Punches upper

The equipment employed for tablet compression is generally categorized according to the number of compression stations and dislocation mode. Therefore, eccentric model presses have only one compression station (one die and one pair of punches, upper and lower) while rotary models have multiple compression stations (each station with one die and one pair of punches, upper and lower). The basic difference between the two types of compression equipment is that for eccentric models the compression force applied during compression is due to the upper punch whereas for rotary models it is mainly applied by the lower punch. 

Compaction simulators (Fig. 20) were designed to mimic the compression cycle of any prescribed shape by using hydraulic control mechanisms that are driving a set of two punches (upper and lower) in and out of the die. All hydraulic compaction simulators are similar in design and construction. A compaction simulator consists of several main units the load frame (column supports and crossheads with punches), the hydraulic unit (pumps and actuators that move the crossheads), and the control unit (electronic console and computer). Usually, a simulator accepts F tooling only, but can be retrofitted to use standard IPX B tooling. Under computer control, the hydraulic actuators maintain load, position, and strain associated with each punch. 

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.

The actual compression process is a cycle of die fill, compaction by intervention of the upper punch using great pressure on the granulation material in the die, and upward movement of both punches to achieve ejection of the tablet from the die. Singe-punch presses have only one die-and-punch arrangement and the compression is quick, with Httle dwell time of the top punch in die. 

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... 

The major forces involved in the formation of a tablet compact are illustrated in Fig. 14 (a single-ended model) and are notated as follows FA represents the axial pressure, which is the force applied to the compact by the upper punch, FL is the force translated to the lower punch, and Fr is the force lost to the die wall. If one remembers that for every force there must be an equal and opposite force, the following relationship is obvious ... 

Fig. 14 Forces developed in the formation of a tablet compact., die wall FA, axial pressure applied by upper punch Fd, force lost to die wall Fr, radial die wall , tablet compact.

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.

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. 

This work was done in collaboration with Professor Hiroshi Yoneyama of Osaka University [124], The procedure used to prepare the LiMu204 tubules is shown schematically in Fig. 21. A commercially available alumina filtration membrane (Anopore, Whatman) was used as the template. Alumina is especially suited for this application because of its high porosity, monodispersity of pore size, and the fact that it can be heated to high temperature without degradation. This membrane contains 200-nm-diameter pores, is 60 p,m thick, and has a porosity of 0.6. A 1.5 cm X 1.5 cm piece of this membrane was mounted on a Pt plate (2 cm X 2 cm) by applying a strip of plastic adhesive tape (also 2 cm X 2 cm NICHIBAN VT-19) across the upper face of the membrane. The Pt plate will serve as the current collector for the LiMn204 battery electrode material. The strip of tape, which will be subsequently removed, had a 1.0 cm circular hole punched in it, which defined the area of the membrane used for the template synthesis of the LiMn204. 

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. 

The use of compaction simulators was first reported in 1976. Since then, a variety of simulators have been developed. Hydraulic simulators, as well as mechanical simulators, are available to characterize raw materials, drug substances, and formulations, as well as to predict material behavior on scale-up. The appeal of simulators is due to the fact that they purport to provide the same compaction profile as experienced on a tablet press while using only gram or even milligram quantities of powders. Compaction simulators can achieve high speeds, as would be experienced on a production tablet press, and can be instrumented to measure a variety of parameters, including upper and lower punch force, upper and lower punch displacement, ejection force, radial die wall force, take-off force, etc. Summaries on the uses of simulators and tablet press instrumentation can be found in (19,20). 

A Hadamard matrix H(8) was applied to estimate the main effects of four parameters applied force at the upper punch (UPF) during precompression, UPF during the final compression, particle size range after milling and the concentration of ethylcellulose added before the final compression. 

In sampling ten tablets, the following parameters were studied the lubrication index (R), the ejection force (F0), the residual force (Fr) and the cohesion index (CI=ratio of the pressure applied to the upper punch and the tensile strength) proposed by Guyot [17]. 

In sampling 120 tablets, the friability, the variability of the tablet weight and the variability of the upper punch force were determined. 

The applied upper punch force (UPF) exhibited a poor influence on several optimized responses. Nevertheless, it is possible to observe that the increment of this parameter is related to adequate values of the responses. In fact, the increase of UPF value (Table 1)... 

Compaction properties of each material were determined with a standardized test performed on a custom-built hydraulic compaction simulator using 8 mm (0.3150 in.) round flat-faced punches. A linear saw-tooth upper punch position profile was selected with a punch velocity of 300 mm/sec for both punch extension and retraction. The lower punch position was at a fixed position within the die during the compaction event. The powder weight loaded into the die for each compression was calculated from the equation below so as to form a cylindrical tablet having a thickness-to-diameter ratio of 0.30 at a theoretical SF of 1.0. These dimensions are typical of commercially elegant tablets. 

On all presses, the upper punch is set to come down to a specific point in the die cavity this position, which is set by the operator, controls tablet thickness. More specifically, this setting controls the compaction force (pressure) and, in turn, tablet hardness. 

The basic mechanical unit of compaction/compression consists of three parts (1) an upper punch, (2) a lower punch, and (3) a die. Producing a finished tablet involves the compaction of a powdered sohd between two punches and within the confines of a die, with the application of an external force [1]. 

A standard IPT Type B tooling was used with a f " round flat tool tip. Tablets were made one at a time, and the compression force as well as the upper punch displacement and lower punch displacement were recorded. Tablet weight, thickness, and breaking hardness were measured for each tablet. 

Rotary compression machines convert powders and granules into hard tablets of quite uniform weight, notably of pharmaceuticals, but also of some solid catalyst formulations. The process is illustrated in Figure 12.8(a). A powder is loaded into a die where it is retained by a lower punch then it is compressed with an upper punch, and the tablet is ejected by raising both punches. 

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