Single-punch tablet presses

Figures 15 and 16 provide a summary of the compression cycles for rotary and single-punch tablet presses. The formation of the tablet compact in these two types of presses mainly differs in the compaction mechanism itself, as well as the much greater speeds achieved with rotary type presses. The single punch basically uses a hammering type of motion (i.e., the upper punch moves down while the lower punch remains stationary), while rotary presses make use of an accordion-type compression (i.e., both punches move toward each other). The former find their primary use as an R D tool, whereas the latter, having higher outputs, are used in most production operations.

In single-punch tablet presses (reciprocating tablet presses), the punches are fixed to the punch holders which travel up and down, and in many cases fixation screws are used. Each make has its own holder design for punches and dies, and consequently for the tooling sets as well. Therefore little can be said in general terms, but it would appear that on the whole the remarks on the rotary press tooling apply correspondingly. 

Precompression using a Frogerais 0A single-punch instrumented press (Ets. Ed. Frogerais), equipped with flat punches 11,28mm in diameter (surface area, 1 cm2). The speed ofthe machine was adjusted to one tablet s... 

Eccentric tablet presses are single station tablet presses that use an eccentric shaft connected to a rotating wheel to control the displacement of the upper punch into the die. The Encychpedia of Pharmaceutical Technology provides a good summary of the construction and function of an eccentric tablet press <25). The details of its operation are not reported here since it is the only simulation of the compression cycle that is of interest to this chapter. In an eccentric press, the displacement profile of the upper punch is sinusoidal and the displacement rate is controlled by adjusting the rotation rate of the eccentric wheel. The lower punch remains stationary during the compression and acts only to enable uniform die filling prior to tablet formation and tablet ejection after tablet formation. 

Tablet Press. The main components of a tablet compression machine (press) are the dies, which hold a measured volume of material to be compressed (granulation), the upper punches which exert pressure on the down stroke, and the lower punches which move upward after compaction to eject the tablets from the dies. Mechanical components deflver the necessary pressure. The granulation is fed from a hopper with a feed-frame on rotary-type presses and a feeding shoe on single-punch presses. A smooth and even flow ensures good weight and compression uniformity. Using the proper formulation, demixing in the hopper is minimized.

Single-punch machines produce approximately 100—150 tablets per minute. Depending on numbers of die per punch units, standard rotary presses can produce 5000 tablets/min, and even more with a double-sided rotary press. The newest high speed presses can achieve 12,000 tablets/min. 

Pharmaceutical compressed tablets are prepared by placing an appropriate powder mix, or granulation, in a metal die on a tablet press. At the base of the die is a lower punch, and above the die is an upper punch. When the upper punch is forced down on the powder mix (single station press) or when the upper and lower... 

Compaction simulators are single-station machines capable of mimicking the in-die compaction event that occurs on a rotary tablet press in real time. Simulators have been used to predict material behavior on scale-up and to evaluate various compaction parameters (punch force, ejection force, displacement, speed, etc.). Hydraulic compaction simulators (ESH) as well as mechanically driven machines (i.e., Presster and Stylecam ) are available for such studies. 

Tablet presses equipped with single-tablet rejection capabilities reject tablets at the point of scrape-off Based on the compression force of the punch station, single tablets are sorted by using a compressed-air blow off or a mechanical fast gate. On single-sided machines (36 stations) both systems work well for both large and small tablets. However, double-sided, highspeed machines may present difficulties for large tablets at high press speeds.

One level of relatively thin tablets or parts with any contour (class I of P/M Figure 187 2) an be pressed with a single punch and force may be applied from one side. The maximum dimension A (Figure 187) depends on the particulate feed and the shape of the compact. Thicker parts (class II of P/M Figure 188), while still requiring only simple tooling, must be pressed from two directions. Holes are obtained by the installation of mandrels or core rods. 

Tablets are produced using tablet presses. While these presses vary in their output, from approximately 3,000 tablets per hour to more than 1 million per hour for the fastest machines, the principle of manufacture remains the same. Powder is filled to a specified depth in a die and compressed between two punches. The compression force is ended by removal of the upper punch, and the lower punch then moves upward in the die to eject the tablet. Presses can be divided into two types, single punch (or eccentric) presses and rotary presses.

Single punch presses are sometimes referred to as eccentric presses because the movement of the punches is controlled by an eccentric cam. The tabletting cycle of a single punch machine is represented schematically in Figure 11.16. The powder hopper is attached to a feed shoe which oscillates horizontally. 

Single punch presses are rarely seen in production environments due to their relatively slow production rates, although there are still a number of old products that can only be successfully produced on this type of machine. They are still used in development laboratories because they require only relatively small amounts of material to produce tablets compared to most rotary machines. 

All commercial types of single station presses have essentially the same basic operating cycle (see Fig. 16), where filling, compression, and ejection of tablets from the die is accomplished by punch movement utilizing cam actions. Material is fed to the die from the hopper... 

All operations take place simultaneously in different stations. Sixteen stations were commonly used in earlier machines with outputs between 500 and 1000 TPM and tablet diameters up to 15 mm. Presses with outputs orders of magnitude greater than the above are now widely available. The dies are filled as they pass beneath a stationary feed frame, which may be fitted with paddles to aid material transfer. The die cavities are completely filled and excess ejected prior to compression. Compression involves the movement of both punches between compression rolls, in contrast to single station operations where only the upper punch effects compression. Ejection occurs as both punches are moved away from the die on cam tracks until the tablet is completely clear of the die, at which point it hits the edge of the feed frame and is knocked off the press. Tooling pressure may be exerted hydraulically, rather than through the use of mechanical camming actions, as is the case with machines produced by Courtoy. 

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