High frequency welding services, also known as Dielectric Sealing or Radio Frequency (R.F.) Heat Sealing is a very mature technology that has been around since the 1940s. High frequency electromagnetic waves in the range of radio frequencies can heat certain polymers up to soften the plastics for joining, heated plastics under pressure weld together. Heat is generated within the polymer by the rapid reorientation of some chemicals dipoles of the polymer, which means that the heating can be localised, and the process can be continuous. A generator produces the energy. The tool used to supply the energy is called an electrode.
Only certain polymers, which contain dipoles can be heated by RF waves, in particular polymers with high loss power. Among these, PVC, polyamides (PA) and acetates are commonly welded with this technology. In practice, two pieces of material are placed on a table press that applies pressure to both surface areas. Dies are used to direct the welding process. When the press comes together, high frequency waves (usually 27.120 MHz) are passed through the small area between the die and the table where the weld takes place. These high frequency welding services (radio frequency) heat the plastic, that under pressure welds, taking the shape of the die.
The electrical energy causes the molecules within the material to start moving, which generates heat, that causes the material to soften and thereby fuse together. No outside heat is applied. It is instead generated within the material. After cooling the welded surface remains under pressure, the material is fused and a weld has been created. The weld seam can be at least as strong as the surrounding material or even stronger.
Four important factors that affect the final weld result are:
These parameters can be adjusted and combined in different ways to achieve the optimal welding result for a specific material.
High frequency welding services are fast and relatively easy to perform, produces a limited degradation of the polymer, even welding thick layers does not create fumes, requires a moderate amount of energy and can produce water, air and bacteria proof welds. Auxiliary materials can also be used to solve some welding problems. This type of welding is used to connect polymer films used in a variety of industries where a strong consistent leak-proof seal is required. In the fabrics industry, HF is most often used to weld PVC and polyurethane (PU) coated fabrics. Other materials commonly welded using this technology are Nylon, PET, PEVA, EVA and some ABS plastics.