Roller Extrusion System

As a new system in the pharmaceutical market the function and usability of a roller extrusion system for pharmaceutical wet granulation will be discussed in more detail. 

Arising from these considerations the planetary roller extruder seems to be particularly suitable for the wet and melt agglomeration of pharmaceutical powder blends. In the following is described a system for continuous wet granulation based on a planetary extruder and the usage thereof. 

Cooing/Heating Spirals Central Spindle Nose 

The system is available for very different outputs from 2 up to l,000°kg/hr, realized by four different machine sizes only. Due to the continuous processing very different batch sizes can be granulated with one machine size. For instance, in the case of a granulator with a nominal output of 10°kg/hr, normally the realizable output is about 2-20°kg/hr, leading to batch sizes from 500°g in 15°min up to 480°kg/24hrs. 

It is to distinguish between feeding of the powder components and if applicable— the liquid components, e.g., binder solutions. 

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Cast film extrusion. In a cast film extrusion process, a thin film is extruded through a slit onto a chilled, highly polished, turning roll where it is quenched from one side. The speed of the roller controls the draw ratio and final film thickness. The film is then sent to a second roller for cooling of the other side. Finally, the film passes through a system of rollers and is wound onto a roll. A typical film casting process is depicted in Figs. 3.53... 

Blown film extrusion is perhaps the most widely used extrusion technique, by production volume. Billions of pounds of polyethylene are processed annually by this method to make products such as grocery sacks and trash can liners. In a blown film system (Figure 14-30), the melt is generally extruded vertically upward through an annular die. The thin tube is filled with air as it travels up to a collapsing frame that flattens it before it enters the nip rollers, which pull the film away from the die. The flattened tube then travels over a series of idle rollers to a slitter,... 

Another modular system is often called laboratory equipment it can be used for small scale production and for the laboratory evaluation of small samples. Fig. 11.26 depicts the design and some of the accessories. In the most simple execution a hopper feeds a pair of rollers which are driven by a hand crank. The rollers can be solid and may be equipped with compacting or briquetting surfaces (see Section 8.4.3) or two perforated, geared, intermeshing pelleting rolls (see Section 8.4.2) are installed to accomplish medium pressure extrusion. In a modular fashion the rollers can be motorized, screw feeders can be added, and the rolls may be oriented vertical or horizontal or in any other direction. As shown in the photographs of Fig. 11.27 the roller frame can be totally enclosed for dust control if toxic or hazardous materials are processed. A panel includes controls and instrumentation for data display and collection. 

Instead of a roller press a pellet mill may be used for densification. The rest of the system is essentially the same. However, for successful extrusion (pelleting) some lubricant (liquid) may have to be added. Although the temperature rise caused by friction in the die holes may often be sufficient to naturally dry-out the small amount of liquid, the resulting granules do still not exhibit the same uniform quality as those originating from sheets made with roller presses. 

There are some characteristic parameters in the blown film process (see Fig. 24.1) the blow-up ratio (BUR), which is the ratio between the final radius (Of) and the radius at the die exit (Uq) the thickness ratio (TR) calculated as the ratio of thickness at the die exit (//q) and the final film thickness (//f) and the draw ratio (DR) defined as the ratio of take-up roller velocity (Vf) to the extrusion velocity (Vq). The stretching force (F ) is the force needed to take up the bubble by the roller system (Fig. 24.1). 

The product directly formed by extrusion is not strong and needs to be handled with considerable care. A system for the proper handling of extrudate is essential. For a product needed in the exact shape of the die or the holes in a die plate, a sophisticated system such as a belt or sequence of rollers having the same speed as the extrudate is needed. For some products, it is sufficient to simply allow the material to fall off the die plate under the action of gravity. This would be satisfactory if the product is to be of a granular form where very close size and shape control are not necessary. 

Sheet material, i.e. material thicker than about 0.25 mm, is usually produced by using a slit-shaped die, whereas thinner material is often produced by a blown film extrusion process in which an annular die is used and air is blown into the centre of the tubular extrudate to blow it into a sort of bubble. At a certain distance from the die the polymer is sufficiently cool to solidify into a film, which is then flattened and collected on rollers. Figure 1.9 illustrates a blown-film system. 

A two component, PUR laminating adhesive system for panel construction, for extrusion or roller application, offering little or no foaming tendency and a very high elongation to break. 

Preferrred systems of application. The nature of the materials being bonded will many times dictate the preferred method of application. Large surfaces may require a spray or roller coat application. Thin plastics or fabrics may require also a roller or spray. Other applications call for an extrusion, while even others will lend themselves better to trowel, spot, spatula, brush, or other types of application. 

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