When it comes to R&D, it is critical as part of product development to predict what will happen when scaling up to Production.  Speed is commonly measured in RPM and tablet output, and yet the factors that limit how fast you produce good tablets (dwell time and time under the feeder) will vary from press to press due to differences in machine size – specifically, their pitch circle diameter and feeder length.

So, let’s take a closer look at R&D rotary tablet presses to see what they can or cannot do to predict scale-up.challenges.

Tangential punch velocity (TV) is a better measure of press speed since it can be normalized for a true comparison between presses.  It is how fast the punch travels around the cam track and can be found by the formula:  , where:

• TV = Tangential punch velocity (mm / second)
• RPM = Turret Revolutions per Minute
• PCD = Turret Pitch Circle Diameter (mm)
• π = 3.14159

This formula shows that size matters when it comes to tablet presses.  The bigger your rotary press, the faster the punches will move given a certain RPM.  R&D rotary presses can therefore struggle to achieve high enough tangential punch velocity to match what will happen later in a larger production press.

To illustrate, I’ve listed the Natoli presses and their top speeds in a table below.

R&D presses with PCD smaller than ~ 200mm may not be able to reach 1000mm/sec TV and so may not reproduce what will happen in a typical Production environment.  One way to compensate in part for a small turret in your R&D press is to increase the RPM.  However, there can be a practical limit to how fast you can raise the RPM while maintaining adequate powder flow.  Another way to match R&D to production parameters is by customizing the punch head flat size to equalize dwell times.   

For more information or help on your Scale-Up challenges, don’t hesitate to contact us at Natoli Engineering.