In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment. In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed
Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/16″—1 5/8″) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.
Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of
Two general classifications of gearing are used for ball Mill drives. These are the spur gear and the helical gear. Helical gearing may be either of the single helical or double helical (Herringbone) design.
These are generally furnished on the smaller diameter mills using V-belt drives or reducer drives. Spur gears and pinions are cut with teeth of the full depth involute tooth form thus assuring maximum tooth strength and long wearing life. The main gear is cut from a special Meehanite metal casting and is constructed split and reversible. The pinion is cut from a steel forging
Several types of ball mill drives can be furnished, made up of various combinations of gearing, motors and transmission equipment. The correct combination to be selected takes into consideration power requirements, gear ratings, floor space, interference from other plant equipment and motor characteristics. The main types are described and illustrated on these pages.
Motors considered are the squirrel cage motor, wound rotor motor, and synchronous motor. One important advantage of the synchronous motor is the possible correcting of power factor within your operation, through its use. When using
Each application dictates the selection of proper feeding arrangement. This depends upon whether the grinding will be open circuit or closed circuit, and dry grinding or wet grinding. The size of feed and tonnage rates are also important factors.
Speed of scoop lip is important. Listed below for your convenience is a table showing critical speeds for various radius scoops. Tip of scoop lip speed should not exceed 90 to 95% of critical speed. Beyond this scoop efficiency decreases and scoop will have the tendency to throw material rather than pick it up.
The single scoop feeder provides a
Essentially tube mills and pebble mills may be considered as ball mills, the basic difference being that the ratio of length to diameter is greater. Usually the shell length is between 2 and 5 times the diameter. These mills are primarily used to grind various materials to 100 mesh and finer. The Tube Mill uses iron or steel balls as the grinding media, and liners of various metals and alloys.
Where iron contamination is detrimental such as in the case of grinding Feldspar for porcelain, Corundum, talc, certain clays, chemicals and glass sand, a pebble mill is indicated. In such
The principle of Grate Discharge grinding is nearly universally adapted in the cement grinding industry. Grate Discharge Ball Mills are the rule rather than the exception. Rod Mills for raw and finish grinding begin to enter the picture. Larger and larger diameter mills become common. Lengths tend to shorten. Cement grinding using Grate Discharge principles developed in the ore milling industry applied to the cement industry. This experience plus the years of manufacturing know how unquestionably qualify Grate Discharge grinding for the Cement Industry.
RAW CEMENT GRINDING
This phase of grinding may be either
This page is devoted to the subject “From the Comminution Theory to Practice by selection of the correct Process Equipment” by taking you step by step through some of the variables encountered in the specific part of Comminution called grinding and how each of these affect your operations. Should it be possible to reduce all of these variables to a simple mathematical formula the selection of a grinding mill would, of course, be simple. Many approaches to this have been made but to date a foolproof formula, both mathematically and practically
The subject of grinding media is still controversial. The following information is general and based upon facts gathered from many operations.
General statements can be made and are worthy of consideration when selecting grinding media. For the best results it has been found that the smallest diameter ball or rod which will break down the particular material to be ground is desirable since greatest surface area is obtained. From the standpoint of economy, the larger the media the higher will be the liner consumption and media consumption. The minimum size of grinding balls should be selected