Feed block

Feed Blocks Static Mixers Continuous Conveyors... 

The lack of simple and reliable application systems is a major problem to be solved before the introduction of this biocontrol agent into practical control strategies. Mixing fungal chlamydospores into a feed supplement was used in most plot and field studies as an application system (Larsen, 2000). Incorporation into various types of feed blocks or mineral licks, as well as slow-release devices, may also become feasible (Thamsborg et al., 1999 Chandrawathani et al., 2003). 

The process is divided into five steps (see Fig. 9) Ecovio is first processed by the extruder to form a melt stream with constant melt temperature and output rate (Fig. 9, 1). In the forming section, the melt streams of several extruders can be merged into one using an adapter feed block or a multilayer die. These devices control the flow of each stream to obtain an even layer distribution (Fig. 9, 2) [30]. Then, the melt stream is transformed into a flat film in the film die. The thickness distribution is controlled automatically by means of expansion bolts. 

Fig. 9 Cast film line. 1 Extruder, 2 forming section - adapter feed block, 3 casting section -die, 4 winder, 5 automation. (Reproduced with permission from Reifenhauser)...

Because of the limited thermal stability of, e.g., Ecoflex /starch compounds, dead spots in the feed block adapter or the film die have to be avoided. As a consequence, reduction of the film width by closing the die with metal bars (deckling) is not recommended for Ecoflex /starch compounds. 

Even though liquid whey has been successfully commercialized in the form of alcoholic and nonalcoholic beverages, these are still a rarity in most countries. Most whey is converted to whey solids as ingredients for human food or animal feeds by traditional processes such as spray drying, roller drying, concentration to semisolid feed blocks, or production of sweetened condensed whey. Jelen (1979) reported other traditionally established processes including lactose crystallization from untreated or modified whey, production of heat-denatured whey protein concentrate, or recovery of milk fat from whey cheese in whey butter. ... 

Streamlined melt lamination area that channels separate flow streams into one laminated melt stream inside feed block. 

Adapter plate between the feed block and the sheet die. 

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.

An alternative to the feed block design is a multimanifold die as depicted in Fig. 8B. The key elements of this design are ... 

The feed block technique is cheaper to implement than the multimanifold approach, but because the melt streams travel some distance before reaching the die exit, irregular flow patterns can develop at the interface of the different melt streams.This is especially... 

TMPAH was used successfully for the homo-, co-, and block polymerizations of IP. In this case, due to the less reactive diene monomer, no additional free nitroxide was necessary to control the polymerization and both low and high molecular weight polymers (Mn=4500 to Mn=100,000) with narrow molecular weight distributions (Mw/Mn= 1.07-1.3) were synthesized [159]. Copolymers with various styrene and (meth)acrylate derivatives, including acrylic acid and HEMA, were obtained, with the content of isoprene varying from 10% to 90% in the comonomer feed. Block copolymers were also produced, starting from either ptBA or pSt macroinitiators however, the alternate order of blocks (i.e., starting from a pIP macroinitiator) was only achieved with St. Chain extension with tBA resulted in inefficient initiation [159], as had been found for pSt-pnBA block copolymers [71]. 

Each type of resin is melted in an individual extruder, and the melts are carefully brought together prior to or in the die, in a manner that keeps them in homogeneous layers, without mixing. The process used to combine the polymers is usually different in the cast and blown film processes. In cast processes, as illustrated in Fig. 7.12, the polymers are typically combined in an adapter, called a feed block, before they enter the coat hanger die. This permits a simpler design for the die itself. Multimanifold dies are used when plastics with widely different flow properties are to be combined, as such systems provide a shorter multilayer flow path before solidification, and thus minimize distortion of the interface. 

When desigtung a new product, a design team begins by specifying the desired optical properties. Then, it designs a stack of on the order of 100-1,000 layers of polymer films. Next, it designs extrusion devices to properly blend the polymer, and feed-block-splitters that divide the flow into 100-1,(K)0 thin films. The effluent films from these splitters are stacked at high extrusion speeds. 

A number of techniques are available for coextrusion, some of them patented and available only under license. Basically three types exist feed-block, multiple manifold, and a combination of these two (Table 3-7). 

The same process can also be used to produce a multilayered film using several extruders, one for each type of resin used, and a feed block to direct the resin... 

Feed block In coextrusion, a massive metal block in which the streams of the several extruders are brought together to form the layers of a single stream just before it enters the die. 

There are basically three different techniques for coextrusion. The first employs feed block dies where the various melt streams are combined in a relatively small cross-section before entering the die. The advantage of this system is simplicity and low cost. Existing dies can be used with little or no modification. Disadvantages are that the flow properties of the different polymers have to be quite close to avoid interface distortion. There is no individual thickness control of the various layers, only an overall thickness control. Figure 9.37 shows a schematic of a feed block sheet die. 

The feed block system and the multi-manifold system are compared in Table 9.1. 

Table 9.1 Comparison of Feed Block and Multi-Manifold Systems...

Feed block system Multi-manifold system... 

There are two approaches to minimizing the interface distortion. One is to reduce the length over which the different melt streams flow together. This is done in multimanifold dies where the different melt streams are combined just before the exit of the die. Another approach is to modify the initial configuration of the layers in such a way that the final layer configuration is the one desired. This approach is called profiling, and this is a method frequently used in feed block coextrusion systems to achieve uniform layer distribution at the exit of the die. This principle is illustrated in Fig. 9.44. 

Profiling can be used with feed block coextrusion systems and also with vane-type coextrusion dies as shown in Fig. 9.41. With 3-D flow simulation the rearrangement of the layers can be predicted. Particles defining a flat interface can be tracked upstream to the input plane to determine the appropriate initial layer geometry. Examples of this approach are discussed by Perdikoulias et al. [45]. 

Another configuration used for coextrusion is a single die for all layers with a feed-block that combines and distributes the various layers so that they all maintain a uniform thickness across the exit of the feedblock. The design of the die is made to produce a product with the desired width and thickness while maintaining thick-... 

In the experiment, the shapes (square, teardrop, circular, and rectangular) that were used are commonly found in the design of feed blocks, dies, and transfer lines. Figure 12.19(a) shows the initial cross section of the material as it flows through a square channel, which measures 0.95x0.95 cm. 

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