Ball mill installation is a must step before it is put into production, which will affect the subsequent use of the ball mill, and even affect the production volume, crushing rate, service life, etc., so the importance of ball mill installation is self-evident.
In addition, the choice of grinding medium is also crucial. In the grinding process, different grinding medium can be used for different materials, models and equipment, which can reduce production costs and improve production efficiency.
There are four chassis should be installed: the front tile base, the rear tile base, the motor chassis and the reducer chassis. During the installation of the chassis, the horizontality and horizontal elevation of the chassis must be checked by a level or level gauge and a steel rule.
At the same time, the width of these wedges should be between 50 and 60 mm; the length should be at least ensured to exceed the centerline of the anchor bolts inside the chassis, and the outside should be exposed to a length of 10 to 50 mm; the slope of the wedge should be between 1:10 and 1:20.
If the actual combined size between the motor cylinder and the hollow shaft is inconsistent with the technical documents of the equipment or the relevant design, the construction may be carried out according to the actual size after obtaining the consent of the relevant unit personnel.
The transverse centerlines of the two main bearing chassis must coincide and allow for a combined error of no more than 0.5 mm. The non-horizontal degree of the main bearing chassis is allowed to differ by 0.1 mm/m, and the error of the non-parallelism is 0.5 mm/m, but the ball mill must be ensured to discharge materials.
Before the installation of the spherical surface of the main bearing, it is necessary to carefully check whether there are blisters, pores, cracks and other defects on the babbitt surface and the spherical surface, and there is no possibility of shrinking the shell in the interval between the hollow shaft and the contact surface of the bushing. phenomenon.
Firstly, before assembling the cylinder and the end cap, check the cylinder to ensure that the ellipse of the cylinder is not larger than 4 of the diameter of the cylinder. And meanwhile, the ovality and surface smoothness of the hollow journal should also be checked.
After the end cap and the cylinder bolt hole are aligned with the positioning pin, put a 1/4 number of bolts and tighten by hand, one-third of which are half tightened, and the concentricity is adjusted within 0.25mm, and then tightened.
Next, the cylinder and end cap assembly are transferred into the main bearing, but the housing must be adjusted to meet the requirements before the cylinder and end cap assembly are installed in the main bearing.
After assembling, the assembled cylinder should be measured and the total length and the length of the center of the two journals are compared with the center distance of the bearing housing to make sure they match with each other, otherwise, the bearing housing or the position of the main base need to be adjusted.
The inner surface of the ball mill cylinder is generally equipped with liners of various shapes that are the main wearing parts of the ball mill, and whose cost is about 2%-3% of the price of the whole product.
Thus, the performance and service life of the lining plate are issues that users are very concerned about, for its performance will directly affect the performance of the ball mill. The following are the 10 requirements for the liner installation.
The greater the density of the grinding medium is, the shorter the grinding time is. In order to increase the grinding effect, the hardness of the grinding medium must be greater than the hardness of the material to be ground.
According to long-term experience, the Mohs hardness of the medium is preferably greater than the hardness of the material to be ground by more than three grades. In addition, the smaller the size of the grinding medium is, the more the contact points it will be.
The loading amount has a direct influence on the grinding efficiency, and the particle size of the grinding medium determines the loading amount of the grinding medium. It must be ensured that when the grinding medium moves in the disperser, the porosity of the medium is not less than 40%.
For different fineness requirements, it is necessary to adjust the ability of the grinding medium to break and grind. The filling rate is high and the grinding ability is strong. On the contrary, the crushing ability is weak. When super fine grinding, the high filling rate is generally adopted.
Grinding medium generally is spherical because other irregularly shaped medium can wear themselves and cause unnecessary contamination. The size of the medium directly affects the grinding efficiency and product fineness.
The larger the diameter is, the larger the product size and the yield are. Conversely, the smaller the particle size is, the smaller the particle size and the the yield are. In actual production, it is generally determined by the feed size and the required product fineness.
