Thermoplastics can be softened by heat and reshaped or processed without the same permanent chemical curing that occurs in many thermoset materials. This characteristic makes many thermoplastics suitable for welding when the correct material, equipment and procedure are used.
What Is Thermoplastic Welding?
Thermoplastic welding joins compatible plastic components by creating suitable conditions at the joint interface for the materials to form a bond.
Depending on the welding process, this may involve:
- heating the parent plastic
- heating or plasticizing filler material
- applying pressure
- controlling travel speed
- maintaining proper joint geometry
- allowing the weld to cool without excessive disturbance
The term plastic welding is commonly used interchangeably with thermoplastic welding, although not every type of plastic can be welded using the same methods.
See the complete Plastic Welding Guide.
Thermoplastic vs. Thermoset Plastic
A basic distinction in plastic joining is the difference between thermoplastics and thermosets.
| Material Type | General Behavior | Typical Heat-Welding Suitability |
|---|---|---|
| Thermoplastic | Can soften when heated and solidify again when cooled, although repeated heating can eventually cause degradation. | Many thermoplastics can be welded with an appropriate process. |
| Thermoset | Forms a permanently crosslinked structure during curing and does not simply remelt like a thermoplastic. | Conventional thermoplastic fusion welding is generally not applicable. |
What Thermoplastics Can Be Welded?
Common materials encountered in thermoplastic welding include:
HDPE
High-density polyethylene used in tanks, sheet fabrication, liners, containment and industrial products.
Polyethylene
Includes LLDPE, LDPE, MDPE, HDPE and HMWPE materials with different properties and applications.
Polypropylene
PP is widely used for thermoplastic tanks, sheet fabrication, ductwork and process equipment.
PVC
Rigid and flexible PVC formulations can be welded using suitable materials, equipment and heat control.
PVDF
PVDF is used in specialized industrial, chemical-resistant and high-purity fabrication applications.
ABS
ABS can be welded for compatible fabrication and repair applications.
PETG
PETG can be welded in suitable sheet and specialty fabrication applications.
TPU
Certain thermoplastic polyurethane materials can be welded, with formulation and hardness considered in filler selection.
Thermoplastic Welding Methods
There is no single welding process for every thermoplastic application.
The appropriate process depends on:
- polymer
- part thickness
- joint geometry
- weld length
- production volume
- required deposition rate
- fabrication environment
- equipment available
Hot Air Thermoplastic Welding
Hot air plastic welding uses a controlled stream of heated air to soften the parent thermoplastic and compatible filler rod.
The operator directs heated air into the joint while applying the welding rod with controlled pressure.
Hot air welding is commonly used for:
- plastic repair
- sheet fabrication
- tank fabrication
- ductwork
- small and medium welds
- detailed fabrication
- field repair
Hot Gas Plastic Welding
Hot gas welding follows the same general concept as hot air welding but uses a heated gas stream suitable for the process.
Terminology varies by industry, and "hot air welding" and "hot gas welding" are sometimes used broadly when describing manual thermoplastic welding.
Speed Welding
Speed welding uses a nozzle designed to guide the thermoplastic welding rod while directing heated air into the weld area.
A speed welding nozzle can help control:
- rod position
- welding pressure
- heat direction
- travel speed
The nozzle should match the diameter and profile of the welding rod.
Extrusion Welding
Extrusion welding uses an extrusion welder to plasticize thermoplastic filler material and deposit it into a prepared and preheated joint.
The process generally uses:
- thermoplastic filler feedstock
- an extrusion mechanism
- controlled filler temperature
- surface preheating
- a welding shoe
- controlled travel speed and pressure
Extrusion welding can provide a much higher filler deposition rate than manual hot air rod welding.
Hot Air Welding vs. Extrusion Welding
| Feature | Hot Air Welding | Extrusion Welding |
|---|---|---|
| Filler | Usually welding rod | Plasticized extrusion feedstock |
| Deposition rate | Lower | Higher |
| Typical use | Detail work, smaller seams, repair | Larger seams and heavier fabrication |
| Equipment | Hot air plastic welder | Plastic extrusion welder |
| Process control | Heat, airflow, rod pressure, speed | Preheat, extrudate condition, shoe, pressure, speed |
Hot Wedge Welding
Hot wedge welding is commonly associated with thermoplastic sheet, membrane and geomembrane joining.
A heated wedge is positioned between overlapping thermoplastic surfaces. Heat and pressure create the seam as the equipment travels along the material.
