|
Welding Tips: Geomembranes
· HDPE: 20 to 40 mil High Density Polyethylene (HDPE) geomembrane material is relatively easy to weld, but when an application requires welding 60 to 80 mil HDPE certain modifications in welding are helpful towards attaining good results.
Since heat rises, it is important to urge the heat flow to the lower sheet. This can be done by placing the lower sheet over a highly heat conductive material such as another geomembrane or geotextile. We have found that placing the lower sheet over an 8-ounce nonwoven polypropylene geotextile will increase the heat transfer rate from the wedge (heat source) to into the lower sheet. Therefore, for field applications with uneven or rocky terrain, we covered a carry-board made of steel or aluminum plate with the nonwoven geotextile, and place the carry-board beneath both layers of geomembrane material.
Furthermore, for thicker materials, more pressure and less speed is required. Try reducing welding speed to approximately 5 to 10 feet per minute and decreasing the pressure roller angle (to approx. 15° of vertical). Continue to use a silicon rubber roller for greatest heat transfer. Remember that using the GT-100 hand-held wedge welder for field production or patching of 60+ mil HDPE will take strength and practice.
For best results, examine the finished product for deformation. The smoother, more aesthetic top sheet surface would indicate a tack weld. Due to a thickness of the material, good welds are characteristic of a more deformed surface. Make sure the heat is sufficient to produce enough smoke, however not to hot to melt or flash the material on contact. A good setting, depending on the age of the heaters, is between 4.5 and 5.
· PVC and VLDPE: Un-reinforced PVC and VLDPE are lightweight materials and require carefull welding techniques. Working with an un-reinforced PVC geomembrane of less than 20 mil requires less heat (Setting of about 4). Suggest using a metal roller with or without the use of a carry-board. Pace yourself for a welding speed of approximately 10 feet per minute. For heavier un-reinforced PVC materials, use slightly more heat and expect weld rate to decrease to about 8 feet per minute. We do not recommend using wedge welding for un-reinforced PVC and VLDPE of weights less than 12 mil.
· Reinforced PVC and CSPE (Hypalon): Prehaps the easiest geomembranes to work with, the reinforced PVC and CSPE are also most forgiving. Make sure the CSPE hasn't either partially or fully cured prior to welding. Curing (by exposure to UV light) will change its structure from a thermoplastic to a thermoset material. It is virtually impossible to weld thermoset materials. Various manufacturers of CSPE offer a spray or liquid solvent that reverses the curing process and prepares the material for wedge welding.
· Polypropylene: Reacts quite well to wedge welding. Depending on the thickness, you may want to refer to the welding hints revealed for HDPE. geosynthetics, civil engineering, geotextiles, geomembranes, plastics, heat sealing, wedge welder, leister
|
