Tablet Press & Tooling Maintenance
A: Stephen Natoli says:
Many factors can reduce the life expectancy of tooling and tablet presses, such as abrasive or corrosive formulations, press or turret wear, improper tooling setup on the press, and mishandling of tooling by technicians. Creating and following a tooling maintenance program can extend tooling life and save you more than 40% on tooling costs.
Implementing a cleaning procedure is essential to maintaining your tablet tooling and presses. Dirty equipment can cause tableting and product-quality problems, such as sticking and picking, while clean tooling decreases premature tool, turret, and cam wear and reduces the risk of product cross-contamination.
Automated cleaning system. Using an automated cleaning system, such as an ultrasonic wash with a rinse and dryer, can ensure proper, consistent cleaning and drying of tooling, with limited handling and potential for damage. A warm-air drying process is ideal for preventing moisture and corrosion because it pushes warm air through areas, such as key slots, punch cups, and die bores that hand drying using a towel might not reach.
Handling. Poor handling of tooling, before or after use in a tablet press, is the main cause of tooling damage. Reducing handling and human interaction with tooling can minimize the potential for damage. Use a transport cart with appropriate baskets and racks during cleaning, transportation, handling, and storage. A specialized tooling rack allows you to transfer, clean, and store tooling without physically handling the tools. A tooling rack also minimizes the risk of punch tips contacting each other during transport, which can create a burr on the tip edge, resulting in tablet defects.
Inspection. You can also extend tooling life by implementing a thorough inspection procedure using equipment that effectively identifies wear. For visual inspection, use a horizontal optical comparator for checking punch tip wear as well as wear to the punch’s relief – the sharp edge of the lower punch tip that scrapes excess material from the die bore during the pull-down process. A comparator magnifies a silhouette of the tooling to allow easy inspection for wear. It also allows you to compare the wear to prescribed limits to ensure proper operation and reduce the possibility of tablet defects.
Use a digital indicator affixed to a post and granite base to measure the working length and cup depth of punches. Measure each set of upper or lower punches independently against an allowable tolerance limit to help ensure proper tablet hardness, thickness and weight consistency.
Visually inspect dies for wear, or ideally, use a hand-held, split-ball bore gauge to detect wear rings in the die bore and reduce the potential for more serious issues. For example, any wear to the punch tip or die bore can lead to material buildup during operation and cause the punch to bind in the die. The built-up material can also become scorched and break off into the formulation, causing dark spots in the tablets. This condition can also cause other damage, such as worn punch guides, punch-head wear, or cam damage when operating with bronze or plastic cams.
Cleaning. Proper cleaning of your tablet press is key for optimal operation. Traditionally, you begin tablet press cleaning by vacuuming all excess formulation dust from the press. Never use compressed air to clean your press because it can force formulation into crevices, bearings, and other areas where it does not belong. Use a soft-bristled brush, a die-seat cleaner, and a noncorrosive cleaner, such as 95-percent or greater, isopropyl alcohol, or a one-step cleaner and lubricant to protect against rust and corrosion.
Tablet press suppliers now offer technologies, such as wash-in-place cleaning, that can reduce the time required for product changeovers and improve operator safety when working with highly potent drugs. These technologies can be costly, however, and are generally unnecessary for tablet manufacturers who aren’t working with highly potent formulations.
Use an approved H-1 protectant oil to treat steel surfaces after cleaning if the tablet press will be sitting idle for a period, especially in an area where temperature and humidity are not controlled well. Avoid using cleaners that contain or require water. Like air, water can make its way into crevices, such as under cam bodies or into bearings, where it can create rust and lead to costly repairs and/or press failure.
Inspection. Proper tablet press inspection is crucial to prolonging tooling life. Regularly inspect tablet press turrets for punch guide damage, die pockets and keyways for wear, and verify punch alignment.
Refurbishing tooling. To repair damaged tooling , such as to remove J-hooks on a punch tip, use a benchtop motor or buffing station with a vacuum, equipped with a large, unsewn buffing wheel. You can also use a buffing wheel to polish the punch cups to minimize sticking. With the proper training, you can use a deburring wheel to repair damage to the inside head angle of the punches caused by upper raising and pull-down cams as well as to repair light-to-medium scratches on the punch barrel when necessary.
The flat area around the perimeter of the punch cup is the land. Restoring land to the punch tip is one of the most important procedures in refurbishing tooling. You can use a 400-grit stone to restore land and remove nicks from the punch tip edge, followed by a light buffing if the wear condition is severe.
Tooling suppliers can provide tooling maintenance and rework services for your existing tooling sets, helping to reduce tooling and tablet-manufacturing costs. Tooling suppliers can also provide you with tooling length matching reports to ensure that you produce consistent, high-quality tablets at the lowest possible cost.
This article was published on November 25, 2019 in Tablets & Capsules Solid Dose Digest.
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