High Frequency Eddy Current Heating
When current-carrying conductor is wound on the soft iron piece then a circulating current is produced in it by electromagnetic induction. Its shape is just like an eddy, so it is called as eddy current.
This eddy current produces loss that is called as eddy current loss. This loss produces heat in the soft iron piece and can be used to heat the material.
Since, the eddy current loss is proportional to the product of square of supply frequency and flux density therefore high frequency supply can be utilised to generate the heat. By controlling the frequency and the flux density the amount of heat can be controlled.
The articles to be heated are placed within a high-frequency current-carrying coil, the alternating magnetic field is set up. Eddy currents are induced in the article and heating is therefore affected. Fig. shows the principle of high frequency eddy current heating.
High frequency current carrying coil is known as magnetic coil or work coil.
The material, which is to be heated, is known as load or charge and the process employed is referred to as high frequency eddy current heating.
The eddy current loss is primarily responsible for the production of heat, but hysteresis loss also contributes to it, in the magnetic materials.
Induced eddy current is of greatest magnitude at the surface of the material to be heated and its value decreases with the distance normal to the surface as we go inside the material.
The supply frequency is employed between 10,000 to 4,00,00 Hz.
Advantages Of High Frequency Eddy Current Heating
- The heat can be made to penetrate into the metal surface to any desired depth.
- The penetration depends upon the supply frequency.
- It is a fast, clean, and easy method.
- There is little wastage of heat since heat is produced directly in the body to be heated.
- The control of temperature is very easy.
- It can easily take place in a vacuum or other special atmosphere, whereas other conventional types of heating is not possible in such places.
- Suitable timing devices can accurately control the amount of heat produced.
- Work coils/electromagnetic coils are not required to fit closely around the object being heated.
- The heating depends upon the shape and size of the articles, materials, etc.
Disadvantages Of High Frequency Eddy Current Heating
- Controlling the heat is very costly because a special type of electronic control is required.
- The efficiency of equipment is quite low.
- The initial cost of equipment is high.
- A special type of equipment is required to produce the different frequencies.
Applications Of High Frequency Eddy Current Heating
- It is a very important application of high-frequency eddy current heating. The bar whose surface is to be hardened, by heat treatment, is surrounded by the work coil.
- An alternating current of high frequency is made to pass through the work coil.
- The desired depth of penetration up to which the surface is to be hardened can be obtained by judicious selection of the frequency of the heating current in the work coil.
- After about a few seconds, when the surface has reached the proper temperature, the a.c. supply is cut off and the bar is at once dipped in water.
- In conventional method of annealing ; the process takes long time, which results in scaling of the metal, a great drawback.
- But in eddy current heating method, the time taken in the process is less and, thus, there is no scale formation.
- Eddy current heating can be economically used for soldering precisely for high-temperature soldering.
- Silver, copper, and their alloys are used as solders.
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