Tablet Press Operation: 6 Factors to Affect Tablet Quality

Tablet press is one of the most complex machines used in pharmaceutical manufacturing environment. Making a clear definition of the basic principles in tablet press operation is essential to having a successful run. Learning key factors can absolutely avoid many obstacles that may interrupt a smooth run.

The main issues in making a tablet are tablet weight, hardness, thickness, friability, content uniformity, appearance, etc. There are 6 points to check and control tablet quality.

► Weight Control

Tablet weight is determined by a volume of granulation filled consistently into the die cavity. A tablet press machine does not preweigh the granulation, but control the weight by the way that remove excess granulation out of the die cavity after overfilling, and push the excess materials into a channel that prevents the materials going back.

Weight variation is a common tablet failure which usually develops in the course of compression. What affect the filling volume of granulation are the related filling components, like feeder, hopper, the property of granules, and the adjustment of the punches and dies. Only the feeder and hopper are set at proper positions, the punch tooling are well adjusted, and the materials are with good fluidity, the weight variation can be least reduced.

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 Thickness Control

Thickness is the result of filling amount of granulation and the compaction pressure. On the assumption that filling amount of granulation is settled, the weight of tablets is constant, but the compaction pressure is the main factor to affect tablet thickness. The more pressure works on, the thinner the tablets will be with consistent weight.

 Hardness Control

Speaking of hardness, never try to solve the hardness issues without having consistent weight first. Certainly, the pills can be harder when more pressure the punches work on with the uniform filling depth on premise.

 Dwell Time

Dwell time of tablet manufacture is the amount of time each individual punch head flat is in contact with compression roller of a rotary tablet press. Defect tablets are formed due to more or less dwell time involved, or excessive or insufficient pressure exerted. As a result, the dwell time relates to punch head flat and press speed.

 Punch Tooling/Tab Tooling Condition

Punch length: Punches should be checked regularly after each cleaning to ensure that they are well maintained and kept in good condition. New punches are manufactured to be ±0.001 in variation. Worm dimensions depend completely on the end product. Some companies allow for a length variation of ±0.004 in, which is extreme.

Die condition: die condition can influence tablet hardness and appearance. As a tablet is compressed, radial forces will create compression rings within the die. Compressing a tablet in a worn die may give rise to capping and chipping. Additionally, tablet band(sides) can not be hard, smooth, and glossy.


 Punch Penetration

Upper punch penetration is how far the upper punch enter the dies. Old presses have a nonadjustable upper-punch penetration set at 6mm, while the new and modern machines have adjustable punch penetration. The air has a long way to escape if the upper punch enters the die at 6mm. Making the tablet higher in the die allows the air to evacuate sooner, better control of consistent hardness, and higher press speed.

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