Crushing. Methods of crushing in different animals and humans. Types of blastulas. Types of blastula crushing Selection of equipment Stage I - crushing

There are several types of classification of the crushing process.

According to the nature of formation and location of blastomeres:

Complete (holoblastic) - characteristic of zygotes containing little yolk (meso- and isolecithal eggs), while cleavage furrows pass through the entire egg, and the yolk they have is included in the vegetative blastomeres;

Incomplete (meroblastic) - characteristic of zygotes containing large reserves of yolk proteins (polylecithal eggs), while the cleavage furrows do not penetrate into the yolk-rich region of the cytoplasm.

Depending on the size of the formed blastomeres:

uniform- blastomeres on the animal and vegetative poles have the same size;

uneven- smaller blastomeres are concentrated at the animal pole than at the vegetative pole.

According to the rate of formation of blastomeres:

synchronous- at the same rate of formation of blastomeres at both poles of the zygote;

asynchronous- at the animal pole the rate of formation of blastomeres is higher than at the vegetative pole.

Highlight four main types of holoblastic cleavage. This classification is based on the relative spatial arrangement of blastomeres:

Radial;

Spiral;

Bilaterally symmetrical;

Wrong (anarchic).

The radial type of fragmentation is characteristic of holoblastic chordates (lancelets, cyclostomes, sturgeons, amphibians), echinoderms and some other groups.

With this type of cleavage, blastomeres of different latitudinal tiers are located, at least in the early stages, quite precisely one above the other, so that the polar axis of the egg serves as an axis of rotational symmetry.

A radial, uniform type of crushing is characteristic of echinoderm eggs (Fig. 23).

The frog egg exhibits a radial, uneven type of crushing. The furrow of the first cleavage division has not yet completed the division of the yolk-rich cytoplasm of the vegetative hemisphere, and the furrows of the second division are already being formed close to the animal pole. Due to the high concentration of yolk in the vegetative region, the furrows of the third cleavage division are located much closer to the animal pole (Fig. 24).

As a result, a region of rapidly dividing blastomeres appears near the animal pole and a region of more slowly dividing blastomeres of the vegetative pole.

The spiral type of cleavage is characterized by the loss of symmetry elements already at the stage of four and sometimes two blastomeres and is characteristic of invertebrates (mollusks, annelids and ciliated worms), united in the Spiralia group.

This type of fragmentation received its name due to the fact that when viewed from the animal pole, successively separating fours (quartets) of blastomeres rotate relative to the animal-vegetative axis, either to the right or to the left, as if forming a spiral when superimposed on each other (Fig. .25).

The sign of spiral cleavage, its dexio-(right-handed) or leo-(left-handed) tropism, i.e. “twisting,” is determined by the genome of the mother of a given individual. It differs in many ways from the radial type of crushing.

First, eggs do not divide parallel or perpendicular to the animal-vegetative axis. The planes of cleavage divisions are oriented obliquely, which leads to a spiral arrangement of daughter blastomeres.

Secondly, the number of contacts between cells is greater than with radial cleavage. Thirdly, embryos with a spiral type of cleavage undergo fewer divisions before the onset of gastrulation. The blastulas that arise in this way usually do not have a blastocoel (sterroblastula).

The bilateral type of crushing (roundworms, tunicates) is characterized by the presence of one plane of symmetry. The most remarkable feature of this type of cleavage is that the plane of the first division establishes the only plane of symmetry of the embryo (Fig. 26).

Each subsequent division is oriented with respect to this plane of symmetry so that half of the embryo on one side of the first furrow is a mirror image of half of the embryo on its other side.

rice. 27. Anarchic fragmentation (according to Tokin, 1987)

With the bilateral type of cleavage, one plane of symmetry is formed: the first groove runs equatorially, then the animal blastomere is divided by a meridional groove, and the vegetative blastomere is divided by a latitudinal one. The result is a T-shaped figure of four blastomeres, which does not have rotational symmetry.

By rotating the vegetative pair of blastomeres, the T-shaped figure is transformed into a rhombic one. This rotation occurs in the interval between divisions, in interphase.

In this case, they can disintegrate, for example, under the impact of waves, but from individual sections full-fledged embryos are formed. As a result of the dense union of blastomeres with each other at the end of cleavage, morula.

The main types of meroblastic cleavage are:

Superficial;

Discoidal.