This process does not normally use conventional round plastic welding rod.
Butt Fusion
Butt fusion is commonly used for thermoplastic pipe systems, particularly polyethylene.
The prepared pipe ends are heated under controlled conditions and then brought together under pressure.
Butt fusion is different from hot air rod welding because it joins the parent components directly rather than adding conventional filler rod.
Socket Fusion
Socket fusion is another thermoplastic pipe joining method in which the outside of the pipe and inside of a fitting are heated using matched tooling and then joined.
As with butt fusion, conventional plastic welding rod is generally not the filler mechanism.
Thermoplastic Welding Rod
Thermoplastic welding rod is filler material used in many hot air, speed welding and related plastic welding processes.
Common descriptions include:
- plastic welding rod
- thermoplastic welding rod
- plastic filler rod
- welding rod for plastic
- plastic welding wire
- thermoplastic filler rod
Choosing Thermoplastic Welding Rod
The first consideration is material compatibility.
For example:
| Parent Material | Typical Filler Starting Point |
|---|---|
| HDPE | Compatible HDPE welding rod |
| Polypropylene | Compatible PP welding rod |
| Rigid PVC | Compatible rigid PVC welding rod |
| Flexible PVC | Compatible flexible PVC welding rod |
| PVDF | Compatible PVDF welding rod |
| ABS | Compatible ABS welding rod |
| PETG | Compatible PETG welding rod |
| TPU | Compatible TPU welding rod |
This is a starting principle rather than proof that every grade within a polymer family is automatically interchangeable.
Thermoplastic Welding Rod Sizes
Common round welding rod sizes include:
| Metric Diameter | Approximate Inch Diameter |
|---|---|
| 3 mm | 0.1181 in. |
| 4 mm | 0.1575 in. |
| 5 mm | 0.1969 in. |
Triangle and specialty profiles are also used.
See Plastic Welding Rod Sizes .
Round Thermoplastic Welding Rod
Round rod is widely used for manual hot air welding and speed welding.
The rod diameter should match the welding nozzle and be appropriate for the joint and welding procedure.
Triangle Thermoplastic Welding Rod
Triangle rod is used in a variety of plastic fabrication applications.
Unlike round rod, a triangle profile may require width, height, angles, corner radii and other dimensions to fully define its geometry.
How to Weld Thermoplastic
The exact procedure depends on the material and welding process, but manual hot air welding generally follows these steps:
- Identify the thermoplastic.
- Select compatible welding rod.
- Clean the welding area.
- Prepare the thermoplastic surface.
- Prepare the joint geometry.
- Select the correct welding nozzle.
- Establish temperature and airflow.
- Make a test weld when possible.
- Heat the parent plastic and filler rod together.
- Apply controlled pressure.
- Maintain a consistent travel speed.
- Allow the weld to cool.
- Inspect and test the finished weld.
See How to Weld Plastic for a detailed manual welding procedure.
Thermoplastic Welding Temperature
There is no single temperature setting for all thermoplastics.
Required heat input depends on:
- polymer
- resin grade
- equipment
- airflow
- nozzle
- rod diameter
- material thickness
- travel speed
- ambient conditions
See the Plastic Welding Temperature Chart .
Approximate Hot Air Welding Starting Ranges
The following are broad hot-air-tool starting references for test welding, not universal welding specifications:
| Thermoplastic | Approximate Hot-Air-Tool Starting Range |
|---|---|
| HDPE | 250–350°C / 482–662°F |
| LDPE / LLDPE | 220–300°C / 428–572°F |
| Polypropylene | 270–350°C / 518–662°F |
| Rigid PVC | 250–320°C / 482–608°F |
| Flexible PVC | 220–300°C / 428–572°F |
| PVDF | 330–400°C / 626–752°F |
| ABS | 250–350°C / 482–662°F |
| PETG | 250–350°C / 482–662°F |
| TPU | 220–350°C / 428–662°F |
Thermoplastic Welding Equipment
Equipment depends on the selected welding process.
Hot Air Welder
Produces controlled heated air for manual thermoplastic welding.
Speed Welding Nozzle
Guides welding rod and directs heat into the weld area.
Extrusion Welder
Plasticizes filler material and deposits a larger thermoplastic weld bead.
Hot Wedge Welder
Used for continuous welding of suitable thermoplastic sheet and membrane seams.
