Electric furnace

The use of electric heating effect of metallurgical furnace - SG electric stove. Electric furnace equipment is usually complete set, including electric furnace body, electric equipment (electric furnace transformer, rectifier, frequency converter, etc.), switch, auxiliary auxiliary equipment (current blocker, compensation capacitor, etc.), vacuum equipment, inspection and control instrument (electrician Instrumentation, thermal instrumentation, etc.), automatic adjustment system, furnace mechanical equipment (inlet and discharge machinery, furnace tilting device, etc.). The electric equipment and detection and control instruments of large electric furnaces are generally concentrated in the electric furnace power supply room. Compared with the fuel furnace, the advantages of the electric furnace are: the furnace atmosphere is easy to control, and even can be vacuumed; the material is heated quickly, the heating temperature is high, the temperature is easy to control; the production process is easy to realize mechanization and automation; the labor hygiene condition is good; the thermal efficiency is high Good product quality, etc. The metallurgical industry mainly for smelting furnace steel, iron alloy, a nonferrous metal, heating and heat treatment. At the end of the 19th century, industrial-scale electric furnaces appeared. Since the 1950s, due to the increase in demand for advanced metallurgical products and the decline in electricity costs with the development of the power industry, the proportion of electric furnaces in metallurgical furnace equipment has increased year by year. Electric furnaces can be divided into electric resistance furnaces, induction furnaces (God photoelectric furnaces), electric arc furnaces, plasma furnaces, electron beam furnaces, and the like. Domestic large-scale electric furnace manufacturers, such as Ningbo City, China Photoelectric Furnace Co., Ltd., etc.

First, the resistance furnace

An electric furnace in which Joule heat generated by current passing through a conductor is a heat source. According to the electric heating method, the electric resistance furnace is divided into direct heating and indirect heating. In the direct heating resistance furnace, the current directly passes through the material, and since the electric heating power is concentrated on the material itself, the material is heated quickly, and is suitable for a process requiring rapid heating, such as heating of a forged billet. This electric resistance furnace can heat the material to a very high temperature, such as a carbon material graphitization electric furnace, which can heat the material to over 2500 °C. The direct heating resistance furnace can be used as a vacuum resistance heating furnace or a protective gas resistance heating furnace. In powder metallurgy, it is commonly used for sintering tungsten, tantalum, niobium and other products.

When using this furnace to heat, you should pay attention to:

(1) In order to make the material heated uniformly, it is required that the conductive cross section and electrical conductivity of each part of the material are consistent;

(2) Since the resistance of the material itself is quite small, in order to achieve the required electric heating power, the working current is quite large, so the contact between the power transmitting electrode and the material is better, so as to avoid the arc burning material, and the resistance of the power transmitting busbar is small to reduce Circuit loss

(3) When supplying AC power, it is necessary to properly configure the short net to avoid excessive resistance and excessive power factor.

Most of the resistance furnaces are indirect heating resistance furnaces, in which a resistor body dedicated to electro-thermal transformation is called, which is called an electric heating body, which transfers heat energy to the materials in the furnace. The electric furnace shell is made of steel plate, the furnace is lined with refractory material, and the material is placed inside. The most commonly used electric heaters are iron chromium aluminum electric heaters, nickel chromium electric heaters, silicon carbide rods and molybdenum disilicide rods. The atmosphere in the furnace may be a normal atmosphere, a protective atmosphere or a vacuum, as needed. The general power supply voltage is 220 volts or 380 volts, and an intermediate transformer with adjustable voltage can be configured if necessary. Small furnace (<10 kW) single-phase power supply, large furnace three-phase power supply. For materials with a single variety and large batch volume, continuous furnace heating should be used. Resistance furnaces with furnace temperatures below 700 °C, most of which are equipped with blowers to enhance heat transfer in the furnace to ensure uniform heating. The electric resistance furnace for melting fusible metals ( lead , lead- bismuth alloy, aluminum and magnesium, alloys, etc.) can be made into a crucible furnace; or a reverberatory furnace having a molten pool, and an electric heating body is installed on the top of the furnace. The electroslag furnace is an electric resistance furnace that realizes electrothermal transformation by slag.

