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Extrusion Welding

extrusion welding.jpg

The operation of individual extrusion welder is different, but below are some general tips for extrusion welding:

Avoid large temperature differences between components as it can cause considerable strain - for example, with a rise in temperature of 10°C a steel tube 10m in length will experience an expansion of 1.2 mm whereas a PE tube 10 m in length will experience an expansion of 34.0 mm.

Welding speed depends on the output capacity of the extruder and the seam volume , some important things to remember are:

  • The welding speed must be constant
  • The welding speed and hot air temperature must be coordinated so a minimum melting depth of 0.5 mm is achieved

All hot air and extrusion joints need to have a root bead on the opposite side to avoid cracking and give more strength to the weld. It is necessary to weld into the welding root.

Starting the weld: Before beginning the welding operation, the welding shoe must be warmed up, since a rough and uneven surface of the welded seam is obtained if welding is carried out with a cold welding shoe. The warm air available or the warm extrudate are suitable for warming up.

Continuing the weld: Keep Extruder perpendicular to weld surface. The welding shoe must be aligned centrally with the weld and must not come into contact with the weld edges around it’s nose.

Weld cooling: The thermal contraction and the shrinking during cooling may cause residual stresses and even blowholes. Especially big extrusion welds of polypropylene tend to show shrink-induced blowholes in the center of the extrudate. In order to avoid this, the weld seam is covered with a special fabric after welding. The fabric must be sufficiently heat resistant. e.g. aramid (Kevlar).

Welding Seam Preparation

Welding area & weld rod must be:
  • dry, clean, free of oil & grease
  • free of notches
  • free of oxidation (to achieve this the joining area is scraped clean just before welding)
Note on compressed air usage:
  • If using compressed air with your hot air tool, ensure that there is a pressure reducer and an oil and water filter before turning the air on

General Welding Parameters

Material Temperature
of plast °C
Temperature
of air °C
Air flow
l/min
PE-HD 210 - 230 °C 210 - 300 °C >300 l/min
PP 210 - 240 °C 210 - 300 °C >300 l/min

Environmental Influences

  Impact Counter Measure
High environmental humidity
Formation of condensation
Bad welding connection Pre-heat welding zone and dry welding surface prior to welding
High material humidity
in welding rod or granules
Vacuoles or blowholes appear in weld Pre-dry welding rod or granules for 3–4 hours at approx. 100°C
Low surrounding temperatures (<5°C) Insufficient pre-heating and the formation of condensation on plastic Erect a heated tent or move welding activities to a heated building
Welding seam cooling too quickly Vacuoles form in the welding seam Cover the seam while cooling, deep seam should be covered in general
Draught
Cooling is uneven or too fast
Insufficient pre-heating and the formation of vacuoles in the welding seam Protect the welding area from draughts

Common Welding Problems

Building of blowholes and vacuoles:
  • Temperature of extrudate too high
  • Humidity of either environment or welding rod too high
  • Moisture present on plastic being welded or wet hands
  • Welding shoe too cold
Rough welding seam surface:
  • Welding shoe too short
  • Welding shoe too cold
  • Welding shoe surface too rough

Move on to evaluating your weld seam quality...

Still have questions? Give us a call at 1-888-438-6324 or email us at info@stanmech.com.

Looking for more in-depth training? Attend our one-day plastics welding course.



STANMECH Technologies Inc. | 944 Zelco Drive Burlington ON L7L 4Y3 | 1-888-438-6324
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