UPMSP Intermediate Metal Craft: Moulding in Ferrous Metals cheat sheet

Foundry PPE set: leather apron, safety shoes, leg guards, goggles or face shield, hand gloves, ear plugs and a dust respirator rated for fine silica dust.

Never charge damp, wet, oily or painted scrap, or a wet ladle/tool, into molten metal; the water flashes to steam and expands about 1600 times, causing an explosive metal blow-out.

Free crystalline silica from sand mixing, shakeout and fettling causes silicosis; control by enclosure, local exhaust ventilation, wet methods and an approved respirator.

Cupola and furnace waste gases contain carbon monoxide; charging floors and furnace platforms must be ventilated and gas-tested before entry.

Cylinder code used in Indian workshops: oxygen black, acetylene maroon; keep them at least 3 m apart, fit flashback arrestors, and keep oil and grease away from oxygen fittings.

Molten-metal burn first aid: cool under clean running water for 10-20 minutes, cover with a sterile dry dressing; ice, oil, butter and ink must never be applied.

Extinguisher selection: dry powder or CO2 for electrical and oil fires, foam for oil, dry sand or dry powder for molten metal; water is never applied to molten metal.

Environmental controls: sand reclamation and reuse, slag and dust disposal to approved sites, fume extraction over pouring and knocking-out, and separate treatment of wet scrubber effluent.

Typical composition: silica sand 70-90 %, clay binder (bentonite) 5-15 %, water 3-8 %, additives such as sea coal, wood flour, cereal, dextrin or molasses 1-5 %.

Classification by use: green sand (moist, poured unbaked), dry sand (mould baked at 175-350 C), loam (clay-water slurry for large moulds), facing sand against the pattern, backing sand behind it.

Properties to control: green strength, dry strength, permeability, refractoriness, collapsibility, flowability-plasticity, cohesiveness, adhesiveness and durability.

AFS grain fineness number = sum(f_i x multiplier_i) / sum(f_i) from a standard sieve stack; a higher number means finer sand, better surface finish and lower permeability.

Permeability number P = V x H / (p x A x t), measured by passing 2000 cm3 of air through a standard rammed specimen 50.8 mm diameter x 50.8 mm high.

Moisture test: dry the sample at 105-110 C to constant mass; % moisture = loss in mass x 100 / original mass. A rapid moisture teller gives the same result in minutes.

Clay content by wash test: the sand is washed through a 53-micron sieve with sodium hydroxide solution and the loss is recorded as clay plus silt.

Typical green compressive strength of a moulding sand is 0.3-0.7 kg/cm2 (30-70 kPa); excess water raises strength briefly but sharply lowers permeability and raises blowhole risk.

Mulling sequence: mix dry sand and clay, add water, mull 5-10 minutes, then temper (mellow) for 2-4 hours so moisture distributes evenly before use.

Shrinkage allowance per metre: grey cast iron 10 mm (1 %), steel 20 mm (2 %), brass 15 mm, aluminium 13-16 mm, zinc 20 mm.

Other allowances: draft 0.5-3 degrees, machining 2-5 mm on faces to be machined, plus distortion allowance and shake (rapping) allowance.

Pattern types: solid, split, match plate, cope-and-drag, loose piece, sweep, skeleton, gated, shell and follow board.

BIS pattern colour code: red = machined surface, yellow = core print, black = unmachined surface, green = seat of a loose piece.

Pattern woods: well-seasoned teak, pine, mahogany or deodar, moisture content below 10-12 %, grain running along the length to resist warping.

Core box types: half, split, dump, loose piece, gang and sweep; the box cavity equals the core size including core sand contraction allowance.

The mould cavity is made to the pattern size plus rapping allowance; the pattern itself is the casting size enlarged by the shrinkage allowance.

A match plate carries the cope and drag halves of the pattern on one plate for machine moulding, which guarantees alignment at the parting line.

Hand tools: shovel, riddle, rammer (peen and butt), trowel, slick, spoon, swab, vent wire, draw spike, lifting screw, gate cutter, sprue pin, strike-off bar, bellows.

Flask parts: cope (top), drag (bottom), cheek (middle); a bottom board supports the drag, and weights or clamps stop the cope lifting during the pour.

