Plastification section

The feed section takes the product from the feeding system and conveys it to the plastification section. At the same time, there must be sufficient free volume to allow gas reflux, e. g., air or nitrogen, to escape from the process section upstream. If the throughput rate of the extruder is less than the input product flow, the product will back up in the feed hopper, indicating that the intake limit has been reached. Along with the known extruder data, such as the screw speed, the screw pitch, and the available volume in the screw channel, other influencing factors, such as the fill rate of the screw channel, the conveying efficiency, the bulk density, and other bulk characteristics of the product sometimes affect the... 

The intake behavior is also substantially influenced by the resistance of the downstream plastification section. If discharged at atmospheric pressure, e.g., via screw feeders, the throughput rate is considerably higher than if the same feed section is succeeded by a plastification section (Fig. 11.4). For instance, if metering a product with a bulk density of 0.35 g/cm3 and a melt phase density of 0.7 g/cm3, it is clear that considerable quantities of gas will have to be extracted upstream through the intake hopper. 

Figure 11.4 The resistance of the plastification section influences the throughput rate of the extruder...

The plastification process is initiated the polymer contacts the hot inner wall of the barrel and/or by mechanical stress of the solid particles in the kneading elements. The melting process is continued by the introduction of mechanical energy into the melted product via shear stresses and/or heat conduction from the melt to the as yet un-melted product. The detailed design of the plastification section depends on the product. 

The efficiency of a forward kneading and plastification section depends greatly on the operating conditions of the extruder. The elements in this section may only be partially full, and entrained gas can therefore pass downstream which increases the risk for the polymer to not melt completely (Fig. 11.6). 

Figure 11.6 Plastification section without backward conveying element...

Comparison of test data with computational results for the plastification section... 

Liquid additives are mostly added downstream of the plastification section because they tend to lubricate the pellets or cause powders to agglomerate in the feed throat. If a significant amount of liquid is to be incorporated, it can be added at several locations. The most effective method for low viscosity liquid incorporation is to inject into a fully filled distributive mixing section. This requires a pressure injection valve and positive displacement pump. For small amounts of compatible liquid, non-pressurized injection into a low degree of fill area of the screw configuration may also be acceptable. 

The processing zones in the extruder are the solid zone - feed section, transformation or plastification zone, the pumping or metering section (screw) and the mold. Feeding in the solid zone is the main determinant of machine output. 

The basic margarine processing steps are emulsification (see also Section 5.7.2c) crystallization of the solid part of the fat phase plastification of the crystallized emulsion. 

In the past (see Section 5.7.1), these operations were carried out separately. In the multitube-cooler plants (votator process) almost exclusively used now, they are performed more or less simultaneously, although there are slight differences. Emulsification is concentrated in the first part and plastification in the last part of the line. 

An injection molding machine (Fig. 7.1) can be divided into six components plastification/injection section, clamping unit, mold including the runner system, control system, and tempering devices for the mold. The most important part of the process is the mold, which is made of at least two parts to allow ejection (demolding) of the molded part. The injection molding process can be divided into six steps. Table 7.1 presents the main function of each step. 

Plastification phenomena at higher temperature (150 C) described above for pure vernonia oil have been observed here for vernonia B-staged materials as well, if the solubility parameters of the epoxy matrix and vernonia rubbery phase are similar. Such formulations are based on less polar diamines for example, the mixture of epoxy resin, DAPM, and vernonia B-staged material. The plastification in this case has been avoided by a two-step curing procedure (see the experimental section). The general rule is to carry out the epoxy resin cure at a lower temperature and build the rigid matrix, then to increase the temperature and cure the less reactive vernonia epoxy groups with the excess of diamine into rubbery particles and simultaneously post-cure the matrix. 

Plastification phenomena, however, are not observed for formulations based on more polar diamines (than DAPM), for instance, DDS. In this case, the solubility parameters of the "polar" epoxy matrix and "nonpolar" vernonia phase are quite different. DDS based formulations, therefore, do not require a two-step curing procedure in order to build the molecular weight of the matrix at lower temperature. They form two-phase thermosets directly at 150 C (see Experimental section). 

The gradual plastification of a composite cross section can be described using the concept of fiber section model, similarly to the modeling of the concrete slabs in section Introduction. The fiber model is presented in Fig. 24. The concept behind this model is rather simple the cross-sectional area of the SCC element is subdivided into fibers represented by their area, Ai, and coordinate location (yi Zi - with origin the centroid of the section). Different material properties (e.g., concrete confined and unconfined, steel, reinforced steel) can be assigned to each of the fibers. Based on the relevant constitutive material... 

The Processing of renewable resources using a short single screw exrtruder with a combined section for solid conveying and plastification, ANTEC 2000, May 7.-11., P. 292-296... 

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