During superficial fragmentation after the fusion of pronuclei, the zygote nucleus is divided into many nuclei, which, with a small amount of cytoplasm, pass through cytoplasmic bridges into the outer layer of yolk-free cytoplasm (periplasm) and are evenly distributed there

(we are talking about centrolecithal eggs). Here the nuclei divide synchronously several more times, located quite close to each other (Fig. 28).

At this stage, even before the appearance of cellular partitions (the so-called syncytial blastoderm), the nuclei are surrounded by special structures of microtubules, then nuclear division becomes asynchronous, cellular partitions are formed between them and a basement membrane is formed, separating the periplasm from the central mass of the yolk. Cleavage furrows appear, but they do not extend deep into the egg. The resulting surface layer of cells is called cellular blastoderm. This type of crushing is characteristic of most insects.

The first two furrows run perpendicular to each other, but then the strict order of the furrows is violated. In this case, only a thin disk of cytoplasm (blastodisc), located at the animal pole, is divided into blastomeres.

TOPIC 5 PHYSICAL BASICS OF THE PROCESS OF ROCK DESTRUCTION

1. Methods of destruction of rocks during crushing and grinding.

2. Properties of rocks that are important during destruction.

3. Crushing stages. Degree of crushing.

4. Hypotheses of crushing and grinding.

Crushing and grinding processes are used to bring the material to the required size, particle size distribution or a given degree of mineral disclosure, i.e., to obtain free mineral grains. In this case, pieces of rock are destroyed by external forces. Fracture is the process of nucleation and growth of cracks and pores. Occurs along weakened sections that have cracks or other structural defects. Fracture occurs after the normal and tangential stresses that arise in the material during its elastic deformations: compression, tension, bending or shear go beyond the strength limit. Tensile strength - the limiting stress value above which the sample collapses almost instantly, and below which it lives indefinitely.

Different crushing and grinding methods differ in the type of underlying irreversible deformation that caused the destruction. In accordance with this, destruction methods are divided into (Fig. 2.1):

1) crushing – occurs after the stress passes beyond the compressive strength;

2) splitting - after the stress passes beyond the tensile strength;

3) fracture - after the stress passes beyond the bending strength;

4) shearing - after the stress passes beyond the shear strength;

5) abrasion - after the transition of stresses in the outer layers of the pieces beyond the shear strength;

6) impact - the impact of dynamic loads on the material, the same deformations occur: compression, tension, bending, shear.

Shearing Abrasion Impact

Figure 2.1 – Methods of destruction of materials

These destruction methods are common to both crushing and grinding operations, but these processes differ in their technological purpose. It is generally accepted that crushing is a process of destruction, as a result of which most of the product has a particle size above 5 mm. When crushed, a product smaller than 5 mm is obtained. The size of 5 mm is accepted conditionally.

All machines used to destroy pieces of rock are divided according to their technological purpose into crushers and mills. Distinctive features of these types of machines are:

Crushers - 1) there is always a gap between the crushing bodies, which is free at idle and filled with material during the working stroke; 2) they produce mainly a lump product with a predominance of large fractions.

Mills - 1) the grinding parts are in contact at idle, and at work they are separated by a layer of material; 2) they produce a powdery product with a predominance of small fractions.

In various machine designs, several methods of destruction can be used at once, but one of them is predominant:

Crushing – in jaw, roller and cone crushers;

Cleavage – in gear and needle crushers;

Impact – in hammer crushers and disintegrators;

Abrasion – in mills.

For destruction processes, the most important are the strength (strength), crushability, grindability and abrasiveness of rocks. Strength is the ability of a solid body to resist destruction from external forces. Characterized by the maximum stresses that can be created in a dangerous section of the body.

From the point of view of the physical and mechanical properties of rocks, it is most advantageous to destroy them by tension. But for design reasons, crushing is mainly used. Therefore, to compare the strength properties of rocks, the compressive stress or strength coefficient developed by prof. Protodyakonov M. M. According to Protodyakonov’s scale, all breeds are divided into 10 categories with strength coefficients from 0.3 for the weakest to 20 for the strongest breeds.

Crushingability is a general parameter for many mechanical properties of rocks and expresses the energy intensity of the crushing process.

Grindability is assessed by the specific productivity of the mill according to the newly formed design class.

Abrasiveness is assessed by the wear of the material on the working surfaces of machines during crushing (grinding) during friction.

The results of crushing (grinding) are assessed according to the degree of crushing (grinding) and the efficiency of the machines. The degree of crushing is the ratio of the size of the pieces of the source material to the size of the pieces of the crushed product.

