Similarly and different plastics can be connected through different methods. For example, welding is a common joining process, especially when adhesives cannot ensure sufficient or permanent connections. Plastic welding involves not just surface bonding but a tight material connection. However, this is only applicable to the so-called thermoplastic (heat-moldable) plastics. Elastomers and thermosetting materials cannot be welded.

■ Thermoplastic Materials: They are mainly composed of linear molecular chains that can slide past each other when heated, allowing the plastic to be shaped and welded.

■ Elastomers: Composed of molecular chains with wide network cross-linking, and they return to their original state once exposed to heat. Therefore, deformation is not possible during the welding process.

■ Thermosetting Materials: Composed of molecular chains with narrow network cross-linking. It is impossible to thermally decompose, melt, and weld their structure.
                      
 

Thermoplastic Plastics

Basically, only identical thermoplastic materials can be uniformly welded. Except for PTFE, all thermoplastic materials can be welded, but there are specific material differences between plastics:

■ ABS (Acrylonitrile Butadiene Styrene)

Convenient and easy welding. The welding temperature is between 270 and 310°C.

■ PS (Polystyrene)

Convenient and easy welding. The welding temperature is between 270 and 310°C.

■ PP (Polypropylene)

Due to the rapid combustion of PP, close attention should be paid to temperature and heating time. The welding temperature is between 230 and 280°C.




                   
 

■ PE (Polyethylene)

Convenient welding, but cannot be bonded with conventional adhesives. The welding temperature is between 220 and 280°C.

■ PVC (Polyvinyl Chloride)

Due to PVC's rapid combustion and the generation of hydrochloric acid, attention should be paid to temperature and heating time. The welding temperature is between 250 and 280°C.

■ PMMA (Polymethyl Methacrylate)

Commonly known as acrylic glass. Convenient and easy welding. The welding temperature is between 120 and 180°C.

■ PC (Polycarbonate)

Convenient welding. The welding temperature is between 270 and 310°C.

Determining Material Characteristics

Material characteristics play a crucial role in an accurate and effective welding process:

1. Melting Point: The temperature at which the material changes from a solid to a liquid state. This determines how much heat is required during the welding process.

2. Melt Flow: The speed at which the molten part of the plastic flows. Hard molten parts often remain in the welding area, resulting in a more uniform process.

Factors Affecting Weldability:

Various external factors can influence the weldability of plastics:

• Negative Impact: Additives, such as flame retardants, can make ultrasonic processing of plastics more challenging.

• Liquid Content (especially in polyamides): High liquid content in plastics can evaporate during the welding process, leading to the formation of bubbles in the welding area and causing the weld seam to be porous.