Download our "How to Weld" guide for thermoplastic welding information, instructions, and more.

Below is an excerpt from our “How to Weld” Guide – download the PDF for complete step-by-step instructions on welding procedures, diagrams, and specific equipment information.


Thermoplastic Welding

It is possible to weld thermoplastic material (plastic that can be softened or shaped by heat) with a Seelye electric hot air welder. This lightweight, hand-held equipment makes it easy for even an inexperienced user to develop the “feel” for welding plastic and to do it economically and with speed after only a few hours of study and practice. Whether fabricating thermoplastic stock or repairing various types of plastic parts, hot air welding is usually performed on plastics with a minimum thickness of 1/16 inch or more. The bond achieved, depending on the type of weld, is generally as strong (90% or greater) as the original material.


User-Friendly Hot Air Welding

Seelye Hot Air Welding Equipment is specially designed for extensive hand-held use without causing the operator fatigue. The equipment is lightweight and very maneuverable. It can be moved easily from one project work area to another. All that is needed is a concentrated effort to learn about the use of the equipment.


Welding Safety

After following Seelye’s step-by-step instructions, as well as those issued by the manufacturers of
the plastic materials, you will be on your way to welding. Hot air welding is safe because there is no flame, spark, or smoke involved. Special venting, hoods and ducting are not required. Observe these simple precautions:

  1. Never attempt to perform hot air welding with a flammable gas.
  2. To avoid burning out the heating element, always remember AIR FLOW FIRST and AIR FLOW
    LAST. Start the air flow before the heating element. Set the air flow between 4 to 6 PSI (depending on which welder is being used and what type of plastic is being welded). Air pressure minimum settings vary depending on welder model.
  3. Never touch metal parts on the welding gun until they have cooled.
  4. Always use pliers to change the tip on a welding gun. Do not over tighten or cross thread.
  5. Disconnect the electricity to the gun but continue the air flow. The gun will cool faster and the
    electric heating element will last longer.
  6. Do not put the welder in a vise to change heating elements.
  7. Keep away from children.


Standard Weld Identification

Similar to metal welding, the same types of welds are performed in hot air welding; these consist of butt welds, fillet welds, lap-joints, edge welds, and corner welds.


Setting Up the Welding Equipment

  1. Connect your Seelye Gun to a clean, dry air supply (compressed air – 90 PSI minimum) or an inert gas.
  2. Your Seelye welder can be plugged into any 110 volt A.C. outlet. Now that you have
    your air supply flowing, plug into the electrical source and allow the welder to warm up
    for several minutes before starting to weld.
  3. Be sure to select the proper welding tip:
    • Tacking Tip is used for fitting up the work. No rod or strip is required.
    • Round Tip is used for small are welds. Any size welding rod can be used.
    • Automatic Speed Tip is used for speed and larger areas. Size of tip will depend on size of welding rod needed.
  4. Always use pliers to install and remove tips. Do not over tighten or cross thread.


Step-by-Step Welding Procedure

  1. Determine whether the type of weld being performed requires a beveled edge. See diagrams in the PDF download guide.
  2. If beveling is required, perform the beveling with a grinder and/or table saw. Bevel a 60° angle.
  3. Clean dust and dirt from materials to be welded. To remove oily substance use Methyl Ethyl Keton (MEK). Be sure materials to be welded are dry before starting to tack weld.


Tack Welding for Work Fit Up

  1. After you have installed the Seelye Tacking Tip, start the air flow, plug in the electrical source, and allow the welding tip to heat for several minutes.
  2. While the tip is heating, line up pieces to be welded. By this stage you should have prepared the plastic pieces carefully, made the necessary bevels, if required, and cleaned and dried the
    pieces to be welded.
  3. No rod or strip is required for tack welding with hot air. Apply the hot Tacking Tip to the area
    or seam where the plastic pieces are to be joined, moving the tip along both pieces at the same
    time, until the plastic fuses (joins) together.
  4. Do enough tack welds to hold the weight of the pieces together. With large pieces, it may be
    necessary to draw the Tacking Tip along the entire seam, fusing the work continuously. This will hold the weld together properly for accurate permanent bonding, which will be performed during the next phase of work.
  5. Avoid overheating the tack points. This causes the plastic material to discolor, char or warp. If you are not properly fitted, start over. Tack welds are easy to break. Before doing a new tack
    weld, grind the tack points down to smooth edges.


Permanent Welding with Hot Air

  1. Before starting the permanent weld, be sure to select the right type of welding rod (or strip). It must be the same type of plastic as the material you will be bonding together. Usually the manufacturer of the plastic material will label the plastic type for easy identification – please view our Plastic Type Info. & Applications page. If you do not know what type of plastic you are welding, refer to our Burn Chart to identify the material you are going to weld.
  2. For maximum welding economy, select a rod diameter size close to the thickness size of the base material. For base Material thickness greater than 3/16” diameter more than one rod will be necessary. Example: To weld a 1⁄4” thick plastic, fill in the beveled area with three beads of 5/32” diameter welding rod.
  3. Select the proper welding temperature and air flow setting.
  4. Install the Round Tip for permanent welding. Allow the Round Tip to heat properly. If you Change the Tacking Tip to the Round Tip while The welding gun is hot, be sure to unscrew the Tacking Tip and screw in the Round Tip using Pliers. Do not overtighten; it should be snug only.
  5. Cut the end of the rod at 60° angle. Hold the cut end of the rod just above the weld starting point. Apply heat to the rod end and the base material seam at the same time until both are tacky. Press the tacky end of the rod down into the tacky starting point of the base materials. Only the surface of the rod and base materials will be tacky, but will bond properly. The rod will continue to hold its basic shape, for the most part, throughout the welding work.
  6. Continue the weld, holding the rod at a 90° angle directly above the weld seam, press firmly and evenly down into the weld joint as you apply heat in the direction of the weld seam with a short fanning motion (see illustration). As the rod and base material become tacky, if you are welding at the proper temperature, a loop will form where the rod joins the base materials and small beads will form on either side of the completed weld.
  7. At the end of the weld, cut the rod with a knife or pliers at a 30° angle. Cut the end of the new rod at a 60° angle to continue.

There should be no charring, discoloration, or warping if proper heat is applied. There should be no stretching of the welding rod. This will weaken the rod bond and can be avoided by taking care to press directly down on the rod rather than pushing the rod along the direction of the weld seam. A few hours of practice welding will give the “feel” for maintaining the right even pressure on the rod straight down into the weld area. Please view our Videos & Tutorials page for more information.


For the complete step-by-step instructions on welding procedures, diagrams, and specific equipment information, please download our How To Weld Guide.

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