Readers of a certain age can still recall when cars had

As appeared in Tablets & Capsules September 2011, Copyright CSC Publishing tablet tooling www.tabletscapsules.com Tablet tooling taxonomy: A summary of options Dale Natoli and Dave Holleran Natoli Engineering This article explores the latest tooling options available to streamline tablet production. While one feature or option does not fit all applications or resolve all problems, these tooling options will benefit most high-speed and standard presses. Readers of a certain age can still recall when cars had classic styling but lacked air conditioning, power steering, anti-lock brakes, and power door locks. Some of us even remember that seat belts were offered only as optional equipment. Yet we still appreciated the leather interior, the white-wall tires, the chrome, the hood ornaments, and the standard AM radio.

Needless to say, today s cars now come with many more safety features and luxuries, some mandatory, some optional. As a result, cars are safer, more fuel efficient, and more comfortable than ever and each can be tailored to your tastes and performance requirements. This arc of automotive innovation is analogous to what has occurred in tablet compression technology over the last 30 years. Today, tablet presses and their requisite tooling have evolved to provide more options that allow more efficient tablet production, faster set up, and less product waste, thus boosting quality and yield. Common punch options During the 1980s, the tablet compression industry introduced higher-speed and more automated tablet presses that allowed end-users tablet manufacturers to interchange tooling that conformed to the Tableting Specification Manual (TSM) [1]. Even so, sometimes the standard TSM tool configuration wasn t optimal and required minor modifications to achieve the expected performance. Furthermore, the standard tool configuration was not always suitable for compressing certain products, since every product has unique characteristics that warrant slight tooling modifications. It s important that tablet manufacturers know what options are available so that they can maximize performance, both of the tablet press and the tooling. Here is a summary of the most popular tooling options. Domed heads. The domed head configuration adapts to both upper and lower TSM punches and maintains the identical top head radius and head flat as Eurostandard tooling [2]. This option, available only for TSM head configurations, is compatible with the American TSM cams and should be considered for all high-speed tablet presses. In fact, as tablet press speeds continue to increase, the advantages of the domed head with its larger top radius are becoming more apparent. One advantage of the domed head is its 5/8-inch head radius. It holds up better than the standard TSM head (5/16-inch head radius) to the enormous stress that occurs when the punch contacts the pressure roller. See Figure 1. Unaddressed, the stress can cause pitting, or voids, in the head flat. The high-speed, high-force Figure 1 Domed vs. angled head impact on the head radius can also create a work-hardening effect when the metal is strained beyond its yield point and contributes to pitting. This form of pitting shortens the service life of the punches and the pressure rollers. By using a domed head, you can smooth the transition into the compression cycle, reducing stress and premature wear of the pressure rollers. Extended head flats. Some tool manufacturers offer head profiles with a larger head flat, which offers the advantage of higher output and/or an increase in dwell time during compression. See Figure 2. The disadvantage of an enlarged head flat is the greater possibility of head fracturing. Head fracturing can occur when the pressure roller s initial contact with the head falls outside of the neck diameter. That initial contact should always be within the diameter of the neck to provide support. Figure 2 Standard vs. extended head flat Standard head flat Rotating heads. A rotating punch head is separate from the punch barrel and tip, allowing you to remove and replace the head as it wears. See Figure 3. To understand why this is important, consider what occurs when you compress round tablets versus non-round tablets. With round tablets, the punches rotate as they are pulled Figure 3 Extended head flat Multi-tip punch with rotating head (exploded view) Barrel Rotating head pins Rotating head Cap Tips Domed head Angled head Cap screw

