Round Tablet Compression Tooling - To Key or Not to Key the Punches

Keys for tablet punches traditionally are used on shaped upper punches to prevent the upper punch from rotating when it is not engaged with the die. This guarantees the upper punch tips will maintain alignment with the die bore. Round tooling (tablet tools for making round tablets) may also be keyed for special circumstances. Let’s delve into these situations.?

Double Impressions?

Unkeyed round punches rotate in the direction of turret rotation during the compression cycle. Rotation between pre-compression and main compression during tablet production may result in double impressions. A round tablet with a logo or a bisect, any punch rotation between pre-compression and main compression can form two separate impressions, misaligned with one another on the tablet's face.?

Well-fitting turret guide seals/brakes can potentially serve as anti-turning devices to prevent round lower punch rotation between pre and main. In other cases, it may be necessary to key round punches to prevent double impressions.??

Round Multi-tip upper punches?

While multi-tip tooling is often configured to make round tablets, the upper punches always need to be keyed even though the tablets being produced are round. This is because multiple punch tips need to stay aligned in their bore circle pattern to the die bores.?

Round Multi-tip lower punches for Micro-tablets?

When producing micro-tablets (4mm or smaller), the lower punch tips can experience substantial torque during compression. This torque can lead to tip bending or buckling due to their small diameters. A rotating head option can alleviate this torque.

Upper & lower Bisects Alignment?

In cases where a round tablet design has a bisect on the upper face and on the lower face, these bisects need to be aligned with one another. In this situation, both upper and lower punches need to be keyed. In rare circumstances, it is desirable for logos on the upper punches to be aligned with logos on the lower punches. Again, keying both the upper and lower punches is required.?

Press Requirements?

While the great majority of rotary tablet presses have punch guide keyways to allow the use of keyed upper punches, this is not true for lower punches. Before selecting a keyed lower punch, it is advisable to confirm your tablet press has lower punch guide keyways.?

Once confirmation that the press can accommodate keyed lowers, the key location for the lower punch must be determined, as the location of a lower punch key is different from the upper punch key location. Contact your press OEM or tooling supplier for details.?Natoli is here to help and answer any questions, 636-926-8900.

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