Tablet machines

For successful tableting, a material must have suitable flow properties to allow it to be fed to the tableting machine. Wet or dry granulation is used to improve the flow properties of materials. In the case of wet granulation, agitative granulation techniques such as fluidized beds or mixer granulators as discussed above are often employed. 

Roll compacting and briquetting is done with rolls ranging from 130 mm dia by 50 mm wide to 910 mm dia by 550 mm wide. Extrudates are made 1-10 mm thick and are broken down to size for any needed processing such as feed to tabletting machines or to dryers. 

All tableting presses employ the same basic principle—they compress the granular or powdered mixture of ingredients in a die between two punches with the die and its associated punches being called a station of tooling. Tablet machines can be divided into two distinct categories ... 

In order to produce an adequate tablet formulation, certain requirements, such as sufficient mechanical strength and desired drug release profile, must be met. At times this may be a difficult task for the formulator to achieve, due to poor flow and compactibility characteristics of the powdered drug. This is of particular importance when one only has a small amount of active material to work with and cannot afford to make use of trial-and-error methods. The study of the physics of tablet compaction through the use of instrumented tableting machines (ITMs) enables the formulator to systematically evaluate his formula and make any necessary changes. 

Tablets were a viable dosage form well before William Brockendon s patent for a tablet machine in 1843. His invention only made them easier to produce. As tablet presses and production-monitoring systems developed,...

P. Ridgeway-Watt, Tablet Machine Instrumentation in Pharmaceutics, J. Wiley Sons, New York, 1988. 

Much information on chemicals, equipment, etc. can be obtained from the various trade journals and newspapers such as Chemical Marketing Reporter. Many companies sell used tabletting machines (e.g., Union Std. Equip. Co. in New York and Chicago and Chemical and Process Mach. Corp. in New York). 

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. 

If a material is subjected to very high compaction forces, it may be formed into sheets, briquettes or tablets. In the tableting machines used for producing pills of pharmaceuticals, the powder is compressed into dies, either with or without the addition of a binder. 

The powder s flow properties are also important because they control the physical processes that are used to manipulate the material. Carrs s index, which is a measure of powder bulk density and angle of repose, provides information on flow properties, which are important when production utilises high-speed tableting machines. 

Tablets of 250 mg with starch concentrations of 5%, 15% and 25% w/w respectively, were prepared. Starch and lactose were mixed for 15 minutes in a Turbula mixer at a rotation speed of 90 rpm.. Magnesium stearate (0.5% w/w) was added and mixing was continued for 2 minutes. The tablets were prepared on a single punch tabletting machine, using 9 mm flat punches. From each mixture tablets were produced at three compression load levels 157,314,472 MPa.

Prepare for each tablet diameter a test set of two upper punches (shorter and longer) as the standard punches (e.g., using a plaster layer). Build in the one punch and run the tablet machine with a placebo product. Then perform the same test with the other punch. 

Riggway WP. Tablet Machine Instrumentation in Pharmaceutics Principles and Practice, NY Halstead Press, 1988. 

Muller FX, Augsburger LL. The role of the displacement-time waveform in the determination of Heckel behaviour under dynamic conditions in a compaction simulator and a fully instrumented rotary tablet machine. J pharm pharmacol 1994 46 468-475. 

Final compression on the same instrumented tablet machine to obtain a 400 mg tablet. 

Process ability Surface area, surface free energy, crystal defects, and deformation potential affect compressibility and machineability on high-speed tableting machines with reduced compression dwell times Particle size distribution and shape affect flow properties, efficiency of dry mixing process, and segregation potential Compressibility, flow ability, and dilution potential affect the choice of direct compression as a manufacturing process... 

Due to the poor flowability of the powder the tabletting machine should be equipped with a special technical device providing a continuous and homogenous filling of the dies. 

Figure 12.8. Operation and specifications of rotary tabletting machines (Carstensen, 1984). (a) Action of the punches of a rotary tabletting machine, (b) Specifications of a Sharpies Model 328 Stokes-Pennwalt Co.), (c) Specifications of a Manesty Rotapress Mk 11 Manesty Machines Ltd. and Thomas Engineering Inc.).

Figure 12.14. Common shapes and sizes of pellets made by some agglomeration techniques, (a) Sizes and shapes of briquets made on roll-type machines, (b) Catalyst pellets made primarily by extrusion and cutting (Imperial Chemical Industries), (c) Some of the shapes made with tabletting machines.

Tableting is an excellent example of compaction. In this operation, loose material, such as a powder, is compressed between two opposing surfaces, or compacted in a die or cavity. Some tableting machines use...

As felt above, the concept of powder blend homogeneity cannot be dissociated from the scale at which a mixture is observed. For continuous mixers, homogeneity must be defined at the level of the blend flowing out of the vessel, and falling down to a conveyor or any other transportation equipment. In the case of a batch mixer, the mixture structure can be particularly complex to define, but in practice and when the mixer is emptied, the content of the vessel is discharged through a pipe to a container or a tableting machine. Hence, in both cases and if we take into account the entire cross-section of the pipe, the mixture flow can be assimilated as a 1-D particle stream. 

Tungsten sulfide as vapor-phase catalyst is used in the form of pellets which are pressed from the powder in commercial tableting machines under a pressure as high as 5000 kg./cm.2 (75,000 p.s.i.). Three-millimeter pellets were used in pilot plants and 10-mm. pellets in commercial plants. 

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