Induction Heating & Melting http://www.inductotherm.com/M2575-0107.pdf

Induction Heating & Melting http://www.inductotherm.com/M2575-0107.pdf

Combustion furnaces пламенная печь

coke [kəuk] кокс

combustion [kəm'bʌsʧ(ə)n] горение, возгорание, сжигание

hollow ['hɔləu] пустой, полый

tubing трубопровод

refractory огнеупорный

metal charge садка металла

furnace ['fɜːnɪs] горн; очаг; печь

instrumentation [ˌɪn(t)strəmen'teɪʃ(ə)n] измерительная аппаратура

furnish ['fɜːnɪʃ] снабжать

tilting mechanism опрокидывающий механизм

refractory огнеупорный материал, огнеупор || огнеупорный; жаростойкий; тугоплавкий

crucible ['kruːsəbl] тигель

nonferrous metals [ˌnɔn'ferəs] цветные металлы

molten ['məult(ə)n] расплавленный

relining ремонт футеровки.

tin reflow оплавление лужёной жести

billet заготовка

bloom блюм

slab сляб (плоская стальная заготовка прямоугольного сечения с большим отношением ширины к толщине; исходный материал для прокатки листовой стали)

Induction Heating & Melting http://www.inductotherm.com/M2575-0107.pdf

Combustion furnaces and induction furnaces produce heat in two entirely different ways.

In a combustion furnace, heat is created by burning a fuel such as coke, oil or natural gas. The burning fuel brings the interior temperature of the furnace above the set point temperature of the charge material placed inside. This heats the surface of the charge material, causing it to heat or melt depending on the application.

Induction furnaces produce their heat cleanly, without combustion. Alternating electric current from an induction power unit flows into a furnace and through a coil made of hollow copper tubing. This creates an electromagnetic field that passes through the refractory material and couples with conductive metal charge inside the furnace. This induces electric current to flow inside the metal charge itself, producing heat that rapidly causes the metal to reach the set point temperature.

Induction furnaces require two separate electrical systems: one for the cooling system, furnace tilting and instrumentation and the other for the induction coil power.

A line to the plant’s power distribution panel typically furnishes power for the pumps in the induction coil cooling system, the hydraulic furnace tilting mechanism and instrumentation and control systems.

Electricity for the induction coils is furnished from a three-phase, high voltage, high amperage utility line. The complexity of the power supply connected to the induction coils varies with the type of furnace and its use.

A channel furnace that holds and pours liquefied metal can operate efficiently using mains frequency provided by the local utility. By contrast, most coreless furnaces for melting require a medium to high frequency power supply. Similarly, power supplies used for heating applications will operate at medium to high frequency.

Raising the frequency of the alternating current flowing through the induction coils increases the amount of power that can be applied to a given size furnace. This, in turn, means faster melting.

Induction Furnaces Come In Many Varieties

Coreless Furnaces

A coreless furnace has no inductor or core, unlike the channel furnace described below. Instead, the entire bath functions as the induction heating area. Copper coils encircle a layer of refractory material surrounding the entire length of the furnace interior. Running a powerful electric current through the coils creates a magnetic field that penetrates the refractory and quickly melts the metal charge material inside the furnace. The copper coil is kept from melting by cooling water flowing through it. Coreless furnaces range in size from just a few ounces to 120 tons of metal and more.

A direct electric heat furnace is a unique type of highly efficient air-cooled coreless furnace that uses induction to heat a crucible ['kruːsəbl] тигель rather than the metal itself. This furnace is used to melt most nonferrous [ˌnɔn'ferəs] цветной metals.

Channel Furnaces

In a zinc coating pot, induction heating takes place in the “channel,” a relatively small and narrow area within the inductor. The channel passes through a laminated steel core and around the coil assembly.

The electric circuit formed by the core and coil is completed when the channel is filled with molten ['məult(ə)n] расплавленный metal.

Once the channel is filled with molten metal, power can be applied to the furnace coil. This produces an intense electromagnetic field which causes electric current to flow through and further heat the molten metal in the channel. Hotter metal leaving the channel circulates upward, raising the temperature of the entire bath.

Typically, channel furnaces are used to hold molten metal whenever it is needed. Channel furnaces are emptied only for relining ремонт футеровки.

Induction Heating

Induction also is widely used for a variety of heating applications for metals as well as for non-metallic materials. For metals, induction heating applications include heat treating, induction welding, semi-solid casting, parts fitting, annealing, galvanizing, galvannealing, tin reflow, coatings, boosters, bar, billets, bloom, slab heating and in many other metal heat treatment applications.

For non-metallic materials, induction heating is used to produce ultra-high temperature carbon composites and for making high-quality optical glass.

Practicalities of Induction Heating http://www.petrieltd.com/index.php/Induction
The fundamental workcoil-workpiece configuration can be adapted to almost any design. The variability in direct and indirect designs is significant with induction heating; an example of direct heating would be when welding two steel items together, whereas an example of indirect heating would be an induction cooker where the hot-plate is heated and the food is placed on the hotplate to cook. This flexibility is one of the main reasons induction heating is so widely used across industry.

The frequency of AC used has several practical implications of how the workpiece is heated. Lower frequencies lead to deeper magnetic-field penetration depths and hence deeper heating profiles. Higher frequencies will result in greater surface heating with respect to the rest of the material. When heated, heat flux flows within the material from the hot to cold regions; hence the longer the workcoil is coupled to the workpiece the deeper the heat penetrates into the material through heat conduction. This will serve to distribute the heat evenly resulting on a more uniform heating profile across the whole workpiece. Where the workpiece is used as an appliance to heat another material, this results in greatly improved heating uniformity. For short-term heating, the greatest heating will be where the magnetic field and hence induced eddy current concentration is greatest. Since the magnetic field can be focused in a very small space through careful workcoil-workpiece design, highly-focused heating can be performed.

Applications of induction heating range from metal processing, for example induction welding, induction brazing, and induction hardening, through to forming and mouldings for the manufacture of plastic components. One of the most common applications is in the food industry, where induction heating is used to replace indirect heating by gas or electric heating elements

Advantages of Induction Heating
The advantages of induction heating for industrial processes are:

· Non-contact – There is no contact between the workcoil and workpiece; this is of importance in direct heating applications, such as welding and brazing, where there may be risk of cross-contamination.

· Rapid Heating – Induction heating can dissipate extremely high power densities within a workpiece resulting in very fast heating times. This is an advantage for direct heating applications where the need to minimise the effects of heat conduction are essential to avoid damaging the workpiece. It is also an advantage in indirect heating applications where heating times are an important parameter.

· Efficiency – Induction heating can be considerably more efficient than conventional heating; up to twice the level of efficiency.

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