Fusion Equipment
Specialized equipment is used for butt fusion, socket fusion and related pipe joining processes.
Preparation Tools
Scrapers, knives, cutters, routers and other tools may be used to prepare thermoplastic surfaces and joints.
See Plastic Welding Tools .
Thermoplastic Surface Preparation
Surface preparation is critical because a correct filler material and temperature cannot compensate for a contaminated or poorly prepared joint.
Depending on the material and process, preparation can include:
- removing dirt
- removing grease or oil
- removing surface oxidation
- removing degraded material
- mechanically scraping the weld area
- preparing a V-groove or bevel
- removing loose particles
- ensuring the joint is dry where required
Why Material Identification Matters
A common thermoplastic welding failure occurs when the parent plastic is incorrectly identified.
For example:
- HDPE and PP can look similar.
- PETG can be confused with other clear plastics.
- rigid PVC and other rigid thermoplastics may appear similar.
- flexible TPU and flexible PVC can have similar appearances.
Color is not a reliable polymer identification method.
Can Different Thermoplastics Be Welded Together?
Different polymer families should not be assumed to be fusion compatible.
For example:
- HDPE should not automatically be welded with PP filler.
- PP should not automatically be welded with polyethylene rod.
- PVC should not automatically be welded with ABS rod.
- TPU should not automatically be welded with flexible PVC rod.
Even within the same broad polymer family, resin grade, fillers, reinforcement, plasticizers and additives can affect welding behavior.
HDPE Thermoplastic Welding
HDPE is one of the most common materials used in industrial thermoplastic fabrication.
Welding processes can include:
- hot air welding
- speed welding
- extrusion welding
- butt fusion
- socket fusion
- hot wedge welding for suitable sheet or membrane systems
See How to Weld HDPE.
Polypropylene Thermoplastic Welding
Polypropylene is widely welded in industrial sheet, tank and duct fabrication.
Compatible PP filler should be selected with consideration for the actual polypropylene grade and formulation.
See How to Weld Polypropylene .
PVC Thermoplastic Welding
Rigid and flexible PVC can be welded with suitable hot air or hot gas processes and compatible filler material.
See How to Weld PVC.
PVDF Thermoplastic Welding
PVDF welding is used in specialized industrial applications where chemical resistance, resin grade and fabrication quality may be important.
The actual PVDF grade and fabrication requirements should be considered when selecting filler and welding procedures.
ABS Thermoplastic Welding
ABS can be hot-air welded for compatible fabrication and repair.
Because ABS formulations can vary, filler selection should be based on the actual parent material rather than color or appearance alone.
PETG Thermoplastic Welding
PETG can be welded in suitable thermoplastic fabrication applications.
Careful temperature control is important because excessive heat can distort or degrade the material.
TPU Thermoplastic Welding
Certain TPU materials can be welded, but TPU covers a wide range of hardnesses and formulations.
The term "polyurethane" alone is not enough to establish welding compatibility.
Thermoplastic Tank Welding
Welding is widely used to fabricate tanks from thermoplastic sheet.
Tank materials may include:
- HDPE
- polypropylene
- PVC
- PVDF
Material selection depends on the chemical, temperature, structural and service requirements of the tank.
Thermoplastic Sheet Welding
Thermoplastic sheet can be fabricated into:
- tanks
- ductwork
- housings
- containers
- liners
- process equipment
- industrial assemblies
The welding process depends on sheet thickness, polymer, joint design and fabrication requirements.
Thermoplastic Repair Welding
Plastic welding can repair some cracked or damaged thermoplastic components when:
- the parent plastic is correctly identified,
- compatible filler is available,
- the damaged area can be properly prepared, and
- the repaired component can safely return to service.
See Plastic Welding Troubleshooting .
Common Thermoplastic Welding Problems
| Problem | Possible Cause |
|---|---|
| Welding rod does not stick | Wrong filler, cold parent material, contamination or poor preparation |
| Weld peels apart | Poor interface fusion or incompatible material |
| Plastic scorches | Excessive heat input |
| Rod stays stiff | Insufficient heat or excessive travel speed |
| Weld cracks after cooling | Poor fusion, wrong filler, poor joint design or excessive stress |
| Bubbles or voids | Overheating, contamination, trapped air or moisture where relevant |
Thermoplastic Welding Safety
Thermoplastic welding involves hot equipment and potentially hazardous decomposition products if materials are overheated.
