Classification of casting Processes

Casting methods may be labeled into following FOUR categories:

1. Conventional Molding Processes

  • Green Sand Molding
  • Dry Sand Molding
  • Flask much less Molding

2. Chemical Sand Molding Processes

  • Shell Molding
  • Sodium Silicate Molding
  • No-Bake Molding

3. Permanent Mold Processes

  • Gravity Die casting
  • Low and High Pressure Die Casting

4. Special Casting Processes

  • Lost Wax Process
  • Ceramic (Shell) Molding
  • Evaporative Pattern Casting
  • Vacuum Sealed Molding
  • Centrifugal Casting

Melting Practices

A quantity of furnaces may be used for melting the metallic, to be used, to make a metallic casting. The desire of furnace depends at the sort of metallic to be melted.
  • Crucible furnaces
  • Cupola furnace
  • Open fireside/Reverberatory furnace
  • Electrical Arc furnace
  • Induction furnace

Crucible Furnace

Crucible furnaces are small potential generally used for small melting applications. This furnace, additionally referred to as as pit furnace; built in a pit and makes use of burning of gas with a blast of air because the supply of heat. Crucible furnace is appropriate for the batch type foundries in which the metallic requirement is intermittent. The metallic is located in a crucible that’s made of clay and graphite. The energy is carried out indirectly to the metallic through heating the crucible through coke, oil or gas. The heating of crucible is performed through coke, oil or gas. The melting of alloy takes place in a pot-like structure, referred to as crucible. The crucible, with the metallic charge in it, is located in the furnace. The hot blast of air from the firebox heats the crucible and melts the metallic rate contained in it.

When the metallic reaches the proper temperature (as visible through lifting the cover of pit), the blast is reduce off. The crucible is taken out and used as a ladle to pour the molten metallic in moulds.

Coke-Fired Crucible Furnace:

Coke-Fired Crucible Furnace

Primarily used for non-ferrous metals Furnace is of a cylindrical form Also referred to as pit furnace Preparation involves: first to make a deep bed of coke in the furnace Burn the coke until it attains the state of most combustion Insert the crucible in the coke bed Remove the crucible when the melt reaches to preferred temperature

Oil-Fired Furnace.

Primarily used for non-ferrous metals Furnace is of a cylindrical form Advantages include: no wastage of fuel Less contamination of the metallic Absorption of water vapor is least because the metallic melts in the closed metal furnace Crucible furnaces are more often than not used for melting of relatively small quantities of low melting point non-ferrous metals and alloys. Control of temperature and chemistry of molten metallic, is poor. The major advantages of those furnaces are that their fabrication, operation and maintenance are easy and the capital value is low.

Open fireside/Reverberatory furnace.

Open fireside/Reverberatory furnace

This furnace is a squat, square brick shape having a shallow fireside that holds the metallic rate. There is a combustion chamber in which powdered coal, gas, or oil is burned. The hot gases from the burning fuel are directed to the fireplace in which they heat and melt the metallic fee. They additionally heat the liner of the fireplace which, in turn, makes the heat reverberate and allows melt the metallic earlier than they leave the furnace through the chimney. The open-fireside furnace is usually used for melting of non-ferrous metals and metal in batch quantities. It additionally finds use for containing of cast iron that has been melted formerly in a cupola furnace. The potential of open fireside furnace is a great deal large than the crucible furnace. It is likewise much less famous than electric powered arc furnace. A furnace or kiln wherein the material below treatment is heated indirectly by using a flame deflected downward from the roof. Reverberatory furnaces are used in copper, tin, and nickel manufacturing, in the manufacturing of certain concretes and cements, and in aluminum. Reverberatory furnaces warmth the metallic to melting temperatures with direct fired wall-installed burners. The number one mode of heat transfer is through radiation from the refractory brick walls to the metallic, however convective heat switch additionally provides additional heating from the burner to the metallic. The advantages furnished through reverberatory melters is the excessive volume processing rate, and low running and maintenance fees. The risks of the reverberatory melters are the excessive metallic oxidation rates, low efficiencies, and big ground area requirements.

