Custom Plastic Extrusion

Why Plastic Extrusion Services From RapidDone?

As a premier on-demand part manufacturing expert in China, RapidDone works with quality plastic extrusion manufacturers and offers great-quality plastic extrusion parts.

Through the years, RapidDone is an expert in most plastic extrusion manufacturing. When you choose to work with RapidDone, that means you choose to work with a plastic extrusion expert team. We can work on all kinds of different section shapes of the product, the minimum thickness we can work on is 0.5mm.

Once the parts are extruded, we can cut them to the required length with tight tolerance. Besides, we can apply additional manufacturing processes for the plastic extruded part to get a customized shape, including CNC milling, drilling.

Similar to aluminum extrusion, it asks for an extrusion tool to produce the part, so it asks for a high MOQ for most of the manufacturers. However, RapidDone offers both short-run plastic extrusion services and high-volume production services. We can take good care of your prototype or low-volume projects that meet your expectation.

At RapidDone, we follow strict quality procedures to keep your part safe. Before your order, we can give you a sample to check the quality. You can also get detailed pictures and dimension check reports for each order before shipment.

RapidDone is committed to providing one-stop solutions for our customers. Work with us, you can assure our experienced staff is always ready to guide you to find your needs on time. So for your inquiries, please feel free to contact us today.

Custom Plastic Extrusion: The Complete Guide

In the plastic extrusion industry, Rapidnone is a trusted manufacturer because of the rich experience in manufacturing, we can offer professional extrusion services.

Based on our manufacturing experience, we create below the ultimate FAQ guide for Plastic extrusion manufacturing. We think this can help people who want to know about plastic extrusion or look for related extrusion services.

Please feel free to talk to our team if you want to know more details beyond that.

What Is A Plastic Extrusion?

Plastic extrusion is a compression process in which material is pressed against a die orifice to provide a long and continuous product with a uniform cross-section.

When applied to plastics and other polymers, it is used to mass-produce structural profiles, tubing, hoses, insulation, and coating for electrical wires and to obtain a uniform raw-material to be used in other sub-processes such as CNC machining.

Thermoplastics and elastomers are the type of plastics mostly used in the extrusion process. Nylon, PVC, polycarbonate, polypropylene, TPU, and Delrin (polyacetal) are widely used to obtain different kinds of products for industrial and residential purposes.

How Is Plastic Extruded?

To begin with the extrusion process, raw-material commonly known as “feedstock” and provided in powder or pellets form is fed to the extrusion barrel, where it is heated, melted, and forced to flow into a die opening by using a rotating-screw mechanism.

An extruder consists of two main components: The barrel and the screw. The barrel function is to contain the plastic material and provide a heat-transfer environment by using electric heaters to melt the raw material.

The screw, which typically rotates at about 60 rpm for most industrial purposes, increases the pressure of the melted plastic and mixes it to create a homogeneous plastic fluid. This process is known as drag flow and the melting and mixing of the pellets are achieved by both thermal and frictional interactions between the small plastic molecules.

The melted homogeneous plastic mix is then further compressed and forced through the die opening to obtain the required profile.

The barrel and screw assembly are comprised of three processing sections:

1. Feeding section:

It’s the first section of the barrel, in which the powder or pellets contained in a hopper get in contact with the screw and are drawn across the assembly as its temperature and mechanical shear is increased.

2. Compression section:

Here the polymer is transformed into a fluid and as it is compressed, the small air spots are filled with melted polymer to create a homogeneous mix.

3. Metering section:

Where the material is further compressed, ensuring a homogeneous mix and the pressure developed is enough to force the plastic through the die.

After leaving the metering section, the plastic fluid is cleansed from impurities by using a breaker plate consisting of a stiff plate with smalls holes in it used to catch the remains of burnt plastic that may stick to the walls of the barrel.

The breaker plate has a second function too, and it is to generate an additional pressure increase for the material to be properly forced through the die.

Upon exiting the die, the final extruded product is cooled by using a low-pressure water and ventilation system and a waterway section with a puller at the end of it.

The waterway contains cool water and allows for proper heat exchanging without damaging the profile and the puller then directs the extruded piece into a saw, where it is cut to the desired length for further processing.

Types Of Plastic Extrusion

There are two ways to extrude plastic: profile or “horizontal” extrusion and blown film or “vertical” extrusion.

Profile extrusion follows the same process described above with one or two screws depending on the raw material to be used. A double screw barrel is mostly used when extruding PVC because it requires more pressure to obtain an appropriate product.

It is also known as horizontal extrusion for its workflow and it’s most likely to be used to obtain solid and hollow profiles with dimensions ranging between 25 and 150 millimeters in diameter.

