GB1384979A - Extrusion die for blowing plastic film - Google Patents

Abstract

1384979 Extruding blown film J J FARRELL 5 April 1973 16397/73 Heading B5A To prevent weld lines in extruded blown film an extrusion die has an annular outlet formed between a body 22 and a core 24, the core having a material supply passage 30 connected by branches 34 to a circumferential recess 36 in which is disposed an annular plate 78 having distribution passages which displace material from branches 34 both radially and angularly to mix the material and distribute it around the entire circumference of the die outlet. The annular plate has spiral grooves 92, Fig. 3, on one face as shown or both faces (Fig. 12, not shown) the depth of which decreases outwardly to zero while leakage between the grooves increases outwardly from zero due to the divergence of the grooved face of the plate from the opposing face of the recess 36, Fig. 11, or another similar plate 80, Fig. 1. The other plate 80 has spiral grooves of similar, different or opposite pitch. In Fig. 1 two different materials are fed concentrically to grooved plates in two circumferential recesses 36 and 110, the two annular streams of material merging at a shallow angle to prevent mixing. A ring accommodated in a recess of front plate 78 is adjustable by bolts 106 to regulate the front stream, and the rear stream is adjusted by a ring 118 around the rear plate 114. The front end of passage 30 is blocked by a tapered plug 32 retained by screws 62 which will yield at excessive pressures to permit plug 32 to lift and relieve the pressure. A safety cover 62 is fitted over the bolts and a cover 68 is fitted over that. Compressed air is supplied through passages 74, 76 into cover 68 and escapes through hole 72 to inflate the extruded tube. In Fig. 11 a die for a single layer sheet has heating coils 174 and a flexible outer die lip 178 which is adjusted by a partly split wedge ring 182.