Mixing extruders

Undesired premature vulcanisation of a rubber compound during the processing operations of mixing, extruding or calendering. See Heat History. 

Dry ingredients (drug, binder, flller) Mixing Extruder... 

Fig. 11.12 Comparison between the theoretical cumulative RTD function for (a) CSTR and (b) the back-mixed extruder. [Reprinted by permission from Y. Lu, Ph.D Dissertation, Department of Chemical Engineering, Stevens Institute of Technology, Hoboken, NJ, 1993.]...

The back-mixed extruder is a variant of the conventional nonintermeshing (tangential) counterrotating TSE represented on Fig. 11.13(a) both counterrotating screws in this LCFR create a dominant downstream flow with no back mixing and with some mixing screw-to-screw flow. By contrast, the two counterrotating screws of the back-mixed reactor... 

Blending can, in a first instance, be carried out in dry condition in the polymer powder or granules the degree of blending is, however, not yet sufficient. To obtain a better dispersion, a blending process in the fluid state is necessary. To achieve this, various types of mixing devices are available, such as roll mills, internal mixers and mixing extruders. 

Lower energy needed to pump, mix, extrude, spray, etc. 

Mixing extruders are automated-feed internal mixers in which the feed is conveyed from the feed hopper into the mixing section (note that the extrusion section is principally used for conveying, not mixing). The mixing section is similar to that of an internal mixer where material is intensively sheared between the rotor and the wall. 

The large containers (e.g., automotive fuel tanks) were made using low concentrations, about 4% of the modified polyamide, in large "accumulator type" blowmolding machines (e.g. manufactured by Sterling Extruders, [USA] Kautex, [Germany]), equipped with low mixing extruder screws and other hardware. The... 

The polymers, whose characteristics are summarized in Table 1, were melt mixed in a Brabender-like apparatus at 200 C and at two residence times 6 min, at 2 r.p.m. and further 10 min. at 32 r.p.m. The blend compositions are listed in Table 2. After premixing, cylindrical specimens were obtained directly by extrusion using a melting-elastic miniextruder (CSI max mixing extruder mod. CS-194), Thermal and tensile mechanical tests were performed on these specimens by an Instron Machine (mod. 1122) at room temperature and at cross-head speed of 10 mm/min. Also made were morphological studies by optical microscopy of sections microtomed from tensile samples and scanning electron microscopy of fractured surfaces of samples broken at liquid nitrogen temperature. Further details on the experimental procedures and on the techniques used are reported elsewhere . 

The high investment sums required for large closed mixer lines for making up mixtures from compact rubber bales led to the use of pulverized and crumped polymers in mixing extruders. 

Section of poorly mixed extrudate with spider lines (two arrowed) from die head. 

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