MATSEC SEC Engineering Technology cheat sheet

Fire triangle = fuel + oxygen + ignition source; removing any one prevents combustion. Class A solids use water/foam, B flammable liquids use foam or CO2, C gases use dry powder, D metals use dry powder, F cooking oils use wet chemical.

Hierarchy of control in order: eliminate the hazard, substitute a safer material/process, engineering controls (guarding, local exhaust ventilation, enclosure), administrative controls (training, rotation, permits), then PPE as the last resort.

Noise action values: lower exposure action value 80 dB(A) / 135 dB(C) peak; upper action value 85 dB(A) / 137 dB(C) peak. Hearing protection is mandatory in a hearing protection zone above the upper value.

Electrical isolation sequence: isolate, lock off and tag, prove dead with an approved voltage tester on the conductors, then re-prove the tester on a known live source before and after the test. Never rely on a switch alone.

Hot work (welding, grinding, brazing): clear combustibles within about 10 m or screen with fire-resisting blankets, use a permit to work, and maintain a fire watch for 30-60 minutes after work stops.

Safe manual handling: feet apart, bend the knees, keep the back straight, hold the load close to the body, do not twist while lifting; use a team lift or mechanical aid for heavy or bulky loads.

COSHH-style assessment: obtain the safety data sheet, identify the exposure route (inhalation, skin contact, ingestion, injection), then apply substitution, extraction or enclosure before respiratory and skin PPE.

Machine guarding: fixed guards where access is not needed during operation, interlocked guards where access is required; the emergency stop must be within reach and must be reset before restart.

All injuries and near misses are recorded in the accident book; escape routes, extinguishers and first-aid points must be kept unobstructed and clearly signed.

Direct stress σ = F/A in N/mm² (MPa); strain ε = ΔL/L and is dimensionless; elastic modulus E = σ/ε up to the limit of proportionality. Typical E: steel ≈200 GPa, aluminium ≈70 GPa, copper ≈120 GPa.

Plain carbon steels by carbon content: mild/low carbon 0.05-0.25% C (ductile, weldable); medium carbon 0.3-0.6% C (heat-treatable); high carbon 0.7-1.5% C (hard, wear resistant). Cast iron contains roughly 2-4% C.

Stainless steel relies on a passive chromium oxide layer; a minimum of about 10.5-12% Cr is needed. Austenitic grades 304 and 316 are non-magnetic and weldable, and 316 contains molybdenum for chloride resistance.

Heat treatments: annealing softens and relieves stress by slow cooling; normalising refines grain by air cooling; hardening austenitises then quenches; tempering reheats below about 600 °C to trade hardness for toughness.

Non-ferrous metals: aluminium density ≈2.7 g/cm³ with good conductivity and a protective oxide film; copper ≈8.9 g/cm³ with very high electrical and thermal conductivity; brass is Cu-Zn and bronze is Cu-Sn.

Polymers: thermoplastics soften on heating and can be remoulded (PE, PP, PVC, ABS); thermosets cross-link permanently and char rather than melt (epoxy, polyester, phenolic); elastomers recover large strains.

Galvanic corrosion needs two dissimilar metals plus an electrolyte. Risk rises with the potential difference and a large cathode-to-anode area ratio; insulate dissimilar joints and avoid stagnant electrolytes.

Hardness test selection: Brinell (10 mm ball, coarse or cast surfaces), Vickers (diamond pyramid, covers soft to very hard in one scale), Rockwell (rapid direct HRC readout for production control).

Fatigue is failure by cyclic stress below the tensile strength, starting at a stress raiser and propagating as a crack; resistance improves with generous fillets, polished surfaces and shot peening.

Vernier caliper: a 50-division vernier gives a least count of 0.02 mm and a 20-division vernier gives 0.05 mm. Reading = main scale value + (coinciding vernier division × least count); check zero before use.

Micrometer: 0.5 mm spindle pitch with a 50-division thimble gives 0.01 mm resolution. Reading = barrel millimetres/half-millimetres + thimble hundredths; use the ratchet or friction thimble to control measuring force.