Ramming rule: layers of 40-60 mm, rammed firmest near the pattern and softer towards the flask wall so that gas can escape; over-ramming causes blows.

Parting sand is fine dry clay-free silica used only between cope and drag; it is never used as facing sand because it has no bonding strength.

Venting: 2-3 mm vent-wire holes spaced 25-50 mm, stopping 10-15 mm short of the pattern surface so metal does not enter the vents.

Hand-moulding sequence: pattern on board, facing sand, fill and ram, vent, strike off, draw the pattern, repair, cut the gate, set the core, close, clamp or weight.

Gaggers are iron rods placed in the cope above the pattern to strengthen the mould; chaplets are placed between core and mould to support the core.

Green sand moulds are poured as made; dry sand moulds are baked (about 175-350 C) for extra strength and lower gas content.

A core forms internal cavities and must be stronger, more permeable and more collapsible than the surrounding mould.

Core binders: linseed oil with cereal (baked 200-230 C), sodium silicate hardened by CO2 gas, no-bake furan resin with acid catalyst, and resin-coated shell sand.

Core prints formed by projections on the pattern locate and support the core; the print seat must resist the buoyancy of the core in liquid metal.

Chaplets are metal supports placed between core and mould; they must be clean and of a metal that fuses into the casting.

Core venting is done with wax threads, vent tubes or a vent-wire channel taken out through the core print to the atmosphere.

Core wash or blacking (graphite, zircon, silica) is applied to improve casting surface finish and resist metal penetration.

Collapsibility is improved by sawdust, hollow cores or fully burnt-out oil binders, so the core crushes when the casting contracts.

Cores are baked with gradual heating to avoid cracking, then stored dry and handled with core carriers or pallets.

Flow order: pouring basin, sprue, sprue well, runner, ingate, mould cavity.

The sprue is tapered downward so it runs full and does not aspirate air; a common pressurised ratio is sprue : runner : ingate = 1 : 2 : 4.

Gating types: top (pencil), bottom, parting-line, step and horn gate; bottom gating fills most quietly and reduces erosion of the mould.

Pouring time for grey iron: t = K x W^(1/3), where W is the casting mass in kg; K is about 2.0 for normal sections, smaller for thin sections.

Chvorinov's rule: solidification time t = B (V/A)^2; the volume-to-area ratio is the modulus, and the riser modulus should be about 1.2 times the casting modulus.

Directional solidification is obtained by placing risers at the heaviest sections, adding exothermic sleeves and padding, and using chills in thin sections.

Ingate area A = W / (density x velocity x pouring time); velocity at the ingate follows v = sqrt(2 g h) from the metal head h.

Continuity A1 v1 = A2 v2 applies along the sprue, runner and ingate, so a smaller ingate raises metal velocity and can erode sand.

A pouring basin with a skim bob or stopper keeps slag back, and the sprue must stay full throughout the pour to avoid slag and air entry.

Cupola charge: pig iron plus scrap, coke and limestone flux; flux is 30-40 % of the coke mass, and the coke-to-metal ratio is commonly 1 : 8 to 1 : 12.

Grey cast iron composition roughly 2.0-4.0 % C, 1.0-3.0 % Si, 0.5-1.0 % Mn; tapping 1350-1400 C, pouring 1300-1350 C.

Steel castings contain 0.05-2.0 % C, are tapped near 1600 C and poured at 1550-1600 C, and are deoxidised with aluminium or ferrosilicon before pouring.

Inoculation with 0.2-0.5 % ferrosilicon controls chill and graphite flake size in grey iron; 0.04-0.08 % magnesium addition produces spheroidal graphite iron.

Limestone (CaCO3) and fluorspar in the flux lower the slag melting point and help remove sulphur and coke ash.

The ladle must be preheated and dry; metal is poured steadily with a short stream, keeping the sprue full and slag back.

Temperature is measured with an immersion platinum-rhodium thermocouple or an optical pyrometer, applying the correct emissivity setting.

Induction furnace melting gives closer composition control and lower sulphur pickup than cupola melting, and allows superheating and holding.

Shell moulding: resin-coated sand is dropped on a metal pattern heated to 230-290 C, producing a cured shell 5-10 mm thick with good finish and accuracy.

