Hot wedge

Hot wedge (thermal sealers) electrically heated jaws are pressed into contact with the thermoplastic material for the duration required to transfer heat to the interface. The profile of the jaws dictates the weld impression. 

Because of their favourable cost-performance ratio, polyvinyl chloride (PVC) coated polyester (PET) fabric is the most common basic material used. It can be applied over the whole spectrum from small temporary to wide-span structures. With a top-coat that protects the PVC from soiling and early ageing, a life-span of up to 20-25 years can be obtained. PVC-PET composites are joined by high-frequency or hot wedge welding. With flame-retardant additives to the PVC coating, fire class B1 can be achieved. 

PFAFF (www.pfaff.com) has developed a very sophisticated hot-wedge welding system called the PFAFF 8320. The equipment is programmable with a touch screen that allows accurate control of all parameters. A revolutionary new two-axis engaging system allows the wedge to be adjusted accurately. 

Table 13.14 Fabrics that can be joined using hot-wedge welding...

Fabric group Fabric subgroup Suitability of hot-wedge welding Comments... 

Holme, I., 1999. Adhesion to textile fibers and fabrics. Int. J. Adhes. Adhes. 19, 455—463. Jones, I., 2013. The use of heat seahng, hot air, and hot wedge to join textile materials (Chapter 11). In Joining Textiles Principles and Applications. Woodhead Publishing, Limited, Cambridge, pp. 353—373. 

The plant roots do not find any points of attack for a mechanical effect in the surface of HDPE geomembranes and along perfectly manufactured extrusion fillet seams or dual hot wedge seams. Secondary biochemical effects do not play a role because of the very high resistance of the HDPE geomembrane to chemicals. Root strength of HDPE geomembranes was therefore confirmed in these tests. 

Texture manufactured by the co-extrusion process (Process 3) is quite uniform and it offers good friction values in combination with fine grained mineral materials. The texture is evenly distributed over the surface, but their friction resistance cannot be varied or at least only to a small extent. The problem of stress eraek resistance must be considered as with the other textures. Sinee the geomembranes are usually textured throughout the whole surfaee, two textured areas must be welded for each hot wedge weld seam. For the individual co-extruded textures as well as for impinged or laminated textures proof must be provided showing that this is possible without any loss of quality in the properties of the weld seams (Sect. 10.3). 

HW-WM Hot wedge welding machine, WG-E warm gas extrusion device... 

Acceptance, monitoring and calibration of working and test equipment relevant to installation and quality control must be regulated in the QMM, for example the test parameters of the hot wedge welding machine such as roller pressure, hot wedge temperature, speed. Maintenance and inspection plans must be available and the actions taken must be recorded. The necessary calibration and inspection... 

Fig. 10.3. Photographs of a hot wedge welding machine. Compact, electronically controlled machines with display, control desk and data logger are offered by several manufacturers. On the right, the travel rollers are seen underneath and on the lower geomembrane as well as the hot wedge over which the two geomembranes are guided...

The dual hot wedge seams and extmsion fillet seams must be tested on the constmction site. The constmction-site tests are supplemented to a certain extent with tests imder laboratory conditions. In the laboratory, long-term... 

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