Roller compaction pressure

Different spectral preprocessing and transformations available in SIMCA P-p (version 10.0, Umetrics, Sweden) were evaluated and the best approach for data handling and manipulation was determined. Data collected on the surrogate tablets were divided into a training set to generate the PLS models, and prediction set to test the PLS models. MCC powder, equilibrated at different RH, was also roller compacted at different roll speeds on a Fitzpatrick IR220 roller compactor fitted with smooth rolls. Powder feed rate and roll pressure were kept constant for all experiments. The key sample attributes measured on the surrogate tablets were also measured for the samples prepared by roller compaction. 

The 10% w/w APAP powder blend was roller compacted. Different moisture contents were achieved by equilibrating and roller compacting the above powder blend under 24, 45, and 65% RH conditions, representing 3.3, 5.0, and 6.3% w/w moisture content, respectively. Compacts were prepared at 5.0, 6.0, and 7.2 rpm roll speeds with the powder feed rate and roll pressure kept constant. Compaction run time was four minutes at each roll speed. Samples were also collected for off-line measurements of... 

The compaction system consists of two, counter-rotating rolls at equivalent speeds. One roll is normally fixed while the other is allowed to float. The floating roll was implemented to control the roll gap. The roll force is applied to the floating roll by hydraulic pressure, which is counteracted by the normal force of the fixed rolls. This force is subsequently applied to the blend in the gap. A schematic of three typical roller compaction system arrangements with a feed screw can be found in Fig. 6.1. 

Dehont et al. assumed that the material in the compaction area remains horizontal and moves at the peripheral speed of the rollers. They also considered that the angle a is independent of the roller diameter size and noted that the flake thickness ei depends on the roller speed, the roller surface, and the compaction pressure. All these parameters influence the density of the flake, d. Dehont et al. concluded that if the same flake thickness was obtained with different roller diameters, the flake density would be greater with larger diameter rollers. This is due to the greater nip angle formed, with the larger rolls allowing more material to be compacted. 

Compaction pressure must be distributed as uniformly as possible across the whole roller-gripped powder mass. 

The chief objective of roller compaction is to consistently make an agglomerate of sufficient strength that meets required density, granulometry, and powder flow specifications. Operationally, the key goal of a compactor is to maintain a range of pressure on the feedstock, independent of the fluctuating powder granulometry and flow fed into the rolls, so that a consistent compact is made. 

Funakoshi, Y. Asogawa, T. Satake, E. Use of a novel roller compactor with a concavo-convex roller parr to obtain uniform compacting pressure. Drug Dev. Ind. Pharm. 1977, 3 (6), 555-573. 

In older roller compactors, the feed screw did not always adequately deliver the powder to the gripping and compaction zone due to stationary side seals which resist the flow. Factors affecting uniform distribution of compaction pressures were investigated by Funakoshi etal. (2S). The distribution of compaction pressures across the entire ribbon was estimated by determining the force needed to drill the ribbon at various locations. 

A concave-convex roller pair was used which maintained their mutual fit when rotating. The rims of the concave roller were varied with different wall slopes (o>) from 45 to 90. The study found the compaction pressures to be uniform over the whole width of the rollers and the amount of uncompacted material (leakage) was reduced when the wall slope of 65 was used. These findings were later supported by another study by Parrott (26). 

Roll gap is defined the narrowest distance between the two rolls. At any given compaction pressure, a specific roller gap will yield a corresponding fixed flake thickness (allowing for some product expansion). A fixed feed rate for a fixed roller speed and compaction pressure maintains the flake thickness. Rollers get too close if the material feed is too low and vice versa. Therefore, in principle, acceleration or deceleration of product delivery system can cause variations in the ribbon thickness and density. By monitoring the roll gap in a feedback loop, a constant material feed can be achieved. 

The bulk of the fertilizer market demand is for the two Coarse grades, necessitating some compaction of the finer grades to produce these. Passage of the finer Standard and Soluble grades of material through closely spaced steel rollers under pressure forms a fused sheet of potassium chloride, because of the plastic nature of this salt. This fused sheet is then broken up and rescreened to raise the proportion of Granular and Coarse products produced. 

Figure 179. Schematic representation of high pressure agglomeration equipment, (a) Reciprocating piston and die (eccenter) press, (b) rotary tabletting machine, (c) ram extrusion or plunger press, (d) roller compacting machine, (e) roller briquetting machine...

Design of the roller surfaces In designing a roller press surface, some fundamental considerations do influence the possible shape, size, and distribution of the cups or indentations.Limitations include the relationships of circumferential pocket dimension/roller circumference and pocket depth/roller diameter as well as the pocket shape. Associated with these are problems of release, clam-shelling (splitting), extrusion, removal of air from the compaction zone, and uneven distribution of feed as well as compaction pressure. In spite of those limitations, a large variety of shapes can be produced. 

Dry granulation involves the aggregation of particles by high pressure to form bonds between particles by virtue of their close proximity. Two approaches to dry granulation are used in the pharmaceutical industry slugging and roller compaction. In either method, the material can be compacted with a binder to improve the bonding strength. 

Roller Compaction. In roller compaction, the powder is compacted by means of pressure rollers (Figure 11.23). The powder is fed between two cylindrical rollers, rotating in opposite directions. The rollers may be flat, which will produce sheets of compacted material, or they maybe dimpled, in which case, briquettes in the shape of the dimples will be formed. If sheets are produced, they are milled and screened to the required size. Roller compaction requires less lubricant to be added than does slugging. 

Compression Molding Compression molding is a molding technique for making composite materials under specific temperature and pressure. The unit cost is reduced by the faster cycle times that are possible when compression molding/ sheet molding compounds (SMC) are made. SMC is a sheet that sandwiches chopped fiber between two layers of resin paste. Chopped fiber drop onto the paste and a second film carrier faces another layer of resin down on top of the fiber. Rollers compact the sheet to saturate the fiber with resin and to squeeze out... 

PVP Concentration. The effect of binder concentration on the properties of granules and tablets prepared by roller compaction is dependent on other processing parameters including feed rate, roll pressure, and speed. Increasing the binder level increases tablet hardness and decreases their friability due to the... 

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