Plastic is one of the most useful materials invented by man. It is cheap to produce, light and has impressive resistance. These properties give plastic a wide range of uses and an interesting range of processing techniques. One of these techniques is plastic extrusion.
This process has been around for a long time and involves several steps such as material preparation, pre-processing, cutting and extrusion, which we will discuss in detail in this article. We will also explore how it works, its type, its advantages and disadvantages and its application.
What is plastic extrusion?
Plastic extrusion is a high-volume manufacturing process in which a thermoplastic material is melted homogeneously. This molten material may be in the form of pellets, powder or granules. The molten material then exits the mold nozzle under sufficient pressure.
The molten plastic exiting the mold die through the extruder takes the shape of the die opening. To better understand plastic extrusion, let's take a look at the extruder parts.
hopper : This is the part of the extruder where the powdered, pelletized or granulated material for the plastic extrusion process is stored.
Filling port : This part of the extruder connects the hopper to the barrel. In other words, it helps guide material from the hopper to the barrel for the plastic extrusion process.
Breaker plate : The filter plate helps maintain pressure. It also serves as a filter and prevents foreign substances from entering the barrel.
Barrel : By applying heat, this part helps soften the plastic material and bring it closer to its melting point. It also houses the rotating screw that applies the pressure needed to push the plastic material through the feed tube.
casing tube : This tube connects the cylinder to the nozzle. In other words, it serves as a channel that transports the molten plastic material from the cylinder to the nozzle.
die : The part is the output of the molten material. The metal matrix gives the molten plastic the desired profile.
Cooling system : The melted plastic cools quickly, facilitating solidification.
How does plastic extrusion work?
So how does plastic extrusion work? It can be divided into four main steps.
Step One: Add Additives
The plastic extrusion process begins with adding additives to the plastic material for the process. This is significantly different from CNC machining. Depending on manufacturing needs, additives can be colorants or UV inhibitors.
Step Two: Melt the Material
The next step in the plastic extrusion process is to feed the plastic material into the hopper. From the funnel it passes through the filling opening to the cylinder. When the temperature is strictly controlled, the cylinder is a cauldron.
Furthermore, the cylinder facilitates the uniform distribution of the plastic material used during the process through a giant rotating screw. Plastic material changes from a solid state to a molten state through heat and rotation.
Step Three: Make the Mold
Upon exiting the cylinder, the molten material pushed by the rotating screw passes through one or more screens at the end of the cylinder. These sieves perform two main tasks at the same time. First, they remove foreign bodies and other contaminants from the melted plastic. Secondly, they ensure that the pressure throughout the system remains constant, providing uniform resistance. Consequently, as the molten material passes through the screens, it becomes more malleable as its temperature increases significantly.
The desired shape is obtained by pushing the molten plastic through the die. This means that the die must have the desired shape, because the shape obtained from the melted plastic will match the shape of the die.
Step Four: Cool
After passing through the nozzle, the next step in the process is cooling. This can be done using multiple cooling rollers or a water shower. The purpose of cooling is to ensure that the shape of your extruded plastic profile does not change.
In general, the plastic extrusion process supports the creation of basic shapes like sheets and tubes. You can create complex shapes using a custom matrix.
Types of Plastic Extrusion Processes
Although there are different plastic extrusion processes, the basic principles remain the same. The type of plastic extrusion process depends on the complexity and intricacy of the nozzle shape. Some types are better suited to processing complex projects than others.
Below are the four main types of this process that industry manufacturers use today:
1. Tube Extrusion
Tube extension follows the same general plastic extrusion process up to the die section. This process is ideal for processing hoses and hollow objects such as tubes and long hoses. It is also ideal for making straws and medical tubes.
To create hollow sections, an extrusion operator inserts a mandrel or pin into the die and then applies positive pressure to the internal cavities through the pin. In cases where multiple holes are required, manufacturers place more than one pin in the center of the die. The number of pins depends on the number of holes desired.
Additionally, the air pressure for the pins in this scenario usually comes from a different source, making it easier to adjust the size of each hole.