Blown film extrusion is reserved for applications in which plastic has a smaller wall thickness. In this process, plastic is fed in the vertical direction to an annular die where is then filled with air, properly cooled, and flattened using rollers to obtain a very thin plastic film.

The film is then located in front of a matrix that has the shape of the final product and it’s pressed against it. A vacuum compressor sucks all the air and properly sticks the film to the shaped matrix, obtaining a neat and thin product with excellent tolerances and finishes.

At RapidDone, we are offering services with profile extrusion manufacturing way.

Plastic Co-extrusion

To obtain a co-extruded product, two or more extruders are needed. In a co-extrusion process, more than one plastic is used and forced into separate dies, so they can be later joined together obtaining an anisotropic material.

Regarding the final product, the different types of plastic used can be clearly distinguished from each other, meaning that a single product can have different mechanical properties in different zones.

If the polymer pellets were to be mixed in a single extruder, the homogeneous mix would maintain the same properties across its length and cross-section. In most cases, the final mechanical properties could decrease in a significant amount due to improper mixing.

Co-extrusion is also known as layer extrusion and its widely used in the automotive industry to enhance the mechanical properties of critical zones for car components. It is also widely used in structural members.

Type Of Industrial Extruders Used For Plastic

There are two ways to classify extrusion machinery and they depend on the number of screws used. This classification allows us to have single-screw and twin-screw extruding equipment.

Single-screw equipment, as its name suggests, uses only one barrel and screw assembly, and it’s preferred for lighter plastics, where the pressure levels required in the compression stage are relatively low.

Twin-screw equipment has a double-barrel with a pair of screws inside. It is widely used in applications where higher pressure is needed and the plastic material used requires a higher compression to obtain a better quality mixture.

There are several advantages of the twin-screw over the single-screw assembly. Apart from the increase in mixing efficiency, the heat exchange rate is also improved, allowing for an easier melting of the polymer and avoiding the creation of residue in the walls of the barrel.

Costs related to twin-screw equipment is higher, but this is no problem because the ability to produce more profiles absorbs the cost increase.

Twin-screw technology is also preferred to process dense plastics that need higher pressures to melt and achieve a homogeneous mixture.

Processes Following Plastic Extrusion

Plastic extrusion is rarely a final production process, and it’s usually followed by some additional manufacturing processes.

1. Cutting Process

The cutting process of plastic profiles is done at the end of the production line, where a manual or automatic saw cuts the profile to a specified standard length. When a manual process is carried on, the saw operator waits for a signal indicating that the desired length has been reached and it needs to be cut.

Manual cutting processes are less precise; this is the main reason why automated processes are preferred. In the automated process, the signal is sent to a computer that activates the saw.

In most cases, a secondary cutting process needs to be carried on to achieve the final length of the product. This process is done in a completely different production line and after inspection of the profile to ensure its quality.

2. CNC Machining Process

Plastic extrusion is often used to obtain solid profiles that work as raw-material for additional machining processes such as drilling, milling, and turning.

Upon its extrusion and cutting, the plastic solid profile is sent to a CNC machine, where its shape is completely changed to obtain the final product. Raw-material obtainment is one of the most frequent applications for the plastic extrusion process.

The fact that plastics are commonly obtained in pellets makes the extrusion process one of the principal manufacturing processes for other applications such as CNC machining, hence its importance for the industry.

Squared and circular solid profiles with dimensions of up to 200 cm in their cross-section are generally used. This allows us to create complex shapes that couldn’t be achieved using the extrusion process.

At RapidDone, we have an experienced team, we are sure to create precision features for your extrusion parts when you need a CNC machining process.

3. Ultrasonic Welding Process

Plastics’ mechanical properties do not allow them to be welded using the same methods as metals. A common practice is to use high-frequency sonic waves to create frictional heat that melts the plastic and forms a molecular bond between two pieces.

Ultrasonic welding is a common post-processing task of the co-extrusion method and allows the combination of a plastic piece with other plastics, vinyl, and even metals.

Plastic welding using ultrasonic waves is a repeatable process used to replace fasteners and adhesives. It is a fast process and the material properties are not greatly affected.

4. Thermal Bending Process

This process consists of applying heat to the plastic surface using electric resistances or water vapor. After a certain increase in temperature, the plastic will be easier to bend without fracturing.

The thermal bending process can be used to either bend or straighten profiles and it’s a process used for further applications or to correct flaws of the extrusion process.

For thin or complex plastic profiles there’s a high chance for the extruded piece to bend as it passes through the die. In these cases, a thermal bending section is added to the production line to ensure that the profile is straightened, ensuring the process efficiency.

When the purpose of this process is to bend straight plastic, it combines the cost-saving benefits of the extrusion process with the free-forming benefits of injection molding.

