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.