Process for joining overlapping thermoplastic membrane components
A method of joining overlapping thermoplastic roofing membrane components in which a first thermoplastic roofing membrane component and a second roofing membrane component are positioned in overlapping relationship between a pair of complementary molding surfaces. Heat is generated in a metal substrate and transferred by thermal conduction from the metal substrate to overlapping portions of the first and second thermoplastic roofing membrane components to locally melt and coalesce a portion or more of the thermoplastic material of the first thermoplastic roofing membrane component and a portion or more of the thermoplastic material of the second thermoplastic roofing membrane component. The molten thermoplastic material of the first and second thermoplastic roofing membrane components forms a zone of coalesced thermoplastic material that, upon cooling, forms a solid weld joint.
1. 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.
2. The method set forth in claim 1 , wherein the alternating current passing through the coil has a frequency in the range of 10 Hz to 10 MHz.
3. The method set forth in claim 1 , wherein the alternating magnetic field does not induce heating within the thermoplastic material of the first edge portion or the thermoplastic material of the second edge portion.
4. The method set forth in claim 1 , wherein the first and second edge portions are positioned in overlapping relationship between the first and second forms such that either the first edge portion or the second edge portion is in direct contact with the metal substrate.
5. The method set forth in claim 1 , further comprising:
actively cooling the zone of coalesced thermoplastic material by positioning a cooling medium adjacent the first edge portion or the second edge portion.
6. The method set forth in claim 1 , further comprising:
actively cooling the zone of coalesced thermoplastic material by flowing a cooling fluid through an internal cooling passage defined in the first or the second form.
7. The method set forth in claim 1 , wherein the zone of coalesced thermoplastic material is formed by heating 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 to a temperature greater than 200 degrees Celsius.
8. The method set forth in claim 1 , wherein the thermoplastic material of the first or second edge portion comprises polyethylene (PE), polypropylene (PP), polystyrene (PS), polyester (PE), polycarbonate (PC), polyurethane (PU), polyamide (PA), polylactic acid (PLA), acetate, vinyl, poly(methyl methacrylate) (PMMA), nitrile, or a block copolymer thermoplastic elastomer (TPE).
9. The method set forth in claim 1 , wherein the thermoplastic material of the first or second edge portion comprises a thermoplastic polyolefin (TPO).
10. The method set forth in claim 1 , wherein the solid weld joint forms a water-tight seal between the first and second edge portions at the weld site.
11. The method set forth in claim 1 , wherein, prior to heating the metal substrate, the outer and inner edge portions of the first and second rectangular components are positioned in overlapping relationship between the generally flat V-shaped welding surface of the first form and the generally flat complementary welding surface of the second form.