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EurAsian Journal of BioSciences Eurasia J Biosci 13, 1391-1404 (2019)

Modern state and tendencies of development of vibration separating machines structures

Valeriy V. Piven 1* 1 Tyumen Industrial University, RUSSIA *Corresponding author: pivenvv@yandex.ru

Abstract The vibration machines are widely used to separate the multicomponent mixtures. Such machines have a great variety of technological and structural schemes that must take into account the separated materials properties changing over wide range. The paper is aimed at analyzing and generalizing the accumulated experience of designing of the vibration machines, at developing the recommendations on their future improvement. Analytical research methods were used. The vibration machines structures were analyzed, which are widely used in various branches of technology to separate the friable mixtures and the multiple fluids with mechanical impurities into fractions of different qualities. The vibration machines are used also to dose the friable materials, to mix, to compact and to transport them. The technological schemes of the vibration separating machines are considered, which are applied in the building industry, the food industry, in making the drilling fluid in the oil and gas industry. The requirements for quality of the separating technological process are analyzed. Influence of dynamic operation modes of the driving mechanisms on the process quality is considered. The methods of designing the vibration separating machines, the methods of determining the natural oscillation frequencies of parts and structural elements of the vibration machines are reviewed. The ways of static and dynamic balancing of the vibration machines parts are surveyed generally. It is necessary to observe the operating devices’ kinematic mode in order to assure a stable separating process on the vibration machines. This factor acquires a paramount importance in the separating processes. Vibration from the machines’ frame structures is transmitted to the separating surface, which leads to the separating quality impairment. The separating devices’ vibrational motion through the machine frames is transmitted to the building structures too. In the long run, the kinematic motion mode is characterized by a totality of the oscillating motions of the separating surface, the machine frame and the building structures. On the basis of the analysis conducted, the conclusions about the main development areas of the technological and structural schemes of the vibration-driven separating machines are formulated. It is proposed, during the designing, to optimize the machines structures with account taken of stiffness of their frames and load-bearing foundations. Keywords: vibration, separating machines, separating quality, dynamic characteristics, optimization, load-bearing structures Piven VV (2019) Modern state and tendencies of development of vibration separating machines structures. Eurasia J Biosci 13: 1391-1404. © 2019 Piven This is an open-access article distributed under the terms of the Creative Commons Attribution License.

INTRODUCTION Various branches of technology widely use the

vibration machines, whose operation principle is based on the operating devices’ vibrational motion. The vibration mechanisms are applied in intensifying the chemical processes, to dose and to transport the fine finders, to mix them, and to separate the friable materials into fractions (Arsentiev et al. 2014, Blekhman et al. 2015, Boylu et al. 2015, Dmitriev et al. 2015, Guo et al. 2011, Ivanov and Vaisberg 2015, Kim et al. 2010, Pastenes et al. 2014, Piven and Umanskaya 2017b). In the latter case the use of the vibrating perforated surfaces - sieves makes it possible to divide (to

separate) friable multicomponent mixtures according to the dimensional features.

The vibration machines are used in making the drilling fluid, in vibratory processing of the parts, in the minerals processing, in the powders division, in making the casting molds and in the vibrating shakeout. The vibration operating devices are used in preparing the raw materials while making the building products, in the food manufacturing, the grain separating, the seed preparation (Astashev and Krupenin 2017, Astashev et

Received: April 2019 Accepted: August 2019

Printed: October 2019

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al. 2016, Glebov et al. 2010, Nikolaev et al. 2015, Wotruba et al. 2010, Vaisberg 2011). Theory and designing of the vibration machines are covered in papers (Blekhman 2013, Blekhman et al. 2011, 2017, Piven 2017, Vaisberg et al. 205).

The vibration machines’ designing problem includes several interrelated stages and consists, firstly, in complication of substantiation of the necessary technological scheme of the machine operation, secondly, in determining the operating devices’ structural parameters, thirdly, - in choosing the kinematic modes. At each stage it is necessary to take into account a variety of the physical and mechanical properties of the separated components, the separated mixture’s fractional composition.

The paper is aimed at analyzing and generalizing the accumulated experience of designing of the vibration machines, at developing the recommendations on their future improvement.

MATERIALS AND METHODS An initial stage in designing the separating machines

is physical and mechanical properties of the separated material components. The machines characteristics to divide the friable mixtures with using the vibration are stated in Table 1.

Peculiarities of Separating Processes in the Food Industry

Because of a great variety of components of the initial material and high requirements for the final product quality, the food production separating is the most complicated process. High requirements for the separating quality led to a great variety and complication of the separating machines’ driving mechanisms.

