Omar Khalid
Identifying the type of plastic is crucial before welding, as different plastics have distinct welding requirements and compatibility constraints. The most common approach to identification involves performing a burn test, where a small piece of plastic is exposed to an open flame, and its burning characteristics, such as flame colour, smoke formation, and odour, are observed. Alternatively, a test weld can be performed to check for adhesion between the plastic and the welding rod. Another recommended method is using a Rod Test Kit (RTK), which provides a safer and more comprehensive range of materials for testing. Additionally, plastic components often have identification codes or symbols that indicate the type of plastic used. Understanding the specific plastic type is essential for successful welding, as it ensures the compatibility of welding techniques and materials.
| Characteristics | Values |
|---|---|
| Identification method | Flame Test, Rod Test Kit (RTK) |
| Flame Test characteristics | Observe flame colour, smoke formation, dripping |
| RTK characteristics | Easy, safe, over 40 materials for testing |
| Common plastics | Polypropylene, ABS, HDPE, LDPE, PP, PVC, Polyethylene, Nylon, Polycarbonate |
| Polypropylene blends | Used for car bumpers, identified by PP symbol, black/dark grey/white colour |
| Polypropylene blends other characteristics | Meltable thermoplastic, blend of polypropylene, synthetic rubber, and other fillers |
| Polyethylene | Used for overflow and washer bottles |
| Nylon | Used for radiator tanks, core supports, other under-hood parts |
| Polycarbonate | Used for body panels and bumpers |
| PVDF | Polyvinylidene Fluoride, produces acrid odour, burns to black ash, flame self-extinguishes |
| TPUR | Polyurethane, produces yellow flame, slight black smoke, faint apple-like odour |
| Acrylic | Produces fruity smell, slow to burn, blue flame with yellow tips |
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What You'll Learn
- Flame/Burn Test: Observe flame colour, smoke, odour, and if it self-extinguishes
- Rod Test Kit: Test for adhesion between the parent material and the rod
- Recycling code: Look for a number from 1-7 surrounded by a triangle-arrow shape
- Nitrogen welder: Identify plastic type and select the correct welding rod
- Common plastics: Polypropylene, ABS, HDPE, LDPE, PP, and PVC
Flame/Burn Test: Observe flame colour, smoke, odour, and if it self-extinguishes
When identifying plastics for welding, one of the most common methods is the flame or burn test. This involves taking a small sliver of the plastic and exposing it to an open flame, such as a match, lighter, or small torch. By observing the flame colour, smoke, odour, and whether the plastic self-extinguishes, you can identify the type of plastic. Here are some common plastics and their characteristics during a flame test:
Polyvinylidene Fluoride (PVDF)
PVDF produces an acrid odour and will burn to a black ash. The flame will self-extinguish.
Polyurethane (TPUR)
This type of plastic produces a yellow flame, slight black smoke, and a faint apple-like odour.
Polyvinyl Chloride (PVC)
PVC is difficult to ignite and does not soften easily. It produces a yellow flame on top and green flame below, along with smoke. The flame extinguishes upon removal, leaving an acidic odour.
Polyoxymethylene (POM)
POM burns easily and melts but does not produce smoke. The flame colour is yellow on top and blue below. After removing the flame, it continues to burn and emits a strong formaldehyde smell.
Polystyrene (PS)
PS ignites easily and forms orange-yellow bubbles. It generates thick black smoke and turns into ash. After removing the flame, the surface remains oily and shiny, with a distinctive styrene smell.
Nylon (PA)
Nylon burns slowly, with a flame that melts and drips. After removing the flame, it slowly extinguishes, creating foam, and releases a unique smell similar to wool or nail polish.
Polycarbonate (PC)
PC is flammable and softens with the formation of bubbles. It produces a small amount of black smoke, and the flame extinguishes upon removal without any distinct odour.
Polytetrafluoroethylene (PTFE)
PTFE does not burn but decomposes under intense heat, releasing a pungent odour of hydrofluoric acid.
Polyethylene Terephthalate (PET)
PET ignites easily and forms bubbles with an orange flame. It produces a small amount of black smoke, and after removing the flame, it slowly extinguishes, leaving an acidic smell.
Acrylonitrile Butadiene Styrene (ABS)
ABS burns slowly, without melting or dripping, and produces a yellow flame accompanied by black smoke. After removing the flame, it continues to burn with a special odour.
It is important to note that the flame test should be performed with caution and in a controlled and safe environment.
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Rod Test Kit: Test for adhesion between the parent material and the rod
Plastic welding is a precise process that requires the correct welding rod to be used for each type of plastic. Using the wrong type of rod can lead to poor adhesion, weakened bonds, and poor longevity of the welds. As only "'like' materials can be welded together successfully, identifying the plastic correctly is vital.
The Rod Test Kit (RTK) is a plastic ID test kit that provides the welder with over 40 different materials for ID testing. It is the easiest and safest way to verify your plastic material type. The RTK rods have been specially selected for weldability and compatibility with a wide range of commonly found plastics in the automotive repair and fabrication industries.
The RTK can be used to determine the type of material in unknown situations. This kit includes all of the major typical types of materials used for most consumer and industrial products for testing adhesion to the parent material. The rods are made of 100% pure plastic LDPE, HDPE, PVC, ABS, and PP. The RTK should be used with an appropriate plastic welding iron, heat gun, or torch with applicable attachments.