I = D/d, (2.1)

Where i is the degree of crushing, D, d are the average or maximum size of a piece in food and crushed product, respectively.

There are no crushing machines that could accept the original ore and produce the final product. Therefore, several crushing methods (stages) are used (see diagram). Depending on the size of the initial and crushed material, the following stages of crushing and grinding are distinguished, the indicators for which are given in table. 2.1.

Table 2.1 – Stages of crushing and grinding

When crushing (grinding) in several successive stages, the total degree of crushing (grinding) is determined as the product of all degrees of crushing in individual stages:

I = i 1 i 2 i 3 i n. (2.2)

Crushers (mills) can operate in an open or closed cycle. With an open cycle, the material passes through the crusher once, while with a closed cycle, the over-size product of the screen continuously returns to the crusher for additional crushing, forming a circulating load. In the case of mills, the sands (large product) of the hydrocyclone or classifier are returned for regrinding. Closed cycles provide a higher degree of crushing (grinding) compared to open ones.

If the crushing product is free grains of a useful mineral, then further crushing does not make sense, since it will only lead to overgrinding of the material. The process is energy-intensive, so prof. G. O. Chechet formulated the principle of NOT CROSSING ANYTHING EXTRAORDINARY. During destruction, the adhesion forces between particles are overcome and a new surface is formed. The energy consumed during crushing (grinding) is spent on: 1) elastic deformation of the destroyed grains, i.e., dissipated into the surrounding space in the form of heat; 2) the formation of a new surface, i.e., it is converted into free surface energy of crushed grains. During grinding, the consumption of useful energy - for the formation of a new surface - is about 1% of its total consumption.

Let the grain be destroyed in the form of a cube with size d, shown in Fig. 2.2.

Figure 2.2 – Change in the total surface of grains during crushing

Then the surface of the particles will be:

Before crushing: S 1 = 6 d 2 1 cube. (2.3)

After crushing: S 2 = 6 (d / 2) 2 8 Cubes = 6 d 2 2; (2.4)

S 3 = 6 (d / 3) 2 27 = 6 d 2 3; (2.5)

………………….. ; (2.6)

S n = 6 d 2 n. (2.7)

Here n is the number of particles.

Thus, as the size of ore pieces decreases, the total surface area of ​​the particles increases.

To evaluate powdered materials, the concept of specific surface area is used, i.e. the surface area per unit weight of the material. In this case:

S yd = 6 d 2 / d 3 δ = 6 / d δ. (2.8)

Let us denote 6 / δ = K. For small particles K = const.

When crushing Q weight units of material with an average size of pieces D, we obtain the same number of weight units of material with an average size d. Surface of material before crushing:

S 1 yd = K Q / D. (2.9)

After crushing:

S 2 yd = K Q / d. (2.10)

The newly formed surface during crushing will be:

ΔS = S 2 – S 1 = K Q / d – K Q / D = K (1 / d – 1 / D) Q (2.11)

There are several hypotheses for energy assessment of crushing and grinding processes. One of them is Rittinger’s hypothesis (1867): Energy consumption for crushing is proportional to the size of the newly formed surface. In mathematical expression it looks like:

E = K 0 ΔS = K 0 K (1 / d – 1 / D) Q. (2.12)

Here E is the energy consumption, K 0 is the proportionality coefficient, in physical meaning it represents the energy consumption for the formation of one square unit of a new surface.

Let us denote: Ko K = K1. (2.13)

Then E = K1 (1/d – 1/D) Q. (2.14)

We multiply and divide the right side of equation (2.14) by D, we get

E = K1 (1/d – 1/D) Q D/ D = K1 (D /d – D /D) Q / D = K1 (i – 1) Q / D. (2.15)

Thus, according to Rittinger, the energy consumption for crushing one weight unit of material is proportional to the degree of crushing i minus one.

According to the hypothesis of Kirpichev (1874) and Kick (1885), the energy required for crushing and grinding a material is proportional to its weight (or volume):

E1 = K0 Q. (2.16)

From expression (2.16) it follows that the energy expended does not depend on the size of the material. The Ko coefficient expresses the energy consumption per unit of weight at a given degree of grinding. You can choose a scheme with the same degrees of crushing in each stage:

I 1 = i 2 = i 3 = …..= i n. (2.17)

Then, taking into account (2.17), the total degree of fragmentation will be:

Where n is the number of crushing stages.

