In modern industry, one of the most popular types of electric furnaces is the electric resistance furnace, or ERF. In furnaces of this type, electricity is converted to the required temperature when a current of a certain value flows through solid or liquid consumables.
Today, resistance electric furnaces are used in all industries and national economy sectors without exception. This type of equipment is used in heating, heat treatment, and thermo-chemical processes. EPS furnaces are used for brazing parts, firing finished products, drying, and heat sintering products from various materials. They are also used to smelt non-ferrous metals.

Types of equipment

Modern industrial EAF furnaces can be divided into two types:

• indirect action,
• direct-acting.

In the first case, the equipment passes an electric current of certain parameters through the heating elements. The heat generated in the process is transferred to the heated products by means of thermal radiation, convection, and thermal conductivity.
Direct-acting EAFs or, as they are also called, electrocontact heating equipment, pass current directly through the products, which makes the temperature rise much faster and the processing time shorter.
Indirect heating furnaces include, for example, vacuum equipment, in which heat transfer can occur only through radiation. Most types of indirect heating furnaces transfer heat by means of both radiation and convection.
Often, these furnaces use a liquid coolant in which the products to be processed are immersed. The processes of thermal convection and heat conduction work here. Baths with a liquid carrier can have an internal type of heating, in which the heating elements are immersed inside the tank, or an external type, in which heating comes from external heating elements.
Direct heating furnaces are mostly used to work with products of regular cross-sectional shape. Reinforcing bars, rods, and wires that are connected to special contact points in the network can be processed here.

Direct-heating furnaces are also used in glass production – modern glass furnaces pass an electric current through liquid glass. In addition, such DFHs are used in the production of carborundum and electrographite, as well as electroslag remelting.

Features of operation

Industrial resistance furnaces are classified by operating temperature. Low-temperature equipment includes EAFs operating in the range up to 700 °C. Medium-temperature furnaces operate in the range from 700° to 1250°C, and the “hottest” installations allow processing products at temperatures above 1300°C.
Depending on the operating temperature, the design of such equipment also differs significantly. The first two types of furnaces use heaters made of metals such as nickel-chromium or chromium-iron-aluminum alloys.
Furnaces with a maximum operating temperature use heating elements made of non-metals – these can be materials such as carborundum, lanthanum chromite, graphite, zirconium oxide. There are also variants made of refractory metals – tungsten, molybdenum, niobium or tantalum heating elements are characterized by durability and reliability.
During the operation of high-temperature furnaces, heating elements increase their electrical resistance over time. Accordingly, it is necessary to select the right step-down transformers that allow for a wide range of secondary voltage changes.
Arm units that operate in the low and medium temperature range are often equipped with special shields that are mounted between the heating elements and the workpieces. This is done to protect the products from direct exposure to the radiation of electric heaters.

Principles of operation and 2 types of heating

Modern electric furnaces can be of the heating or melting type. The latter option is often used for processing and melting of various non-ferrous metal alloys. Based on the operating modes, all available electric furnaces are divided into batch and continuous operation equipment.
In furnaces of the first type, the materials to be processed are placed in the working volume of the tank and do not move during heating. The temperature at any point in the working area in a batch furnace is constant, while it simultaneously changes at certain time periods.
In batch furnaces, the processed products are loaded into the working tank and constantly move along its entire length, which makes it possible to obtain a certain product temperature at the outlet. At each point in the working area, the temperature can be the same or different, while it remains constant throughout the entire processing time.
Such features of the processing process determine the scope of application of continuously variable heat treatment. Such equipment allows for greater productivity when it comes to processing the same parts in two types of furnaces.

This makes it possible to use continuously variable furnaces in industrial production with a large volume and number of identical parts. Large-scale production of bearings, automotive complexes, casting of parts for light industry – these and many other industries use continuous furnaces.
Batch furnaces are in demand when it is necessary to produce many heterogeneous parts, each of which requires a specific heating mode. Such equipment is equipped with special units for automatic movement of products in the heating zone. This complicates the design and increases the cost of the EAF itself.