Cory Terry, Manager of Parts and Accessories, Natoli Engineering Company discusses how to maintain tablet compression tooling
Using the unsewn cotton wheel method often doubles the usable life of the tool
“How long should a set of tools last?” is one of the most common questions we as a tablet compression tooling manufacturer hear from our customers. The answer depends on many factors, including tablet configuration, characteristics of the material being compressed and the type of steel used to make the tooling. But when evaluating the life of punches and dies, several steps can be taken to prolong and protect your investment.
Tooling is a significant investment for tablet manufacturers. Although individual punches and dies may represent only a small portion of production costs in relation to the purchase and maintenance of machines such as fluid bed dryers and tablet presses, across the life of a product many sets of tooling will be necessary and will amount to a sizable expenditure.
Excessively worn or improperly maintained tools could generate a tremendous liability to the production team by creating a perception of poor quality to the consumer. Tablet manufacturers will receive the most use and highest quality tablets from their tooling if it is properly maintained.
Proper Lubrication: automatic lubrication systems can provide false assurance that appropriate lubrication is being supplied to all the necessary areas of the punches. Some automatic lubrication systems require centrifugal force to push the lubricant into distribution channels. However, automatic lubrication may not have reached critical lubrication points at press start-up, which can lead to damage on mating parts of the punch, including guides, keyways, cams, and pressure rollers, as well as premature wear to the tools themselves.
A tool that is not properly lubricated will cause excessive friction, increasing the operating temperature of the punch. The result is a thermal expansion of the punch barrel, which reduces the space allowed for lubrication. This expansion can lead to emergency stops, tool binding and tool damage. Simply applying a food-grade barrel lubricant to the punch barrel and a food-grade grease to the head of the punch with the correct brush prior to set-up and operation will ensure proper lubrication on tablet press start-up.
Proper Cleaning: dirty tools can cause tool binding, which can result in damage to the tooling and the tablet press. Keeping tools clean will decrease the chance of premature tool wear and allow lubrication to be more effective and the machine to run more efficiently – which will increase product yield.
The ideal cleaning procedure is one with minimum human interaction so that tooling is cleaned consistently and the potential for damage is greatly reduced. Ultrasonic cleaning with an automatic dryer is the optimum procedure as it provides tooling with increased exposure to the cleaning solution. Ultrasonic cleaners use high-frequency pressure waves to cause cavitation to agitate a liquid (usually cleaning solution and/or water), which in turn creates tiny bubbles that loosen and remove debris.
This action is highly effective for removing all traces of product and/or contaminants from tooling. The ultrasonic waves penetrate all surfaces of the tooling, including hard-to-clean areas such as key slots, cups and die bores. And can cause debris such as oil, grease and biological residue to break up and disperse. In addition to using an ultrasonic wash unit, it’s critical that tools are rinsed and dried properly because any residue left from cleaning solution or water can cause corrosion or discoloration of the tooling.
Figure 1: ultrasonic cleaning quickly and easily provides a safe, thorough cleaning of punches and dies
The benefits of ultrasonic cleaning include:
Left: before ultrasonic cleaning. Right: after ultrasonic cleaning.
Proper Maintenance: over time, tooling loses its luster and can develop nicks, scratches, and/or a wear pattern commonly called J-hook. These imperfections can cause quality issues such as tablet capping, laminating, sticking, and picking as well as unnecessary downtime in production.
By far, the best method to polish and refurbish punches is to use a large unsewn cotton buff wheel. It’s not just polishing but refurbishing that extends tool life and permits tools to be put back into service. Polishing tools properly refurbishes the punch cups, restores land and allows for minor repairs of punch heads, back angles and barrels. Unlike the process of automated polishing, manufacturers using the cotton wheel method often double the usable life of their punches. However, polishing done by an inexperienced technician could destroy a set of tools. Great care should be taken that only a small amount of material is removed during this process, and only a well-trained and experienced tooling technician should complete this maintenance procedure.
Proper Handling and Storage: proper handling and storage can be as simple as using tooling storage bins. These bins separate tools and keep them from striking one another. It’s surprising just how many tools need to be replaced each year due to mishandling and “accidents” add up. In some cases, tablet compression technicians simply lack a systematic handling procedure. Damage such as nicks and dings on and around the punch tip cause black specs and product discoloration as well as capping, lamination and other visual defects.
Other handling solutions include racks and cabinets that provide adequate protection during storage and transport. The use of a desiccant pack inside the sealed tooling storage box or drawer is recommended as well.
The working length of the tool is critical in production as it ensures consistent tablet parameters are met throughout the set. Punches should be visually inspected and measured before being transferred into storage. Working lengths of the set should be within the tolerance range determined by internal standard operating procedures (SOPs).
In most cases, tools that are out of specification with working length can be lightly machined and put back into service. If working length is out of specification, contact your tooling supplier to discuss repair options.
By maintaining the integrity of tooling through proper lubrication, cleaning, maintenance, handling, and storage, the tablet production team can ensure consistent and efficient tablet manufacturing while prolonging tool life and reducing downtime. Implementation of a consistent tool maintenance programme will help protect the company’s investment, reduce variable costs, maintain or increase output and improve tablet quality.