Working Principle of High Frequency Welding Machine

Working Principle of High Frequency Welding Machine

Principle

High-frequency (HF) welding of plastics is very often applied whenever PVC and PU products have to be welded. Well-known products whereby HF welding is applied are car mats, baby cushions/pillows, screen canvas, waterbeds, inflatable boats, drip and blood bags, deck canvases, conveyor belts, rain clothing, writing materials, tents, air filters, advertising canvases, etc.

Principle and advantages
The principle of HF welding is based on dielectric heating of the material to be welded. The material to be welded is put between two metal plates (the electrodes), whereupon a high-frequency voltage is connected to the plates. As a result, the molecules in the material start vibrating, which will result in heating up to the melting (fusing) temperature. By bringing two layers of material into the HF field at the same time and pressing them together, the layers will melt together (fuse) and a strong welded joint will be formed.

In a high-frequency field some materials generate more heat than others, and are therefore more suitable for HF welding. This has to do with the extent to which the molecules of the material allow themselves to vibrate as a result of the HF field. This is known as the loss factor of the material. The greater the loss factor of the material, the easier it is to weld the material using high-frequency equipment. Particularly easy to weld are thermoplastics, such as PVC and PU; these materials are specifically welded using high-frequency welding machines. Much more difficult to weld with HF equipment are, for example, PE and various hard plastics.

The great advantage of HF-welding is the speed: because the material is heated from the inside out, the fusion takes place very quickly, often already within a few seconds. With all other kinds of heating, like with filaments, hot air or infrared radiation, the heat has to be added from the outside, in which case the heat must first penetrate the material.

The HF welding machine
The HF welding machine consists of two components: the HF generator and the welding press.

The HF generator
The high-frequency generator develops the HF field at a frequency of 27.12 MHz and supplies a power, depending on the application, of 500 Watt to 60 kW. Up to 2 kW one uses semiconductors in the generators, but for higher powers one still uses an oscillator tube.