Steel rule: graduation 1 mm, realistic reading accuracy about ±0.5 mm. Suitable for marking out and rough checks, not for precision fits or tolerance verification.

Drilling spindle speed N = 1000·v/(π·D), with v in m/min. HSS in mild steel ≈25-30 m/min, in aluminium ≈60-100 m/min, in brass higher still with reduced rake; use coolant and peck drilling for deep holes.

Hacksaw blade selection: 18 TPI for thick or soft sections, 24 TPI general purpose, 32 TPI for tube and thin sheet. Keep at least three teeth in contact with the work and cut on the forward stroke.

Files cut on the forward stroke only. Single-cut for sharpening and finishing, double-cut for fast stock removal, draw filing across the work for a fine finish; clean clogged teeth with a file card.

Portable angle grinders: the wheel must be rated at or above the tool's no-load speed, the guard must be fitted, cutting discs must not be side-loaded, and a face shield plus goggles are required.

Squares: try square for general 90° checking, engineer's square for precision, combination square for 45° and depth. Always verify a square against a known straight edge before trusting it.

Go/no-go gauges check a feature against both limits simultaneously; the go end must enter and the no-go end must not, giving fast pass/fail inspection without a reading.

Turning parameters: cutting speed v = πDN/1000 (m/min); feed in mm/rev; depth of cut = (D - d)/2. A three-jaw self-centring chuck suits round or hexagonal bar, a four-jaw independent chuck suits irregular or off-centre work.

Taper turning: half-angle α satisfies tan α = (D - d)/(2L). Methods are swivelling the compound slide, using a taper turning attachment, or offsetting the tailstock for small angles.

Milling: conventional (up) milling has cutter rotation opposing the feed and tends to lift the work; climb (down) milling gives a better finish and thinner chips but requires a backlash eliminator.

Drilling sequence: spot with a centre drill, drill a pilot hole for large diameters, peck-drill deep holes to clear chips, then ream for H7 tolerance and surface roughness around Ra 0.8-1.6 µm.

Common CNC G-codes: G00 rapid positioning, G01 linear interpolation at feed, G02/G03 circular interpolation clockwise/counter-clockwise, G04 dwell, G21 metric units, M03 spindle on clockwise, M05 spindle stop, M06 tool change, M30 end of program.

Tool materials ranked by hot hardness: carbon steel, then HSS (usable to about 600 °C), cemented carbide (about 1000 °C), coated carbide, ceramic and cBN, and diamond which is restricted to non-ferrous and non-abrasive work.

Coolant functions: cool the tool and workpiece, lubricate the chip-tool interface, flush chips away, and limit thermal distortion and corrosion. Delivery may be flood, mist or air blast depending on material.

Surface grinding uses an abrasive wheel with millions of cutting edges to achieve fine finish and tight tolerance; dressing restores wheel sharpness, form and free-cutting behaviour.

Lathe safety: never leave the chuck key in the chuck, stop the spindle before measuring, clamp the work securely, and keep hands, clothing and hair clear of rotating parts.

Manual metal arc (SMAW): E6013 is a general-purpose rutile electrode for sheet and general fabrication; E7018 is a low-hydrogen basic electrode for high-strength or restrained joints and must be stored dry and used from a heated quiver.

GMAW (MIG/MAG) uses a consumable wire electrode with DCEP. CO2 gives deep penetration and low cost; a 75-85% argon/CO2 mix gives a smoother arc and less spatter on thin sheet.

GTAW (TIG) uses a non-consumable tungsten electrode, separate filler rod and inert argon shielding; it suits thin sheet, stainless steel and aluminium, with AC used for aluminium to break up the oxide layer.

Oxy-acetylene: a neutral flame is about 3200 °C. Acetylene cylinder valves are opened no more than about 1.5 turns, flashback arrestors are fitted at both regulators, and oxygen fittings must never contact oil or grease.

Soldering and brazing: soldering filler melts below 450 °C (lead-free Sn-Ag-Cu melts around 217-227 °C); brazing filler melts above 450 °C but below the parent metal melting point. Both rely on capillary action and a flux to remove oxides.

