BALL MILLS

BALL MILLS

Very low cost of operation and maintenance
High quality production with high capacity
Very simple conditions for maintenance

Ball mills are the best and most effective method for crushing and powdering a variety of dry and wet materials, including minerals, types of building materials, sand and cement, lime and ceramics, and many other materials.

Zimaxon Industrial Group engineers have been able to design and sell many types of ball mills of high quality based on their knowledge and expertise, with the backing of years of useful experience. Currently, Horizontal Ball Milling Machine of this company is recognized as a fully reliable device for use in various industries.

The most important features of ball mills that work with shoe bearings include:

Low costs of repair and operation
High reliability
High capacity
With much smaller dimensions and sizes than the mills trunnion bearings base

Internal structure of ball mill:

External milling armor
diaphragm categorized
Utilize the external wall
Benefit from the Grinding charge

Structure of Ball mill

Shell of mill

After cutting the plates, bend them and welded Partitioned plates together and eventually expose them to extreme heat to strengthen them. Then, using the non-destructive and engineered tests, the whole machine is checked and verified. All ball mills part like ball bearings and machine are carefully tested to ensure their accuracy and efficiency.

Place of Mill

On the oscillating sweeping blades of the ball mill they are fitted with Shoe-type bearings that for lubricated using a dynamic diesel lubrication system. They are designed and constructed to fit the shape of the rings easily and fit perfectly. Engineers at Zimaxon Industrial Group have designed the mill creatively on trunnion bearing.
Generally, the ball mill contains a DMG 2, two large gear and a gearbox, a small gear for the mill and a shaft counter. In addition, these ball mills also have an auxiliary drum for use at the time of the main drum failure.

Two-part mills

Iron cement, cement and many other similar materials are usually crushing and milling used in two part mills or two chamber cement mills. Both parts of this mill are embedded in a high performance VTP.

According to Blaine’s theory, these mills can cut up and pour up to 6500 cm2 /g of material. The mill is equipped with an armored lift in the initial part, which uses larger grinding mills with high grinding power. In the next section, mills use a smaller mill that is used to end the cutting and milling process.

In the classified diaphragm, a control sensor is also installed to allow only a certain amount of milling material in each mill segment. In the roller mill, materials are transferred to another part by using an external wall and molded.

When the material is heated, the equipment for cooling the material transmits them to two rooms embedded in the mill to cool the water using embedded water spray. If the mill is equipped with a compact drive and a roller, part of the mill is equipped with an armored classifier without an aperture.

The ball mill is equipped with two compartments for raw materials and a compartment for pre-drying materials

The materials used in the kiln lines are usually made using mills with one to two compartments with a special compartment for pre-dryer chamber. These types of mills are equipped with a circuit and use high-performance VTP for separation.

The material is dried by using a furnace or heating gas, and a cooling room is also used to cool it. This kind of ailment is often applied to materials that have a moisture content of more than 8%. After the process done on the material in this type of mill, the crushed material is less than 0.5% moisture and is crushed or powdered at 12 to 14% R90.

To use this ball mill, first all the materials are placed in the dryer compartment to get their moisture well before entering the damper stage. In the Damper area, the materials are separated and the coarser and heavier materials are directed to the mill ball. The same seats and drivers used in cement mills are used precisely for this mill.

Pneumatic mills

This type of mill has a pre-dryer for milling and a compartment for milling materials. After the pre-drying step, the materials are placed on the floor of the mill and directed to the LRT’s high-quality separation unit. The product will ultimately be packed in a filter or cyclone. Usually materials that have a very high humidity are grinding through a pneumatic grinder.

The mill is used to dry the material from a high temperature using a gas injected into the dryer, and then the milling and separation work is done. Pneumatic mill is very popular because of its simple design and high performance. Pneumatic mills are generally used for grinding coal and petroleum coke, which are designed in a high separation environment LTR-U with a pressure drop of over 3.5 times.

Mills seated on trunnion bearings

Our engineers at Zimaxon Co., as one of the most advanced mills company in Iran, have been designing and manufacturing a large number of ball mills, unique and classical on swing trunnion bearings, which are used in many industries.

