Application of value engineering techniques to grinding process modelling led to the identification of two basic functions of the ball mill-classifier circuit. In terms of a specified circuit product size which is used to differentiate between coarse or oversize material and fines or undersize material, these basic functions are (a) breakage of the coarse material and (b) removal of the fines. It was proposed that it may be useful to relate circuit design and operating variables to these basic circuit functions, which although related, are conceptually quite distinguishable. If each could be quantified by a suitable parameter, then either or the two together may be correlated to overall circuit efficiency, and hence used to link individual design and operating variables to overall circuit performance.
Major design and operating variables in closed circuit ball milling of a specified feed to a desired product size are summarized in Table 1. The purpose of process modelling is to establish cause and effect relationships between physical design and operating variables and the performance objectives of the circuit. Subsequently, output and efficiency can be maximized. The fundamental issue addressed by ball mill circuit modelling is thus depicted in Figure 1 (McIvor, 1989).
In the simplest form of plant experimentation, a key performance parameter (such as the fineness of the final product) is measured with and without a specific change to the circuit. Within the constraints imposed by the accuracy of measurements and assumptions about the constancy of other inputs (including the ore characteristics), the relative values of this parameter are used to evaluate the effect of the change on circuit performance.
Bond work index analysis takes this method of experimentation several steps further. During comparative testwork, variations in the ore grindability, grinding energy input, and feed and product sizing are measured and accounted for through the grinding circuit model embodied in the work index formulation. For each set of data, both the circuit operating work index and the laboratory test work index of the circuit feed are determined. Relative work index efficiencies with and without the change to the circuit can then be calculated and compared.
Consider a ball mill circuit processing material of a given feed size and at a given throughput rate to a target product size, the latter which once again distinguishes the fines from the coarse material. The production rate of fines or new product size material can be calculated from the circuit feed and product size distributions and the throughput rate of the circuit. Based on the energy expended in the ball mill, the production rate of new product size material (tonnes/h) equals the amount produced per unit of energy applied (tonnes/kwh) times the rate at which energy is applied (kwh/h). The rate at which energy is applied is the power draw of the ball mill. If we then define the production per unit, of energy applied as the energy specific production rate of the circuit, then we can write the following equation:
All the production of new product size material takes place in the mill as coarse is ground into fines. However, the proportion of the total mill power applied to size reduction of coarse particles is equal to the fraction of coarse solids inventory, or the so defined circuit classification system efficiency.
The mill specific grinding rate reflects both the efficiency of the mill environment in breaking the coarse particles, as well as the grindability characteristic of the ore over the particular size reduction range.
To arrive at a term which reflects only the efficiency of the mill environment, we must factor out the grindability of the ore, such as the net grams per revolution measured in a Bond work index test. This will yield the specific grinding rate in the plant ball mill relative to the measured specific grinding rate in a standard test mill, and may be termed the grinding rate ratio.
The grinding rate ratio may be considered dimensionless because each revolution of the test mill requires a fixed amount of power. It is based on breakage of only the coarse material in both the plant ball mill and the standard laboratory test mill. It is therefore proposed that the grinding rate ratio is a direct measure of the relative overall breakage efficiency of the environment of the plant ball mill.
The above described parameters for system breakage and classification system efficiency factor the overall task of the ball mill circuit into its two distinct basic functions, namely, fines generation and fines removal. The effect of design and operating variables on each can be studied separately, and when the product of the two is maximized, maximum overall circuit efficiency will be achieved. Equation 2 may be re-written as:
This has been termed the ball mill circuit functional performance equation (McIvor, 1989). It states that the output of new product size material of a ball mill circuit with a given feed size is determined by:
a. the total mill power draw; b. the classification system efficiency, which defines the fraction of the total mill power effectively applied to the grinding of coarse material; c. the grindability characteristic of the ore over the size reduction range of the circuit; and, d. the breakage efficiency of the ball mill environment on the coarse material.
While all four factors clearly influence the circuit output, overall circuit efficiency will be determined by classification and breakage efficiency. Specific design and operating variables can now be considered in terms of their individual effects on classification and breakage efficiency, and subsequently on the overall efficiency of the circuit. This provides an intermediate level of ball mill circuit performance characterization, as shown in Figure 5.
