The most typical welding methods:

• butt fusion welding of plastics
• poly-fusion welding of plastics
• electro-fusion plastic welding
• plastic welding by use of additional materials

Principles of butt fusion welding

Butt fusion welding (or pressure welding) is a contact welding, i.e. the surfaces to be welded are heated by a heating body. When welding pipes, the surfaces are heated by a „mirror“, plastic sheets are heated by a strip heater.

Before the actual pressing on the heating body, the welded ends are treated smoothly, all grease is cleaned and mechanical impurities are removed. Subsequently, the welded ends are pressed towards the heating body under clearly defined pressure and are heated to reach the welding temperature. Then the pressure is reduced to a minimum and the second phase of the warming process, the so-called pre-heating in depth is started. After the second phase, the welded areas are removed from the heating body, the heating body is put aside and the welded areas are to be put together in the shortest time possible. Then, the phase of the pressure increase starts. The pressure put on the welded ends increases up to point when the welding pressure is reached. The welded parts shall be kept together under this pressure till the joint gets cold.

Principles of poly-fusion welding

Poly-fusion welding is a contact welding of plastic pipes and fittings. Welded parts need to be heated to the desired welding temperature. To be heated, these parts shall be slipped on the heating rods of relevant dimensions fitted to the heating body. After finishing the warming process, the parts to be welded are removed from the heating rods and are fitted together without any further turning. The surfaces of heating rods are slightly conical in order to establish a sufficient welding pressure for creating a connection between pipes and fittings. This method allows developing sufficient pressure even with small axial forces, so manual welding of pipes is possible up to the diameter of 63 mm. After the connection between a pipe and a fitting, it is necessary to fix the welded surfaces during the shortest time possible, the joint can be fully loaded not earlier than one hour after welding.

Principles of electro-fusion plastic welding

The principle is similar to poly-fusion welding, but the heating process is not made by a heating body, but by heater coils built in the basic material.

The ends of pipes to be joined are cleaned (oxidation layers and grease is removed), the ends are inserted into the electrofusion fitting. The cable of the welding apparatus is connected to the electrofusion fitting. The welding parameters such as voltage, power and time are entered usually in two ways – manually on the keyboard according to table data or by use of a reading pen decoding the bar code given on the electrofusion fitting. The data may be corrected by the welding apparatus with respect to the outside temperature. After starting the welding process, the apparatus regulates the power input of the electrofusion fitting, the material of the fitting as well as of the ends to be welded is heated. After this phase, the joint cools down and may not be loaded.