Ball mill

In this article, the latest methods and practices of producing, modeling and controlling the grinding process in the ball mill are discussed. It should be noted, however, that this paper also focuses on basic kinetic and the energy models in the ball mill process, and our intention, therefore, to present and review these materials is to actually describe and analyze the various strategies available for more control strategies.

Keywords: Process control, Ball mill, grinding circuit

Introduction

Today, in many industries, ball mills are used as one of the most advanced and best methods for grinding and reducing the size of various types of particles with different physical, chemical and mechanical characteristics and nature, which each of these ball mills may have a different conditions and may be a different technology.

Although ball mills are often used to grind and crush materials such as ores, minerals, limestone and many other such materials, ball mills in today’s industries have many more and more diverse applications.

Generally, ball mills are used in industries such as minerals and mining, metallurgy, cement processing and production, petrochemical industry and various chemical industries, in the pharmaceutical industry, in the cosmetics industry, in the tile and ceramic industry, agriculture, and any other industry in which the need for crushing materials, the preparation of coarse and hard materials, etc., is used in many test laboratories and factories.

Contrary to many imaginations, ball mills are not only made for crushing and reducing the size of particles and materials. Ball mills can also be used for mixing, blending, dispersing and amorphous materials, or even for the preparation of mechanical alloys.

The ball mill building is made up of a cylindrical vessel, which is carefully connected to the two ends to allow rotation around the central axis to be rotated easily. This grinding mill uses a girth gear to connect the shell and the shaft moves it with the main drive to rotate it.
For ball mills, commonly used synchronous motors equipped with an air clutch or gear, it can be easily circulated by connecting to the main gear mill. The power of these transfer motors is usually considered to be enough to grind and grinding various types of raw materials such as stones, ore, etc., depending on the performance of the ball mill.

The ball mill uses a rotary motion and uses the kinetic energy movement to grind and crushing the material.

The ball mill is very diverse and is often made in different sizes and designs, and even the materials used in the production of these mills are different. Generally speaking, what determines the type of ball mill in different industries is issues such as material size, equipment used for loading raw materials (feeders) and even the system of discharge of produced materials. Given this, it should be noted that the size of the mill is usually determined by the ratio of length to diameter, which is about 0.5 to 3.5.

Usually, a spout feeder or a single or double helical scoop feeder is used to load raw material into the ball mill.
The drainage system or discharge system is different in the ball, and each one may be designed differently. The ball mill, in terms of the drainage system, can have an overflow discharge system, a diaphragm or grate discharge mill and a center-periphery discharge mill.

Ball mills with an internal surface are usually the best choice for industrial applications because they have a steel body of grinding and the other equipment used in these mills is perfectly suited to industrial applications depending on the types of industry. For this reason, the contents of the mill can be built with the best possible weight to prevent falling or dropping or cascades down.

Usually ball mills use three types of grinding media:

Different metal balls like all kinds of steel balls
Varied cylindrical metal known as Clypeus
Types of ceramic balls made of high density or regular.

Usually, balls are made from any type has a standard sizes range from 10 to 150 mm and are used depending on the type of mill. Although most types of steel and other metals are used to manufacture and supply these types of balls, ceramic types and other types of balls are sometimes made and used.

The Clypeus balls have a slightly conical shape in the cylinders of a grinding ball mill and the edges of each of these balls are round, their diameter and length are considered equal and they have different dimensions, generally in the state of 8 x 8 to 45 x 45 mm depending on the type of application they are made.

In order to get maximum efficiency from the ball, due to the high density and specific surface of the balls, their shape has been well developed.
Porcelain balls are a high-density ceramic ball that, in order to withstand high wear resistance by using aluminum oxidized in the ball structure, these balls are produced with a very high thickness and hardness.
The main characteristics of the mill body and their higher efficiency depend on the mass and size, ware rate, the impact on the failure rate and the efficiency of grinding energy.