2. Blown film extrusion
The blown film extrusion process is a very popular process for producing items such as shopping bags. As with plastic pipe extrusion, the die is the main difference between blown film extrusion and normal extrusion.
The blown film extrusion die is a vertical cylinder with a circular opening ranging from a few centimeters to more than three meters in diameter. A pair of pressure rollers pull the molten plastic up and out of the nozzle for this process.
Pressure rollers are usually located high above the nozzle, at a distance of four to twenty meters. The exact height of the pressure roller depends on the cooling required. Furthermore, the speed of the pressure rollers determines the wall thickness or film dimension. As the film moves upward, a ring of air around the nozzle helps cool it.
An air outlet in the center of the nozzle allows compressed air to be pumped into the center of the circular extruded plastic profile to create a bubble. This results in some expansion of the circular extruded plastic cross-section. This ratio, also called the inflation rate, varies from a few percent to more than 200 percent of the original diameter.
Finally, pressure rollers help flatten the resulting bubble into a double-layer film with a width equal to half the circumference of the bubble. This double-layer film can be used in a variety of ways, from cutting into different shapes to rolling or printing. It can also be heat sealed to make bags and other items.
3. Flat film extrusion
This process is very similar to blown film extrusion, but the difference is in producing the desired shape. In this type of extrusion, the drawing and rolling process is the most important requirement to achieve the desired shape. This includes determining the surface structure of the film and its thickness.
The lamination process gives the product the desired shape and facilitates its cooling and permanent solidification.
4. Sheath extrusion
This type of plastic extrusion is ideal for the production of insulating wires. The aim is to give the material a plastic coating. Two main extrusion tools are used to coat wires: printing and coating.
Both types of tools have their uses, but the type of tool used to coat the wires depends on the proximity required between the plastic material and the wire.
When close contact or adhesion between wire and material is required, the pressure tool is ideal. However, when close contact and contact are not required, the plating tool is more suitable.
The main difference between these types of tools is the position of the pin in the die. If the pin sits flush with the die, it is a facing tool. With printing tools, however, the end of the pin remains in the crosshead. This means that the molten plastic coats the wire while it is still in the die. Pressurization here occurs when the wire and molten plastic leave the die.
Material Options for Plastic Extrusion
There are numerous material options available for plastic extrusion. However, the material you use in your project depends on the desired result.
Below is a list of material options for plastic extrusions.
1. ABS (acrylonitrile butadiene styrene) : ABS is made from polymerized styrene and acrylonitrile in the presence of polybutadiene is stronger than pure polystyrene. The styrene content of ABS acrylonitrile butadiene styrene gives it a waterproof surface and a shiny appearance. On the other hand, polybutadiene makes it resistant regardless of temperature.
2. Acrylic : This compound has wide uses and industrial applications and excellent light transmittance, and can replace glass. Acrylic offers an ideal balance of weather resistance, strength and clarity and can also be colored, diffused and matte depending on the specification. It is similar to acrylonitrile styrene acrylate (ASA).
3. PVC (polyvinyl chloride) : This is one of the most used plastic polymers in the world. It has a wide range of applications in almost all sectors. There are two basic forms of polyvinyl chloride: rigid PVC and soft PVC.
4. Flexible PVC (polyvinyl chloride) : This material is popular due to its low cost and versatility. It also offers an ideal balance between weather resistance, tear resistance and tensile strength.
5. Rigid PVC (rigid polyvinyl chloride) : Rigid PVC offers a balance between impact resistance and UV stability. This material is used for pipe construction and custom plastic profile extrusion applications such as refrigerators, windows and doors. Its rigidity makes it a viable replacement for wood and metal in many applications.
6. CPVC (Chlorinated Polyvinyl Chloride) : CPVC has an inherent UL94 flame resistance rating and is available in natural colors. It also offers a balance between rigidity, high temperature resistance and impact resistance.
7. Mineral filled polypropylene : This material performs well regardless of thermal conditions. It is stable over a wide temperature range.
8. Polycarbonate : This material offers a good balance of multiple properties, including stiffness, abrasion resistance, impact resistance, tintability, and high and low temperature behavior.
9. Styrene : Like polycarbonate, styrene is a material that offers an ideal balance between toughness, tintability, strength and rigidity.
