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672,668. Mixing machines. ABBEY, A. (Dow Chemical Co., and National Rubber Machinery Co.). April 22, 1948, No. 11160/48. Class 86 [Also in Groups V, VIII, XXV and XXVI] A machine for milling, mixing and extruding plastic materials comprises a pair of housings 8, 9 in each of which are formed a pair of semi-cylindrical recesses which when the housings are fitted together form a pair of adjacent cylindrical chambers 31, 32, Fig. 6, 7 which receive cylindrical rolls 20, 21 mounted in bearings in the machine frame. Two helical grooves 50, Figs 7, 16, are formed in one or each chamber, the two grooves in any one chamber being of opposite hand. The two chambers communicate through an opening in the wall between them, the rolls 20, 21 approaching each other in milling proximity through the opening. One or more feed inlets and one or more discharge outlets into which extrusion dies may be fitted, are provided intermediate the ends of the rolls, the arrangement of the helical grooves being such that material is forced from an inlet to an outlet. With one inlet and outlet only the groove or grooves not used for this movement are used to protect the adjacent roll bearings from the plastic material by directing back to the outlet material forced beyond it; Fig. 23 (not shown). As described one of the rolls is driven from a motor 3 through reduction gears (not shown) and gearing 10, 12, 13, 18 and the other roll is driven from the first in the opposite sense. The housings 8, 9 are hinged about a shaft 7, means being provided (see Group XXV) to open and close the housings by vertical movement of a rod 65, the housings balancing each other. Two feed inlets 34, 35 are formed in the upper housing, Fig. 16, and a central discharge opening 44 in the lower housing, Fig. 7. The grooves 50 in each chamber 31, 32 are staggered so that material in one groove arriving at the nip of the rolls is split into three parts, one continuing in the same groove and the other two going into adjacent turns of the groove in the other chamber. The rolls 20, 21 are smooth between the inlets and outlets but in the region of the inlets (and slightly beyond) have feeding grooves which decrease in depth, Fig. 11. The grooves 50 extend partly across the inlets and overlap the grooves. on the rolls. Blocks 70, 71, 70a, 71a, of various sizes may be fitted into the inlets 34, 35 to adjust the size of the inlets. A die can be fitted into the outlet 44 and has surfaces forming continuations of the lands between the grooves 50 in the lower housing adjacent the outlet 44 to ensure that substantially all the material passing the nip of the rolls at this point is extruded. Heating or cooling conduits 49 are provided in the housings 8, 9. Electrical heaters may be provided. The rolls are bored for the circulation of heating or cooling fluid. Modifications. For compressible material the grooves 50 may become progressively narrower or shallower towards the discharge orifice. The chambers 31, 32 may comprise replaceable liners in which the grooves 50 are formed and the inner and outer surfaces of the liners may be eccentric to varying degrees. The rolls may also be adjustable to and from each other so that by using different liners and adjusting the rolls the size of nip between the rolls may be altered. The feed inlets may be in the bottom housing and the outlets in the top housing instead of vice versa or both may be in either top or bottom housing. With two feed inlets the outlet may be nearer one than the other. The feed inlets may be over either roll instead of over the nip. Fig. 26 shows an arrangement in which a central inlet 109 feeds to two outlets 107, 108, the roll bearings 105, 106 being clear of the housings 100 and the roll shafts passing through the housings with a small clearance to allow a constant seepage of plastic material. This avoids possible contamination with lubricant from the bearings. A feeding funnel adapted to be cooled by a circulating fluid may be inserted into the feed inlets, Fig. 22 (not shown), to avoid premature heating of the plastic material. Alternatively the funnel may be warmed. One or both rolls may be plain, the grooves 50 adjacent a plain roll then extending the full length of a chamber. The apparatus may comprise a plurality of pairs of rolls with their respective housings, all the chambers formed in the housings being interconnected. The chambers 31, 32 and the rolls therein may be conical instead of being of uniform diameter. Specifications 536,421 and 672,667 are referred to.
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