A plastic extrusion welder combines thermoplastic filler material, controlled heating, surface preheating and welding pressure to produce larger weld beads than are normally deposited with hand-fed hot air welding rod.
Extrusion welding is commonly associated with plastic tanks, thick thermoplastic sheet, liners, containment systems, ductwork and other industrial plastic fabrication.
What Is Extrusion Welding?
Extrusion welding is a process for joining compatible thermoplastics.
The extrusion welder accepts thermoplastic feedstock, heats and plasticizes that material, and forces it through a welding shoe or die into a prepared joint.
At the same time, the surface of the parent plastic is typically preheated immediately ahead of the extrusion bead.
The combination of:
- compatible filler material,
- properly prepared parent material,
- controlled filler temperature,
- appropriate preheat,
- welding pressure, and
- controlled travel speed
allows the thermoplastic materials to fuse at the joint.
How Does a Plastic Extrusion Welder Work?
1. Filler Feed
Compatible thermoplastic rod, wire or other approved feedstock enters the extrusion welding equipment.
2. Plasticizing
The extrusion section heats and works the filler material until it reaches the required processing condition.
3. Surface Preheat
The parent thermoplastic is heated immediately before the molten filler is deposited.
4. Welding Shoe
A welding shoe helps shape the molten filler and apply pressure as the extruder moves along the joint.
5. Weld Bead
Molten thermoplastic filler is deposited into the prepared joint at a controlled rate.
6. Cooling
The weld solidifies as the thermoplastic cools after the extrusion welder passes.
What Is a Plastic Extrusion Welder?
A plastic extrusion welder is specialized equipment designed to plasticize thermoplastic filler and deposit it into a weld joint.
Common search terms for this equipment include:
- plastic extrusion welder
- extrusion welding gun
- hand extrusion welder
- plastic extruder welder
- HDPE extrusion welder
- polypropylene extrusion welder
- thermoplastic extrusion welder
- plastic welding extruder
Equipment designs vary considerably in output, feedstock requirements, temperature controls, preheat systems and welding shoe design.
What Plastics Can Be Extrusion Welded?
Extrusion welding is particularly common with polyethylene and polypropylene fabrication.
| Material | Filler Consideration | Related Guide |
|---|---|---|
| HDPE | Use compatible HDPE filler material | HDPE Welding Rod |
| Polyethylene | Match the appropriate PE family and grade | Polyethylene Welding Rod |
| Polypropylene | Use compatible PP filler material | PP Welding Rod |
| PVDF | Use equipment, filler and procedures suitable for the specific PVDF grade | PVDF Welding Rod |
| Other Thermoplastics | Suitability depends on polymer, formulation, equipment and procedure | Thermoplastic Welding |
HDPE Extrusion Welding
HDPE extrusion welding is widely used in industrial thermoplastic fabrication.
Applications can include:
- HDPE tanks
- large fabricated containers
- thick polyethylene sheet
- containment structures
- industrial liners
- ductwork
- process equipment
- large thermoplastic repairs
Successful HDPE extrusion welding requires compatible filler, appropriate surface preparation and properly controlled welding conditions.
For more information see How to Weld HDPE.
Polypropylene Extrusion Welding
Polypropylene extrusion welding is commonly used to fabricate PP tanks, ductwork, process equipment and heavy sheet assemblies.
The filler should be compatible with the parent polypropylene. Homopolymer, copolymer, filled and modified PP grades may behave differently during processing.
Read How to Weld Polypropylene.
Extrusion Welding Rod and Feedstock
The thermoplastic filler supplied to an extrusion welder is often called:
- extrusion welding rod
- extruder welding rod
- plastic extrusion welding rod
- extrusion welding wire
- plastic welding feedstock
- extrusion welder feedstock
Depending on the equipment, the feed material may be supplied as round rod, wire, pellets or another specified feed form.
Extrusion Welding Rod Sizes
Some extrusion welders accept round thermoplastic welding rod, but the required diameter depends on the machine.
Common plastic welding rod diameters encountered in the industry include:
| Rod Diameter | Approximate Inch Diameter | Important Note |
|---|---|---|
| 3 mm | 0.118 in. | Use only if compatible with the extrusion welder feed system |
| 4 mm | 0.157 in. | Common plastic welding rod size; equipment compatibility must be confirmed |
| 5 mm | 0.197 in. | Feed compatibility depends on the particular extrusion welder |
| Other Sizes | Varies | Extrusion welding equipment may require another specific diameter |
See the complete Plastic Welding Rod Sizes Guide.
4mm vs. 5/32-Inch Welding Rod
A common source of confusion is the relationship between 4mm welding rod and 5/32-inch welding rod.
They are extremely close in size, but they are not mathematically identical:
- 4 mm = approximately 0.1575 inch
- 5/32 inch = 0.15625 inch
For a hand welding operation the difference may appear small, but an extrusion welder's feed system can have specific dimensional requirements. Follow the equipment manufacturer's feedstock specification.
