R253 Tablet Press

R253 Highlights

The R253 can be equipped with a number of special features to overcome issues of flowability, enhance wear resistance and to maximize both the quantity and quality of tablets produced.

Tooling options

Special tooling features include high-pressure heads, core rods and multi-tip punches.

(1) Punch holders for high compression forces:

Generally speaking, pharmaceutical presses are equipped with standardized mushroom-head tooling, as compression and ejection forces are limited for small oral intake tablets. However, for industrial applications, higher compression and ejection forces are required. Once compression forces rise above 60kN, we strongly recommend the use of the GEA proprietary punch holder design for long lasting trouble-free compaction at the lowest cost. 

The GEA punch holders are different from the EU or TSM standard in three ways:  

1. The patented high-pressure heads are milled in such a way that the contact with the compression roller is a line, as opposed to the single point contact between a mushroom- head punch and the compression roller. The line contact reduces the specific pressure at the contact point considerably, resulting in a longer life time of the punch head.
2.  As the punch holder is not subject to heavy wear, we always propose tooling split into two parts: the punch holder and the punch tip. In this way, both can be exchanged separately.
3.  Rollers on the side of the high-pressure head roll in a cam track compared to the friction movement of a mushroom-head in the cams. These rollers also allow for a longer dwell time at pre-compression and for smooth wear-free ejection.  
   

(2) Core rods:

Pellets with vertical holes are made using core rods held and centred by the lower punch. A central ring is positioned on the turret part between the dies and the lower punch guides. This ring is used to secure the core rod holder pins at the correct height. During the complete compression cycle the core rod remains flush with the die table surface. Whilst filling, the powder flows around the core rod into the die. Occasional powder remains on top of the core rod get wiped off by a scraper blade. A top punch with a central hole closes off the die and the pellet is compressed. Core rod material properties and surface finish must be carefully chosen to avoid rupturing of the core rod during pellet ejection.

(3) Multi-tip tooling:

To increase production output for smaller tablets, multi-tip tooling is one of the possibilities. A number of smaller punch tips are fastened on a larger punch holder. The production output is multiplied by the number of tool tips without changing the dwell or de-aeration time.

Powder in-feed options

A number of features are available to improve the flow of powders with poor flowability and to ensure fragile powders are not damaged.

(1) Double-paddle feeder:

The double-paddle rotary feeder is, at present, the most used feeder type, because the time the die travels under the feeder is longer than with other feeder types. This enables faster tablet output speeds. The first paddle of the feeder is located above the overfill cam, while the second paddle is situated above the dosing cam recycling the powder back to the first paddle.

Advantages of the double-paddle feeder: 

• Independent drive for each paddle, with individual speed setting  
• Light weight 
• No sprockets or belts for transmission between paddles 
• Easy to remove, open and clean 
• Exchangeable paddle shapes for different powder characteristics 
• Available with slide-in wear plate, allowing the feeder to make contact with the turret surface. This minimizes the quantity of powder outside the feeder, increasing yield. 

(2) Vibra-fluid feeder: 

A vibratory device improves the flow of difficult powders.  

(3) Powder dosing valve or PDV: 

Presses are often fed from IBCs or silos. As these run empty, the powder pressure in the press feeder and hence the die varies, resulting in tablet weight variations. The tablet weight control system on the press or the operator can adjust the die fill, but the PDV is a much easier way to keep the feeder pressure constant. A sensor detects the powder level in a transparent tube and controls the motor of the powder scraper. When the scraper does not rotate the powder flow stops. In addition to keeping the powder pressure constant, the PDV prevents powder segregation. Another advantage is that the PDV can be used with abrasive powders. 

Perfecting the ejection

Several solutions are available to make sure the pressed components are not damaged or deformed during ejection.

(1) Mitigating the impact of high ejection forces: 

When proprietary punch holders with bearings rolling on cams are used, ejection forces up to 10kN can be sustained without excessive wear and tear. 

(2) Die wall lubrication:  

As a rule, lubricants enabling smooth ejection are blended into the powder. However, for some applications this is not an option, because most solid lubricants reduce tablet hardness or contaminate the powder. An alternative to adding a lubricant to the powder blend, the die wall lubrication system deposits a thin oil or grease film on the die wall to ensure smooth tablet ejection. A complete solution is available to control the amount of lubricant on the die wall.

(3) Punch face lubrication: 

When punch face sticking is a problem, a magnesium stearate film can be deposited on the punch faces.  

(4) Tablet take-off system: 

The tablet take-off replaces the standard tablet chute and is a great feature for removing fragile tablets from the press and/or bringing tablets on a single line for further processing. 

Process control

(1) Air compensator for constant density compression

A top and bottom air compensator is installed when full symmetrical compaction is required. 

An air compensator, a feature exclusive to GEA tablet presses, is connected to both top and bottom compression roller and functions as a cushion. The pressure in the air compensator is set in such a way that during every pellet compression cycle, the rollers travel a few tenths of a millimeter, making sure that every compression is performed at the set compensator pressure. Every pellet will be pressed to equal density and height variations will reflect differences in die fill and powder property variations. 

(2) Air compensator for constant thickness compression

The pressure set in the compensator equals the maximum compression force the tooling tips can take. When the set threshold is crossed, the air compensator will move instantly and protect individual punch tips from overload. The press will stop and the overload position will be indicated.