It is necessary to adhere to the kinematic mode of operation of the sieve surfaces to assure a stable separating process at the vibration machines. The driving mechanisms assure the separating surfaces’ oscillations as well as give rise to undesirable vibration of the machines’ load-bearing structures, which, in the long run, lowers the separating quality.

The majority of separating processes in the grain-processing branches are based on the vibration machines’ application: clarification of the initial material from impurities, the fractionating, the sorting.

Depending on a destination, the machines’ distinguishing features are a type of the drive, a number and location of the oscillating separating boxes, a nature of their motion. The separating machines’ characteristic is presented in Fig. 1.

The A1-BIS (А1-БИС), A1-BSF (А1-БСФ), A1-BLS (А1-БЛС), ZSM (ЗСМ), ZVS-20 (ЗВС-20), ZPS (ЗПС), R8-UZK-50 (Р8-УЗК-50), “Classifier” separators are a large group of the grain-cleaning machines. Such machines are used in flour-grinding enterprises, elevators, feed-milling plants (Glebov et al. 2010). Their main task is to separate the light impurities according to the aerodynamic features, coarse and fine impurities – according to the dimensional features. The separating vibration machines have the same basic diagram in the building industry, the metal mining industry, while fractionating the powders.

If the mineral and organic impurities differ from the grains only in weight with the same aerodynamic and dimensional specifications, the A1-BZK (А1-БЗК) concentrators and the R3-BKT (Р3-БКТ) stone-separating machines are used.

When grinding the grains the products obtained are sorted in the sifting machines. Different density of materials is used in order to assure homogeneous fractions in terms of the endosperm content while sorting the grit-dunst products. This division feature is implemented in the sieve purifiers.

The R3-BTsA (Р3-БЦА) vibratory centrifugal dresser, which makes it possible to sow the flour particles, is used as a supporting machine to process the non free flowing tail fraction from the A1-BVG (А1-БВГ) finisher.

The vibration separating machines’ driving devices are divided into two groups by a type of the input energy conversion into the mechanical oscillations (Fig. 2). The kinematically solid drives are the simplest according to their structures. Their advantage is that irrespective of

Table 1. Characteristic of machines and equipment to divide friable mixtures Separating features Ways of division Operating devices Oscillation form Branch name of the machine Main Concomitant

1 2 3 4 5 6

Dimensions Density, form Sieve Sieves (screens) Straight-line, circular and elliptical in a horizontal

or vertical plane

Vibrating sieves (drilling facilities), screens (mining industry) sieve separators and

shaking machines (food industry)

Form Coefficient of external friction, density

Vibration transportation

Dimpled or rough surfaces

Straight-line inclined to a horizontal plane

Vibratory separators (separating of powders, grain products)

Density Form, dimensions Demixing Rough surfaces (flat or conical)

Circular in a horizontal plane, circular spheric

Fractionating rock separators (food industry)

Density Coefficient of external friction, form

Vibratory pheumatic without screening Rough flat surface Straight-line inclined to a

horizontal plane Vibratory pneumatic separators (food

industry) Density and dimensions Form Vibratory pneumatic

with screening Sieves and air passages Straight-line inclined to a horizontal plane

Vibratory pneumatic screens (mining industry), pneumatic tables (food industry)

Elasticity Density, coefficient of friction Shock-and-vibration

Inclined, smooth bearing surfaces with vertical

side walls

Horizontal, straight-line and backwards

Sorting tables, paddy machines (food industry)

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the oscillation frequency, the oscillating mass and the process load they assure the specified oscillation amplitude of the operating device. In this drives group, heavy inertia forces act on the machine components, which is their disadvantage.

The second group of the operating devices with straight-line oscillations includes the inertia oscillators of directional operation. This mechanical system is more balanced, the dynamic loads on the parts decrease. The sieves oscillation amplitude in machines with such a

Fig. 1. Classification of the vibration machines with flat sieves

Fig. 2. Classification of the operating devices’ drives of the separating machines

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drive depends on a mass of the operating devices and the separated product as well as on a ratio of frequencies of the natural and forced oscillations.

Depending on a number of the oscillating sieve boxes, the vibration machines can be single-mass and two-mass machines. With several sieve boxes or with installation of several separating surfaces in a box it is possible to obtain the different qualities fractions of the processed product simultaneously with precipitation of fine impurities. A technology of their further purification is chosen depending on the fraction composition and a destination of the finished product.

