Types of moulding sand

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3 Types of moulding sand 1. Green sand: Green sand which is also known as natural sand is the mostly used sand in moulding. It is basically the mixture of sand, clay and water. The clay contain of green send is about 30% and water contain is about 8%. Clay and water used to increase binding strength of sand. This sand is mostly used to casting both ferrous and nonferrous material. It is fine, soft and has good porosity. This sand is easily available at low cost. - See more at:

4 Types of moulding sand 2. Dry Sand: If the green sand mould is baked or dried in an oven, the moisture of this mould will be evaporate. This sand is known as dry sand. It has high strength so it can be used in large casting. The mould prepared by it, is known as dry mould.

5 Types of moulding sand 3. Loam sand: Loam sand is the mixture of sand and clay with water. It contains up to 50% clay and 18% water. This sand is used for big size casting. This sand does not use pattern and the mould made by sweep or skeleton pattern.

6 Types of moulding sand 4. Facing sand: It is main sand which is in direct contact with molten metal. It is used for making faces of mould. This sand is with direct contact with pattern. This sand dose not used in other casting or the facing sand is the fresh sand and don t reuse. It is mainly the mixture of silica sand and clay. It has high strength and refectoriness. -

7 Types of moulding sand 5. Backing sand: This sand is used to back up the facing sand. The total flask in poured by backing sand after pouring facing sand. It is mainly the used sand so it has blackish in color. It is used to support facing sand -

8 Types of moulding sand 6. Parting sand: This sand is free from the moisture and clay content. It is used to separate cope and drag. This sand does not stick with pattern. -

9 7. Core Sand: This sand is used to making core. This is the mixture of normal silica sand with oil. It is also known as oil sand. The oil used in silica sand is linseed oil or light mineral oil with binders. For large casting water is also add into the mixture of silica and oil.

10 Casting Processes Process Advantages Disadvantages Examples Sand many metals, sizes, shapes, cheap poor finish & tolerance engine blocks, cylinder heads Shell mould Expendable pattern Plaster mould Ceramic mould better accuracy, finish, higher production rate Wide range of metals, sizes, shapes complex shapes, good surface finish complex shapes, high accuracy, good finish limited part size patterns have low strength non-ferrous metals, low production rate small sizes connecting rods, gear housings cylinder heads, brake components prototypes of mechanical parts Investment complex shapes, excellent finish small parts, expensive jewellery impellers, injection mold tooling Permanent mould good finish, low porosity, high production rate Costly mold, simpler shapes only gears, gear housings Die Excellent dimensional accuracy, high production rate costly dies, small parts, non-ferrous metals gears, camera bodies, car wheels Centrifugal Large cylindrical parts, good quality Expensive, few shapes pipes, boilers, flywheels

11 Shell mould casting - metal, 2-piece pattern, 175 C-370 C - coated with a lubricant (silicone) - mixture of sand, thermoset resin/epoxy - cure (baking) - remove patterns, join half-shells mold - pour metal - solidify (cooling) - break shell part

12 Expendable Mould Casting - Styrofoam pattern - dipped in refractory slurry dried - sand (support) - pour liquid metal - foam evaporates, metal fills the shell - cool, solidify - break shell part

13 Plaster-mold, Ceramic-mold casting Plaster-mold slurry: plaster of paris (CaSO 4 ), talc, silica flour Ceramic-mold slurry: silica, powdered Zircon (ZrSiO 4) - The slurry forms a shell over the pattern - Dried in a low temperature oven - Remove pattern - Backed by clay (strength), baked (burn-off volatiles) - cast the metal - break mold part Plaster-mold: good finish (Why?) plaster: low conductivity => low warpage, residual stress low mp metal (Zn, Al, Cu, Mg) Ceramic-mold: good finish high mp metals (steel, ) => impeller blades, turbines,

14 Investment casting (lost wax casting) (a) Wax pattern (injection molding) (b) Multiple patterns assembled to wax sprue (d) dry ceramic melt out the wax fire ceramic (burn wax) (c) Shell built immerse into ceramic slurry immerse into fine sand (few layers) (e) Pour molten metal (gravity) cool, solidify [Hollow casting: pouring excess metal before solidification (f) Break ceramic shell (vibration or water blasting) (g) Cut off parts (high-speed friction saw) finishing (polish)

15 Vacuum casting Similar to investment casting, except: fill mold by reverse gravity Easier to make hollow casting: early pour out

16 Permanent mould casting MOLD: made of metal (cast iron, steel, refractory alloys) CORE: (hollow parts) - metal: core can be extracted from the part - sand-bonded: core must be destroyed to remove Mold-surface: coated with refractory material - Spray with lubricant (graphite, silica) - improve flow, increase life - good tolerance, good surface finish - low mp metals (Cu, Bronze, Al, Mg)

17 Die casting - a type of permanent mold casting - common uses: components for rice cookers, stoves, fans, washing-, drying machines, fridges, motors, toys, hand-tools, car wheels, HOT CHAMBER: (low mp e.g. Zn, Pb; non-alloying) (i) die is closed, gooseneck cylinder is filled with molten metal (ii) plunger pushes molten metal through gooseneck into cavity (iii) metal is held under pressure until it solidifies (iv) die opens, cores retracted; plunger returns (v) ejector pins push casting out of ejector die COLD CHAMBER: (high mp e.g. Cu, Al) (i) die closed, molten metal is ladled into cylinder (ii) plunger pushes molten metal into die cavity (iii) metal is held under high pressure until it solidifies (iv) die opens, plunger pushes solidified slug from the cylinder (v) cores retracted (iv) ejector pins push casting off ejector die

18 Centrifugal casting - permanent mold - rotated about its axis at 300 ~ 3000 rpm - molten metal is poured - Surface finish: better along outer diameter than inner, - Impurities, inclusions, closer to the inner diameter (why?)

19 Casting Design: Typical casting defects

20 Casting Design: Typical casting defects