Pre-compression Pressure Rolls Optimizing Compaction Time

This week’s Tech Tip is all about optimizing your press setup to reduce tablet defects by exploring the geometric relationships between punch heads, pressure rolls, and your punch penetration setting.? Capping, low hardness, and poor friability are all tablet defects that can occur from inadequate tamping during pre-compression.? Tamping may be enhanced by prolonging compaction time (the total time in milliseconds that the pressure roll is in contact with the punch head).? Let’s learn more about them.

The equation for compaction time can be expressed as:

For example, the Natoli RD30 is an R&D rotary press with a pre-compression roller diameter of 125mm and a pitch circle diameter of 200mm.? Using a TSM domed “B” punch (9.53mm head flat diameter and 15.88mm outside head radius, a punch penetration setting of 3mm, and a press speed of 50RPM, the Compaction Time is:

This example has a result of 59.22 milliseconds.? These values can be helpful for SUPAC since you can compare values between running an R&D and production machine.? Knowing the relationships can be helpful.

What this can teach us is that some of these inputs will increase compaction time while others reduce it.? Things that increase compaction time include:

· Punch head flat size – larger head flats increase compaction time.

· Punch head outside head radius – larger outside head radii increase compaction time.

·?Pressure Roll size – larger pressure rolls give you longer compaction time.

· Punch Penetration – deeper punch penetration increases compaction time, though there is a trade-off with air escape since air must travel further to exit the cavity with deeper penetration settings.

Conversely, larger PCD values will result in smaller compaction times.? Note that compaction time is different than dwell time as dwell only counts time under maximum compression (when the pressure roll is in contact with the punch head flat).? When it comes to pre-compression, compaction time is of greater importance than dwell time.

For help in evaluating press settings or optimizing your parameters, please contact Natoli Engineering.

Todd Martin

Sr. Technical Service Engineer