These programs and the simulation algorithms are discussed below. Note that in some Grinding Circuit Simulations, a residence time distribution model is used. In the MRRC simulation package, however, only the two extremes of well mixed and plug flow through the mill are considered. This approach reduces the amount of input information and computation required in the simulation. Predictions obtained from a simulation are for the mill product size distribution, that is the size distribution after grinding but before separation.
Before the MRRC package can be used, a Bond design exercise must be completed. A wet ball mill with 40% volumetric loading and 2.44 meters diameter inside liners was chosen as a test mill. This choice means that the only efficiency factor which is non-unity will be for the mill in open circuit and this factor is equal to 1.2 (Rowland and Kjos, 1978) . The size in micrometers that 80% of the weight of the feed and product passes, F80 and P80, were kept constant for each grinding simulation at 1200 and 175 micrometers respectively. The feed rate was varied in each simulation in order that the power predicted from equation 1 corresponded to the 2.44 meter diameter test ball mill. A number of simulations corresponding to differing operating conditions for the test ball mill have been carried out. These are summarized in Table 2. With the predicted results, the effect of the following operating conditions on the mill product size distribution can be tested:
Study of the results predicted from the plug flow simulation of the test mill with overflow discharge illustrate the effectiveness of the MRRC grinding simulation package. Figure 1 shows size distribution data for the feed and for the products of three different configurations for the mill. Note that these size distributions are of the mill product before it is separated, and of the hydrocyclone products assuming 100% efficiency at the nominal size of separation. Curve 2 is the predicted size distribution when the mill is operated in an open circuit. This distribution gives a product with a 80% passing size of 177 micrometers, which provides confidence in the results of the MRRC grinding models. The effects of differing sizes of separation may be studied by comparing curves 3 and 4 in Figure 1 and the circulating load values in Table 4. First it may be noticed that the grind becomes coarser when the nominal size of separation is changed from 250 to 125 micrometers (80% passing size of 389 micrometers for a 125 micrometer separation as opposed to an 80% passing size of 250 micrometers with a 250 micrometer separation). This coarser grind might be expected because, with the smaller size of separation, the circulating load is larger, and hence, the residence time of the ore in the mill is shorter. In addition, with the 125 micrometer separation, the predicted weight distribution in the separator feed is less dispersed, (cf. the gradients in straight line parts of curves 3 and 4), which is a desired attribute if the next stage of processing is flotation.
The size distribution plots and circulating loads for the same mill using the well-mixed, simulation are shown in Figure 2 and Table 4, respectively. The behavior of these plots indicate that with well mixed flow, changes in the mill operation have the same effects on the product weight distributions, as with plug flow. However, the predicted mill products are much coarser in open circuit, e.g., the 80% passing size is 550 micrometers compared to an 80% passing size of 177 micrometers in the product predicted using the plug flow simulation. The reason for this is in the nature of the well mixed flow assumption. If the flow through the mill is assumed well mixed, particles in the feed can exit from the mill instantaneously. Therefore, the reduction in the size of some of the feed particles may be minimal, thereby leading to a coarse product grind. On comparing the results in Figures 1 and 2, it appears, at least for the case of a ball mill with an overflow discharge, a plug flow approximation is closer to the true nature of flow through the mill. This is reasonable on studying residence time distribution data which often exhibit fairly sharp peaks.
When a grate controls the discharge from the mill, although the assumption that the mill contents are perfectly mixed at all times can be applied, the product is not necessarily identical to the mill contents, since feed particles larger than the grate size cannot exit instantaneously. Hence, a grate discharge not only gives control over the mill product but it may also introduce a distribution of residence times into the simulation. The effect of changing the grate opening size on the product weight distributions from the test ball mill in open circuit may be observed in Figure 3 with the expected result that the smaller the grate size the finer the grind. In fact, the product of a mill with 250 micrometer grate is finer than the product from the same mill with an overflow discharge.
A useful feature of the MRRC grinding simulation package is that the effects of non-design operating conditions can be easily tested. When the test ball mill is run in open circuit the design feed rate is 27.42 tonnes/hour. Figure 4 compares the predicted size distributions from the open circuit ball mill with feed rates of 20.0, 27.62 and 35.0 tonnes/hour respectively. As might be expected, the larger the feed rate the coarser the grinding mill discharge product.
