Author: Site Editor Publish Time: 2024-02-06 Origin: Site
As we discussed in last article, the location of certain functionality can have a profound effect on the capability of the twin-screw extruder and effectiveness of the compounding operation. Fortunately, the twin-screw extruder offers many cost-effective options. Most manufacturers ,like Nanjing Jieya,provide segmented twin-screw barrels consisting of individual sections that are four, five or six diameters long. Each barrel section is independently heated and cooled to provide precise barrel-temperature control.
The most common barrel section design is, of course, the closed barrel section . This barrel section fully encases the polymer melt on all four sides of the extruder with only a figure 8 opening through the center for the screws. Liquid feed, if needed, can be introduced into the system through an injection nozzle connected to a closed barrel or a combi barrel
Once the polymer and any other additives are fed completely into the extruder, the material is conveyed through the extruder, the polymer is melted, and all of the additives and polymers are mixed. Closed barrel sections provide temperature control on all sides of the extruder, whereas open barrels have fewer heaters and cooling channels.
The typical length of an extruder should be determined based on the screw configuration required for the process. However, the individual modular barrel can be in different lengths and diameters. The barrel temperature can also be controlled individually or in grouped zones. In addition, the modular barrels could be configured differently.
Normally, the extruder will be assembled by the manufacturer with a barrel layout that matches the process configuration that is required. In most compounding systems, the extruder will have an open barrel in Barrel 1. This feeding section is followed by several closed barrels for conveying the solids, melting the polymers, and mixing the molten polymer and additives together. A combi-barrel may be located at Barrel 4 or 5 to allow side feeding of additives, followed by a few more closed barrels for continued mixing. The vacuum vent is located near the end of the extruder, followed by the last closed barrel before the die.
For an extruder that is at least 10 barrel sections long (L/D ≥40) is to place this vent two barrel sections upstream of the die. Quite often, if the extruder head pressure rises too high, molten polymer could back up in the vent. During a compounding run, the head pressure can vary, especially with a tight screen. If the viscosity of the polymer melt is low, the polymer will back up and flow out of the vent. Locating the vent two barrel sections before the discharge essentially eliminates this possibility, resulting in more stable operation.(remarks:the content is organized from internet)
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