High Quality Content by WIKIPEDIA articles! VSI mill (vertical shaft impactor mill) is the type of fine grinder which is used a free impact of material particles with a wear plate. Any hard or friable materials can be ground with low value of metal waste. This type of mill is combined with a classifier for fine tuning of a product size.Mill uses for hard and friable materials. Wood, most metals and plastics are inoperable. Raw material must be dry. Capacity strongly depends on characteristics of material and a product size.