RU2819319C1 - Vibration resonance planetary-ball mill - Google Patents

Abstract

FIELD: grinding of material.

SUBSTANCE: disclosed is a vibration resonance planetary-ball mill comprising a housing with symmetrically built-in cylindrical linings, it is also equipped with grinding chambers freely installed in the cylindrical lining of the housing and made with possibility of rotation around its own axis and planetary rolling along the inner surface of the lining, torsion-rod elastic suspension, having the same stiffness in the vertical plane, and a device for exciting resonance oscillations, the latter is composed of parametric resonant drive with motor with rotary-pendulum exciter with oscillators mounted on its shaft. Grinding chambers are made in the form of hollow cylinders closed with covers on both ends, inside which there are grinding bodies and ground material. Vibrating mill is made with possibility to select frequency of rotation of electric motor shaft.

EFFECT: invention ensures reduction of energy consumption of the vibration grinder at simultaneous increase of stability of the operating mode of parametric oscillations.

1 cl, 2 dwg

Description

The invention relates to machines for fine grinding of materials, namely to devices for vibration and planetary mills. The areas of application of the proposed invention are: the diamond mining industry, the cement and mining industries, powder metallurgy, and the production of fine materials.

Planetary mills are known, consisting of grinding drums, drum gears, bearings, a fixed planetary gear and a carrier. Such devices are designed for grinding fragile materials to fine and ultra-fine grinding with low productivity. As the dimensions increase (to increase the productivity of processing large flows of material), the reliability of the design decreases sharply and the mills fail. The disadvantages of such machines are large problems with scaling, the need to use complex gear mechanisms, low reliability and short service life of bearing units.

Vibrating planetary grinders are known, consisting of grinding chambers, vibrators, and a grinding roller. In such devices, the material being processed is crushed by a grinding body (massive roller). These include, for example, vibrating roller mills and roller abrasives. Compared to vibrating ball mills, vibrating roller mills have a higher specific productivity for grinding solid ore materials.

The vast majority of vibration machines for technological purposes have an unbalanced vibration exciter and operate in the mode of forced oscillations in frequency ranges far from the resonance region. In the specified range, the oscillation mode of the machine is weakly sensitive to changes in the properties of the material being processed, its loading and the parameters of the external energy source.

The resonant (energy efficient) oscillation mode of the mill working body during forced oscillations is practically impossible to implement due to the high sensitivity to changes in the process load and the parameters of its oscillatory system. To maintain the required vibration modes of the working body throughout the entire technological cycle, feedback elements are introduced into the control system of the vibrating machine, which leads to an increase in cost and a decrease in the reliability of the machine as a whole. But it is the nonlinearity of the technological load that makes the use of traditional means of automatic control and maintenance of the resonant state of machines operating in forced oscillation mode ineffective [1].

In this regard, the urgent task arises of increasing the operating efficiency of a vibration planetary mill due to a stable and stable resonant mode of oscillation of the working body without automatic controls. The problem posed can be solved by the proposed device, built on the basis of the obtained promising research results [2], [3].

As a prototype, a vibrating roller mill was adopted, containing a housing connected to the base by elastic connections (springs), grinding chambers, a grinder (massive roller) and an unbalance shaft, which is driven into rotation by an electric motor [4].

The disadvantages of the prototype are:

the over-resonant operating mode of an unbalanced vibration drive is accompanied by irrational energy consumption, since a large reactive power circulates in the oscillatory system;

To run in a massive grinding body, a large amplitude of vibration of the grinding chamber is required. The amplitude of oscillations during over-resonance adjustment of the operating mode increases with an increase in the mass of the unbalances of the inertial exciter, which, in turn, leads to an increase in friction in the bearing supports and a decrease in reliability;

difficulties in setting up stable synchronous movements of the imbalances of vibrators and grinding bodies;

adhesion and compaction of the crushed material when the chopper is rolled along the inner surface of the grinding chamber.

The purpose of the present invention is to eliminate the disadvantages of the above-mentioned devices and create an energy-efficient vibration planetary mill with automatic adaptation to constant disturbances during the grinding process.

