11.1   Extrusion Fillet Welding System

Extrusion fillet welding is used for patches and around details such as pipes and sumps. An extrusion weld is produced by using a 4 or 5 mm diameter welding rod. The welding rod is applied as a "welded bead" at the edge of two overlapped Poly-Flex liners, resulting in an extrusion seam.

11.2   Liner Preparation for Extrusion Fillet Welding

The two liners to be joined must be positioned to create an overlap of at least 6 inches. Follow the same general guidelines as specified for liner preparation for hot wedge welding.

11.3   Extrusion Equipment Preparation

1. A generator must be kept in the proximity of the seaming area. It must either be fitted with rubber tires, or be placed on a stable and smooth moveable base, such as an excess of liner, so that no damage will be inflicted upon the liner or subgrade by its movement. The generator's fuel (gasoline or diesel) must be stored off the liner.
   
2. A hand-held electric rotary grinder having a circular disk grinding plate approximately 4.5 inches in diameter and adequate #80 grit paper must be available. Sandpaper coarser than #80, e.g. #60, is not acceptable for smooth liners.
   
3. A hot air welder capable of 600° C must be available to tack the liner after they are properly positioned.
   
4. All extrusion fillet seaming devices must be equipped with a properly functioning temperature controller which displays the extrusion temperature.
   
5. All types of extrusion fillet seaming devices have teflon dies, varied in shape and size, through which the extrudate passes onto the liner. These dies must be inspected for wear, sharp notches and creases, and for their appropriateness to the application at hand.

1. Surfaces shall be clean and dry.
   
2. For liners 50 mils and thicker, the upper sheet's leading edge must be ground to a 45° bevel (Figure 3). It is imperative that the sheet be lifted up and away from the lower sheet during the beveling so that no deep gouges are cut in the lower sheet. Beveling should therefore be done before tack welding.
   
3. A hot air device should be used to "tack" the two sheets together. The hot air gun prepares the seam for the extrusion welder by creating a light bond between the two sheets, securing their position. The hot air gun is not meant to create a primary seam. No heat distortion should be evident on the surface of the upper sheet.
   
4. The area which is to receive the extrusion bead shall be ground to remove surface contamination and surface tension. Grind marks should not be deeper than 10% of the sheet thickness. Optimally, they should be about 5% of the sheet thickness (Figure 4). The only purpose of grinding is the removal of oxide layers and dirt from the liner surfaces and the roughening of their interface for the extrudate. All material dust generated by grinding the liner sheets must be blown away from the seaming area.
   
5. Grinding marks should not extend beyond 1/4 inch of either side of the extrudate after its placement. For example, if the final extrudate bead width is 1.5 inches, the width of the grinding trail should not exceed 2 inches.
   
6. Seaming must take place no more than 10 minutes after grinding, so that surface oxide layers do not reappear where the extrudate must be placed.
   
7. The welding rod shall be free from dirt, dust, moisture and tangles at all times.

   

8. The extrusion welder's barrel shall be purged of all heat-degraded extrudate for approximately 30 seconds before starting a seam. This must be done every time the extruder is restarted after two or more minutes of inactivity. The purged extrudate shall not be discharged on the surface of the liner or on prepared subgrade, where it could damage the liner.
   
9. Molten extrudate is deposited along the overlapped seam. The center of the extrudate passes directly along the edge of the upper liner, at sufficient width to completely cover the edge and most of the outlying grind marks, at least to within 1/4 inch of their extremity.
   
10. The bottom portion of the welding die shall stay in intimate contact with the sheet surface and conform to various seam angles and configurations.
    
11. The extrudate should be approximately twice the specified sheet thickness, measured from the top of the bottom sheet to the top or "crown" of the extrudate (Figure 5). Excessive squeeze-out (or "flashing"), as illustrated, is acceptable, if it is equal on both sides and will not interfere with subsequent vacuum box testing. The presence of squeeze-out may indicate that the extrusion die was not riding directly against the liner, that the extrudate temperature was improper for adequate flow, or that the seaming rate was too slow.
    
12. Where possible, inspect the underside of the lower liner for heat distortion. This can be done at the end of seams, and wherever samples are cut out of the seam. A slight amount of thermal "puckering" on relatively thin liners (less than 50 mil) is acceptable. It indicates that heat penetrated entirely through the sheet. However, if the underside is greatly distorted, either lower the temperature or increase the rate of seaming. For liners 80 mil and greater, no thermal "puckering" should take place.
    
13. If the seaming process must be interrupted at mid-seam, the extrudate should trail off gradually, not terminate in a large mass of solidified extrudate. Where such welds are abandoned long enough to cool, they must be ground prior to continuing with new extrudate over the remainder of the seam. Grind where the extrudate trail-off begins. This restart procedure must be followed for patches, pipes, fittings, appurtenances and "T" and "Y" shaped seams.

    

1. A smooth insulating plate or heat insulating fabric is to be placed beneath the hot welding apparatus after usage. The tip die and barrel must not be placed on any liner or other geosynthetic surface, as it is extremely hot and can cause severe damage.
   
2. The extrudate bead should be visually inspected for alignment, height, and surface texture uniformity. The extrudate should be free of bubbles and pock marks which indicate the undesirable presence of air, water or debris within the extrudate rod or pelletized polymer.
   
3. Grind marks should not be visible more than 1/4 inch beyond the extrudate. These should be very light and not contain heavy gouges. Grinding is considered excessive when it is deeper than 10% of the liner thickness. It is unacceptable to apply additional extrudate over the original extrusion fillet seam in an area of excessive grinding. A cap strip shall be placed over the entire portion of the seam where excessive grinding is located.