Z-Max

One of the great improvements to rotary tablet presses was the incorporation of turret punch guide seals.? These seals between the punch turret guides and the punch barrel help keep lubricating oil from dripping down onto tablets and help keep formulation dust from getting up into the guides and onto pressure rolls causing binding and tool damage.? These seals only work when the punch barrel maintains contact with seals throughout the punch’s vertical movement through the cams.? The maximum stem length (a.k.a. Z-Max value) establishes the allowable punch stem’s length that can safely be used for a particular tablet press.? The Z-Max depends on the tablet press make and model.

For example, Natoli tablet presses have the following restrictions on Z-Max:

Some things to keep in mind:

· Larger Z-max values for a tablet press indicate more flexibility in what can be done with the design of the tooling to accommodate upper punch penetration, tamping, or placement of bellows / dust cup relief.

· Tools that will be used for more than 1 tablet press should be designed to accommodate all the intended machines.? For Z-max, that means using the smallest Z-max value.

· Bilayer products pose a special challenge for Z-max in that tamping depths may preclude use of a standard dust cup relief or a standard barrel-to-tip transition.? Knowing the tamping depth and intended press is critical to success.

If your tablet press doesn’t have turret punch guide seals, then Z-max values are not applicable.? That said, seals are a wonderful thing to have in a tablet press, often giving you substantially longer run times.? Nearly any rotary press can be retrofitted to have guide seals. Natoli Engineering offers retrofits including snap-in soft seals at reasonable prices.? For more information, contact Natoli Engineering.

Todd Martin

Sr. Technical Service Engineer