bonding plasticsWelding and welding of plastics involves the plasticisation of the surfaces to be joined and the joining material under heat and pressure. This is done by the diffusion of the polymer macromolecules, i.e. by their diffusion-reaction and chemical reactions occurring between them using heating equipment. The sequence of operations varies: in some cases, the materials are brought into close contact first and then the surfaces to be joined are heated; in other cases, the reverse is true - the surfaces to be joined are heated first and then brought into contact with each other; or the surfaces to be joined are brought into contact with each other and heated at the same time. When welding plastics, the particles of the plasticised material and the binder disperse. Once cooled, a permanent bond is formed. When welding thermoplastics, as when welding metals, the following processes take place in the weld zone: energy dissipation and transformation to ensure the activation of the welded surfaces; the interaction of the active weld surfaces when they come into contact with each other; the formation of the material structure in the contact zone.

Methods of welding plastics

Gas welding

Gas welding, also known as hot air welding, is welding with heat. It involves simultaneously heating the parts to be welded with a jet of hot gas, heated in a special device. A heat gun has been developed that produces a jet of hot air that softens both parts of the plastic being joined. Gas welding is carried out with or without filler material, either manually or with special tools that mechanise the welding process. Filler rods must not be used when welding fabrics and films. Two sheets of plastic are heated using hot gas and then joined together. Hot gas welding is a commonly used method for manufacturing products such as chemical tanks, water tanks, heat exchangers and water fittings. This rapid welding process can be carried out continuously.

Radial welding

This is the welding of plastics using an extruder. This type of welding is considered to be the most convenient and economical. The extruder feeds an already melted or softened mass into the weld, which is pressed by a guide nozzle. This device is used for joining parts of great thickness. Welding with the extruder starts with preparation, i.e. cleaning, and then the welds are tightly joined. The welding process can be carried out at a moderately fast pace, bearing in mind the temperature setting for the thermoplastic type. Once the work is complete, the component must remain stationary until it has cooled completely. The benefits of working with an extruder are mainly: lower energy consumption, improved heat transfer, no need for a clamping device, full control over the quality of the weld.

Contact welding

Contact welding, also known as resistance welding or hot electrode welding, involves pressing components with a heated tape against a cold substrate or squeezing components between two heated tapes. It is one of the most common methods of joining films. The principle of contact welding is that the joining area is heated to the viscous state of the polymer by a heating device, which transfers heat directly during contact with the surface.