Views:43 Author:Site Editor Publish Time: 2019-09-26 Origin:Site
In the process of practical consumption, not all plastic materials can stop welding. Plastics that can be welded by ultrasonic wave belong to thermoplastics. As long as thermoplastics with the same or similar molecular structure can stop welding and chemical separation between molecules on the welding surface, the closer the parent material is, the better the welding effect. The better the fruit. The following figure is a comparison of welding compatibility of some common plastics. We also need to think about the factors that affect the quality of welding to get better welding results. When stopping welding, pressure, time and heat absorption (melting amount) are the three elements to ensure welding quality.
When proper pressure is applied to the weld appearance, the welding data will transit from elasticity to plasticity. It can also promote the diffusion of molecules and squeeze out the residual air in the weld, thus increasing the sealing performance of the weld surface.
Appropriate hot melting time and sufficient cooling time should be required. When the thermal power is fixed, the virtual welding will appear when the time is insufficient, and the deformation of the welded parts will be formed when the time is too long, and the slag will overflow, and sometimes the hot spot (discoloration) will appear in the non-welded parts. It is necessary to ensure that the welding surface absorbs enough heat to reach the state of abundant melting, to ensure the abundant diffusion and fusion between molecules, and to ensure sufficient cooling time to make the weld reach sufficient strength.
The most appropriate amount of melting can be achieved only when the melting time and thermal power are harmonized and adjusted to ensure sufficient intermolecular fusion and eliminate the phenomenon of virtual welding. In addition to the level of welding equipment and operator's skill, various factors coming from inside or outside of plastics have a certain influence on welding quality, which should be paid attention to.
Hygroscopicity of plastics
If wet plastic products are welded, the water contained in them will turn into steam after being heated and appear bubbles on the welded surface, which will weaken the sealing performance of the welded surface. PA, ABS and PMMA are the most serious hygroscopicity data. The products made from these materials must stop the boring treatment before welding.
Fillers in Plastics
For example, glass fiber, talc powder, mica and so on, they change the physical properties of the data. The content of filler in plastics is closely related to the solderability and welding quality of plastics. Plastics with filler content less than 20% can stop welding normally without special disposal. When the filler content exceeds 30%, due to the lack of external plastic proportion and insufficient intermolecular blending, the sealing performance will be reduced.
Cleaning of Welding Surface
Welding appearance must be clean and free of impurities in order to ensure adequate welding strength and air tightness.
In addition to selecting the right weldable materials and sweeping away the unfavorable factors affecting the welding effect, appropriate welding methods should be adopted according to the material variety, product shape and cost. According to the different heating softening methods adopted, plastic welding methods can be divided into external heating source softening, mechanical movement softening, species and electromagnetic softening.