Tablet press types

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.

Roll presses can produce large quantities of materials at low cost, but the product is fess uniform than that from molding or tableting presses. The introduction of the proper quantity of material into each of the rapidly rotating pockets in the rolls is the most difficult problem in the briquetting operation. Various types of feeders have helped to overcome much of this difficulty. 

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.

A powder compact s TS is the stress required to separate its constituent particles in tensile mode. This is measured for the tableting indices by transverse compression of the square compacts, using narrow platens. Stresses build within the sample until it fails in a tensile mode that is perpendicular to the direction of platen movement. Tablets that are manufactured on a traditional tablet press and that have high TS are considered hard and generally robust, and so this is a highly desired attribute for immediate release and other tablet types. 

No matter what type of tablet press was used in R D or in the pilot plant, there is no possible way to experience the phenomenon on a full-size batch and the associated time of the compaction run. One must be aware of the possible build-up of... 

Geometric dwell time is an indicator of a linear speed, sort of a yardstick that allows one to compar e speeds of different tablet presses. It is defined here as the time required for a punch to traverse a horizontal distance of 9.5 mm (when the flat portion of the IPT Type B punch head is in contact with the compression wheel). 

The basic unit of any tablet press is tooling consisting of two punches and a die, called a station. The upper and lower punches come together in the die that contains the tablet formulation. Principally, two different types of machines are used, the eccentric and the rotary press. The eccentric press produces about 50-130 tablets per minute. The rotary press has a multiplicity of stations arranged on a rotating table with the dies. A few or many thousands of tablets can be produced per minute. There are numerous models of presses, manufactured by a number of companies, ranging in size, speed, and capacity. 

A direct correlation between the results of an eccentric press and a rotary press cannot always be drawn. In addition there are many different tablet presses with different settings and possibilities. These problems can be overcome by using a compaction simulator early in the development stage. An advantage of such a simulator is its versatility, that is, all types of presses can be simulated with small amounts of solid. The problem, however, is that such a simulator is very expensive. 

While blending times and tablet press parameters may not be fully established for early phase clinical supply manufacturing of solid oral dosages, those variables have a much lower potential to directly affect product safety than sterility, endotoxin contamination, or objectionable types and levels of particulates do for sterile, parenteral clinical supplies. Because clinical supplies can be incompletely characterized, and are usually given to patients already in weakened conditions, those processes and their related validation data necessary to guarantee patient and product safety (e.g., sterilization and aseptic fill) are expected to be in place as early as Phase I clinical supply manufacture. ... 

Effervescent tablets are normally produced by machines with external lubrication systems. Most tablet machine manufacturers can add this type of equipment to their rotary machines. Products with a high proportion of acetylsalicylic acid can be manufactured without any traditional lubricants. Consequently, conventional rotary tablet presses can be used. Effervescent acetylsalicylic acid tablets are produced on ordinary high-speed rotary presses at the Pharmacia plant in Helsingborg, Sweden. 

There are two types of tablet press. The excentric press has one die and one pair of punches. The rotary press has a larger number of dies which are fitted, with their corresponding punches, into a rotating turret. 

It has long been known that for some formulations, changing the speed of operation of the tablet press or changing the type of press can have a profound effect on tablet quality. Such circumstances may arise, for example, when changing from a slow excentric press in formulation development to a high speed rotary in production. 

A compaction simulator must be able to mimic the full compression cycle of the unit operation. Early attempts at compaction simulation utilized mechanical property testing equipment (e.g., Instron and Lloyd type machines) to compact powders into compacts. Although these machines were well suited to apply appropriate compression loads, they were not designed for the high velocities and accelerations necessary to simulate the double-ended compression cycle of a rotary tablet press (2). 

Mechanically powered compaction simulators are also available to replicate the compression event of tablet presses (3). These machines leverage the design of traditional rotary tablet presses where the punches are forced between a set of roll wheels to enable the compression event. The punch type and roll wheels can be changed to replicate the compression event of different press types. In some models, the fill station, compression station(s), and ejection station arc aligned in series on a linear track, where the punches and die travel along this track from station to station to complete the fUl-comprcss-ejection cycle. 

The reciprocating movement of the piston(s) and the relatively small volume of the die cavity severely restrict the capacity of this type of equipment even if modern, multistation, rotary tabletting presses are considered. With the production of larger pieces in, for example, hydraulic presses or roller briquetting machines, the accuracy in weight, shape, and dimensions is no longer obtained. 

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.

When the bulk containing the binder is uniform, it is compressed on pneumatic, hydraulic, or ram-type presses. Compression can be carried out in presses provided with suitably designed cavities or in metallic pans. The pans ate filled with the powder mass, and a plunger with a cross-sectional shape similar to that of the pan is used to compress the tablet. The resulting tablets ate commonly used with powder puffs or cosmetic bmshes. 

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... 

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