Twin screw profile

The production of rigid PVC profiles is described with reference to state-of-the-art twin screw profile extruders and downstream equipment from Battenfeld. Features of the machinery are described, and particular details are given of the profile dies, calibration block, calibration table, haul off and profile saw. 

Figure 12.39 Section of twin screw profile with a reverse flight melting and conveying section (Zone 4) followed by a conveying and mixing section containing kneading blocks (Zone 5).

Figure 12.41 Picture of intermeshing gear mixers in a twin-screw profile.

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

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. 

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. 

Keum, J. and White, J. L., Heat Transfer Coefficients and Screw Temperature Profiles in Modular Twin Screw Extrusion Machines, SPE ANTEC Tech. Papers, 50,108 (2004)... 

Single- and twin-screw extruders with customised screw profiles are used to produce low density PETP-PP foams in the presence of reactive compatibiliser and coagents. Low density PETP foam is also produced from... 

The industrial use of twin-screw extruders for this purpose revolves extensively, but not exclusively, around intermeshing co-rotating variants. Closely in-termeshing counter-rotating designs are widely used for profile extrusion of UPVC dry-blends since they permit close temperature control and exhibit a high conveying efficiency due to the positive displacement of material where the screws intermesh [150]. 

S. Bawiskar and J. L. White, A Composite Model for Solid Conveying, Melting, Pressure and Fill Factor Profiles in Modular Co-rotating Twin Screw Extruders, Int. Polym. Proc., 12, 1331 (1997). 

Fig. 6.44 The channel-depth profile (a) in a cross section normal to the axis, and (b) an axial cross section. [Reprinted by permission from M. L. Booy, Geometry of Fully Wiped Twin Screw Equipment Polym. Eng. Sci., 18, 973 (1978).]...

Fig. 10.70 Comparison between experimental and computational pressure profile results. [Reprinted by permission from T. Ishikawa, S. I. Kihara, and K. Funatsu, 3-D Numerical Simulations of Nonisothermal Flow in Co-Rotating Twin Screw Extruders, Polym. Eng. Set, 40, 357 (2000).]...

S. Satija and C. S. Tucker, Effect of Screw Root Profile on PMMA Melting in Counterrotating Non-intermeshing Twin Screw Extruder, SPE ANTEC Tech. Papers, 40, 248-255 (1994). 

V. L. Bravo, A. N. Hrymak, and J. D. Wright, Numerical Simulation of Pressure and Velocity Profiles in Kneading Elements of a Co-rotating Twin Screw Extruder, Polym. Eng. Sci., 40, 525-541 (2000). 

Erdmenger s patent for single-flighted and double-flighted self-cleaning kneading discs is considered to be the basic patent of the twin screw extruder. The patent describes the eccentric disc as well as the traditional profiles. 

This patent lays claim to eccentric screw profiles in the twin-screw extruder. Its eccentricity is arranged such that the barrel is cleaned by a single tip only. 

Although there are very few twin-screw (TS) extruders in comparison to the many more single-screw extruders, they are used also to produce products such as window and custom profile systems. Their major use is in compounding applications. The popular common twin-screw extruders (in the family of multi-screw extruders) include tapered screws or parallel cylindrical screws with at least one feed port through a hopper, a discharge port to which a die is attached, and process controls such as temperature, pressure, screw rotation (rpm), melt output rate, etc.143... 

The extrusion of foamed products with twin screw extruders has been reviewed (375). The machinery, tools and processes for the production of foam core pipe, sheet and profile have been listed and the market reviewed (124,333). Technical details of PVC-U foam sheet extrusion lines, including dies and calibrators, have been given (258). 

Counter-rotating twin screw extruders are used almost exclusively for the production of uPVC pipes, profiles and sheet because they treat material more gently than single screws. Parallel screw and conical twin screw extruders are compared. Cincinnati Milacron Austria introduced its Argos parallel twin screw extruders last year. These machines are intended to complement the company s Titan conical screw range. Coextrusion of foamed core pipes is also described. 

Shearer, G. Tzoganakis, C. Distributive mixing profiles for co-rotating twin screw extruders. Adv. Polym. Techol. 2001, 20 (3), 169-190. 

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