The ball mill speed usually identifies three main types of operating modes of the milling machine: low speed (cascading), rapid rotational speed (cataract) and very high spin speed or super speed (centrifuge). The effect of each of these speed, varies on materials on the ground, because each of these speeds has a specific trajectory of motion charging path in the mill.

In addition, it should be kept in mind that other factors may also affect the milling process, such as dry or wet substances, or that wet materials may be added to the milling material during the milling process. For this reason, in this research, the dimensions of different mills in dry conditions or wet conditions are also mentioned.

In general, the ball mill in the process of grinding or crushing raw materials into smaller particles depends on several factors, most notably:
• Various material specifications such as mass, volume, size, hardness, density, charge size, type and other specifications of raw materials that are loaded in the mill
• Specifications such as type, mass, density, or ball size distribution in the ball mill
• Spin rate or speed of rotation of the mill
• Density and volume of Slurry in the wet mill operation

We will continue to provide further details on these factors.

One of the most important characteristics of a ball mill can be the amount of material produced by these mills per hour, which is usually estimated in tones and measured.

Of course, it should not be forgotten that the ball mill’s production capacity depends on several factors, the most important of which is the size of the mill, the type of grinding structure (overflow or grate discharge), the speed of rotation, the size of the raw material loaded in the mill, the size of the desired final product Based on feed size (reduction coefficient), type of material, shaft power used in the ball mill, and raw material gravity.

We intend to consider all the parameters defined in the ball mill in this study and finally we propose an experimental relationship that will measure the mill capacity as a ratio of power to shaft and energy consumption in the grinding process to describe well.

Due to the fact that the ball mill usually operates in industrial conditions in milling circuits, it is usually possible to achieve the best particle size by classifying the materials according to their required size. The open and closed circuit ball in Figure 1 is shown as simple as possible.

Fig. 1

In the first case, all of the output materials are separated in one part, and therefore classification does not have much effect on the milling process.

In the second case, the grinding material is returned to the mill feed using a classifier, and the process continues so that all the materials are converted into the final product. Usually, in order to increase the grinding efficiency, different interconnections between the ball mill and dividers may exist.

The main purpose of grinding raw materials is to reach the final product with the desired size and structure in such a way that all the materials in the same size and shape are mined and there is no impurity in it, such as a variety of metals or other pollutants that May affect the final product. This process will further increase the power of the grinding circuit and even reduce the final cost of production.

To achieve these goals, the appropriate size of the grinding material and the reduction of the overall cost of the production process, various mathematical models and methods are used.

In this paper, we will attempt to examine the most important principles for modeling the grinding process by examining some of the most important of these methods and strategies, and then we will analyze various strategies to identify the best design and control of the structure and Finally, using the obtained data, we chose a suitable method for controlling the process, depending on the type of ball mill operation.

Modeling of the process

II.1. Basic fragmentation mechanisms

The unveiling of the mill process and the main idea in modeling all crushing processes is necessary to obtain a good and proper mathematical relationship between the feed size and the size of the final product.

However, the passage of time makes the main raw material, or the chopped feed used in the process of production, has a decreasing trend, because the increased energy of grinding media creates disturbances in the bonding forces.

In general, one of the three divisional mechanisms below is the main factor of this size reduction.

– When abrasive process is used to cause local low tension stress occurs, as a result of this wear, particles that are attached to the particle mother or larger particles are separated from the mother and particles that are approximately the same size as themselves. (Figure 2a)

a b

Fig. 2

When intense stress occurs slowly but during the entire grinding process (compression), it creates a particle cleavage, resulting in more particles of 50 to 80 percent of the initial particle size. (Fig. 2b)
When exerted by intense and rapid stresses, it causes fractures in larger particles or mother particles, resulting in particles that are smaller in shape but with relatively large particle size distribution. (Fig. 2)

Of course, it should not be forgotten that these three different mechanisms will never fall apart alone, and issues such as the type of mill, the different operating conditions, or even the type of material that is being grinded, also greatly affects the process of reducing particle size, and probably leads to Exacerbate or reduce each of these three mechanisms.