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Ball mill, also known as ball grinding machine, a well-known ore grinding machine, widely used in the mining, construction, aggregate application. JXSC start the ball mill business since 1985, supply globally service includes design, manufacturing, installation, and free operation training. Type according to the discharge type, overflow ball mill, grate discharge ball mill; according to the grinding conditions, wet milling, dry grinding; according to the ball mill media. Wet grinding gold, chrome, tin, coltan, tantalite, silica sand, lead, pebble, and the like mining application. Dry grinding cement, building stone, power, etc. Grinding media ball steel ball, manganese, chrome, ceramic ball, etc. Common steel ball sizes 40mm, 60mm, 80mm, 100mm, 120mm. Ball mill liner Natural rubber plate, manganese steel plate, 50-130mm custom thickness. Features 1. Effective grinding technology for diverse applications 2. Long life and minimum maintenance 3. Automatization 4. Working Continuously 5. Quality guarantee, safe operation, energy-saving. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, to reduce the ore particle into fine and superfine size. Ball mills grinding tasks can be done under dry or wet conditions. Get to know more details of rock crushers, ore grinders, contact us!
Ball mill parts feed, discharge, barrel, gear, motor, reducer, bearing, bearing seat, frame, liner plate, steel ball, etc. Contact our overseas office for buying ball mill components, wear parts, and your mine site visits. Ball mill working principle High energy ball milling is a type of powder grinding mill used to grind ores and other materials to 25 mesh or extremely fine powders, mainly used in the mineral processing industry, both in open or closed circuits. Ball milling is a grinding method that reduces the product into a controlled final grind and a uniform size, usually, the manganese, iron, steel balls or ceramic are used in the collision container. The ball milling process prepared by rod mill, sag mill (autogenous / semi autogenous grinding mill), jaw crusher, cone crusher, and other single or multistage crushing and screening. Ball mill manufacturer With more than 35 years of experience in grinding balls mill technology, JXSC design and produce heavy-duty scientific ball mill with long life minimum maintenance among industrial use, laboratory use. Besides, portable ball mills are designed for the mobile mineral processing plant. How much the ball mill, and how much invest a crushing plant? contact us today! Find more ball mill diagram at ball mill PDF ServiceBall mill design, Testing of the material, grinding circuit design, on site installation. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, get to know more details of rock crushers, ore grinders, contact us! sag mill vs ball mill, rod mill vs ball mill
How many types of ball mill 1. Based on the axial orientation a. Horizontal ball mill. It is the most common type supplied from ball mill manufacturers in China. Although the capacity, specification, and structure may vary from every supplier, they are basically shaped like a cylinder with a drum inside its chamber. As the name implies, it comes in a longer and thinner shape form that vertical ball mills. Most horizontal ball mills have timers that shut down automatically when the material is fully processed. b. Vertical ball mills are not very commonly used in industries owing to its capacity limitation and specific structure. Vertical roller mill comes in the form of an erect cylinder rather than a horizontal type like a detachable drum, that is the vertical grinding mill only produced base on custom requirements by vertical ball mill manufacturers. 2. Base on the loading capacity Ball mill manufacturers in China design different ball mill sizes to meet the customers from various sectors of the public administration, such as colleges and universities, metallurgical institutes, and mines. a. Industrial ball mills. They are applied in the manufacturing factories, where they need them to grind a huge amount of material into specific particles, and alway interlink with other equipment like feeder, vibrating screen. Such as ball mill for mining, ceramic industry, cement grinding. b. Planetary Ball Mills, small ball mill. They are intended for usage in the testing laboratory, usually come in the form of vertical structure, has a small chamber and small loading capacity. Ball mill for sale In all the ore mining beneficiation and concentrating processes, including gravity separation, chemical, froth flotation, the working principle is to prepare fine size ores by crushing and grinding often with rock crushers, rod mill, and ball mils for the subsequent treatment. Over a period of many years development, the fine grinding fineness have been reduced many times, and the ball mill machine has become the widest used grinding machine in various applications due to solid structure, and low operation cost. The ball miller machine is a tumbling mill that uses steel milling balls as the grinding media, applied in either primary grinding or secondary grinding applications. The feed can be dry or wet, as for dry materials process, the shell dustproof to minimize the dust pollution. Gear drive mill barrel tumbles iron or steel balls with the ore at a speed. Usually, the balls filling rate about 40%, the mill balls size are initially 