around the cam track through the various stages of tablet compression. As the punches rotate, the wear and stresses on the back angle of the head are distributed around the entire back-angle bearing surface. However, when compressing non-round tablets, the punches do not rotate and wear is concentrated at a single point, leading to premature head wear. By using a rotating head when compressing non-round tablets, however, wear is distributed over the entire surface of the back angle. Result: less head wear and longer punch service life. Mirror-finished heads. Some high-speed tablet presses use heavy-metal cams, such as bronze and bronze alloys. These materials eliminate premature head wear and prolong tool life, but they may also contaminate the lubricant, turning it blackish-green. This occurs because most punch heads are polished using fine emery cloth or fine abrasive pads. These leave microscopic radial lines on the contact surfaces of the heads that act like a file on the softer cams, abrading them. The result is premature cam wear and small filings that foul the lubricant and discolor it. By polishing the punch heads to a mirror finish using a soft cotton wheel and fine polishing compound, you can prolong cam service life and keep the lubricant cleaner. Bakelite relief and double-deep relief. It is important to maintain a sharp edge around the lower-punch tip relief. A sharp edge assists with the pull-down cycle of the lower punch after tablet ejection. Should any product residue adhere to the die wall, the sharp lower-punch tip relief will cut through it and scrape the die clean, reducing the possibility of wedging and re-compression between the punch tip and die wall. The risk posed by product wedged between the punch tip and die wall is excessive heat that causes the punch tip to expand. That, in turn, could cause the punch to bind, wear the head prematurely, or discolor and contaminate the tablet with burnt specks. Bakelite relief allows the punch tip to move freely in the die. A double-deep relief increases the depth of the lower-punch relief and provides the same results as the Bakelite relief. The Bakelite relief, however, adds to the cost of the punch, while the double-deep relief usually carries no extra charge. See Figure 4. Figure 4 Bakelite and double-deep relief vs. normal relief Short lower-punch-tip. The lower-punch tip creates a tremendous amount of friction as it travels the full length of the die during the various stages of tablet compression. When compressing sticky products or products with a low melting point, the friction can cause the lower punch to bind. By reducing the bearing surface of the lower-punch tip, the punch travels more easily in the die, which reduces friction and operating temperatures. See Figure 5. Figure 5 Comparison of normal and short lower-punch-tip Normal tip Punch-barrel chamfers. Punch-barrel chamfers are required when punches are used on presses fitted with rubber or plastic guide seals. See Figure 6. Punches with a barrel chamfer make installation easier for these press models compared with punches that have the common 90-degree break. Plus, without a chamfer, punches that are forced past the seals may cause damage, allowing lubricant to seep from the upper-punch guides and contaminating the product. If the lower guide seals are damaged and product seeps into the lower-punch guides, the product Figure 6 Chamfers Shorter tip Bakelite relief Barrel-to-tip chamfer Neck-to-barrel chamfer Must be sharp Must be sharp Double-deep relief Normal relief

Figure 7 Punch keys will mix with the lubricant and cause tight punches and possibly press seizure. A barrel chamfer on the head end of the punch can also reduce the punch-guide wear that occurs when punches are cocked from the torque of rotation as the punch travels vertically in the guides. Key types and positions. Punch-barrel keys are mandatory for upper punches when compressing nonround tablets. The upper-punch key aligns the punch tip for correct re-entry into the die. (Keys are not generally required for lower punches because they do not leave the die during the compression cycle and thus stay aligned.) Keys may also be required when compressing round tablets that include embossing in order to prevent the punch from spinning after compression, which would damage the embossed tablet and increase the likelihood of a double impression on the tablet face. Lower-punch keys may be required when the orientation of the top and bottom embossing must be consistent. Keys fitted to upper punches are available in two configurations: 1) the standard Woodruff key, sometimes referred to as a pressed-in key or half-moon key, and 2) the feather, or flat, key, often referred to as the European key. See Figure 7. The Woodruff key is available in two styles: standard and Hi-Pro. The Hi-Pro key has a tab on each side of its exposed top section and rests on the barrel. The tabs keep the key secure by eliminating the rocking action common to the standard Woodruff key. Another option is to fasten the Woodruff key to the barrel with screws, which maximizes security on high-speed presses. Because the Woodruff key is pressed into position, it can swell the barrel at the key slot, causing excessive drag and sometimes galling the upper punch and punch guide. The feather key is a longer flat key and comes in a variety of lengths, depending on the tablet press. Unlike the pressed-in Woodruff key, the feather key fits into a milled slot and is secured using machine screws. The height and radial position of a key is critical to maximizing press performance. Unfortunately, no standard addresses key position because each of the many tablet press designs can have particular requirements. However, if the key is placed too low or is too long, it can interfere with the upper-punch guide seal and damage it and/or allow lubricant seepage to contaminate the product. If the key is too high, it can travel out of the key slot at the top of the punch guide, causing severe damage to the punches and press. Punch configurations for small and micro-sized tablets. It s common to experience difficulties maintaining tablet hardness, thickness, and weight while compressing small and micro tablets. That s because compressing small tablets is a sensitive process that generally requires small amounts of force. In some cases, the tablet is compressed simply by the weight of the punch, and applying excessive force distorts the punch tip and alters the critical working length, rendering tablet consistency virtually impossible. Tip breakage is also frequent and can damage other punches and the tablet press, most commonly the feed frame. Thus, a special tool configuration is recommended for compressing tablets smaller than 0.125 inch (3 millimeters). See Figure 8. The configuration modifies the Figure 8 Tool configuration for compressing tablets smaller than 0.125 inch (3 millimeters) Woodruff key [0.750 ] [19.05 mm] Hi-Pro Woodruff key Undercut die Screwed-in Hi-Pro Woodruff key [0.313 ] [7.95 mm] Feather key Upper punch Lower punch with strengthened tip