Generally, a number of major concepts are commonly used in modeling the grinding process. Certainly there are raw materials that define the classes of different particle size because these particles naturally exist in different sizes.
A standard sieves should be used to measure the quantity of particles in each class. Generally, solid state theory is used in a series of steps in the partitioning process with two main operations:

(i) In the first step, you should choose one of the raw materials that are supposed to be crushed or grinded.

Secondly, in the second step, by crushing the raw material components for production, you specify the size you want to produce to reach the size distribution of the desired item.

Using this operation, two structures can be identified: the Si function in this function is Si, i = 1, 2, …, n, and the breaking function bij, n ≥ i ≥ j ≥ 1. In this function, n shows the number of size classes. In this structure, the fracture performance or failure rate with the selective Si performance is shown. Xi to indicate the probable size of the particles in each step, according to the piece given to the mill for the milling, and in this operation we consider xi as the least probable particle size.

In this regard, S1, S2, …, Sn denotes the mass of material in each class, depending on the size of the mill that is considered for the mill and converted to smaller particles. The mill operation or the breaking of bij, which, of course, can be called the distribution function, is generally described by the distribution of the size of the parts produced after grinding and breaking the particle size Xj.

Therefore, b1j, b2j, …, bnj is the mass fractions of the particles after milling process and the breaking of particles in the class size j, that are essentially related to the particle mass in classes 1, 2, …, n.

Fig. 3 graphically illustrates the particle fracture process. In the left column, an initial distribution sample of the primary feed is shown to the milling machine. Using solid arrows, the use of the different forces described in each class is show, and using dash arrows to describe the movement of parts of the same size or slightly less on each floor.

The fracture functions are displayed in the third column and finally displayed in the fourth column of the final product that has been produced at the desired and smaller sizes. During this process, in the lower-level categories, the level of crude feed is distributed in class 1 size.
Ultimately, with the milling process and the breakdown and distribution of raw material or feed over a given time, the mass of mass 1 is eliminated in general, although ultimately the total mass remains constant.

Fig. 3

Having a communication process in modeling performance and breaking performance is one of the most important parameters that should be considered in this modeling. In the milling literature in general, three types of models have to be considered: the matrix model, the kinetic model and the energy model.

To give a specific principle to a general principle for the development of any model, such as establish mass balance or energy equilibrium equations, which relates to mass or energy components involved in the process, should not be forgotten. Matrix models should be used at times when the size reduction is mainly in a discrete process with each discrete step including three selection breakdown classification.

The important thing to keep in mind is that when a fixed mill is in steady state for batch milling modeling, the milling process and the reduction of raw material size should be seen as a continuous process. In this case, the mathematical models must be combined with the combination of time parameters and considers the working time. Therefore, in this case, matrix models are less responsive to kinetic models and energy models.

II.2. Kinetic and energy models

Currently, various types of grinding mill machines and even different milling circuits are used when modeling the grinding process. The basic assumption that is often taken into account is that the content of the crushed matter is the same and is completely mixed with the movement and rotation of the mill and the displacement of the grinding media. For this reason, they call this model a very complex model, or sometimes as a perfectly mixed model.

Of course sometimes, the grinding of the mill is well-mixed in the radial direction, but it is not thoroughly grinding in the axial direction. The second assumption is that particles of any size are ultimately broken up uniformly and in the normal or in the same way, and that no agglomeration process occurs during the milling process of this raw material and during the breaking of the material.

Given this, perhaps the best method for grinding processes is kinetic models, since they perform process descriptions over different size intervals based on mass equilibrium equations. In this case, it is assumed that the mill in the radial direction completely mixes the material and, in the axial direction, to some extent mixes the material, and in the second step a more kinetic model must be used. For this purpose, the following model should be used:

^dwi ⁽ ^l ^, ^t ⁾ = − S _i w_i ( l , t ) + ∑ⁱ⁻¹ S _j b_ij w _j ( l , t ) + D _i ^d ² ^wi ⁽₂^l ^, ^t ⁾ − u_i ^dwi ⁽ ^l ^, ^t ⁾ ,

dtdldlj=1

In this form:

indicates the mill time;

l – Represents the spatial coordinates in the axial direction of the mill;

w_i (l , t) – Indicates the mass fraction of material in the i-th size class

b_ij –Grinding Break Function;

S_i – Grinding selection function;

D_i – Milling mix Coefficient;

u_i – Indicates the speed of material transport in the axial direction of the mill

The change in the mass fraction value in this method is shown in the class of size i at a time interval [t, t + dt] on the left side of the equation.

