Punch and die

Antiadherents. Some materials strongly adhere to the metal of the punches and dies. Although not a frictional effect, this results in material preferentially sticking to the punch faces and gives rise to tablets with rough surfaces. This effect, called picking, can also arise in formulations containing excess moisture. 

Measurement of the punch and die forces plus the relative displacement of the punches can provide raw data which, when suitably processed and interpreted, facilitate the evaluation of many tableting parameters. Many of the workers first involved in instrumenting tablet presses concentrated on deriving relationships between the applied force (FA) and the porosity (E) of the consolidating mass. 

In the past year—to give you an example—the US has been flooded with small amphetamine tablets known as minibennies. Ballistics examination indicates that most of these tablets originate from three sets of punches and dies used on multiple punch tableting machines. To date, over 30 million minibennies have been purchased or seized. 

One very common beneficial interaction involving an excipient is the interaction between magnesium stearate and the metal of tablet punches and dies, or the equivalent parts on a powder encapsulation machine. Magnesium stearate is an example of a boundary lubricant. As such it has a polar head and a fatty acid tail. It is believed that the polar head of the magnesium stearate is oriented toward the die wall or tablet punch face. In these ways it is able to reduce the ejection force (the force required to eject the tablet from the die after compaction) and prevent sticking to the punch faces. The other boundary lubricants, e.g., calcium stearate and sodium stearyl fumarate, will also function in a similar manner. However, the so-called liquid film lubricants function in a very different manner (19). 

The TS of the compacted samples was determined by transverse compression with a custom-built tensile tester. Tensile failure was observed for all the rectangular compacts when compressed between flat-faced platens at a speed ranging between 0.006 and 0.016 mm/sec. Platen speed was adjusted between materials to maintain a time constant of 15 2 seconds to account for viscoelastic differences the constant is the time between the sample break point and when the measured force equals Fbreak/e in the force versus time profile, where the denominator is the mathematical e. Specially modified punch and die sets permitted the formation of square compacts with a centrally located hole (0.11 cm diameter) that acted as a stress concentrator during tensile testing. This capability permitted the determination of a compromised compact TS and thus facilitated an assessment of the defect sensitivity of each compacted material. At least two replicate determinations were performed for each mechanical testing procedure and mean values are reported. 

Lubricated (to prevents the powder/granulation and the tablet from sticking to punches and die, and to enable the formed tablet to be ejected from the die wall and released cleanly from the punch faces)... 

RDX/SantowaxM 91/9 RDX/Be Square Special Wax The compns containing the Santowax M (product of Monsanto Chemical Co Santowax M is a meta-diphenyl benzene, a hard microcrystalline wax very stable to heat with a mp of 181-84°F) were found most suitable with respect to ease of manuf and non-adherence to punches and dies. They were more satisfactory than the standard Compn A-3. Both the Santowax M and the Be Square Special Wax coated the RDX crystals well the polyvinyl acetate/dibutylphthalate did not. The PVA/DBP, during the RDX coating... 

Hard coatings have been applied to many types of forming tools, such as deep-drawing punches and dies, wire - drawing dies, injection moulding dies, etc. It was shown that the application of coating resulted in an eight - fold increase in service life at 80% reduction in tool costs. 

Powders compressed into flat-faced tablets by action of punch and die, comminuted and screened to form feed for final compression. Dry granulation, slugging, pre-compression Heavy duty tableting press... 

Tablet antiadherent Agent that prevents the sticking of tablet formulation ingredients to punches and dies during tablet production Magnesium stearate, talc...

There are three types of lubricants employed in solid dosage form manufacture. The first class of lubricant is the glidant. The flow properties of a powder can be enhanced by the inclusion of a glidant. These are added to overcome powder cohesiveness. The two other classes of lubricant are antiadherent excipients, which reduce the friction between the tablet punch faces and tablet punches, and die wall lubricant excipients, which reduce the friction between the tablet surface and the die wall during and after compaction to enable easy ejection of the tablet. The level of a lubricant required in a tablet is formulation dependent and can be optimized using an instrumented tableting machine. 