An oscillation form of the separating operating devices depends on a destination of the processed product, its physical and mechanical properties. When separating the grain material to prepare the seeds, an alternating motion of the sieve surfaces is used the most frequently, which assures a more qualitative precipitation of fine impurities according to the thickness by outsiftings. With circular forward motions of the separating surface in a horizontal plane, round fine impurities are precipitated by the outsiftings more qualitatively according to the width. A promising area is the use of the plane-parallel motion of the sieve surfaces in a vertical plane in a circular or elliptic trajectory.

The operating device’s motion trajectory depends on a type of the driving mechanism, elastic constraints and oscillating mass. With the alternating motion of the operating devices, the elastic constraints are done in the form of plate springs made of multiply plywood or steel, as well as springs and metal-rubber supports. With the plate-parallel motion of the operating devices in a vertical plane, the elastic constraints are steel springs in the form of a semi-ring and metal-rubber supports.

The oscillating motions of the separating operating device in vibration machines can be harmonic or pseudoharmonic depending on their a structure and elastic characteristics of constraints. Linear characteristics of elastic constraints assure the harmonic nature of oscillations. The metal-rubber supports have a nonlinear characteristic, in this case an oscillating process will be pseudoharmonic.

The majority of vibration machines have a kinematically solid drive and they operate in a high-frequency above-resonance mode, in which the forced frequencies exceed the natural oscillation frequency. This assures the stable motion of the sieve surfaces. A number of characteristics of the vibration machines, which are stated in Fig. 1, are coinciding with each other.

The presented classification of the vibration separating machines (Fig. 1) makes it possible to unite the machines with different drives into relevant groups according to some features and to develop the general methodology of their building and designing.

A stable kinematic mode of the separating devices operation is necessary to assure a quality of performing the separating’s technological process. This must be

assured by the driving mechanism’s structure as well as relevant stiffness of the load-bearing structure. Both of these conditions must be built into at a designing stage.

The conducted analysis of scientific and technical and patent literature on this area showed that the most promising areas of developing the vibration separating machines are as follows:

− improvement of the driving mechanisms’ structures;

− optimization of dynamic parameters of the sieve boxes operation for specific motion trajectories;

− development of technological solutions for more efficient use of the main and concomitant division features;

− automation of processes of the machine loading and equability of feeding the initial material, and adjusting the operating devices operation modes;

− assurance of stability of dynamic parameters of operation of the machines’ separating devices in the main and transient operation modes;

− decrease of vibration of the machines’ load-bearing structures, optimization of stiffness of the frame structure elements, and the load-bearing foundations on which they are installed.

The Vibratory Sieves Use in Preparing the Drilling Fluid in the Oil and Gas Industry

The drilling fluids are purified during the drilling by means of removing the coarse particles (more than 75 micron) and fine particles of the drilled solids and other particles from the drilling fluid coming from a well (Golovin et al. 2014).

The coarse particles are removed by means of screening through vibrating sieves. The vibratory sieves are driven by means of an eccentric mechanism (Fig. 3а) or a debalance mechanism of inertia action (Fig. 3b).

The debalance mechanism makes it possible to change the oscillation amplitude depending on the physical and mechanical composition of the initial mixture by means of the debalance loads shift. The vibratory frame motion trajectory is a closed circumference or an ellipse. When the separated fluid has a great mass and when the mass is commensurable with the sieve box mass, the specified trajectory of the sieve surface motion can be broken.

The technological schemes of the vibratory sieves operation provide for arrangement of the sieve surfaces in several tiers (Fig. 3b) with a possibility of adjusting their angle of slope. Such a layout makes it possible to increase the separating surface area, and to assure its equivalent use by means of selecting the sieve holes sizes depending on the initial mixture composition.

While purifying the higher viscosity drilling fluid or upon availability of a great number of coarse impurities, it is recommended to increase the sieve slope angle and the oscillation amplitude. When the vibration direction is

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close to perpendicular towards the sieves surfaces, the conditions of the sieves self-purification from the outsiftings components, which stick in the holes, are improved.

In the modern vibration sieves LVS-3M (ЛВС-3М), which are used to purify the drilling fluid in the drilling installations’ circulation systems, which are manufactured by the group of companies “NEFTEGAZMASH-TECHNOLOGIES”, the linear oscillations with the 24 HZ frequency and the maximum oscillation amplitude of the vibrating frame of 2.3 mm are used (Fig. 4).

One of the modern tendencies of development of the vibratory sieves structures is the switching over to the use of the sieve cassettes on the stiff plastic or metallic basis (Fig. 5). This excludes the net sagging and assures its more reliable fastening.

