The PACCO Mill is a high energy mill and one of the most versatile ad widely used designs in the pharmaceutical industry. The principle of size reduction in the hammer mill is one of high-velocity impact between the rapidly moving hammers / knives / blades mounted on a rotor and powder particles. This mill can produce a wide range of particle sizes, even down to micrometer size. The particle shape, however, is generally sharper and more irregular than that produced by compression methods.
The force imparted by the hammers and the screen opening size and shape control the degree of particle size reduction.
Some of the characteristics include:
– They can be used for size reduction of wet or dry granulations and milling of raw materials
– There is a wide range of interchangeable feed throats and variable feed screw systems available to optimize the feed rate
– Hammers can rotate horizontally or vertically, based on the rotor configuration, and at variable speeds
– Hammers can be fixed or free-swinging
– Hammers with blunt or impact edges are preferred for pulverizing and knife or sharp edges are preferred for chopping or sizing of granules
– Screen openings generally vary from 0.3 to 38mm, with round or square perforations, diagonal or straight slots, or with a rasping surface
– Feed rate and dryness of the granules are important variables relative to the material
– Types of hammers, rotor speed, screen type, thickness, and opening size are important variables relative to the machine
– Ease of setup, clean-up, minimum scale-up problems, and ability to handle a wide variety of size and type of feedstock are some advantages
– Heat buildup, screen wear, and potential clogging of screens are some of the limitations
– Integrated designs are available for dust contamination