Tablet production systems should be able to produce tablets in a reasonable time and without loss of material. Usually they consist of two punches and a die, as schematically shown in Figure 1. The material is placed into the die cavity, which is closed on the lower side by the lower punch. A tablet is formed when the powder is compressed by the punches as described above. The forces evolving to produce a tablet can be up to 80 kN for pharmaceutical purposes [32] for the production of bigger tablets they are even higher. Usually they range between 10 and 30 kN. Thus punches and dies are produced from hardened steel.

Rotary tableting machines work with a number of punch and die sets which move in a circle. The dies are fixed in a round die table and the die table circulates. Together with the dies the lower and upper punches circulate on tracks. The lower punches close the dies. The densification process is bilateral since both punches pass the compression wheels and the force is evolving on the upper as well as on the lower side of the powder bed. The produced tablets show the same hardness on the upper and lower surfaces. 

High-Speed Rotary Tableting Machines High-speed rotary machines work with the same principles as all other rotary machines. They possess a huge number of punch and die sets and often two filling stations. Another possibility is to use punch and die sets which are able to produce several tablets simultaneously. Special tooling can be used for this purpose however this is not the subject of this chapter. As... 

The sensitivity of force measurement is dependent on the distance between the force transducer and where the force occurs. Thus for force measurement, instrumentation of the punches is more advantageous than instrumentation of the machine frame. However, since punch and die sets have to be exchanged between different runs of the machines, instrumentation of the punch holder, the machine frame, or the roller pin is most widely spread. 

Adhesion forces between the material and punches and dies result in sticking of the tablets at the punches and dies. These adhesion forces are further influenced by RH and this has also to be kept in mind. When the adhesion forces at the punches and dies are greater than the cohesion forces between the particles inside the tablet, the tablets stick at the punches and can cap. 

When the lubricant should not be part of the tablet formulation, for example, when bonding properties of the drug are low, external lubrication is necessary [197], For single-tablet production the punches and dies can be manually lubricated with a fluid. In production several methods have been developed to place the fluid on the surface of punches and dies [198], Filaments applied at the punches to lubricate the die or special caps with fluid lubricant are possible solutions. However, external lubrication also has disadvantages [199],... 

Morehead, W. T., and Rippie, E. G. (1990), Timing relationships among maxima of punch and die-wall stress and punch displacement during compaction of viscoelastic solids, J. Pharm. Sci., 79,1020-1022. 

The turret head is fixed to the main shaft of the gear box. It is manufactured in two pieces (upper and lower) which guarantee the alignment between punches and dies. The gear box is mounted on the lower section under the die table and is responsible for transmitting the draft movement of the motor toward the turret head. 

Punches and dies are essential tools in the tableting process and therefore are critical to the quality of the tablets produced. Both tools are designed for long life under normal conditions of working, but, in spite of this, they are not proof against careless handing. 

It is important for those working with a tablet press to be familiar with the terminology used in the industry concerning the punches and dies. Table 1 describes the commonly used terms related to press tooling. Some of the press tooling parts can be identified in Figure 5. 

Straight portion of stem effective inside die bore Portion of punch stem which is undercut or made smaller than punch tip straight most common for lower punches in order to reduce friction from punch tip and die wall Complete set of punches and dies to accommodate all stations in tablet press... 

Upper punch, lower punch, and die which accommodate one station in tablet press... 

Regarding the importance of compression tooling to the performance of the tablet press and the quality of the tablets, it is of paramount importance that punches and dies are handled with care. The first criterion is the identification of the tooling that is, punches and dies should be identified according to the standard and be designated by upper punch without key, upper punch with key, lower punch with key, lower punch without key, or die, the reference of the standard (e.g., TSM, EU, JN, ISO), and the punch or die diameter. Punches and dies should also have a marking that includes at least the manufacturer s identification, the number of the punch in the series, and/or the identification number. Upon... 

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