10. TPA (Thermoplastic Alloy) : This alloy is ideal for making caulking strips, gaskets and other products. It has good compression set, good stability and elongation at low temperatures.
11. Polyethylene : This material offers a balance between strength, dyeability and low temperature behavior.
12. TPV (Thermoplastic Vulcanized) : This material has excellent tear strength, weather resistance and flexibility at low temperatures. It also has good tensile strength.
13. Polypropylene : This polymer has an ideal balance between strength, impact resistance, dyeability and low temperature behavior.
Plastic extrusion applications
Extrusion plastics have numerous areas of application and are used in different industries. The most important application areas for this process are listed below.
1. Wire insulation
Plastics are natural insulators and when you add their flexibility, they are the ideal choice for insulating live wires. Most plastic lined pipes on the market today are made from plastic extrusion because they are more durable.
2. Tubes and hoses
This is one of the most common plastic extrusion applications with simple die requirements. Most pipes and hoses on the market undergo plastic extrusion during production.
3. Windows and doors
Manufacturing windows and doors with plastic extrusion improves their longevity. This is especially true when plastic extrusion manufacturers use PVC. This material is very resistant to UV rays.
4. Blinds and shades
Another application of plastic extrusion can be found in blinds and shades. For example, the wooden look of most blinds is made from polystyrene, manufactured using plastic extrusion technologies.
Advantages and Disadvantages of Plastic Extrusion
The plastic extrusion process offers manufacturers several advantages, including flexibility and versatility. Here are some other benefits of plastic extrusion.
Advantages of plastic extrusion
After extrusion handling : After extrusion and before cooling, it is still easy to change the shape of the hot plastic. This gives manufacturers a lot of leeway and ensures that the final product is of the highest quality.
Relatively cheap : Compared to other plastic development processes, plastic extrusion is cost-effective. The reason for this is that it does not require complex tools.
Flexibility : With a constant cross-section, plastic extrusion offers considerable flexibility. In other words, plastic extrusion profiles can create complicated shapes if the cross section does not change.
Disadvantages of plastic extrusion
Resize : When removed from the plastic extruder, the hot plastic expands many times. This leads to deviations from the original product dimension. Additionally, it is difficult to determine how much the size of the hot plastic would change.
Limited products : There is a limitation on the type of products produced using this technique. Furthermore, producing a different product would require a large investment in a different type of extrusion equipment.
Plastic Extrusion vs. injection molding: what's the difference?
Although both processes lead to the production of plastic, they are very different from each other. Here are some differences between plastic extrusion and plastic injection molding.
1. Plastic extrusion molding is best for producing 2D products, while injection molding is ideal for producing 3D products.
2. In plastic extrusion, the shape of the plastic matches the shape of the nozzle from which the extrusion takes place, while in injection molding, the mold gives the molten plastic its final shape.
3. Typical cross sections can be easily produced using plastic extrusion. Injection molding, on the other hand, would require complicated shapes to obtain atypical cross sections.
4. Injection molded products are more stable than extruded products. Injection molding is more expensive than plastic extrusion. The reason for this is the expensive die requirements needed to produce the mold. However, this also makes the injection molding process more efficient.
University Degree
Extrusion technologies have many prerequisites, design requirements, and other important considerations. Furthermore, plastic extrusion has a wide range of applications, from sheets and films to coatings, tubes and hoses. To get the best result, always look for reputed plastic extrusion companies for your plastic manufacturing needs.
Common questions
What types of plastic extruders are there?
There are three general types of plastic extruders: single screw extruders, twin or multiple extruders, and piston extruders. However, double screws and single screws are more commonly used.
What are extruders used for?
They are ideal for producing long, continuous products such as hoses, wire covers and tire wires. They are also perfect for creating custom plastic profiles that can be easily cut to the desired size.
How much does plastic extrusion cost?
The cost of plastic extrusion depends on the complexity of the project and the type of raw material used. However, the process typically costs less than $1,000.
Can plastic extrusion produce panels?
Yes, films can be produced by plastic extrusion. This is possible using the film extrusion process.
