Plastic welding is to connect parts made of different materials, so that thermosetting plastics and hot-melt plastic parts can be connected with each other, or plastic parts can be connected with metal. There are different welding processes for different parts, such as hot plate welding and hot-melt welding, high-frequency induction welding, ultrasonic welding, high-frequency welding (high-frequency welding), friction welding, hot-air welding Infrared lamp plastic welding. There is a special relationship between their welding characteristics and their corresponding welding processes

1. Hot plate welding and hot melt welding

Use heating tools, such as hot plate, hot strip or 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 and hardened, so that the two plastic parts are connected with each other. This processing method is called heating tool welding. It is suitable for welding plexiglass, rigid polyvinyl chloride, soft polyvinyl chloride, high density polyethylene, polytetrafluoroethylene, polycarbonate, polypropylene, low density polyethylene and other plastic products. At present, this process is commonly used in the connection of PP-R pipe fittings.

2. High frequency induction welding

The metal insert is placed on the surface of the plastic weldment, and it is temporarily combined with appropriate pressure, and then it is placed in the alternating magnetic field, so that the metal insert is combined with the plastic due to the heat generated by the induction potential, and the welded product is obtained after cooling. This welding method is called induction welding. This welding method is suitable for almost all thermoplastic welding.

3. Ultrasonic welding

Ultrasonic welding is also thermal welding. Its heat is obtained by high frequency mechanical vibration of plastics excited by ultrasonic wave. When ultrasonic wave is led to the surface of plastics to be welded, plastic particles will be excited by ultrasonic wave and vibrate rapidly to produce mechanical work. With the re transformation into heat, the surface temperature of plastics to be welded rises and melts, while the temperature of non welded surface will not rise. The ultrasonic wave is introduced into the plastic to be welded through the welding head. When the welding head stops working, the plastic will immediately cool and solidify. According to the structure of ultrasonic welding machine, all kinds of thermoplastic can be welded.

4. High frequency welding (high frequency welding)

Put two pieces of laminated plastic between two electrodes, and let the electrode pass through high frequency current. Under the action of alternating electromagnetic field, the free charge in the plastic will naturally produce repeated displacement (polarization) with the same frequency (but a little lag), which makes the polarized molecules vibrate frequently and produce friction. The electric energy will be converted into heat energy until melting, and then external force will be applied to combine with each other The purpose of welding is called high frequency welding. It is suitable for plastic film or sheet made of polar molecules, such as PVC, polyamide, etc.

5. Friction welding

Using the friction heat generated by the friction between thermoplastic plastics, make them melt on the friction surface, and then press and cool them to make them combine. This method is called friction welding. This method is suitable for cylindrical products.

6. Hot air welding

Hot air welding is convenient to use and easy to operate, especially suitable for the welding of plastic plate. This processing method is to heat the compressed air (or inert gas) through the heater of welding gun to the temperature required for welding plastic, and then use the preheated gas to heat the weldment and welding rod to make them reach the molten state, so that the welding can be carried out smoothly under small pressure To combine.

7. Infrared lamp plastic welding

In the United States, infrared lamp welding seems to have developed into a connection method especially suitable for some applications. In these applications, compared with other welding methods such as ultrasonic welding, vibration welding and hot plate welding, infrared lamp welding has advantages in cost and performance.

One of the advantages of infrared lamp welding is that it uses non-contact heating method to heat the plastic workpiece, even the complex three-dimensional surface to be welded can also be plasticized. Therefore, infrared welding technology is especially suitable for complex surface parts and large structural plastic parts.