Method of ultrasonic splicing tire tread strip edges

A method of splicing together a pair of beveled mating edges of an unvulcanized rubber compound tire tread strip which is free of any internal reinforcing cords and has a thickness of at least 1/8 inch, including the steps of:

• (a) bringing the beveled edges of said tire tread strip of unvulcanized rubber compound into a partial overlapping contiguous relationship to form a splice joint extending angularly between outer opposed surfaces of t he strip;
• (b) pressing a contact face of an ultrasonic welding horn against one surface of the strip at the splice joint at a first pressure within the range of 20 psi to 80 psi;
• (c) applying ultrasonic energy against said one surface for a first time period within the range of 2 to 12 seconds at the first pressure range to heat and soften the rubber compound without vulcanizing along a first portion of the splice joint adjacent said one surface sufficiently for the compound to bond together across said first portion of the splice joint without bonding a second portion of the splice joint located adjacent the other surface of the opposed strip surfaces;
• and
• (d) maintaining a second pressure against said one strip surface by the face of the ultrasonic generator for a second time period within the range of 0.5 to 2 seconds after stopping the application of the ultrasonic energy permitting the softened rubber compound to cool sufficiently to form a stronger bond between the beveled edges of the splice joint along said first portion adjacent the said one strip surface.