In this case, the crushing energies in each stage will be equal to each other:

E 1 = E 2 = E 3. (2.19)

Taking into account expressions (2.16) and (2.19), the total crushing energy throughout the entire scheme will be:

E = K0 Q n. (2.20)

To eliminate the degree in expression (2.18), we perform its logarithm and express n:

Lg I = n lg i, (2.21)

N = log I / log i (2.22)

Let's substitute relation (2.22) into formula (2.20) and get:

E = K0 Q log I / log i. (2.23)

For the same material and at the same degree of crushing at each stage, the values ​​of K0 and i will be constant, therefore we can denote

K2 = K0 / log I, (2.24)

Then the energy of crushing (grinding) will be determined taking into account relation (2.23) as:

E = K2 Q log I, (2.25)

The mathematical expression for the degree of fragmentation (2.1) can be represented as

D / d = (1/d) / (1/D). (2.26)

Lg I = lg [ (1/d) / (1 / D)] = lg (1 / d) – lg (1 / D). (2.27)

Taking into account relations (2.25) and (2.27), the expression for the crushing energy will have the form:

E = K2 [ log (1 / d) – log (1 / D) ] Q. (2.28)

Formula (2.28) is a mathematical expression of the Kick-Kirpichev hypothesis, similar to the expression of the Rittinger hypothesis. According to Rittinger, energy consumption is proportional to the surface, according to Kiku-Kirpichev - to the volume. Accordingly, these laws are called the surface and volumetric laws of crushing (grinding). Experimental and industrial data have shown that these laws are valid only in certain size ranges. Rittinger's hypothesis agrees well with practice for fine grinding, and the Kick-Kirpichev hypothesis for coarse crushing.

Academician Rehbinder (1941) proposed a hypothesis covering any case of destruction of mineral resources, the mathematical expression of which has the form:

A = σ ΔS + K ΔV. (2.29)

Here A is the work expended on the destruction of a solid body, σ is the surface energy per unit of solid surface (σ is the excess free energy in the boundary layer), ΔS is the surface newly formed during destruction, ΔV is the part of the volume of the body that has undergone deformation, K is work of elastic and plastic deformation per unit volume.

For large crushing of large pieces of ore, K ΔV >> σ ΔS, since the increment of the surface is insignificant, and the work will be mainly proportional to the volume (Kirpichev’s hypothesis):

AK ≈ K ΔV = КK D 3. (2.30)

When breaking small pieces of ore (grinding) σ ΔS >> K ΔV, since the surface increment is significant. In this case, the work is almost proportional to the size of the new surface formed (Rittinger’s hypothesis):

AR ≈ σ ΔS = KR D 2. (2.31)

Rebinder's hypothesis connects the destruction process with the physical and mechanical properties of rocks and minerals (surface energy, hardness).

Let's divide both sides of equation (2.29) by ΔS and get:

A / ΔS = σ ΔS / ΔS + K ΔV / ΔS, (2.32)

A / ΔS = σ + K ΔV / ΔS. (2.33)

Let us denote in expression (2.33):

σ + K ΔV / ΔS = H s . (2.34)

Then, taking into account relations (2.33) and (2.34), we obtain:

H s = A / ΔS. (2.35)

The value of H s should be considered as a hardness coefficient equal to the work of formation of a unit of new surface. At the same time, the value of H s is related to the surface energy by relation (2.34). Thus, the greater the surface energy of a solid body, the greater its hardness, and, consequently, the greater the work that must be spent on destruction - the formation of a new surface.

Rehbinder's hypothesis is suitable for any size range, since it reduces to Rittinger's or Kirpichev's law at certain values ​​of size. This hypothesis takes into account both types of energy - surface and potential energy of deformation in the volume of the crushed body.

The American scientist Bond (1950) proposed a hypothesis intermediate in relation to the laws of Rittinger and Kirpichev:

According to Bond's hypothesis, elementary work is proportional to the increment of the parameter, which is the geometric mean between the volume and the surface:

Practice shows a certain connection between the work index according to Bond and the rock strength coefficient according to Protodyakonov.

Degree of crushing

The degree of crushing is the ratio of the size of the maximum pieces or grains of the source material to the size of the maximum piece of the product.

The degree of crushing shows how many times the size of the piece decreased during crushing.

Thus, the degree of crushing is calculated based on the ratio of the sizes of the limiting openings of the sieves through which pieces of crushed material and crushed product pass.

Crushing stages

Depending on the size of the starting material and the crushed product, the crushing stages have names:

• Stage 1 - coarse crushing
• Stage 2 - medium crushing
• Stage 3 - fine crushing

Depending on the required size of the material before beneficiation, it can be crushed in one, two or even three successive stages.

