There are three essential parameters for a plastic weld: temperature, pressure, and time.
All thermoplastics have a specific temperature range for effective welding. The plastic manufacturer can often give you an appropriate range of welding temperatures for their material. However it is important to know that the perfect welding temperature for the application can vary depending on environmental conditions such as temperature or sunlight exposure. For example, if you are plastic welding in a colder than normal environment you may need to slightly increase your welding temperature.
For hand welding, the air flow temperature is the only set point to consider. With extrusion welding there are different set points for both the air temperature and the temperature of the extruded plastic
If your temperature is too low, you won’t get enough weld penetration and your welding rod/extrudate and base material will not blend together properly. If your temperature is too high, you will degrade the plastic and again the materials will not blend together properly. In either case, your weld will not be the strongest possible.
See our article on Finding the Correct Welding Temperature for your Project for more information including temperature guidelines.
A weld’s strength comes from the proper blending of the plasticized base material with the plasticized welding or filler rod; this is not possible if the pressure is too high or too low.
The correct pressure when hand welding is learned through feel, practice, and experience.
When extrusion welding, the required welding pressure is applied via the plasticized filler pushing between the base material and the welding shoe. Excessive pressure is characterized by excessive overfill behind the welding shoe and excessive root expulsion. Inadequate pressure is characterized by inadequate filling of weld (if the weld area is not filled, it has nothing to push against to provide pressure) and poor root penetration.
The time required for a plastic weld is determined by the speed of welding. Too fast and the materials do not have sufficient time to plasticize and the pressure is applied for too short of a time; too slow and the plastic will overheat and begin to degrade. It is important to keep a constant speed when welding to ensure uniform results.
When plastic welding, speed is determined by the rate at which the materials plasticize and we get a proper preheat. For hand welding, this is learned through feel, practice, and experience. When extrusion welding, we determine at what speed we are getting an adequate preheat and then we adjust our extrusion rate to ensure we are adequately filling the welding groove at this speed.
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Want to learn more? We offer a One-Day Plastic Welding Course.