In Grinding, selecting (calculate)the correct or optimum ball sizethat allows for the best and optimum/ideal or target grind size to be achieved by your ball mill is an important thing for a Mineral Processing Engineer AKA Metallurgist to do. Often, the ball used in ball mills is oversize just in case. Well, this safety factor can cost you much in recovery and/or mill liner wear and tear.
Size analyses of mineral products are usually made by screening with a set of sieves having mean apertures arranged in the Tyler scale, which is a geometric progression with a constant ratio equal to the square root of two. For this reason it is convenient to represent particle size as a logarithmic function of the particle diameter
The variable, x, may be defined as the logarithm to the base s of the ratio of the particle diameter to the reference diameter, d. The inverse of the transformation given in equation 1 is given by equation 2:
where yi is the weight fraction in the size interval between xi-l and xi; N is the total number of size intervals. If the reference diameter is equal to the maximum sieve aperture represented in the screen analysis and this is taken as the axis for the first moment, xo is zero and the first moment is the value of x corresponding to the mean particle size:
These higher moments contain the essential information concerning the form of the distribution function; that is, they are parameters that measure various aspects of the way in which the weight fraction is distributed about the mean. The second moment, or variance, measures the width of the distribution; the third moment measures the skewness or asymmetry; the fourth moment measures the kurtosis or peakedness; etc. Obviously, higher moments are increasingly dependent on values of the weight fraction remote from the mean which represent only a small fraction of the sample. For this reason, moments beyond the fourth are usually not considered. The third and fourth moments are usually represented as dimensionless ratios with respect to the second moment:
Moment analysis is a well-established method for analyzing and characterizing statistical distribution. Quoting from one of the standard treatises in mathematical statistics: For all ordinary purposes, therefore, a knowledge of the moments, when they exist, is equivalent to a knowledge of the distribution function: equivalent, that is, in the sense that it should be possible theoretically to exhibit all the properties of the distribution in terms of the moments.The procedures that have been developed for computation of moments and deriving distribution functions that best fit the data are fully discussed in a book by Elderton which has recently been published in a new edition. The application of moment analyses to particle size distribution data is discussed in a previous paper by the author.
When uniform sized samples of cryptocrystalline quartz were crushed by impact in a drop-weight machine, the reduction in size, as measured by the change in the mean value of x, was found to follow the relationship in equations 8 and 9
Equation 8 is an empirical relationship derived by multiple regression analyses of various combinations of independent variables from the data on the impact crushing experiments. The logarithms of E, the impact energy per unit weight of mineral, and d0, the initial mean particle diameter, gave the greatest decrease in variance between the observed and expected values. The threshold energy, Eo, which is the energy corresponding to zero size reduction, varies approximately inversely as the diameter of the particle being crushed.
Analyses of other data obtained by Hukki, using a double pendulum apparatus for impact crushing, gave slightly larger values for the coefficients in equations 8 and 9 and the exponent of do was slightly larger than one. If the exponent of do is assumed to be unity, the equation derived for the combined data from the Hukki and Bureau of Mines experiments gives the equations 10 and 11
These equations represent a best fit of data from 39 experiments on impact crushing of quartz particles ranging in size from .156 to 5.75 cm in diameter. The standard error for x is .387 as compared with 1.192 for the observed data.
The form of the distribution curve was found to be primarily a function of the size reduction. The distribution function of the initial uniform sample is a delta function. As soon as any size reduction occurs, there is a transfer of material to a wide range of sizes thereby increasing the dispersion. The change in distribution is asymetric since crushing transfers material only to the finer sizes, and so the skewness, as measured by 1, initially has a very large value. In other words, as a uniform sample is progressively decreased in size, there is a progressive increase in dispersion as measured by 2 and a decrease in skewness as measured by 1.
These changes are shown in Figure 1 which depicts the changes in distribution that occur in size distribution when quartz samples are subjected to increasing impact energy. As size reduction proceeds, the effect of the initial uniform distribution is gradually obliterated and both ant! tend to approach steady values. The variance tends to approach a steady value of 18 which corresponds to a standard deviation of 4.25 or a little more than four intervals in the Tyler sieve scale. The skewness levels off at a value between 1.6 and 1.8.
