Welding plastic is very similar to metal welding in that one must know what kind of plastic is involved, its melting point, and how to make a proper weld joint. Remember to that plastic welds will appear similar metal welds and that a grinding and finishing process must be done before the weld will be complete. This is only a brief overview of plastic welding and contains only basic information that may be needed to do all types of plastic welding and finishing.
Plastics that can be welded are called “thermoplastics” meaning that when heated to a sufficiently high temperature, they will soften and therefore can be welded. The most common types of thermoplastics are Polyethylene, Polypropylene, Polyvinyl Chloride (PVC), Polyurethane and Acrylonitrile Butadiene Styrene (ABS).
Hot air welding is most effective if the material is more than 1/16” thick. A good weld will produce a joint that is about as strong or stronger than the original material.
It is necessary that you practice on scrap material to get the “feel” of plastic welding before starting on an actual project. Plastic welding takes practice just like metal welding.
The welding rod must be the same material as the material you are attempting to weld.
In some cases you may be able to determine the material you are working with from information provided by the manufacturer of the product; in other cases you will not.
One method of determining the type of plastic is by using the “Burn Test”. This is accomplished by observing how it burns, the color of the flame, and the smell of the smoke. It may be necessary to remove a small sliver of the material to perform the burn test.
The following chart provided the descriptive characteristics of the thermoplastics when subjected to the “burn test.”
|No smoke, blue flame, candle wax odor||Polyethylene (PE)|
|No smoke, orange flame, and odor||Polypropylene (PP)|
|Black sooty smoke hanging in the air, sweet odor||Acrylonitrile Butanadiene Styrene (ABS)|
|Self-extinguishing, won’t flame||Polyvinyl Chloride (PVC)|
|Black smoke, sputtering effect||Polyurethane (TPUR)|
Once you have identified the material you want to weld, you can select the correct matching material welding rod.
The correct temperature of the airflow from the heat gun is very critical to producing a good weld. Too much heat or not enough heat will result in weak welds.
The following shows the correct welding temperatures for the various types of thermoplastics:
|Type of Plastic Material||Welding Temperature|
|Acrylonitrile Butanadiene Styrene (ABS)||500°F|
|Polyvinyl Chloride (PVC)||525°F|
To test the temperature output, apply heat to the welding rod you have selected. If the temperature is correct, the rod should get tacky and then very soft. If the rod starts to liquefy, the temperature is too hot.
Plastic welds are very similar in appearance to metal welds and many of the same welding techniques are used. Note that the edges of the parts to be welded are beveled. This is important to make a smooth weld. The following drawings show the various types of common welds.
07062 – is placed on the heat gun as a base for 07201 and 07091
07201 – is used if you are using a rigid welding rod
07091 – is used if the rod material is flexible or rigid
The temperature control dial should be set between 7 and 8 on Models HL 1802 E and HL 2002 LE. The temperature control on the HL 1800 E should be set between 2 and 3 and on the HG 2000 E thumb wheel it should be set between the 2 and 3 notches.
1. Practice on scrap material before attempting to work on your project.
2. Install the welding tip on the heat gun.
3. Cut the end of the plastic welding rod at a 60° angle. It is recommended that the welding rod be as long as the joint being welded. This will prevent a weak spot in the weld where the rods may be joined.
4. Clean the parts you are going to weld with a damp cloth, and then dry with a dry cloth. Next, align the parts in the position you want to weld them. It may be necessary to clamp them in position.
5. Turn the heat gun on and let it warm up for about 30 seconds and set it to the proper welding temperature.
6. Hold the weld rod close to the starting point and apply heat to the rod and the base material until both are tacky. (The rod will start to soften). Press the welding rod down to the starting point on the joint to be welded at a 90° angle.
7. Continue moving the heat gun and the rod along the joint, applying some pressure on the rod as it melts into the joint, and move the heat gun in a slight half-moon motion. Keep applying the heat directly over the joint. Move at an even speed and with a constant pressure across the joint. Do not stretch the rod, as this will create a weak section in the weld.
8. At the end of the weld, cut the rod off with a knife or side cutter. Be sure to let the welding material cool to room temperature before testing the strength of the weld.
Caution: Plastic welding requires practice. Practice will give you the “feel” for the correct pressure to apply on the rod, how fast to move across the weld, and what to look for to determine the strength of the weld.
The following drawings indicate what proper and improper welds may look like: