How to weld polyurethane sheets to make tanks

Written by c.l. rease
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Polyurethane is a thermoplastic, which means that you can use heat to melt--and therefore weld--pieces of polyurethane together. Like all thermoplastics, you must reach the plastic's melting temperature to create a proper weld joint. If you exceed the plastic's melting temperature, the surface of the plastic will scorch. When scorching occurs, the impurities that rest on the surface will interfere with the quality of the weld. If the welds are on a plastic tank, this can cause leaks or the welded seams could burst.

Skill level:
Moderately Challenging

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Things you need

  • Hand-held plastic welder with speed tip
  • Safety glasses
  • Stout bladed knife
  • Angle finder
  • Polyurethane filler rod
  • Side cutters

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  1. 1

    Turn on the hand-held plastic welder and set the temperature dial to 302 degrees Celsius. Set the welder aside and allow it to warm up while you prep the polyurethane sheets.

  2. 2

    Put on your safety glasses.

  3. 3

    Bevel all the edges of the sheet that need to be welded by dragging the knife blade along each edge at a 30-degree angle. Make the bevel as deep as the polyurethane sheet is thick. For example, if the polyurethane sheet is 1/4 inch thick, the bevel should extend from the inside edge of the plastic 1/4 inch in on the top edge of the sheet.

  4. 4

    Ensure that the bevels are correct by setting the angle finder to 150 degrees and resting the bar of the angle finder on the outer edge. If the head of the angle finder rests flush on the bevel, you have a 30-degree bevel.

  5. 5

    Align the seams of the polyurethane sheets and aim the tip of the plastic welder at the aligned seam.

  6. 6

    Drag the speed tip along the seam. When you notice the polyurethane beginning to melt, tack the two pieces together.

  7. 7

    Place the outlet of the plastic welder into the tacked seam, feed a length of plastic filler rod into the speed tip and pull the plastic welder along the seam as you push the filler rod into the tacked seam.

  8. 8

    Trim the excess filler rod from the polyurethane sheet after you run past the end of the seam. You will need to make multiple passes with filler rod to fill the bevelled edge. With each pass along the seam, stagger the end of the filler rod to offset the connections between filler rods when the seams are longer than the length of the filler rod.

  9. 9

    Allow the weld joint to cool before handling the welded polyurethane sheet.

  10. 10

    Bevel the area where the weld joint meets the ends of the polyurethane sheet.

  11. 11

    Tack and weld each seam of the polyurethane sheet as above until all the seams of the polyurethane tank are welded.

  12. 12

    Fill the welded polyurethane tank with water after it has completely cooled and inspect each seam for water leaks. If you find a leak, run another pass along the seam with the plastic welder and filler rod to stop the leak.

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