Pendulum
Welding
Where cracks or splits pass through tight corners, it may be difficult to use the normal speed welding nozzle. In such cases the technique of pendulum welding is effective.
 Prepare the crack in the normal way, then feed the welding rod manually into the 'V' groove at an angle of between 80 and 90 degrees to the groove. Exert about 2.5 Kg downward force on the rod while playing the hot air tool, fitted with standard nozzle 31A, onto the base of the rod and into the 'V' groove in a constant pendulum action. The bias of the action is determined by the comparative thicknesses of the component material and the welding rod.
Both
must be in the same molten state at the point of fusion.
Dressing and finishing is the same for speed welded material.
Welding
Defects
The table and
pictures below detail common causes of weld defects.
|
The
weld was started correctly but completed too quickly.
No wash indicates haste or too low a temperature.
The hot air tool was not allowed to attain the correct operating temperature and the weld was finished too soon, leaving a hole.
Too much pressure has been applied to the rod, leaving a low and deformed bead. Filling may be necessary.
The
welding temperature was too high, blistering the
sides of the weld. The repair area may be brittle.
|
 |
Welding Defects
and Causes
Poor
weld
penetration
or poor
bonding |
--Incorrect
weld site preparation
--Weld
speed too fast/temperature too low
--Weld
attempted with dissimilar materials
--Poor
technique
|
Uneven
weld bead
width
Charred
weld
|
--Welding
rod stretched
--Uneven pressure applied to welding rod
--Welding
speed too slow
--Temperature too high
|
Warping |
--Repair
area overheated
--Parts
fixed under tension
--Poor
site preparation
|
Weld
Dressing
A successful
weld forms a slightly raised, smooth, even bead across
the component surface. Welds must be flatted only when
they are cold; warm welds clog the sanding disc.
Remember that plastic is a soft material that yields easily to abrasives. For this reason, use a 120 grit disc first, then progress to 180 and finally 320 to produce a smooth finish. Always use new, clean, sharp papers. Allow a 7 to 10cm margin around the weld area for dressing to provide a key for painting.
Painting
Plastics
There
are many paint schemes that are suitable for use on plastic
components. Check with the vehicle manufacturer for approved
schemes.
 Surface preparation prior to painting can be completed with fine grade abrasive paper, followed by a thorough cleaning which is essential for good paint adhesion. Cleaning agents should be compatible with the recommended paint scheme.
A
repaired plastic component should be completely repainted
to ensure invisibility of the repair.
The
finished component should be as strong as the original
and provide an unblemished cosmetic finish.
|
