FLAT DIE

Control cabinet 2, extmder 3, flat die 4, chill roU 5, septet (seven roUs) 6, hot plate 7, septet (seven roUs) 8, heat-setting oven 9, trio (three roUs) 10,... 

Melt Extrusion. By far the most important method for producing film and sheeting materials reties on one or another of the various melt extmsion techniques (5). The main variations of melt extmsion are the slot (or flat) die-cast film process, the blown films process, and the flat die sheeting-stack process. These may be combined with one or more steps such as coextmsion wherein multilayer film or sheet is formed, biaxial orientation, and in-line coating (6). 

Forgings are produced by pressing or hammering ingots or billets either into simple shapes on flat dies or into complex shapes in cavity dies. Several sets of dies may be employed in arriving at the final shape. Equipment varies from simple drop hammers and mechanical presses to large hydrauHc presses. 

The antistatic properties of the step 2 product were evaluated by preparing tapes of blends with polystyrene by extruding in a twin-screw extruder using a flat die at 200°C. The contact angle of the tapes was measured using the sessile drop method and water as the measuring liquid. Testing data not supplied by author. 

The flat dies, or slot dies as they are sometimes called, are used to produce webs in a variety of processes. They all have an interior manifold for distributing the plastic and lips for adjusting the final profile of the web (extrudate). Some dies have movable restrictor bars for changing the manifold for proper melt distribution (Figure 17.10). All flat dies have flexible lips that can be adjusted by bolts to remove humps or bumps in the web s profile. Die lips can have their adjustment bolts push only, where internal plastic melt pressures are adequate to keep the lips positioned against the bolts, or can be push/pull for low pressure applications. Direct acting or differential thread designs (for minute adjustments) are available. Profile variations of at least 3% or less can be achieved with flat dies. 

For flat die extrusion of sheet, critical variables are temperature control, residence time and flow channel streamlining. Recent developments have been presented (175, 176). Sheet and film extrusion lines include cooling and polishing rolls. 

A method is proposed for using chrome tanned leather wastes produced by the footwear and clothing industry as fillers in polymer matrices. A technique for processing the composite obtained by continuous extrusion is also demonstrated. In order to evaluate the technique, a series of PVC-leather fibre composites was prepared and extruded through a flat die to produce sheets. The process produced a leather-like sheet that could be used in several applications. The influence of the filler content on the processability and final properties of the composite sheets was evaluated. The tests revealed that the sheets were flexible and exhibited suitable water absorption levels for several applications in the footwear and clothing industry. Finally, the tests showed that this composite could be formulated and processed at high productivity levels and at a low cost. 28 refs. 

Figure 89 depicts sketches of typical pelleting machines.With the exception of the first method (a), which applies a flat die, all other machines feature cylindrical dies and operate in a very similar manner as roller presses. The general principle is modified such that the material is pulled into the nip but then is extruded through bores in the dies and often scraped off with a knife . Equipment types (b) and (d) represent directly the modified roller press principle. Machine type (c) uses a press roller located within the cylindrical die and therefore resembles ring roll presses (see Section 4.2.2.4.4). To improve the grip and increase densification force gear pelleters (e) are applied which are said to produce pellets of superior quality. 

Figure 89. Schematic representation of different pelleting machines, (a) Flat die and edge rollers, (b) two hollow cylindrical dies, (c) one hollow cylindrical die with internal solid press roller, (d) one hollow cylindrical die with external solid press roller, (e) gear pelleter...

Figure 180. Schematic representation of pelleting equipment, (a) screw extruder, (b) pelleting machine with flat die and muller-type press rollers, (c) pelleting machine with one solid and one hollow roll, (d) pelleting machine with two hollow rolls, (e) pelleting machine with internal press roll, (f) gear-type pelleter...

Figure 330. (a) Typical concave pelleting die rings. (Courtesy of Sprout-Bauer, Muncy, Pa., USA.) (b) Flat dies and roller assemblies. (Courtesy of Amandus Kahl Nachf., Reinbek/Hamburg, FRG)... 

Figure 333. Diagrams showing two different designs of flat die pellet presses. (a) Bottom drive, (b) top drive for very wet pastes or sticky materials...

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