Adhesives: strength depends on surface preparation (abrade and degrease), gap control and full cure. Two-part epoxy is structural, cyanoacrylate is fast but brittle, anaerobic adhesive locks threads, hot-melt is for packaging and light assembly.

Bolt grade designation: 8.8 means nominal tensile strength 800 MPa and yield stress = 0.8 × 800 = 640 MPa. Tightening torque T ≈ K·F·d, with K ≈ 0.2 for dry steel threads.

Weld defects: porosity from trapped gas or damp electrodes, undercut from excessive current or arc length, slag inclusion from poor inter-pass cleaning, lack of fusion from low heat input, plus spatter and distortion.

Distortion control: use tack welds, balanced or backstep sequences, minimum heat input, jigs and pre-setting, and stress relief after welding where the joint is highly restrained.

First-angle projection places the object between the observer and the projection plane: the view seen from the left is drawn on the right of the front view, and the view from the top is drawn below it.

Third-angle projection places the projection plane between the observer and the object: the top view is above the front view and the left view is on the left. The truncated-cone symbol identifies which system is used.

Line conventions (ISO 128 / BS 8888): continuous thick for visible outlines, continuous thin for dimensions and hatching, dashed for hidden detail, chain thin for centre lines and cutting planes.

Dimensioning rules: state true sizes and never scale from the drawing; dimension to visible outlines; never repeat a dimension; avoid crossing dimension lines; place the smallest dimensions nearest the feature.

Sections: the cutting plane is shown by a chain line with arrows; hatching uses thin lines at 45°; adjacent parts are hatched at different angles or spacings; shafts, bolts, pins and ribs cut longitudinally are left unsectioned.

Fits on a hole-basis system: H7/h6 is a clearance fit, H7/k6 a transition fit, H7/p6 an interference fit. Tolerance is the difference between upper and lower limits; allowance is the minimum clearance.

Isometric projection uses three axes at 30° to the horizontal with true lengths along the axes; hidden detail is normally omitted and circles appear as ellipses.

CAD practice: build a 3D model then generate orthographic views automatically; use layers for line types, blocks for standard parts and parametric constraints for design intent; exchange data as DXF, DWG or STEP.

Surface texture: Ra is the arithmetic mean roughness in micrometres. Typical values are about 3.2 for turned surfaces, 0.8 for ground surfaces and 0.1 for lapped surfaces.

Gear ratio = teeth on driven gear / teeth on driver = N2/N1. Speed changes inversely with the ratio and torque changes directly, with power roughly constant apart from losses.

Belt drives: velocity ratio = driver pulley diameter / driven pulley diameter; slip reduces accuracy; a crossed belt reverses rotation. Chain and toothed-belt drives give an exact ratio and transmit higher torque.

Grashof condition for a four-bar linkage: s + l ≤ p + q (shortest + longest ≤ sum of the other two) guarantees at least one link can rotate fully, giving crank-rocker or double-crank motion; otherwise all links only rock.

A quick-return mechanism (slotted link or Whitworth) converts continuous rotation into a reciprocating ram with a faster return stroke; the time ratio is cutting time divided by return time.

Screw jack: for a square thread the ideal mechanical advantage is 2πr/pitch, and the torque needed is T = W·p/(2πη) plus collar friction, where η is efficiency.

Springs obey F = kx within the elastic limit. Springs in parallel add stiffness (k = k1 + k2); springs in series combine as 1/k = 1/k1 + 1/k2.

Bearings: ball bearings for radial and light combined loads, roller and taper roller for heavy loads, plain bearings relying on a hydrodynamic oil film. Lubrication cuts friction and removes heat.

Efficiency η = output/input = (load × load distance)/(effort × effort distance) = mechanical advantage / velocity ratio; no real machine reaches 100%.

Keys and splines transmit torque between shaft and hub. A key fails in shear with τ = F/(b·l); couplings connect shafts and tolerate small angular, parallel or axial misalignment.

Ohm's law V = IR; power P = VI = I²R = V²/R. Resistances add in series; in parallel 1/R = 1/R1 + 1/R2 + …, so the total is always less than the smallest branch.

