To provide garments with a high level of waterproofing, seams are often sealed, since water can penetrate through the needle holes left during stitching.
There are two methods for sealing seams on water-resistant clothing:
- Taping the seams with a special tape. Used in garments where parts made of waterproof materials are stitched together with needle and thread. The tape, heated by a jet of hot air, melts and seals the needle holes in the fabric.
- Seam welding. Used in products where parts need to be joined without needles and threads.
The edges of the parts are aligned and firmly pressed together against the support. Then the welding tool (tip), connected to an ultrasonic transducer, is brought to the joint and the generator is switched on.
Under the influence of ultrasound, the components at the contact zone heat up to temperatures that make the material highly plastic. First the surfaces make physical contact and molecules are activated by the breaking of chemical bonds; then a chemical interaction between the materials occurs. The result is a flat, elastic seam that is completely impermeable to moisture.