Sources

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Sources

RF heaters are used in many industries to heat, melt or cure dielectric materials.

Materials such as plastics, rubber and glue are electrical and thermal insulators;

consequently they are difficult to heat using conventional methods. The frequency of

operation of RF heaters is in the range 10 MHz to 100 MHz with output powers from

less than 1 kW to about 100 kW. This document does not address RF induction heaters

that operate at lower frequencies and are used to heat materials which are good

conductors of electricity such as metals and crystals.

The most common use of RF heaters is the sealing or welding of polyvinyl

chloride (PVC) by applying RF power to PVC materials compressed between two

electrodes. The power dissipated per unit volume of dielectric material is proportional to

the frequency of the source, the square of the voltage on the electrodes and the dielectric

properties of the material. A schematic diagram of an RF sealer is shown in figure 1.

Figure 1. Schematic diagram of a radiofrequency (RF) sealer

Mainframe

RF generator

 Hydraulic press

 Electrode

Some examples of the use of RF heaters include:

(a) manufacture of plastic products such as toys, loose-leaf binders, rainwear,

waterproof containers, furniture covers and packaging materials;

(b) curing of glue used in the manufacture of wood laminates;

 Die

 Bed plate

Material to be sealed is placed

between the die and the bed

plate, under pressure, prior to RF

energy being applied.

 RF current

p

ath

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