Extrusion ribbon

In many cases supports are shaped into simple cylinders (1-5 mm in diameter and 10-20 mm in length) in an extrusion process. The support powder is mixed with binders and water to form a paste that is forced through small holes of the desired size and shape. The paste should be sufficiently stiff such that the ribbon of extmded material maintains its shape during drying and shrinking. When dried, the material is cut or broken into pieces of the desired length. Extrusion is also applied to make ceramic monoliths such as those used in automotive exhaust catalysts and in DeNOx reactors. 

The dispersibility of an organic pigment which is to be incorporated in a polyolefin is of particular importance. This is especially true for the coloration of extrusion films and for HDPE or PP ribbon made from stretched blown film or from sheeted extrusion film, as well as for the coating or melt spin dyeing. 

The alloys are first produced by rapid solidification and are amorphous in nature. They are either directly fabricated as powders, by a process such as high-pressure gas atomisation (HPGA), or by melt-spinning of ribbons, which are subsequently pulverised to form a powder (<150 /im). The powders are then consolidated by hot extrusion between 950-1050°C where the initial amorphous structure breaks down and forms a fine dispersion of stable borides in a ductile Fe-based matrix. 

PF had been proposed as the terminal complex (23) and associated pores were reported on the outer membrane EF (24). Due to their proximity to the site of cellulose ribbon extrusion from the cell surface, these structures were assumed to be responsible for cellulose synthesis. A model was advanced in which cellulose synthase was localized on the outer membrane, which invoked adhesion sites between the outer and plasma membranes as a mechanism to explain the transfer of uridine-diphosphoryl-glucose (UDPG) from the cytoplasm to the cellulose synthases (25,26). However, when the outer and plasma membranes of Acetobacter were isolated separately by density-gradient centrifugation, the cellulose synthase activity was localized only in the plasma membrane fraction (27). Therefore, the linear structures observed on the Acetobacter outer membrane, while they may be associated in some manner with cellulose biosynthesis, are probably not the cellulose synthase terminal complexes. Since no ultrastructural evidence for adhesion sites between the outer and plasma membranes has been presented, a thorough investigation of the mechanism of / (1-4) glucan chain translocation from the cytoplasmic membrane to the outer membrane in Acetobacter xylinvm is now in order. 

Rubbers are also being extruded, in a not essentially different way from plastics. Cooling of the extrusion cylinder is necessary to prevent premature vulcanisation as a result of the heat developed by internal friction. The extruder is fed by ribbons, obtained from milled sheets. End products are hoses, profiles, and cable mantles. On-line vulcanisation can be achieved by passing the extrudate through a steam channel, while the rate of extrusion is adjusted to the rate of curing. For this purpose high-rate vulcanisation recipes have been developed. Steam temperatures of about 200 °C are being applied (15 bars pressure). Treads for motorcar tyres are also extruded they are wrapped round the pre-formed carcass and then formed and vulcanised in a press. 

Fig. I.—Proposed Model of Cellulose Assembly in Acetobacter xylinum. [d-GIu-can chain aggregates from organized, multiple-enzyme complexes, and extrusion pores crystallize into microfibrils, which then assemble into bundles and the normal ribbon at the cell surface.]...

USP 2780997 (1957) 8t CA 51, 7014 (1957) (Manuf of colloidal proplnts by creating NC with acetone, followed by incorporating NG, nitrate salts, etc. The resulting gelatinous mass is extruded at high sheer from a die in the form of a sheet, ribbon, filament, etc and then the material is dried while being maintained under tension along the line of extrusion) J)A.Kraus,... 

Once the centres are cooled to 30-35°C they are deposited or extmded in a number of layers. Extrusion is made by screw or roll type extruders. The rope or ribbon is cut after cooling to the required size and coated generally with a tempered chocolate paste. 

The unsintered tape is not directly produced in the final thickness and width. Rather, it is made by the extrusion of either a round or rectangular bead (thick ribbon) followed by calendaring which converts it to a thin tape. Calendaring is necessary to obtain tapes that are thin enough to be conformable to the pipe threads. Normally, the lower limit of thickness is 50-75 pm, but 25 pm thick tape can be made by calendaring. The important properties of electri-... 

Molecular weight can be controlled by addition of a small amount of monobasic acid. This polyamide melts at 265°C and is highly czystaUine. The polymer can be run directly to spinning machines to produce fiber, or it can be extruded as a heavy ribbon which is chilled and chipped. The pol3uner may be remelted to spin into fiber, or it may be used for extrusion of molded objects, or it can be made into molding powders. 

In some cases, it may be more convenient to meter lithium to a reaction as a measured length of rod, wire, and ribbon. Because of the softness of the metal, these operations are simple to perform. In laboratory tests a die chamber 3.75 inches in diameter was fitted with orifices ranging from 0.125 to 0.5 inch in diameter. Extrusions were run at 32° and 100°C. Pressures required to cause a flow of... 

This chapter includes, first, a general description of blown film and ribbon extrusion, including the most important parameters that need to be controlled. In... 

On the other hand, the ribbon extrusion process consists of the following steps extrusion of a polymer melt through a small rectangular die, stretching, and cooling with air or water. Depending on the cooling distance, nonisothermal or isothermal conditions can be considered. 

The ribbon extrusion process is studied using the following assumptions steady state, incompressible flow, the velocity component in the stretching direction is the only function of this direction, each cross section remains... 

Figure 24.2 Schematic representation of the ribbon extrusion process.

The physical and mathematical description of the ribbon extrusion process was first given by Pearson [24], who simplified the conservation equations by using a onedimensional, isothermal, Newtonian fluid approach, and neglected the effects of polymer solidification. As in the case of blown film processes, several modifications and models have been proposed for the ribbon extrusion process (Table 24.2). 

Considering the assumptions previously mentioned for the study of ribbon extrusion and the fact that the flow is mostly elongational, which means that the shear components are neglected, the velocity gradient (e) and the volumetric flow rate Q) are given by the following equations ... 

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