In ultrasonic welding, there are other factors that need to be considered, including the effects of the injection process, water absorption, mold release agents, lubricants, plasticizers, additives, flame retardants, recycled materials, colorants, and plastic grades.
(1) Water absorption of plastic:
The water absorption of plastics is an important factor in the performance of ultrasonic welding. If the plastic contains too much water, during the ultrasonic welding process, when the temperature reaches the boiling point of water, the water in the plastic evaporates and vaporizes, and the welded interface is foamy, which makes the ultrasonic welding strength low, and it is difficult to obtain sealing performance and high. The appearance of the quality; in addition, too much moisture will also lead to prolonged welding time and increased welding costs.
Plastic parts with water absorption should be ultrasonically welded immediately after injection. If welding is not possible immediately, it should be sealed with a PE bag containing a desiccant; the absorbent plastic parts without a sealed package should be dried before welding.
(2) Release agent:
The release agent is often sprayed directly into the mold cavity to help the plastic part escape from the cavity by reducing the friction between the plastic part and the cavity. Unfortunately, in ultrasonic welding, the release agent also reduces the surface friction of the two plastic parts at the welding interface, and the ultrasonic welding process relies on the surface friction to generate heat, and the release agent reduces the ultrasonic welding performance. In addition, the chemicals in the release agent also affect the acquisition of the desired weld strength.
Therefore, for plastic parts that require ultrasonic welding, it is necessary to avoid the use of the release agent during the injection process. If you have to use a release agent, you must clean the plastic parts before soldering, but only some release agents can be cleaned. Dry release agents are recommended, which have minimal impact on ultrasonic weldability and do not even require cleaning prior to soldering. Try to avoid using mold release agents such as silicon, fluorine, zinc stearate and aluminum stearate.
Lubricants such as waxes, zinc stearate, aluminum stearate, stearic acid and fatty acids are added to the plastic for improved flow and increased injection performance. However, in ultrasonic welding, the lubricant reduces the friction coefficient of the welding interface, thereby affecting the ultrasonic welding performance of the plastic.
In order to improve the mechanical properties of plastics, fillers are added to plastics. Commonly used fillers are glass fiber, carbon fiber, talc and calcium carbonate. Glass fibers are added to the plastic to increase the mechanical strength and dimensional stability of the plastic. Ordinary mineral fillers, such as fiberglass and talc, increase the ability of plastics to conduct vibrations and improve the ultrasonic welding properties of plastics, especially for semi-crystalline plastics. In general, 10% to 20% of glass fiber will significantly improve the ultrasonic welding performance of plastics.
However, the fact that the ratio is too large brings other problems. For example, if the proportion of filler is 30%, but at the local welding interface, the true ratio may have exceeded 30%, so that there is not enough plastic melting at the welding interface to obtain the desired welding quality. When the proportion of the filler exceeds 40%, it is highly probable that more material is not weldable at the welding interface than solderable material, which means that the ultrasonic welding performance becomes poor.
(5) Return material:
Recycled materials are often added to plastics due to the recyclability of plastics and the cost of parts and materials. Ultrasonic welding allows the addition of material in the plastic, because the material itself is the same plastic, but the proportion of the material can not be too large, and the material can not be degraded or contaminated, otherwise there will be welding quality problems. In order to ensure the quality of the welding, it is recommended that the proportion of the return material is as small as possible.
Pigments have little effect on the ultrasonic weldability of plastics unless the proportion of pigment is too high. White and black usually require more pigmentation than other colors, and may cause some soldering problems. Different colors of the same plastic may require different welding parameters and can be obtained by tuning.
(7) Plastic grade:
The plastic grade has a great influence on the ultrasonic welding properties of plastics. Different grades of the same plastic may have different melting points and different flow characteristics.
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