Tablet rotary press

Fig. 20 Automated high-output rotary tablet press. (Courtesy of Fette America.)...

Rotary tablet press Typical number of stations per press = 20-40 Typical throughput = 9,000 - 300,000 tablets/hr Tablet diameter = 10-30 mm [28]... 

Subsequent to these successful pilot scale trials, the formulation was scaled-up to the production launch site. Once again, only those parameters recognized as critical were modified during manufacture. The compression parameters that were modified were speed and hardness. A total of four production-sized batches were manufactured, with the first batch being compressed on a 43 station Fette 2080 rotary tablet press, and three subsequent batches compressed on a 36 station Fette 2090 rotary tablet press. Three compression speeds and three compression forces were successfully evaluated... 

To consider the subject of scale-up of the compaction and tableting process, one must consider the production of one tablet in 30 minutes, if one were a new graduate student using the Carver Hydraulic Laboratory Press for the first time, to a single-stroke Model E or Model F press at 60 tablets per minute, to a full-scale rotary tablet press at more than 2000 tablets per minute. 

Single-stroke Stokes or Manesty model E or model F presses Three- to six-station rotary tablet press (e.g., Korsch)... 

These rotary tablet presses range from machines with 16-90 or more stations of matched tooling. Specific details for each manufacturer would be best obtained from the supplier s literature. 

Upon compaction scale-up of the formula to a higher-speed rotary tablet press, die cracking was noticed. 

To test the foregoing dimensionless relationship, two powders (Avicel Pl 1101, a ductile, viscoelastic material, and Emcompress, a brittle material, blended with 0.5% magnesium steaiate) were compressed on the PressterTw, a single-station mechanical replicator of rotary tablet presses. In the first set of experiments, a 16-station Manesty Betapress (a research-scale press) was simulated at two speeds, 60 and 100 rpm. In the second set, a 36-station Fette P2090 (a medium-scale production press) was simulated at two speeds, 55.8 and 70 rpm. It should be noted that 100 rpm of the Beta-press corresponds to 55.8 rpm of the Fette 2090 in terms of the linear speed of the turret. Basic parameters for the two tablet presses arc presented in Table 3. 

The pharmaceutical industry produces tablets almost exclusively on rotary tablet presses from pilot plant to commercial manufacture. The output from different tablet presses may range from a few thousand tablets per hour to more than 1 million tablets per hour. By design, the compression event occurs using three parts a die, lower punch, and upper punch. The dies and punches are mounted on a rotating turret. The shape of the die controls the shape of the tablets, while the distance between the lower and upper punch tips at the maximum compression force determines the thickness of the tablets. The tablet compression process is divided into three steps powder filling into the die, compression, and tablet ejection from the die.85... 

Oates, R. J., and Mitchell, A. G. (1989), Calculation of punch displacement and work of powder compaction on a rotary tablet press,/. Pharm. Pharmacol., 41, 517-523. 

Laich,T., and Kissel,T. (1998), Automatic adaptation of lubricant quantity by control of an external lubrication. Tests on a reciprocating and on a rotary tablet press, Pharm. Ind., 60(10), 896-904. 

It is suggested that four mechanisms are basically involved in the process of compression of particles deformation, densification, fragmentation, and attrition. The process of compression is briefly described as follows small solid particles are filled in a die cavity and a compression force is applied to it by means of punches and then the formed monolithic dosage form is ejected. The shape of the tablet is dictated by the shape of the die while the distance between the punch tips at the point of maximum compression governs the tablet thickness, and the punch tip configuration determines the profile of the tablet. The compression cycle in a conventional rotary tablet press will be described in detail in this chapter and is illustrated in Figure 1. 

A rotary tablet press machine (Figure 2) comprises a housing in which the compression set and subsets (upper and lower roller assemblies) are mounted, the turret head, the upper cams, the weight control assembly and the lower cams, the hopper,... 

FIGURE 2 Rotary tablet press machine (a) left-side view (b) black-side view. (1) Cabinet, (2) compression, (3) turret, (4) gear, (5) weight control assembly and lower cams, (6) plate cams, (7) guarding, (8) hopper system, (9) feed frame assembly, (10) take-off chute, (11) aspiration assembly, (12) electrical system. 

Rotary tablet presses could be designed to be single, double, or triple sided. A single-sided press comprises one hopper, one set of compression rolls, and one takeoff chute unit whereas double- and triple-sided presses comprise two and three each... 

First rotary tablet press traced to Wyeth, 1872. Pulse of Pharmacy [Wyeth] 1959,13 (1). 

