Kneading block

H. T. Chan and D. A. DuFresne, Kneading Block Melting Study, SPE ANTEC Tech. Papers, 53, 302 (1995). 

For example, the Coperion (formerly-Wemer Pfleiderer) designation KB 45/5/40 denotes a kneading block (KB) 40 mm long, made of five kneading paddles, staggered 45° part. 

Fig. 10.65 Experimental apparatus used by McCullough and Hilton (109). (a) Transducer circumferential locations, (b) kneading block used for the ZSK 30 barrel. [Reprinted by permission from V. L. Bravo, A. N. Hrymak, and J. D. Wright, Numerical Simulation of Pressure and Velocity Profiles in Kneading Elements of a Co-TSE, Polym. Eng. Set, 40, 525-541 (2000).]...

Reprinted with permission from K. Funatsu, S.I. Kihara, M. Miyazaki, S. Katsuki and T. Kajiwara, 3-D Numerical Analysis of the Mixing Performance for Assemblies with Filled-Zone of Right- and Left-handed Double-Highted Screw and kneading Blocks in TSEs, Polym. Eng. Sci., 42, 707 (2002).]... 

Number of Compacted Particulate Compressions Occurring during the Passage over a 1 (L/D) Kneading Block... 

The TSMEE in the M-M mixing mode was used with three kneading blocks of 5/45/42 forwarding elements. Experiments were conducted at two melt temperatures, 180° and 140°C, and two rotor speeds, 60 and 120 rpm. The results and conclusions that emerged from the study are discussed in the following subsections. 

M. Esseghir, D.W. Yu, and C. G. Gogos Rheology-driven Mixing Mechanisms in TSMEE Kneading Blocks, SPE ANTEC Tech. Papers, 41, 1994 (1995). 

In the extruder, not only shear flow is present, but also extensional flow occurs as well. This is illustrated in Fig. 3.20 for the deformation of a fluid element. Wherever cross-sections narrow, such as at the tips or between kneading blocks and the wall, the fluid elements are compressed and extended. This effect is particularly relevant for non-homogenous polymer melts, e.g., immiscible blends, in which the disperse phase can be split by extensional deformation. For more details, see Chapter 9. 

When conveying solids with a low bulk density, high fill rates in the intake zone can cause fluidization, if the air that is drawn in cannot escape from the extruder. This can be avoided by a partially filled downstream plastification zone (e. g., with conveying kneading blocks) and a vent opening installed downstream of the plastification zone. 

Kneading block assembly Solid conveying zone... 

Figure 4.7 Geometric values and process variables of a double-flighted kneading block...

Figure 4.8 Melt streams in a kneading block zone - broad primary stream in the feed direction and narrow leakage flow [12]...

Figure 4.9 Energy input as a function of throughput for polyamide melting with kneading block and MPE plastification zones [13]...

Partially filled mixing zone with conveying kneading blocks so that the air can escape in the direction of flow through a downstream vent opening. 

Wide-disc kneading blocks achieve the most effective dispersion because they generate the greatest shear stresses. This also leads to high energy input, however, which increases the melt temperature and reduces the viscosity of the predominantly shear-thinning polymer melts, which in turn leads to a reduction of shear stress. Therefore, dispersive mixing is an optimization problem. 

Pressure build-up zones are located in the extruder in the discharge zone and upstream of each backward pumping screw element, e.g., mixing elements, re-conveying, or neutral kneading blocks. 

Figure 5.17 Triple-flighted eccentric kneading blocks [5]...

Kneading blocks with this configuration are described as neutral (non-conveying). They are always filled completely and create a pressure drop. 

The nozzle (5) and the back-feeding kneading block (3) are obstacles to flow that generate a drop in pressure. The screw sections upstream of this must build up the pressure needed to overrun the obstacle. The back-feeding kneading block (3) ensures that at least a part of the kneading zone is wholly filled, which promotes the mixing effect. 

Figure 9.6 Principle of operation of a kneading block distributive mixing results from transverse flow...

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