Heating Ring Dali Electric recommends
Converting electrical energy into thermal energy to heat objects. It is a form of electrical energy utilization. Compared with general fuel heating, electric heating can achieve higher temperatures (e.g., arc heating can reach temperatures above 3000°C), and it is easy to realize automatic temperature control and remote control. Car electric heating cup
The heated object can be maintained at a certain temperature distribution as needed. Electric heating can generate heat directly inside the heated object, thus having high thermal efficiency and fast heating speed. According to the process requirements of heating, it can achieve uniform overall heating or local heating (including surface heating), and it is easy to realize vacuum heating and controlled atmosphere heating. During the electric heating process, there is less waste gas, residue, and dust, keeping the heated object clean and not polluting the environment. Therefore, electric heating is widely used in production, scientific research, and experiments. Especially in the manufacturing of single crystals and transistors, mechanical parts and surface quenching, smelting of ferroalloys, and manufacturing of artificial graphite, electric heating methods are adopted.
Classification by Working Method
According to different methods of electrical energy conversion, electric heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and dielectric heating.
Resistance Heating Ring
Using the Joule effect of electric current to convert electrical energy into thermal energy to heat objects. It is usually divided into direct resistance heating and indirect resistance heating. In the former, the power supply voltage is directly applied to the heated object, and when current flows, the heated object itself generates heat. Electric heating ironing machine
Objects that can be directly resistance heated must be conductors but have high resistivity. Since heat is generated inside the heated object itself, it is internal heating with high thermal efficiency. Indirect resistance heating requires special alloy materials or non-metallic materials to make heating elements, which generate heat and transfer it to the heated object through radiation, convection, and conduction. Since the heated object and the heating element are separated, the type of heated object is generally not limited, and operation is simple.
Materials used for heating elements in indirect resistance heating generally require high resistivity, low temperature coefficient of resistance, small deformation at high temperatures, and not easy to become brittle. Commonly used materials include iron-chromium-aluminum alloys, nickel-chromium alloys, and other metal materials, as well as silicon carbide, molybdenum disilicide, and other non-metallic materials. The maximum working temperature of metal heating elements can reach 1000–1500°C depending on the material; non-metallic heating elements can reach 1500–1700°C. The latter is easy to install and can be replaced while hot, but it requires a voltage regulating device during operation and has a shorter lifespan than alloy heating elements. It is generally used in high-temperature furnaces, places where the temperature exceeds the maximum working temperature allowed for metal heating elements, and some special occasions.
Induction Heating Ring
Using the thermal effect of induced current (eddy current) generated when a conductor is in an alternating electromagnetic field to heat the conductor itself. According to different heating process requirements, the frequency of the AC power supply used for induction heating includes power frequency (50–60 Hz), intermediate frequency (60–10000 Hz), and high frequency (above 10000 Hz). Power frequency power supply is the commonly used industrial AC power supply, with most countries using 50 Hz. The voltage applied to the induction device from the power frequency power supply must be adjustable. Depending on the power of the heating equipment and the capacity of the power supply network, high-voltage power (6–10 kV) can be used through a transformer, or the heating equipment can be directly connected to a 380 V low-voltage grid.
Intermediate frequency power supply has long used intermediate frequency generator sets. It consists of an intermediate frequency generator and a driving asynchronous motor. The output power of such sets is generally in the range of 50–1000 kW. With the development of power electronics technology, thyristor inverter intermediate frequency power supplies are used. This intermediate frequency power supply uses thyristors to first convert power frequency AC into DC, and then convert DC into AC of the required frequency. Due to its small size, light weight, no noise, and reliable operation, it has gradually replaced intermediate frequency generator sets.
High-frequency power supply usually uses a transformer to raise the three-phase 380 V voltage to about 20,000 V, then uses a thyratron or high-voltage silicon rectifier to rectify the power frequency AC into DC, and then uses an electronic oscillator tube to convert DC into high-frequency, high-voltage AC. The output power of high-frequency power supply equipment ranges from tens of kilowatts to hundreds of kilowatts.
Objects for induction heating must be conductors. When high-frequency AC current passes through a conductor, the skin effect occurs, meaning the current density is high on the surface and low in the center.
Induction heating can achieve uniform overall heating and surface heating of metal objects; it can melt metals, be used for metal brazing, perform various heat treatments (quenching, tempering, normalizing) on metals, and through heating for forging; in the high-frequency range, by changing the shape of the heating coil (also called inductor), arbitrary local heating can be achieved.
