing raises temperature.

Bearing failure causes: misalignment, overloading, inadequate or contaminated lubricant, incorrect mounting (brinelling from hammer blows), excessive preload, and inadequate clearance.

Seals: static seals (gaskets, O-rings) and dynamic seals (lip/radial shaft seal, gland packing, mechanical seal, labyrinth seal); packing is tightened to allow slight leakage for lubrication.

Fits for bearings: rotating inner ring on a shaft uses an interference fit (e.g. k5/m5), outer ring in a housing uses a clearance or transition fit, so the ring can creep and be dismantled.

Velocity ratio for belt drive: N₁D₁ = N₂D₂ (neglecting slip), so N₂/N₁ = D₁/D₂. With belt thickness t, effective diameter = D + t; slip reduces output speed.

Belt types: flat belt (crossed for reverse direction, quarter-turn for right angle), V-belt (wedge action in groove, higher power, less slip), timing/toothed belt (no slip, exact ratio), round belt.

Belt length (open drive, approximate): L = 2C + π(D₁ + D₂)/2 + (D₁ − D₂)²/(4C), where C is the centre distance.

Chain drive: no slip, positive ratio, suits long centre distances and high torque; needs lubrication and correct sag (about 2% of span); sprocket ratio N₁T₁ = N₂T₂ using tooth counts.

Gear terminology: module m = pitch circle diameter / number of teeth (m = D/T); circular pitch p = πm; addendum = m, dedendum = 1.25m (standard); pressure angle commonly 20°.

Gear trains: simple train ratio = product of driven teeth / product of driver teeth; compound train multiplies stage ratios; idler changes direction only, not ratio.

Gear types: spur (parallel shafts), helical (smooth, quiet, axial thrust), bevel (intersecting shafts), worm and worm wheel (right-angle, high reduction, self-locking), rack and pinion (rotary to linear).

Couplings: rigid (flange, muff) for aligned shafts; flexible (Oldham for parallel offset, universal joint for angular, pin-bush for shock absorption); clutch allows engagement while running.

Mechanical advantage MA = load / effort; velocity ratio VR = distance moved by effort / distance moved by load; efficiency η = MA / VR × 100%.

Law of the machine: P = mW + C, where P is effort, W is load, m is the slope constant, and C is the friction effort; maximum MA = 1/m.

Lever: effort × effort arm = load × load arm. Class I has the fulcrum between effort and load (crowbar, scissors); Class II has the load between them (wheelbarrow); Class III has the effort between them (tongs, forearm).

Simple pulley (single fixed) changes direction only, with MA = 1. A movable pulley with one rope gives VR = 2; a block and tackle with n rope falls gives VR = n.

Wheel and axle: VR = R/r (wheel radius / axle radius). Screw jack: VR = 2πL/p, where L is the lever length and p the pitch.

Inclined plane: VR = length of incline / height = 1/sin θ. Wedge is a double inclined plane; the screw is an inclined plane wrapped around a cylinder.

Differential pulley block: VR = 2R/(R − r), where R and r are the radii of the two upper pulleys; Weston differential pulley is self-locking.

Reversibility: a machine is self-locking if η < 50% (load cannot reverse the drive, as in a screw jack); η > 50% makes it reversible.

Heat is energy in transit due to temperature difference (unit joule, J); temperature measures the thermal state (K, °C); 1 kcal = 4.187 kJ.

Sensible heat changes temperature: Q = mcΔT. Latent heat changes phase at constant temperature: Q = mL (latent heat of fusion of ice ≈ 334 kJ/kg, vaporisation of water ≈ 2257 kJ/kg at 100 °C).

Specific heat capacity: water c ≈ 4.187 kJ/kg·K; steam cₚ ≈ 2.1 kJ/kg·K; ice ≈ 2.1 kJ/kg·K.

Zeroth law: bodies in thermal equilibrium share the same temperature, which makes thermometers valid. First law: energy is conserved; for a closed system Q − W = ΔU. Second law: heat cannot flow spontaneously from cold to hot, and no heat engine can reach 100% efficiency.

Absolute temperature: T(K) = t(°C) + 273.15; absolute pressure = gauge pressure + atmospheric pressure (≈ 101.325 kPa).

Ideal gas law: PV = mRT; for a fixed mass P₁V₁/T₁ = P₂V₂/T₂. Universal gas constant R₀ = 8.314 kJ/kmol·K; R = R₀/M.

Processes: isothermal (T constant, PV = constant), adiabatic (no heat transfer, PV^γ = constant), isobaric (P constant, V/T constant), isochoric (V constant, P/T constant).

Thermal efficiency of a heat engine η = W_net / Q_in = 1 − Q_out/Q_in; Carnot efficiency η = 1 − T_cold/T_hot (both in kelvin) is the maximum between two reservoirs.

Boiler classification: fire-tube (hot gases inside tubes, e.g. Cochran, Lancashire - low pressure, limited capacity) and water-tube (water inside tubes, e.g. Babcock and Wilcox, Stirling - high pressure, high capacity).

Boiler mountings are fittings for safety and operation: safety valve, water level indicator, pressure gauge, fusible plug, blow-down cock, feed check valve, and steam stop valve.

