The Benefits Of Tablet Tooling Standardisation

Tooling standardisation in the tablet manufacturing industry is a topic that has concerned tabletting professionals for decades. I Holland, authors of the Eurostandard, the most widely adopted tooling standard globally, have been striving for some time to promote a consensus in this area.

Why was a standard needed?

Conception of the Eurostandard began in the 1970s when conversion from Imperial measurements (inches) to metric measurements (millimetres) first began to take effect, creating a recognised need to reduce variables in tooling specifications/standards set by original equipment manufacturers (OEMs).

As European tablet press manufacturers started to gain ground in the 1980s against UK press manufacturer Manesty's former market domination, German DIN standards began to be applied to tablet tooling. DIN standards were designed for general engineering components, limits and fits, but the clearances created by this system are not always appropriate for tablet tooling. This is because the powder compaction process is very different to typical mechanical processes that benefit from contact lubrication using general engineering components. Therefore, this system did not address the issues that a dedicated tooling standard should have done.

In 1990, I Holland invited prominent tablet press and tooling manufacturers to come together to formulate a dedicated standard. Unfortunately, this received little or no interest from the other parties — possibly due to fears of losing a competitive advantage. Despite this, the first edition of the Eurostandard was developed and published in 1992. By the time the 2nd edition was released in 1996, the Eurostandard had been adopted as the accepted standard for the vast majority of tablet tooling markets outside North America.

Simultaneously, during the midnineties a group of French pharmaceutical companies and tooling manufacturers contacted the International Organisation for Standardisation (ISO), to investigate the possibility of establishing a European standard for tablet tooling. This exercise culminated in the formulation of the internationally acknowledged ISO 18084.2005 (E) for punches and dies.

The author says…

Finding a global standard

Recent calls to combine legacy tooling standards and bring them in line with the internationally recognised ISO standard have become much more widespread. In today's global pharmaceutical market place, where many solid dose companies have manufacturing plants around the world, there are numerous benefits to having only one standard for tablet tooling including:

• interchangeable tooling between tablet presses of different manufacture both in-plant and across different locations worldwide

• reduced tooling inventories; saved costs

• shorter lead times because of tooling supplier rationalisation

• standardised procedures; procurement, operation and maintenance

• standardised equipment and processes for validation and inspection

• uniform quality and grade of tooling across all products/sites

• more international technical exchange for development and problem solving.

Given these benefits, it should come as little surprise that ISO 18084 is coming to be recognised as the right standard for the tablet tooling industry. In fact, there is evidence that the ISO standard is being increasingly adopted among global pharmaceutical companies, for whom the benefits of rationalisation are greatest.

In addition to the Eurostandard and ISO 18084, it should be noted that other tooling standards do exist. For example, North America almost exclusively uses the Tablet Specification Manual (TSM) (formerly IPT) standard.

While punch and die configurations are similar across all standards, there are several critical differences.

Head profile and cam angles

Figure 1 illustrates variations in the profile of the punch head form, which include:

• head radius/angle

• dwell flat

• head thickness

• head length

• under-head (cam) angles.

The ISO/Eurostandard 'domed' head incorporates a radius that blends into the 'dwell flat', which gives a smoother lead onto compression rollers, reducing wear on both tooling and the tablet press. This also ensures sufficient dwell time for optimised granule compaction and allows the tablet manufacturer to produce a quality product. Version 7 of the TSM also recommends that all new punches adopt this domed head shape.

Figure 1: Variations in head profile and nominal punch length.

Variations found between the ISO/Eurostandard and TSM underhead cam angles (Figure 1) result in incompatibility of tooling between European and TSM tablet presses, meaning that interchangeability is restricted and that tooling inventories increase.

Nominal punch length

The nominal (overall) punch reference length is governed by the dimensions of the tablet press turret (Figure 1 shows the differences across standards). This means that a Euro/ISO standard length punch cannot be used in a TSM tablet press and vice versa. Standardisation of overall punch length would ensure compatibility across all tablet presses and reducing the cost of tooling inventory for tablet manufacturers.

Keying angles/turret rotation

All shaped and multitipped upper punches need to be fitted with an antiturn key to ensure correct alignment into the die. The positioning of this key relative to the tablet shape is important on high-speed presses to optimise ejection and take off of the tablet from the press. As a result of the different turret rotations this becomes a challenge. Most modern tablet presses utilise a turret that rotates in an anticlockwise direction (e.g., IMA, Fette, Korsch and Kilian machines), while others rotate clockwise (e.g., Cadmach and Manesty machines). In addition, there are wide variations in keying angles between tablet press manufacturers (Figure 2). These differences in angle and rotation cause problems with the correct presentation of the tablets to the take off plate and in ejection, which can cause tablet breakage. To ensure the correct key position of shaped/multipunches, the set of tools must be specially manufactured to suit the type of machine, which increases costs and potential inventory. Currently, there is no move to create a universal position on keying angles/turret rotation. This will need to be agreed upon and driven by major tablet press manufacturers.

Figure 2: Key angle positions.

Clearances and tolerances

Unlike typical mechanical processes, powder compaction inevitably results in granule coming between the lower punch tip and die bore, resulting in resistance. Consideration should be given to the clearance between such surfaces.

Lower punch tip to die bore clearance

Clearances and tolerances (Figure 3) are critical to ensure accurate functionality of the tooling, and reduce wear of tooling and press components. The clearances between the punch tips and die bores are crucial to ensure good, problemfree tablets and to eliminate problems such as capping (Figure 4). The ISO standard stipulates the use of 'DIN Norm' for tolerances, adopting the same size and clearance for both upper and lower punches irrespective of tablet size. This creates a wider variation in clearance between the lower punch tip and die bore regardless of granule size, which can cause granule leakage past the lower tip and result in potential wear and damage to tooling and press parts.

Figure 3: Punch tip to die bore clearance / tolerance.

Upper punch tip to die bore clearance

ISO adoption of DIN Norm on upper punches also results in insufficient clearance leading to rejected tablets through capping. To counter this, all dies have to be tapered at both ends to enable air to escape from the tablet. This requirement increases tooling costs for the tablet manufacturer.

Figure 4: Capping, the laminar separation of the tablet body or cup. Capping can occur during tablet compaction or any of the other processes up to and including the packaging phase.

The Eurostandard and the TSM both avoid these issues by adopting customised clearances. This offers advantages over ISO standards, although there are differences between the two, with the Eurostandard adopting a tighter clearance range to help improve general operation and product yield.

Conclusion

Although there are other small variations between the standards, such as seal groove configuration, these do not prevent interchangeability and are not detrimental to the running of the tablet press. All of these differences are surmountable. In recognition of the need to eliminate these variables and specifically take into account the sensible and efficient provisions for cross-platform/press compatibility laid out in ISO 18084, the Eurostandard has been updated to make it compatible with the ISO standard.

A single global tooling standard should be highly desirable for the industry; however, even if tablet press manufacturers could be convinced that adoption is in their commercial interest, it will take time for these changes to evolve. Leading tablet press manufacturers are always seeking to innovate and move the industry forward so tooling standards will always require revision. In turn, this means that highquality tooling suppliers will always need to retain the ability to solve complex problems and preserve the skill set within their workforce to manufacture bespoke tooling compatible with any press worldwide.

In conclusion, I believe that calls for the standards laid out in ISO 18084:2005(E) to be adopted as the global standard should be fully endorsed. However, I also believe that the Eurostandard already represents a comprehensive global standard because it is the most widely adopted tabletting tooling standard worldwide and is compatible with ISO.

Steve Deakin is Business Development Director at I Holland.