Maximum productivity and energy efficiency of vibration mills can be achieved by creating resonant oscillating systems. The task comes down to spending the minimum amount of energy during its transition from the engine to the working element. The greater the power imparted to the load, the higher the intensity (transfer of energy from the mill drive to the material being ground) and grinding efficiency (grinding fineness).

An effective way to excite resonant mechanical circular oscillations is to use Raman parametric resonance [5], [6].

The technical result of the invention is to increase energy efficiency, energy intensity (the amount of power reduced to a unit volume of the working chamber) and reliability of a vibrating planetary ball mill while simultaneously increasing the productivity of material grinding.

The technical result of the claimed invention is achieved by the fact that in a vibration resonant planetary ball mill containing a housing with symmetrically built-in cylindrical linings and grinding chambers of rotation with grinding media and the material being processed, the means for resonant oscillations along a circular path of which are an elastic suspension of equal rigidity in two mutually perpendicular directions to which it is connected to a fixed base and a parametric rotary-pendulum exciter driven into rotation in a vertical plane by the electric motor shaft, and the resonant tuning of the means for communicating resonant translational circular oscillations is determined from the relation of combinational parametric resonance

ω=λ ₁ +λ ₂ ,

where ω is the frequency of parametric excitation (rotation frequency of the electric motor shaft);

λ ₁ =νω - partial natural frequency of swinging oscillators (pendulums) of the rotor-pendulum inertial element;

ν is a dimensionless parameter that determines the natural frequency of pendulum swings in a rotating coordinate system (0<ν<1);

- partial natural frequency of translational vibrations of the mill body along a circular path;

C=C _x =C _y - rigidity of the elastic isotropic (elastic properties are the same in the directions of the x, y axes) suspension;

M is the total mass of the mill.

The destruction of the material occurs due to mixed destructive loads of grinding bodies on the material being processed (impact and abrasion).

The diagram of a vibration resonant planetary ball mill is shown in Fig. 1. The body 2 is connected to the fixed base 6 by an isotropic elastic suspension 5 of the same rigidity C (Fig. 1). A parametric resonant drive 1 is installed in the middle of the housing, on both sides of which cylindrical linings 4 are mounted, inside of which cylindrical grinding chambers (hollow cylinders with covers) 3 with grinding media 7 and the material being processed 8 are installed. The parametric resonant drive is an electric motor mounted on a shaft of which a rotary-pendulum inertial element is installed, the plane of rotation of which is located in the vertical plane.

The form of working resonant oscillations at frequency λ ₂ is the translational movement of the mill body in two mutually perpendicular directions along the Ox, Oy axes. The required shape of the trajectory of the body is provided by an isotropic elastic suspension, for example, a torsion bar.

In fig. Figure 2 shows a diagram of a rotary-pendulum system of a parametric resonant drive [7]. The balanced disk 9 of the rotary-pendulum exciter has three periodically alternating closed running tracks 10 of a circular profile, the centers of which are offset from the axis of rotation of the disk by equal distances . The treadmills are equipped with identical balanced pendulums 11 of mass m each with the possibility of running in. The rotor-pendulum inertial element contains N=3 rolling bodies. The assembled disk with mass m ₀ is rigidly fixed to the shaft of the electric motor, which is installed on the body 2 of the mill with mass M, which has two degrees of freedom: translational motion x, y along a circular path in the plane of rotation of the rotor in the direction of the coordinate axes Ox, Oy. To increase the amplitude of external influence, a drive shaft is used, on which disks are installed in a single structure so that the treadmills of one pair are rotated around the rotor axis at an angle:

γ ₀ =π/s,

where s is the number of disks relative to another.

Thus, in the general case, a rotary-pendulum inertial element can contain N=2s pendulums located in pairs in parallel planes. In this case, the electric motor is removed from the oscillatory system and connected to the drive shaft through a coupling.

The position of the treadmills is determined by the angles:

ψ _k =ωt+2πk/N,

where k=1, 2, 3;

N=3 - number of pendulums,

and the position of the pendulums is determined by the angles:

ϕ _k =A _k cos(ω ₁ t+2πk/N).