Plastic Materials Used in The Extrusion Process

The plastic extrusion process can be used in almost plastic engineering material, and the favorite plastic materials used to create extruded profiles are as below based on our manufacturing expericence.

1. PVC Material

Polyvinyl chloride, also known as PVC is one of the most known plastic materials. PVC profiles are easily obtained by extrusion, allowing for different diameters and wall thicknesses.

Extrusion of PVC profiles allows for the use of additives to be melted with the plastic inside the barrel. Additives are chosen depending on the final application of the extruded profile.

2.ABS Material

Widely used in the 3D printing industry for its high mechanical properties, Acrylonitrile butadiene styrene is also extruded to obtain the raw material for machining processes.

ABS can be easily machined using mills, drills, and lathes. The extrusion process of this plastic is required to produce the raw material for these secondary processes.

3. Nylon Material

Extruded into rods, tubes, and sheets for its high wear and impact resistance. The most common polyamides to be extruded are Nylon 66, PA 6, and PA 12. Nylon profiles are used in the food industry for its high mechanical strength.

4. Polycarbonate Material

PC is a strong plastic material with a high temperature and impact resistance, making it suitable for structural processes in both machinery and the construction industry. Polycarbonate extrusion is also used as a primary process to obtain raw-material for machining purposes.

5. Polypropylene Material

PP is a flexible polymer used for blown film and sheet extrusion due to its high flexibility. For its low density, it is widely used in many applications where weight reduction is crucial. When processed using blown film extrusion, PP is transformed into plastic packages. PP extrusion is one of the most popular plastic manufacturing processes.

6. Thermoplastic Polyurethane Material

TPU’s are known for their high flexibility and the wide variety of manufacturing processes that can be used to obtain a product made of these polymers. TPU extrusion is a common process due to its diversity of cross-sectional shapes. Extruded TPU is used for tubing, wiring, and structural profiles as well.

7. PEEK Material

Polyether-ether-ketone may be one of the hardest polymers to extrude to its temperature sensibility. Peek is extruded for medical applications because it allows us to obtain tubing and profiles with smaller dimensions. Peek is also extruded as a solid to be machined in secondary processes.

Peek solid profiles are often machined to obtain pieces such as gears, variable section plastic shafts, and other machine components.

To carry out a proper peek extrusion process, the temperature must be evenly distributed and the cooling process has to be very efficient.

8. High-density Polyethylene Material

HDPE’s are often used for process pipes in industrial processes. HDPE extrusion is used for electrical insulation and due to its low water and vapor permeability is lower than other plastics, it is used for industrial, residential, and automotive tubing.

9. Polyacetal Material

Also known as Delrin, polyacetal it’s a thermoplastic polymer recognized for its high rigidity and the ability to be extruded with high tolerance precision.

Delrin extrusions are used for rods, tubing and to extrude raw material to be used in further machining processes.

Finishes For Plastic Extrusion

Another secondary operation required to complete a plastic extrusion process is the surface finishing. Some of the finish processes applied to extruded plastic are:

1.Painting

Special painting is applied as a cheap way to increase the UV resistance of the profile. It is used for outdoor applications in the industry as well as for non-industrial purposes. Some painting methods include high-gloss, low-gloss, matte, simulated wood, and metallic finish.

2. Insulation coating

since plastic extruded profiles are used in the electrical industry, the special coating is used to enhance the insulating characteristics of plastic.

3. Annealing

To enhance the mechanical properties of some plastic such as TPU and polypropylenes, an annealing process is done to the product after extruding and stacking. These processes may take up to 20 hours at temperatures ranging between 80 and 120 degrees Celsius.

4. Texturizing

wood grain and metallic patterns may be texturized into the extruded profile to achieve a more aesthetic look. Texturizing may enhance the durability of the profile in outdoor applications where it is exposed directly to UV rays.

Common Profiles Used In Plastic Extrusion

Plastic extrusion allows for the creation of diverse cross-sections or profiles. The most common profiles are circular, square tubing, circular solid, and rectangular solid. The latest two are mainly used as raw-material for machining processes such as turning and milling.

PVC tubing is very popular as well as HDPE extrusion when it comes to piping.

Angles, T’s, and even more complex profiles are also extruded of plastic material to be used in structural, automotive, and naval applications.

The ability to obtain solid, hollow, and complex profiles with a low manufacturing cost makes plastic extrusion one of the preferred manufacturing processes.

Plastic Extrusion Applications

Extruded profiles have a long-range of applications for both industrial and residential purposes. Plastic has decent mechanical properties and its lightweight allows it to be used in the automotive, naval, and aerospace industry.

Electrical wire coating is made of extruded polymers due to their natural high insulation and in some cases when higher insulation is required, the extruded profile passes through a series of fortification processes to ensure its proper performance.

