1. Ultrasonic waves propagate in plastic parts. Plastic […]
1. Ultrasonic waves propagate in plastic parts. Plastic parts more or less absorb and attenuate the ultrasonic energy, which will have a certain impact on the ultrasonic processing effect. Plastics are generally divided into amorphous materials. According to the hardness, there are hard rubber and soft rubber. There is also the distinction of modulus. In layman's terms, the ultrasonic processing performance of plastic with high hardness and low melting point is better than that of plastic with low hardness and high melting point. Therefore, this involves the issue of the distance of ultrasonic processing.
2. The influence of processing conditions of plastic parts on ultrasonic welding
Plastic parts undergoing different processing forms such as injection molding, extrusion or blow molding and different processing conditions will form factors that have a certain impact on ultrasonic welding.
A: Humidity defects: Humidity defects are generally formed in the process of making streaks or loose plastic parts. Humidity defects attenuate useful energy during welding, cause water seepage at the sealing position, and lengthen the welding time. Therefore, plastic parts with high humidity should be made before welding. Drying treatment. Such as polyoxymethylene and so on.
B: The influence of the injection molding process:
The adjustment of injection molding process parameters will cause the following defects:
①Dimensional changes (shrinkage, bending deformation)
④ Poor uniformity
C: Shelf life: After the plastic parts are processed by injection molding, they are generally placed for at least 24 hours before welding to eliminate the stress and deformation of the plastic parts. Plastic parts made of amorphous plastic through injection molding do not meet this requirement.
D: Recycled plastic
The strength of recycled plastics is relatively poor, and the adaptability to ultrasonic welding is also poor. Therefore, if recycled plastics are used, various design dimensions must be considered as appropriate.
E: Release agent and impurities
Release agents and impurities have a certain effect on ultrasonic welding. Although the solvent and impurities on the processed surface can be shaken away during ultrasonic processing, the sound waves that require sealing or the frequency of the high ultrasonic working principle are higher than the upper limit of human hearing (about 20,000 Hz) are called ultrasonic waves, or called Ultrasound. The propagation laws of ultrasonic reflection, refraction, diffraction, and scattering in the medium are not essentially different from the laws of audible sound waves. But the wavelength of ultrasound is very short, only a few centimeters, even a few thousandths of a millimeter. Compared with audible sound waves, ultrasonic waves have many peculiar characteristics: propagation characteristics-the wavelength of ultrasonic waves is very short, and the size of ordinary obstacles is many times larger than the wavelength of ultrasonic waves. Therefore, the diffraction power of ultrasonic waves is very poor. It is in a homogeneous medium. It can propagate in a directional straight line, and the shorter the wavelength of the ultrasonic wave, the more remarkable this characteristic. Power characteristics ─ ─ When sound propagates in the air, it pushes the particles in the air to vibrate back and forth to do work on the particles. Sound wave power is a physical quantity that expresses the speed of sound wave work. At the same intensity, the higher the frequency of the sound wave, the greater the power it has. Due to the high frequency of ultrasonic waves, the power of ultrasonic waves is very large compared with ordinary sound waves. Cavitation ─ ─ When ultrasonic waves propagate in liquid, small cavities will be created in the liquid due to the violent vibration of liquid particles. These small cavities expand and close rapidly, causing violent collisions between liquid particles, resulting in pressures of thousands to tens of thousands of atmospheres. This violent interaction between the particles will cause the temperature of the liquid to rise suddenly and play a good stirring effect, so that two immiscible liquids (such as water and oil) emulsify, and accelerate the dissolution of solutes. chemical reaction. The various effects caused by the action of ultrasonic waves in the liquid are called ultrasonic cavitation.Ultrasound equipment