Roller compaction screw feed system

The compaction system consists of two, counter-rotating rolls at equivalent speeds. One roll is normally fixed while the other is allowed to float. The floating roll was implemented to control the roll gap. The roll force is applied to the floating roll by hydraulic pressure, which is counteracted by the normal force of the fixed rolls. This force is subsequently applied to the blend in the gap. A schematic of three typical roller compaction system arrangements with a feed screw can be found in Fig. 6.1. 

As a dry granulation technique, roller compaction has to be considered as a simple continuous process able to convert powder into granules (Fig. 6). The system comprises powder hoppers, feeding screws, a roller press, a mill, and, optionally, a recycling unit. 

In several experiments, Miller studied the effects of using horizontal twin auger feed screws under partial vacuum (Alexanderwerk Inc., Horsham, Pennsylvania, model 50/75 compactor). The feed powder was vacuum deaerated just before roller compaction. The experimental design showed that the compactor s deaeration feed system significantly increased compaction output and minimized powder leakage when compacting very low density blends (<0.35 gcm ). ... 

Fig. 6.2-63 Pharmaceutical compaction/ granulation system with vertical roller arrangement, horizontal feed screw, and granulation by two-stage milling (courtesy Alexanderwerk, Remscheid, Germany)...

A history of hopper and feed screw designs showed that each design evolved to facilitate and improve powder flow to the compactor feed screw conveyance system. Feed hopper designs shown in Roller Compaction Technology for the Pharmaceutical Industry depict designs used in older compactor models (23). Dehont et al. described the powder compaction feeding systems that were in use up to 1989 (24). 

Another modular system is often called laboratory equipment it can be used for small scale production and for the laboratory evaluation of small samples. Fig. 11.26 depicts the design and some of the accessories. In the most simple execution a hopper feeds a pair of rollers which are driven by a hand crank. The rollers can be solid and may be equipped with compacting or briquetting surfaces (see Section 8.4.3) or two perforated, geared, intermeshing pelleting rolls (see Section 8.4.2) are installed to accomplish medium pressure extrusion. In a modular fashion the rollers can be motorized, screw feeders can be added, and the rolls may be oriented vertical or horizontal or in any other direction. As shown in the photographs of Fig. 11.27 the roller frame can be totally enclosed for dust control if toxic or hazardous materials are processed. A panel includes controls and instrumentation for data display and collection. 

---