A promising area is also the use of vibration motion of the sieve boxes in an elliptic trajectory, which makes

Fig. 3. Structural diagrams of vibratory sieves: а – with a drive from the eccentric mechanism; b – with a drive from the debalance mechanism; c – technological schemes of operation of the sieves with different-tier position (figures 15-0; 30-15… show a share of the fractional yield in percentage terms out of the initial material; +60 means the yield of more than 60%)

Fig. 4. General view of the vibration sieve LVS-3M

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it possible to decrease the dynamic loads on the machines’ parts, without the separation quality impairment.

Layout and technological solutions of the devices for purifying the drilling fluid are developed towards the use of combined sieve-hydrocyclone separators (Golovin et al. 2014). Such separators are hydrocyclone sludge removers that are installed over the vibratory sieve (Fig. 6). The pulp comes to the sieve surface from sludge removers, which makes it possible to separate an additional quantity of the drilling fluid before the pulp tipping.

Within the circulation system, the drilling fluid cleaning equipment is installed in a specific sequence: well – gas separator – sludge rough purification unit (vibratory sieves) - degasifier - sludge fine purification

unit (desanders and desilters, separator) – unit of adjusting the content and composition of the solids (centrifuge, hydroclone clayjector).

This technological scheme of the drilling fluid purification is not universal. For instance, if there is no gas in the fluid the degasation equipment is excluded.

Vibratory Screens in Manufacturing the Building Materials

When manufacturing the building materials, along with a task to purify the processed material from the impurities, it is necessary to divide the final product into fractions which have different quality according to dimensional features (Vaisberg 2011). A similar technological operation is performed with the powder fractionation in the chemical industry, the food production.

The Sweco company, belonging to “Schlumberger” holding company, is one of the international leaders in manufacturing the specialized separating equipment. The Gyramax swing screen of Sweco (Fig. 7) assures the quality of fractionation into micronic fractions with efficiency to 98% with the dry material productivity of 250 tons per hour. The debalance driving mechanism of this screen assures a circular forward motion in a horizontal plane for the sieve frame (Fig. 8).

Fig. 5. General view of the vibratory sieve SB1LM with a tension flexible cassette

Fig. 6. General view of a sieve-hydrocyclone separator with the Pulsar vibratory sieve, with the desander and desilter

Fig. 7. Technological scheme of Gyramax swing screen operation

Fig. 8. Diagram of hanger bracket and motion trajectory of the sieve box of the Gyramax swing screen

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For intensifying the sieve separating processes, depending on the initial mixture’s granulometric size composition, it is necessary to optimize the structural and kinematic parameters of the sieves operation. In the multifrequent vibration screen ULS, due to the use of multifrequent technology Kroosher®, the separated mixture components are influenced by a wide range of the oscillation frequency. This makes it possible to decrease the oscillation amplitude of the sieve box and, simultaneously with that, to increase the oscillation amplitude of the net itself in several times (up to 10 mm).

The acceleration, which is transmitted to the net, exceeds the free-fall acceleration in 500 - 1000 times. The powerful pulses effect assures the net self-purification and improves its screening ability.

Vibration Separating Machines in the Grain-processing and Food Industry

The Bühler company is the world leader in manufacturing the separating equipment for the food and the processing industry (Kornev 2016). Depending on a type of the processed product, its destination, requirements for the final quality, the company developed the processing lines of different productivity. For example, the Classifier MTRC separator of Bühler is used for the preliminary grains purification in the

elevators, feed-milling plants, at the first stage of purification in the seeds preparation lines (Fig. 9).

The use of a vibration sieve with two separating surfaces coupled with an aspiration channel assures the productivity of 24 tons per hour with the main purification and 100 tons per hour – with the preliminary purification.

The sorting of intermediary products of grain milling in the flour milling plants is the most complicated work in terms of technology. The vibration machines, which perform this function, are called the screening plants (Fig. 10).

The screening plant’s vibratory drive must assure the equal separating conditions for the components that are in the multitiered sieve unit (Fig. 11).

Fig. 9. General view of the Rotostar small size screening plant of Bühler

Fig. 10. General view of the Rotostar small size screening plant of Bühler

Fig. 11. Technological scheme of the Rotostar screening plant: А – initial product; В – tail fraction; С – outsiftings fraction

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RESULTS AND DISCUSSIONS Requirements for Quality of the Technological

Process Performance and the Main Dynamic Characteristics of the Vibration Separating Machines

The vibration separating machines emit the impurities from the main material flow and they divide it into fractions differing in dimensional features.

Requirements for quality of performance of the purification technological process are the following indicators: division completeness, main product losses into waste.

