Gregg Shemanski discusses various types of grinding methods and their applications in the May 2015 issue of Powder & Bulk Solids.
Different Approaches to Grinding Abrasive Materials
I have been grinding materials or particle size reduction for over 30 years. I was introduced to making powder out of lead pigs in a ball mill at my first job, and have been working in the field of particle size reduction in one form or another for most of my life. The purpose of this article is not to show a complete listing of all types of particle size reduction machinery, but to list the ones that I have used and found to be effective in their capabilities in grinding very hard or abrasive materials. This grinding takes a little more thought and consideration for wear and the potential contamination that may become imparted on the material which is being attempted to be ground.
Primary Reduction Jaw Crusher
In quarry operations, very large jaw crushers can be found. These are primarily used to reduce shot blast size materials such as limestone and road bed materials to a wide variety of sizes. In specialty particle size reduction, one discovers very hard to grind or specialty materials. In the area of very abrasive or just extremely hard materials (i.e. mohs of up to 7 or 8), jaw crushers of 36 x 24 in. have been found to be able to reduce large chunks of material from about 24 in. top size to -6 in. For very abrasive products that are ground, it is one of the most economical ways of reducing the particle size. The need to replace jaws for processing hard, abrasive materials is routine, but it sure beats trying to hydraulically jackhammer the materials. Jaw crushers can easily work in tandem with other jaw crushers. The smaller the jaw opening, the smaller the top size of the finished material can be delivered. Often the need is to initially take up to 24-in. material and reduce it to a nice beginning size for secondary grinding machines (a maximum size of 3-4 in.). To accomplish this, the primary jaw (36×20 in.) has been successfully used as a pre-crusher to feed a 16×10-in. jaw crusher. Average top size has been around 3 in. with minimal fines and minimal wear using this equipment configuration, although very large and some smaller jaw crushers are also available. The use of manganese steel wear parts is preferred, but other materials of construction can be engineered to each specific need.