What is Extrusion Welding?
If you’re searching for dependable plastic welding techniques, try extrusion welding. Over many years it has globally become a reliable method for combining thermoplastics to achieve exceptional durability. It is a tried-and-true process used in various industries like plastic fabrication.
Understanding Extrusion Welding
Extrusion welding is a method for joining thermoplastic materials that involves melting and fusing them. It uses an extrusion welding gun and plastic weld rods to create a strong bond between like plastics.
All plastic fusion welding involves just three essential variables. Heat, Pressure & Time. The plastic material is heated for a certain time, after which it is restrained under pressure while it fuses, again at a certain pressure for a certain time.
It is a common fabrication technique because it is versatile, fast, and efficient. Compared to other approaches, it may be used with various thermoplastics and can deal with irregular shapes. Aside from that, it can certainly be faster than other methods of plastic welding.
Continue reading to learn more about the step-by-step process of extrusion welding.
Extrusion Weld Gun Parts
The Extrusion Welding Gun is known as the Munsch Gun, named after the company that originally developed the hand held extrusion machine. Below are the parts of an extrusion welding gun and the functions of each.
Hot Air Blower
The hot air blower sits on top of the extrusion gun and contains a heater which can either be ceramic or metal. It generates heat that thermoplastics need to make them fuse together and weld. The blower transfers this heat by a fan blowing it down through a tube to the weld area.
Extruder
The extruder feeds in the thermoplastic weld rod filler material, chops it up into small pieces, melts it and forces it through a heated mechanical screw to the end of the gun at the weld shoe.
Weld Shoe
The shape of the Weld shoe required depends on the shape of weld wishing to be performed. The shoe has a ‘nose’ at its front which prevents the melt from flowing forward, assists in applying weld pressure, and promotes forward movement of the machine during welding. The ‘nose’ should match the welding groove shape but should not touch the base material. The ‘sliding’ surfaces, or rails along the side of the shoe, should keep the shoe raised just enough to prevent the nose touching the base material being welded.
The molten weld rod pushes out through the nozzle just behind the nose of the weld shoe. Then the pressing surface applies the required pressure as it moves along, pressing the molten weld rod material into the melted base material. It is the shoe which transfers necessary pressure being exerted by the welder on the munsch gun.
Now that you know the parts of an extrusion welding gun, let’s discuss the process.
The Extrusion Welding Process
Now that you know the parts of an extrusion welding gun, let’s discuss the process.
Step 1: Preparation Phase
Scrape the surface to remove the oxidized layer which always occurs on the outside of the plastic materials. You may also use a die grinder or similar tool to ensure you achieve at least 0.2mm of the surface removed. Failure to remove the oxidized layer will create a barrier between the surfaces to be welded.
Do not use Grinding or Sanding / flap wheels as they tend to burn and leave deposit residue behind which can affect the success of the weld.
Then wipe the surfaces clean to free them of any contaminants that may weaken the fusion joint once welded. An approved cleaning agent must be used. A lint-free cloth with isopropyl alcohol or alcohol impregnated wipes and generally used for best results.
To avoid recontamination, do not touch the material after cleaning is done.
Ensure material is dry before commencing the actual welding process.
After, make sure to align the surfaces properly.
Set up Munsch Extrusion gun:
Set the required flow rate on the Munsch gun.
Set the required temperature/s on the Munsch gun.
Ensure the extrusion Munsch gun has reached temperature and has been purged through.
Ensure the welding shoe has been cleaned out.
Ensure the deflector is in place while warming up the gun. This assists the welding shoe to be brought up to required temperature and held there, while awaiting commencement next phase.
Step 2: Heating & Welding Phase
The right heating temperature depends on the thermoplastic material being used. For example, polyethyleneusually falls between 220°C to 280°C depending on its type and grade of material. However they do vary, and it is always recommended to follow the manufacturer’s guidelines.
The heated air blowing from the gun should be directed at the base material, in the immediate area where the weld is proposed to start and allowed to melt about 2mm into the surface. It is good practice to prick the surface ahead to determine that this is the case.
After feeding the weld rod into the bore, initiate the feed of weld rod by pulling the trigger on the munsch gun.
Start weld.
