SPOTLIGHT

What are some challenges with multi-tip tooling, and how can these be overcome?

Dale Natoli and Robert Sedlock at Natoli

Multi-tip tooling isn’t new to the pharmaceutical industry; the unique tool configuration has been used for more than 150 years. At the start of the tablet compression industry, single-station tablet presses were used in production and were commonly outfitted with multi-tip tooling to increase tablet production and reduce labour, maintenance, energy, space requirements and the number of presses. When the high-speed 16-station rotary tablet press was introduced in the late 1800s, the single-station press and multi-tip tooling lost popularity.

Soon after the introduction of the rotary tablet press, the industrial, confectionery and food industries implemented multi-tip tooling, and today the pharmaceutical industry is following suit.

Multi-tip tooling is available in two common configurations: assembly (or multi-piece) and solid. When choosing the configuration, consider the tool type, tablet size and the number of tips per punch. Also consider tool handling practices, cleaning and inspection. Rotating heads are a common feature for multi-tip punches, especially on lower punches, and should be considered for any multi-tip punch use. The supplier will help you decide which configuration is best – most tooling suppliers have selection guidelines for each tool type.

It is important to point out the critical stages of the rotary tablet press process, recognise the impact multi-tip punches have at each step and how to overcome the common challenges found in the tablet compression industry.

Challenges of multi-tip tooling

There are multiple areas of concern during the die filling process in which multi-tip punches are directly affected.

Each of these areas may need to be addressed when moving from a single tip to a multi-tip punch set-up.

Hopper and feeder are the first areas of concern. The feeder delivers the powder from the hopper to the die table. Using multi-tip punches, more product will need to be drawn from the feeder, requiring a higher feeder speed than is used for single-tip punches.

The die fill process is also an area of concern. The lower punch is pulled down from the fill cam to allow overfill of the die cavity. The excess powder is then pushed out when the punch reaches the dosing cam. A worn-out tool, or a low-quality tool that is not within specification, can cause weight issues and punch binding as materials build up on the die wall. Multi-tip punches can exacerbate these issues and require special attention to tool quality. Working with a knowledgeable and experienced tooling manufacturer will ensure proper tool design and press set-up.

The next point to consider is the pull-down cam. Immediately following the dosing cam is either a tail-over die or pull-down cam. Both are designed to keep the powder in the die cavity before the upper punch enters the die. When utilising multi-tip punches, it is imperative that the pull-down cam doesn’t pull the lower tip from the die cavity. This modification should be treated similar to that of the fill cam.

Pre-compression is a de-aeration stage. This allows the removal of air and initial consolidation of particles to help with the main compression process. A multi-tip application may also benefit from the use of pre-compression, but with the increased number of tablets produced, the press speed can be reduced.

The main and final compression force on the rotary tablet press is a result of the amount of powder in the die cavity and the distance between the upper and lower punch tips. Assuming a concentric pressure roller and punches that are within working length tolerance, the resulting compression force will be similar for each turret station if the powder is uniform in fill. It is of special importance that the multi-tip punch working lengths are within tolerance since these force systems have no way of determining which tip is causing the issue.

The ejection stage follows the main compression and de-compression event. The ejection force is the resulting residual radial die wall force and coefficient of friction between the tablet band surface and the die wall surface. A multi-tip punch will most likely increase the ejection force and may cause excessive cam and lower punch head wear. Formulating with the appropriate amount of powdered lubrication can solve this issue.

The take-off or the tablet removal from the lower punch face is the final stage of the tabletting process. All the tablets on a multi-tip punch must be removed properly from the take-off bar. If the tablets are not striking the take-off bar properly then the tablet may chip or facture. Some processes or tablet designs require the lower punches to protrude slightly above the die table. This can also cause tablet defects since the leading edge tablets that are removed first can strike the trailing edge punch tips that are slightly protruded. This requires correct positioning of the take-bar angle.

Solutions for maximum productivity of multi-tip tooling

Before investing in multi-tip tooling, verify that your tablet press has turret punch guides and die sockets that are in good condition, with no excessive wear. Worn guides and/or worn die pockets can create punch-tip misalignment, which in turn causes premature tip wear, excessive head and cam wear, and tool binding in the punch guide and tip binding in the die. You can easily check the condition of the turret with a turret inspection kit, which is available from most tooling manufacturers. Inspect the turret for wear periodically, regardless of whether single-tip or multi-tip tools are used. Inspection will alert you to premature tool wear and tooling failure.

For tablet presses with tablet rejection systems, many companies use validation punches, which are identical to the other punches except for a slight deviation in their working and overall lengths. The validation punch verifies the operation of the reject system by producing tablets of different hardness, thickness and weight. While some pharmaceutical companies are turning to multi-tip tooling, other companies are more reticent, investigating the effect on product flow, compression and ejection forces, and tablet reject systems, among others.

Is your product a candidate for multi-tip tooling? Reach out to Natoli’s customer service team at natoli.com/contact for questions or assistance.

Natoli Engineering is your partner in achieving manufacturing excellence. Contact us today to learn how we can support your tablet and capsule production needs. For more information, visit our website or reach out to our team of experts who are ready to assist you in optimising your manufacturing process.

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