Roller compactor feed screw designs

Fig. 12 Roller compaction compacts. Roller compactor feed screw designs twin feed screw and single feed screw. (Courtesy of R. W. Miller, personal files.)...

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). 

Certainly, a key enhancement that highlights today s pharmaceutical industry s state-of-the-art roller compactors, is programmable logic controllers (PLCs). They are used to control and monitor mechanical parts that regulate screw feed rate, roll speed, roll pressure, roll gap, vacuum deaeration, and mill speed. This section will not discuss PLC designs as it relates to compactor design features and advancements. 

Irmovatively designed feed screw systems are used commercially in roller compactors worldwide. An example is shown in Fig.6. 

Currently, one manufacturer of roller compactor equipment for the pharmaceutical industry has a fixed roll-pair system. This type of roll design system relies on powder gravity feed and a specially designed compression feed screw to continuously deliver powder feed stock to the fixed roll pair. Fig. 10. 

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 ). ... 

The Alexanderwerk Inc. roller compactor (Fig. 18) is modular designed with a horizontal twin feed screw... 

The Fitzpatrick Co. roller compactor (Fig. 20) features two feed screws in series one horizontal and the second vertical. This system is designed to transfer powder bulk into a set of cantilevered rolls positioned in the horizontal mode one is fixed, the other floats. Operator interface allows for on-line monitoring and controlling feed screw speeds, roll pressure, and roll gap. Features such as on-line help and diagnostic functions, maintenance, and calibration screens are displayed. All functions are interfaced and adjustable by PLC for process control and report generating. The machines have vacuum deaeration and roll cooling capabilities. The sizing unit is separate from the compactor and is either a rotor bar or a hammer mill. 

The newly designed equipment involved a compactor fitted with two horizontal feed screws, which featured vacuum deaeration. Specifically, the roller compactor was equipped with a conical storage hopper containing a variable speed agitator. Bulk powder was fed directly from the top of the hopper to the top of twin horizontal auger feed screws, which directly transported the powder to the nip roll area (13). Top and side views of the design features are shown in Figure 17. ... 

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