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band heaters
Dec 20, 2017

band heaters

table of Contents

Structure and Application

2 Introduction to the heating ring

3 work classification

▪ Resistance heating ring

▪ Induction heating coil

▪ Arc heating ring

▪ Electron beam heating ring

▪ Infrared heating ring

▪ Media heating ring

4 working principle

5 electric heating ring use

Classification of electric heating coils

▪ Cast aluminum heating ring

Structure and Application

The heating ring is wrapped with a thin metal plate (aluminum plate, stainless steel plate, etc.). Typical applications are, for example, electric thermos. The metal tubular electric heating element is cast in the aluminum plate, the aluminum plate or the welding or the mosaic in the aluminum plate, the aluminum plate above constitutes each kind of shape the electric heating plate, the electric heating. Typical applications are, for example, rice cookers, electric irons, electric coffee makers and the like.

Introduction of heating ring

The electric energy is converted into heat energy to heat the object. Is a form of energy use. Compared with the general fuel heating, electric heating can obtain higher temperature (such as arc heating, the temperature can reach more than 3000 ℃), easy to achieve automatic temperature control and remote control, on-board electric heating cup

Can be heated as necessary to maintain a certain temperature distribution of the object. The electric heating can directly generate heat inside the heated object, thus the thermal efficiency is high, the heating rate is fast, and the whole uniform heating or partial heating (including surface heating) can be realized according to the heating process requirement. In the electric heating process, the resulting emissions, residues and smoke less, can be heated objects to keep clean, does not pollute the environment. Therefore, the electric heating is widely used in the production, research and testing and other fields. Especially in the single crystal and transistor manufacturing, mechanical parts and surface hardening, smelting of ferroalloy and artificial graphite manufacturing, and so on, have adopted electric heating.

How to work

According to the different energy conversion methods, electrical heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating and media heating.

Resistance heating ring

The use of current Joule effect of electric energy into heat to heat the object. Usually divided into direct resistance heating and indirect resistance heating. The former power supply voltage is directly added to the heated object, when a current flows through, the object itself is heated electric ironing machine

It will heat. Direct resistance heating of the object must be a conductor, but have a higher resistivity. As the heat generated in the object itself is heated, the internal heating, thermal efficiency is high. Indirect resistance heating by a special alloy or non-metallic materials made of heating elements, heat generated by the heating element, through the radiation, convection and conduction to the heated object. Since the object to be heated and the heating element are divided into two parts, the kind of the object to be heated is generally not limited, and the operation is simple.

Indirect resistance heating of the heating element materials used, the general requirements of large resistivity, resistance temperature coefficient is small, small deformation at high temperatures and not brittle. Commonly used iron aluminum alloy, nickel-chromium alloy and other metal materials and silicon carbide, molybdenum disilicide and other non-metallic materials. Metal heating elements of the maximum operating temperature, depending on the type of material up to 1000 ~ 1500 ℃; non-metallic heating elements of the maximum operating temperature of up to 1500 ~ 1700 ℃. The latter easy to install, can be replaced by the hot stove, but it needs to work pressure regulator device, the life of the heating element than the short alloy, generally used for high-temperature furnace, metal heating element temperature exceeds the maximum allowable working temperature and some special occasions.

Induction heating coil

The use of conductors in the alternating electromagnetic field generated by induced current (eddy current) caused by the thermal effect of the conductor itself heat. According to different heating process requirements, the induction heating frequency of the AC power frequency (50 ~ 60 Hz), intermediate frequency (60 ~ 10000 Hz) and high frequency (higher than 10000 Hz). Frequency power supply is usually used in industrial AC power supply, the vast majority of countries in the world frequency is 50 Hz. The voltage applied to the induction device by the commercial power supply for induction heating must be adjustable. According to the size of heating equipment power supply capacity and capacity, you can use high-voltage power supply (6 ~ 10 kV) through the transformer power supply; can also be directly connected to the heating equipment 380V low voltage power grid.

