Electric Heating & Welding diplomaa.pptx

Electrical heating and welding

1. CSMSS COLLEGE OF POLYTECHNIC CHHATRAPATI SAMBHAJINAGAR Topic ELECTRIC HEATING Prepared By Mr. Pradip R. Jadhav

2. Vertical Core Type Induction Furnace (Ajax Wyatt furnace) When an ac supply is given to the furnace, a strong alternating electromagnetic field is produced in the laminated core. The molten metal in the V channel acts as a short-circuited secondary coil carrying a heavy induced current which generates heat in the charge. As the V channel resistance is high the heat is produced and distributed evenly due to the convection currents and by stirring action of electromagnetic force.

3. Vertical Core Type Induction Furnace (Ajax Wyatt furnace) A hydraulic system is used for tilting the furnace for pouring out the metal. The vertical core type induction furnace is suitable for continuous operation services. When this furnace is operated from a normal supply frequency its efficiency is about 75%. The vertical core type induction furnace comes in standard size that varies from 60 kW to 300 kW, and all are single-phase. The vertical core type induction furnace is mainly used for melting and refining of brass and other non-ferrous metals.

4. Coreless Type Induction Furnace The furnace in coreless induction heating is made up of ceramic crucible cylindrical in shape surrounded by coils that act as the primary winding of the transformer as shown below. The charge to be heated is kept in the crucible and it acts as the secondary of the transformer. When the ac power supply is given to the coils of the induction furnace, the coils setups alternating flux. The flux set up by the primary winding will induce the eddy currents in the charge. These eddy currents heat up the charge to its melting point.

5. Coreless Type Induction Furnace As its name implies, no core is provided in the coreless induction furnace .

6. Advantages of Coreless Induction Furnace The coreless induction furnaces are fast in operation. They have low operating cost. These can be operated intermittently. Their charging and pouring is simple. The melting time is very low. There is precise control of power in case of coreless induction furnace. The operation of the coreless induction furnace is free from smoke, dirt and noise.

7. Applications of Coreless Induction Furnace Production of steel Melting of non-ferrous metals such as bronze, brass, copper, etc. For Vacuum melting Melting for precision casting Electronic industry In brazing, soldering, hardening and annealing, etc.

8. Compare Core Type with Core-less Type Induction Furnace Sr. No. Points Core type induction furnace Core less induction furnace 1 Leakage Flux Less leakage flux More leakage flux 2 Power factor is good Power factor is poor 3 Frequency Required Works at normal frequency High frequency supply is required 4 Weight & size Weight & size is more No magnetic core weight & size of furnace reduces 5 Capacity Design for high capacity Design for low capacity 6 Crucible used Crucible used is either Horizontal or Vertical Crucible of any shape is used 7 Cost Initial cost is less Initial cost is more as High frequency supply is required 8 Application Used to melt only conducting metals Both conducting and non-conducting charge can be heated. 9 Time required Time required for heating is more as normal frequency is used. Due to high frequency, high voltage supply, time required for heating is less Power Factor

9. Dielectric Heating The process of heating in which a high-frequency alternating electric field or radio waves or microwave electromagnetic radiation are used to heat the dielectric materials is known as  dielectric heating. Dielectric heating is mainly used for heating of insulators like wood, plastics and ceramics, etc. which cannot be heated easily and uniformly by the other methods of heating. The frequency of the input supply required for dielectric heating ranges from 10 MHz to 15 MHz and the applied voltage is 20 kV.

10. Principle of Dielectric Heating The dielectric heating method works on the same principle of the capacitor (i.e. electrostatic). As we known the dielectric heating can only be used for heating of non-conducting materials. In this method of heating, the dielectric material to be heated is placed between two conducting electrodes across which alternating voltage of high frequency is applied.

11. Dielectric Heating

12. Advantages of Dielectric Heating The main advantage of dielectric heating is that it is affordable. It provides  uniform heating , in contrast to other electric heating methods.  Plastics and other non-conducting materials are well-heated by dielectric heating. Heating takes a reasonable amount of time.  Controlling heat is simple.  The amount of heat generated varies with the frequency used.

13. Disadvantages of dielectric heating Its  efficiency is only 50%  and so it is said to be its biggest drawback. Only substances with significant dielectric losses can be heated. In some cases, high-frequency input causes radio interference. It is not able to longer suitable for heating large or thick materials.

14. Applications of Dielectric heating Drying tobacco, paper, wood, and rayon. Welding of PVC. Stress annealing textile fibers. Heating of bones and tissues. Gluing and bonding of woods. Sterilization of cereals and medical equipment. Processing of rubber synthetic materials and chemicals during manufacture Heat-sealing of plastic sheets.  Preparation of thermoplastic resins. Sewing of raincoats, and umbrellas made of plastic film material Diathermy-treatment of certain body pains and diseases, etc. 

15. Eddy Current Heating When the heating of the charge is done by the induced eddy currents in charge, it is known as  eddy current heating. To heat the charge by eddy current heating process, the charge is placed inside a current carrying coil. The current is the  high frequency alternating current . For this reason, this method is also called the high frequency eddy current heating. The alternating magnetic field produced by the coil sets up eddy currents in the charge to be heated. Consequently, the charge gets heated-up. The coil used for creating the magnetic field is known as  heater coil  or  work coil. As the power loss due to eddy currents (i.e., eddy current loss) is given by, Pe∝B 2 f 2

16. Eddy Current Heating

17. Eddy Current Heating

18. Applications of Eddy Current Heating The eddy current heating is used for surface hardening process. The eddy current heating is a convenient method for annealing. Eddy current heating also used for soldering precisely. It is used for drying of paints. Eddy current heating is also employed for welding process. It is used for forging of bolt heads and rivet heads. It is also used for melting of various metals. For sterilization of surgical instruments, the eddy current heating is used.

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