The swings of the pendulums at angles ϕ _k (k=1, 2, 3), as well as the translational movements x, y of the mill body along a circular path constitute the degrees of freedom of the oscillatory system under consideration. Thus, the dynamic model of a vibration resonant planetary ball mill is represented by two dynamically interacting subsystems. The first is a subsystem of equal interacting pendulums of a rotor-pendulum inertial element, having the same partial natural frequencies λ ₁ =νω in the rotating coordinate system Aξηζ. Here:

where mρ _с is the static moment of the pendulums;

- moment of inertia of the pendulum relative to the rolling axis;

J _Ck is the moment of inertia of the pendulum relative to the axis passing through its center of mass;

r is the radius of the pendulum axle;

i=r/ρ _c - gear ratio of the pendulum running in to the treadmill;

;

ρ _c =BC _k .

The second subsystem consists of grinding chambers (working body) installed inside the housing with the ability to rotate around its own axis, and planetary movement around the center of the cylindrical linings - rolling along the inner surface of the cylindrical linings.

The device works as follows. Energy is supplied to the oscillatory system of the mill due to the uniform rotation of the rotary-pendulum inertial element of the parametric drive 1 with an angular velocity ω, which leads, when the threshold condition is met:

ε>4n ₀ nν/(1-ν),

where ε=ν ² Nμ/2 is a coefficient proportional to the ratio of the total mass of the pendulums of the rotor-pendulum inertial element to the mass of the entire mill;

;

n ₀ , n are the relative linear damping coefficients of the pendulums and the total mass M, respectively;

ω ₁ =νω≈λ ₁ - generation frequency of pendulums, which is close to their own swing frequency for self-excitation of multiple Raman parametric resonance ω=ω ₁ +ω ₂ .

Here, the oscillations of the pendulums lead to the automatic formation of unbalance of the inertial element of the exciter “invisible unbalance” (point C _d in Fig. 1), rotating with a frequency ω ₂ ≈λ ₂ , that is, with a frequency close to the natural frequency of the body oscillations . When setting ν=0.25, the angular speed of rotation of the “invisible unbalance” is 25% lower than the speed of rotation of the drive shaft ω ₂ =0.75ω. Since ω ₂ ≈λ ₂ , the centrifugal force of inertia of the center of mass of the “invisible unbalance” pendulums excites resonant oscillations of the mill body along a circular path, and body oscillations, in turn, excite the rolling of the grinding chambers 3 along the inner surface of the cylindrical linings 4 with an angular velocity ω _about =λ ₂ ≈ω ₂ . As a result, the self-organized involvement of the system bodies in collective resonant interaction occurs, that is, the mutual stimulation of vibrations of the system bodies and the rolling of the grinding rotation chambers (hollow rollers) inside the cylindrical linings. During running-in, the grinding chambers of rotation exert an effect on the mill body similar to the action of a centrifugal vibration exciter, thereby creating an additional centrifugal force that maintains the resonant state of the oscillatory system. The gear ratio of the angular speed of rolling ω _rev to the angular speed of its own rotation ω _rev is determined by the expression:

i=r _p (r _p -R),

where r _p is the outer radius of the grinding chamber;

R is the internal radius of the cylindrical lining during external rolling (the direction of its own rotation and rolling are opposite). When r _P <R the gear ratio is negative.

In the oscillatory system of the mill, even before reaching the resonant mode, due to uncontrolled small disturbances, there are natural oscillations with frequencies λ ₁ =νω and . Oscillations with these frequencies significantly exceed all other noise oscillations in root-mean-square amplitude. The entry of the machine into the resonant zone leads to an increase in the amplitude of noise components with frequencies λ ₁ , λ ₂ and self-excitation of a Raman parametric resonance.

In the proposed device, the interconnection of oscillations is significant. The unbalanced centrifugal force of inertia of the rotor-pendulum inertial element arising as a result of the swings of the pendulums causes resonant oscillations of the mill body with synchronous running of the grinding chambers, causing resonant swings of the pendulums. The energy spent on running in the grinding chambers is partially transformed into an oscillatory system due to the effect of vibrational resonance maintaining rotation. The presented dynamic feature of a vibration resonant planetary ball mill, coupled with a parametric resonant rotor-pendulum exciter, the efficiency of which is 1.5 times higher than traditional centrifugal unbalanced vibrators, makes it possible to ensure high stability and stability of the operating mode, increase the intensity of “pumping” energy into the crushed material, increase the energy intensity of the mill and, thereby, the efficiency of grinding, reduce the specific energy consumption during grinding and the noise of the machine as a whole.