The first and second stage, which relate to the particle masses and particles in this class, are shown on the right. Thirdly, describes the degree of dispersion of the axis, and in the fourth stage, which is the last step, the conveyance of the material or particles will be shown axially at the speed of the UI. With this description, a differential equation (1) has the following boundary conditions:

Here fi (l ) represents the mass of feed fraction in the size class i and l is the length of the mill

With conditions 2-4 in Equation 1, we are actually showing the basic kinetic model of the process. Of course, this kinetic model has a number of well-known models that determine the specific operating conditions of the mill.

Now the basic assumption is that the mixture is mixed in the direction of axially and in radial direction uniformly and completely, and for this reason, fully mixed model or completely mixed or complex model for this equation is used. The third and fourth equations can exceptionally be ignored in this particular case and design the kinetic model of the mill as follows [3, 25, 46]:

Here’s is the diagonal matrix of composite elements si

i = 1, 2, …, n,

B is a smaller

triangular matrix

with component b_ij ,

n ≥ i > j ≥ 1, w(t) is

direct with component

w_i (t ), i = 1, 2, …, n,

and I shows the identity matrix. Matrix (B − I )S

in (6) has a

less triangular

form with

oblique component −S₁ , − S ₂ , …, − S_n .

Under the

supposition that functions b_ij

and S_i

are known and time independent, the resolving

of (6) is give by

We can even use the cumulative form of Equation 5 to model the grinding process. for example:Now, in class size, we see that the conditions are equal to the mass of the feed. For this relation, the most accurate and most suitable formula is wi (t) i = 1, 2, …, n, which is used as the Reid solution for the batch mill equation and is shown in [3, 23].

is the cumulative fractional mass fraction of particle that have a size larger than xi and is smaller than the size of the particles of class i.

For the pre-supposes, a basic knowledge of the breakage and selection functions b_ij and S_i, we can use the solution obtained in the solution of equations 5 and 8.is the cumulative fractional mass fraction of particle that have a size larger than xi and is smaller than the size of the particles of class i.

Of course, experimental procedures and successive therapies can also be found for some particular processes, although, because these types of topics do not have known basic functions, achieving the results of a purely experimental, is not easy-to-learn match. Several different methods can be used to determine the fracture functions and some of the usual breaking performance charts. In the explicit form of the cumulative equation of grinding 8 is also shown in Figure 3.

To describe the grinding process, you can even use mathematical models based on energy-balance equations. In model 21, a linear model that is similar to model 5 is used, which has been further developed, in which we chose the batch milling kinetics for a particular energy as an independent variable and instead of milling time.

Even in many cases, mathematical models can be used based on energy balance equations to describe the grinding process. Accordingly, in model 21, which is a kind of linear model similar to model 5, is shown with the difference that more development has been given. In fact, in this model, the kinetics are known as milling for a particular energy as an independent variable and the place of milling time.

So far, many scholars and scientists have been conducting precise and specific tests to measure the specific energy consumed in ball mills in various conditions and operations, and even in the case of different materials.

Generally, the results of these experiments in raw mill conditions and with detailed analyzes showed that the dispersive failure rate of the measurement with the specific energy entering the mill and even the fracture distribution functions can be constant and constant. So, using a model like the following model can be well responsive in a structure that equations modeling for energy balance:

the

is the energy-normalized breakage rate parameter and E

S_i^E

is the specific energy entering to the

milldefined as

In order to better understand this issue, we have compared the simplified model of the mass balancing presented in Form 5 with the equilibrium energy model presented in Form 10. The two linear models presented in the formulas of equations 5 and 9 are almost straightforward and can easily be used, and each of them has a high degree of kinetics for studying first-order breakage kinetics in the process.Note that in Equation (10) we consider p as the input of power to the mill and Was the mass of the feed material in the mill.