Generally speaking, in the continuous grinding process, the size of the grinding medium is distributed regularly. The medium size ratio is directly related to whether the grinding ability can be exerted and how to reduce the wear of the medium.
In the process, it will not always maintain at a fixed medium ratio. So, the method of replenishing large balls is used to restore the grinding of the system. It is difficult for the mill to maintain at a fixed medium ratio for a long time.
In the production process, it is necessary to explore the appropriate ratio according to the type of material and the characteristics of the process, and remove the too small medium in time to reduce the cost.
The wear resistance and chemical stability of the grinding medium are important conditions for measuring the quality of the grinding medium. The non-wearing media needs to be supplemented by the need of abrasion, which not only increases the cost, but more importantly affects the production.
As common grinding equipment, ball mills are widely used in power, chemical, mining, cement and other processing sectors. At present, there are many kinds of ball mills popular in the market, with various functions and different prices.
Therefore, enterprises often face a dazzling situation when purchasing. Generally, when selecting a ball mill, the company must combine the material properties, abrasive requirements, production environment, energy consumption and other factors through scientifically comparing to select the ball mill that is most suitable for its use requirements.
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A crushing plant delivered ore to a wet grinding mill for further size reduction. The size of crushed ore (F80) was. 4.0mm and the S.G. 2.8t/m3. The work index of the ore was determined as 12.2kWh/t. A wet ball mill 1m 1m was chosen to grind the ore down to 200 m. A 30% pulp was made and charged to the mill, which was then rotated at 60% of the critical speed. Estimate:1.the maximum diameter of the grinding balls required at the commencement of grinding,2.the diameter of the replacement ball.
A 1.0 1.5m ball mill was loaded with a charge that occupied 45% of the mill volume. The diameter of balls was 100mm. The mill was first rotated at 25rpm. After some time, the rotation was increased to 30rpm and finally to 40rpm. Determine and plot the toe and head angles with the change of speed of rotation.
A 2.7m 3.6m ball mill was filled to 35% of its inner volume. The charge contained 100mm diameter steel balls. The mill was rotated at 75% of critical speed. The ore size charged was 2.8mm and the product size (P80) of 75 m. The work index of the ore was 13.1kWh/t. Determine the production rate of the mill when operated under wet conditions.
Hematite ore of particle size 4000 m is to be ground dry to 200 m (P80). The work index of the ore was determined and found to be equal to15.1kWh/t. Balls of diameter 110mm were added as the grinding media. The mill was rotated at 68% of the critical speed and expected to produce at the rate of 12t/h. The combined correction factors for Wi equalled 0.9. Calculate:1.the volume of the mill occupied by the grinding media,2.the mill capacity when the mill load was increased by 10% of its original volume.
The feed size of an ore to a 1.7m 1.7m wet ball mill operating in closed circuit was 5000m. The work index of the ore was determined under dry open circuit conditions and found to be 13.5kWh/t. The mill bed was filled to 30% of its volume with balls of density 7.9t/m3. A 20:1 reduction ratio of ore was desired. The mill was operated at 80% of the critical speed. Assuming a bed porosity of 40%, estimate the mill capacity in tonnes per year.
A ball mill is to produce a grind of 34 m (P80) product from a feed size of 200 m at a rate of 1.5t/h. The grinding media used was 90% Al2O3 ceramic ball of S.G. 3.5. The balls occupied 28% of the mill volume. The mill was rotated at 65% of the critical speed. The work index of the ore was 11.3kWh/t. Estimate the size of the mill required.
A wet overflow ball mill of dimensions 3.05m 3.05m was charged with nickel ore (pentlandite) of density 4.2 having a F80 value of 2.2mm. The mass of balls charged for grinding was 32t, which constitutes a ball loading of 35% (by volume). The mill was rotated at 18rpm. Estimate:1.power required at the mill shaft per tonne of ball,2.power required at the mill shaft when the load (% Vol) was increased to 45%.