Fig.7.

Main technical data of the fine crusher KMD-1750T

Crushing cone base diameter, mm1750

Tensile strength of compressed crushed material, MPa, no more than 300

Width of the receiving slot on the open side (during the opening phase of the profiles), mm80

Largest size of food pieces, mm70

Range of regulation of the width of the unloading gap in the phase of approaching profiles, mm5--15

Difference in the width of the unloading gap at four points (in the phase of approaching profiles), mm, no more than 4

Crushing product coarsening factor (with minimal discharge gap), no more than 3.8

Productivity on material with a temporary compressive strength of 100--150 MPa and a moisture content of up to 4% in an open cycle (with a single passage of the material through the crusher), m3/h, not less than 85--110

Pressing force of the bowl by springs, kN (tf) 2500 (250)

Crushing cone swing frequency, swing/min260

Drive motor:

power, kW160

rotation speed, rpm740

Weight of crusher with lubricant distribution (without electrical equipment, lubrication unit, foundation plates, fittings, special devices), kg50200

Weight of the heaviest crusher assembly units, kg:

bed assembly with support ring and springs 22100

crushing cone 8700

adjusting ring with casing 10,000

drive shaft 1770

crusher assembly without drive shaft and loading device 47200

The crusher (Fig. 14.1) crushes materials between a stationary outer crushing cone and a gyratory moving (swinging relative to a fixed point with a constant amplitude) internal crushing cone.

The crusher consists of the following components:

frame 8, support ring 3, regulating ring 2 with a fixed crushing cone and columns 23, movable crushing cone 4, drive. The frame 8 is a cylindrical steel casting with two pipes located on the side wall and at the bottom. The lower flange of the frame is bolted to the foundation, and a support ring 3 is installed on the upper flange, which is pressed against the frame by bolts with shock-absorbing springs.

The fixed cone is protected from wear by armor 19, secured to the cone with brackets 22. In the upper part, the crusher is closed with a casing 24, on which a receiving funnel 25 is installed, from where the materials to be crushed fall onto the distribution plate/loading device. A bronze (bimetallic) bushing 9 is pressed into the lower branch pipe of the frame, inside which an eccentric shaft 10 with a conical wheel 7 is mounted

A bronze conical bushing 11 is installed in the eccentric bore of the shaft, which includes the shaft 13 of the movable crushing cone. The eccentric shaft 10 rests on a thrust bearing 12, consisting of a set of bronze and steel disks. The movable crushing cone is lined with armor 20. The tight fit of the armor 19 and 20 to the surface of the movable and fixed cones is ensured by zinc or plastic filling 21. The lower part of the movable cone rests on a spherical bearing 6 mounted on the support bowl 17. To prevent the ingress of dust and small particles of crushed material material, a hydraulic seal 18 is built into the gap between the movable cone and the support bowl, in the bath of which water or waste oil circulates. The crushing cone is driven from the electric motor through a shaft 16 mounted on bronze bushings in the housing 15; a bevel gear 14 is mounted on the shaft 16, rotating the wheel 7. Lubrication and cooling of the bearings of the drive shaft, eccentric unit, spherical thrust bearing and gear transmission are carried out from a centralized circulation lubrication system with liquid lubricant.

To monitor the operation of the lubrication system, an oil flow indicator, thermometers and pressure gauges are installed.

The size of the gap between the armor of the crushing cones is changed by rotating the adjusting ring 2 along the thread relative to the support ring.

When unbreakable objects enter the crusher under the influence of forces significantly exceeding normal ones, the shock-absorbing springs 5 ​​are compressed, the stationary cone, together with the support ring, is raised and the unbreakable object passes through the crusher.

classification repair crusher crushing disintegrator

Purpose: Study of processes and methods of crushing minerals.

Plan:

1.
Purpose of crushing operations.

2.
Laws of fragmentation.

Key words: crushing, quality of crushing, soft ores, medium, hard ores, destruction methods, splitting, fracture, impact, abrasion, cutting, coarse, medium, fine crushing, degree of crushing, crushing work, Rittinger equation.

1. Crushing and grinding – processes of destruction of minerals under the influence of external forces to a given size, required granulometric composition or required degree of opening of minerals. When crushing and grinding, the material should not be over-grinded, as this worsens the results of mineral processing (fine particles with a particle size of less than 20 - 10 microns are enriched unsatisfactorily) and increases the cost of the process. Crushing -

.