The division completeness is determined according to the formula:

𝐸𝐸 =(𝐴𝐴1 + 𝐴𝐴2 + … + 𝐴𝐴𝑛𝑛)(𝐵𝐵1 + 𝐵𝐵2 + … + 𝐵𝐵𝑛𝑛)

𝑎𝑎2 + 𝑏𝑏2 = 𝑐𝑐2

where А1, А2, ... Аn is a relative quantity of a weed of this type in the waste in percentage terms out of the total quantity of the initial material;

B1, B2,….Bn is a relative quantity of a weed of this type in the initial material in percentage terms.

The vibration separating according to the dimensional (geometrical) features is implemented on sieves (screens). The relative material motion along the separating surface is one of the main conditions of screening of the outsiftings components through the sieve holes. This is assured by the sieve vibratory motion and its angle of slope.

Theoretical description of the material motion process along the separating surface, as a rule, boils down to the regularities of motion of some components of the friable mixture (Blekhman 2013).

In order to assure the highest probability of the components screening along with the screening-friendly dynamic mode of the component and sieve motion, it is necessary to assure the longest time of their interaction. With the alternating motion of the sieves those conditions are assured when the components are in motion without throwing with two momentary stoppages for each oscillation period.

The main research on this problem is aimed at improving a technological scheme of the material passing through the operating devices. It is necessary to determine the optimal dimensions and forms of the sieves holes, their overall dimensions and the angles of slope, kinematic parameters of the driving devices’ operation.

The sieve hole dimensions are selected proceeding from the dimensional features of the separated components, technological requirements for composition of the fractions obtained, conditions of the particles demixing in the material layer moving along the separated surface.

The sieve angle is determined by frictional properties of the mixture components, its friability, and it must be

agreed with a kinematic mode of the sieves operation. As the angle of slope and a coefficient of the kinematic operation mode are increasing, a speed of movement of the materials in the sieve increases too. The separated material must be on the sieve for a time sufficient for demixing and screening through the holes. As a rule, the sieve angle towards the horizon is 4о -15о.

When selecting the sieve angles, it is necessary to take into account a kinematic mode of the sieve motion. A smaller sieve angle, as a rule, requires an increase in the sieve oscillation frequency. This gives rise to an additional dynamic load on all links of the machine, especially, with an incomplete equilibrium of sieve pans. As the angle of slope increases, the overall dimensions and, therefore, its mass increase too.

The kinematic operation mode is determined by the acceleration’s amplitude value А∙ω2, which is obtained by the sieve with an oscillatory motion, which, in its turn, depends on the oscillation amplitude А and the oscillation frequency ω. In the long run, a choice of kinematic mode of the sieves operation depends on the separated material. When purifying the wheat seeds it is from 9 to 28 m/s2, to purify the drilling fluid - 40 – 90 m/s2.

The mathematical expression for determining a relative speed of the material motion in the sieve depending on the angle of slope and directivity of the sieve oscillation, the oscillation frequency and amplitude, the mixture layer thickness is determined by Gortinsky (Blekhman 2013). The increase in the oscillation directivity angle favors the non-free-flowing mixture distension, improves its demixing, but it can lead to significant increase of a speed of the components motion or their galloping on the sieve surfaces, which reduces the probability of the components screening.

The analysis of research on making the vibration separating more efficient shows that the main scientific results and recommendations for designing are obtained without account taken of influence of the machines’ load-bearing structures vibration upon the separation process, whose component influences the motion process and the components’ screening ability significantly. Ignoring of this factor in theoretical calculations at the stages of the experimental research in the machines with different stiffness of their load-bearing structures does not make it possible to objectively compare the results obtained.

Influence of Vibration of the Machine’s Load-bearing Structure upon the Technological Process, the Operating Personnel and the Reliability Indicators of the Machine Parts

Departure of the kinematic mode of the vibration machines motion from the optimal values leads to the impairment of quality of the purification technological process.

Oscillatory motion of the load-bearing frame structure of the vibration machine is one of these factors.

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This oscillatory motion appears because of incomplete dynamic balance of the inertial forces of the oscillating parts. Insufficient stiffness of the load-bearing structure of the machine and a floor, on which it is installed, amplifies these oscillations. As a result, actual values of the oscillation amplitude of the sieve boxes can increase by 30 – 40%, while varying randomly. Additional vibration motions of the sieve boxes also decrease the equability of distributing the separated material along the sieve surface.

Vibration reduces the reliability and operational life of the vibration machines, the thread connections’ couplings are broken, the bearings and the parts of the crank group are worn away, the welded connections are destroyed. Vibration increases during the operation. Failures due to vibration reach 80% out of their total number.