Second, the electric furnaces used in industry are classified into two types: periodic working furnaces and continuous working furnaces.

The cycle type working furnace is divided into: box type furnace, sealed box type furnace, pit type furnace, bell cover furnace, trolley furnace, and dumping drum furnace.

Continuous operation furnaces are divided into: kiln type furnace, push rod type furnace, roller bottom furnace, vibrating bottom furnace, rotary hearth furnace, stepping furnace, traction furnace, continuous drum furnace, conveyor belt furnace and so on. Among them, conveyor belt furnaces can be divided into: mesh belt furnaces, stamped chain plate furnaces, cast chain plate furnaces, and the like. ..

Third, electric furnace

The electric heating furnace can use a metal heating element or a non-metal heating element to generate a heat source, and has a simple structure and a wide application. It is widely used in annealing, normalization, quenching, tempering, carburizing and carburizing and nitriding. Wait. The main metal heating elements include Ni-Cr heating wires (most common, up to 1200 ° C), Mo-Si alloys and pure metals such as W and Mo; non-metallic heating elements including SiC (most common, up to 1600 ° C) ), LaCrO 3 and graphite rods (heated to 2000 ° C under vacuum or protective atmosphere).

Fourth, the advantages of electric furnace

(1) It is easy to obtain high temperature compared with a fuel furnace.

(2) It can be heated from the inside of the material to heat it up.

(3) It is convenient to use in controlled atmosphere furnaces and vacuum furnaces.

(4) The electric furnace does not have the heat loss of the exhaust gas of the fuel furnace, so the thermal efficiency is high.

(5) It is easy to control the temperature, which is convenient for remote control and fine adjustment.

(6) It can perform rapid heating.

(7) Good operation performance and no pollution to the environment.

Five, the shortcomings of electric furnace

(1) It is necessary to increase the cost of power distribution equipment.

(2) High electricity costs.

(3) When the resistance heating temperature exceeds 1000 °C, the refractory material may be electrically conductive, and it is necessary to pay attention to the insulation problem.

Six, the main types of electric furnace

(1) Concept of industrial furnace: industrial furnace

Industrial furnace: divided into electric furnace and burning furnace (narrow industrial furnace refers to the burning furnace)

(2) Main products of electric furnace

Seven categories: resistance furnace, induction furnace, vacuum furnace, electron beam furnace, heat treatment (or smelting) unit, heat treatment auxiliary equipment, combustion furnace.

(3) Resistance furnace: three major components: heater, furnace lining, heat-resistant components

1, divided into two major categories of periodic and continuous

2. Characteristics of the periodic furnace:

(1) The charge is simultaneously added and taken out at the same time

(2) The charge is basically not moving during heating (except in special cases: such as drum furnace, roller hearth furnace)

(3) The work area strives for uniform temperature

3. Classification of periodic resistance furnace

(1) Box furnace

(2) Trolley furnace (divided into self-propelled and traction type), used for annealing, after the workpiece is cooled by the furnace after heating

(3) Pit furnace

(4) Cover furnace (mainly used for annealing, heating cover can be hung)

(5) Bottom-lift type hood furnace (cover fixed, lifting base, suitable for large furnaces)

(6) Tumbler furnace

(7) Sealed box furnace (also known as multi-purpose furnace, which can perform heat treatment processes such as carburizing, smooth quenching, carbonitriding, etc. Heating by radiant tube, the radiant tube is sealed by a resistance wire fixed by refractory ceramic disc In a heat-resistant steel pipe, such a structure makes the furnace atmosphere have no effect on the heating element)

4, continuous resistance furnace

(1) Push furnace

(2) Conveyor belt furnace

(3) Mesh belt furnace (suitable for annealing, sintering, brazing and solution treatment of thin and small parts. Structure similar to conveyor belt furnace)

(4) Continuous drum furnace

(5) Roller hearth furnace (the tray moves on the roller)

(6) Rotary hearth furnace

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