Main
Welding
The
most important rule in plastic welding is that it is
only possible to weld like with like. Hence the need
to identify the plastic material and select a matching
welding rod.
The
main welding operation begins with preparation of the welding
rod. Cut the end to a pencil point using a trimming knife
or side cutters; this provides a progressive fill in the
'V' groove, particularly where it starts in the center
of a panel, preventing the formation of bulbous protrusions
of plastic.
Fit speed welding nozzle 27B to the LEISTER TRIAC hot air tool, set the correct temperature for the material and allow the tool to warm up for two minutes before starting.
Insert
the trimmed welding rod through the nozzle feeder until
approximately 5mm protrudes on the underside. Hold the
tool so that the speed welding nozzle sole runs along the
crack parallel to the component surface.
The
protruding rod must be held beyond the start of the 'V'
groove so that heat is directed onto the start point for
welding.
When the surface plastic shows signs of slight "wetting", move the welding nozzle along the groove. The nozzle toe should rest on the rod in the groove while under the heel and there should be an air gap of 3mm. Feed the rod steadily into the nozzle with a downward hand pressure of about 2.5Kg, sufficient to push the softened rod into the groove. To judge what a pressure of 2.5Kg feels like, take a short piece of weld rod and use it to press down on a set of scales until 2.5Kg registers. (Do not apply downward force to the weld via the hot air tool itself). Wherever possible, the weld should be completed in one continuous run along the contour of the crack.
Correct mating between the welding rod and the material occurs when the rod is seen to soften and the new rod moves down the nozzle feed. As the rod melts into the groove, two smooth, continuous ridges will appear at the edges, accompanied by a slight wash at the sides of the weld. Do not move too quickly, failing to create a wash, nor too slowly, thereby overheating and even scorching or distorting the plastic.
When the weld has been completed, remove the hot air tool, sliding the nozzle off the remaining welding rod. Once cool, the unwelded rod end is cut off as close to the weld as possible.
The completed weld appears as a smooth, continuous line with the wash still visible alongside it, confirming that the rod has welded successfully with the component.
During the welding, previously unseen cracks may open up. These are not new but are impact cracks that have been present since the initial damage. These must be treated and welded as any other crack damage.
If
the weld is successful, reinforcement welds can be added
to the reverse of the material across the axis of the repair.
The same preparation and weld operations apply.
Potentiometer
Control Setting for LEISTER TRIAC 1G3 with:
Thermoplastic
Code |
Welding
Temperature °C |
Tack
Weld
Nozzle 28 |
Pendulum
Weld
Standard Nozzle 31A |
Speed
Weld
Nozzle 27 (3mm) |
Speed
Weld
Nozzle 27B (5.7mm) |
| ABS |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
| ABS/PC |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
| PA |
400 |
4.1 |
4.1 |
4.6 |
4.8 |
| PBT |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
| PC |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
| PE
hard (HDPE) |
300 |
3.0 |
3.0 |
3.3 |
3.5 |
| PE
soft (LDPE) |
270 |
2.8 |
2.8 |
2.8 |
3.0 |
| PP |
300 |
3.0 |
3.0 |
3.3 |
3.5 |
| PP
EPDM |
300 |
3.0 |
3.0 |
3.3 |
3.5 |
| PUR
Thermoplastic |
300/350 |
3.0/3.4 |
3.0/3.4 |
3.3/4.0 |
3.5/4.2 |
| PVC
hard |
300 |
3.0 |
3.0 |
3.3 |
3.5 |
| PVC
soft |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
| XENOY
(PC Alloy) |
350 |
3.4 |
3.4 |
4.0 |
4.2 |
|
