OPUS

Joining Method Heat Fusion Weld


Thermoplastic pipe which cannot be solvent cemented maybe joined using heat fusion.  Fusion heats two piping product surfaces to an appropriate temperature, changing the resin’s molecular structure to an amorphous, pliable state, and then fusing them together by application of prescribed force until cooling occurs, returning the material to a crystalline state and creating one homogeneous pipe. The three basic methods of fusing plastic pipe are butt, socket, and electro-resistance. 

Butt welding involves a special machine that clamps and aligns two pieces of pipe. The machine holds one pipe stationary. The other can be precisely moved back and forth. A facing tool is placed between the ends of the pipe, the ends of the pipe are brought together, and the facing tool machines each end perfectly smooth. Next, the facing tool is removed and a hot plate is then placed between the pipes, the pipes are brought together against the plate at a specific pressure and for a specific time. Finally, the plate is removed and the pipes are pressed together at a specific pressure for a specific time until cooled.

The socket method uses pipe inserted into fittings. At a joint, a coupling is used. In this method, the heating device is a cylinder machined so the fitting slides over one end while the pipe slides into the other. A special cold ring is clamped at a specific distance on the pipe to control the depth of insertion into the heated cylinder, and to aid is the cooling and shaping of the weld. After a specific amount of time, the fitting and pipe are removed from the heated cylinder and pressed together for a specific amount of time until cooled. The socket method employs a larger surface area than is used in the butt welding process.

Electrofusion uses fittings that have built in resistive wire. After the joint is prepared, the pipe is inserted into the fitting and electrodes are attached to terminals on the fittings. Voltage is applied for a specific time, which heats both the fitting and the pipe by means of the resistive wires in the fitting. Like the other two methods, the joint is clamped and held for a specific time to allow cooling. 

A fourth method is used to attach fittings to the sidewall of a pipe. This method is called saddle or sidewall fusion. In this method, the sidewall of a pipe and a special electrofusion branch saddle fitting are prepared, heated, and clamped together until cool. Like the other methods, special equipment and tools are required.



Relevant Materials And Systems

Polyethylene (PE) Pipe

Manufactures and Suppliers Participating in OPUS