GB1318670A - Machine for simultaneous biaxial stretching of plastics sheets - Google Patents

Abstract

1318670 Tentering apparatus ERWIN KAMPF MASCHINENFABRIK 19 Nov 1971 [26 Nov 1970] 53868/71 Heading B5B [Also in Division D1] Apparatus for returning grippers to a start position in a machine for the simultaneous biaxial stretching of thermoplastic sheets comprises a guide rail 7 for the grippers 6 (represented in the Fig. by guide bolts 5), a return screw 8 including an axially compressible guide screw 14, and a reversing means 20 for returning the clips to the working section of the apparatus, an interim storage space 19 being provided between the return screw and the inlet to the reversing wheel 20. In operation the grippers are transported from the end of the stretching apparatus in the direction of arrow 3 by a chain 1 and carrier dogs 2 and are passed along guide rail 7 by return screw 8 to the reversing means 20. The screw 8 comprises a core shaft 9 mounted for rotation on bearings bracket 10; a first sleeve 11 having a helical groove 12 with a pitch corresponding to the spacing of carrier dogs 2; a cylinder core 13 which serves as a guide to an axially compressible helical spring 14 secured at its upstream end in an edge cutout 15 and at its downstream end in an edge cut out 18 of a second sleeve 16 mounted on the shaft 9. The sleeves 11, 16 and cylinder core 13 are fixed to the shaft 9 so as to rotate therewith, sleeve 16 having a helical groove 17 and being axially shiftable on the core. Helical spring 14 and helical groove 17 have a regressive pitch to feed the grippers to the storage space 19 so that the number of grippers therein remains constant, i.e. the lead and speed of screw 9 and reversing means 20 are synchronized. In an alternative embodiment (Fig. 5, not shown) the apparatus is also provided with stop means for preventing grippers from entering the storage space 19 when this is full up and means for axially shifting sleeve 16 to compress helical spring 14 and thus prevent a build up of pressure on the stop means by the advancing grippers. This arrangement allows replacement of worn or damaged grippers in the storage space 19 without the necessity of stopping the stretching apparatus. To this end a gripper 6 and a replacement gripper 6<SP>1</SP> (Fig. 6) may be mounted on a turnstile 35 comprising opposed wings 37 carrying rail sections 38, 39 whose cross-section is identical with that of guide rail 7 so that when necessary the turnstile can be swung through 180 degrees to bring replacement gripper 6<SP>1</SP> into alignment with guide rail 7 and worn or damaged gripper 6 to a position from which it may be replaced.