Mixing powders is a common task in many industrial processes, as well as being a necessity in the production of most pharmaceuticals. Due to its frequency in so many production processes, there are a multitude of techniques and equipment available to mix dry powders. These different processes can be divided neatly into two distinct groups: wet and dry granulation.

Wet Granulation Techniques and Equipment

Wet granulation uses a liquid to aid in the mixing of the powders, usually with a heat source to dry the powders after the mixture is completed. Fluidized-bed granulators, mixers and tumbling granulators are examples of wet granulation equipment. With a Fluidized-bed granulator, liquid binders and solvents promote mixing and the particles of the powder are mixed using jets of heated gas. This type of system is not suitable for any compounds that might react violently to heat. As it is, it is important that heat dispersion systems be in place with a fluid-bed granulator to correctly manage waste heat. A tumbling granulator is a centrifuge that mixes a solution of solvents, binders and powders by spinning at high speeds. These systems have a fairly high recycling rate of unused powder as larger, usable product naturally stays closer to the bottom of the spinning drum and lighter, unusable particles can be recovered as they are moved up the sides of the drum. These smaller particles can then be gathered and reintroduced back into the system. A mixer is a simpler design of impellers and choppers that stirs the liquid, agitating the solution of powder and liquids until it is well mixed.

Dry Granulation Techniques and Equipment

The core technique of dry granulation is compression instead of using heat. When working with volatile powders and unable to use heat, compression is a viable alternative. Presses are usually employed in this process of which there are several varieties. Tablet and roll presses use compression to preform dry granulation. A tablet press is capable of creating complex shapes with exact specifications, combining powders together with extreme force. A roller press forces material through two rolling cylinders. In rolling presses the feed rate of the material is essential for a good result and sometimes a two stage process is required; a preliminary stage of wet processing and then a second stage of dry processing.

Conclusion

With any industrial process involving mixing equipment of powders it is critical to analyze the compounds and choose the correct process. With each process there are many different configurations of equipment to choose from, each with their own benefits. Experts should always be consulted before choosing the proper equipment for the job.