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through the resistance of the metal generates heat, just as current flowing through the resistance element of a conventional electric range's coil generates heat; the difference is that here, the heat is generated directly in the pot or pan itself, not in any part of the cooker. By controlling the strength of the electromagnetic field, we can control the amount of heat being generated in the cooking vessel – and we can change that amount instantaneously.

Nothing outside the vessel is affected by the field – as soon as the vessel is removed from the element, or the element turned off, heat generation stops.

With current technology, induction cookers require that all your countertop cooking vessels be of a "ferrous" metal (one, such as iron, that will readily sustain a magnetic field). Materials like aluminum, copper, and pyrex are not usable on an induction cooker.

And there are now available so-called «inductions disks» that will allow nonferrous cookware to be used on an induction element; using such a disk loses many of the advantages of induction – from high efficiency to no waste heat – but those who want or need, say, a glass/pyrex or ceramic pot for some special use, it is possible to use it on an induction cooktop with such a disk.

On the horizon is newer technology that will apparently work with any metal cooking vessel, including copper and aluminum, but that technology – though already being used in a few units of Japanese manufacture – is probably quite a few years away from maturity and from inclusion in most induction cookers. If you are interested in a new cooktop, it is, in our judgement, not worth waiting for that technology. (The trick seems to be using a significantly high-frequency field, which is able to induce a current in any metal; ceramic and glass, however, would still be out of the running for cookware even when this new technology arrives – if it ever does.)

There is also now the first of the new generation of «zoneless» induction cooktops. These essentially make the entire surface of the unit into a cooking area: sensors under the glass detect not only the presence of a pot or pan or whatever, but its size and placement – and then energize only those mini-elements directly under the cooking vessel. You can thus put any size or shape of vessel – from a small, traditional round pot to a gigantic griddle or grill – down anywhere, in any alignment, and the unit will heat it, and only it (or, of course, several «its», as may be).

11. Переведите с русского на английский

Устройство индукционного нагрева – это электромагнитное устройство для нагрева индукционными токами, которые возбуждаются в металле

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нагревательного элемента переменным магнитным полем. Индукционный электронагреватель представляет собой трансформатор, состоящий из первичной обмотки и специальной вторичной обмотки в виде труб. Металл нагревательного элемента под воздействием магнитного поля, создаваемого катушками, нагревается и передает тепло теплоносителю, которым может быть вода, масло, газы и т.д.

12. Задание

12.1. Прочитайте текст и составьте вопросы так, чтобы выделенные слова были на них ответами

Induction Heating and Melting

Combustion 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.

12.2. Прочитайте и переведите текст

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,

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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.

Coreless Furnaces

A coreless furnace has no inductor or core. 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 can melt 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 rather than the metal itself. This furnace is used to melt most nonferrous 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 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.

12.3. Ответьте на вопросы к тексту

1.What are the two separate electrical systems in induction furnace used for?

2.What features should electricity for the induction coils have?

3.What kind of electricity is necessary for a channel furnace that holds and pours liquefied metal?

4.How does the frequency of the alternating current flowing through the induction influence the speed of melting?

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5.What are the two types of coreless furnace?

6.What is used to keep the copper coil from melting?

7.What kind of current is used to melt the metal charge material inside the furnace?

8.Is it possible to use coreless furnaces for melting different amounts of metal?

9.How does a coreless furnace work?

10.Where is the channel situated?

11.When is the electric circuit formed by the core and coil completed?

12.When are the channel furnaces emptied?

13.Is it possible to hold molten metal in a channel furnace?

set point – заданное значение refractory – огнеупорный metal charge – садка металла tilting – опрокидывание

13. Переведите текст письменно на русский язык

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, 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.

Reflow – пайка расплавлением дозированного припоя (в ИС); пайка расплавлением полуды (в печатных платах)

14. Прочитайте и перескажите текст

Ewing was born in Dundee, the youngest of three sons of the minister of St Andrew's Free Church. He took a degree in engineering at Edinburgh University and shortly after graduating he became Professor of Mechanical Engineering at the new University of Tokyo.

It was whilst there that he carried out research into earthquakes, which were frequent in Japan, and devised a new type of seismometer. He also studied magnetism and gave the name to the phenomenon of hysteresis.

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He eventually returned to Scotland to be the Professor at Dundee. He was horrified by the slum dwellings that had appeared, and contrasted the conditions endured by the working classes unfavourably with those of similar people in Japan. He protested that there was no reason why a working man's children should have an infant mortality rate three times greater than his more prosperous neighbours. He worked with the local authorities and mill owners to make life more pleasant for everyone, particularly with regard to improving the sewerage systems.

He was appointed Professor of Mechanism and Applied Mechanics at Cambridge in 1890 where he developed his earlier work on the magnetic properties of metals and held the post until 1903. He worked with Charles Parsons on developing the steam turbine. During this time, Ewing published his famous book on 'The Steam Engine and other Heat Engines'.

In 1897 he took part in the trials of the experimental vessel Turbinia when she achieved the unprecedented speed of thirty-five knots over the measured mile. During his tenure the school grew at an enormous rate: a Tripos was instituted (1892), a laboratory founded (1894) and in 1899 a new wing was opened in memory of John Hopkinson.

In 1898 Ewing was elected to a Professorial Fellowship at King's. In 1903, Ewing left Cambridge to take over as Director of Naval Education in Greenwich.

At outbreak of war in 1914 he was put in charge of code breaking which earned him many nick names in the popular press, such as: Eavesdropper Ewing, The Cipher King, The U-boat trapper.

Room 40 was the number of Ewing's room at the Admiralty and it was a name that became associated with code breaking.

In May 1916, Ewing was offered the Vice-Chancellorship of Edinburgh University, which he accepted. That university in its turn also went through a period of unprecedented expansion and development under his leadership. Whilst at Edinburgh, Ewing had a tradition of asking guests to his house to draw (with eyes tightly shut) the outlines of a pig. The results were kept in the 'pig book', many of the results, drawn by such dignitaries as Winston Churchill, Charles Parsons and William Bragg, appearing in the book.

The James Alfred Ewing Medal was awarded at the discretion of the Council of the Institution of Civil Engineers for specially meritorious contributions to the science of engineering in the field of research. First awarded in 1938, and still awarded today.

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