There are two methods for construction welding of HDPE geomembrane: double seam hot melt welding and single seam extrusion welding. Under normal circumstances, the welding mainly uses a dual-drive self-propelled HDPE geomembrane welding machine, which uses dual-track hot-melt welding. For parts that cannot be welded by the welder, an extrusion hot-melt welder should be used to form a single weld seam for surfacing. When welding, one thing needs to be paid attention to. The welding rod used for welding must be produced with the same raw material as the geomembrane to ensure the reliability of welding.

  The welding of HDPE geomembrane shall meet the following requirements:

  1. Preparation before welding

  a. Inspection of the lap width after film laying: the lap length of the welded seam of HDPE film is not less than 100mm;

  b. Before welding, clean up the overlapped film surface within the range of about 200mm. Wipe off dust and dirt with a damp cloth to keep this part clean and dry. There should be no scratches, stains, moisture, Dust and other impurities that hinder welding and affect construction quality;

  c. Trial welding

  Before the formal welding operation, the equipment parameters should be set according to experience, and a small piece of film of 300×900mm is taken for trial welding. Then carry out the shear and peel test of the weld on the tensile machine. If it is not lower than the specified value, the parameters will be locked and the formal welding will be started based on this. Otherwise, the parameters must be re-determined until the test is qualified. When the temperature and wind speed change greatly, the parameters should be adjusted in time, and the test should be repeated to ensure that the welding machine performance, site conditions, and product quality meet the specifications. The date, time, and ambient temperature must be marked on the sample;

  d. When the ambient temperature is higher than 40 ℃ or lower than 5 ℃, HDPE geomembrane cannot be welded. If construction is necessary, the welding machine should be preheated before welding.

  2. Double seam hot melt welding construction requirements:

  a. The welding process is divided into: adjusting pressure, setting temperature, setting speed, welding seam overlap inspection, installing film into machine, starting motor;

  b. After starting up, carefully observe the temperature rise displayed by the instruction meter to make the equipment fully warm up;

  c. When inserting the film into the welding machine, the overlap size must be accurate and the action must be rapid;

  d. During welding, the welder should pay close attention to the condition of the weld and adjust the welding speed in time to ensure welding quality;

  e. Keep the weld seam straight and tidy during welding, and take measures to deal with the uneven part under the film as soon as possible to avoid affecting the smooth operation of the welder. When a special fault is encountered, the machine should be shut down in time to avoid scalding the film.

  3. Construction requirements for single seam extrusion welding:

  a. Check whether the lap width at the weld is appropriate, the film at the joint should be flat, with moderate tightness, so as not to form a "fish mouth";

  b. Positioning bonding: Use a hot air gun to bond the overlapping parts of the two films, and the distance between bonding points should not be greater than 60-80mm. To control the temperature of the hot air, the HDPE geomembrane must not be scalded, nor can it be easily torn;

  c. Roughing: Roughing the film surface within the width of 30-40mm at the welding seam with a roughing machine to achieve thorough cleaning and form a rough surface;

  In order to increase the contact area, but the depth should not exceed 10% of the film thickness, and the hair should be operated gently to minimize damage to the film surface. For films with a thickness of 2mm or greater, a 45° bevel shall be made;

  d. When welding, the machine head should be aligned with the seam, and the welding deviation is not allowed, and slip welding and skip welding are not allowed;

  e. The thickness of the weld center should generally be 2.5 times the thickness of the impermeable membrane and not less than 3mm;

  f. When a seam cannot be welded continuously, the welded seam of the stubble part shall be roughened at least 50mm, and then lap welding shall be carried out;

  g. The welding rod used must be kept clean and dry before entering the machine, and the welding rod must not be wiped with oily, dirty gloves, dirty cloth, cotton yarn, etc.;

  h. According to the temperature, the welding seam is immediately cooled;

  i. When the extrusion welding operation is interrupted for some reason, the extrusion amount of the electrode must be slowly reduced, and the welding should not be interrupted suddenly, and the welding should be performed from the interruption to the roughening when re-construction.

  Four, matters needing attention when welding

  a. Adjacent HDPE geomembrane welds should be staggered and overlapped as much as possible. The joints formed between the membrane blocks should be T-shaped, and cross-shaped should be minimized. The longitudinal die should be strengthened by an extrusion welder at the intersection of the welds;

  b. It is not allowed to press out dead bends when welding the film. When laying HDPEHDPE geomembrane, set aside the amount of expansion and contraction caused by temperature changes according to the local temperature change range and the performance requirements of HDPEHDPE geomembrane;

  c. In the welding process of extrusion welding machine, the slider of the gun head should be checked frequently, and the slider should be replaced in time when the wear is serious, so as not to damage the film surface;

  d. The HDPE geomembrane should be powered by a generator with good voltage stabilization performance when welding, and a voltage regulator must be used when local power is used in special circumstances;

  e. Each weld needs to be numbered; the weld should also be marked with welder number, time, and temperature (head and tail);

  f. The HDPE geomembrane should have been overlapped before the double seam hot melt welding, and the HDPE geomembrane should have been covered before extrusion welding, or the distance from the damaged area should have overlapped at least 120 cm.

 Often, many projects are due to the pursuit of simplicity and speed in the operation process without strict compliance with the construction specifications, and finally left unpredictable hidden dangers for the project. A good construction depends on high-quality geomembrane 50% and strict on-site construction.