This section provides an overview for extruders as well as their applications and principles. Also, please take a look at the list of 9 extruder manufacturers and their company rankings.
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An extruder is a piece of equipment that produces molded products such as tubes and sheets by heating the input material to soften it and extruding it with the screw of a cylinder.
From pellets or minced raw materials, they are processed into various shapes, such as round or square pipes, tubes, ducts, and sheets, depending on the shape of the die. Since raw materials are fed sequentially from the hopper, continuous production is possible. This is useful for mass production.
In extrusion molding, the shape is given by the die and then hardened by cooling processes such as water cooling and air cooling to maintain the shape. When the material is sufficiently hardened, it is taken back and cut to make the product. Extrusion has a long history and has a wide range of applications, from food processing to metal and plastic molding.
Extruders are used to process metals, such as aluminum and copper, and thermoplastic materials into molded products by heating and melting them and then giving them shape through a die. Taking the production of synthetic fibers from plastic as an example, strands of plastic are obtained by drawing the molten plastic obtained from the extruder's outlet as it is cooled and stretched.
Extruders can also be used for continuous production of foams. The molten plastic is melted by pressurizing a foaming agent into the molten plastic. As the foaming agent is pushed out of the die outlet to normal pressure, the pressure difference causes the foaming agent to be released, resulting in a foam body.
Besides the industrial field, another application of extruders is the processing of food products such as sausages, pasta and beef noodle, and pet food. Extruders can add steam to heat the food, reducing microorganisms in the food and simultaneously sizing the starch.
The role of extruders appears to be a simple one: to give shape to dissolved raw materials. However, in order to produce a stable product, it is important to optimize the conditions at each location according to the raw material and target shape.
First, the raw material fed into the hopper is adjusted to a constant speed using a weight feeder or other means to prevent clogging, and then the cylinder is filled with the raw material. A heater in the cylinder heats the material to soften it, and the speed of the screw is adjusted to extrude the material while applying the appropriate pressure to obtain the desired shape, such as a tube or bar shape.
The extrudate is cooled enough to retain its shape in a cooling unit before being taken back and cut. The key is temperature control at each stage of the process. If the temperature of the extruded material is too high, the shape given at the die exit may not be retained because of the high viscosity and the time required for cooling.
Also, if the cooling process is too fast, the molded product will be distorted, which may cause rupture. In addition to heating from the heater, extruders heating also generates frictional heat between the screw and the material or between materials.
Therefore, temperature oscillation (hunting) will occur even when the machine monitors the set and actual temperatures and adjusts them automatically.
Extruders are classified by the extruders' construction, die configuration, and post-processing methods. Extruders can also be classified by the number of screws into single-screw and multi-screw.
When multiple raw materials are used, not only melting but also uniform mixing is required, so multi-axis extruders with high mixing performance are often used. The configuration and direction of the rotation of the screw must be determined according to the raw material.
The shape of the molded product of the raw material is largely determined by the shape of the mouthpiece, called the die, of the extruders. Therefore, the types of extrusion molding are often called according to the shape of this die and the subsequent process. Typical moldings include tubular, bar, and sheet shapes.
In addition to standard shapes, complex shapes and multi-layered moldings can also be obtained. Extruded foam products can also be produced by adding a blowing agent.
*Including some distributors, etc.
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