High Frequency (radio frequency) presses
The high frequency (HF) or radio frequency (RF) technology is used in the many different areas.
HF energy (high-frequency energy) is present in an electric field. By means of “dielectric” or “inductive” heating this energy is converted into heat energy.
Inductive heating is only applicable for metallic materials (highly electrically conductive materials). The dielectric heating is only applicable for poor electrical conducting materials. The method for drying and preheating of resin powder is called iner alia and is used for the welding of plastic films.
The wood industry uses high frequency presses to dry wood and to heat adhesives. The key advantage of the dielectric heating, in relation to conventional heating modes, such as contact, convection and radiation heat, is that they are not depending on the temperature conductivity of the material. Therefore, materials with any volume and cross-sectional dimensions can be heated in a very short time. If there is a body of various components, a selective heating of certain materials (parts) is possible. This advantage has significantly contributed to the establishment of the dielectric heating in the timber industry. This allows to heat up the adhesive joint. The adhesive is cured without substantially increasing the temperature of the surrounding layers of wood. The time can be reduced to less than 30 seconds.
The following features of the dielectric heating should be mentioned:
- Immediate heating of the treated materials after the high frequency power is switched-on – no heat losses.
- Constantly increasing the temperature in nearly homogeneous materials. It’s not possible to overheat local areas.
- Various heating of different materials (eg, wood and glue), so selective heating of certain substances are posssible.
- Due to the special arrangement of the electrodes, individual parts of a body can be heated with high frequency technology.
- The geometric dimensions of the body and its volume have no influence on the rate of heat.