Investment (lost-wax) casting: wax pattern, ceramic slurry and stucco shells, autoclave dewaxing, shell firing, then pouring; used for turbine blades and precision parts.

Pressure die casting: hot-chamber for zinc, cold-chamber for aluminium, magnesium and copper alloys; high production rate, negligible machining, but porosity risk.

Centrifugal casting variants: true centrifugal for pipes and bushes, semi-centrifugal for wheels, centrifuging for clustered small parts.

CO2 (sodium silicate) moulding hardens the mould in seconds by passing carbon dioxide through the sand, suitable for medium and large moulds.

Full mould (lost-foam) uses a polystyrene pattern that vaporises as metal enters, giving no parting line and no draft requirement.

Vacuum (V-) process holds dry unbonded sand with a plastic film under vacuum, and the pattern is reusable.

Permanent mould (gravity die) casting uses reusable metal dies, mainly for aluminium and copper alloys, and is not suited to high-melting ferrous metals.

Blowholes and gas porosity are round with smooth walls, caused by high moisture, low permeability, hard ramming or unvented cores.

Shrinkage cavities are rough, dendritic and usually internal; caused by inadequate risering, wrong riser location or poor feeding path.

Misrun and cold shut arise from low pouring temperature, slow pouring or sections too thin for the metal to meet before freezing.

Hot tears are intergranular cracks formed during solidification and contraction, promoted by restrained shrinkage, high sulphur and phosphorus, and rigid cores.

Scab, rat tail and buckle are sand expansion defects; control with sea coal or wood flour additives, lower moisture, and softer, uniform ramming.

Sand inclusion and wash occur when mould or core sand is dislodged; strengthen mould corners, use properly mulled sand, and gate so the stream does not erode the mould.

Metal penetration is a rough metal-sand interface; use finer sand, higher green strength and a mould or core coating.

Swell and drop come from soft ramming; flash and fin come from worn flasks, poor clamping or insufficient weighting.

Inspection methods: visual and dimensional, dye penetrant (surface), magnetic particle (surface and near-surface in ferromagnetic metals), ultrasonic and radiography (internal), hydrostatic pressure test.

Fettling operations: knocking out sand, cutting off gates and risers, chipping fins and flash, grinding, shot blasting, tumbling and final sand blasting.

Stress relieving of grey iron castings: heat to 550-600 C, hold about 1 hour per 25 mm of section, then furnace cool slowly.

Annealing of steel castings: heat to 850-950 C, soak for uniformity, then furnace cool to soften and remove internal stress.

Normalising: heat to 900-950 C, hold, then cool in still air; refines grain structure and raises strength and hardness.

Hardening and tempering: austenitise, quench in water or oil, then temper immediately to relieve quenching stresses and obtain the required toughness.

Malleablising of white iron: a long anneal near 900-950 C decomposes cementite into temper carbon (whiteheart or blackheart malleable iron).

Surface preparation grade Sa 2.5 (near-white blast) is the usual requirement before painting castings.

Grinding wheel safety: ring-test for cracks, mount between correct flanges, keep the guard in position and never exceed the marked rpm.

Casting mass W = volume x density; densities in g/cm3: grey iron 7.2, steel 7.85, aluminium 2.7, copper 8.9, brass 8.5, zinc 7.1.

Shrinkage allowance: L_pattern = L_casting (1 + s/100), with s = 1 for grey iron, 2 for steel and about 1.5 for aluminium.

Vernier caliper least count = 1 main-scale division - 1 vernier division; a 0.5 mm main division with 50 vernier divisions gives 0.02 mm.

Micrometer least count = screw pitch / number of thimble divisions; 0.5 mm divided by 50 divisions gives 0.01 mm.

Mensuration: circle area = pi r^2; cylinder volume = pi d^2 h / 4; cone volume = pi r^2 h / 3; sphere volume = 4 pi r^3 / 3.

Flow relations for gating design: continuity A1 v1 = A2 v2 and Bernoulli's p/(rho g) + v^2/(2g) + z = constant.

Temperature conversion: F = 9/5 C + 32 and C = 5/9 (F - 32).

Electrical relations used for furnace and motor problems: Ohm's law V = I R and power P = V I.

Taper and percentage: slope of a taper = (D - d) / (2L); percentage = (part / whole) x 100.