IF power was used in a long time the frequency of generating units. It consists of intermediate frequency generator and drive asynchronous motor. This unit's output power is generally 50 to 1000 kW range. With the development of power electronics technology, the use of thyristor inverter frequency power supply. This intermediate frequency power supply thyristor first frequency alternating current into direct current, then DC into the required frequency of alternating current. As a result of this frequency conversion equipment volume small, the weight light, does not have the noise, the movement reliable and so on, has gradually substituted the intermediate frequency generating set.

High-frequency power supply is usually first with the transformer to the three-phase voltage of 380 volts to about 20,000 volts high voltage, and then use the thyristor or high-voltage silicon rectifier rectifier AC frequency rectified into direct current, and then electronic oscillation tube DC into high-frequency, high-voltage AC. High-frequency power supply equipment output power from tens of kilowatts to hundreds of kilowatts.

Induction heating of the object must be a conductor. When the high-frequency AC current through the conductor, the conductor skin effect, the conductor surface current density, the conductor center current density.

Can be used for metal brazing, metal can be (quenching, tempering, normalizing) and other heat treatment, as well as forging with diathermy; in the high temperature of the metal; Band, change the heating coil (also known as the sensor) shape, but also any local heating.

Arc heating coil

The use of high-temperature arc heating objects. Arc is the phenomenon of gas discharge between two electrodes. The voltage of the arc is not high but the current is large, and its strong current is maintained by the large amount of ions evaporated on the electrode, so that the arc is susceptible to the influence of the surrounding magnetic field. When the arc between the electrodes, the arc column temperature up to 3000 ~ 6000K, suitable for high-temperature melting of metal.

Arc heating with direct and indirect arc heating two. Direct arc heating of the arc current directly through the object to be heated, the object must be heated arc electrode or a medium. Indirect arc heating of the arc current does not pass through the heated object, mainly by the heat of the arc radiation heat. Arc heating is characterized by: arc temperature is high, energy concentration, steel-making electric arc furnace solution pool surface power up to 560 ~ 1200 kW / square meter. However, the noise of the arc is large, and the volt-ampere characteristic thereof is a negative resistance characteristic (drop characteristic). In order to maintain the stability of the arc during arc heating, the instantaneous value of the circuit voltage is greater than the arc voltage value at the moment the arc current instantaneously crosses, and in order to limit the short circuit current, a certain value resistor must be connected in series in the power circuit.

Electron beam heating ring

The use of electric field under high-speed movement of electrons bombard the surface of the object, so that it is heated. Electron beam heating is the main component of the electron beam generator, also known as electron gun. The electron gun mainly consists of a cathode, a focusing electrode, an anode, an electromagnetic lens and a deflection yoke. The anode is grounded and the cathode is connected with the negative pole. The focused beam is usually at the same potential with the cathode, and the accelerating electric field is formed between the cathode and the anode. The electrons emitted by the cathode accelerate to a very high speed under the action of an accelerating electric field, are focused by an electromagnetic lens, and then controlled by a deflection yoke so that the electron beam is directed to the object to be heated in a certain direction.

The advantages of electron beam heating are: ① control the current value of electron beam Ie, can easily and quickly change the heating power; ② use of electromagnetic lenses can be free to change the heated part or can be free to adjust the electron beam bombarded part of the area; ③ can Increase the power density, so that the bombardment point of the material in an instant evaporation.

Infrared heating ring

The use of infrared radiation objects, objects absorb infrared, the radiation energy into heat to be heated.

Infrared is an electromagnetic wave. In the solar spectrum, at the red end of the visible light, is an invisible radiation. In the electromagnetic spectrum, the infrared wavelength range of 0.75 ~ 1000 microns, the frequency range of 3 × 10 ~ 4 × 10 Hz. In industrial applications, infrared spectrum is often divided into several bands: 0.75 to 3.0 microns for the near infrared zone; 3.0 to 6.0 microns for the middle infrared zone; 6.0 to 15.0 microns for the far infrared zone; 15.0 to 1000 microns for the very far infrared Area. Different objects on the infrared absorption capacity is different, even if the same object, different wavelengths of infrared absorption capacity is not the same. Therefore, the application of infrared heating, according to the type of objects to be heated, select the appropriate infrared radiation source, so that the radiation energy is concentrated in the absorption of heated objects within the wavelength range to get a good heating effect.

