Thermal-welding processes

Thermal welding process can be of two kinds direct and indirect. Each kind of thermal welding may be further classified, as shown below, according to the method used to provide heat. 

Other thermal welding processes that are less common than those described above but still used in industry are infrared welding and laser welding. These are generally used in specialty processes or with applications that require unique methods of heating because of the joint design or nature of the final product. 

Thermosetting plastics (e.g., epoxies diaUyl phthalate polyesters melamine, phenol and urea formaldehyde and polyurethanes) are joined either mechanically or by adhesives. Their thermosetting nature prohibits the use of solvent or thermal welding processes however, they are easily bonded with many adhesives. 

Arguably, thermal-welding processes can be considered a subset of adhesive bonding. With thermal-joining processes, the substrate itself (in molten form) acts as the adhesive. Once the substrate is liquefied, the principles of adhesion determine the strength and durability of the bond. In addition, thermal methods can be used to activate a hot-melt adhesive rather than the textile substrate. 

The main growth area for adhesives is in heat-activated tapes or films, where there is substantial overlap with thermal-welding processes. Thermal bonding is increasingly used at the expense of adhesive bonding for the following reasons ... 

Thermal welding is confined to fabrics that have high thermoplastic synthetic fibre content such as nylon, polyester, polypropylene, acrylic, and certain fibre blends. As a general mle, the textiles to be welded must be made of the same thermoplastic or be physically and chemically compatible with one another. Fabrics that have a thermoplastic coating (e.g., polyvinyl chloride, PU, and polypropylene) are also amenable to thermal-welding processes, since in these cases the coating acts as the adhesive. Weldability will vary with the type of material, its thickness, and its form (coating, film, fibre). 

In certain industries, such as the automotive industry, plastic materials are often chosen because of their fast joining ability. Thus, thermoplastics are often preferred over thermosets, because they can be joined via thermal welding processes in a few seconds. 

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