Types of Melting Furnaces Used In Manufacturing Foundries

To make a metal cast, one needs to liquefy the metal first. For metal liquefaction, a foundry needs to have a melting furnace. One of the foremost requirements of any foundry is a melting furnace. Foundries in India and around the globe have witnessed an evolution in the technology of melting furnaces. In this blog, we are going to cover the predominantly used furnaces used in foundries. Before heading to choose the type of furnace, every foundry must consider the following few factors that influence the decision:

The alloys that will be used
The melting point of the alloys
Quantity of metal to be liquefied and its melting capacity
The economy of installation and operation of the furnace
Management of environmental and disposal needs

Once you have the answers to these, you can go ahead in choosing the melting furnace based on your requirements. The following are the most commonly used furnaces in foundries:

Cupola Furnace

One of the oldest furnaces used in casting, cupola furnaces are cylindrical chimneys lined with clay, bricks or blocks on the inside, to protect against heat, oxidation and abrasion. The melting process involves prepping the furnace by adding materials like coke, limestone and ferroalloys before adding the metal. This results in a chemical reaction that leaves the impurities floating on the molten metal’s surface. This inefficiency in impurity management during melting is the main reason why we see most iron foundries in India, shifting from Cupola furnaces to other efficient options.

Crucible Furnace

Of all the furnaces, crucible furnaces are the simplest and the most basic ones. Though they come in different sizes, the process remains the same – every crucible is simply placed over a heat source to melt the contents. Based on the heat source, crucible furnaces may be distinguished as resistance-heated & fuel-heated and based on the design as movable & tiltable crucibles. Their capacity to withstand extremely high temperatures, minimum investment requirement and simplicity of maintenance and operation, make this type stand out. They are best suited for small quantities of metal liquefying, especially for jewellery making due to the ease of changing the metal and additives quickly. However, this furnace proves to be uneconomical for large quantities of metal as the energy and operation time consumed is very high.

Electric Arc Furnace

This furnace replaces external heating by inserting carbon electrodes into the contents to be melted, then passing current through an electric arc that completes the circuit and thus generating the required heat. Sometimes, oxygen is also added to enhance the melting process. After melting, the contents are discharged into another smaller furnace (to keep the molten metal hot before casting) or into a ladle by tilting the entire furnace. Electric arc furnaces are primarily used for recycling metal scraps to produce new casts.

Induction Furnace

The most predominantly used furnace by SG iron foundries, the induction furnace, works on the science and principle of induction just as the name suggests. The inductor, i.e., the coil made of copper, is specially manufactured for each furnace based on its shape. This coil acts as a powerful electromagnet and transfers energy to the molten metal. By introducing alternating currents, a reversing magnetic field is created. This causes eddies in the molten metal by initiating a self-stirring action while achieving the optimum melting point. From quality, ease of operation, capacity to energy efficiency, this furnace checks every advantage a melting furnace is expected to have. The entire melting process, irrespective of the type of furnace used, has one thing to be wary of; steam. Water trapped in the additives and metal alloys or steam in the furnaces should be wiped clean to ensure the safety of the foundry workers as even the slightest traces of water leads to splashing of the metal and even explosions. Using a drying oven is one of the best ways to ensure that all components and materials involved are completely dry. Once you have all these basics in place, the melting process and the overall casting process becomes less complicated and more perfect, aiding you to deliver the highest grade of castings for your customers.