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In many cases, in fact, it's not how hard you can com- press a product that results in sufficient tablet hardness, but how long the product is compressed at peak force, which is known as dwell time. This can be fine-tuned by selecting punches with the appropriate head flat. The length of this surface at the top of the punch determines how long the product remains under compression. To prolong dwell time, some tooling vendors offer punches with extended head flats. These longer flats can also pro- duce incidental advantages, including less wear to com- pression rolls and ejection cams. While not strictly related to tablet press performance, the amount of floor space today's equipment requires is smaller than ever. That means better efficiency in the use of GMP space, which is at an all-time premium. Today, relatively small presses are easy to install in tight confines and can produce tablets at a rate formerly possible only using much larger machines. Anybody involved with planning a manufacturing facility should take notice. Another operational improvement concerns bi-layer tablets. If any aspect of tabletting resembles an art, this is it. Operators must not only maintain target tablet specifi- cations as the press operates at high speed, but they must prevent poor bonds between layers, cross-contamination between the two products, and poor yields. To make the job easier, new presses allow you to rapidly and accurately sample the first layer without allowing partial tablets to reach the discharge chute for acceptable tablets. New presses also control the weight of each layer of the tablet, not just the overall weight. They do this by using the punch penetration of the first layer as a means to trigger compression force control. Furthermore, the additional compression stations that the presses use to make bi-layers can be used either to lightly compress (tamp) the first layer of a bi-layer or serve as an additional pre-compres- sion station for mono-layer tablets. It's a way to increase dwell time without using special punches. Maintenance Once your company has made a substantial invest- ment in a state-of-the-art, high-speed modern tablet press, the next step is keeping it in tip-top shape. No piece of equipment can be run hard day in, day out with- out being maintained. While today's presses perform bet- ter than ever, they're still a mix of high precision and tank-like strength that requires regular preventive mainte- nance. The term preventive maintenance is used so often, that people can forget what it's all about: reducing the need for regular maintenance. The point is to pay close atten- tion to the press so that unplanned events—and unplanned downtime—are kept to a minimum. And while it's important to maintain the entire press, it makes sense to pay very close attention to everything within the compression zone, the site of the most important actions. Check the punch seals and scrapers regularly, and when you need to remove and install punch seals, use the tools recommended by the tablet press manufacturer or supplier. Seals on the underside of the feeder, especially those enclosing the fill channel, warrant extra attention. A good rule of thumb is to assume that any moving part in the compression zone—but especially those above or near the die cavities—must be monitored closely. The objective is to ensure that only the intended product can make it into the cavities, nothing else. Some manufacturers offer upper punches that accept bellows seals, which are accordion-like and completely enclose the space between the bottom of the upper punch barrel (near the tip) and the bottom of the upper punch section of the turret. These seals greatly reduce the possibility that contaminants—which usually appear as dark specks on the tablet—can reach the die cavities. The risk of such contamination tends to increase with the speed of the tablet press and its run time, especially if the lubrication settings aren't maintained as the press manu- facturer recommends. Modern presses owe their phenomenal precision at high speed to many different electronic components, which must be checked and maintained regularly, just like the Modern feeders operate independent of the tablet press' main motor, giving operators more control, including the ability to change the rotational direction of the feeder paddles and to use a variety of paddle configurations. This double-sided press enables you to sample the first layer of a bi-layer tablet. Tablets & Capsules September 2016 15