Compounding extruder

Bulk molding compound BMC is also called dough molding compound (DMC). It is a molding compound (extruded log form) that is not produced in sheet form. It consists... 

During extrusion, the blend components are fed into the feed throat of the extruder. Compounding extruders are starve fed. This means that material is conveyed away from the feed throat more rapidly than the raw materials are fed into the barrel. Therefore the volume of raw material introduced is always less than the total available volume of the flights... 

Tread-type rubber compound extruded in a variety of thicknesses and widths for use in tyre retreading. The standard section is in the shape of a regular trapezium, but variations are made to suit particular types of tyre and different makes of moulding equipment. 

Output, which depends on the extruded compound. For example, for given compounds extruded with a given extruder, the linked outputs (base 100 for PVC) can roughly be... 

Fig. 25. Ko-kneader intensive compounding extruder [Courtesy Buss. AG] (a) Schematic diagrams of slotted screw and barrel pins, (b) ko-kneader with barrel in open position...

In the manufacture of cellulose ester plastic, the appropriate ester is blended with plasticizer and other additives, such as stabilizers, ultraviolet inhibitors, dyes, and pigments, commonly in a large sigma-blade mixer. The mixture thus obtained is heated to its softening temperature and kneaded until it is homogeneous. This is done on hot milling rolls, in a compounding extruder, or in a Banbury mixer. The molten mass of plastic that results is formed into small rods or strips that are then cut into cylindrical or cubical pellets, which ordinarily have dimensions of about J inch (3 millimeters). See Fig. 2. 

Tasks and Design of the Processing Zones of a Compounding Extruder... 

In all cases to give the best results additives must be dispersed well and to this end, melt-mixing by means of a compounding extruder can be very helpful— giving continuous output typically in the form of rods that can be cut subsequently to form pellets of regular size. However, in some instances lower levels of dispersion can be tolerated, in order perhaps to reduce costs or to give flexibility in operations. 

The efficiency of compounding extruders may be enhanced in a number of ways, and twin-screw units are designed also for special purposes. Mixing elements in a variety of forms (reversed flights, kneading discs, pins, etc.) may... 

Fig. 5 Schematic diagram of a twin-screw compounding extruder. (From Ref. f)...

Miyagawa, Y. Sato, H. Okabe, T. Nishiyama, T. Miyajima, M. Sunada, H. In vivo performance of wax matrix granules prepared by a twin-screw compounding extruder. Drug Dev. Ind. Pharm. 1999, 25, 429-435. 

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