Extruded plastics are similar to extruded metals, however, the difference, as the name implies, is in the material used.
Plastics extrusion is a normally high volume manufacturing process where a polymer material, enriched with the desired additives, is melted and formed in a continuous process.
There are many kind of plastic extrusion equipments corresponding to above extrusion types. We will discuss about some common equipments as below:
Firstly, one of plastic extrusion equipment is sheet or film extrusion machine
It is a sheet extrusion line consists of an Extruder (single or twin screw), equipped with a Screen Changer and a Gear Pump, followed by a Static Mixer (sometimes feeding a Coextrusion Feed block that is preceded by one or more additional extruders sets as described above), feeding a flat sheet die.
The sheet is then cooled by a 3 (or more) roll stack (sheet take-off) with temperature, pressure and roll gap control.
Lastly the sheet is cut to length, wound into rolls or run inline into a secondary process
Secondary extruders are called “co-extruders” and can also be a variety of sizes but normally fall toward the smaller end of the spectrum and are normally smaller than the main processing extruders. The number of co-extruders used is limited only by the space in the processing line. Some processes can cheat by utilizing the same co-extruder for multiple application requirements (as long as the material required is identical the co-extruder can be utilized for more than one location. (An example of this is stripes on the outside of drinking straws. If the strips are the same color, one machine can be used for all the strips). Co-extruders can be mounted on the floor or suspended over the die head as required
The plastic layer around an electrical wire is a good example of overjacketing. During this process the wire coating, the bare wire or some bundles of jacketed wires, filaments, etc is surrounded by a plastic layer using a type of extruder. The extruder used for this usually has a tool that is perpendicular to the extruder screw so that a wire may run true without the need to run down the entire machine. In the tool or mould there is a guidance for the wire which centers it in the middle of the viscous material flow.
For coating a wire, there are mainly two different kinds of extrusion tooling used. These are called “pressure” tooling or “jacketing” tooling. The selection of the type of tooling to be used depends on the fact that whether the specific application needs intimate contact or if it needs polymer adhesion to the wire or not. In case there is the requirement of an intimate contact or adhesion, pressure tooling is used or else, jacketing tooling is selected.
Jacketing Tooling vs Pressure Tooling
Jacketing tooling differs with pressure tooling on the parameter of pin’s position with respect to the die. In case of jacketing tooling, the pin is extended all the way and flushed with die. Upon feeding the bare wire through the pin, it does not directly makes contact with molten polymer unless it leaves the die. In pressure tooling, the pin’s end is retracted in the crosshead, where it contacts with polymer at a higher pressure.
The process of tubing extrusion or extruded tubing process is used to manufacture products like medical tubing and drinking straws. This process is exactly similar to the process of regular
extrusion, until the stage of die. To extrude the hollow sections, a pin or mandrel is placed inside the die and in various cases, positive pressure is applied through the pin onto the internal cavities.
For specialty applications, it is required to make tubings with a number of lumens or holes. For such applications, tooling is created with the placement of more than one pin in die’s center for the production of required number of lumens. In large number of cases, the pins are available with air pressure from a range of sources. This way, it becomes easy to adjust individual lumen sizes with the adjustment of pressure to the individual pins.
Extrusion coating is using a blown or cast film process to coat an additional layer onto an existing rollstock of paper, foil or film
Extrusion Coating machines often meet a variety of applications
For coating thin layer of polyolefin’s (Mainly LDPE / PP) on substrates like Paper, Cotton Cloth, Woven Fabrics, Jute fabric, Aluminum foil, BOPP film, Polyester film, etc. up to 5200 mm Web width applications.
For coating Circular Woven fabric, for producing multilayer laminates along with the various substrates like Paper, Aluminum foil, Polyester film etc.
Extrusion compounding is the final one we will discuss about plastic extrusion equipment types
Compound extrusions or extrusion compound is a pre-process for the other process of thermoplastic injection molding. This is the compound extrusions and foam extrusion process in which one or more polymers are mixed with additives to get qualitative plastic compounds. The developed product is mostly in pellet form irrespective to the type of feed that may be powder, pellet, and/or liquid. This product is used in various other plastic forming processes like injection molding and further extrusion. The size of machine which is required for this process ranges from small lab machines to the biggest extruders available in the industry. These run at the rate of approximately 20 tons per hour and are used by various chemical companies which are producing the base resins.
In this process, generally the preference is given to twin-screw extruders as these provide improved mixing at the lower melt temperatures. A large number of these extruders have barrels and screws that include smaller segments like venting, mixing, conveying, and additive feeding that allows the design to be changed for meeting production as well as product requirements. However, single-screw extruders can also be used for this process, especially when suitable screw design & static mixers are present after the screw. Further, along with the equipment, the selection of components to be mixed such as viscosities & additive carriers is also very important
Filler Masterbatch and Color Masterbatch from Us Masterbatch are the products of this process, compound extrusion which is added to plastic production as additives and the solution to help businesses in the plastic industry save a lot of money for the final product. They are used for blown film, injection molding, woven sacks, thermoforming, yarn, etc