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. 

Tablets remain one of the most popular dosage forms for consumers. Convenience, portability, and ease of administration are a few of the factors that drive the market for tablets. Pharmaceutical production also favors tablets owing to the low cost of manufacture compared to other dosage forms. To reduce associated costs and balance the limited drug substance available, tablet development usually begins at a small scale. Manual equipment (i.e., Carver press) or a singlestation tablet machine (i.e., F-Press, EKO) may be used to manufacture tablets one at a time. Small-scale rotary tablet presses (e.g., B3B, BetaPress) are usually used for early clinical trials and formulation optimization prior to scaling up onto a production machine (e.g., Fette 2090 or 3090).

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 scrape-off occurs immediately after ejection. Fig. 2 illustrates a tablet stripper on a rotary tablet press. Typical forces during tablet scrape-off are 2N or less. Scrape-off forces of 6N or higher result in tablets sticking to the lower punches and subsequently picking or, under extreme circumstances, shearing the bottom of the tablet. Frequently, shearing of the lower portions of the tablet due to scrape-off problems is mistaken for capping. However, this can be easily distinguished by examining the lower punches and rotating the press manually.

Pharmaceutical tablets are generally produced on rotary tablet presses (Fig. 3), where upper and lower punches reside in the upper and lower turret, respectively. The dies are inserted in the die table and secured by die lock screws. The upper and lower turret and the die table are precisely aligned. The movement of the... 

Modern rotary tablet presses are typically designed in separate machine sections (press zones). Typical sections... 

Upper precompression and main compression rollers insertion depth adjustments Insertion depth for both precompression and main compression is adjusted in the upper cam section. The insertion depth determines the location of tablet formation in the die cavity relative to the top of the die table as shown in Fig. 5. It is measured as the distance at which the upper punch enters into the die at the tangent between the upper punch head and the compression roller. Insertion depth can be varied between 2 and 6 mm on most machines and is typically maintained between 3 and 4 mm. For precompression and main compression, the insertion depth should be maintained at approximately the same position. On most modern rotary tablet presses, the adjustments for precompression and main compression insertion depth are independent. However, on many older designs, the precompression roller is attached to the main compression roller assembly and its position is measured relative to the main compression roller position. In this way, the ratio of precompression to main compression remains constant as machine adjustments are made. 

Because the compression characteristics of powders are time-dependent (the exact extent of this dependency depends on the primary modes of deformation), the final tablet properties depend not only on maximum compression forces but also on the rate at which these forces (rate of deformation) are applied and removed. On a rotary tablet press, the rate of deformation is determined by the tangential velocity of the punch and the compression roller diameters. The tangential velocity of the punch is a product of the press speed and the die table circumference (i.e., die table rpm x 3.14 x pitch circle diameter). As the tangential velocity increases, the rates of compression and decompression increase while the overall compression time decreases. The roller diameter affects both the rate of compression and decompression. As the diameter increases, the rates of compression and decompression decrease. 

Although most rotary tablet presses operate by maintaining fixed roller positions during compression, some designs incorporate a compression compensator system in which the counterforce for compression is air pressure. This system compresses to a constant force and allows roller movement when the preset force is achieved. Under these conditions, potential exists to increase the time that the force is maintained near its peak value (approximately 90% of maximum). Compression to a constant force should theoretically provide a more uniform tablet hardness and more uniform dissolution profiles while allowing a greater variation in tablet thickness. 

Lower Punch Brakes. Most rotary tablet presses are equipped with lower-punch brakes that are Teflon tipped and spring loaded to apply constant pressure to the lower punches. Alternatively, some manufacturers apply pressure to a friction belt that provides resistance on the lower punches. The lower-punch brakes act as a retention system for holding the lower punches in place during press setup. More importantly, these systems help to minimize lower-punch chatter at high press speeds thus minimizing tablet weight variation. Some press manufacturers use the lower punch seals to retain the lower punches. 

Most high speed rotary tablet presses employ automatic lubrication systems during operation. Effective punch... 

Many modern rotary tablet presses use off-the-shelf load cells for force measurement. These load cells are highly accurate, durable, and easily replaced and calibrated. However, the final accuracy and repeatability of force measurement in the machine not only depend on the quality of the load cell, but also on the design of the compression assembly and the placement of the load cell within the assembly. 

Conventional rotary tablet presses are controlled by periodically taking tablet samples from the discharge chute and checking their tablet weight, thickness, and... 

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