Roll press control

Fig. 5.4. Feed hopper with adjustable tongue for flow control of smoothly-flowing materials to roll presses. (Courtesy Vulcan-Koppern, Inc.)...

Sheskey, P.J. Hendren, J. The effects of roll compaction equipment variables, granulation technique, and HPMC polymer level on a controlled-release matrix model drug formulation. Pharm. Technol. 1999, 23 (3), 90-106. Johanson, J.R. Roll Press Feed Systems. Proceedings of the 24th Institute for Briquetting and Agglomeration, October 1995 Vol. 24, 149-163. 

Stress transmission in powders controls flow out of hoppers, feeders, filling of tubes, and compaction problems such as tableting and roll pressing. (See Powder Compaction. )... 

Roll presses provide a mechanical advantage in amplifying the feed pressure Fo to some maximum value F . This maximum pressure Pjn and the roll compaction time control compact density. Generally speaking, as compaction time decreases (e.g., by increasing roll speed), the minimum necessary pressure for quality compacts increases. There may be an upper limit of pressure as well for friable materials or elastic materials prone to delamination. 

Wet mass rheology heavily impacts performance through controlling both developed pressures and extrusion through the die, as in the case of paste extrusion (see Paste Extrusion and Screw and Other Paste Extruders subsections). In addition, the developed pressure in the roller nips behaves in a similar fashion to roll presses (see Roll Presses subsection). 

Membrane Fabrication, Lamination and Reinforcement. The thermoplastic copolymer of TFE and PVEX monomer can be extruded or molded into a thin film by conventional methods. Extrusion is most appropriate for continuous production of large membranes because it facilitates control of film thickness. Lamination can be performed with a roll press to obtain multilayer membrane. To improve their mechanical properties, membranes are generally reinforced with an inert material such as fabric made of PTFE (67, 68), fibriled PTFE (69), or wire netting (70). 

Double-roll presses and rotary table presses are available for briquetting bituminous coal. Different processes for controlling the briquetting process were derived by development of methods for measuring pressing pressure with double-roll presses. Normally double-roll presses have a roll diameter between 24 and 60 in. (600-1500 mm) and the compression ratio does not usually exceed 2.5 1. In general, the compression time for the briquette form is less than 0.05. 

These microlevel processes of compaction control the final flaw and density distribution throughout the compact, whether it is a roll pressed, extruded, or tab-leted product, and as such, control compact strength, hardness, and dissolution behavior. Compaction processes will not be discussed further here, with the remainder of the chapter focusing on wet granulation, agitative processes. For further discussion regarding compaction, see Chapter 6 and Refs. 1, 2, and 10. 

Roll coating utilizes a patterned roll, which is partially immersed in a reservoir of heated adhesive and transferred directly to the web material. Metering blades, similar to the principle of doctor blades used in flexographic printing, are pressed against a patterned roll to control coating thickness prior to transfer. Extrusion slot... 

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