A grate discharge mill of dimensions 4.12m 3.96m was loaded to 40% of its volume with gold ore. The mill drew 10.95kW power per tonne of balls. To grind the ore to the liberation size the mill was run at 72% of the critical speed when charged with balls 64mm in size and 7.9t/m3 density. Determine:1.the fraction of the mill filled with balls,2.the mass of balls charged.
The feed size to a single stage wet ball mill was 9.5mm of which 80% passed through a 810 m sieve. The mill was expected to produce a product of 80% passing 150 m. The feed rate to the mill was 300t/h. The ball mill grindability test at 65 mesh showed 12kWh/t. The internal diameter of the ball mill was 5.03m and the length-to-diameter ratio was 0.77. The steel balls occupied 18% of the mill. The total load occupied 45% of the mill volume. If the mill operated at 72% of the critical speed, determine:1.the mill power at the shaft during wet grinding,2.the mill power at the shaft during dry grinding.
A 5.5m 5.5m ball mill is lined with single wave liners 65mm thick, which cover the entire inside surface. The centre line length was 4.2m and the trunnion diameters 1.5m in diameter. The mill was charged with an ore and 100mm diameter steel balls as the grinding media so the total filling of the cylindrical section was 40% and the ball fractional filling was 0.15 %. The slurry in the mill discharge contained 33% solids (by volume). The mill was expected to rotate at 12.8rpm. Estimate the total power required (including the power required for the no load situation).
There is now a new generation of mobile crushing and screening plant systems, which have been developed based on the motivation of reducing truck haulage. Newly designed mobile crushing and screening plant systems have the advantages of mobility, flexibility, economy, and reliable performance, making this system very appealing for small- to medium-sized projects or projects where a number of resources are separated by distance. Similarly, the advantages of mobile crushers are lower capital cost (up to 30% less), higher mobility, and higher salvage value at the end of the project life. Mobile crushing plants are not suited to large long-life projects, heavy rainfall climates, or arctic climates. The design considerations, operability, and maintainability require careful consideration. The equipment selection would also be based on different criteria to fixed plant (Connelly, 2013).
The iron ore lump obtained from ROM crushing and screening plants will continue to break down into 6.3mm particles during material handling from the product screen to stockpiles, port, and customer. Drop test conditioning of diamond drill core and crusher lump samples has been developed to simulate material handling and plant stockpiling (Clout et al., 2007). The outcomes of the lump simulations in Figure 2.9 indicate that most of the breakage of lump to 6.3mm fines occurs after the first significant drop height; thereafter, the lump consistently shows the same lower rate of breakage to the extent of testing. Breakage functions can be developed, like the curves in Figure 2.7, for specific iron ores and their hardness categories and then used in subsequent plant engineering design and lump degradation modeling. Different iron ores will show different breakdown characteristics, with very hard iron ores showing a slower rate of breakdown, whereas friable lump breaks down so rapidly that it is unlikely to be economically viable as a lump product (e.g., Figure 2.9, ROM 15 Friable).
Figure 2.9. Simulation of lump yield with cumulative mechanical breakdown in material handling from crusher to port. Lump yield for various hardness types derived from crushing and screening of run-of-mine (ROM) feed.
Large volumes of concrete derived from reliable consistent sources can be regarded as virtual quarries where a mobile crushing plant is used at the site. Examples include RCA derived from the decommissioning of concrete pavements from redundant military airfields or demolition of large concrete framed buildings/industrial facilities.22 In such cases, the availability of a material of consistent quality in large quantities makes their exploitation attractive.
