Twin-roll mill

Compound mixing was performed on different compounding equipment. For EVA organoclay-based nanocomposites, a laboratory twin-roll mill and an internal mixer heated to 145 °C were used. A corotating twin screw extruder from Leistritz, Germany, with a 27-mm screw diameter and an aspect ration of 40 L/D was used to generate polyethylene nanocomposites. The mass temperature was 190 °C at the extruder die. 

Information on the nanocomposite morphology was obtained by transmission electron microscopy (TEM) and x-ray diffraction (XRD) observation. Compounding was done on a twin-roll mill, and exfoliated silicate sheets were observed together with small stacks of intercalated sheets." This structure may be described as a semi-intercalated semi-exfoliated structure that did not change principally with the vinyl acetate content of the EVA matrix, even a larger number of stacks were observed for EVA with lower vinyl acetate contents." There were no great differences within the morphology of these nanocomposites. 

FIGURE 7.10 Heat release rates for compounds made by twin-roll mill with various filler blends of MWCNTs and organoclays. Heat flux = 35 kW/m. (From Ref. 62, copyright 2005, John Wiley Sons, Ltd. with permission.)... 

Ko-kneader improved the PHRRs compared to those with the corresponding twin-roll mill compounding (Figure 7.11). 

The final quality and reproducibility of rubber compounds mixed from scratch on a two-roll mill, or finalisation of compound batches mixed in an internal mixer, depend to a large degree on the skill of the mill operative. In order to overcome to some extent the reliance on operative skill and to ensure reproducible mix quality many mills are now fitted with stock blender units. These consist of a driven twin roller system, of similar overall length to the mill rolls, fitted above the mill frame. 

Fig. 6.18 Schematic representation of pressure generating devices based on building blocks 4 (a) roll coating (b) roll mill (c) calender (d) twin roll extruder.

Other common continuous mixers involve substantial modification of single and twin screw extruders, aimed at improving distributive mixing capability in particular, and leading to the development of continuous mixers such as the Transfermix (50) and the Buss Ko-Kneader (51). Another approach in continuous mixer development is to transform batch mixers into continuous ones. Thus, the roll-mill can be converted into a continuous mixer by feeding raw material on one side and continuously stripping product on the other side. In addition, the Banbury mixer was imaginatively transformed into the Farrel Continuous Mixer (FCM) by Ahlefeld et al. (52), and, later, two similar continuous mixers were developed by Okada et al. (53) at Japan Steel Works and by Inoue et al. (54) at Kobe Steel. 

The first mixer was an annular container with a spiked rotor for rubber compounding [Hancock, 1823]. The calender/two roll mill was patented by Chaffe in 1836 and manufactured by Parrel Co. A counter rotating twin shaft internal mixer with elliptical rotating discs or sigma-blades was developed by the end of the last century [Freyburger, 1876 Pfleiderer, 1880]. The first hand-operated extruder was a ram press, used for forming NR or GP, then later NC. 

The first mixer was an annular container with a spiked rotor for rubber compounding (Hancock 1823). The calendar/two-roll mill was patented by Chaffe in 1836 and manufactured by Farrel Co. A counterrotating twin-shaft internal mixer... 

Without going too much into equipment description details, it is enough to note that there are three-, four-, and five-roll mills, and single- and twin-worm simplex and duplex refiners. 

Finally, testing with a three-roll mill and simplex single-worm and simplex twin-worm refiners is essential. Only testing for adeqnate color dispersion, surface roughness, plasticity, and temperature assure the proper selection of refining equipment. 

Materials used, kindly obtained from DSM (the Netherlands), were PP 13E 10 (polypropylene) and two types of EPDM, Keltan 514 and Keltan 578. Before exposure to irradiation PP was first compression moulded into sheets with a thickness of 1 mm. Blends were made on a two roll mill (Schwabentahn, T = 185°C) and the blends were also compression moulded into 1 mm thick sheets. Some of the blends were made on a corotating twin-screw extruder (Berstorff ZE25) and were pelletized. Both sheets and pellets were exposed to electron beam irradiation which was performed... 

Blending and mixing are important unit operations in the polymer blend industry. Hancock patented the first internal mixer in 1923. Freyburger in 1876 improved the device to a more efficient counter-rotating twin-shaft machine. The Banbury mixer is a modification of this patent. The Parrel Co. introduced two-roll mills, then the Ram extruder surfaced in 1797. Screw machines that were capable of manufacturing... 

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