Arc Heating Ring
Using the high temperature generated by an electric arc to heat objects. An electric arc is a gas discharge phenomenon between two electrodes. The arc voltage is not high but the current is large, and the strong current is maintained by a large number of ions evaporated from the electrodes, so the arc is easily affected by the surrounding magnetic field. When an arc forms between electrodes, the temperature of the arc column can reach 3000–6000 K, suitable for high-temperature melting of metals.
Arc heating has two types: direct and indirect arc heating. In direct arc heating, the arc current passes directly through the heated object, which must be one electrode of the arc or the medium. In indirect arc heating, the arc current does not pass through the heated object, and heating mainly relies on the radiant heat of the arc. The characteristics of arc heating are: high arc temperature, concentrated energy, and the surface power of the molten pool in an electric arc steelmaking furnace can reach 560–1200 kW/m². However, the arc is noisy, and its volt-ampere characteristic is negative resistance (drooping characteristic). To maintain arc stability during arc heating, ensure that the instantaneous voltage of the circuit is greater than the arc ignition voltage when the arc current passes through zero instantaneously, and to limit short-circuit current, a resistor of a certain value must be connected in series in the power supply circuit.
Electron Beam Heating Ring
Using high-speed electrons accelerated by an electric field to bombard the surface of an object, thereby heating it. The main component for electron beam heating is the electron beam generator, also called an electron gun. The electron gun mainly consists of a cathode, a focusing electrode, an anode, an electromagnetic lens, and a deflection coil. The anode is grounded, the cathode is connected to a negative high potential, the focusing electrode is usually at the same potential as the cathode, and an accelerating electric field is formed between the cathode and anode. Electrons emitted from the cathode are accelerated to very high speeds under the accelerating electric field, focused by the electromagnetic lens, and then controlled by the deflection coil to direct the electron beam toward the heated object in a certain direction.
The advantages of electron beam heating are: ① By controlling the current value
Ie of the electron beam, the heating power can be changed conveniently and quickly; ② Using the electromagnetic lens, the heated part can be freely changed or the area bombarded by the electron beam can be freely adjusted; ③ The power density can be increased so that the material at the bombarded point evaporates instantly.
Infrared Heating Ring
Using infrared radiation to irradiate objects, which absorb infrared radiation and convert radiant energy into thermal energy for heating.
Infrared is an electromagnetic wave. In the solar spectrum, it lies beyond the red end of visible light and is an invisible form of radiant energy. In the electromagnetic spectrum, infrared wavelengths range from 0.75 to 1000 micrometers, and frequencies range from 3×10 to 4×10 Hz. In industrial applications, the infrared spectrum is often divided into several bands: 0.75–3.0 μm is the near-infrared region; 3.0–6.0 μm is the mid-infrared region; 6.0–15.0 μm is the far-infrared region; 15.0–1000 μm is the extreme far-infrared region. Different objects have different abilities to absorb infrared radiation, and even the same object absorbs different wavelengths of infrared radiation differently. Therefore, when using infrared heating, it is necessary to select an appropriate infrared radiation source according to the type of object being heated, so that the radiant energy is concentrated within the absorption wavelength range of the object to achieve good heating results.
Electric infrared heating is actually a special form of resistance heating, using materials such as tungsten, iron-nickel, or nickel-chromium alloys as radiators to form a radiation source. When electrified, it generates heat due to its resistance and produces thermal radiation. Common electric infrared heating radiation sources include lamp type (reflective), tube type (quartz tube type), and plate type (flat type). The lamp type is an infrared bulb, using a tungsten filament as the radiator, sealed in a glass bulb filled with inert gas, similar to an ordinary lighting bulb. When electrified, the radiator heats up (at a lower temperature than ordinary lighting bulbs) and emits a large amount of infrared radiation with a wavelength of about 1.2 μm. If the inner wall of the glass bulb is coated with a reflective layer, the infrared radiation can be concentrated in one direction, so the lamp-type infrared radiation source is also called a reflective infrared radiator. The tube-type infrared radiation source uses a quartz glass tube with a tungsten filament inside, so it is also called a quartz tube infrared radiator. The infrared wavelengths emitted by lamp-type and tube-type sources are in the range of 0.7–3 μm, with relatively low operating temperatures, and are generally used for heating, baking, drying in light and textile industries, and infrared physiotherapy in medical treatment. The plate-type infrared radiation source has a flat radiation surface composed of flat resistance plates. The front side of the resistance plate is coated with a material with high reflectivity, while the back side is coated with a material with low reflectivity, so most of the heat is radiated from the front side. The operating temperature of the plate type can reach over 1000°C, and it can be used for annealing welds of steel materials and large-diameter pipes and containers.
Note: The above information and technical parameters are compiled and released by Yangzhou Dali Electric Co., Ltd.
