Most crammer augers use a standard flight pitch, as that usually provides the best overall results, unless there is actual data available on other helix angles for that particular material. Since the auger is operating vertically downward, the rate typically meets or exceeds the rates noted for tubular screw conveyors that are based on no elevation change. Naturally some margin for error must be allowed, as there are no exact formulas and no exact measurements of the materials’ characteristics. It estimates the screw speed and horsepower needed How Hopper Crammers Can Help Feeding to feed some materials, allowing you to specify the auger and drive system. Kase Conveyors has a handy screw guide on its website that I have found useful. That is always an unknown and is based almost entirely on experience. But they do not provide for compaction of very low-bulk-density materials. To design the auger there are helpful tables of tubular screw-conveyor data on the internet that take into account similar material characteristics. With that data you can size the hopper for adequate capacity to service the extruder’s desired output and start to develop the crammer design.

Bulk density can be measured by simply filling a calibrated container and weighing it.

Bridging is related to both the angle of repose and the packing. Packing can be estimated by putting a cup-full into a plastic bag and squeezing it. The free-flowing characteristics can usually be estimated by the angle of repose and by passing the material through a large funnel. The goal of a properly designed crammer is to deliver material to the extruder screw uniformly without generating much temperature rise or excessive pressure.

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