Vibration affects the employees’ bodies adversely, decreases the capacity for work. GOST 12.1.012-90 “Vibration safety. General requirements” is a regulatory document establishing the requirements for the vibration safety. A vibrational load is characterized by the vibrational acceleration, the vibrational velocity, the exposure time, the frequency range. For the vibratory separating machines, the vibrational acceleration standard value is 0.1 m⋅s-2, the vibrational velocity – 0.2⋅10−2 m⋅s−1. The data on measurements of the load-bearing structures’ vibration show that the actual values, for example, of the vibrational velocity are 4 -7 times higher than the standard values.

Equilibration of Movable Parts of the Separating Machines

A driving mechanism of the vibration separators with the kinematically solid drive is a crank mechanism, in whose parts, inertial forces, which are variable in terms of a direction and a magnitude, appear. In addition, alternating dynamic forces act on the mechanism supports, the load-bearing structure and the foundation. Coincidences of natural oscillation frequencies with a disturbing force frequency lead to a dramatic increase of the oscillation amplitude. With an above-resonance operation mode this occurs during the machine acceleration and stoppage.

For lowering the harmful vibration it is necessary: 1. To reduce the source vibrational activity

through optimizing the parameters of the physical and mechanical processes, decreasing the friction in the kinematic pairs, reducing the dynamic reactions through balancing the moving masses.

2. To optimize the machine structure to reduce the inertial forces, to tune away from the resonance.

3. To suppress oscillations dynamically, which partially balances the dynamic influence generated by the source.

4. To carry out the vibration isolation between the vibration machine and the foundation, on which it is installed.

Balancing of the vibration machines is considered in paper (Timofeev et al. 2017). The inertial forces must be balanced in order to balance the pressures in the mechanisms kinematic pairs and to balance the machine’s pressures upon the floor or the foundation, on which it is installed.

When balancing the machine’s pressures upon the foundation, it is regarded as a whole and the law of variation of dynamical load is determined. Then the center of mass is found and the central moments of inertia are determined.

The forces acting on the vibratory separator are reduced to the main vector and to the main moment in the center of mass. A condition of the machine’s dynamic balancing is equality to zero of the main vector and the main moment of inertial forces relative to the reduction center: Рх = 0; Ру = 0; Рz = 0; Мх = 0; Му = 0; Мz = 0.

With the static balancing the resultant inertial force Р must be equal to zero, and the inertia moment М may not be equal to zero. In this case, acceleration of the machine’s center of mass is equal to zero. When the vibration machine is fastened to the foundation rigidly, its center of mass remains motionless.

For the instantaneous balancing, it is necessary to obtain that the main moment of the inertial forces was equal to zero. Experimental research shows that in the case of two-level vibration machines with motion of sieve boxes in the opposite phase the moments of inertial forces are not balanced. The inertial forces are balanced by 65 – 70%.

For the static balancing, it is necessary to distribute the movable parts so that their common center of mass was motionless. This is achieved through the main correction mass, by a similarity method, by a zero vector method.

In the case of one-level vibration machines the balancing is carried out by means of placing the debalance on the crank shaft. In this case there appears an additional component of the inertial forces from a counterbalance. For reducing the vertical oscillations, the reciprocating mass is balanced by 60 – 70%, and the elastic constraints are introduced in a vertical direction.

In order to balance a vertical component of the inertial forces, a kinematic scheme, which includes two gears with debalances, is used (Fig. 12). In this case there appear moments from debalances, with the magnitude of М = Р⋅r , where r is a radius of the pitch circle of the gear.

When designing is carried out with the specified mass and dimensional characteristics, it is difficult to assure an exact dynamic and static balancing of the vibration machines. Only the first harmonics of the main vector and the main moment of the inertial forces are

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balanced. This makes it possible to decrease the inertial forces in 5 – 10 times.

One of the options of the dynamic balancing of a one-level vibration machine is the use of two slider-crank mechanisms with counterbalances on the gear wheels, which are in gear (Fig. 13).

It is possible to obtain the complete balancing of vibration machines with two symmetrically located sieve boxes (Fig. 14). The dimensions and mass of the boxes unequal the most frequently, the hanger brackets stiffness can be different too. The sieve boxes location on either side of the oscillatory shaft leads to the increase in the machines’ overall length.

While balancing the vibration separating machines by means of counter weight, there appear overturning moments from the centrifugal forces of inertia. In this case, for one-level machines there is optimized a distance from a vertical axis and a horizontal axis of the eccentric shaft to the machine’s center of gravity.

In the two-level machines an additional elastic constraint is introduced, and a distance from the machine’s supporting plane to the center of gravity is

increased. This leads to the decrease in the torsional oscillations.