Boiler accessories improve efficiency: economiser (preheats feed water using flue gas), air preheater, superheater (raises steam temperature above saturation), and feed pump.

Boiler efficiency η = heat utilised in steam / heat supplied by fuel = m_s(h₂ − h₁)/(m_f × CV) × 100%.

Equivalent evaporation: mass of water evaporated from and at 100 °C per kg of fuel; factor of evaporation = (h − h_f)/2257.

Steam engine: reciprocating piston machine; the ideal Rankine cycle has four processes: pump (isentropic compression), boiler (constant pressure heat addition), turbine (isentropic expansion), condenser (constant pressure heat rejection).

Steam turbine types: impulse (pressure drops only in nozzles, constant pressure over moving blades, e.g. De Laval) and reaction (pressure drops across both fixed and moving blades, e.g. Parsons); compounding reduces rotor speed.

Steam quality: dryness fraction x = mass of dry steam / total mass of mixture; enthalpy h = h_f + x·h_fg; wet steam carries water droplets that erode turbine blades.

Four-stroke cycle: suction, compression, power (expansion), exhaust - two crankshaft revolutions per cycle. Two-stroke cycle completes in one revolution with ports and a scavenging transfer passage.

SI (petrol) engine: fuel-air mixture drawn through a carburettor or injected, spark plug ignites the charge, compression ratio typically 8–12. CI (diesel) engine: fuel injected at the end of compression and ignites from heat, compression ratio typically 16–22.

Valve timing: inlet valve opens before TDC and closes after BDC; exhaust valve opens before BDC and closes after TDC; valve overlap improves scavenging.

Engine terminology: bore, stroke, TDC, BDC, swept volume = (π/4)D²L, clearance volume, compression ratio = (swept + clearance)/clearance, and indicated/brake power.

Four-stroke power: IP = P_m L A N/(60 × 1000) for four-stroke (N = rpm/2 power strokes per minute); brake power BP = 2πNT/60; mechanical efficiency = BP/IP.

Fuel properties: calorific value (petrol ≈ 44 MJ/kg, diesel ≈ 42–45 MJ/kg), octane number rates petrol anti-knock quality (iso-octane = 100), cetane number rates diesel ignition quality (cetane = 100).

Combustion problems: detonation (knocking) in SI engines is reduced by higher octane, lower compression, and retarded timing; diesel knock is reduced by higher cetane number.

Emissions and cooling/lubrication: CO, HC, NOx, and particulates are controlled by catalytic converters and EGR; cooling is air or water jacketed; lubrication reduces friction and carries heat away.

Centrifugal pump: liquid enters the impeller eye and is thrown outward by centrifugal action; priming is essential because the pump cannot handle gas; the volute casing converts velocity head to pressure head.

Reciprocating pump: positive displacement with a piston or plunger, suction and delivery valves; delivers a nearly constant quantity regardless of head, but flow is pulsating; an air vessel smooths the flow.

Pump head and power: water power = ρgQH (W); pump efficiency = water power / shaft power; pump output Q = area × velocity.

Specific speed of a centrifugal pump Ns = N√Q / H^(3/4); low Ns suits high head and low discharge, high Ns suits high discharge and low head.

Cavitation occurs when local pressure falls below vapour pressure, producing bubbles that collapse and erode the impeller; it is prevented by adequate NPSH, low suction lift, and a cool liquid.

Compressors: reciprocating (positive displacement, high pressure ratio), rotary (screw, vane, roots blower), and centrifugal/axial (high flow, lower pressure ratio); multistage compression with intercooling saves work.

Compressor relations: isothermal work = P₁V₁ ln(P₂/P₁); for a single-stage reciprocating compressor, volumetric efficiency falls as clearance volume and pressure ratio rise.

Fans and blowers move large volumes of air at low pressure; a fan typically develops a pressure rise below about 1 kPa, a blower up to about 100 kPa, and a compressor above that.

Maintenance types: preventive (scheduled inspection and replacement before failure), predictive/condition-based (vibration, oil analysis, thermography), corrective (after failure), and breakdown maintenance (run to failure).

Reliability metrics: MTBF (mean time between failures), MTTR (mean time to repair), availability = MTBF/(MTBF + MTTR), and OEE = availability × performance × quality.

Lubrication and wear: friction and wear are reduced by correct lubricant viscosity and quantity; contamination control (filtration, sealing) extends bearing life; a planned lubrication schedule prevents failures.

Safety: PPE (helmet, goggles, safety shoes, gloves, ear protection); machine guards must be in place before operation; lock-out/tag-out isolates energy before repair; never clean a running machine.

Fire safety: Class A (solid), B (flammable liquid), C (gas/electrical), D (metal) fires; use CO₂ or dry powder on electrical fires; water conducts electricity and must never be used on live electrical equipment.

Drawing sheet and lines: A0 to A4 ISO sizes; visible outlines are continuous thick lines, hidden edges are dashed, centre lines are chain lines, dimension lines are thin continuous lines with arrowheads.

Orthographic projection: first-angle projection (Indian standard) places the view on the far side of the object - the top view below the front view; third-angle places it on the near side - the top view above.

Dimensioning and scales: dimensions show the true size, not the drawing size; scale = drawing length / actual length; common scales are 1:1, 1:2 (reducing), and 2:1 (enlarging).