Using infrared thermal radiation to heat the welded reinforcement. The energy light waves emitted by the infrared heat source are absorbed on the surface of the welding rib. The heat absorbed on the surface enters deeper positions of the welding ribs through thermal conduction.
An important parameter in the infrared welding process is the heating rate. Thermoplastic materials melt and flow during heating. If heated too quickly, the material will degrade, posing a risk of combustion or carbonization. When many plastics undergo infrared welding, the surface of the plastic absorbs infrared heat quickly, but the internal heat conduction is slow, which can easily lead to overheating and degradation of the plastic surface. Infrared welding, like hot plate welding, must ensure that the welding ribs have sufficient material softening depth to achieve reliable welding performance.
The rate at which materials absorb infrared radiation is related to three characteristics: absorption rate, transmittance, and reflectivity. These characteristics are influenced by material type, color, fillers, and other factors. In addition, the radiation ability (wavelength and power) of infrared lamps also affects the efficiency of thermal radiation transfer and heating rate.
The energy density of infrared light waves reaching the plastic surface also affects the heating rate. The energy density is related to two factors:
(1) The distance between the infrared heat source and the heating surface;
(2) Infrared energy focusing method.
In short, there are many factors that affect the speed at which plastics absorb infrared radiation, and the key is to control this speed to avoid material overheating and degradation.
For example, black opaque materials with high glass fiber content have a fast absorption rate of infrared on the surface, but the internal heat conduction speed of the material is not fast, which can easily lead to overheating of the outer surface. A white material without fiberglass has a heat conduction velocity inside the material that is greater than the surface infrared absorption velocity, so there is no risk of surface overheating. However, the entire welding time will be longer.
