Process for joining overlapping thermoplastic membrane components
A method of joining overlapping thermoplastic geomembrane components in which a first thermoplastic geomembrane component and a second thermoplastic geomembrane component are positioned in overlapping relationship between a pair of complementary molding surfaces, with one or more of the complementary molding surfaces being defined by an electrically conductive metal susceptor. Heat is generated in the metal susceptor and transferred by thermal conduction from the metal susceptor to overlapping portions of the first and second thermoplastic geomembrane components to locally melt and coalesce a portion or more of the thermoplastic material of the first thermoplastic geomembrane component and a portion or more of the thermoplastic material of the second thermoplastic geomembrane component. The molten thermoplastic material of the first and second thermoplastic geomembrane components forms a zone of coalesced thermoplastic material that, upon cooling, forms a solid weld joint.
1. A method of joining overlapping thermoplastic geomembrane components to form a geomembrane liner or a geomembrane cap, the method comprising:
providing a first geomembrane component having a first edge portion comprising a thermoplastic material;
providing a second geomembrane component having a second edge portion comprising a thermoplastic material;
providing a pair of first and second forms having complementary molding surfaces, with the complementary molding surface of the first form being defined by an electrically conductive metal susceptor;
positioning the first and second edge portions in overlapping relationship between the first and second forms adjacent the metal susceptor such that opposed surfaces of the first and second edge portions contact each other to establish a faying interface therebetween at a weld site;
positioning an electrically conductive coil adjacent the metal susceptor and on the opposite side of the faying interface as the metal susceptor such that the faying interface is positioned between the metal susceptor and the electrically conductive coil;
heating the metal susceptor by passing an alternating current through the electrically conductive coil to generate an alternating magnetic field that acts on the metal susceptor and induces heating within the metal susceptor such that heat is transferred by thermal conduction from the metal susceptor to the first and second edge portions of the first and second geomembrane 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;
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 geomembrane components together at the weld site to thereby form a geomembrane liner or a geomembrane cap.
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 complementary molding surface of the first form is defined by the metal susceptor, and wherein the first and second edge portions are positioned in overlapping relationship between the first and second forms such that the complementary surface of the second form presses the first and second edge portions against the complementary surface of the first form and against one another at the weld site.
5. The method set forth in claim 4 , wherein the complementary surface of the second form exerts a force on the first and second edge portions of the first and second geomembrane components in a direction perpendicular to the faying interface established between the opposed surfaces of the first and second edge portions.
6. 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 susceptor.
7. 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.
8. 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.
9. 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.
10. 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).
11. The method set forth in claim 1 , wherein the thermoplastic material of the first or second edge portion comprises a thermoplastic polyolefin (TPO).
12. 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.