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
Ball Mills and stirred mills are applied across a wide range of applications, but for each ore there is optimum efficient range. The figure to the left shows the typical application ranges for ball mills and stirred mill. The Vertimill is always more efficient than a ball mill with energy savings ranging from 30% to greater than 50%. The transition point from the Vertimill to an SMD/IsaMill varies depending on the ore properties but generally is in the range of 20 to 40 microns. A detailed test program can be carried out to determine the optimum energy efficient circuit.
homemade ball mill
By this drawing, it is suggested that a typical laboratory rod or ball mill might be fabricated from 20 cm (8 inch) diameter schedule 40 type 316 stainless steel pipe and would be about 38 cm (15 inches) long.
The stainless steel grinding rods for this size of mill may be a graduated charge from 25 to 10 mm diameter (1 inch to 1/2 inch) but variations in size are not essential. Some mineral processing laboratories use a 30 cm diameter x 61 cm long (12 inch x 24 inch) rod mill with 30 and 45 mm rods (1 1/4 inch and 1 3/4 inch). A similar but smaller 30 cm x 30 cm (12 inch
Tube Mills consist of revolving cylinders, the interior of which is perfectly plain. They contain a number of hard balls. They differ from ball mills essentially in having the inlet for ore at one end and the outlet at the other, and in the absence of provision in the machine itself for the return of uncrushed material (oversize). It is therefore necessary for the cylinders to be of greater length than in ball mills. The number of balls used is also much larger, and, according to one view, the reduction of the ore is effected by grinding rather than by impact, as in ball mills
Here is a trick for knowing if your flotation feed grind size is fine enough to achieve adequate mineral liberation without doing a full mineralogy study.
- If your key mineral is sufficiently liberated, it should float and be recovered in the first few minutes in an initial %mass that stabilizes quickly
= the green curve.
- If, your valuable minerals are still badly locked, the longer you float, the more %mass you pull, the more your recovery increases
= the red curve.
Sadly, I have seen unsavvy “metallurgist” do recovery VS flotation time tests only to falsely conclude they needed more flotation time to get a higher metal recovery. Selective flotation is allowed by a minimum liberation level in which you maximize metal recovery in a minimum mass. Recognizing the partners can save you much needless pain.
Now I do not advocate unnecessary grinding, but you need what you need. I have seen some
In the Griffin Mill, there is a single roller suspended in a similar way to the rollers in a Huntington mill. The roller is about 18 inches in diameter, and rolls on the inside of a die ring 30 inches in diameter. It takes material up to 1½ inches in diameter, and crushes either wet or dry. It does not appear to be used anywhere either as an amalgamator or to prepare ore for amalgamation, but is described here for convenience. In December, 1904, 34 Griffin mills and 14 Huntington mills were in use in Western Australia preparing ore for cyaniding.
Among other roller mills, the Bryan Mill is one
The Huntington Roller Mill, here described as a type of the many good roller mills now in use, is best suited for the fine crushing of ores which are not too hard. It consists of an iron pan, at the top of which a ring, B (Fig. 40), is set, and attached to this are three stems, D, each of which has a steel shoe, E, fastened to it. The stems are suspended from the ring and are free to swing in a radial direction, as well as to rotate round their own axes, whilst the whole ring, B, with the stems and shoes, revolves round the central shaft, G. The shoes or rollers, as they are
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