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Induction Furnaces for Precision Casting

Precision Casting (also called “Investment Casting”) is the modern derivation of the ancient lost-wax casting process. The use of mechanization and automation systems has allowed modern industries to use this casting technique for the production of mechanical components on a large scale.

Precision Casting used to be a foundry technology for small pieces and items manufacturing, but thanks to the experience acquired, robotics development and the availability of new materials, today it is possible to obtain molds from the investment casting process with weights exceeding 150 kg.

The wax models are constructed, then placed in special tanks that contain thermosetting resins and ceramic granules. These latter together polymerize, creating a resistant outer coating. When the mold is getting cast, the wax melts and comes out of the shell, leaving only the piece to solidify.

To produce any object, it is first necessary to make a mold, choosing two alternative techniques:

  • preparation of a Brass / Aluminum model geometrically identical to the piece to be produced, but of bigger volume to make a mold of low-melting-point Alloy.
  • construction of an Aluminum / Steel mold from a solid block, with one or more cavities representative of the piece to be produced.

The steps of the Precision Casting process:

  1. Mold Pattern: The sprays are obtained by injecting the semi liquid wax and the Aluminium mold.
  2. Spray assembly: The spray complete with the gate are assembled around a central sprue, in order to form a type of cluster. On the wax cluster are put the ceramic coats.
  3. Shell assembly: The ceramic shell is constructed from layers of ceramic material superimposed to form an adequate thickness to resist the metallostatic forces.
  4. Dewaxing: After complete drying of the shell, we proceed to the elimination of the wax with a machine called “autoclave”.
  5. Shell baking: The shell is emptied from the wax and baked at high temperature in a heating furnace. GMS designs and manufactures Rotary Furnaces with gas burners to preheat the ceramic shells and has a heating power of 450.000 kCal, 3 adjustment zones with 3 burners each, the maximum capacity of 24 shells and reaches the maximum working temperature up to 1.200 ˚C.
  6. Casting: The cast Steel is poured inside the hot ceramic shell and consequently cooled.
  7. Knockout: The ceramic shell is removed from the solidified Steel cluster, then sand blasted.
  8. Finishing: The precision casting pieces released from the spray are processed with heat treatment and consequently machined.

Medium Frequency Electric Induction Coreless Furnaces for Precision Casting

01.

“Roll-Over”Medium Frequency Induction Coreless Furnaces

The GMS Roll-Over Furnace for PrecisionCasting is a type of air furnace which consists of a crucible wound by a coil installed on a rotation mechanism providing a rotation of 180˚.

A pipeline system allows the Operator to pour inert and insoluble argon in molten metal, and to pour liquid or gaseous argon into the crucible to isolate the free surface of the highly reactive metal from the oxygen in the air. The Furnace is activated by regulating the electric power in the coil, where current passes generating a magnetic field induced inside it, right where the metal Alloy billet of the weight necessary to fill the shell is placed.

The induced magnetic field generates current in the ingot which causes it to heat up due to the Joule effect, until it melts; the exact temperature of the metal is checked with a thermocouple, until the desired temperature is reached; a holding power is set to keep the Alloy temperature constant; the shell is extracted from the furnace by means of a fork manipulator moved by the foundry Operators, then positioned and locked on the crucible, in a previously studied configuration; the speed-controlled rotation mechanism is activated and the molten metal is being poured completely into the shell. The spray is finally picked up by the Operator and placed under an aeration system to extract the hot vapors; sometimes an exothermic powder is used to heat the surface of the metal when ignited in order to move the thermal center of gravity upwards as much as possible and reduce the depth of the primary and secondary withdrawal cones in the molten metal.

During this casting process, the rotation speed of the crucible is set at a value that avoids the formation of defects inside the shell, such as incomplete melting or cold junction resulting due to internal fluid dynamics.

The technical specifications of the GMS Roll-Over MF 005/200 Induction Coreless Furnace for Precision Casting of Steel Alloys:

  • Nominal Power: 200 kW.
  • Operating frequency: 2.400 Hz.
  • Useful Capacity: 50 kg.
  • Melting time: 10 min.

All GMS Furnaces are powered by IGBT Converters which enable eventual power sharing between the individual Melting Units.

“Roll-Over”-type Medium Frequency Induction Coreless Furnace

02.

Gravity Medium Frequency Induction Coreless Furnaces

The GMS Gravity Furnace for Precision Casting is a type of air furnace which consists of a crucible wound by a coil installed on a rotation mechanism providing a rotation of 90˚.

During this casting process, the rotation speed of the crucible is set at a value that avoids the formation of defects inside the shell, such as incomplete fusion or cold junction resulting due to internal fluid dynamics.

The technical specifications of the GMS Gravity Medium Frequency Induction Coreless Furnace for Precision Casting of Steel Alloys:

  • Nominal Power: 200 kW.
  • Operating frequency: 2.400 Hz.
  • Useful Capacity: 50 kg.
  • Melting time: 10 min.

Gravity Medium Frequency Induction Coreless Furnace

Gravity Medium Frequency Induction Coreless Furnace

IGBT (Insulated Gate Bipolar Transistor) Technology for Medium Frequency Induction Coreless Furnaces for Precision Casting

GMS designs and manufactures IGBT Converter Units with the IGBT Technology ranged from 40 to 4.000 Hz and the output power up to 15 MW, specially designed for feeding of Medium Frequency Induction Coreless Furnaces for Precision Casting.

GMS IGBT Converters are designed to ensure:
  • Harmonic index lower than the maximum limits envisaged by current legislation.
  • Optical fibre data transmission.
  • High Machine efficiency (Energy Saving).
  • Remote control of the Machine via the Internet.
  • Lower CapEx.

IGBT Technology for Precision Casting Furnaces