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Identify the warning signs and follow best practices for refurbishment to improve tablet press yields.
Oral solid dosage drug manufacturers are regularly faced with making substantial equipment investments, and that certainly applies to rotary tablet presses. Although modern presses do boast the potential for lengthy, useful lives, the efforts made to exploit that should always be commensurate with the scope of the initial capital outlay. Increasing economic pressures have resulted in efforts to pay closer attention to preventive maintenance, although there comes a time when equipment refurbishment may prove absolutely necessary.
Original equipment manufacturers (OEMs) are often, and not surprisingly, an invaluable source of recommendations on how to maintain presses properly. Many also offer their own refurbishment services, thus one can turn to them for advice on what to look out for, and the best methods for undertaking such endeavors. It is the goal of this article to suggest some guideposts for approaching the idea of refurbishment, when such has been deemed necessary.
The decision on when to refurbish a machine will depend largely on the press owner, their own standard operating procedures for preventive maintenance, and whether or not their approach to this maintenance is proactive or reactive. There are, however, some rather obvious indicators that refurbishment work may be a good idea. Some common warning signs on a tablet press may include:
It is crucial for the press owner to identify the degree to which they wish to refurbish their press, early on in the process. This planning prevents the problem similar to that found when one brings a car to a mechanic for one issue but is ultimately informed that everything needs to be replaced. Refurbishment costs can spiral out of control should this important step be overlooked. Some press users simply wish to ensure their machine is brought back to a state of mechanical soundness; others wish for the same, but also strive for cosmetic improvements and computer upgrades.
The ideal way to approach a repair or refurbishment endeavor is to have an OEM representative physically pre-inspect a press at the user’s site. Much guesswork is thus removed, and it will foster a clearer understanding of scope and projected costs. This understanding often facilitates the prioritization process for the press owner, allowing them to budget for repairs and improvements deemed absolutely necessary. It is strongly recommended that the user pursues such an inspection, and requests a detailed quotation, prior to any work commencing (especially for projects necessitating the press be shipped elsewhere for work to be performed).
There are some other important items to think about when considering refurbishment, especially if the work is to be performed by another party:
While the order in which things should be checked may vary, the following items should always be carefully considered when performing refurbishment work on a tablet press. In all cases, repair or replacement of faulty and worn components should follow, as applicable.
Turret. The turret assembly represents the core of any tablet press, and it is the most tolerance-critical component. It should be inspected for excessive wear or damage. Punch bores, die cavities, and the die table surface should be checked. Runout, the uneven wear found at the outer edge of the turret, should be minimal (if it exists at all).
Cams. All cams and cam tracks should be carefully inspected for excessive wear and/or damage. Lower punches that drop lower than they should can contribute to erratic weights and low yields. Worn cams can allow for other unintended punch movements, leading to premature wear of other parts that come into contact with the punches.
Compression rolls. Compression roll surfaces and bearings should be inspected for surface wear and/or excessive “play.” Rolls exhibiting any form of pitting should always be replaced; if metal fragments adhere to punch heads they will be transferred to the next roll, creating other pits, and so on.
Gearboxes. All adjustment gearboxes (i.e., for compression and dosing stations) should be inspected such that factory specifications can be maintained. These components play a major role in maintaining the precise volumetric control that modern presses are capable of.
Load cells. Load cells should be tested and verified for normal operation; “weight” control on a tablet press is typically derived from force measurement at the compression station load cells, thereby necessitating good signal strength and clarity.
Main drives. The main drive should be inspected and cleaned. The main drive gearbox should be inspected for excessive wear and/or “play.”
Chutes and ejection assemblies. Discharge chutes and ejection assemblies (where applicable) should be inspected and tested for proper function; very minor adjustments to these components can make the difference between good yields and a clean room, or tablets flying all about.
Shrouds and guards.Shrouding should be inspected and proper fitment confirmed; a metal shroud that makes even minimal contact with a rotating turret, for just one revolution, can instantly create lasting damage.
Electrical and safety interlocks. Electrical and safety interlocks should be carefully checked for proper function; tablet presses contain some very heavy components that move at high speed, and such inertia should be respected by ensuring all safety features are performing as intended.
When electing to have refurbishment work performed by an OEM, minor cosmetic damage is typically covered by an initial proposal; more substantial cosmetic needs, uncovered during in-depth dismantling and assessment, should be agreed to only after consultation with, and approval by, the press owner. As stated previously, one should practice due diligence before embarking on a refurbishment project and decide early on as to what is critical versus what is unnecessary. This is especially important when the work is to be performed by a party other than the end user themselves, or an OEM.
Given the level of sophistication found in most modern tablet presses, including many of those built as many as 20 years ago, refurbishment work should include the calibration of all applicable equipment and devices (i.e., load cells, compression roll gearboxes, dosing stations, etc.). Calibrating the various sub-assemblies should be considered of paramount importance, and all efforts should be made to calibrate to the OEM’s original factory specifications. Proof of the procedures having been performed, normally in the form of a calibration sticker, should ultimately be affixed to the equipment.
Tablet presses are generally capable of impressive performance, but the most sophisticated examples are made up of many hundreds of different parts that must work in concert with one another. It often takes only one or two off-song components to ruin the show. The good news is that, barring extreme damage, most presses can be brought back to a level of original factory performance, provided the owner embarks upon a sensible refurbishment program.
Take the time to consult with your OEM, as they are bound to have information that is unavailable elsewhere. It is likely they may offer their own refurbishment services, and chances are there are few, if any, things to be found that will surprise or confound their technicians. Detailed repairs and detailed refurbishment deserve detailed know-how. The improvements most commonly reported by press owners who have undertaken a careful refurbishment program are those leading to greatly improved yields, which is of primary importance for tablet manufacturing.
Vol. 43, No. 3
When referring to this article, please cite it as M. Bundenthal "Tablet Press Refurbishment: Why and How?" Pharmaceutical Technology 43 (3) 2019.
Matt Bundenthal is director, sales and marketing at Fette Compacting America, firstname.lastname@example.org.