punches and dies and is used in conjunction with a shallow fill cam that minimizes lower-punch travel in the die. The punch modification shortens the punch tips and eliminates the lower-punch relief. Shortening the tip s to their minimum strengthens the tip and in - creases the maximum compression force considerably. Eliminating the lower-punch tip relief reduces the clearance between the tip stem and the die bore, adding support to the tip stem and decreasing distortion. Note that shortening the tip will increase the barrel length, and therefore the bottom of the die must be cut away to accept the longer barrel when the tablet is ejected. Multi-tip punches. Normally, one punch compresses one tablet, but not always. Multi-tip punches, more common in Europe, have only recently become accepted in the USA. The multi-tip tool configuration is engineered to compress more than one tablet at a time, with the total number of tablets dictated by the punch size, tablet size, compression and ejection forces, and the characteristics of the granulation. There is a tremendous advantage to using multi-tip punches when considering production, operating efficiency, and overall capacity. Operator safety, the greater number of tablets produced in a given area, and open floor where additional tablet presses would have gone are only a few of the advantages. But increased production is not a slam-dunk. It can be achieved, but should not be expected. To estimate how much production might increase, multiply the number of tablets currently produced by the number of punch tips and then multiply that figure by 0.9. Multi-tip punches come in two configurations, as a solid punch or as an assembly with multiple parts. See Figure 9. Figure 9 Solid and assembly-type multi-tip punches (exploded view) The solid-punch configuration is easier to clean and ensures that the punch tips align in the die; unfortunately, if even one tip is damaged, the entire punch is unusable and must be discarded. With the solid configuration, it is also more difficult to polish individual punch faces using a soft cotton wheel. The assembly-style multi-tip punch, however, allows you to separate the punch tips from the punch body by removing a cap and/or set screws. If a punch tip is damaged, you simply remove and replace it and return the punch to service. To clean the assembly punch, it must be disassembled, cleaned, dried thoroughly, and reassembled. That can require substantial labor. With multi-tip punches, tablet compression and ejection forces become greater as does operating temperature, and all should be monitored closely to reduce premature wear, tablet sticking, and/or discoloration. Pre ma ture tooling wear will be evident by excessive wear on the punch head and tablet press cams. We recommend using a rotating head on the lower punch when it has multiple tips, because the torque of the rotating turret tries to spin the punch in the guide. A rotating head will reduce the stress by spinning, and thus alleviate pressure on the punch tips and allow them to travel the length of the die without binding. Die options Tapered dies. A die that tapers on either one side or both has numerous advantages. See Figure 10. For instance, a die tapered on both sides enables you to turn it over and double its service life. But the biggest advantage of a tapered die is exhausting air trapped in the product as the upper punch enters the die at the start of the compression cycle. That function is especially helpful when using deep-cup punches, running fluffy granulations, or operating high-speed presses. A tapered die also allows the press to create a harder tablet using the same amount of pressure that a die requires. Furthermore, the taper helps reduce capping and laminating because it allows the tablets to expand more slowly as they are ejected from the die, reducing stress. Because the Figure 10 Multi-tip punch with replaceable tips Typical tapered die Multi-tip punch with solid tips Taper [0.003 0.187 ] 2 [0.076 4.750 mm]