In the model 5, we made a detailed study using differential equations in exact and complete forms, and in literature with different hypotheses and degrees of approximation. Generally, in Model 5, we examined the best solution in milling time in particle size as a solution, and we came to the conclusion and recognized it.

But to do this, we can estimate the model, like the model 9, rather than the exact time of the analysis of the breakage kinetics using the specific energy consumed by the model.

In addition, as a fully functional control parameter in the process, we can measure the accuracy of the input power to the mill, instead of using the measured data. However, for the purpose of milling, in an analysis of other crushing systems such as the roll mill, an energy model such as that given in model 21 can be used in a more useful way. It should also be kept in mind that apart from linear models, more developed nodes and mathematical models can be used in grinding, such as the choice of nonlinear models, time dependent models, or breakage functions [7, 20].

Often, the methods mentioned and many other methods for studying the dynamic properties of the breaking process, the computer method that simulates the work process is based on a discrete element [31, 32, 38].

III. Process control methods

It is very difficult to control a grinding machine because of factors such as nonlinear character, unspecified processes, possible and unpredictable mistakes in mathematical models, the existence of variables of the process of interaction with different dynamics, the effect of unwanted disturbances, delay time Extremely high operating conditions are unclear and dependent on various and violent factors and the use of tools such as precision sensors and reliable all-in-one control of grinding machines.

In addition, it is also important to achieve different factors, such as increasing the output power of the circuit and the quality of the expected final product, or minimizing production costs in order to achieve greater efficiency and more efficient control of the mill process.

III.1. Process variables and characteristics

By the control viewpoint, the ball mill grinding circuit should be operated as a multivariate connected system that has very strong interactions between all process variables.
For example, in a very simple and integrated structure, a closed loop circuit in a wet mill has a ball mill, a sump and a spliter or divider [10, 13, 33, 39]. What is shown in Figure 4.

Fig. 4

Types of process input variables depicted in the figure above

u1: water flow rate of mill feed
U2: feed rate of fresh ore
U3: speed fraction in the mill critical
U4: rate of water flow of sump dilution
U5: flow rate of sump discharge

The values of these variables are used to control the output variables listed below and are shown in the figure:
Y1: The mass fraction of products or feed given with smaller particle sizes than the quantities available
Y2: Concentration of product solids
Y3: product flow rate
Y4: sump’s slurry level
Y5: Concentration of sump solids

Of course, it should be kept in mind that some of the possible malformations may occur in this process, which are most likely to have the greatest impact on the process, ore hardness changes, and changes in feed size. For this purpose, in the form of a matrix form, we can define the inputs and outputs of this model.

(11)	…	,
	.
	…
where	is the transfer function relating the i-th input and j-th output for

i, j = 1, …, 5.

In this circumstances, it is attempted to determine the transfer functions by applying the step change test and measuring the dimensions of the output of the final product.

There is no doubt that a lot of experiments are to be conducted to get accurate results. In addition, some of the parameters, such as configuration and grinding circuit equipment, are factors that sometimes require different sets of input and output variables to make a model [8, 33, 40].

What is certain is that there are many obstacles and problems to control the ball mill process, the most well-known and most important of which can be as follows:

Non-linear mills, such as ball mills, have measurable disturbances that do not have a dynamic model for them.

There are tight interconnections between the variables of this type mill, so that each input variable may be associated with several output variables.
Although a lot of time constant can be defined in the process, it should be kept in mind that many of the input / output pairs require a much longer and more unpredictable time.
The system model of the ball mill has many integrals.
In the milling process of some parameters, time as the age of the circuit is variable
Ball mills still sometimes have technological constraints that can sometimes be seen in manipulated and controlled variables.

Finally, you cannot be sure of the measurements and rely on a high-end model.

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