Coat-hanger sheeting die

Sheeting dies. One of the most widely used extrusion dies is the coat-hanger sheeting die. A sheeting die, such as the one depicted in Fig. 3.14, is formed by the following elements ... 

Figure 6.12 Schematic diagram of a coat hanger sheeting die.

Calculated pressure profile for three different coat hanger sheeting dies... 

Comparison of experimental data with numerical simulation for the three coat hanger sheeting dies shown in Fig. 12.16... 

Figure 2.25 illustrates a T-type die and a coat-hanger-type die, which are used for both film and sheet extrusion. The die must produce a smooth and uniform laminar flow of the plastic melt which has already been mixed thoroughly in the extruder. The internal shape of the die and the smoothness of the die surface are critical to this flow transition. The deckle rods illustrated in Figure 2.25 are used by the processor to adjust the width of the extruded sheet or film. 

Perhaps a more common sheeting die is the so-called coat hanger die, presented in detail in Chapter 3. For a given manifold angle a we must determine the manifold radius profile, R(s), such that a uniform sheet or film is extruded through the die lips. 

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. 

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.

The most common extrusion die for sheet products is the coat hanger-type manifold die as shown schematically in Fig. lA and as a section view in Fig. IB. The key elements of Fig. lA are ... 

A homopol5mier of vinylidene fluoride was ex-trudedt J using a coat hanger die with a width of 590 mm to produce a sheet at a thickness of 150 pm at a die temperature of 270°C. A chill roll at a temperature of 70°C chilled the hot film. This film was biaxially oriented by four times the original length in the extrusion (machine) direction and six times in the transverse direction (perpendicular to the extrusion direction). The film was at a temperature of 100°C while it was oriented at a stretch rate of 10 mm/min in both directions. 

The most common die configuration for production of cast film and sheet is a coat-hanger die (Fig. 7.7), named because of its resemblance to a common coat hanger. T-shaped dies are also used. The die opening is wider and thicker than the finished film. As the film is drawn down between the die and the chill roll, it contracts in width and thins, due to tension on the film being produced and polymer relaxation effects. 

Internals of coat hanger die for cast film and sheet... 

Multilayer co-extrusion is another technique used in the preparation of starch/ synthetic sheets or films [164, 263-266], in which TPS is laminated with appropriate biodegradable polymers to improve the mechanical, water-resistance and gas-barrier properties of final products. These products have shown potential for applications such as food packaging and disposable product manufacture. Three-layer co-extrusion is most often practiced, in which a co-extrusion line consists of two single-screw extruders (one for the inner starch layer and the other for the outer polymer layers) a feedblock a coat-hanger-type sheet die and a three-roll calendering system [164]. Biodegradable polyesters such as PCL [164, 264], PLA [164, 263], and polyesteramide, PBSA and poly(hydroxybutyrate-co-valerate) [164] are often used for the outer layers. These new blends and composites are extending the utilization of starch-based materials into new value-added products. 

Sheet Die n A heavy-walled, extremely rigid steel structure, bolted to an extruder head, whose inner passages form the molten plastic leaving an extruder screw into the shape of a flat sheet. Most modern sheet dies are of the coat hanger type with multi-zone temperature control, and contain adjustable choker bars and die lips for close control of lateral variation in the sheet thickness. See Coat Hanger Die, Choker Bar, and Flexible-Lip Die. 

Figure. 12.53 Schematic diagram of the coat-hanger design of a film or sheet die.

---