The labor productivity of a worker during manual crushing varies widely. When crushing hard rock, it is 1.0-1.5 per shift. When crushing individual pieces on grates with holes measuring 450x360 mm a team of 10-12 workers can supply a factory with up to 400 T ore per shift.

Mechanical crushing and grinding

The main method of crushing is mechanical crushing, in which forces are applied to the material due to the energy of movement of the crushing body. Energy consumption varies within very wide limits depending on the properties of the ore, mainly on the crushing size. It becomes especially large with fine and ultrafine grinding.

Disintegration in the aquatic environment

A special type of crushing is disintegration - loosening in the form of weakly cemented rocks, mainly clayey ones. It is carried out to release the mineral grains that make up the rock without crushing them. The forces overcome during the disintegration process are significantly less than the forces of molecular cohesion in hard rocks. The presence of small amounts of moisture dramatically increases the strength of clayey rocks. When the rock is saturated with water, the connection between individual grains decreases as a result of the swelling of the clay and the weakening of its cementing effect, which ultimately leads to complete loosening of the rock. The degree of plasticity of clay has a great influence on the rate of destruction of rocks, determining their different “washability”.

Wet disintegration is usually enhanced and accelerated by additional mechanical action - rubbing, impact, dynamic impact of a water scab, etc.

The processes of crushing and grinding can be preparatory processes (for example, at processing plants before the enrichment of minerals) or have independent significance (crushing and screening plants, crushing and grinding of coal before coking, before pulverized combustion, etc.).

When crushing a material, it is necessary to take into account its strength, i.e. the ability to resist destruction under; external influence. In terms of strength, all minerals are divided into four categories depending on their tensile strength under compression or crushing:

Soft (coal, shale), which have a breaking compressive stress< 100 кг/см 2 ;

Medium hardness (sandstones, limestones) 100...500 kg/cm 2 ;

Hard (granite, marble) 500...1000 kg/cm 2 ;

Very hard (ores of non-ferrous and rare metals) > 1000 kg/cm 2.

The strength of minerals depends on the type of deformation, mineralogical composition, crystal size, fracturing, porosity, and weathering. The crushing method refers to the type of impact of destructive force on pieces of crushed material.

When crushing and grinding, the following methods of destruction are used (see Fig. 10): crushing (a), splitting (b), breaking (c), cutting (d), abrasion (e) and impact (f). One or another method of destruction is selected depending on the physical and mechanical properties, the material being crushed and the size of its pieces.

Fig. 10. Methods for breaking ore pieces:

a - crushing; b - splitting; c - fracture; g - cutting;

d - abrasion; e – blow

Crushing that occurs after the stress passes the compressive strength limit; used for hard ore of various sizes;

- splitting as a result of wedging (in this case tensile stresses appear in the material) and subsequent rupture of pieces; used for soft and brittle ores;

- fracture due to bending and shearing; used for materials of various sizes and strengths;

- abrasion of pieces by the sliding working surface of the machine, in which the outer layers of the piece are subjected to shear deformation and are gradually cut off due to the transition of tangents;

- stresses beyond strength limits: used for soft ores and ores of medium hardness;

- the blow is used for material of any size, especially often for brittle ores (bauxite, limestone).

The basic rule “do not crush anything unnecessary” is implemented in practice by constructing crushing schemes in stages: not in one operation, but in several stages, repeatedly, sequentially reducing the size of the piece. It is impossible to crush pieces of ore in one stage due to the design features of crushing devices, which operate effectively only at limited degrees of crushing. Therefore, it is more rational to crush and grind the material from the original size to the required size in several sequentially operating crushing and grinding apparatus. In each of these apparatuses, only part of the overall process, crushing or grinding, is carried out, called the crushing or grinding stage.

Degree of crushing (or grinding) shows the degree of size reduction in the process of destruction of lump material. It is characterized by the ratio of the sizes of the maximum pieces in the crushed and crushed material or, more precisely, the ratio of the average diameters before and after crushing, calculated taking into account the size characteristics of the material,

max/dmax;

i=D avg /d avg,

where i is the degree of crushing; D max and D avg– respectively, the maximum and average sizes of crushed material; d max and d avg– respectively, the maximum and average sizes of crushed material.

The degree of fragmentation achieved in each individual stage is called private. The total degree of fragmentation is obtained as the product of partial degrees

i total = i 1 i 2 ,…,i n .

