What is Dielectric Heating?The process of heating in which a high-frequency alternating electric field or radio waves or microwave electromagnetic radiation are used to heat the dielectric materials is known as dielectric heating.Dielectric heating is also known as electronic heating, radio frequency (R.F.) heating, high frequency heating and diathermy.Dielectric heating is mainly used for heating of insulators like wood, plastics and ceramics, etc. which cannot be heated easily and uniformly by the other methods of heating.The frequency of the input supply required for dielectric heating ranges from 10 MHz to 15 MHz and the applied voltage is 20 kV.Principle of ... Read More

During the welding process by the gas welding or arc welding, the gas flame or electric arc can be moved towards the direction of weld progression or opposite to the direction of the weld progression. Depending upon the direction of the move of flame or arc with respect to the weld bead, the welding techniques can be classified into two types viz −Forehand WeldingBackhand WeldingForehand WeldingThe gas or arc welding technique in which the flame or electrode advances in the direction of the weld progression is known as forehand welding. It is also known as push welding or forward welding. ... Read More

There are various methods to control the temperature of the resistance heating at certain selected points in a furnace or oven, as per certain limits. The temperature control of resistance heating may be required in order to hold the furnace temperature constant or to vary it as per the requirements and it can be carried out manually or automatically.In case resistance furnaces or ovens, the developed heat is given by, $$\mathrm{\mathit{H}\:=\:\mathit{I^{\mathrm{2}}Rt}\:=\:\frac{\mathit{V^{\mathrm{2}}}\mathit{t}}{\mathit{R}}}$$Therefore, the temperature of resistance furnaces can be controlled by any of the following methods −By intermittent switching or ON-OFF ControlBy changing circuit configurationBy varying the applied voltageBy varying number ... Read More

The device which receives electrical energy as input and converts it into the heat energy is known as a heating element.The wire employed for the heating element may be circular or rectangular. By determining the electrical input and its voltage, the size (or diameter) and length of the wire required as the heating element to produce the given temperature can be calculated.Design of Heating ElementConsider the heating element is in the circular shape. Therefore, the length and diameter of the heating element can be calculated as follows −According to the Stefan's law, the heat dissipated is given by, $$\mathrm{\mathit{H}\:=\:5.72\:\mathit{Ke}\mathrm{\left [ ... Read More

Shielded Metal Arc WeldingThe shielded metal arc welding (SMAW) is a type of electric arc welding in which coalescences of metals is produced by heat from an electric arc created between the tip of a consumable electrode and the surface of the base material at point of welding.The shielded metal arc welding (SMAW) is also known as manual metal arc welding (MMAW), flux shielded arc welding or stick welding. The shielded metal arc welding is a manual arc welding process which uses a consumable electrode coated in flux to lay the weld. An electric current, either AC or DC, is ... Read More

Materials Used for Heating ElementAn electric heating element is a device which converts electrical energy input into heat energy output. No single element, metallic or non-metallic, is used for designing the heating elements. Different alloys have been tried to obtain different temperature. The various heating alloys are given as follows −The alloys commonly used for low and medium temperature services are −Alloy of Nickel and Chromium, where Ni = 80 % and Cr = 20%. The Ni-Cr alloy is suitable for temperature up to 1200 °C.Alloy of Nickel, Chromium and Iron, where Ni = 65%, Cr = 15% and Fe ... Read More

Induction Heating FurnaceAn electrical furnace in which the heat is produced by induction heating of metal, is called the induction heating furnace. The induction heating furnaces have the capacities range from less than 1 kg to 100 tons and are used to melt various metals like iron, copper, aluminium, etc.Indirect Core Type Induction FurnaceThe indirect core type induction furnace works on the principle of Faraday’s law of electromagnetic induction (mutual inductance). The schematic of an indirect core type induction furnace is shown in the figure below.In this type of induction furnace, a heating element is heated by induction, which transfers ... Read More

Indirect Arc FurnaceAn electric arc furnace in which the heat is produced by striking the arc between two electrodes and then transferred to the charge to be heated is called an indirect arc furnace.In an indirect electric arc furnace, the electric arc does not come in contact with the charge but heat is transferred through radiation from the electric arc to the top surface of the charge and through conduction from the top surface to the bottom layer in the charge.Construction and WorkingThe construction of the indirect arc furnace is shown in the figure. The figure shows a rocking arc ... Read More

Eddy Current HeatingWhen the heating of the charge is done by the induced eddy currents in charge, it is known as eddy current heating.To heat the charge by eddy current heating process, the charge is placed inside a current carrying coil. The current is the high frequency alternating current. For this reason, this method is also called the high frequency eddy current heating. The alternating magnetic field produced by the coil sets up eddy currents in the charge to be heated. Consequently, the charge gets heated-up. The coil used for creating the magnetic field is known as heater coil or ... Read More

Electric Resistance FurnaceThe resistance furnaces or ovens are the insulated closed chambers with a provision for ventilation. The resistance furnaces or ovens are used for heat treatment of metals, commercial or domestic heating, pottery work, etc.The different elements of the furnace can be energies from DC or AC supply of the rated voltage. The star-delta formation provides a wide variation of the temperature.In case of batch type resistance furnace, the charge is inserted in the furnace. The figure shows a typical batch type resistance furnace. Here, it is heated for a specific time at a specific temperature and then removed. ... Read More