The manner in which energy is employed in a ball mill to effect size reduction is much more complex than in simple impact crushing. The application of energy in a drop-weight machine is similar to that occurring in a stamp mill, in which a considerable size reduction is produced by a single impact of relatively high energy input. In a tumbling mill, such as a ball mill, the size reduction occurs by repeated application of kinetic energy of less intensity by impact and rolling action of a large number of crushing media, in certain circumstances an appreciable amount of size reduction may occur by abrasion.
A series of studies has been made at the University of California in Berkeley on the grinding of dolomite in a ball mill. These tests were made in a specially designed mill in which the input energy can be measured.
A series of impact crushing experiments was made on a sample of the same dolomite used by Berlioz. The results of those experiments are summarized in Table 1. The results of these experiments permit comparison of the size reduction by impact and by ball mill grinding for the same energy input. Differences in the behavior of the particle size distribution may also be observed.
A comparison of the size reduction by impact and ball mill grinding is shown in figure 2. The ball mill experiments show the size reduction versus energy input for 7 series of experiments in which the weight of dolomite was 660, 1320, 1980, 2640, 3300, 3960, and 5420, respectively. The charge was composed of equal portions of -7 +8 and -8 +10 size fractions. The ball load was 455 stainless steel balls one inch in diameter, having a total weight of 30 kg. The particle size distribution was observed after 20, 40, 60, 80, 100, 150, 200 and 300 ball mill revolutions. The energy input was calculated from the net torque (corrected for the torque for the empty mill) and the number of revolutions.
For light ball loads the ball mill is less efficient as might be expected. As the load exceeds 1980 gm it has no influence on size reduction. The relationship between size reduction and input for optimum grinding in the ball mill is represented by the solid curve. The corresponding relationship for crushing by impact is represented by broken lines.
It is evident, as might be expected, that for moderate size reduction (x<5) the input energy is utilized much more effectively in the drop-weight machine than in the ball mill. For example, reduction to one-half of the original particle size requires about 4-3 kg cm per gm by impact as compared to 18.5 kg-cm by ball mill; that is, the energy requirements are less than 25 percent as much for impact crushing as for ball milling. For great size reduction the application of energy by a single impact becomes less effective so that there would be no advantage in applying more impact energy than would be required for about a four-fold reduction of particle diameter; this is equivalent to x = k. The energy required would be about percent that required for an equivalent size reduction in the ball mill.
The change in particle size distribution during ball milling is shown by the graphs of the variance and skewness in Figure 3. Here again, the points representing variance for those experiments with light ball mill loads show a noticeable divergence from those for optimum loading. The skewness is not affected by the load.
The differences in distribution between the products from the ball mill and those from impact crushing can be observed by comparing the solid lines, which represent the ball mill products, with the broken lines, which represent the products from the drop-weight experiments. The greatest difference is in the variance. The products from the ball mill show considerably greater dispersion over the size range and this dispersion develops sooner as the mean size is decreased. On the other hand, the skewness decreases earliest for impact crushing. The differences in size distribution are essentially difference in degree of dispersion and asymmetry. Actually there is a surprising similarity in the evolution of the distribution from uniform particle size to a typical skewed bell-shaped curve as the size is reduced whether by the ball mill or impact crushing.
The comminution process may be represented mathematically in terms of a set of state variables that define the mean size and size distribution of the feed to and product from a grinding machine. Three variables are required to specify the particulate state of the mineral undergoing size reduction; these variables define quantitatively the mean particle size, degree of dispersion and asymmetry of the distribution. Such a set of variables may be calculated by moment analysis of the screen analysis of the aggregate being studied. Conversely, if the mean, variance, and skewness of a size distribution are known, a gamma distribution function may be derived that will approximate the weight fraction in any given size range.
When a sized fraction of particles is subjected to comminution, the size distribution undergoes progressive change characterized by a steady increase in the variance or second moment and an abrupt decrease in skewness or third moment. As size reduction proceeds further, both the variance and skewness approach steady values and the form of the distribution becomes more and more stable.