Electrical infrared heating is actually a special form of resistance heating, that is, tungsten, iron nickel or nickel-chromium alloy and other materials as a radiator, made of radiation source. After energization, heat radiation is generated due to its resistance heating. Commonly used electric infrared radiation source of radiation type (reflective), tube type (quartz tube) and plate type (flat type) three. Lamp type is an infrared light bulb, with tungsten wire as the radiator, tungsten wire sealed in inert gas filled glass case, as ordinary lighting bulb. Radiation body after heating (the temperature is lower than the general lighting bulb), thus emitting a large number of wavelengths of about 1.2 microns infrared. If the glass shell wall coated with reflective layer, infrared radiation can be concentrated in one direction, so the lamp type infrared radiation source is also known as the reflection type infrared radiator. Tubular infrared radiation tube is made of quartz glass, the middle is a tungsten wire, it is also known as quartz tube infrared radiator. Lamps and tube-type infrared emission wavelengths in the 0.7 to 3 micron range, lower operating temperature, generally used for light, spinning industry, heating, baking, drying and medical infrared therapy. The radiation surface of the plate-type infrared radiation source is a flat surface, which is composed of a flat resistance plate. The front surface of the resistance plate is coated with a material having large reflection coefficient, and the opposite side is coated with a material having a small reflection coefficient, so that most of the heat is radiated from the front. The working temperature of the plate can reach above 1000 ℃, which can be used for annealing the weld of steel material and large diameter pipe and vessel.

Because the infrared has a strong penetrating power, easy to be absorbed by the object, and once absorbed by the object, immediately converted to heat; infra-red heating before and after the energy loss is small, easy to control temperature, high-quality heating, infrared heating applications developed rapidly.

Medium heating ring

The insulating material is heated by a high-frequency electric field. The main object of heating is a dielectric. The dielectric is placed in an alternating electric field and is repeatedly polarized (a phenomenon in which an electric charge acts as an opposite polarity on the surface or inside the dielectric), thereby converting electric energy in the electric field into heat energy.

Medium heating uses a high frequency electric field. In the short-wave and ultrashort wave band, the frequency of several hundred kilohertz to 300 megahertz, known as the high-frequency dielectric heating, if more than 300 MHz to reach the microwave band, known as microwave dielectric heating. High-frequency dielectric heating is usually carried out in the electric field between two plates; microwave dielectric heating is carried out in the waveguide, the resonator or in the radiation field of the microwave antenna.

When the dielectric is heated in a high-frequency electric field, the electric power absorbed per unit volume is P = 0.566 fEεrtgδ x 10 (w / cm)

If the heat, said:

H = 1.33 fEεrtgδ × 10 (cal / sec · cm)

Where f is the frequency of the high-frequency electric field, εr is the relative permittivity of the dielectric, δ is the dielectric loss angle, and E is the electric field intensity. The electric power drawn by the dielectric from the high-frequency electric field is proportional to the square of the electric field intensity E, the frequency f of the electric field, and the loss angle δ of the dielectric. E and f are determined by the applied electric field, and εr depends on the nature of the dielectric itself. Therefore, the object of dielectric heating is mainly the material with larger dielectric loss.

Medium heating As the heat generated in the dielectric (heated objects) inside, so compared with other external heating, heating speed, high thermal efficiency, and uniform heating.

Media heating can be used to heat thermogels, to dry cereals, paper, wood, and other fibrous materials; to preheat the plastic before molding, and to cure vulcanized rubber and wood, plastics, and the like. By selecting the appropriate electric field frequency and device, it is possible to heat the adhesive only while heating the plywood without affecting the plywood itself. For homogeneous materials, the overall heating may be carried out.

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