In the UK, there are a growing number of processing centres which combine conventional aggregate processing equipment (such as crushers and screens), with a washing plant. Such facilities have the ability to handle mixed construction demolition and excavation waste (including soil). For commercial reasons, the main output is generally a range of RA products (such as unbound fills, capping, sub-base and pipe bedding) rather than a segregated RCA.15
Annually 1 million tons of mineral demolition wastes mainly consisting of concrete and bricks, is produced in Finland. The crushed materials have in field studies on test roads showed favourable geotechnical properties for use in road constructions. The test samples from two crushing plants were chemically characterised and the leaching behaviour was studied by using column, two-stage batch leaching and pH static tests. Only sulphate and chromium leaching from the crushed material was detected. There was a good agreement between column and batch leaching tests. The contents of harmful organic compounds were very low. Based on experience and the results of the experimental study, a practical sampling and testing strategy for an environmental quality assessment system was developed. A two-stage batch leaching test was chosen for the quality control of demolition waste. Preliminary target values for leaching of sulphate, Cr, Cd, Cu and Pb were set. Both geotechnical and environmental properties of the crushed material indicate that the use of demolition waste in road constructions is acceptable and can be recommended to replace landfilling of this material. However, a detailed demolition plan is most important in order to have an acceptable material for utilisation in earth constructions.
Building garbage recycling equipment in Western developed countries is generally mobile crushing station and mobile screen station, which can be divided into two categories, i.e., wheeled and tracked, shown in Figs 8.5 and 8.6. They can be used either alone or in combination with multiple devices. Characteristics of rubber-tired mobile crushing plant are as follows:
the installation form of integrated complete sets of equipment eliminates complex installation work caused by site and infrastructure of fission components, thus cutting down the consumption of the material and working hours.
The machine adopts all-wheel drive and it can realize spin insitu. Standard configuration and quick change device with perfect function of security protection is especially suitable for narrow space and complex area.
Compared with the traditional crushing screening equipment, the mobile crushing station has characteristics of mobility, reconfigurability, and automation. The crushing, screening, and debris sorting of construction waste can be realized if these features are applied to the recycling of construction waste, which can completely meet the requirements of comprehensive treatment of construction waste. In addition, the combination of different types of mobile crushing station screened by the mobile screen substation, which manage the primary and secondary crushing of construction waste, cannot only improve the performance of recycled aggregates, but also get the recycled aggregates piled up in accordance with the aggregate graded, facilitating the recycle of recycled aggregates.
In the process of construction waste treatment with mobile crushing station, the interaction of the waste concrete with itself contains a mix of collision and friction with each other using vibrating equipment, such as vibrating feeder and the original vibrating screen, which can reduce relatively loose waste mortar on its surface. Compared with the mechanical rub method, there is an effect gap between the two, but it plays the same role as well, which improves the performance of the recycled aggregates to some extent.
New renewable equipment can not only break, but also sieve. Mobile crushing screening equipment produced by Atlas Copco, take PC1375 type I crusher, for example, its high efficiency and flexibility, simplicity of operation, product design for easier transportation make it very suitable for field use in harsh environment, and most important of all, products broken by this device is of high capacity and good quality. PC1375 type I crusher is equipped with a special design of 19-mm-thick conveyor belt with high-strength steel wire, which effectively prolongs its service life. Its standard configuration is high-intensity magnetic belt, which can separate all the metal materials out before conveying crushing material to the dump, producing clean broken end products and the separated metal materials can earn extra income. The discharging mouth of the crusher is equipped with rollers, the impact absorption plate with special design is composed of replaceable rubber and steel, and the conveyor belt is removable, which makes obstruction cleaning and equipment maintenance very convenient.
There are, however, an increasing number of urban buildings built using contemporary earth walling, particularly in Western Australia where the revival of rammed earth as a modern building medium has been particularly prolific.
Alan Brooks, an SRE contractor based in Perth says almost 90% of his current work is urban. He sources limestone rubble and recycled concrete from crushing plants often within the city itself so they can rely on quick deliveries of materials eliminating the need for stockpiling on small sites. Urban SRE is now their main business and they have developed tricks to streamline their production and keep costs down. In other parts of Australia this trend toward more urban earth wall construction is also growing.