In grinding, operating Efficiency compares the operating work index of a comminution machine to the Bond work index from bench scale crushing and grindability tests or/and pilot plant tests. Economic Efficiency is comparing the income from production to the planned income from production.
Energy as consumed in comminution machines and the required energy as determined, from bench scale laboratory or pilot plant tests to perform the required size reduction are the key factors in determining the operational efficiency of comminution machines.
Bond Work Indicies obtained from bench scale crushability and grindability tests or from pilot plant tests are used in the Bond Equation to determine the energy required to produce the required size reduction in comminution circuits. The Bond Equation as found in reference 5 is:
W = kwh per short ton. Wi = Work Index determined from crushing and grinding tests. P = The size in microns (micrometers) that 80% of the product is finer than. F = The size in microns (micrometers) that 80% of the feed is finer than.
When accurate mill ore feed rate in dry tons per hour, mill power draw in kilowatts, and mill feed and product size analyses in microns are available the Bond Equation can be used to measure the operation of comminution machines, reporting it as operating work index. The equation for operating work index as given in the paper Tools of Power Power (6) is
Wio = Operating Work Index as kwh per either short ton or metric tonne. W = Measured power in kwh per either short ton or metric ton. P = The size in microns (micrometers) that 80% of the product is finer than. F = The size in microns (micrometers) that 80% of the feed is finer than.
W as calculated using the Bond Equation can be converted to kwh per metric tonne by multiplying it by 1.102. If the measured power for the operating data used in the operating work index equation is given as kwh per metric tonne then the calculated operating work index is power per metric tonne.
Fred Bond defined Work Index as The comminution parameter which expresses the resistance of material to crushing and grinding. Numerically the Work Index is the kwh per short ton required to reduce the material from theoretically infinite feed size to 80 percent passing 100 microns. Wi and Wio both fit Fred Bonds definition for Work Index. Operating work indices can be compared to work indices from bench and pilot scale tests run on samples of circuit feed taken for the same time period, as the operating data. By definition, both work indices cover exactly the same amount of size reduction, namely from an infinite feed size to a product size of 80% passing 100 microns.
When (Wio/Wi)x100 is less than 100 this indicates the circuit, based upon this comparison, is operating efficiently. When it is greater than 100 this indicates the circuit is operating inefficiently. A large difference, either low or high, could indicate that the two work indicies are not on the same basis. For operating efficiency calculations, it is necessary that the efficiency factors are applied so that both work indices, used in the comparison, are on the same basis.
Operating efficiency, based upon using operating work indices, is also a useful tool in comparing the variations in grinding mill operations such as: mill speed, mill size, size of grinding media, mill discharge arrangements, liner designs etc.
A) Total Apparent Volumetric Charge Filling including balls and excess slurry on top of the ball charge, plus the interstitial voids in between the balls expressed as a percentage of the net internal mill volume (inside liners).
B) Overflow Discharge Mills operating at low ball fillings slurry may accumulate on top of the ball charge; causing, the Total Charge Filling Level to be higher than the Ball Filling Level. Grate Discharge mills will not face this issue.
C) This value represents the Volumetric Fractional Filling of the Voids in between the balls by the retained slurry in the mill charge. As defined, this value should never exceed 100%, but in some cases particularly in Grate Discharge Mills it could be lower than 100%. Note that this interstitial slurry does not include the overfilling slurry derived from the difference between the Charge and Ball Filling.
D) Represents the so-called Dynamic Angle of Repose (or Lift Angle) adopted during steady operation by the top surface of the mill charge (the kidney) with respect to the horizontal. A reasonable default value for this angle is 32, but may be easily tuned to specific applications against any available actual power data.
The first step in mill design is to determine the power needed to produce the desired grind in the chosen ore. The most used equation, for this purpose, is the empirical Bond equation (Bond, 1960, 1961; Rowland and Kjos, 1978).