Electric arc furnace

Electric arc furnace

An arc furnace is used to melt ferrous alloys, specially metal. The recognition of arc furnaces is due to their High melting rates, High pouring temperature, Ability to supply excessive quality of metallic of just about any preferred composition, and Ability to preserve the molten metallic at regular temperature for longer periods of time. The furnace roof is swung aside and the metallic rate is introduced. The roof is replaced, observed through lowering the 3 carbon electrodes (of approximately 700 mm in diameter and 1.5 to 2 m in length), and finally the power deliver is switched on. A non-stop electric powered arc is formed among the carbon electrodes and the metallic rate. The course of the heating current is usually through one electrode, throughout an arc, through the metallic fee, and returned through any other arc to any other electrode. The height of electrodes in the furnace may be adjusted, relying upon the amount of metal present. The metallic melts in approximately hours. The power deliver is then switched-off, the electrodes are raised, and the furnace is tilted to get the molten metallic in a ladle. A direct arc furnace has a thermal efficiency as high as 70%. Temperatures as high as 1900°C may be generated; Sizes as much as 100 tonnes.

In Indirect electric powered arc furnace,

The electrical arc is struck among graphite electrodes and the metallic rate does not shape part of the electrical circuit.

The furnace rocks from side to side in order that the metallic rate comes in contact with the hot refractory lining and choices up heat for melting. In addition, the radiations from the arc and the recent refractory lining of the furnace help the metallic rate in melting. While the furnace rocks, metallic fee parts get combined up thoroughly, melting is fastened, molten metallic receives stirred up, and over heating of the refractory lining is avoided, which ultimately ends in its extended life. The angle of rocking of furnace is adjusted in any such way that the liquid metallic level stays under the pouring spout. When the metallic has completely melted, the furnace is tilted to be able to allow the liquid metal to go with the drift out of the tap hole. The temperatures and the thermal efficiency acquired in indirect arc furnace are decrease than the ones acquired in an immediate arc furnace. This furnace is usually used for melting of copper and its alloys, cast iron and metal Both direct and indirect arc furnaces be afflicted by the disadvantages that their

  1. Noise pollutants is excessive, and
  2. Running costs (in phrases of costs of electrodes, refractories, and electric strength) are high.

Induction furnace

Induction furnace

Induction heating is a heating method.
This type of furnace is becoming very famous due to the fact of
  • Very excessive melting rates,
  • Much less pollution.
There are  fundamental forms of electric powered induction furnaces:
  • High-frequency (or coreless) induction furnace
  • Low-frequency (or channel-type) induction furnace.
The excessive frequency unit comprises a crucible around which a water cooled coil of copper tubing is wound. High-frequency (up to 10 Kc/s) electric current is passed through the coil to generate an alternating magnetic area.
The changing magnetic area induces secondary currents in the metallic price in the crucible, for this reason heating and melting the metallic rapidly.
The furnace gives properly manipulate of temperature and composition of molten metallic. As there may be no contamination from the source of heat, the furnace has the functionality of manufacturing very pure metallic. Though nearly all common alloys may be melted with this furnace, it is
particularly beneficial where relatively small quantities of special alloys of any type are needed.

The heating through the induction method happens when an electrically conductive material is located in a various magnetic field. Induction heating is a rapid form of heating wherein a current is brought on at once into the part being heated. Induction heating is a non-contact shape of heating.

The heating system in an induction furnace includes:

  • Induction heating power deliver,
  • Induction heating coil,
  • Water-cooling source, which cools the coil and numerous inner components in the power deliver.

The induction heating power deliver sends alternating current through the induction coil, which generates a magnetic discipline. Induction furnaces work at the principle of a transformer. An alternative electromagnetic discipline induces eddy currents in the metallic which converts the electrical electricity to heat with none physical touch among the induction coil and the work piece. The furnace consists of a crucible surrounded through a water cooled copper coil. The coil is referred to as number one coil to which a excessive frequency current is supplied. By induction secondary currents, referred to as eddy currents are produced in the crucible. High temperature may be acquired through this approach. Cored furnaces are used nearly solely as holding furnaces. In cored furnace the electromagnetic field heats the metal among coils. Coreless furnaces heat the metallic through an external number one coil.

Advantages of Induction Furnace

Advantages of Induction Furnace

  • Induction heating is a clean form of heating
  • High charge of melting or excessive melting performance
  • Alloyed steels may be melted with none loss of alloying elements
  • Controllable and localized heating

Disadvantages of Induction Furnace

  • High capital cost of the equipment
  • High running cost

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