Plastic welding is a relatively common welding method. Through secondary processing, the characteristics of plastic melting by heating are used, and the plastic of the two parts is melted by heat, and the two parts are integrated under the action of external force. There are many types of plastic welding processes, which are specifically divided into the following types?
1. Heating tool welding
Use a heating tool, such as a hot plate, a hot strip or a soldering iron, to directly heat the two plastic surfaces to be welded until there is enough molten layer on the surface, then remove the heating tool and immediately press the two surfaces until the molten part is cooled Hardening to connect two plastic parts to each other. This processing method is called heating tool welding. It is suitable for welding plexiglass, rigid PVC, soft PVC, high density polyethylene, polytetrafluoroethylene, polycarbonate, polypropylene, low density polyethylene and other plastic products. At present, the more common connections such as PP-R pipe fittings use this process.
2. Induction welding
Place the metal insert on the surface of the plastic weldment and temporarily combine it with appropriate pressure, and then place it in an alternating magnetic field, so that the metal insert will be combined due to the induction of electric potential and heat, which will cause the plastic to melt. Welded products are obtained by cooling, and this welding method is called induction welding. This welding method is suitable for almost all thermoplastics.
3. Ultrasonic welding
Ultrasonic welding is also thermal welding. The heat is obtained by using ultrasonic to excite the plastic for high-frequency mechanical vibration. When the ultrasonic wave is directed to the surface of the plastic to be welded, the plastic particles will be excited by the ultrasonic wave and vibrate rapidly to produce mechanical work. When it is converted into heat, the temperature of the welded plastic surface rises and melts, and the temperature of the non-welded surface does not rise. Ultrasound is introduced into the welded plastic through the welding head. When the welding head stops working, the plastic immediately cools and solidifies. According to the structure of the ultrasonic welding machine, various thermoplastics can be welded.
4. High frequency welding
Place the two laminated plastics between the two electrodes, and let the electrodes pass high-frequency current. Under the action of the alternating electromagnetic field, the free charge in the plastic will naturally repeat at the same frequency (but slightly lagging behind). Displacement (polarization) causes the polarized molecules to vibrate frequently and generate friction. Electric energy is converted into heat energy until it melts, and then external force is applied to combine with each other to achieve the purpose of welding, which is called high-frequency welding. It is suitable for plastics composed of polar molecules, such as films or sheets made of polyvinyl chloride and polyamide.
5. Hot air welding
Hot air welding has the characteristics of convenient use and simple operation. It is especially suitable for the welding of plastic plates. This processing method is to pass compressed air (or inert gas) through the heater of the welding torch and be heated to the temperature required for welding plastics. This preheated gas heats the weldment and the electrode to reach a molten state, so that the welding can be combined under a small pressure.
There are many types of plastic products, and the products usually used are also relatively wide, which indirectly affects the development of welding technology.