Method of seaming plastic fabrics

A method for bonding a first plastic fabric layer to a second plastic fabric layer, said first and second plastic fabric layers being woven from yarns of a synthetic polymeric resin and being overlapped with one another for bonding, said method comprising the steps of:

• providing an ultrasonic welding apparatus having a horn for delivering ultrasonic energy to said overlapped first and second plastic fabric layers at a location where said first and second plastic fabric layers are to be bonded to one another;
• providing an anvil toward and against which said horn is moved to clamp said first and second plastic fabric layers together for bonding:
• disposing said first plastic fabric layer on said anvil;
• disposing said second plastic fabric layer over said first plastic fabric layer on said anvil;
• moving said horn toward and onto said overlapped first and second plastic fabric layers on said anvil at a preselected rate of speed;
• activating said horn to deliver ultrasonic energy to said overlapped first and second plastic fabric layers when the force with which said horn clamps said overlapped first and second plastic fabric layers against said anvil reaches a preselected level;
• increasing said force above said preselected level of force while delivering ultrasonic energy to said overlapped first and second plastic fabric layers to soften said yarns from which said first and second plastic fabric layers are woven without melting said yarns and to compress said softened yarns together;
• deactivating said horn to stop its delivery of ultrasonic energy when said horn has reached a preselected distance from said anvil;
• maintaining said force for a preselected hold time, to allow said synthetic polymeric resin of said yarns to cool and to harden under compression;
• and
• removing said horn from said overlapped first and second plastic fabric layers.