Repair Method D: hot air welding
Repairing Thermoplastics with Hot Air Fusion Welding
With practice, you will find welding plastics with hot air to be quick, strong, and very cost effective. Using our specialty welding rods, you will be able to repair virtually any type of thermoplastic part. With R-13 welding ribbon, you will be able to repair broken tabs and mounts on polypropylene based plastics like TPO without having to worry about strength.
V-Groove Damaged Area
Line up the outer surface of the tear with 6481 Aluminum Body Tape or with clamps. You can also tack the tear together with 2200 Insta- Weld 1 thin adhesive.
V-groove the part with either the 6121-T Teardrop Cutter Bit or the 6200VG V-Groovin’ Tool making a V-groove almost all the way through the plastic where the plastic is cracked or needs to be welded. This will ensure the weld has optimal penetration into the plastic and will produce the strongest possible joint. The only exception to this is when making a weld using the R-13 welding ribbon. In that case, the increased surface area of the welding material makes up for the lost penetration in the seam.
Remove the paint in the area surrounding the v-groove and radius into the v-groove with coarse sandpaper.
Figure 1 shows the V-groove made at the point where the pieces of plastic will be welded together. Notice the depth of the groove, this will allow a piece of plastic to have maximum weld penetration by allowing the welder to make one or more passes, filling the groove from the bottom to the top with filler rod.
Set the Temperature and Airflow
The key to properly setting the temperature and airflow is to match the type of filler rod you are using. Typically, the lowest balance of airflow and temperature that you can get to work for the material you are welding will produce the most satisfactory welds.
For the 6050HA, the airflow is usually set somewhere in the ballpark of 3 psi.
For the 6055, the airspeed is usually set in the lowest speed range.
At a distance of approximately ¼” to ½”, direct the airflow at the rod or base material for a couple of seconds. The rod and the base material should turn glossy as the surface begins melt. If it takes longer than several seconds, you may need to either increase the temperature or adjust the airflow. Should the plastic begin to turn glossy and begin to bubble after only briefly heating the material, you will need to reduce the heat or adjust the airflow.
Aim the airflow and the welding rod
Hold the welder with the tip between ¼” and ¾” away from the material to be welded. Heat the base material and the rod until both become shiny and tacky. (Figure 2)
Because the base material acts as a heat sink it typically requires more heat than the rod.
The objective is melt the rod and base material simultaneously, so when they are pressed together they melt together, not just melt to one another.
Welding the Joint:
Holding the welding rod at about a 45 degree angle away from the welder, begin pressing the rod into the v-groove of the material. Holding this angle on the rod, work your way down the v-groove steadily, melting the rod and the base material together. (Figure 3 and 4)
Make sure the rod and the base material are heated equally to ensure a good weld. If the base material is allowed to overheat, the surface may scorch or the substrate will melt. Should the rod be heated and the base material left too cool, you will not get adequate penetration of the weld and the weld will be very weak.
The approximate speed of a hot air weld is roughly 6 to 8 inches per minute depending on the thickness of the base material.