Mechanical Conveying in Pharmaceutical Production

A screw conveyor is an efficient way to move powder and an expensive way to extend a cleaning validation. It adds a trough, a flight, two end bearings, a shaft seal at each end and a set of crevices where the flight meets the shaft, and every one of those has to be reached by the cleaning method and shown clean to a defined limit.

That is the real cost, and it is not in the purchase price. A machine that saves an hour of transfer time and adds a day to every changeover is a poor exchange in a plant whose constraint is changeover rather than capacity.

Containment is the second constraint. A conveyor has a shaft penetrating its enclosure, and a shaft seal on a potent compound is a containment component that needs a performance figure. Opening the machine for cleaning exposes everything it has touched.

Product damage is the third. Granules and tablets are damaged by flights and by the gap at the end of a trough, and a conveyor chosen for rate can turn a good granulation into one with a different particle size distribution.

Mechanical transfer used only where a closed alternative genuinely cannot do the job, with that comparison documented rather than assumed.

Where it is used: crevice free, fully drainable, dismantled without tools, with bearings and drives outside the product space and seals specified for the cleaning regime as well as for the dust.

A containment performance figure for the shaft penetrations, and a product damage assessment for anything granular.

For plastics processing gentleness is chosen and then undone by speed, because a mechanical transfer run fast enough makes the streamers it was bought to avoid.

The first step is the comparison. Vacuum transfer moves powder through a tube with no moving part in the product path, discharges through a valve, and has a product contact surface that is a smooth pipe. For most pharmaceutical duties it is both the cleaner and the cheaper answer once validation effort is counted, which is why it has displaced mechanical transfer in so many plants.

Where mechanical transfer wins, usually on a cohesive material, a tablet or a granule that cannot be sucked, the design is driven by dismantling. Tool free end plates, a flight that lifts out, seals that come away by hand and a trough with no internal ledge or weld crevice.

Bearings and drives sit outside the product space without exception, and the shaft seal is specified twice: once for containment performance against the compound, once for compatibility with the cleaning agent, which is usually the harsher of the two.

Finally the machine is documented for qualification: materials, surface finish, containment figure, cleaning method, swab points and the reassembly procedure that makes the cleaning repeatable.

• Closed vacuum transfer evaluated first and the comparison documented.
• Crevice free, fully drainable construction that dismantles without tools.
• Bearings and drives outside the product space in all cases.
• Shaft seals specified for containment performance and for the cleaning agent.
• Product damage assessed for granules and tablets before the conveyor is selected.
• Materials, cleaning method, swab points and reassembly procedure documented for qualification.

• Cleaning validation approach and every surface it has to reach, which is the dominant cost of a mechanical machine here.
• Containment band of the compound and the shaft seal performance that follows.
• Product fragility, especially for granules and tablets.
• Whether a closed transfer can do the same job, which it usually can.
• Documentation required for qualification, including reassembly.
• Changeover frequency, since that is what multiplies the cleaning cost.