Today we will cover a couple common tablet defects that may occur during tablet ejection and how to troubleshoot these issues.  Since capping has been previously addressed, we’ll talk specifically about edge chipping and tablet splitting.

Edge chipping (loss of material to the tablet along an edge) can be considered a tablet defect from visual examination or by friability testing.  It is crucial to identify where exactly the edge chipping is occurring.  Is it between the tablet sideband the top face of the tablet, the bottom face, or both.

For edge chipping across the top edge of the tablet, a close examination of the press setup is helpful:

• Tablet take-off bar may be too high off the die table (this is the most common issue).
• Tablet take-off bar may also be incorrectly positioned about the die bore, where tablets first make contact with the end of the take-off bar.
• For small tablets, the take-off bar position can sometimes be adjusted closer in toward the die center.
• For thin tablets, take-off can be jerky with excessive upper punch penetration.
• Tablet take-off orientation angularly may not properly match tablet geometry and orientation. Generally, you want the tablet’s long axis to be parallel to the tablet take-off blade or within 5°.

For edge chipping across the bottom edge of the tablet, there are other places to look for a root cause:

• Lower punch position at tablet take-off is not flush with the top of the die table (this is the most common issue). It is important to note that all die tables lift and fall a bit as they rotate, so setting a lower punch ejection height should be done when the die table is rotated to present its lowest position.  Also, punches vary slightly in their overall length, so it can be helpful to use the shortest punch in the set for setting a lower punch ejection height when addressing edge-chipping problems.
• The tablet discharge chute may not be flush with the die table. If it protrudes above the die table, then tablet edge chipping may occur on the lower face.

For edge chipping across both edges of the tablet, the root cause is most often low tablet tensile strength.

• Increase tablet hardness to improve tablet tensile strength if possible.
• Reduce the press speed to provide gentler tablet ejection.
• Taper die bores to reduce ejection pressure and tablet stress.

Tablet Splitting during ejection most commonly occurs with tablets that have protruding bisects and/or indents (side scores). 

• Revise tablet design to increase the effective cross-sectional area of the tablet at splitting. This may include changes to the tablet’s size and shape for improved proportions.  Please contact your tooling supplier for assistance in tablet design.
• Increase tablet hardness to improve tablet tensile strength if possible.
• Formulation changes may be needed to improve tablet tensile strength.
• A reduction in press speed may be needed in cases where the formulation and/or tablet design cannot be changed.

For more information or help, please contact us at Natoli Engineering.