The effect of dielectric and thermal properties of plastic mold materials on the high frequency welding of three‐dimensional foam components

Abstract

High-frequency heating processes are widely used in industry, for example, for food processing, wood drying, or plastic welding. A recent development in this field uses radio-frequency heating to fuse particle foam beads to complex components. The aim of using the modified process is to reduce the energy consumption of particle foam fusion. Within this process, the molds used must be electrically insulating to ensure the building of an electrical field. For this purpose, mold made of two different plastics were analyzed.Additional to the dielectric, mechanical, and thermal expansion, the thermal conductivity of the mold materials are of great interest. Although welding is finished quickly, cooling to the demolding temperature is comparably long.To achieve shorter cooling and therefore shorter process times, the mold materials were modified by two different thermal conductive but electrically insulating fillers. By the use of the thermally optimized mold materials, a reduction in cooling time of up to 40% was possible. At the same time, the heating step was hardly affected. Mechanical properties were enhanced while thermal expansion was reduced.

Investigation of Recycled Expanded Polyamide Beads through Artificial Ageing and Mechanical Recycling as a Proof of Concept for Circular Economy

“…Current research is focusing on the steam-reduced or steam-free processing of particle foam beads. In the field of steam-free processing technologies, radiation-based concepts using dielectric heating of plastics by applying electromagnetic waves, such as microwaves or radio frequency, are being investigated [ 10 , 11 , 12 , 13 ]. Another possibility is the variothermal mould temperature control, in which a bead bond is generated by thermal conduction.…”

Influence of dielectric properties of polybutylene terephthalate and respective foam beads on process behavior in radio‐frequency welding

“…12 At the beginning of the process, the particles are filled in the mold with defined compression, where an oscillating voltage with a frequency of 27.12 MHz is applied to the active electrode. 13 The resulting electromagnetic field between the electrodes can interact with the materials inside and generate molecular vibrations. [14][15][16] Similar to a microwave oven at home, this generates intermolecular friction that leads to local heating of the material, which saves energy by minimizing losses in the mold and its surroundings.…”

“…At the beginning of the process, the particles are filled in the mold with defined compression, where an oscillating voltage with a frequency of 27.12 MHz is applied to the active electrode 13 . The resulting electromagnetic field between the electrodes can interact with the materials inside and generate molecular vibrations 14–16 .…”

RF Welding of Dielectric Lossless Foam Particles by the Application of a Dielectric Heatable Coating with High Recycling Potential

“…A previous study [9] investigated a novel approach for welding three-dimensional foam components through the radio-frequency (RF) welding process, which is usually used for the processing of thin films [10] and layered fabrics [11]. The heating of a particle foam made of expanded thermoplastic polyurethane (eTPU) and the used tools based on polyethylene terephthalate (PET) and polyoxymethylene (POM) were analyzed [9].…”