Assignment of skilled technical staff

Requiring personnel with welding certificates

Protecting welding area from climatic influence (solar radiation, effects of humidity, wind and temperatures below +5 °C)

Preheating, covering under canopies, heating, closing

The parts to be welded must have the same temperature level. Dependent on the material and the environmental conditions the welding filler absorbs moisture at the surface. During extrusion welding this adsorbed moisture can cause bubbles in the seam and a rough seam surface. This phenomenon increases with increasing seam thickness (a-value).

To prevent the problem of “moisture” during the welding process the following aspects should be considered:

• Installation of a water/oil trap into the air system
• Avoiding temperature differences of the parts to be welded (condensation water)
• Storage of the welding filler as dry as possible
• Pre-drying the welding filler if necessary PE 80 °C/PP 100 °C/PVC 60 °C, for at least 12 h)
• Weld high a-values (≥ 18 mm) in several passes [FI-Simona]

Inspection of incoming goods

Visual controlling of the components to be welded (notches, scratches, etc.)

Control of welding additives, when used

Welding additive should generally consists of the same material as the joining parts and has to be clean and dry

Cleaning semi-finished products           

Cleaning of the bonding surfaces and also damaged surfaces (particularly those arising from the effects of weather and chemicals) mechanically back to undamaged material immediately before welding.

Cleaning agents (e. g. acetone) which dissolve, attack or modify the surface of the plastic or cause them to swell must not be used.

Control effect of humidity on the welding filler

Dependent on the material and the environmental conditions the welding filler absorbs moisture at the surface. During extrusion welding this adsorbed moisture can cause bubbles in the seam and a rough seam surface. This phenomenon increases with increasing seam thickness (a-value).

To prevent the problem of “moisture” during the welding process the following aspects should be considered:

• Installation of a water/oil trap into the air system
• Avoiding temperature differences of the parts to be welded (condensation water)
• Storage of the welding filler as dry as possible
• Pre-drying the welding filler if necessary PE 80 °C/PP 100 °C/PVC 60 °C, for at least 12 h)
• Weld high a-values (≥ 18 mm) in several passes [FI-Simona]

Select appropriate shape of the welding shoe

The extruded welding filler is formed and pressed down by a welding shoe. The following factors depend on the shape of the welding shoe:

• Filling volume
• Filling speed
• Material flow
• Seam sealing and form
• Even pressure

Monitoring parameters which affect joint seam quality

• Welding filler melt temperature
• Base material melt temperature
• Hot gas temperature
• Welding extrudate throughput
• Hot gas volume
• Welding speed (forward feed)
• Welding pressure

Non-destructive testing of welding seam

Visual inspection, ultrasonic testing, x-ray testing