Basic precautions include:
- use appropriate ventilation
- avoid breathing fumes
- do not intentionally burn or scorch plastic
- protect against hot nozzles and molten plastic
- follow welding equipment instructions
- follow polymer safety information
- use appropriate personal protective equipment
- take additional precautions when working on tanks or confined spaces
Thermoplastic Welding Rod Manufacturer
New Image Plastics Manufacturing produces thermoplastic welding rod for fabricators, distributors, OEMs and industrial customers.
Materials include:
- LLDPE
- LDPE
- MDPE
- HDPE
- HMWPE
- polypropylene
- rigid PVC
- flexible PVC
- PVDF
- PETG
- ABS
- TPU
- other suitable thermoplastic materials
See Plastic Welding Rod Manufacturer .
Custom Thermoplastic Welding Rod
Custom manufacturing can include:
- custom thermoplastic materials
- custom diameters
- round welding rod
- triangle welding rod
- specialty profiles
- custom colors
- spool packaging
- OEM production
- private labeling
See Custom Plastic Welding Rod .
Frequently Asked Questions
What is thermoplastic welding?
Thermoplastic welding joins compatible thermoplastic materials using controlled heat, pressure and a welding process appropriate for the polymer and application.
Is plastic welding the same as thermoplastic welding?
Plastic welding is commonly used as a broad term for thermoplastic welding, although not every plastic is a weldable thermoplastic and not every polymer uses the same process.
What thermoplastics can be welded?
Common examples include HDPE, polyethylene, polypropylene, PVC, PVDF, ABS, PETG and certain TPU materials, depending on grade, formulation and welding method.
What is thermoplastic welding rod?
Thermoplastic welding rod is filler material used in processes such as hot air plastic welding. The filler should be compatible with the parent thermoplastic.
Can HDPE be thermoplastic welded?
Yes. HDPE can be joined using several processes including hot air welding, extrusion welding and appropriate fusion methods.
Can polypropylene be welded?
Yes. Polypropylene is commonly welded in tank, sheet, duct and industrial fabrication.
Can PVC be welded?
Yes. Suitable PVC formulations can be welded using compatible filler and controlled heat. Care must be taken to avoid overheating and decomposition.
Can different plastics be welded together?
Different polymer families should not be assumed to be compatible. Identify the parent materials and establish compatibility before welding.
What is the best temperature for thermoplastic welding?
There is no universal temperature. The required settings depend on the polymer, grade, welding process, equipment, airflow, nozzle, material thickness and travel speed.
What is the difference between hot air welding and extrusion welding?
Hot air welding typically heats the parent plastic and welding rod directly, while extrusion welding plasticizes filler material inside an extrusion welder and deposits it into a preheated joint.
Where can I buy thermoplastic welding rod?
Thermoplastic welding rod can be purchased from industrial suppliers, distributors and directly from manufacturers. New Image Plastics Manufacturing produces standard and custom thermoplastic welding rod in the USA.
Thermoplastic Welding Resource Center
- Plastic Welding Guide
- Plastic Welding Rod
- Plastic Welding Rod Sizes
- Plastic Welding Temperature Chart
- How to Weld Plastic
- How to Weld HDPE
- How to Weld Polypropylene
- How to Weld PVC
- Hot Air Plastic Welding
- Extrusion Welding
- Plastic Welding Tools
- Plastic Welding Troubleshooting
- HDPE Welding Rod
- Polyethylene Welding Rod
- Polypropylene Welding Rod
- PVC Welding Rod
- PVDF Welding Rod
- ABS Welding Rod
- PETG Welding Rod
- TPU Welding Rod
- Plastic Welding Rod Manufacturer
- Custom Plastic Welding Rod
- Plastic Welding Rod Supplier
- Plastic Fabrication
Need Thermoplastic Welding Rod?
New Image Plastics Manufacturing produces thermoplastic welding rod for professional plastic fabricators, distributors, OEMs, equipment companies and industrial customers.
Materials include LLDPE, LDPE, MDPE, HDPE, HMWPE, polypropylene, rigid and flexible PVC, PVDF, PETG, ABS and TPU.
Manufacturing capabilities include 3mm, 4mm and 5mm round welding rod, triangle rod, specialty profiles, custom colors, spool packaging, custom extrusion, OEM and private-label production.
New Image Plastics Manufacturing
Canal Fulton, Ohio, USA
Phone:
330-854-3010
Email:
newimageplastics@sbcglobal.net