Scott Kinsmore is a rammed earth contractor in Melbourne. He says he is building higher walls on smaller urban sites. The engineering for higher walls with more point-specific loads on small-site buildings is challenging and often requires more steel to be built within the wall structures. This can be frustrating and costly for the wall builder. Increasingly, Australian urban architects are meeting the challenges of sensible passive solar design and low embodied energy materials. While much of the current computer modelling that drives our 5 Star Energy Rating programmes is insulation-centric, some designers are using earth walling as a way to limit the embodied energy of their buildings as well as increasing their passive solar capacity.
Particles of sizes in the range of 1400m can be defined as dusts, with particles larger than 100m in size settling down near the source of formation. The total size range can be divided into three classes larger than 20m, 201m, and less than 1m these can be termed as large particles, fines and ultrafines, respectively (Leonard, 1979). The size distribution of dust generated in a crushing plant is indicated in Fig. 12.1. It should be noted that it is more difficult to separate smaller particles from the air stream as they have a greater tendency to remain in suspension (Kumar, 1987).
The amount of dust generated depends upon the type of handling and transportation equipment used. A sensitive location of dust control is generally at the conveyor transfer points, screens, crushers, bins, silos and loading and unloading points (Leonard, 1979). The dust control problem is usually restricted to dry handling of coal preparation plants.
Respirable dust is generally defined as particulate matter less than 10m in diameter according to the US Environmental Protection Agency (EPA). Respirable dust can get into the lungs of human beings and cause pneumoconiosis on prolonged exposure. The quality of air must be maintained so that the concentration of respirable dust does not exceed 2mg/m3. If the quartz content of an air sample exceeds 5%, the average concentration of respirable dust should be less than 2mg/m3 (Meyers, 1981).
The necessity for storage arises from the fact that different parts of the operation of mining and milling are performed at different rates, some being intermittent and others continuous, some being subject to frequent interruption for repair and others being essentially batch processes. Thus, unless reservoirs for material are provided between the different steps, the whole operation is rendered spasmodic and, consequently, uneconomical. Ore storage is a continuous operation that runs 24h a day and 7 days a week. The type and location of the material storage depends primarily on the feeding system. The ore storage facility is also used for blending different ore grades from various sources.
For various reasons, at most mines, ore is hoisted for only a part of each day. On the other hand, grinding and concentration circuits are most efficient when running continuously. Mine operations are more subject to unexpected interruption than mill operations, and coarse-crushing machines are more subject to clogging and breakage than fine crushers, grinding mills, and concentration equipment. Consequently, both the mine and the coarse-ore plant should have a greater hourly capacity than the fine crushing and grinding plants, and storage reservoirs should be provided between them. Ordinary mine shutdowns, expected or unexpected, will not generally exceed a 24h duration, and ordinary coarse-crushing plant repairs can be made within an equal period if a good supply of spare parts is kept on hand. Therefore, if a 24h supply of ore that has passed the coarse-crushing plant is kept in reserve ahead of the mill proper, the mill can be kept running independent of shutdowns of less than a 24h duration in the mine and coarse-crushing plant. It is wise to provide for a similar mill shutdown and, in order to do this, the reservoir between coarse-crushing plant and mill must contain at all times unfilled space capable of holding a days tonnage from the mine. This is not economically possible, however, with many of the modern very large mills; there is a trend now to design such mills with smaller storage reservoirs, often supplying less than a two-shift supply of ore, the philosophy being that storage does not do anything to the ore, and can, in some cases, has an adverse effect by allowing the ore to oxidize. Unstable sulfides must be treated with minimum delay, the worst case scenario being self-heating with its attendant production and environmental problems (Section 2.6). Wet ore cannot be exposed to extreme cold as it will freeze and become difficult to move.