In this equation, E is the specific energy required for the grind, and F80 and P80 are the sizes in micrometers that 80% of the weight passes of the mill feed and product respectively. The parameter Wi, known as the work index of the ore, is obtained from batch bench tests first devised by Bond (1961). The power calculated on using equation 1, (Bond, 1961; Rowland and Kjos, 1978), relates to:
1) Rod milling a rod mill with a diameter of 2.44 meters, inside new liners, grinding wet in open circuit. 2) Ball milling a ball mill with a diameter of 2.44 meters, inside new liners, grinding wet in open circuit.
When the grinding conditions differ from these specified conditions, efficiency factors (Rowland and Kjos, 1978) have to be used in conjunction with equation 1. In general, therefore, the required mill power is calculated using the following equation
where n is the number of efficiency factors, EFi, used and fo is the feed rate of new ore to the mill. The power calculated from equation 2 can be looked up in published tables (Rowland and Kjos, 1978) and the correct mill size and type can be selected.
The philosophy in the development of the MRRC grinding simulation package was to build interactive software that could be used as an inexpensive means of providing a semi-quantitative check on a grinding mill design. In addition the software is designed to slot in to a general mineral processing package now undergoing development at the MRRC.
Current ball milling theory suggests that grinding capacity is influenced by the size of balls charged to the mill. In selecting the appropriate ball charge, the first objective is to determine that ball size which will grind the coarse particles most efficiently. This size should be the largest ball size charged to the mill. The second objective is to provide the correct ball size distribution to grind the finer particles in the composite ball mill feed. This objective may necessitate charging a second, smaller ball size with the maximum ball size. The practice of charging a pre-determined ratio of two or more ball sizes to a mill is called rationed ball charging.
Maximum ball size is determined by several factors, including composite feed size, Bond Work Index, mill speed, mill diameter, and circulating load. An empirical equation was published by Azzaroni in 1981 to describe the relationship between these variables. The Azzaroni equation indicates that the correct ball size for the 2.93 m mill is 81 mm. Years of experience show that a 76 mm ball grinds the coarse particles most effectively.
Ball size distribution is governed by the wear law of the mill and by the wear characteristics through the cross-section of the balls charged to the mill. With this in mind, it is interesting to make a qualitative comparison of the ball size distributions which should be generated by 76 mm pearlitic carbon steel balls versus 76 mm martensitic alloy steel balls in the 2.93 m mills.
The 76 mm pearlitic carbon steel balls used have a relatively flat hardness gradient from surface to center. Therefore, the inherent wear characteristic of these balls should be nearly constant during their life in a mill.
Martensitic alloy steel balls are much harder, than pearlitic carbon steel balls throughout their cross-section. However, 76 mm martensitic balls generally have a hardness gradient. This gradient reflects varying amounts of soft transformation products such as bainite and pearlite in the ball micro-structure. The wear rates of these products are higher than that of martensite at equivalent carbon content. As a result, the inherent wear rate of martensitic balls increases slightly at the ball becomes smaller. Therefore, for a given ball mill with a constant wear law, the resultant seasoned 76 mm martensitic ball chart should contain more large balls, fewer small : balls, and less surface area than a seasoned charge of 76 mm pearlitic carbon steel balls. The reduced number of small balls, combined with a lower ball charge surface area, might explain the 6% lower grinding efficiency of a 76 mm martensitic ball charge compared to a 76 mm pearlitic ball charge.
We analyzed the ball size distributions resulting from charging 76 mm pearlitic carbon steel balls versus charging 76 mm martensitic alloy steel balls. This analysis was made using a computer simulation program that Lorenzetti et al described in 1977 to assess ball size distributions. Results for the 2.93 mills indicated that the martensitic steel ball charge should reduce consumption by at least 30%. However, the surface area of the charge should decrease 5% compared to the pearlitic , steel ball charge because of the hardness gradient effect described above.
The apparent correlation between lower ball charge surface area and decreased grinding capacity for martensitic balls warranted further investigation. We recommended a mill test using a rationed charge of martensitic alloy steel balls. The martensitic balls would reduce consumption. The rationed charge would increase the surface area of the ball charge.
The best alternative to the spoken word would be to compile your own record of equipment performances via running lab tests on every available choice of media mill, followed by in-house, long-term testing for complete confidence in your final choice. Although thorough, this method is both very time consuming and costly in material, travel and installation expenses.