Apply constant pressure on the welding gun to maintain a consistent weld along the joint. If the weld shoe has the correct ‘nose’ on the front, the munsch gun will move by itself along the weld. Generally, a weld should progress at about 300mm per minute. A constant pressure of about 2.5kg should be applied to the base of the shoe to ensure proper fusion of the material surfaces and the filler weld rod.
The plastic weld rod should be the same thermoplastic material as the thermoplastic base material. It is recommended to use a virgin polymer weld rod, that does not have regrind or recycled material. We recommend SuperFUSION weld rod, which comes in a whole range of thermoplastic material types, colours, sizes and shapes, and is guaranteed to be void free.
The joint must be immobilized to ensure no movement occurs during the welding and cooling phases.
Step 3: Cooling Phase
Once you’re done with the welding gun, allow the fusion joint to cool down without movement.
Once cooled, inspect the joint to ensure no issues such as misalignment, gaps, burn marks or voids are present.
Refer to the manufacturer’s guide of the specific thermoplastic material you used, to know how much time is required to cool down.
For polyethylene with welds 10 to 20mm thick, 10 minutes is sufficient. Note that the thicker the material, the more time is needed.
Ensure you follow manufacturer guidelines relating to cool down and shut down of the extrusion welding gun, this supports longevity of your equipment.
Advantages and Applications
Now that you understand the basic steps of plastic welding through the extrusion welding method, let’s explore the advantages that make it a dependable technique in plastic fabrication.
Durable: Extrusion-welded joints are cohesive, which makes their structural integrity durable. This helps them withstand external forces that may weaken them.
Precise: The Munsch extrusion welders are designed to provide a consistent and uniform flow of molten poly material. This uniformity ensures that the material is deposited evenly, resulting in uniform and consistent welds.
Versatile: Extrusion welding can be used for different types of thermoplastics. It is also adaptable to irregular shapes, which makes it versatile.
Visual Appeal: Due to its precise nature, it usually results in smoothly welded material.
Disadvantages and Limitations:
Although extrusion welding is a reliable technique, it has its limitations and disadvantages, as listed below.
Size: Extremely large or thick thermoplastics may require multiple passes or additional setups for a successful weld. These types of welds need testing to confirm the weld procedure is adequate for the task.
Heavy Component: Some extrusion welding guns are heavy and may require specific skills and strength from the welder, or even additional weld gun supporting systems to achieve a successful weld.
How to Choose the Right Equipment:
The right welding gun and accessories you will need depend on the project you’re working on. As a general guide, take note of the following:
Material Compatibility: Use a welding gun that is compatible with the type of material, thickness of the thermoplastic you will be welding, and the size of the weld rod you are proposing to use. For example, a two to ten millimeter wall thickness would require the Munsch Mini Extrusion Welder. For thicker plastics within the range of 8 - 30 mm, the Munsch MAK-32-B Extrusion Welder (Single Heat Source) is ideal. See the table below
Accessory Availability: Check if your manufacturer has a wide range of accessories. At FHS Poly, you can find a variety of options to assist you in welding, from SuperFusion Weldrod, Flat and 90 degree Scrapers, Iso Wipes, rollers, carbide burrs for die grinders, spare welding shoes including blanks for your own special applications, debeaders, turbo pipe peeling tool or rotational peelers, along with competency training.
Welding Shoes: Check if your manufacturer offers various welding shoe attachments. At FHS Poly, you can be assured that we offer genuine Munsch Welding Shoes in a range of different sizes.
User-Friendly: Use a welding gun that is easy to use. An easy pick would be one of Munsch’s extrusion welding guns. They are all programmable and have easy-to-replace parts from their Munsch MAK-18-S/B Extrusion Welder to their Munsch ECO-M series.
FHS Poly can provide you the assurance of backup parts, service, calibration, and repairs.
Frequently Asked Questions (FAQ):
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Extrusion welding joins thermoplastics by extruding molten plastic along a heated joint.
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It's suitable for various thermoplastics like HDPE, PP, LDPE, LLDPE, PVC, PVDF etc. However, welding parameters, particularly the Melt Flow Rate, do vary per material.
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Follow these safety precautions during extrusion welding:
Wear PPE.
Ensure proper ventilation.
Avoid touching the heated parts like the welding gun’s nozzle or the molten weld rod.
Keep the area clean and free of trip hazards.
Be very mindful of electrical hazards at all times.