Vacuum Box Testing for Extrusion Welded Liner
Spray the soap solution on the top of the seam, and place the vacuum box over the wetted seam area. Ensure that a leak tight seal is created. Maintain a vacuum of approximately 3-5psi for 15 seconds. Examine the liner through the viewing window for the presence of soap bubbles. All areas where soap bubbles appear should be marked and repaired.
Air Pressure Testing for Double Fusion Welded Liner
Seal both ends of the tested seam. Insert needle or other approved pressure feed device into the channel created by the double-wedge fusion weld. Energize the air pump to a pressure between 20-35 psi, close the value, and sustain the pressure for at least 5 minutes. If pressure loss exceeds the allowable drop or does not stabilize, locate the faulty area, repair and retest.
HOT WEDGE WELDING
Hot Wedge Welding is the primary seaming method for the Geomembrane. The high temperature wedge is used to melt the facing overlapped surfaces and then press them together with two nip/drive rollers. This makes a permanent bond between the two Geomembrane.
A Good Seam of Hot Wedge Welding should include:
1. A small amount of squeeze-out should be visible which indication shows that proper seaming temperatures have achieved; however, when an excessive amount extrudes out of the seam zone, temperature or pressure should be reduced.
2. The liners that are ready for welding should be clean and free of moisture.
3.The width of the tracks should be equal.
4. Nip/drive roller marks should always appear on the surface of the liner.
EXTRUSION WELDING
Extrusion welding method is commonly used for repairs and detail works. Extrusion welder provides a hot extrudate (molten plastic) by using 4 or 5 mm diameter welding rod made of the same material as the liner. The hot extrudate is deposited on the edge of two overlapped liners, resulting in an extrusion beam. A hot air device is used to preheat the liners in the weld area to tack these two liners together.
All degraded materials should be purged before welding. The welding area should be ground to remove the oxide layer and dirt from the surface, and to roughen the interface of liner. Grinding depth should not exceed 10% of the liner thickness.
Temperature and seaming rate play important roles in obtaining a good seaming strength. |
