In the pharmaceutical industry, tablets are the most widely used forms to deliver medicines to patients. Tablets are more acceptable than medicines in liquid form. However, tablets must be extremely stable with excellent dose uniformity to be well accepted in the industry. Even with the apparent simplicity of a tablet, its manufacture can be rather challenging. Production is dependent upon the choice for the most appropriate powder processing equipment.
Powder processing equipment in the pharmaceutical industry
Powder processing equipment plays a very big role in the process of size reduction to increase surface area and improve formulation dissolution properties. Powder processing equipment will ensure that sizes of particles are consistent to allow for a better quality of mixture for single dosage forms like tablets and capsules. The most common size reduction machines used in the pharmaceutical industry fall into categories: mechanical impact and impact through fluid energy. Powder processing equipment that relies on mechanical impact include hammer mills and pin mills while fluid energy mills or micronizers include spiral jet mills, loop jet mills and fluidized bed jet mills for particle size reduction.
The importance of feed rate in particle size reduction
When using size reduction machines, feed rate will determine particle size distribution. The feeder is important in controlling the residence time of particles in the powder processing equipment and eventually on the resulting particle size distribution. There are different feed devices used in the industry that includes rotary valves, vibratory tray devices, single screw feeders and twin screw feeders. The choice for feed device depends on the product flow characteristics but normally the twin screw feeder is a common choice. The twin screw feeder is often acceptable for materials that are free-flowing with constant density.
Feed rates for pharmaceutical size reduction ranges from 20g/hour on a small jet mill to 840kg/hour on production mills. As with all feeders, the feed rate range depends on the type of screw configuration including the drive type and turn down ratio. Depending on the requirements for accurate feed, the screw feeder can be supplied through volumetric or gravimetric configuration. However, it should be noted than when feeding materials with high variations in bulk density, volumetric feeders will have significantly high fluctuations in feed rates due to resulting fluctuations in the filling of screws. In instances when cohesive materials have to be processed, it is possible in volumetric mode to have almost no material discharging while the screws are running. This is particularly noticeable in instances where there is bridge building or packing in the hopper.
Most milling and micronization operations in the pharmaceutical industry involve particle size reduction of highly potent active ingredients. As the potency of dry ingredients increases, the more that there is a need for an isolator in the milling and feeding operations. Using the isolator has its benefits; it protects the operator from the risks of the drug and at the same time, it protects the drugs from any hazards found in the outside environment. When using isolators in powder processing equipment, they must be easily dismantled for cleaning.