Fuzzy pid based Temperature Control of Electric Furnace for Glass Tempering Process

2.2 
 
Resistance
 
Heating
 
and
 
Melting furnace 
 
Resistance heating is the simplest and oldest electric-based method of heating and melting 
metals and nonmetals. Efficiency can reach close to 100% and temperatures can exceed 
3,600ºF. With its controllability, and rapid heat-up qualities, resistance heating is used in many 
applications from melting metals to heating food products. Resistance heating can be used for 
both high-temperature and low-temperature applications. There are two basic types of this 
technology: direct and indirect resistance heating [7]. 
Resistance heating applications are precisely controlled, easily automated, and have low 
maintenance. Because resistance heating is used for so many different types of applications, 
there are a wide variety of fuel-based processes heating systems, as well as steam-based 
systems, which perform the same operations. In many cases, resistance heating is chosen 
because of its simplicity and efficiency [7]. 
2.2.1 Direct resistance heating furnace 
 
Direct resistance (also known as conduction heating), an electric current flows through a 
material and heats it directly. This is an example of the Joule Law or effect5 at work. Typically, 
metal is clamped to electrodes in the walls of the furnace and charged with electric current. 
Electric resistance within the load generates heat, which heats or melts the metal. The 
temperature is controlled by adjusting the current, which can be either alternating current or 
direct current. The material to be heated must conduct at least a portion of the electric current 
for direct resistance to work. Metals with low conductivity, such as steel, create more 
resistance and more heat, which makes the process more efficient. Direct resistance heating is 
used primarily for heat treating, forging, extruding, wire making, seam welding, glass heating, 
and other applications. Direct resistance heating is often used to raise the temperature of steel 
pieces prior to forging, rolling, or drawing applications [7]. 

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Fuzzy PID Based Temperature Control of Electric Furnace for Glass Tempering Process
M.Sc. Thesis, Addis Ababa University, December 2016 
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