For these reasons, it is necessary to eliminate possible vendors and predict results through knowledge of both the theoretical side and practical side of wet grinding and media mill technology. Knowing what to expect and what not to expect before spending money on comparison testing will increase your confidence and reduce your time spent on making a decision.
After comparing notes from each manufacturer, it will be easy to narrow down to three or four vendors if you know what to look for and what questions to ask. You can then enter product trials with confidence and a reasonable expectation of performance. Having fulfilled your expectations, a final choice should not be too difficult.
Since cooling capacity dictates the installed motor power, by comparing the energy density of each media mill type, it is clear to see which ones have the most cooling capability to allow for the maximum grinding capacity.
Higher energy density is not only beneficial for increased milling capacity, it also allows the grinding of hard particles, which require higher milling energy density for size reduction. The other benefit is that the chamber volumes are much smaller than a lower energy density mill with equivalent installed motor power. The reduced volume can be as much as 10 times smaller. This is a significant saving in grinding media costs.
The relationship between mass-specific energy and particle size reduction is illustrated in Figure 1. Figure 1 represents a series of single-pass milling experiments performed on a horizontal mill under fixed media conditions but with varying product flow rates and agitator speeds. The specific energy for each experiment was calculated and plotted versus median particle sizes produced at that grinding condition.
These experiments illustrate the fixed relationship between final particle size and the mass-specific energy of grinding for a given mill and media type. Regardless of flow rate or agitator speed, to achieve a target fineness of grinding, a specific amount of energy is required. Decreasing this energy requirement means having to run at higher milling efficiency. This is achieved by changing the grinding media, process milling method or using a more efficient mill.
The specific energy requirement is the best parameter for choosing the most efficient mill. The mill that works at the lowest specific energy will save you the most time and money over the life of the equipment. The specific energy is ultimately determined through actual product testing, but there are a few indicators to predict which mill will be the most efficient.
The grinding beads are the main points of contact where energy from the mill is transferred to the pigment particles, causing reduction in their size. Since the grinding beads are the actual perpetrators of attrition on the pigment particles, by increasing the number of beads or points of contact in the mill one will increase the opportunity for collision and shearing between the bead and the pigment particle.
The number of media beads or contact points per liter can be calculated through the equation in Figure 2. Grinding media diameters with the number of beads per liter at 87% filling load are listed in Table 1. The exponential increase in beads or contacting points as the diameter is reduced gives evidence to higher milling efficiencies.
Figure 3 depicts the effects of media size on grinding times. From this plot, it is shown that a target fineness of 80% < 2 microns is normally achieved in 315 minutes of recirculation milling with 1.0 to 1.4 mm grinding media. By reducing the media diameter to 0.6 to 0.8 mm after 90 minutes, the target grind is achieved in only 150 minutes.
The leading technology to prevent packing of beads is now through media recirculation. Media recirculation allows the grinding beads to flow with product towards the discharge under higher product flow rates but then separates the beads from the product through centrifugal force via a special rotor and stator and redirecting the beads back into the beginning of the grinding cycle. This method allows for the highest flow rates using the smallest grinding beads to achieve superior milling efficiency.
Each experiment began with running pure water from feed tank #1 through the mill. The solids content at the discharge registered 0 mV, which corresponded to 0% solids. Beginning at time zero, a slurry of known concentration from feed tank #2 was introduced into the mill. The outlet concentration was analyzed via the g-ray emitter and scintillation counter over time.
Figure 4, a sample plot of the outlet's change in concentration per time, shows that the outlet of the mill is registering particles at time zero when the slurry is first introduced. This suggests that some particles immediately pass through the mill as others spend significantly more time. For this experiment the flow rate would normally fill the chamber in nine minutes. As seen from the plot, it takes 30 minutes to achieve steady-state concentration in both step functions.
The variables in the designed experiment were the slurry flow rate through the mill, the agitator tip speed and the slurry concentration. The graph in Figure 6 shows the relationship of each of these milling parameters to the Peclet number.
