Vacuum deaeration equipment design

Study determined the compact throughput, compact density, and fines (not compacted during vacuum deaeration) when using a new equipment feed system design. The parameters controlled and monitored during the compaction process were vacuum deaeration pressure, roll pressure, roll and screw speeds, room temperature, and humidity. 

The equipment feed design consisted of a funnel-shaped powder hopper (with no vacuum deaeration system) that was located directly above the rolls. The powder hopper was retrofitted with vacuum deaeration capability. A high compression feed screw, fitted inside the funnel hopper, fed the powder directly into knurled rolls. The compaction trials were conducted with and without vacuum deaeration. The compact was carefully collected directly on a 10-mesh screen. Powder particles, that were not compacted (i.e., those particles which were not attached to the compact, for example, fines bypassing roll compaction and the non-adhering compacted powder particles) were weighed and separated. The compact was not milled. The parameters are noted in Table 4. 

The conclusions drawn from this trial indicated vacuum deaeration, employed in the described equipment design, increased the compaction rate, reduced the fines (non-compacted powder), and increased the compact density (R.W. Miller, unpublished notes, June 1996). 

Other designs apply vacuum deaeration in a screw feeder or in the hopper of a force feeder arrangement to improve the effect of standard feeders. Similar results can be obtained with equipment called Vacu-Press it consists of two counter-rotating rolls of which one is hollow, perforated, covered with filter cloth, and evacuated. Material is slightly densified in the nip and deaerated under the influence of vacuum. 

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. ... 

Miller s experiments evaluated the effects of powder density screw feed speed, roll speed, roll pressure, vacuum deaeration pressure, compaction rate, and the compaction leakage rate. Test results demonstrated that the first compactor s deaeration and feed system designs significantly increased compaction output. The new equip-... 

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