HDPE Butt Fusion Machines
Butt fusion is a thermofusion process which involves the simultaneous heating of the ends of two pipe/fitting components which are to be joined, until a molten state is attained on each contact surface. The two surfaces are then brought together under controlled pressure for a specific cooling time and a homogenous fusion joint is formed. The resultant joint is fully resistant to end loads and has comparable performance under pressure to the pipe itself.
An electrical heater plate is used to raise the temperature of the pipe ends to the required fusion temperature. Butt-fusion can be used to join both PE80 and PE100 materials for the pipe sizes of 90mm and above of the same SDR.
The butt welding machines used to weld PE pipes have controls to ensure the welding parameters are strictly adhered to. The following parameters are controlled:
heater plate temperature
ovality and alignment
interface pressure
bead width
heat soak time
changeover time
Control of these is necessary to ensure premature failure of the weld does not occur. The field conditions under which PE pipe is welded have a considerable effect on the strength of the joint. In order to achieve an acceptable weld three elements are essential:
Cleanliness: because contamination will ruin joints
Technique: Most owners of PE pipe systems require that people performing butt welding of PE pipes are qualified by completing a recognized training course.
Correctly designed equipment with proper maintenance: Correct welding temperatures, welding procedures and pipe facing tools must be maintained in tolerance and in good condition.
The resulting joint, if it has been properly made, is as strong as the original pipe and can withstand all the loads applied during routine installation and operation.
During the fusion process internal and external ‘weld beads’ are formed. Techniques have been developed to minimize the size of the beads, however as they do not add anything to the overall strength they may be safely removed if required. The removed weld beads can be inspected as part of a quality control programme.
HDPE Electrofusion Machines
Electrofusion is a simple method of joining PE pipes by incorporating an electrical heating coil which melts the plastic of both the fitting and the pipe, causing them to fuse together.
The characteristics of the fitting to be welded, such as the fusion time, are registered via a barcode on the fitting. An electrofusion control unit (ECU) supplies the electrical energy necessary to heat the coil. When the coil is energized, the material adjacent to it melts and forms an expanding pool which comes into contact with the surface of the pipe. The continued introduction of heat energy causes the pipe surface to melt and a mixing of pipe melt and fitting melt takes place; this is vital to produce a good weld. Following the termination of the heat cycle, the fitting and the pipe are left to cool and the melted material solidifies to form a sound joint.
Hot and cold zones, sometimes called melt and freeze zones, are formed after energizing the coil. The length of these zones is particularly important. Each zone ensures that fusion is controlled to a precise length of the socket of the fitting and that the melt pressure is also controlled throughout the entire surface of the socket ensures uniform heat distribution.
The basic fusion parameters: temperature, pressure and time, are controlled by the ECU which is programmed to establish these parameters from the barcode read from the fitting itself. The ECU also provides a permanent record of the procedure followed.
