The twin-screw extruder is characterized by the “building block” design of both the screw and the barrel. The extruder screw design consists of a number of components mounted on the mandrel, such as threaded elements, kneading blocks, toothed mixing discs, retaining rings, etc. The barrel is also composed of different barrel sections, such as fully enclosed, with exhaust port, with filling port.
This extruder screw design has the following main advantages
First, the extruder screw design , according to the specific requirements of the material, recipe, the various screw components, and barrel components in order to combine, so as to ground to complete the set mixing task. You can also change the order of the screw and barrel combination, to achieve the best use of different materials, formulations, to achieve the purpose of a multi-purpose machine, a multi-purpose machine.
Second, another advantage of the extruder screw design is that the threaded components and barrel components can be partially replaced, avoiding the scrapping of the screw or barrel as a whole and reducing maintenance costs.
Third, the modular design of the barrel is usually embedded with bimetallic bushings to improve the wear resistance of the inner surface of the barrel. To achieve the temperature course, there is a separate heating/cooling design on each barrel, thus enabling a combination of cooling and heating functions.
Building block screw
Block type barrel
Segmentation of the screw and its function
The extruder screw design is generally divided into five segments: conveying section, melting section, mixing section, exhaust section, and homogenizing section.
Screw design PDF
Conveying section
Conveying materials to prevent overflow.
Screw arrangement: this section of the screw basically consists of positive conveying threaded elements, but the thread guide can be from large to small, in order to improve the material to the screw groove fullness.
Temperature setting: the temperature is slightly close to the melt, arranged in a gradient with appropriate temperature.
Melt section
In the barrel heater heat transfer to the barrel and screw elements (kneading disc) on the material extrusion, shear generated by the heat, the material began to melt, after passing through the section, basically become molten.
Screw arrangement: set the pinch block, shear element, or reverse thread, and pay attention to the inter-phase arrangement.
Temperature setting: melt section is 10~20℃ above the melting point of the base material so that the material is fully melted and evenly distributed.
Mixing section
The residual solid phase transported from the melt section finally melts into the melt. This section of the screw consists of a large lead forward conveying threaded elements, the material is filled with low, not established pressure, so the material to be added in this section (polymer or additives) to join (with a side feeder or vertical feeder to join).
Screw component arrangement: The screw in this section consists of a large lead with positive conveying threaded elements
Temperature setting:The mixing section is 10~20℃ above the melting point of the base material (as high as possible), so that the material is fully melted and evenly distributed to ensure that the mixture is fluid.
Exhaust section
Discharge water vapor, low molecular weight substances, and other impurities.
Screw combination arrangement: This section consists of a large lead forward conveying threaded components, the mixture of the screw groove is filled with a low degree (less than 1), so there is a large free surface area that can be upstream material melting, gas generated when mixing and side feeder to join the material when the gas brought in under atmospheric pressure to exhaust to the air.
–The general idea is: reverse thread (R-LH) or reverse stick (KG) + conveying thread + large lead or multiple small lead threads.
Homogenizing section
Conveying and pressurization, to establish a certain pressure, so that the material at the die opening has a certain density, while further mixing, and finally achieve the purpose of smooth extrusion granulation.
Screw combination: The thread block guide is gradually smaller or the screw groove is gradually smaller to realize the pressurization and reduce the length of the backpressure section while paying attention to the use of a single head thread and wide screw thread to improve the discharge capacity and avoid bubbling material.
Temperature setting: According to the degree of glossy drop, the temperature should be lowered appropriately, but the high temperature of the die head is good for discharging material.
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