Upon analysis of the particle size distribution for each milling condition, the relationship is confirmed between the Peclet number and the residence time distribution. Figure 7 is a sample of various milling conditions under different Peclet numbers and their corresponding particle size distributions. This plot confirms that high product flow rates yield tighter residence time distributions and thus tighter particle size distributions.
Start from premix tank and pass through the mill into a finished tank. Flow rates are generally slow enough to achieve target fineness in one pass. For multiple pass, the finished tank is manually positioned into the premix tank position. Two to three passes maximum. For low specific-energy requirements.
Start from one tank and mill one complete pass into another tank. By opening and closing valves, the second tank is passed through the mill back to the first tank. Repeat pendulum passes until target fineness is achieved. For medium to high specific-energy requirements.
Start from premix tank and slow pass through two mills in series into a finished tank. Generally the first mill uses larger media than the second for breaking down large agglomerates. This method is for low to medium specific-energy requirements.
Start from mixing tank and pass through the mill and back into mixing tank. Requires ideally mixed tank. Ideal for high specific energy requirements and high recirculation flow rates. A minimum of 5 to 10 theoretical tank turnovers is required to prevent unmilled particles left in tank.
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It is necessary to create a good control system at the factory to ensure the stability at the product quality. It must be studied meticulously in all stages of production so that the quality of product is good.
More functional and useful features have been added compared to the former ones with the development of electronics and automation in roller mills. Torque motors are used which we have made the R&D work for the years especially in the area of product supply. The product level is determined via sensor or loadcell integrated into the roller mill bottle and the feeding speed can be set according to the incidence rate. This provides a continuous product flow. Also the possible damage to the machine is minimized if there is any impaction through the sensors which can be put in different places, and the failure can be identified and rectified before the growth of failure. Lubrication systems are not on bearings one by one in the new generation of CERES II roller mills, they have been taken at a central point with easy access. Thus the lubrication is provided easily and in a short time. We can provide to lubricate in a stable form by controlling the centralized lubrication systems with the PLC system.
The front of the roller mills is made openable to make the roll changing operation more quickly and easily in roller mills and two rolls can be easily taken out along with the bearings. Thus, the changing of rolls can be made in a short time and production will have to stop for long periods.
THE EFFECT OF ROLLER MILL ROLLS TO GRINDING There are two types of roller mill rolls as Crushing roller mill rolls and reduction roller mill rolls; 1. Crushing roller mill rolls make an angle on rollers in order to fulfill the wheat cutting-opening, excavating- eroding and crushing and spliting missions, to do so, it has extending threads. Their numbers, angles, and heights in centimeters vary depending on how these threads will destroy and cut the product. Unless appropriate selection of roller threads, there will be problem related to efficiency and quality.
2. Reduction roller mill rolls are straight roller mill rolls. The task of reduction roller is gradually to convert semolina obtained in the crushing system into the flour and to make flake by crushing bran and germ particles. They make the compress, crushing and shredding tasks. Expansion occurs at the edges because of heat released due to compression and crushing in these rolls; A little camber is given to the middle part in order to ensure crushing in parallel and equally while running the rolls. This camber varies depending on the density and structure of the product to passage. If appropriate camber is not selected, a complete crushing can not be provided and thus quality defects with yield losses are seen.
ENERGY CONSUMPTION IN ROLLER MILLS Thanks to the advancement and the good use of technology today, the effort to make optimum production has increased with the minimum energy in the mill. Because the competition is increasing day by day. Therefore, machine manufacturers put in effort to make machines that can operate at maximum capacity by spending less energy. Also the selection of machine and the preparation of diagram according to the feature, capacity of raw materials to be processed and of product to be produced in making the factory projects directly affects the energy consumption. As a result of the development of machines, energy consumption has reduced rather than the former.
GRINDING GAP AND PARTICLE SIZE Grinding gap and particle size are reduced towards the end from roller mills which the grinding begins. The reason for this is that each process has disintegration and contraction while making gradually cutting, sorting and scraping actions during the separation of endosperm and bran. Therefore the grinding gap will be less in the next crushing process. This range varies depending on the chracteristics of the desired product, the performed diagram, tonnage and the humidity of the milled product.
