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Plastic welding ''i.e.'' welding for semi-finished plastic materials is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat (except solvent welding). Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semifinished plastic materials. Based on the way of heat generation mechanism at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods, as shown in Fig 1. On the other hand, production of a good quality weld can not only depend on the welding methods, but also weldability of base materials. Therefore, the evaluation of weldability is of important critically before welding operation (see Rheological Weldability for plastics).〔 ==Welding techniques== A number of techniques are used for welding of semi-finished plastic products as given below: ===Hot gas welding=== Hot gas welding, also known as ''hot air welding'', is a plastic welding technique using heat. A specially designed heat gun, called a ''hot air welder'', produces a jet of hot air that softens both the parts to be joined and a plastic filler rod, all of which must be of the same or a very similar plastic. (Welding PVC to acrylic is an exception to this rule.) Hot air/gas welding is a common fabrication technique for manufacturing smaller items such as chemical tanks, water tanks, heat exchangers, and plumbing fittings. In the case of webs and films a filler rod may not be used. Two sheets of plastic are heated via a hot gas (or a heating element) and then rolled together. This is a quick welding process and can be performed continuously. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plastic welding」の詳細全文を読む スポンサード リンク
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