There are analytical methods of balancing the mechanisms. In order to determine the optimal structural parameters of the vibration machine parts (mass, moments of inertia) under the specified law of motion of the leading links and the resistance forces, there is a minimum difference between the theoretical and specified values of the support reactions. In this methodology, with a great volume of initial information, it is difficult to take into account the whole totality of significant factors and to obtain an objective result required for the practice.

While performing the analytical calculations for static balancing, a method of linearly independent vectors is used. While implementing the method, a closedness equation of the kinematic chain is analyzed jointly with a vector equation describing the center-of-mass coordinates.

The unbalance, which is caused by inaccuracy of the parts manufacturing, can be eliminated by a dynamic balancing on the balancing stands. By means of the mass addition or removal from the part, the revolution axis becomes the principal central axis of inertia.

The considered balancing methods often lead to the increase of the machine’s dimensions and mass. So, in order to reduce the influence of harmful vibration in the vibration machines and, especially, in its separating devices, it is necessary to optimize the machine’s load-bearing structure in terms of stiffness of its constituents.

Dynamic Oscillation Suppression and Vibration Isolation

The dynamic oscillation suppression is carried out by means of additional devices – dynamic suppressors. The main types of dynamic suppressors are presented by three main schemes:

1. Oscillation dampers that absorb energy supplied by a disturbing moment. This type includes the dry fraction suppressors, hydraulic and shock suppressors that decrease the oscillation amplitude.

2. Dynamic oscillation suppressors balancing the disturbing forces or changing the oscillation frequency of the system without the energy dissipation. This type of suppressors includes the couplings with nonlinear characteristics, the pendulum dampers, the devices for cutting out the rotating mass in a near-resonant mode, the springs with overbalance moving in an opposite phase with disturbing forces.

Fig. 12. Balancing of a vertical component of the inertial force

Fig. 13. Option of complete balancing of the slider-crank mechanism

Fig. 14. Complete balancing of two slider-crank mechanisms

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3. The dynamic oscillation suppressors with devices creating additional friction forces. A partial energy dissipation and partial balancing of disturbing forces occur. Such devices are additional mass connected with the main oscillatory system by a link that has elastic and viscous characteristics. These are various rubber dampers, dynamic dampers with springs.

The dynamic suppressors assure the suppression of bending, longitudinal, torsional and other kinds of oscillations. When installing the dynamic suppressors, the vibratory activity decreases in places where they were installed. Vibration can increase in other parts and units. When substantiating the vibration suppressor parameters, the necessary ratio of mass of the suppressor and the oscillating parts, a ratio of frequencies of their own oscillations are determined.

In the vibration separating machines, it is reasonable to install the vibration suppressors on the sieve boxes and the machine frame. Such machines have a sinuous nature of disturbing forces, so the vibration suppressors must have a linear characteristic.

If it is impossible to eliminate the machine vibration by means of the balancing or vibration suppression, the vibration isolators are used. The theory, the calculation of stiffness of the structure and the vibration isolators are covered by papers (Anh and Nguyen 2016, Cheung et al. 2013, Elias et al. 2016, Gardonio and Zilletti 2015, Jang et al. 2012, Wagner and Helfrich 2017, Piven and Umanskaya 2016a, 2016b).

The vibration isolators are installed between the disturbance source and the protection object. Depending on a ratio of mass of the object and the source and the operating accelerations in the oscillatory system, the force or kinematic excitation appears. During the vibration separating machines’ operation, the elevated foundation vibration and the force excitation appear. The vibration with force harmonic excitation is aimed at decreasing the amplitude value of force of pressure upon the constraint transmitted to a nonmoving object. By means of the vibration isolation it is possible to achieve the contraction of an amplitude of the forced oscillations of the vibration source.

The vibration isolators are classified according to a way of damping or according to an elastic element material (rubber-metal, spring and solid-metal, with air or dry friction, undamped). The rubber and metal-rubber supports are applied in the vibration machines’ sieve boxes with straight-line oscillations. These supports suffer a number of shortcomings: change of dynamic properties with continuous operation and the temperature change, insufficient reliability of joining of the rubber solid monolith with the metallic reinforcement.

A choice of the foundations stiffness during the vibration machine operation depending on its frequency characteristics. The machine’s natural frequencies must differ significantly from frequencies of the forced oscillations of the sieve boxes. It is established that

during rigid fastening of the machine, the natural oscillation frequencies must range within 120÷150 sec-1. The use of vibration isolators (installation of elastic rubber or wooden pads) decreases the dangerous frequency of natural oscillations to values of 15÷20 sec-1.

