Flex lip adjustment

Fig. 1 Coat hanger-type sheet die concept (A) (1) central inlet port (2) manifold (distributes melt) (3) island (along with manifold, provides uniform pressure drop from inlet to die lip (4) die lip (die exit forms a wide slit) and schematic of sheet die (B) (1) upper die plate (2) lower die plate (3) manifold (4) island (5) choker bar (6) choker bar adjustment bolt (7) flex die lip (8) flex lip adjustment bolt (9) lower lip (10) die bolt (11) heater cartridge.

Flex-lip adjustable along the width of the die and provides the final tuning to create imiform flow across the die. 

The first is the flex lip adjustment. A number of bolts along the width of the die allow local closing of the final land gap. This allows fine adjustments of the extru-date thickness at discrete points. The gap can be adjusted by as much as 1 mm or more if the flex lip is properly designed. The choker bar is not used as often as the... 

Fig. 8 Coextmsion feed block manifold and sheet die (A) (1) sheet die with flow restriction (2) adapter plate (3) feed block asembly (4) core material layer inlet (5) upper material layer inlet (6) lower material layer inlet and coextrusion multimanifold sheet die (B) (1) lower melt channel (2) upper melt channel (3) lower choker bar (4) lower choker bar adjustment bolt (5) upper choker bar (6) upper choker bar adjustment bolt (7) flex lip.

The examples shown in Fig. 9.12 are methods for local balancing of the land length. Another method of adjusting the shape of the die is to incorporate moveable elements in the channel such as choker bars, flex lips, and membranes. These elements are frequently used in film and sheet dies. However, they can be used in other types of dies as well. 

By incorporating a removable lower die lip, the die can be used, for instance, for 1-mm sheet extrusion and for 4-mm sheet extrusion by changing only the lower die lip. Without the removable die lip, another sheet die would have to be used because the flex lip can only adjust over a limited range. In some automated extrusion lines, the gap of the sheet die is adjusted automatically. This is done with heat expandable die lip bolts [20], first developed by Welex in the early 1970s. A similar type of sheet die using thermal bolts is now also offered by Egan Machinery Company and a number of other companies. 

The upper layer can be adjusted with a choker bar, while the final combined layer thickness can be adjusted with the flex lip. 

Unlike the coat hanger flat film dies, no simple final film adjustment is possible by lip flexing. Consequently, the order of magnitude of thickness accuracy in tubular dies is 10% as compared to 5% in flat sheet and film dies. This larger margin of accuracy in blown film dies is compensated by die rotation, which permits the distribution of the thickness variation across the entire width of the product. 

A Fast-Gap system (trade mark of Extrusion Dies, Inc.) on a die extends the adjustment range, and eliminates the parting line of a removable lower lip. This device provides an additional 5 mm of adjustment ( 2.5 mm), by simply turning a hex headed power screw on the end of the die. The operator can now also flex open the lip to clean it, and then close it back to the run position, saving time and reducing scrap. 

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