Storage has the advantage of allowing blending of different ores so as to provide a consistent feed to the mill. Both tripper and shuttle conveyors can be used to blend the material into the storage reservoir. If the units shuttle back and forth along the pile, the materials are layered and mix when reclaimed. If the units form separate piles for each quality of ore, a blend can be achieved by combining the flow from selected feeders onto a reclaim conveyor.
Depending on the nature of the material treated, storage is accomplished in stockpiles, bins, or tanks. Stockpiles are often used to store coarse ore of low value outdoors. In designing stockpiles, it is merely necessary to know the angle of repose of the ore, the volume occupied by the broken ore, and the tonnage. The stockpile must be safe and stable with respect to thermal conductivity, geomechanics, drainage, dust, and any radiation emission. The shape of a stockpile can be conical or elongated. The conical shape provides the greatest capacity per unit area, thus reduces the plant footprint. Material blending from a stockpile can be achieved with any shape but the most effective blending can be achieved with elongated shape.
Although material can be reclaimed from stockpiles by front-end loaders or by bucket-wheel reclaimers, the most economical method is by the reclaim tunnel system, since it requires a minimum of manpower to operate (Dietiker, 1980). It is especially suited for blending by feeding from any combination of openings. Conical stockpiles can be reclaimed by a tunnel running through the center, with one or more feed openings discharging via gates, or feeders, onto the reclaim belt. Chain scraper reclaimers are the alternate device used, especially for the conical stock pile. The amount of reclaimable material, or the live storage, is about 2025% of the total (Figure 2.11). Elongated stockpiles are reclaimed in a similar manner, the live storage being 3035% of the total (Figure 2.12).
For continuous feeding of crushed ore to the grinding section, feed bins are used for transfer of the coarse material from belts and rail and road trucks. They are made of wood, concrete, or steel. They must be easy to fill and must allow a steady fall of the ore through to the discharge gates with no hanging up of material or opportunity for it to segregate into coarse and fine fractions. The discharge must be adequate and drawn from several alternative points if the bin is large. Flat-bottom bins cannot be emptied completely and retain a substantial tonnage of dead rock. This, however, provides a cushion to protect the bottom from wear, and such bins are easy to construct. This type of bin, however, should not be used with easily oxidized ore, which might age dangerously and mix with the fresh ore supply. Bins with sloping bottoms are better in such cases.
Pulp storage on a large scale is not as easy as dry ore storage. Conditioning tanks are used for storing suspensions of fine particles to provide time for chemical reactions to proceed. These tanks must be agitated continuously, not only to provide mixing but also to prevent settlement and choking up. Surge tanks are placed in the pulp flow-line when it is necessary to smooth out small operating variations of feed rate. Their content can be agitated by stirring, by blowing in air, or by circulation through a pump.
Recycled concrete aggregate (RCA) comes from demolition of Portland cement concrete. Given that the original concrete might have been strong or weak, dense or open graded, fresh or weathered, then the aggregates pieces can be expected to vary similarly. If the RCA comes from a central recycling plant the consistency will have been addressed, to some extent, by blending of materials from different sources. If the material is coming from an on-site crushing plant then it will reflect more directly, and more immediately, the type of concrete being crushed.
The crushing process produces agglomerations of the original concretes aggregates with adhered mortar. These agglomerations are, typically, more angular than conventional aggregates. Also the crushed concrete will produce fines from the mortar element, the amount being controlled to a large extent by the strength of the original concrete. Thus high-strength concrete will typically crush to produce very sharp, even lance-like, blade aggregates with low proportions of fines, whereas the weakest concrete may crush to produce almost the original coarse aggregates plus a large proportion of fines made of the old mortar. In the crushed mortar component, be newly exposed. The effect of this will be a slow strength gain as this cement starts hydrating either with water that has been deliberately added, or with water attracted hygroscopically from the surrounding environment. Thus RCA is, to some degree, a self-cementing material with RCA from strong concretes (those with high cement contents in the original mix) often exhibiting a higher self-cementing ability.
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