Special Casting Process | Special Casting Techniques | Special Casting Methods

Introduction to Special Casting Process

Now a day’s special Casting process has been developed to effect a saving time and expense to produce a better quality casts. In comparing to Sand Casting the main difference is, in this process do not in all cases require drying or Baking of moulds or cores or rapid hardening action takes place due to chemical reactions in them.

01-lost wax method-gated patterns-chess piece manufacturing

Classification of Special Casting Process:

01-types of solidification process - types of special casting process

Need for special casting process

· Sand mould casting process gives satisfactory results at low cost.

· All metals may be cast in sand moulds and there is no limitations as regards the size of the casting which can be made.

· Sand casting enjoys wide applications and a very large quantity of castings even today is produced through sand casting only.

· However, sand moulds are single purpose moulds as they are completely destroyed
after the casting has been removed from the moulding box.

· It becomes therefore obvious that the use of a permanent mould do a considerable saving in labour cost of mould making.

· There are certain other limitations also possessed by conventional sand casting technique which necessitated the developments of Special casting processes.

Advantages of special casting process over sand casting

· Greater dimensional accuracy.

· Higher metallurgical quality.

· Lower production cost (in certain cases).

· Ability to cast extremely thin sections.

· High production rates.

· Better surface finish on the castings; therefore low labour and finishing costs.

· Minimum need for further machining of castings.

· Castings may possess a denser and finer grain structure.

· Castings are slightly stronger and more ductile than solid mould castings.

Coreless Induction Furnace | Induction Furnace Melting | Induction Furnace Basics

Induction Furnace

The principle of induction melting is that a high voltage electrical source from a primary coil induces a low voltage, high current in the metal or secondary coil. Induction heating is simply a method of transferring heat energy.

Principles are:

The principle of induction heating is based on the following two laws:

1. Electromagnetic induction

2. The joule effect

01-induction furnace - coreless induction furnace - electromagnetic induction

The high frequency induction furnaces use the heat produced by eddy currents generated by a high frequency alternating field. The inductor is usually made of copper in order to limit the electric losses. Nevertheless, the inductor is in almost all cases internally water-cooled. The furnace consists of a crucible made of a suitable refractory material surrounded by a water cooled copper coil. In this furnace type, the charge is melted by heat generated from an electric arc. The coil carries the high frequency current of 500 to 2000 Hz.

01-induction copper coil - copper inductors - water cooled induction heater

The alternating magnetic field produced by the high frequency current induces powerful eddy currents in the charge resulting in very fast heating. Various configurations are available, with two or three electrodes high melting capacity (25 to 50 tons/hr) and they are used primarily for casting steel.

These currents also provide certain amount of agitation to the melting charge resulting in efficient mixing. Molten metal can be poured by tilting the furnace.

01-induction furnace-schematic arrangements of induction furnace

Advantages:

· Induction furnace does not need electrodes like electric arc furnace.

· Better control of temperature

· Better control of composition of the melt

Disadvantages:

· An induction installation usually implies a big investment that must be considered and compared to alternative heating techniques.

· Induction heating is preferably used for heating relatively simple shapes.

Materials to be casted:

· Steel

· Steel alloys