UPMSP Intermediate Metal Craft: Moulding in Ferrous Metals flashcards

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

Foundry PPE

Leather apron, safety shoes, leg guards, goggles or face shield, gloves and a dust respirator protect the foundry worker against molten-metal splash, silica dust and noise.

Silicosis

A lung disease caused by inhaling respirable free silica dust during sand mixing, shakeout and fettling; it is prevented by exhaust ventilation, wet methods and approved respirators.

Water and molten metal

Water trapped in damp scrap, wet tools or a wet ladle turns instantly to steam and expands about 1600 times, throwing molten metal explosively; charges and tools must be dry.

Green sand

A moulding sand containing roughly 5-15 percent clay and 3-8 percent water, used moist and unbaked; it is the cheapest and most widely used sand in ferrous foundries.

Permeability number

A measure of how easily gases pass through rammed sand, obtained by forcing 2000 cm3 of air through a standard 50.8 mm diameter by 50.8 mm high specimen.

AFS grain fineness number

The weighted average of sand retained on a standard sieve stack; a higher number means finer sand, giving a better surface finish but lower permeability.

Shrinkage allowance

The enlargement of a pattern to compensate for liquid and solid contraction of the metal: about 10 mm per metre for grey iron and 20 mm per metre for steel.

Draft allowance

A taper of 0.5-3 degrees given to the vertical faces of a pattern so it can be withdrawn from the mould without tearing the sand walls.

Core print

A projection on the pattern that forms a matching seat in the mould, locating and supporting the core against the buoyancy of the liquid metal.

Riddle

A sieve used to break up and aerate facing sand and to remove lumps, metal shot and foreign matter before the sand is placed against the pattern.

Vent wire

A thin steel wire used to pierce 2-3 mm holes in a rammed mould so that steam and gases can escape instead of forming blowholes in the casting.

Chaplet

A small metal support placed between the core and the mould surface to hold the core against metal buoyancy; it must fuse into the casting metal.

CO2 core process

A core or mould made from sodium silicate bonded silica sand, hardened in seconds by passing carbon dioxide gas through it, so no baking oven is needed.

Core wash

A graphite, zircon or silica based coating brushed or sprayed on a core to improve the casting surface finish and resist metal penetration into the sand.

Core collapsibility

The ability of a core to crush after the metal has solidified, so that contraction of the casting is not restrained and hot tears are avoided.

Chvorinov's rule

Solidification time equals a constant B multiplied by the square of the volume-to-surface-area ratio; thicker sections freeze last and therefore need feeding.

Riser

A reservoir of molten metal connected to the mould cavity that feeds the casting as it contracts during solidification, preventing internal shrinkage cavities.

Aspiration

Air drawn into the gating system when the sprue does not run full; it is prevented by a tapered sprue and a pouring basin kept full of metal.

Cupola

A vertical shaft furnace charged with alternate layers of coke, limestone flux and metal; it melts grey cast iron continuously and is tapped at the bottom.

Inoculation

The addition of a small amount of ferrosilicon to molten grey iron just before pouring, used to control chill depth and refine the graphite flakes.

Pouring temperature

The temperature at which liquid metal enters the mould; grey cast iron is poured around 1300-1350 C and steel castings around 1550-1600 C.

Shell moulding

A process in which resin-coated sand is dropped onto a metal pattern heated to 230-290 C, forming a thin cured shell that gives good finish and dimensional accuracy.

Investment casting

A lost-wax process where a wax pattern is coated with ceramic shells, dewaxed, fired and poured; it produces fine detail in alloys that are hard to machine.

Centrifugal casting

Metal poured into a rotating die is thrown outward by centrifugal force, producing dense pipe and bush castings that are free from central shrinkage porosity.

Blowhole

A smooth-walled, round internal gas cavity in a casting, caused by high sand moisture, low permeability, excessively hard ramming or an unvented core.

Hot tear

An intergranular crack formed while a casting is solidifying and contracting against a strong mould or core, commonly associated with high sulphur and phosphorus.

Misrun

A defect in which the metal fails to fill a thin section or a distant part of the mould because pouring temperature, metal head or fluidity is too low.

Stress relieving

Heating a casting to about 550-600 C, holding until the temperature is uniform, then cooling slowly in the furnace to remove residual casting stresses.

Shot blasting

A surface cleaning operation in which steel shots are thrown at high velocity onto the casting to remove sand, scale and oxide and leave a uniform finish.

Vernier least count

The difference between one main-scale division and one vernier division; with 0.5 mm main divisions and 50 vernier divisions the least count is 0.02 mm.

Micrometer least count

The screw pitch divided by the number of divisions on the thimble; a pitch of 0.5 mm with 50 thimble divisions gives a least count of 0.01 mm.

Casting weight

The volume of the casting multiplied by the density of its metal, using about 7.2 g/cm3 for grey iron, 7.85 for steel and 2.7 for aluminium.