TEMPERATURE CONTROL IN ROLLER MILL AND ROLL BEARINGS Temperature control is very important in especially reduction (liso) in other words straight roller mills. While making crushing and blasting operation in these roller mills, it may occur more heat. The crushing and blasting operation performed here should be applied so as not to impair the gluten and strach features of the flour. The roller mill rolls temperature should not be more than 40 to 45 degrees. If this remperature is more, there would be deterioration in the bread value of flour, also it begins to appear the deformations on the roller mill rolls and this temperature spreads to the bearings. The oil used in the bearings become thinner and exudes outward, in this case the life of the bearings is reduced.
STABILITY OF PRODUCT QUALITY It is necessary to create a good control system at the factory for ensuring the stability in the product quality. It must be studied carefully in all phases of production so that product quality is good. Things to pay attention are as follows: The supply of the right raw materials according to the product to be produced, the classification and storage of these raw materials, The making of the right wheat blending according to the product to be produced, Routine checks on time cleaning machines for cleaning of wheat in a good way, The wheat humidity is important for a standard milling. To be done right the quenching operation required to the wheat, After quenching according to the physical properties of wheat, the rest time is very important for coming to ideal humidity of the wheat. To rest at the right time. To maintain the tonnage constantly at the grinding part, Routin controls are made so that roller mill settings are stable.
FEEDING IN ROLLER MILLS The roller mill supply settings must be done in good way to obtain the maximum efficiency in the roller mills. Because if the product to rolls comes in the form of curtain and continuously among the roller mill rolls, grinding and milling process will be stabil; thereby the product coming to the sieves will be continuous and homogeneous. The feeding process is very important for the stability of product quality. Sensor and load cell system faciliates fairly in adjusting the product coming to the roller mills and the product given to the roller mill rolls. If the product to roller mill is thicker, the closeness of the roller mill rolls to each other is not importance, a shortage is seen in performing the crushing. So grain curtain setting and speed setting should be adjusted very well.
GRINDING CAPACITY Grinding capacity is calculated according to the factorys capacity. Crushing roller mill rolls should be up to approximately 40 percent of the total roller mill length, Reduction (liso) roller mill rolls are up to 60 percent of the total roller mill lenght. The average lenght of the roller mill is based on the account of12mm / 100kg /24 hours. This account is valid for standard flour mills. It varies according to the ratio of the products in the passages.
ROLLER MILL SETTINGS Roller mill settings can be adjusted according to three basic principles. The first is a setting done by hand. When the product is squeezed equally by keeping from both ends of the roller mill rolls, the decision is taken by touching The second is a setting done by eyes. Flaking and fragmentation of the milled product at both ends are looked with eye. The third is based on heat; the temperature in the roller mill rolls is synchronized with the heat meters from the both ends of the roller mill rolls and manually if there is no heat meter. It is effective to find the healthy setting to use these three method together while the roller mills are set. Also the product received from two sides of the roller mill rolls in the crushing roller mills can be adjusted, and can be adjusted according to the rate of product under the sieve by passing through laboratory sieve. For example about 30-35 percent of the particles must pass below 1000 microns sieve in B1 roller mills.
ROLLER MILL CARE AND MAINTENANCE PERIOD Maintenance and repair is a system that we still are forced to fix nowadays. As Aybakar, we committed to provide the necessary training on maintenance and repair to our customers. Our customers technical teams are trained at our factory and in customers factories prior to delivery of the machine.
The necessary maintenance intervals to be performed are as follows: Weekly maintenance Control of air supplies Control of roller mill rolls belt Control of the belt roller mills Cleaning of the roller engines Combining and opening the roller mill rolls
LUBRICATION Lubrication process may vary depending on operating speed and ambient temperature. Aybakars proposal is that lubrication is made from the central system per 1000 hours. By a single point lubrication with 8 bearing of 4 roller in our single storey CERES II roller mills, central system has been designed and approximately 640-800 grams of oil should be pressed. Double storey CERES II roller mills has been designed by lubricating of 8 roller from 16 single point and approximately 2560-3200 grams of oil should be pressed.Get in Touch with Mechanic