Extrusion Welding vs. Hot Air Rod Welding
| Feature | Hot Air Rod Welding | Extrusion Welding |
|---|---|---|
| Filler delivery | Rod is normally hand-fed or guided through a speed nozzle | Filler is plasticized inside an extrusion welder |
| Filler volume | Generally lower deposition rate | Generally higher deposition rate |
| Common use | Smaller welds, detail work and repairs | Larger joints and heavier fabrication |
| Surface heating | Hot air heats parent material and filler rod | Parent surface is preheated before molten filler is deposited |
| Bead shaping | Controlled by operator, rod and nozzle | Often controlled partly by a welding shoe |
For hand welding information, see Hot Air Plastic Welding.
Extrusion Welding vs. Plastic Extrusion Manufacturing
The terms sound similar but describe different operations.
Plastic Extrusion Manufacturing
Plastic extrusion manufacturing continuously forces molten polymer through a die to manufacture a product such as:
- plastic welding rod
- tubing
- profiles
- filament
- strip
- custom extruded shapes
Extrusion Welding
Extrusion welding uses a smaller extrusion system as part of a welding process to deposit thermoplastic filler into a prepared joint.
New Image Plastics Manufacturing produces thermoplastic welding rod and custom extruded profiles used by plastic fabricators and other industrial customers.
Plastic Extrusion Welding Equipment
A typical extrusion welding operation may involve:
- hand extrusion welder
- compatible thermoplastic feedstock
- preheat air system
- welding shoe
- joint preparation tools
- scrapers
- cleaning equipment
- temperature controls
- appropriate safety equipment
What Is an Extrusion Welding Shoe?
The welding shoe is the portion of many extrusion welders that contacts or closely follows the prepared joint while the molten filler is deposited.
Depending on the welding equipment and joint, the shoe can help:
- shape the weld bead
- contain molten filler
- apply pressure
- control bead geometry
- guide the extrusion welder along the joint
Welding shoe geometry should be suitable for the joint design and equipment.
How to Extrusion Weld Plastic
Identify the Parent Thermoplastic
Confirm whether the material is HDPE, another polyethylene grade, polypropylene, PVDF or another thermoplastic.
Select Compatible Filler Material
Choose extrusion welding feedstock compatible with the parent plastic and approved for the welding equipment.
Clean the Welding Area
Remove dirt, oil, grease and contamination using methods appropriate for the material.
Prepare the Surface
Mechanically prepare the thermoplastic surface as required for the welding procedure.
Prepare the Joint
Bevel, groove or otherwise prepare the joint to the geometry required for the material thickness and weld design.
Install the Correct Welding Shoe
Select a welding shoe appropriate for the joint geometry and extrusion welder.
Establish Extruder and Preheat Conditions
Set the filler-processing and surface-preheat conditions according to the thermoplastic, equipment and qualified welding procedure.
Make a Test Weld
When possible, establish the process on representative material before welding the finished component.
Preheat the Parent Surface
Maintain the correct preheat immediately ahead of the extrusion bead.
Deposit the Extrusion Bead
Move the extrusion welder through the joint while maintaining consistent filler output, preheat, pressure and travel speed.
Allow the Weld to Cool
Allow the thermoplastic weld to cool sufficiently before applying significant load.
Inspect the Completed Weld
Evaluate the joint for bead consistency, fusion, voids, gaps, contamination, overheating and other visible defects.
Extrusion Welding Temperature
There is no single universal extrusion welding temperature.
An extrusion welding process can involve more than one temperature condition:
- filler material processing temperature
- extruder barrel or heating-zone settings
- extrudate temperature
- preheat air temperature
- parent-material surface condition
The proper settings depend on:
- polymer type
- resin grade
- filler formulation
- extrusion welder design
- output rate
- preheat airflow
- welding shoe
- material thickness
- joint design
- travel speed
For general thermoplastic hot-air information see the Plastic Welding Temperature Chart.
Why Surface Preheating Matters
The molten filler coming from an extrusion welder must fuse with the parent thermoplastic.
If molten filler is simply deposited onto a surface that has not reached the proper welding condition, the bead may appear attached while having poor fusion at the interface.
Correct surface preheating helps bring the parent thermoplastic into the appropriate condition immediately before filler deposition.
Why Extrusion Welds Fail
Potential causes include:
- incorrect filler material
- wrong parent-material identification
- contaminated surfaces
- poor surface preparation
- insufficient preheat
- excessive preheat
- incorrect filler processing conditions
- wrong welding shoe
- incorrect travel speed
- poor joint geometry
- voids in the bead
- insufficient welding pressure
- excessive mechanical stress after welding
See Plastic Welding Troubleshooting.
Cold Extrusion Welds
A weld can have a substantial-looking bead and still have inadequate fusion.
Possible signs of insufficient fusion include:
- bead separates from the parent material
- poor wetting at the bead edges
- visible gaps
- bead can be peeled from the surface
- failure occurs directly along the weld interface
Insufficient surface preheat is one possible cause, but filler compatibility, contamination, preparation and processing conditions should also be investigated.
