The influence of welding processes on the weld strength of flame-retardant materials

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• 作者：Fabian Evers ; Volker Schöppner ; Patrick Lakemeyer
• 关键词：(IIW Thesaurus)Thermoplastics ; Tensile strength ; Ultrasonic welding ; Heated tool welding ; Laser welding ; Friction welding ; Combustion
• 刊名：Welding in the World
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：61
• 期：1
• 页码：161-170
• 全文大小：
• 刊物主题：Metallic Materials; Continuum Mechanics and Mechanics of Materials; Theoretical and Applied Mechanics;
• 出版者：Springer Berlin Heidelberg
• ISSN：1878-6669
• 卷排序：61

文摘

Due to continually rising fire-safety standards, the use of plastics containing flame-retardant additives has increased strongly in recent years and is continuing to increase. The flame-retardant reaction of these materials prevents flames and the associated thermal energy from using the polymer as a source of flammable material, thus suppressing and slowing the spread of the flames. This, however, works (so to speak) against the energy needed to melt the polymer, which in turn can cause a reduction in weld strength. In this study, the behavior of flame-retardant plastics is examined for the four standard welding processes hot plate welding, vibration welding, ultrasonic welding, and laser welding. During the experiments, both a halogen and a nitric flame retardant are investigated in Polyamide 6.6, Polyamide 6, and polybutylene terephthalate, and their effect on weld strength was determined. It transpired that the activation of the flame retardant and the directly related loss of weld strength in the joint depend considerably on the welding process and its parameters. For hot plate welding, the temperature of the heated tool as well as the heating time is of considerable significance for the joint quality. Reaching a temperature above the activation temperature of the flame retardant resulted in notable reductions in weld strength, caused by the activated additive. These weld strength reductions can be to some extent held in check by suitable process parameters; in this case, there are boundary levels of activation which must not be exceeded, in order to ensure a sufficiently high joint strength. This behavior varies, however, from that shown in ultrasonic welding. Here, no activation of the flame retardant was observed, meaning that the flame-retardant additive acts only as a filler material on the joint strength. For vibration welding, there is an observable effect resulting from concentrations of flame retardant; this effect can be partially or entirely neutralized by a suitably high joining pressure, which pushes the concentrated areas into the welding bead and thus reduces or eliminates the damage to the weld itself. Laser welding leads to a high degree of activation in the flame retardant and therefore results in a significant drop in joint strength. To briefly summarize, it can be said that welding processes with external heat sources are to be more critically evaluated than processes with internal energy generation when welding flame-retardant polymers.