To test for adhesion between the parent material and the rod, you can perform a short test weld. If the plastic welding rod stays firmly affixed to the base material after it has thoroughly cooled, you have a successful material match.
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Recycling code: Look for a number from 1-7 surrounded by a triangle-arrow shape
When identifying plastics for welding, it is important to remember that only "like" products can be welded together successfully. Therefore, identifying the plastic type is crucial. One way to identify the type of plastic is by looking for the recycling code, usually surrounded by a triangle-arrow shape. This code will be a number from 1-7 and will help you determine the parent material.
For example, if you are working with car parts, about 95% of late-model car bumpers are made from polypropylene blends, identified by a PP symbol. These plastics are sometimes labelled as TEO or TPO and are always blends of polypropylene, synthetic rubber, and other fillers. Polypropylene is one of the most common plastics used in car parts, along with polyethylene, ABS, nylon, and polycarbonate.
If you are unable to identify the plastic type by the recycling code, there are other methods to determine the plastic type. One method is to perform a short test weld, also known as a "test burn", to determine if the plastic welding rod stays affixed to the base material after cooling. Another method is to perform a burn test or flame test, where you expose a small piece of the plastic to an open flame and observe characteristics such as flame colour, smoke formation, and odour.
Alternatively, you can use a Rod Test Kit (RTK), which provides a safer and easier way to verify the plastic type. The RTK offers over 40 different materials for testing and is designed for weldability and compatibility with commonly found plastics.
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Nitrogen welder: Identify plastic type and select the correct welding rod
When fusion welding with a nitrogen plastic welder, the first step is to identify the type of plastic you're working with. This is because, in most instances, only "like" products can be welded together successfully. There are two common ways to identify plastics: the "Flame Test" and the "Rod Test Kit" (RTK).
The "Flame Test" involves taking a small sliver of the parent material and igniting it over a Bunsen flame with a pair of tweezers. By observing the way in which the plastic sliver burns, the colour of the flame, and the smoke formations, you can get an accurate indication of the plastic type. For example, PVDF (Polyvinylidene Fluoride) produces an acrid odour and will burn to a black ash, while TPUR (Polyurethane) produces a yellow flame, slight black smoke, and a faint apple-like odour.
The "Rod Test Kit" (RTK) is the recommended method as it is easy and safe. The RTK provides over 40 different materials for ID testing and is compatible with a wide range of commonly found plastics. The RTK rods are also UV-stabilized.
Once you have identified the plastic type, you can select the correct welding rod. Common types of plastics used on auto parts include polyethylene, ABS, nylon, and polycarbonate. Polyethylene is often used on overflow and washer bottles, nylon is used on radiator tanks and under-hood parts, and polycarbonate is used on body panels and bumpers. Your welder should come with different profiles of natural polypropylene rods, including round, narrow ribbon, and wide ribbon, as well as black polypropylene and grey TPO rods.
When welding, remember the four important factors for plastic welding: "T.F.A.P.S.", which stands for Temperature, Flow, Angle, Pressure, and Speed. For example, the PP/TPO setting on the nitrogen welder's dial will generate an airflow of about 700°-800°F (370°-425°C). The flow should be set between 10 to 15 liters per minute, depending on the plastic's thickness. The speed of your weld should be about 4 to 6 inches (10 to 15 cm) per minute, and it is important to move steadily while keeping proper downward pressure on the rod.
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Common plastics: Polypropylene, ABS, HDPE, LDPE, PP, and PVC
Identifying plastic types before welding is crucial, as only "like" materials can be welded together. Common plastics used in welding include Polypropylene, ABS, HDPE, LDPE, PP, and PVC. Here's how you can identify these plastics:
Polypropylene
Polypropylene (PP) is commonly used in car bumpers and can be identified with plastics identification codes or a welding test. The welding test involves using a Flame Test or a Rod Test Kit (RTK). The Flame Test involves igniting a small sliver of the material with a Bunsen burner and observing the flame colour, smoke formations, and whether it drips. However, this method is not recommended due to the introduction of flames and the inhalation of fumes. The RTK is a safer alternative, providing over 40 materials for testing and specially selected for weldability.
ABS
Acrylonitrile Butadiene Styrene (ABS) is another common plastic used in welding. Similar to Polypropylene, ABS can be identified using plastics identification codes or a welding test. The RTK includes ABS and various ABS blends, ensuring accurate identification.
HDPE
High-Density Polyethylene (HDPE) is commonly welded using techniques like extrusion welding and hot gas welding. HDPE is also included in the RTK, making it easy to identify before welding.
LDPE
Low-Density Polyethylene (LDPE) is another type of plastic that can be used on HDPE materials in certain applications. LDPE can be identified using the RTK, which includes this material among its testing options.
PP
Polypropylene (PP) and Polyethylene (PE) are both included in the RTK for identification. It is important to distinguish between these two plastics before welding, as they may have different welding requirements.
PVC
Polyvinyl Chloride (PVC) is available in flexible and rigid forms and is included in the RTK. Identifying PVC before welding is crucial to ensure the correct welding techniques and materials are used.
In summary, identifying common plastics like Polypropylene, ABS, HDPE, LDPE, PP, and PVC is essential before welding. While identification codes are often present, welding tests like the Flame Test and RTK can also be used to ensure the correct plastic type is determined. The RTK, in particular, offers a safe and accurate method for plastic identification.
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