TABLETING 77
The MERITS of MULTI-TIP PUNCHES
Robert Sedlock presents a case study on multi- tip punches and their impact on compression forces
M
ulti-tip punches are a cost-effective way to increase tablet
output without the need for additional tablet presses. Te use of multi-tip punches follows a similar principle as a single-tip tool for the rotary tablet press but there are operating techniques that must be understood for a successful tableting process. Two common multi-tip tool configurations for B and D tooling are assembled and solid type tools. When choosing which configuration best fits your needs, some things to consider are tool type (B or D), tablet size, number of tips and particle/ powder characteristics. Assembled punches consist of a punch body, caps and tips, which accommodates replacing the tips without the need to purchase a whole tool body. Te solid design offers easier cleaning, minimised assembly times, reduced rust potential and less risk of cross contamination. Rotating heads are a common feature for multi-tip punches, especially on lower punches and should be considered for any multi-tip punches due to the use of keyed punch barrels. Here, we point out the critical stages of the rotary tablet press process and describe what impact multi-tip punches have at each step and how to overcome the common challenges found in the tablet compression industry.
Tere are six 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 level is the first area
of concern. When product is initially loaded into the tablet press hopper, the powder must have adequate flow properties to successfully enter the feeder system. When multi-tip punches are installed on the press, the rate of product consumed is greatly increased and requires loading the hopper more often. Feeder speed is the next issue
to consider. Te 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.
Te die fill process is also a consideration. Te lower punch is pulled down from the fill cam to allow overfill of the die cavity. Te 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. Work with a knowledgeable and experienced tooling manufacturer to ensure proper tool design and press set up.
Te 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
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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. Tis modification should be treated similar to that of the fill cam.
Compression stage Pre-compression is a de-aeration stage. Tis 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. Te last area of concern is that of main compression. Te final compression force on the rotary tablet press is a result of
Fig. 1. The one-, two- and four- tip tools used in the study
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