Process for joining overlapping thermoplastic membrane components

A method of joining overlapping thermoplastic roofing membrane components, the method comprising:

• providing a first roofing membrane component having a first edge portion comprising a thermoplastic material, wherein the first roofing membrane component comprises a first rectangular component and the first edge portion is defined by an outer edge portion of the first rectangular component;
• providing a second roofing membrane component having a second edge portion comprising a thermoplastic material, wherein the second roofing membrane component comprises a second rectangular component and the second edge portion is defined by an inner edge portion of the second rectangular component defined by a slit in the second rectangular component;
• providing a first form and a second form having complementary molding surfaces, wherein the first form includes a pair of vertical sidewalls joined together by a vertically extending curvilinear section that together define a generally flat V-shaped welding surface and the second form comprises a metal substrate that defines a generally flat complementary welding surface;
• positioning the first and second edge portions in overlapping relationship between the first and second forms adjacent the metal substrate such that opposed surfaces of the first and second edge portions contact each other to establish a faying interface therebetween at a weld site;
• heating the metal substrate such that heat is transferred by thermal conduction from the metal substrate to the first and second edge portions of the first and second roofing membrane components to locally melt and coalesce at least a portion of the thermoplastic material of the first edge portion and at least a portion of the thermoplastic material of the second edge portion and form a zone of coalesced thermoplastic material along the faying interface at the weld site, the heating comprising positioning an electrically conductive coil around the first and second edge portions adjacent the metal substrate and passing an alternating current through the electrically conductive coil to generate an alternating magnetic field that acts on the metal substrate and induces heating within the metal substrate;
• and cooling the zone of coalesced thermoplastic material to form a solid weld joint of resolidified thermoplastic material that fusion welds the first and second edge portions of the first and second roofing membrane components together at the weld site.