Process and device for producing bubble-film

Method for fine correction of the thickness profile of a film bubble in blown film manufacture, in which a cooling gas stream which is uniform over the circumference of a film bubble is produced with a main cooling ring, in which there is automatic measurement of the film thickness at circumferential positions around the circumference of the film bubble, and in which the cooling gas stream discharged by the main cooling ring is modified at individual circumferential positions in response to the thickness measurements, wherein the modification is achieved by a portion of the supplied cooling gas being drawn off at the circumference of the film bubble and suction at individual circumferential positions around the film bubble being varied to increase film thickness uniformity.

Device for regulating the thickness of a film bubble in blow film manufacture, comprising an unsegmented main cooling ring surrounding a film bubble, an additional cooling ring forming an annular nozzle subdivided into individual segments and separate from the main cooling ring, said nozzle having a die gap, the die gap terminating in a cooling gas stream discharged by the main cooling ring, and devices for controlling the cooling gas stream in the individual segments in response to automatic measurement of the film thickness around the circumference of the film bubble, said devices being for controlling the cooling gas stream and said devices comprising separate blowers for each individual segment and/or separate adjusting means associated with the individual segments for controlling angle of incidence (.phi.), the positions of the segment with respect to the bubble surface, or the temperature of the cooling gas, thereby to increase film thickness uniformity.

Method for manufacturing blown films in a film blowing machine wherein a cooling ring surrounds a film bubble and has an annular die gap for cooling air, in which the cooling air throughput in the individual circumferential areas of cooling ring is controlled to correct the thickness profile of the film bubble, and wherein a portion B of the cooling air is diverted at positions distributed in the circumferential direction of the cooling ring for controlled reduction of the cooling air flow at the film bubble with the air being diverted by adjustable guides or guide blades and wherein the total flow resistance for the diverted and the nondiverted cooling air in the circumferential segment is kept substantially constant independently of the positions of the guide blades.

Device for regulating the thickness of a film bubble in blow film manufacture, wherein a cooling ring surrounds a film bubble and has an annular die gap for cooling air, said die gap having a throughput cross section, and wherein the cooling air throughput in the individual circumferential areas of cooling ring is controlled to correct the thickness profile of the film bubble, and wherein a portion of the cooling air is diverted at positions distributed in the circumferential direction of the cooling ring for controlled reduction of the cooling air flow at the film bubble with the air being diverted by adjustable guides or guide blades and wherein the total flow resistance for the diverted and the nondiverted cooling air in the circumferential segment in question is kept substantially constant independently of the positions of the guide blades, wherein the cooling ring has a crown of discharge openings located radially outside the die gap, said discharge openings having throughput cross sections, and wherein the adjustable guides or guide blades are so disposed in the cooling air flow inside the cooling ring that they deflect a portion of the cooling air stream to the discharge openings and, by their adjustment, modify the throughput cross sections of the outlet openings and of the die gap to cause the total flow resistance to remain substantially constant.

Method for manufacturing blown films in a film blowing machine with a cooling ring surrounding a film bubble and having an annular die gap for cooling air, in which there is automatic measurement of the film thickness, and in which, in response to the measurements of the thickness of the film bubble, the cooling air flow is controlled in the individual circumferential areas of the cooling ring by segmentwise narrowing or widening of the die gap, wherein at least partial compensation is provided for the change in flow resistance produced by the change in the gap width, with the cooling air flow being throttled in segments upstream of the die gap as a function of the gap width.

Device for manufacturing blown films in a film blowing machine with a cooling ring surrounding a film bubble and having an annular die gap for cooling air, in which, to correct the thickness profile of the film bubble, the cooling air flow is controlled in the individual circumferential areas of the cooling ring by segmentwise narrowing or widening of the die gap, wherein at least partial compensation is provided for the change in flow resistance produced by the change in the gap width, with the cooling air flow being throttled in the affected segments upstream of the die gap as a function of the gap width, and wherein the outer edge of the die gap is delimited by radially adjustable slides, wherein a throttling device is associated with each slide, in the cooling air flow upstream of the die gap, said device being coupled drivewise with the slide and being actuated to produce greater throttling of the cooling air flow when the slide is moved in the direction of greater gap width.