Abstract: In a method of fusion welding resin articles difficult to melt due to a fusion retarder present in the articles in the form of a fusion retarding element or structure, the articles having surface portions in contact with each other so as to be bonded one to another, a fusion accelerator is applied to the surface portions, with the accelerator being capable of destroying the fusion retarder when heated. After or simultaneously with this step, the resin articles are heated so that the fusion accelerator destroys the fusion retarder, so as to cause the surface portions to melt, before finally allowing the resin articles to cool down.

Abstract: Plastics sheets having edges to be bonded one to another as well as a plastics joint having at least two weldable regions are prepared, each region having an embedded wire extending along the region. Subsequently, the plastics sheet edges are placed on or in the weldable regions, and an electric current is supplied through the wires to emit heat for fusion bonding each edge to the corresponding weldable region. Alternatively, each of the plastics sheets has at least one edge having an embedded wire so that they are welded to each other, without aid of any joint. The joint has U-shaped grooves or ear-shaped protrusions adapted to engage with the plastics sheet edges, and the wires are embedded in the grooves or protrusions.

Abstract: A method of automatically controlling the fusion process of thermoplastic resin articles is done in a stepwise fashion. In response to a start signal, a current is applied to an electrical resistance heating element for fusing together facing resin surfaces. Electrical characteristics of the resistance heating element are calculated upon increase of the power to a given level and the specific heat of the resin is calculated through ON-OFF control of the resistance heating element. The power is then raised through stages based on the electrical characteristics of the resistance heating element and the specific heat to determine variation coefficients of the characteristics and specific heat at each stage and through further ON-OFF control. Finally, the power increase is stopped as the variation coefficient of specific heat reaches or becomes smaller than a given value.