DE2444839

1471702 Pelletizing by extrusion JAPAN STEEL WORKS Ltd 10 Oct 1974 [8 Jan 1974] 43979/74 Heading B5A [Also in Division G3] In pelletizing apparatus, rotating cutter blades are advanced towards a die. When contact between the blades and the die surface is electrically detected, the blades are retracted by a predetermined distance or compressed against the die by a predetermined force. As shown in Fig. 1, melted synthetic resin strands are extruded through nozzles 16 of a die 3 and cut into pellets by rotating blades 1. The pellets are cooled and solidified by water flowing through a cutting-box 24. The blades 1 are mounted on a holder 6 resiliently secured to the end of a shaft 2, Fig. 2 (not shown), which is rotated by a sleeve 22 driven by belts 12. The axial position of the shaft 2 and associated cutter is controlled by a sleeve 7 which is moved by a worm drive 8, 9 connected to an electric motor controlled from a panel 18. The shaft 2 can be rapidly withdrawn by an air-powered piston 13. In operation, the shaft 2 is initially retracted by the piston 13 and the worm drive 8, 9. The piston is then driven forward, allowing the shaft to be advanced slowly by the worm drive, the cutter blades being continuously rotated. When the blades 1 contact the die 3, they also contact electrodes 4 causing a transducer 5, Fig. 5 (not shown), to feed a pulse signal to the control 18. A digital circuit 17, Fig. 4 (not shown), holds a preset count which is counted down by pulses derived from a counter 14 responsive to the distance moved by the shaft 2. When zero is reached, a control signal is produced to turn off the worm drive, leaving the blades 1 in contact with the die and under a predetermined pressure against it. If the blades wear during use, and contact with electrodes 4 is lost, the signal from the transducer 5 disappears, so that the worm drive starts again to restore contact of the blades and die and apply the desired pressure. Alternatively, when contact is achieved, the worm can be driven in the reverse direction to set the blades at a desired spacing from the die.