Local vibration isolation is not used in the vibration separating machines with a kinematic solid drive. The sieve boxes are fastened to the machine frame by means of laminose wooden or steel hanger brackets. The hanger brackets are elastic supporting constraints assuring the directional motion of the operating devices. The hanger brackets operate simultaneously with the driving devices and they download it. With all the variety of the balancing units, vibration suppressors and vibration isolators, they fail to assure the complete elimination of harmful vibrations.

Making of the Separating Machines’ Load-bearing Structures Stiffer

The separators’ sieve boxes, which make the vibration motion, are fastened to the machine’s load-bearing structure. Vibration of the load-bearing structure itself introduces an additional component into the sieve surfaces’ oscillatory motion, which influences the separating process quality.

When designing the vibration machines’ load-bearing structures, there is not carried out a sufficient substantiation of the machine’s structure, calculations for strength and stiffness of some structure’s elements and the machine on the whole. The stiffness implies an ability of the structure’s elements to resist the external influence with the least deformations. The structure’s stiffness depends on the material’s elastic properties, geometric characteristics of sections, a type of supports.

Frame structures of the vibration separating machines consist of some elements of various gauge of the rolled metal products. The frame structures are statistically indeterminate systems with redundant internal constraints. For their calculations, a finite elements method, a displacement method and a force method are used. These calculations make it possible to determine the dangerous sections, to optimize the linear dimensions of some elements, to determine the most rational load acting points.

When researching the vibration machines’ frame structure, it is necessary to determine the natural frequencies and the oscillation forms of the structure elements. This is necessary so that, at an initial stage of the machine designing, it was possible to tune away from the resonance (Piven and Umanskaya 2017a). With all the variety of calculation methods of optimizing the space frameworks, they make it possible to determine the optimal parameters of some parts. Stiffness and mass of the whole load-bearing structure are not minimized. Special difficulties of solving similar tasks arise during designing the machines, in which the

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vibration is deliberately set by the driving operating devices to implement the technological process. When placing the vibration machines upon the production buildings’ floors, the calculation tasks are getting more complicated. It is necessary to take into account the introduction of physical and mechanical characteristics of the structure and the floor materials into the calculation algorithm.

CONCLUSION Conclusions on Analysis of a Problem of

Increasing the Load-bearing Capacity of Structures of the Vibration Separating Machines and the Main Areas of its Solution

1. In the vibration separating machines, because of disequilibrium of the sieve boxes, the movable parts, insufficient stiffness of the structure elements, the vibratory displacement of the load bearing structures exceed the critical standards in several times.

2. Oscillations of the lead-bearing structures of the vibration separating machines increase the oscillation amplitude of the sieve surfaces to 40% to the optimal values. This leads to deterioration of the separating quality, the dynamic load increment, the increased wear of parts.

3. The existing methodologies of designing the vibration separating machines do not make it possible to take into account their peculiarities as machines with the deliberately set vibration. Additional vibration is not taken into account during the calculated determination of the separating quality.

4. In order to improve the vibrational separating quality, to increase the vibration machines reliability, it is necessary to reduce the vibratory displacements of the machines’ load-bearing structures.

5. It is possible to improve the vibration characteristics of the separating machines through optimizing the frame structures, which makes it possible to rationally place its structural elements with the minimum mass with account taken of the dynamic loading and the fulfillment of strength conditions.

RESULTS The Main Areas of Improving the Structures

of the Vibration Separating Machines The conducted analysis of the researched scientific

problem made it possible to formulate the following main areas of its solution:

1. Research of dynamics of the vibrational separating process with account taken of the vibration characteristics of the machines’ load-bearing structures and the physical and mechanical properties of the separated components. This will make it possible to specify the kinematic parameters of the driving mechanisms operation and necessary stiffness of the load-bearing structures.

2. Determination of a necessary quantity and characteristics of the elastic constraints in the driving mechanisms links and improvement of these mechanisms’ structures on this basis.

3. Research of influence of the residual disequilibrium of inertial forces in the vibration separating machines upon their dynamic characteristics and quality of the technological process performance with setting the allowable values of disequilibrium. Improvement of schemes and structures of the dynamic balancing.

4. Optimization of the oscillatory motion trajectory of the separating operating devices depending on their destination. Improvement of the existing driving mechanisms and development of new ones.

5. Research of influence of the elastic properties of foundations upon the vibration characteristics of the separating machines. Determination of requirements for the building part in assembling the vibration separating machines. Improvement of building structures for installing the vibration machines.

6. Development of a mathematical model of optimizing the load-bearing structures of the separating machines and their drives. Improvement of the methodologies of designing the vibration separating machines.

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