3080 cm diameter but gradually wore away as the ore was ground. In general, ball mill grinder can be fed either wet or dry, the ball mill machine is classed by electric power rather than diameter and capacity. JXSC ball mill manufacturer has industrial ball mill and small ball mill for sale, power range 18.5-800KW. During the production process, the ball grinding machine may be called cement mill, limestone ball mill, sand mill, coal mill, pebble mill, rotary ball mill, wet grinding mill, etc. JXSC ball mills are designed for high capacity long service, good quality match Metso ball mill. Grinding media Grinding balls for mining usually adopt wet grinding ball mills, mostly manganese, steel, lead balls. Ceramic balls for ball mill often seen in the laboratory. Types of ball mill: wet grinding ball mill, dry grinding ball mill, horizontal ball mill, vibration mill, large ball mill, coal mill, stone mill grinder, tumbling ball mill, etc. The ball mill barrel is filled with powder and milling media, the powder can reduce the balls falling impact, but if the power too much that may cause balls to stick to the container side. Along with the rotational force, the crushing action mill the power, so, it is essential to ensure that there is enough space for media to tumble effectively. How does ball mill work The material fed into the drum through the hopper, motor drive cylinder rotates, causing grinding balls rises and falls follow the drum rotation direction, the grinding media be lifted to a certain height and then fall back into the cylinder and onto the material to be ground. The rotation speed is a key point related to the ball mill efficiency, rotation speed too great or too small, neither bring good grinding result. Based on experience, the rotat
ion is usually set between 4-20/minute, if the speed too great, may create centrifuge force thus the grinding balls stay with the mill perimeter and dont fall. In summary, it depends on the mill diameter, the larger the diameter, the slower the rotation (the suitable rotation speed adjusted before delivery). What is critical speed of ball mill? The critical speed of the ball mill is the speed at which the centrifugal force is equal to the gravity on the inner surface of the mill so that no ball falls from its position onto the mill shell. Ball mill machines usually operates at 65-75% of critical speed. What is the ball mill price? There are many factors affects the ball mill cost, for quicker quotations, kindly let me know the following basic information. (1) Application, what is the grinding material? (2) required capacity, feeding and discharge size (3) dry or wet grinding (4) single machine or complete processing plant, etc.
A simulation method for the two-stage ball milling circuit was described.The model reproduced the performance of an industrial mill circuit.Simulation results indicated that the mill operated under non-optimal conditions.Adjusting the cut size of the classifier could increase the mill capacity by 50%.
A two-stage ball milling circuit for the grinding of molybdenum ore was investigated based upon the grinding kinetic model. To this end, batch grinding tests at the laboratory-scale were conducted to obtain the specific rate of breakage and the primary breakage distribution in wet and dry environments. The test results were then scaled-up to the conditions of a full-scale ball milling circuit for grinding molybdenum ores. A two-stage ball milling circuit algebra was employed to predict the capacity, circulation ratio, and size distributions. Comparison of the simulated results and the observed values showed that the model represents accurately the actual milling process in the plant. Simulation results indicated that the classification in the milling process was operated under non-optimal conditions, and that an increase in the mill output of more than 47% was possible simply by modifying the cut size of the classifier.
An overfilling indicator for wet overflow discharge ball mills.Mathematical descriptions of volume-based slurry residence time in ball mills.121 sets of plant survey data used to establish the slurry residence time patterns.The residence time thresholds as the overfilling indicator defined from the database.
The lack of constraints in ball mill capacity in the published ball mill models may result in unrealistic predictions of mill throughput. This paper presents an overfilling indicator for wet overflow discharge ball mills. The overfilling indicator is based on the slurry residence time in a given mill and given operational conditions. Mathematical descriptions of the method to estimate the volume-based residence time of slurry are presented. A database consisting of 121 sets of industrial overflow ball mill surveys worldwide was used to establish the pattern of the slurry residence time in the full scale operational overflow ball mills. According to the pattern, the residence time thresholds beyond which overfilling a ball mill is likely to occur were defined. For a ball mill with an internal diameter smaller than 5.9m, the volume-based residence time threshold is set at 2min; and for a ball mill larger than 5.9m in diameter, the threshold is set at 1min. In addition to being incorporated in ball mill models to warn of any unrealistic simulations, the overfilling indicator can also be utilised at ball mill operation sites to guide the mill throughput control and optimisation.