Patent GB-974822-A (GB)
Title: Improvements in methods and apparatus for mixing rubber with particulate solid material
Inventor: BENNETT WILLIAM DOUGLAS
IPC: B29C48/475
Filed: 1960-03-15
Abstract: 974,822. Extrusion machines. DUNLOP RUBBER CO. Ltd. March 13, 1961 [March 15, 1960], No. 9035/60. Heading B5A. [Also in Divisions B1, B8 and G1] In a method and apparatus for the continuous mixing of rubbers with particulate materials, the rubber is extruded as a strip of controlled weight per unit length and fed to a mixing unit to which the particulate material is also supplied at a controlled rate. In Fig. 1, natural and synthetic rubbers are extruded from the extruders 1, 2 on to weighing conveyers 24, 25 and thence to a unit 3 which forces the materials through mixers 5, 6, 7, 8 whence they are extruded from the die 55 as a single or double strip 56, 57. Vulcanizing pellets are added by the integrating unit 9 and other solid materials from the storage and mixing vessel 4 by the weighing conveyer 32; liquids from a mixer 43 are sprayed into solids in a mixer 40 and the compounded material transferred by a screw conveyer 46 to the vessel 4. The extruders 1, 2 are supplied by bale feeders 10, 11 (see Division B8 and Figs. 2, 3 and 4, not shown) with rubber in bale form 12, 13; each extruder comprises a barrel as at 18 having a two-part screw 14a, 14b, of which the part 14a is formed as two part-cylindrical components enclosing a shaft 160 formed as an extension of the part 14b. The part 14a is exposed by an opening 156, see Fig. 6 (not shown), in the casing 157 and has an undercut flight 165 to shave rubber off the bale. The flight 169 of the screw part 14b decreases in depth towards the die 20, which is of the type having knives 178 to relieve stresses in the strip. A plunger 179 cuts a groove in the strip and is actuated by the associated weighing conveyer 24 or 25 to vary the depth of the groove and thus maintain a constant weight per unit length of the strip. There are passages 148, 150, 189 in the screw, casing and die respectively for cooling water and a thermocouple 188 for measuring its temperature. The forcing unit 3, Fig. 7, has a screw having a part 27a of form suitable for engaging the strips 22, 23 which are fed from the weighing conveyers 24, 25 into the apertures 29, 30; and a part 27b which decreases in depth towards the output end compact the materials and force them through the mixers 5-8. A third aperture 31, see Fig. 8 (not shown), receives solid materials from the weighing conveyer 32; there are passages 192, 193, 194 in the screw and casing for cooling water. The screw terminates in a blade 208 which fits within a coaxial passage 209, Fig. 11, of the mixer 5, the passage having axial grooves 211, see, also Fig. 12 (not shown), co-operating with the blade 208. The mixers 5-8 are of the type described in Specification 937,652 having a cylindrical passage 308 with a transverse mixing screw as at 300, 310 and inwardly projecting fins 307; the casing, screws and fins have passages as at 304, 305, 306 for cooling water. The mixer 5 has an inlet orifice 298 opening into a hemispherical entry surface 297. The storage and mixing vessel 4, Fig. 10, comprises a continuously rotated drum 34 having vanes 259 and a stationary stirrer in the form of an axial screw 258 having a passage 257 for heating water. The drum is covered with heat insulation 251. Material from the screw conveyer 46 is discharged into an inlet passage 260, and is discharged from the drum by a shaker 270 to the screw conveyer 38 and thence to the endless band weighing conveyer 32, a block 294a being provided to form the material on the conveyer into a layer of uniform thickness. The discharge passage continues below the screw conveyer 38 and surplus material is received in the container 277. The apparatus is supported on a load cell 286 which controls the rate of operation of the screw conveyer 46 to maintain a constant amount of material in the drum 34. The integrating unit 9 (see Fig. 13, not shown), comprises a conventional vibrating bowl feeder and solenoid operated step-by-step feeding device supplying pellets consisting of a mixture of rubber and vulcanizing ingredients. A control unit 54 (not described) controls the speeds of extruders 1 and 2, forcing unit 3, integrating unit 9, and mixers 5 and 8 by means of information obtained from a punched card; the speed of screw conveyer 38 from information supplied by weighing conveyer 32; and the depth of plunger 179 from information supplied by weighing conveyer 24.