Problem: Extremely fine and low weight materials present difficulties in feeding to compaction rolls in a typical roll press. In the most severe cases, densification is not possible. In other cases, the capacity of a given machine is limited, typically to a fraction of what would normally be achieved for a given roll press. At the same time, poor flowability of the fine light powders results in erratic feeding which yields inconsistent product quality.
One commercial example called for the densification of a fine light powder with a current bulk density of 0.05 to 0.08 kilograms per liter to a final bulk density of 0.25 kilograms per liter. Along with the density requirement, it is important that the final product be dispersible in the current application. In other words, it could not be over-pressed. Typical deaeration devices could not achieve the degree of densification required.
Solution: Implement a quality manufacturing process with the goal of improving product quality. In this example, Bepex created a special compactor feeding device, employing forced removal of air from the product was developed. In the simplest form, a conventional compactor feeder hopper was fitted with pads that exposed the processed material to porous membranes. The chambers around the membranes were connected to a high pressure blower or vacuum pump, to forcibly remove air from the product. In order to insure that the porous membranes remain clear, mechanical sweeping or reverse pulse cleaning is employed.
More complicated industrial process systems employ a combination of feed screws, as example, slow turning horizontal screws feeding vertical screws to deliver material to the compacting rollers. The multi screw feeders allow for installation of larger settling bins, but even in these cases, a vacuum assist on the screw chambers is required.
Benefits and Results:
Numerous materials have been processed in the Bepex Process Development Center as well as in commercial settings in order to test and improve manufacturing quality. Materials range from spray dried food products to ultra fine ground minerals. In all cases, the vacuum systems allow the compactor feed system to overcome their inability to fully grab and deliver the proper amount of material to the compaction rolls.
A single vacuum assist feeder can eliminate the need for separate predensifying devices, such as vacuum drums, vacuum screws or bin live bottoms. Besides the advantage of consistent product resulting from consistent feeding to the compacting rollers, typical increases in capacity seen range from 20 to 150%.
In the referenced example of quality improvement in manufacturing, a specially designed vacuum assisted feeder allowed for consistent delivery of material at the required final bulk density and hardness at rates in excess of 3 tons per hour.