The number of crushing stages is determined by the initial and final size of the crushed material. The number of crushing stages when preparing ores for grinding is usually two or three. One- or four-stage crushing is used in the processing of potassium salts, at iron ore crushing and sorting factories, four-stage crushing is used at large magnetic processing plants with a capacity of 40 - 60 thousand tons/day, processing strong magnetite ores of flagstone form.

2.

The stronger and harder the mineral, the more force must be applied in order to overcome the internal adhesive forces of the ore particles and crush it into pieces. The adhesion forces between crystals are significantly less than the adhesion forces within the crystals. When external forces are applied, destruction occurs predominantly along weakened sections that have various structural defects (cracks).

The efficiency of crushing is very small. Most of the energy is spent on friction between pieces of crushed material, machine parts and is consumed in the form of heat generated. Useful work during crushing is spent on the formation of new exposed surfaces and is proportional to the size of this surface.

The laws of crushing (grinding) characterize the dependence of the work spent on crushing (grinding) on ​​the results of crushing (grinding), i.e. product size.

Job A(J) spent on crushing (grinding) is proportional to the newly formed surface of pieces (particles) of the crushed product

where is the temporary compressive strength N. m/m 2;

Area of ​​the newly formed surface, m2;

K R – proportionality coefficient, N. m/m 2 ;

D – characteristic size of the piece, m.

The equation corresponds to Rittinger's hypothesis (1867).

If, during the destruction of a cube-shaped piece, energy is spent mainly on volume deformation, then in this case the work performed is directly proportional to the change in its original volume and is determined by the Kick formula

A = = K k D 3,

where: K and K k are proportionality coefficients, N. m/m 3 ;

V – deformed volume, m3;

P.A. Rehbinder (1941) combined both hypotheses and in this case the total crushing work

A = K R D 2 + K k D 3.

According to Bond's hypothesis (1950), the total crushing work is proportional to the geometric mean between the volume and surface area of ​​the piece:

A = K B = K B D 2.5

All formulas differ in proportionality coefficients and exponents of the diameter of the crushed piece. According to the general hypothesis, the crushing work can be represented in the form

where, K – proportionality coefficient in general form; m = 2 3.

When the degree of crushing is high (fine crushing, grinding), the volume deformation work can be neglected and in this case Rittinger’s law is applied. When the degree of crushing is small (large crushing), the work of forming new surfaces can be neglected, and then the Kirpichev-Kick law is suitable. Formula P.A. Rebindera has universal meaning. Bond's Law occupies an intermediate position.

Due to the extreme diversity of physical properties of rocks, as well as the need to crush feedstock and obtain products of various sizes, many designs of crushing machines have been created. Currently, they are striving to build not universal crushing machines, but specialized ones that make it possible to achieve the best results. n each individual operation.

Crushing machines must meet the following requirements:

The design and dimensions of the machine must correspond to the size of the pieces and the properties of the material being processed, the purpose of the operation and the specified productivity.

Unloading of crushed material must be carried out continuously. Periodic unloading reduces crushing efficiency.

Crushing should be carried out evenly and with minimal dust formation. The degree of crushing should be adjusted quite simply.

Energy consumption should be as low as possible.

Maintenance should be simple and safe, replacing wear parts should be easy.

The most valuable parts of the crusher must be protected from damage by cheap safety devices.

The fundamentals of the theory of crushing machines were created by prof. L. Bevenson and Z. B. Kantorovich. The work of many other Soviet scientists and engineers was devoted to the study of the operating conditions of individual crushing machines, which led to the identification of optimal operating conditions for crushing and grinding machines and the creation of new designs.

Conclusions:

Crushing - This is the process of reducing the size of pieces of ore by breaking them under the influence of external forces that overcome the forces of internal cohesion of crystals of a solid substance. Conventionally, it is believed that crushing produces products with a particle size of up to 5 mm. Crushers of various designs are used for crushing. Crushing is carried out both dry (basic) and wet (for clay ores).

Sometimes crushing of minerals is done manually . However, this is a time-consuming and expensive operation, and therefore it is advisable only in some special cases, namely:

a) if the extracted mineral contains a small number of individual large pieces, the size of which exceeds the loading opening of crushing machines;

b) during manual ore sorting - to separate joints. In the first case, crushing is most often carried out on grates covering the bunkers.

When crushing and grinding, the following methods of destruction are used: crushing, splitting, breaking, cutting, abrasion and impact. One or another method of destruction is selected depending on the physical and mechanical properties, the material being crushed and the size of its pieces.