AC quantities: for a sine wave V_rms = V_peak/√2. A 230 V rms 50 Hz supply has a peak of about 325 V; most of Europe including Malta uses 230 V, 50 Hz.

Three-phase star connection: line voltage = √3 × phase voltage while line current equals phase current. In delta, line current = √3 × phase current while line voltage equals phase voltage.

Star-delta starting reduces starting current and starting torque to one third of direct-on-line values; it can only be used on motors whose windings are rated for delta running.

Protection: an MCB clears overload and short circuit, a 30 mA RCD detects earth leakage and gives additional protection against electric shock, and a fuse ruptures on overcurrent. Earthing holds exposed metal at earth potential.

Components: resistor limits current, capacitor stores charge and blocks DC, inductor opposes changes in current, diode conducts one way, transistor switches or amplifies, relay or contactor isolates a control circuit from a power load.

Sensors and control: NTC thermistor resistance falls as temperature rises, LDR resistance falls with light, strain gauges change resistance with strain. In PLC ladder logic, series contacts give AND, parallel contacts give OR, normally closed contacts give NOT.

Logic gates: AND gives 1 only when all inputs are 1; OR gives 1 when any input is 1; NOT inverts; NAND and NOR are universal gates from which any other function can be built.

Resistor colour code digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold band = ±5% tolerance, silver = ±10%.

Design sequence: brief, then a measurable specification, then concept generation, evaluation and selection, detail design, prototyping, testing, evaluation against the specification, and iteration.

Gantt charts show task duration, sequence and overlap. The critical path is the longest chain of dependent tasks, has zero float, and sets the minimum project duration; delaying any task on it delays the project.

Material selection uses property charts such as strength versus density (specific strength) combined with cost, availability, manufacturability, corrosion resistance and recyclability.

Coursework evidence typically includes annotated concept sketches, CAD drawings, a risk assessment, materials and cost lists, a build log with dated photographs, test data, and an evaluation against each specification point.

Quality: tolerance stack-up decides whether parts assemble and function; quality control checks conformance of the product, quality assurance controls the process; go/no-go gauges speed batch inspection.

Costing: total cost = materials + bought-in parts + labour (rate × time) + overheads + margin. Higher production volume spreads fixed costs and lowers unit cost.

Safe design: comply with relevant standards, eliminate or guard entrapment, shear, nip and electrical hazards, and allow for maintenance, cleaning and end-of-life disposal.

Design for manufacture and assembly: minimise part count, use standard fasteners, design for single-axis assembly, provide tool access and chamfered lead-ins, and avoid unnecessary tight tolerances.

Energy units: 1 kWh = 3.6 MJ = 1000 Wh; power = energy/time. One tonne of oil equivalent is about 41.9 GJ.

Efficiency η = useful energy output / energy input × 100%. Losses appear as heat, friction, sound and electromagnetic losses; system efficiency is the product of the component efficiencies.

Wind power P = 0.5 ρ A v³ Cp; output rises with the cube of wind speed and with swept area. The Betz limit is Cp ≤ 0.593 and practical rotors achieve Cp ≈ 0.35-0.45.

Solar PV: module efficiency is typically 15-22%. Output falls as cell temperature rises (about -0.4% per °C), and shading and soiling cut output sharply. Rating is at standard test conditions of 1000 W/m² and 25 °C.

Heat transfer: conduction Q = kAΔT/d; building elements are rated by U-value in W/m²K, where a lower value means better insulation. Draught-proofing cuts convection losses and reflective foil reduces radiation.

Life cycle assessment covers raw material extraction, manufacture, transport, use and disposal. Embodied energy is compared with operational energy; recycling aluminium uses only about 5% of the energy needed for primary production.

Simple payback = capital cost / annual saving. Whole-life costing also includes maintenance, replacement, fuel price risk and disposal or salvage value.

Sustainability tools: the 3Rs (reduce, reuse, recycle), circular economy thinking, ISO 14001 environmental management, carbon footprint scopes 1-3, FSC-certified timber and low-VOC finishes.