TECHNICAL INFORMATION ON EXTRUSION WELDING
HARTWIG SPITZHORN, TECHNICAL PROJECT MANAGER KWERK GMBH
Components with thick walls can be, amongst others, joined together by the extrusion welding process. For PVC this procedure has only limited use and for PVDF special screws become necessary. Welding is done with wire of 3 mm resp. 4 mm and a homogenous and completely plasticized welding additive. The joint surfaces have to be warmed up and joining will be realized unter pressure.
Extrusion welding is characterized by the following features:
- Using of a welding additive with the same molding compound.
- The welding additive is plasticized homogeneously and completely.
- The surfaces to be joined are heated to welding temperature with hot air.
- The extruded compound is brought into form with a welding shoe and
pressed into place.
By means of the hot gas leaving the nozzle of the welding machine, the joint surfaces of the parts to be welded, are heated to welding temperature. The welding additive, continuously being extruded out of the manually operated unit, will be pressed into the welding groove. The welding pressure will be applied by means of the welding shoe, which is fixed directly to the extruder according to the welding shape. The compound stream pushes the unit forwards and regulates the welding speed. Heating up of the joint surfaces must match the welding speed.
Design of the welding shoes:
The extruded welding additive will be distributed with a welding shoe and then pressed into place. Welding shoes must be adapted to the particular type of seam (V-weld, fillet weld). General rule: The wider the weld seam, the longer the shoe should be.
The following factors depend on the shape of the welding shoe:
- Filling volume,
- Injection speed,
- Angle of impact,
- Material flow,
- Seam seal.,
- Uniform pressure.
Air temperature 270 290 ºC for PP, PE
Mass temperature 230 ºC for PP, PE
Air volume 350 400 l/min for PP, PE
Welding seam preparation:
Directly before welding the surfaces to be connected, the adjacent areas
and any damaged surfaces (especially if there are weather or chemical influences) must be machined down to intact zones. This could be done in an appropriate way by means of a scraper.
Cleaning agents that attack or alter the surface of the plastic must not be used.
Finishing of the welding seam:
Welding seams should always be made so that no subsequent machining is necessary. Extrusion welding seams should have an uniform smooth surface and flawless welded edge zones. To avoid notches in the seam root a root sealing run or seam securement can be hot-gas welded. The extrudate that occasionally oozes out at the edge of the welding shoe must especially in the case of joints exposed to high loads be removed manually without notches using an appropriately shaped card scraper or triangular scraper.
Influence of moisture:
From time to time, plastics absorb moisture, in most cases only loaded onto the surface.
This moisture vaporizes during welding. The accumulated moisture can take the form of bubbles in the welding seam or in a rough surface of the seam, which can result in light loss of strength. Also humid hot gas might have this effect.
- Pre-drying of the welding additives, if possible.
- Installation of a water separator in the air system.
- Avoid differences in temperature between the parts being
Avoidance of void formation in the welded seam:
Voids develop only after the welding process itself. They can be reduced by altering the level of moisture, the cooling rate and welding shoe geometry, but not by varying other welding parameters.
Voids occur especially when walls are thick and/or at low working temperatures (not working temperatures). They arise because after solidification of the seam surface a stable outer skin forms which counteracts volume contraction.
Slow and hence low-bubble cooling of the welding seam is achieved by using a covering fabric, featuring a sufficient heat resistance. This also reduces stresses and strains in the seam area.
Butt joint with V-seam
Butt joint with DV-seam
T-joint (fillet weld) with HV-seam
HV seam with fillet weld
Double HV seam with double fillet weld, prepared weld without gap
Specification of the welding shapes in the case of T-joint (fillet weld):
< 20 mm wall thickness: HV-seam; material is not chamfered
≥ 20 mm wall thickness: HV-seam; material is chamfered inside the tank
≥ 40 mm wall thickness: double HV-seam; material is chamfered on both sides
Factors involved enabling flawless welding seams:
- Temperature of the welding additive,
- Temperature of the base material,
- Hot gas temperature,
- Compound discharge of the extrudate,
- Hot gas flow,
- Welding speed,
- Welding pressure.
INFORMATION TO OUR DELIVERY PROGRAM
Plastic pipe systems
Overview of plastic pipe systems
Technical information on ABS pipe systems
Technical information on PVC U pipe systems
Technical information on PVC U transparent pipe systems
Technical information on PVC C pipe systems
Technical information on PP pipe systems
Technical information on PP-R pipe systems
Technical information on PE pipe systems
Technical information on PVDF pipe systems
Chemiedur - pipe
Technical information on UP-GF (FRP) pipe systems
UP-GF (FRP) pipes
UP-GF (FRP) molded parts and connection
UP-GF-PP (FRP) molded parts and connection
UP-GF (FRP) adhesive collars
UP-GF (FRP) loose flanges
Calculator for cutting pipes
Guidelines for sawing plastic pipe
Leftovers in plastic pipe
Standardization of plastic pipes and molded parts
PVC U pipes deviations
Pressure loss in pipe systems out of PVC U, PVC C and ABS pipe systems
Distinction between Rp, R and G threads
Screw lengths for flange connections
PVC U transparent ball valves
Plastic needle valves
Plastic Valves according to ATEX
New EU guideline 2014/34/EU
Plastic Valves in EX zones
Y-Strainers PP-EL DN 15 - DN 50
Check valves PP-EL DN 15 - DN 50
Angle seat valves PP-EL DN 15 - DN 50
Bonding of plastic pipes
Video showing the bonding of pipes
Guidelines for extrusion welding
Grids / support grids
Grids out of PP -el electrically conductive
Profile support grids out of PP -el electrically conductive
Molded ventilation parts
PVC transparent hose with fabric inlay
Industrial tanks and chemical containers
Dosing tanks and outer containers 35 1000 Liter
Salt dissolving tanks 60 -5000 Liter
Storage tanks and vats
Storage tanks for water
Safety and collecting troughs
Industrial tank delivery program
Dosing tanks with agitator
Dosing tank agitators
Dosing tanks with attachments
Dosing tanks made of sheet material
Customized chemical containers
Dosing tanks with level indicators
IBC screw caps DN 150/DN 200
IBC adapters out of PE
IBC adapters out of PP
MULTI FLEX BLOCK for IBC BULK CONTAINER
Attachment parts for tank construction
CO2 - absorbes
Filter housings and filter cartridges
PENTEK 3G Slime Line filter housings
PENTEK 3G Standard filter housings
PENTEK Big Blue filter housings
PENTEK PP high temperature filter housings
PENTEK PP all nature filter housings
PENTEK filter bags for Big Blue filter housings
PENTEK surface filter cartridges
PENTEK filter cartridges for depth filtration
PENTEK filter cartridges with activated carbon
CINTROPUR filter systems
CINTROPUR water filters
Blind flanges, loose flanges, rectangular flanges
Table of chemical resistance for plastic pipe systems
Machined plastic parts
Milled plastic parts
Loose flanges and blind flanges made of sheet material
Static mixers made of plastic
Single-type and double-type strainers
Pot strainer DN 300
Angle seat strainer DN 500
Variable area flow meters
Configuration tool for flow meters
Laboratory filter presses
Injection molded parts
Scraper made of PE for filter press
OUR - PREMIUM PARTNERS -