Depending on the size of the crushed material and the crushed product, the following crushing stages are distinguished:

Coarse crushing (from 1100...300 to 350...100 mm);

Medium crushing (from 350...100 to 100...40 mm);

Fine crushing (from 100...40 to 30...5 mm).

The crushing process is very complex and depends on many factors, which include: the strength and viscosity of the ore, humidity, shape and size of the pieces, etc.

Security questions:

1.
What is crushing?

2.
What methods of destruction exist during crushing?

3.
How do destruction processes differ from each other?

4.
What is manual crushing and in what cases is it carried out?

5.
What does the degree of crushing mean and how is it determined?

6. What characterize the laws of fragmentation?

7. How do the Rittinger and Kirpichev-Kick formulas differ?

8. What are the requirements for crushing devices when preparing them for operation?

Seminar topics:

Crushing as an integral process of preparation for enrichment.

Crushing processes. General characteristics.

Manual and mechanized crushing.

Laws of fragmentation.

Homework:

Crushing processes are usually carried out in three stages:

Coarse crushing – from 1200 to 300 mm

Medium crushing – from 300 to 75 mm

Fine crushing – from 75 to 15 mm

Each stage is characterized by the degree of crushing (i), that is, the ratio of the diameter of the maximum pieces of ore entering crushing (D max) to the diameter of the maximum pieces of ore after crushing (d max):

The degree of crushing, calculated by the formula, characterizes the crushing and grinding processes insufficiently fully; let us assume that when crushing or grinding two materials that have the same size characteristics, products with the same maximum pieces, but with different size characteristics, are obtained. The total plus characteristic for one product is convex, and for another it is concave. This means that the second product is crushed smaller than the first, but if you calculate the degrees of crushing in relation to the sizes of the maximum pieces, they will turn out to be the same. From this it can be seen that the degree of crushing is more correctly calculated as the ratio of the average diameters, which are found taking into account the size characteristics of the source material and the crushed product.

The degree of crushing achieved in each individual stage is called the partial degree of crushing.

i 1 = = 4; i 2 = = 4; i 3 = = 5.

The total degree of fragmentation is equal to the product of the partial degrees of fragmentation.

i total =i 1 *i 2 *i 3 = 4 * 4 * 5 = 80

The degree of crushing is determined by the capabilities of the crushing equipment.

Usually for

I stage of crushing i = 3-5

II stage of crushing i = 3-5

III stage of crushing i = 3-8 (10)

The crushing stage is a single crushing operation or a combination of crushing and screening operations.

5.3 Crushing methods

The crushing method is understood as the type of impact of destructive force on pieces of crushed material. The destruction process can occur as a result (Fig. 5.1):

crushing (cheap method) splitting (for brittle ores)

abrasion impact (for medium hard material)

Rice. 5.1 Crushing methods

The crushing method is selected depending on the physical and mechanical properties of the crushed material and the size of the pieces. There are rocks that are strong or hard and rocks that are less strong or soft; rocks are tough and brittle. The ability of rocks to resist destruction also depends on the presence of cracks in the pieces and the way they are exposed to the surrounding force. Rocks have the greatest resistance to crushing, less resistance to bending, and the least resistance to tension. A combination of destruction methods is often used.

5.4 Crushing technology

For structural reasons, as well as due to the undesirability of overgrinding, in modern beneficiation practice, crushers are used that operate mainly by crushing and impact with additional abrasive and bending effects on the crushed material.

It is advisable to carry out large, medium and fine crushing of hard (strong) and brittle rocks by crushing, and of hard and viscous rocks by crushing with the participation of abrasion. It is advisable to carry out coarse crushing of soft and brittle rocks by splitting, and medium and fine crushing by impact. All minerals are crushed by impact and abrasion.

Coarse, medium and fine crushing are usually dry; wet crushing is used only in cases where the crushed material contains clay, which they try to wash off simultaneously with crushing. Washing, for example, is carried out during crushing of clayey iron manganese ores. Washing water is supplied to the working space of the crushers. In some cases, water is supplied in small quantities from the spray into the feed hopper of the coarse crusher. The purpose of this water is to moisten the crushed material and thereby reduce dust formation.

Sometimes the materials that make up pieces of minerals have different physical and mechanical properties. After crushing or grinding such minerals, under specially selected conditions, some harder and more durable minerals will be presented in large pieces, while others, less hard and brittle, will be presented in much smaller pieces. Subsequent sifting of the crushed product will make it possible to separate some minerals from others, i.e. produce more or less complete enrichment of minerals. Crushing or grinding in this case has the meaning of an enrichment operation and is called “selective crushing”.