Welding Methods For Geomembranes
Twin Wedge Welding. Hot air wedge welding consists of placing a heated wedge, mounted on a self propelled unit, between two over-lapped sheets such that the surface of both sheets are heated above the membranes melting point. After being heated by the wedge, the overlapped panels pass through a set of pre-set pressure rollers, which compress the two sheets together to form a weld. The fusion welder is equipped with a temperature readout device that continuously monitors the temperature of the wedge.
Twin Wedge Welded Seam Testing
The welded seam created by a hot air wedge welder is composed of a primary seam and a secondary track that creates an unwelded channel. This unwelded channel allows the completed weld to be tested by inflating the sealed channel with air to a predetermined pressure usually 1 bar for 5 minutes duration and observing the stability of the pressurised channel over time. For further information please consult “geosynthetics and welded gas resistant membrane installation quality plan”.
Extrusion welding consists of introducing molten resin along the seam of the two overlapping sheets to be welded. Pre-heating of the laps and the molten polymer causes some of the material of each sheet to melt resulting in a homogeneous bond between the molten weld bead and the surfaces of the sheets.
Extrusion Welded Seam Testing
If requested prior to membrane installation, spark testing can be used for non - destructive testing of extrusion welds. After seam preparation, but prior to welding, a length of copper wire can be embedded into the seam over its entire length, after the completed weld has cooled the suitably adjusted spark tester ( 10 Kv / mm ) shall be passed over the extruded weld, any sparks observed indicate a seam failure, these should be marked on the seam. For repair at a later stage and then retested. For further information please consult “geosynthetics and welded gas resistant membrane installation quality plan”
Hot Air Welding
In areas inaccessible to the previous noted forms of welding or where site conditions dictate, overlap welds may be effected with the use of proprietary hot air guns and hand rollers. The equipment used must be specifically designed for the purpose with multi-stage variable adjustment on both heat and blower settings. The overlapped membrane is heated to softening point and fused together using the hand rollers to form a homogeneous fusion welded joint over a minimum width of 50mm.
Hot Air Welded Seam testing
Hot air welded joints may be tested using the Air Lance Method. A compressed air source will deliver 55 PSI minimum to a 5mm nozzle. The nozzle will be directed to the lip of the field seam in a near perpendicular direction to the length of the field seam. The nozzle will be held 100mm maximum from the seam and traversed at a rate not exceeding 12m per minute. Any loose flaps of 3mm or greater will require repair.
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