MATSEC SEC Engineering Technology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hierarchy of control

Ranked order of risk control: eliminate the hazard, substitute a safer option, apply engineering controls such as guarding or extraction, then administrative controls, with PPE used only as the last resort.

Fire classes A to F

A: solids, use water or foam. B: flammable liquids, use foam or CO2. C: gases, use dry powder. D: metals, use dry powder. F: cooking oils, use wet chemical.

Permit to work

A documented authorisation for high-risk tasks such as hot work or confined-space entry. It records the precautions, isolations and responsible persons, and is signed before work starts and on completion.

Flammable range LEL to UEL

The concentration band of vapour in air between the lower and upper explosive limits within which ignition occurs. Below the LEL the mixture is too lean, above the UEL too rich, to burn.

Young's modulus

The slope of the stress-strain curve in the elastic region, E = stress/strain, measured in GPa. It indicates stiffness: steel is about 200 GPa and aluminium about 70 GPa.

Annealing of steel

Heating steel above its critical temperature then cooling very slowly, often in a furnace. This softens the metal, relieves internal stresses, refines grain structure and improves machinability.

Galvanic corrosion

Corrosion caused when two dissimilar metals are joined in the presence of an electrolyte. The more anodic metal corrodes, and the rate increases with the potential difference and cathode-to-anode area ratio.

Thermoplastic and thermoset polymers

Thermoplastics soften on heating and can be remoulded repeatedly, for example PE, PP and ABS. Thermosets cross-link permanently, cannot be remelted and char instead, for example epoxy and phenolic.

Vernier caliper least count

On a 50-division vernier the least count is 0.02 mm. The reading is the main scale value plus the coinciding vernier division multiplied by 0.02, with zero error checked first.

Micrometer measuring principle

A 0.5 mm screw pitch with a 50-division thimble gives 0.01 mm resolution. The reading is the barrel value plus the thimble division, taken with a ratchet to limit measuring force.

Hacksaw blade pitch selection

Use 18 teeth per inch for thick or soft sections, 24 for general work and 32 for tube and thin sheet. At least three teeth should touch the work at any time.

G00 and G01 codes

In CNC programming G00 is rapid positioning without cutting, used to move between features, while G01 is linear interpolation at a programmed feed rate for actual cutting.

Climb versus conventional milling

In conventional milling the cutter rotation opposes the feed and tends to lift the work. In climb milling the cutter moves with the feed, giving thinner chips and a better finish but requiring backlash elimination.

Carbide versus high speed steel

Cemented carbide keeps its hardness to about 1000 °C against roughly 600 °C for HSS, allowing three to five times higher cutting speeds, but it is brittle and needs a rigid machine setup.

Brazing temperature range

Brazing uses a filler that melts above 450 °C but below the melting point of the parent metals. The molten filler is drawn into the close joint gap by capillary action.

MIG shielding gas choice

Carbon dioxide gives deep penetration at low cost for thick steel. An argon-carbon dioxide mix gives a smoother, more stable arc, less spatter and better control on thin sheet.

Causes of weld porosity

Porosity is gas trapped in the solidified weld. Causes include damp electrodes, oil, paint or rust on the joint, moisture in the flux, incorrect gas flow and a contaminated shielding gas supply.

Bolt grade 8.8 meaning

The first figure gives nominal tensile strength of 800 MPa; the second gives the yield ratio, so yield stress is 0.8 × 800 = 640 MPa. Such bolts suit structural joints.

First angle projection layout

The object sits between the observer and the projection plane, so the view seen from the left is placed on the right of the front view and the top view is placed below it.

Hidden detail line

A line of short evenly spaced dashes used in orthographic views to show edges, corners and outlines that are not visible from that viewing direction but are needed for clarity.

Section view hatching

Cut material is shown by thin continuous lines at 45 degrees. Adjacent components are hatched at different angles or spacings, and shafts, bolts and pins cut lengthwise are left unsectioned.

Gear ratio and torque

Gear ratio equals teeth on the driven gear divided by teeth on the driver. Speed falls by that ratio while torque rises by it, with power approximately constant apart from losses.

Grashof four-bar condition

A four-bar linkage has at least one fully rotating link when shortest plus longest link is less than or equal to the sum of the other two lengths, giving crank-rocker or double-crank motion.

Mechanical advantage and efficiency

Mechanical advantage is load divided by effort; velocity ratio is effort distance divided by load distance. Efficiency is mechanical advantage divided by velocity ratio, multiplied by 100 for a percentage.

Ohm's law

For a resistive circuit, voltage equals current multiplied by resistance, V = IR. Combined with power P = VI this allows current, voltage, resistance and power to be calculated from any two known values.

RMS value of sine wave

The root mean square value of a sine wave equals the peak value divided by the square root of two. A 230 V rms mains supply therefore has a peak of about 325 V.

Residual current device 30 mA

An RCD compares current in live and neutral conductors and trips when the difference, indicating earth leakage, reaches its rated value. A 30 mA unit gives additional protection against electric shock.

Star-delta motor starting

The motor starts connected in star, reducing the voltage across each winding by a factor of root three, so starting current and starting torque fall to one third of direct-on-line values.

Critical path in planning

The longest sequence of dependent tasks in a project network. It has zero float and determines the minimum project duration, so any delay on it delays the whole project.

Design specification purpose

A specification is a measurable statement of the requirements, constraints and criteria a solution must meet. It guides concept selection and provides the basis for objective testing and evaluation.

Wind power equation

Available wind power is P = 0.5 ρ A v cubed Cp, where rho is air density, A the swept area and Cp the power coefficient. Output rises steeply with wind speed.

Simple payback period

Capital cost of an efficiency measure divided by its annual saving, expressed in years. It is quick to calculate but ignores maintenance, fuel price changes and the life of the equipment.