Preparing a sand mould with the pattern for casting an aluminium block

Objective:

  • To carry out the sand moulding process.
  • To prepare the casting of aluminium metal after preparation of sand mould.

Theory:

Casting is one of the oldest and most popular method of producing metallic products, where by molten metal is poured into a cavity known as the mould and allowed to solidify then cool. After complete solidification, the castings are removed from the mold. Most castings require some cleaning and finishing operations. The casting thus produce is almost an exact replica of the mould.

The mould making essentially consists of preparing a cavity having the same shape as the part to be cast by means of ‘pattern’. Green sand refers to an intimate mixture of sand, bentonite clay and water. In green sand moulding process, clay along with water is used as binder. Normally a pair of flasks is used for preparation of mould. The upper flask is referred to as ‘Cope’ and the lower one as ‘drag’. During mould making a suitable ‘gating system’ and a riser’ are also provided. The gating system is the network of channels used to deliver the molten metal into the mould cavity form outside.

Diagram:

Apparatus / Equipment & materials Required:

 Following are the apparatus used in preparing mould

  1. Bellow: A bellow is used to blow loose sand particles from the pattern and the mould cavity
  2. Hand rammer: It is used for ramming the sand in mould.
  3. Hand riddle: It consists of wire mesh fitted into a circular wooden frame. It is used for cleaning, removing foreign matter from sand.
  4. Sprue pin: It is tapered wooden rod which is placed in the cope to make sprue cavity.
  5. Trowels: Used to finish flat surfaces of the mould, cut in gates, make joints or repair mould.
  6. Smoothers and corner slicers: These are employed to repair and finish corners, edges, round and flat surfaces.
  7. Gate cutter: It is a piece of sheet metal with some particular shape. It is used to cut the gate.
  8. Flask: It has two parts, upper part is known as cope and the lower part is known as drag.
  9. Vent Wire: Vent wire is a thin rod or wire carrying a pointed edge at one end and a wooden handle at the other end. Vent wire is used to make small holes called vents in the sand mould.
  10. Green sand xi. Binding agent (like: Bentonite) xii.  Water   xiii.Mouldbox(Cope&Drag)                 xiv.  Draw Screw   xv. Lifter   xvi. Runner & Riser  xvii.  Ladle       xviii. Induction furnace      xix.  Crucible      xx.Tong xxi.  Gloves     xxii.   Bellows.
  • Mould preparation:                                                                                          
  1. Place the drag part of the pattern with parting surface down on ground or moulding board at the center of the drag (flask).
  2. Riddle moulding sand to a depth of about 2 cm in the drag and pack this sand carefully around the pattern with fingers.
  3. Heap more moulding sand in the drag and ram with rammer carefully.
  4. Strike off the excess sand using strike bar.
  5. Make vent holes to within 1 cm of the pattern surface in the drag.
  6. Turn this complete drag and place the cope portion (flask) over it.
  7. Place the sprue and riser pin in appropriate positon.
  8. Complete the cope half by repeating steps (ii) to (v).
  9. Remove the sprue and riser pins and make a pouring basin. Separate the cope and drag halves, and place them with their parting faces up.
  10. Moisten sand at the copes of the pattern and remove pattern halves carefully using draw spikes.
  11. Cut gate and runner in the drag. Repair and clean the cavities in the two mould halves.
  12. Place the core in position, assembled the two mould halves assemble and clamp them together.
  • Melting and Pouring operation:
  1. Melt the metal in the induction furnace. Use appropriate fluxes at proper stages and measure metal temperature from time to time.
  2. Pour the molten metal into the pouring ladle at a higher temperature than the pouring temperature. As soon as the desired pouring temperature is reached, pour the liquid metal into the mold in a steady stream with ladle close to the pouring basin of the mold. Do not allow any dross or slag to go in.
  3. Allow sufficient time for the metal to solidify in the mold. Break the mold carefully and remove the Casting.
  4. Cut-off the riser and gating system from the casting and clean it for any sand etc.
  5. Inspect the casting visually and record any surface and dimensional defects observed.

DISCUSSION:

SAFETY PRECAUTIONS: 

Mould making: 

  1. Wear gloves and a long sleeve shirt to protect your hands and arms from dust.
  2. If possible use wear respiratory protection whilepreparing mould.
  3. Work in a well-ventilated area.
  4. Always wash your hands after handling moulding sand. So that hazardous materials could not transfer to food, which could be ingested.

Casting:

  1. Inspect ladle before use.
  2. Move slowly while removing crucible from furnace and moving to mold.
  3. During transfer molten metal from the induction furnace to mould should be done very carefully.
  4. Pouring of molten metal to be uniform.
  5. Opening of casted item from the mould box to be carefully done.

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