Twin-screw compounding

As with pipe, siding manufacturing is highly optimized for efficient production at high rates and minimal costs. Siding uses powder compounds, twin-screw extmders, and vacuum sizing/cooling. 

The minimum residence times in compounding twin screw extruders for an average production run range from 5-15 seconds. 

Although changes in design have permitted higher speeds and pressure, the primary use of twin-screw extruders is still compounding. Twin screws are used in approximately 10 percent of all extrusion processes. 

A twin-screw extruder fitted with a stuffer box. The twin-screw extruder continues to blend the compound as it passes through although with the dryer. 

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

Corotating TSEs are widely applied in the compounding of thermoplastics. The extmder consists of two screws which intermesh each other. The screw concept consists of modules with different screw elements. Eigure 35.26 shows typical examples of screws which are applied in twin-screw extmsion. Eigure 35.27 shows typical screw elements which have been used in TSE applications in mbber compounding. A few attempts to apply corotating TSEs into mbber mixing... 

Huneault, M. A., Shi, Z. H., and Utracki, L. A., Development of polymer blend morphology during compounding in a twin-screw extruder. Part IV A new computational model with coalescence. Polym. Eng. Sci. 35(1), 115-127 (1995). 

As the screw turns, it conveys the pellets from the feed zone towards the melting zone. A combination of external heating and mechanical work melts the polymer as it is transported towards the metering zone. The metering zone pumps a uniform stream of molten polymer to a forming device, such as a profile die. Other types of extruders that employ two or more screws are commonly used for compounding polymer blends. The principles of twin screw extrusion will be discussed in Chapter 12. 

Create a table listing two or more advantages and disadvantages of each of the following compounding systems batch mixers, continuous mixers, single screw extruders and twin screw extruders. 

Why is most compounding of powder additives with polyolefins achieved via either continuous mixers or twin screw extruders ... 

A manufacturer observed that the compound produced by one twin-screw extruder exhibited much better dispersion than that produced in a similar extruder making the same compound. The only difference between the two extruders was the age of the screws and barrel. What could be causing the observed difference ... 

Twin screw extruders introduce the necessary shear to thoroughly compound the dry blend into a polymer melt. They achieve this by utilizing aggressive mixing and kneading elements on the screw. Unfortunately, processing speeds are limited by the requirement that temperatures must be kept low to prevent excessive degradation. 

It was observed that brominated phosphate blends easily into various resins in a single or twin screw extruder. Compounding rates also are increased. It has been assumed that this is partly due to its high degree of solubility in aromatic solvent. This is in contrast with the polymeric flame retardants which are more difficult to incorporate or compound into various resins. 

Report 116 Compounding in Co-rotating Twin-Screw Extruders, Y. Wang, Tunghai University. 

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