For structural purposes, plastic serves as a lightweight material with excellent mechanical properties and has been used lately to create economic houses in most third world countries. These economic houses consist of prefabricated modules made with plastic profiles that are easy to assemble and resistant enough to stack these modules one above the other.

Plastic profiles are also bent and used as the frame for naval and automotive vehicles. These frames have the advantage of being extremely lightweight, flexible, and strong enough to support the required loads.

The food industry machinery also requires plastic structural members. These members have reduced friction coefficients and enough resistance to perform their duty in a very efficient way.

The Benefits/Advantages Of Plastic Extrusion

The benefits of using the plastic extrusion process to obtain plastic products are listed below:

• Mass production.
• Excellent tolerances.
• Complex shapes are manufactured fast in a continuous process.
• Additives can be added to the extrusion barrel to improve the final product properties.
• Initial and manufacturing costs are cheaper compared to other plastic manufacturing processes.
• The creation of an anisotropic material can be done using a co-extrusion process.
• Some various secondary processes and finishes can be applied to extruded plastic profiles.
• Most of the plastics used in the process can be recycled. This means that almost no waste is generated in the production line.

Quality And Defects Present In The Plastic Extrusion Process

When performed correctly, a plastic extrusion process results in a high-quality product with excellent dimensional tolerances and mechanical properties. These products can be further improved using secondary processes such as machining, annealing, and coating.

Based on our manufacturing experience, even though it’s a simple process, improper configuration of the machinery could end up in some of the next defects:

1. Melt fracture

Caused by high stresses that act on the extruded plastic immediately after it passes through the die. If the pressure is higher than it should be, internal stresses in the melted profile cause the product to fail and fractures appear all over the surface.

If the pressure is too high at the entrance to the die section right after the breaking plate, and if the entrance is a sharply reduced area due to the profile shape, turbulent flow causes the melted plastic to separate.

These fractures can’t be permitted because they affect the overall performance of the profile.

 2. Shark-skinned extrusions

When the melted plastic flows through the die opening, friction occurs between the interface of steel and melted plastic resulting in a velocity profile across the cross-section. Tensile stresses are developed in the profile’s surface as it is stretched to keep up with the fast-moving center core, causing minor fractures in the surface that roughs it up.

Sharkskin is associated with a fast flow of melted plastic and the wearing of the die. To avoid shark-skinned surfaces, inspections must be performed to the die between extrusions and the RPMs of the screws must be properly configured.

Sharkskin is the most common defect associated with plastic extrusion.

3. Bambooing

As its name suggests, this defect makes the profile’s surface look like a bamboo pole with prominent marks occurring all over the surface. It is caused when the velocity gradient caused by friction rises to extreme levels and is associated with extreme wear of the die. Bambooing can be seen as a severe case of sharkskin.

4. Cross-sectional deformations

Caused by inadequate cooling and handling of the extruded product, cross-sectional deformations are less severe because they are treated with stretching and straightening of the profile.

Plastic Extrusion Limitations

Limitations corresponding to the plastic extrusion are the same as most extrusion processes. Here we mention some of the most important based on our manufacturing experience in Rapid Done.

• Cross-section remains constant for the whole length of the product.
• Large and expensive machinery is needed to extrude the plastic.
• The heating process and the high torque required for the screw and barrel assembly consumes a considerable amount of power.
• A die must be purchased or built for each cross-section required.

Plastic Extrusion Design And Engineering Tips.

Design and manufacturing engineering are all about experience and having the proper criteria. Based on our more than ten years’ experience in Rapid Done, here are a few design tips for plastic extrusion intended to nourish those who always enjoy learning a little bit more about manufacturing topics:

1. Record all the extrusion data possible for each material and die. This is done to speed up future processes that include the same material/die configuration.

2. Constantly inspect the die, even though melted plastic flows easily through the die, impurities can damage its surface and increase friction, affecting the quality of the extruded product.

3. When designing the die, try to avoid sharp edges. Adding small fillets instead of sharp edges allows for a better flow and decreases the chances of melt fractures.

4. Cover the hopper to avoid any debris from entering the barrel and screw assembly. Keeping impurities away from the barrel is the key to a good extrusion process.

5. If possible, try using an automated cutting process to add even more precision to your products.

6. Make sure that the cooling line right after the extruder is clean and free from dust and debris. The water source must be clean to avoid altering the surface finish and try using sprayed cool water.

7. For most applications, it is recommended to use single-screw extruders with a 24 to 1 length to diameter ratio and twin-screw assemblies with 30 to 1 length to diameter ratio.

8. Make sure that the temperature level of the barrel and screw assembly is properly set. Low temperatures may cause melt fractures due to improper melting on the last stages of the screw and high temperatures may burn down the polymer, generating plastic slag and affecting the quality of the extrusion.