UPMSP Intermediate Metal Craft: Moulding in Ferrous Metals key terms

Fine quartz particles small enough to reach the deepest lung airways, released when sand is mixed, rammed, knocked out or ground. Prolonged exposure causes silicosis, so foundries control it with extraction, wet methods and respirators.

Capture hood and duct system placed close to a dust- or fume-producing operation such as sieving, mixing or pouring, drawing contaminated air away before the worker breathes it. It must be inspected and maintained to remain effective.

Violent steam explosion occurring when molten metal contacts water, damp sand, wet tools or a wet mould. The metal is fragmented and blasted outward, so moulds, ladles and tools must be thoroughly dry before pouring.

Moulding sand mixture of silica grains, clay binder, water and additives used in its moist condition without baking. It is cheap and adaptable; 'green' describes the damp state, not a colour.

Clay mineral, mainly montmorillonite, used as the principal binder in green sand. It absorbs water and coats the sand grains, giving strength while remaining permeable; sodium bentonite develops higher green strength than calcium bentonite.

Stress at which a standard rammed moist sand specimen fails in compression, measured on a sand testing machine. It indicates whether the mould will survive handling and pouring; too low causes erosion, too high encourages gas defects.

Ability of a compacted sand mass to let gases and steam escape through its pore network. It is measured by passing air through a standard specimen; low permeability traps gas and produces blowholes.

Single number expressing the average size of sand grains, calculated from a sieve analysis. Higher values mean finer sand, giving smoother castings but lower permeability and higher binder demand.

Enlargement added to a pattern so the casting cools to the required dimensions. Ferrous metals contract during solidification and cooling; grey iron shrinks less than steel because graphite formation offsets contraction.

Slight taper applied to vertical pattern faces so the pattern can be withdrawn without tearing the mould. It is usually a few degrees and is also needed on core prints and deep pockets.

Projection on a pattern, or the matching recess in the mould, that locates and supports a core. It must be long and strong enough to carry the core's weight and resist metal buoyancy.

Pattern assembly with the cope and drag halves fixed on opposite sides of one plate, so both mould halves are produced from a single location. It suits moulding machines and gives accurate, rapid production.

The upper and lower halves of a moulding flask. The cope is the top part and the drag the bottom; they separate at the parting line and must align accurately when closed.

Compacting moulding sand around a pattern with a rammer, usually in layers, to achieve uniform hardness. Soft ramming allows metal penetration; over-ramming lowers permeability and traps gas.

Pricking small holes through the mould or core so steam and gas can escape to atmosphere. Good venting reduces blows and gas porosity, especially in deep pockets, blind cavities and cores.

Sand shape placed inside a mould to form an internal cavity, passage or undercut in the casting. It must be strong, permeable and collapsible, and is usually removed by knockout after solidification.

Material such as resin, drying oil or sodium silicate that bonds core sand grains and hardens by baking, gas curing or chemical reaction. The choice fixes core strength, collapsibility and curing method.

Small metal support placed between a core and the mould wall to prevent the core from lifting or shifting under buoyancy. It melts into the casting, so it must be clean and metallurgically compatible.

Vertical channel that carries metal from the pouring basin into the gating system. It is tapered downwards so it stays full and does not aspirate air as the metal accelerates.

Horizontal channel distributing metal from the sprue to the ingates. Its size and shape control flow and help separate slag and sand before metal enters the mould cavity.

Final opening through which metal enters the mould cavity. Its position, size and number govern filling pattern, turbulence and feeding, and poor placement can cause cold shuts.

Reservoir of liquid metal connected to the casting that compensates solidification shrinkage. It must remain liquid after the casting has frozen; size and position are based on modulus calculations.

Ratio of cross-sectional areas of sprue, runner and ingates, for example 1:2:4. A pressurised system is smallest at the ingates; an unpressurised one keeps the choke upstream to reduce turbulence.

Vertical shaft furnace charged with alternate layers of coke, metal and limestone, with air blown through tuyeres. It melts grey iron continuously and economically, but composition control is looser than with electric furnaces.

Electric furnace in which alternating current in a coil induces eddy currents in the metal charge, melting it by resistance heating. It gives close control of composition and temperature for iron and steel.

Adding a small amount of reactive alloy, commonly ferrosilicon, to molten grey iron shortly before pouring. It encourages fine graphite and reduces chill, improving machinability and strength.

Temperature of the metal as it enters the mould. Too low causes misruns and cold shuts; too high increases shrinkage, gas absorption and sand erosion. It is set above the liquidus by a superheat margin.

Process in which molten metal is forced at high pressure into a reusable steel die. It gives accurate, smooth castings at high production rates, but ferrous metals are seldom used because die life is short.

Process in which a wax pattern is coated with ceramic slurry, the wax melted out, and the fired shell filled with molten metal. It produces fine detail and close tolerances, including in steels.

Process in which sodium silicate-bonded sand is hardened by passing carbon dioxide through it, forming a silica gel bond. It gives a quick, hard mould or core without baking, but collapsibility and bench life are limited.

Smooth-walled rounded cavity in a casting caused by trapped gas, typically from damp sand, low permeability or inadequate venting. Small internal blowholes may be tolerated; surface or clustered ones usually cause rejection.

Void formed where the last metal to solidify received no feed metal. Internal cavities have rough, dendritic walls; surface sinks may also appear. Correct riser size and placement prevent them.

Discontinuity where two metal streams meet but fail to fuse, leaving a seam. Low pouring temperature, sluggish filling and thin sections are common causes; it is a serious structural defect.

Incomplete filling of the mould cavity because the metal solidified before reaching the far end. Thin walls, low pouring temperature, poor gating and cold moulds contribute to it.

Operations that remove gates, risers, fins and excess metal from castings and clean the surfaces. It includes chipping, grinding, shot blasting and inspection, and generates dust, noise and vibration.

Cleaning process in which steel shot thrown by a wheel or compressed air strikes the casting, removing sand, scale and rust. It also peens the surface; dust extraction is essential because fine silica dust is released.

Rule stating that solidification time is proportional to the square of the volume-to-surface-area ratio, called the modulus. It is used to size risers so they freeze after the casting they feed.

Percentage of poured metal that becomes acceptable casting, calculated as casting weight divided by total poured weight, multiplied by 100. Efficient gating and riser design raises yield and saves melting energy.

Measuring instrument with a main scale and a sliding vernier scale, read by aligning graduations. It measures outside, inside and depth dimensions, commonly to 0.02 mm, and should be zero-checked before use.