Sterile solids are more difficult to subdivide accurately and precisely into individual dose containers than are liquids. The rate of flow of the solid materials tends to be slow and irregular, particularly if the powder is finally divided. Small granular particles flow most evenly. Uniform particle size and good flow properties of solids are necessary for uniform and effective filling by machines. For powder showing poor flow, the containers with a relatively large opening must be used, even so, the filling rate is slow and the risk of the spillage is ever present. For these reasons, the tolerances permitted for the contents of such containers must be relatively large.
Relatively freely flowing solids are filled using filling machines. One type of machine for delivery of measured quantities of solid material employs an augar in the stem of the funnel-shaped hopper. The size and rotation of the augar can be adjusted to deliver a regulated volume of granular material from the funnel stem into the container.
In another filling machine, a adjustable cavity in the rim of the filling wheel is filled by vacuum as the wheel passes under the hopper. The contents are held by vacuum until the cavity is inserted over the container when a jet of sterile air discharges the solids. This machine also dispenses dry solid that flow less freely.
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