Signs of Excessive Heat
Depending on the thermoplastic, excessive heat can cause:
- discoloration
- burning or scorching
- bubbling
- material degradation
- excessive deformation
- poor bead shape
- reduced material properties
Material-specific limits and equipment instructions should be followed.
Extrusion Welding Plastic Tanks
Extrusion welding is frequently used in the fabrication of large thermoplastic tanks.
Depending on the tank design, extrusion welds may be used for:
- wall seams
- bottom joints
- reinforcement components
- nozzle connections
- baffles
- internal components
- external attachments
Extrusion Welding Geomembranes and Liners
Extrusion welding may also be used in suitable thermoplastic liner and geomembrane work, particularly around details, patches, penetrations and other areas where an extrusion bead is required.
The required procedures depend on the liner material, specification, equipment and project requirements.
Extrusion Welding for Plastic Fabrication
Industrial applications can include:
Plastic Tanks
Fabrication of large thermoplastic tanks and containment equipment.
Thick Plastic Sheet
Joining heavier thermoplastic sheet where larger weld beads are appropriate.
Ductwork
Fabrication of thermoplastic ventilation and process duct components.
Containment Systems
Welding compatible thermoplastic components used in containment structures.
Industrial Liners
Detail welding and repairs in suitable thermoplastic lining systems.
OEM Components
Production welding of custom fabricated thermoplastic parts and assemblies.
Plastic Welding Rod Manufacturer
New Image Plastics Manufacturing produces thermoplastic welding rod for plastic fabricators, distributors, OEMs and industrial customers.
Materials include:
- LLDPE
- LDPE
- MDPE
- HDPE
- HMWPE
- polypropylene
- rigid PVC
- flexible PVC
- PVDF
- PETG
- ABS
- TPU
- other thermoplastic materials
Available capabilities include round welding rod, specialty profiles, custom sizes, color matching, spool packaging and private-label manufacturing.
For equipment that requires a particular extrusion-welding feedstock diameter or configuration, provide the equipment requirements when requesting material.
Frequently Asked Questions About Extrusion Welding
What is extrusion welding?
Extrusion welding is a thermoplastic joining process in which an extrusion welder plasticizes compatible filler material and deposits it into a prepared, preheated joint.
What is an extrusion welder?
An extrusion welder is specialized plastic welding equipment that melts or plasticizes thermoplastic filler and deposits it into a weld joint while the parent material is appropriately preheated.
Can HDPE be extrusion welded?
Yes. HDPE extrusion welding is widely used for industrial tanks, sheet fabrication, containment systems, liners and other suitable polyethylene applications.
Can polypropylene be extrusion welded?
Yes. Compatible polypropylene can be extrusion welded using suitable PP filler, equipment and welding procedures.
What size welding rod does an extrusion welder use?
It depends on the equipment. Some machines accept round welding rod, while others may use another feed form or specific diameter. Check the extrusion welder manufacturer's specification.
Is 4mm welding rod the same as 5/32 inch?
They are very close but not exactly the same. Four millimeters is approximately 0.1575 inch, while 5/32 inch equals 0.15625 inch.
Is extrusion welding stronger than hot air welding?
The two processes are used for different weld sizes and applications. Joint performance depends on material compatibility, joint design, surface preparation, equipment settings, welding procedure and workmanship rather than simply the name of the process.
Why does an extrusion weld peel off?
Possible causes include insufficient preheat, incompatible filler, contamination, poor surface preparation, incorrect processing conditions or improper welding technique.
Do extrusion welders use plastic welding rod?
Many extrusion welders use thermoplastic rod or wire as feedstock, while some equipment uses pellets or another feed form. The required feedstock depends on the machine.
Related Plastic Welding Guides
- Plastic Welding Guide
- Hot Air Plastic Welding
- Plastic Welding Rod
- Plastic Welding Rod Sizes
- Plastic Welding Temperature Chart
- How to Weld Plastic
- How to Weld HDPE
- How to Weld Polypropylene
- HDPE Welding Rod
- Polyethylene Welding Rod
- Polypropylene Welding Rod
- PVC Welding Rod
- PVDF Welding Rod
- Plastic Welding Tools
- Plastic Welding Troubleshooting
- Plastic Welding Rod Manufacturer
- Custom Plastic Welding Rod
- Thermoplastic Welding
- Plastic Fabrication
Need Plastic Welding Rod or Extrusion Welder Feedstock?
New Image Plastics Manufacturing produces thermoplastic welding rod for industrial plastic fabricators, distributors, OEMs and repair operations.
Materials include polyethylene, HDPE, polypropylene, PVC, PVDF, PETG, ABS, TPU and other thermoplastics.
Capabilities include 3mm, 4mm and 5mm round rod, specialty diameters, triangle profiles, custom profiles, custom colors, spool packaging and private labeling.
If your extrusion welder requires a specific feedstock diameter or configuration, provide the equipment requirements when requesting a quote.
Phone: 330-854-3010
Email:
newimageplastics@sbcglobal.net