taper decreases ejection force, it helps prolong the service life of the lower-punch heads and the ejection cam. It also reduces friction and allows the press to operate at a lower temperature. In addition, tapered dies help align the upper-punch tip when it enters the die, eliminating premature tip wear; this is especially helpful when running a press with worn upper-punch guides. A standard taper on a BB or D die is 0.003 by 3/16 inch deep, but the taper can be tailored to meet special requirements. Tapered dies also have disadvantages. Because the taper is conical, with the largest open area at the top, the upper punch can wedge between the punch tip and die wall as it presses into the die. In addition, excess product can migrate between the punch tip and the die bore because the clearance between them is greater than standard. If the upper punch wedges and sticks in the die, it will be evident by spotty tablets and/or premature wear at the back angle of the upper punch. Die materials. Dies are usually manufactured from D3 premium steel. That grade does not provide toughness, but it provides superior wear. In fact, because dies are not subjected to the same pressures or shock as punches, they can be manufactured from a larger selection of materials, as described below. Carbide-lined dies. The most common die for abrasive formulations is a carbide insert heat-shrunk into a softer steel sleeve to provide a cushion for the brittle carbide. See photo. These sleeves are normally made of S7 and A2 tool steel. Carbide dies demand a much higher investment but the cost is justified by their superior wear properties and the tablet quality; die service life is easily increased tenfold in most cases. Because the carbide die is much harder, it is more brittle and subject to fracturing under excessive loading. If the carbide liner is too thin at its narrowest point, it can fracture due to die-lock pressure and the stress of compression. This is also true of the steel sleeve. The tooling manufacturer should be consulted to determine whether the tablet size allows for a carbide liner. the same wear characteristics as carbide. Ceramic-lined dies are recommended for corrosive products because they reduce the coefficient of friction throughout the many cycles of tablet compression, especially during the fill and ejection cycles. Steel types Choosing a steel type is generally left to the tooling manufacturer unless a specific type has been requested. The criteria for selecting a steel type includes the quantity of tablets to be produced, the abrasiveness or corrosiveness of the granulation, the pressure required for compression, and the cup configuration. There are two categories of steel common to the industry: standard and premium. The names imply that one is superior in quality to the other, but that is not the case. Standard steels are the most commonly used grades, and premium steels are for special applications. The cost is generally higher for premium steels due to the higher quality of the steel purchased by the tooling manufacturer. Premium steels tend to be harder, but at the same time more brittle, than standard steels, and more prone to fracturing under excessive pressure. Thus, they may not be suitable for deep-cup configurations. Standard steels are available in the following grades: S5, S7, S1, and 408. Premium steels are available in D2, D3, 440C stainless steel, and O1. Table 1 shows the relationship between the toughness and the wear resistance of several tool steels. Toughness increases 9 8 7 6 5 4 3 2 1 Table 1 Tool steels: Relationship between toughness and wear resistance 408 S5 S1 S7 O1 D3 1 2 3 4 5 6 7 8 9 Wear resistance increases A2 440C D2 Carbide- and ceramic-lined dies increase service life tenfold or more over unlined dies. Ceramic-lined dies. Ceramics typically either partially stabilized zirconium or alumina are becoming widely used in industrial applications and generally have Conclusion Whether your goal is to increase output or reduce set-up times, choosing the right tooling options is crucial. Note, however, that many options still require some trial-anderror testing, and accurate recordkeeping is therefore essential. Use all available industry resources, such as tablet press and tooling manufacturers, to assist with the tooling choices. Chances are they have resolved difficulties similar to yours for other customers and have the expertise to recommend the correct options for most tabletting operations.

Finally, make sure the tablet press and tooling manuals are easily accessible to the people responsible for press setup, compression, and tooling. And keep in mind the three basic rules of tabletting: 1. Keep compression forces as low as possible. 2. Clean and lubricate the press and tooling properly. 3. Keep punches and dies in good condition. These guidelines, along with strong communications, will result in an efficient tabletting operation that produces high-quality tablets. T&C References 1. Tableting Specification Manual, Seventh Edition, 2006 American Pharmacists Association, Washington, DC. 2. For more information about Eurostandard tooling, see Rich Kirk s article Accounting for differences in TSM and EU tooling in the July 2010 issue of Tablets & Capsules and Dale Natoli s Back Page essay Combine the TSM and ISO tooling standards in the October 2010 issue. Further reading Pharmaceutical Dosage Forms: Tablets, Third Edition, Volume 3: Manufacture and Control, Chapter 1: Tooling for Pharmaceutical Processing; Dale Natoli, Natoli Engineering Company. Dale Natoli is vice president and Dave Holleran is director of customer service at Natoli Engineering, 28 Research Park Circle, Saint Charles, MO 63304. Tel. 636 926 8900, fax 636 926 8910. Website: www.natoli.com.