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Maintaining the ball mill charge and monitoring the feed rate will help to ensure maximum efficiency of the grinding system. System interlocks monitor the operating condition of the grinding mill and will shut down the mill if conditions deviate from operating parameters. Regular monitoring of the feed rate, ore hardness, mill power draw, mill charge volumes (charge weights), and periodic visual checks of the ball volume (with the charge ground out of the mill and the mill stopped) will give the trends of ball consumption per ton of material ground. With the information gathered per the above, a schedule of ball charge addition (quantity and intervals) can be established and maintained.

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Ball mill, a pulverizing machine consisting of a rotating drum which contains pebbles or metal balls as the grinding medium, can grind ores and other materials typically to 20 mesh or finer in a variety of applications, both in open or closed circuits.

Add balls into the ball drum to approximately 33%. The figure is not fixed, as long as it is within the range of 30%-45%. As the ball mill rotates, the balls 'stick' to the inner surface of the ball drum due to the centrifugal force and are lifted on the rising side. At a certain angle, balls cascade down to the centerline of the ball mill because gravity overcomes the centrifugal force. And the ore is reduced to the required size by impact (balls impacting with the ore) and attrition (ore rubbing against other bits of ore and the milling balls).

Based on the discharge methods, there are overflow ball mills, grate discharge ball mills; according to whether water is needed in the processing, there are wet ball mills and dry ball mills; based on the shape of grinding medium, there are ball mills and rod mills; based on the drum length to diameter ratio, there are ball mills and tube mills. A typical ball mill will have a drum length that is 1 or 1.5 times the drum diameter. Ball mills with a drum length to diameter ratio greater than 1.5 are referred to as tube mills.

Ball mills are usually applied in the comminution stage as grinding machines to reduce the size of the feed. It can be applied in both primary and secondary grinding. In primary grinding, it is fed from crushers such as jaw crushers. If the ball mill is used for secondary grinding, it is fed from other grinders, e. g. rod mills or SAG mills.

A ball mill is a cylindrical device used in grinding materials like ores, alloys, coal, coke, fibers, cement clinker, refractory material, ceramics, limestone, quartz, gypsum, metal oxides, slag, etc. But ball mills cannot be used in the preparation of some pyrotechnic mixtures such as flash powder because of their sensitivity to impact.

Therefore, ball milling machines are widely used in cement, silicate products, new building materials, refractory materials, fertilizers, beneficiation of ferrous and non-ferrous metals, glass, ceramics, mining, and other industries.

Robust design results in long service life and less required maintenance. Therefore, wearable parts of Fote ball mills are made of high-quality raw materials to extend their service life. The shell of the ball mill drums, linear, grinding medium, to name a few.

As fine grinding is typically used on regrind applications, the feed tonnages to fine grinding circuits are small compared to head tonnages, typically 10 to 30 tph. However, the specific energies are often much larger than those encountered in intermediate milling and can be as high as 60 kWh/t. Total installed power in a fine grinding circuit can range from several hundred kW to several MW; for example, the largest installed Isamill has 3 MW installed power.[3] This quantity is small compared to the power used by a semi-autogenous mill and a ball mill in a primary grinding circuit; a ball mill can have an installed power of up to 15 MW, while installed power for a SAG mill can go up to 25 MW. However, the energy used for fine grinding is still significant. Moreover, as this paper seeks to demonstrate, large energy reduction opportunities are frequently found in fine grinding.

Grinding can be classified into coarse, intermediate, and fine grinding processes. These differ in the equipment used, the product sizes attained, and the comminution mechanisms used. The boundaries between these size classes must always be drawn somewhat arbitrarily; for this paper, the boundaries are as given in Table II. As shown in the table, coarse grinding typically corresponds to using an AG or SAG mill, intermediate grinding to a ball mill or tower mill, and fine grinding to a stirred mill such as an Isamill or Stirred Media Detritor (SMD). Of course, various exceptions to these typical values can be found.

The phenomenon of overgrinding is largely the result of using media that are too large for the product size generated. The smallest ball size typically charged into ball mills and tower mills is inch (12.5 mm), although media diameters as small as 6 mm have been used industrially in Vertimills.[11]

Millpebs have been used as grinding media to achieve fine grinding in ball mills. These are 5- to 12-mm spherical or oblong cast steel pellets, charged into ball mills as a replacement of, or in addition to, balls. While Millpebs can give significantly lower energy use when grinding to finer sizes, they also can lead to high fines production and high media use.

Numerous researchers, for example, Buys et al.,[17] report that stirred milling increases downstream flotation recoveries by cleaning the surface of the particles. The grinding media used in stirred mills are inert, and therefore corrosion reactions, which occur with steel media in ball mills, are not encountered. Corrosion reactions change the surface chemistry of particles, especially with sulfide feeds, and hamper downstream flotation.

where W is the specific grinding energy (kWh/t), W i is the Bond ball mill work index (kWh/t), F80 is the feed 80 pct passing size (μm), and P80 is the product 80 pct passing size (μm).

Signature plot (specific energy vs P80 curve) for Brunswick concentrator Zn circuit ball mill cyclone underflow; F80 = 63 μm. The plots give results for grinding the same feed using different mills and media. After Nesset et al.[7]

The connections (if any) between k and A and various operating conditions remain unknown. Because of the relatively recent advent of stirred milling in mineral processing, fine grinding has not been studied to the same extent as grinding in ball mills (which of course entail much larger capital and energy expenditures in any case). One of the research priorities in the field of stirred milling should be the investigation of the effects of F80 and media size on the position of the signature plots. If analogous formulas to the Bond ball mill work formula and the Bond top ball size formula can be found, the amount of test work required for stirred milling would be greatly reduced.

In ball milling, the Bond ball mill work index can be used to determine specific energy at a range of feed and product sizes. The Bond top size ball formula can be used to estimate the media size required. No such standard formulas exist in fine grinding. Energy and media parameters must instead be determined in the laboratory for every new combination of operating conditions such as feed size, media size, and media type.

In contrast to laboratory-scale testing for ball mills and AG/SAG mills, test work results for stirred mills can be used for sizing full-size equipment with a scale-up factor close to one. Larson et al.[19,20] found a scale-up factor for the Isamill of exactly 1, while Gao et al.[8] imply that the scale-up factor for SMDs is 1.25.

In ball milling, the product particle size distribution (PSD) can usually be modeled as being parallel to the feed PSD on a log-linear plot.[4] When grinding to finer sizes in ball mills, the parallel PSDs mean that large amounts of ultrafine particles are produced. This consumes a large amount of grinding energy while producing particles which are difficult to recover in subsequent processing steps such as flotation.

In stirred milling, the most commonly used media are ceramic balls of 1 to 5 mm diameter. The ceramic is usually composed of alumina, an alumina/zirconia blend, or zirconium silicate. Ceramic media exist over a wide range of quality and cost, with the lower quality/cost ceramic having a higher wear rate than higher quality/cost ceramic. Other operations have used sand as media, but at the time of writing, only two operations continue to use sand.[8,27,33] Mt Isa Mines has used lead smelter slag as media; however, it is now using sand media.[10,27] Mt Isa is an exception in its use of slag, as a vast majority of operations do not have a smelter on-site to provide a limitless supply of free grinding media. However, in locations where slag is available, it should be considered as another source of media.

A number of opportunities exist to reduce the energy footprint of fine grinding mills. There are no general formulas, such as the Bond work formula and Bond top size ball formula in ball milling, to describe the performance of stirred mills. Therefore, improvement opportunities must be quantified by performing appropriate test work. 2ff7e9595c