An automatic reduction-free reduction in the frequency ω ₂ of rotation of the center of mass of the “invisible unbalance” pendulums by 1.3 times leads to a decrease in friction in the bearing supports of the electric motor shaft, as well as to a decrease in the inertia forces and rigidity of the elastic system by almost half. Consequently, the inertial loads on the mill’s structural elements, elastic suspension and foundation are reduced by the same amount. This circumstance allows us to obtain an overall gain in terms of the reliability of the proposed device.

This invention has been designed and constructed according to the above principles and considerations. The experiment has established that running in the grinding chambers increases the amplitude of vibrations of the mill body and increases the efficiency of the resonant operating mode. The conducted studies and tests showed reliable and stable operation of the proposed device. The analysis established that the vibration resonant planetary ball mill combines the advantages of planetary and vibroball mills and does not have their disadvantages, which gives it new qualities:

1. Self-excitation, self-maintenance of stable stable self-controlled resonant oscillations of the mill body along a circular trajectory of large amplitude with simultaneous running-in of the grinding chambers.

2. High energy intensity due to the collective resonant interaction of oscillating and rotating bodies.

3. High energy efficiency. The installed power of the vibration drive is reduced by more than half compared to the dominant inertial and kinematic vibration exciters in industry.

4. Increasing the grinding efficiency due to the nature of the movement inside the grinding load allows for the implementation of several destructive forces (impact, abrasion, mixed), which increases the grinding efficiency.

5. Simplicity and reliability of design. Lack of complex gear mechanisms and other special frequency conversion devices.

The proposed solution meets the criteria of “novelty”, “inventive step” and “industrial applicability”.

Information sources

1. Astashev V.K., Babitsky V.I., Vulfson I.I. and others. Machine dynamics and machine control: Handbook // Ed. G.V. Kreinina. M: Mechanical Engineering - 1988. 239 p.

2. Antipov V.I., Dentsov N.N., Koshelev A.V. Energy relationships in a vibration machine based on multiple Raman parametric resonance // Bulletin of the Nizhny Novgorod State University. N.I. Lobachevsky. 2013. - No. 5. - pp. 188-194.

3. Koshelev A.V. Efficiency of a vibration grinding machine with parametric excitation // Bulletin of mechanical engineering. - 2016. - No. 5, p. 27-31.

4. Rudin A.D. To the calculation of vibration mills with dynamic rolling of grinding media // Ore enrichment - 1985 - No. 1, p. 30-34.

5. Antipov V.I., Antipova R.I., Ruin A.A. Method for excitation of resonant mechanical vibrations and a device for its implementation: Patent No. 2486017 RF B06B 1/16 // Bull. No. 18, 2013.

6. Koshelev A.V. Experimental study of the efficiency of a parametric resonant drive // Fundamental Research. 2014. - No. 11, p. 996-999.

7. Antipov V.I. Vibration exciter: Patent No. 2072661 RF MKI V06V 1/16 // Bulletin. No. 3, 1997.

Claims (1)

Vibration resonant planetary ball mill containing a housing with symmetrically built-in cylindrical linings, characterized in that it is equipped with grinding chambers freely installed in the cylindrical linings of the housing and configured to rotate around its own axis and planetary rolling along the inner surface of the linings, torsion-rod elastic a suspension having the same rigidity in the vertical plane, and a device for exciting resonant oscillations, made in the form of a parametric resonant drive containing an electric motor on the shaft of which a rotary-pendulum exciter with oscillators is installed, while the grinding chambers are made in the form of hollow cylinders, closed with lids both ends, inside of which there are grinding media and the crushed material, and the vibration mill is made with the ability to select the rotation speed of the electric motor shaft - partial natural frequency of swings of the oscillators of the rotor-pendulum exciter, - partial natural frequency of the mill, C - rigidity of the elastic suspension, M - total mass of the mill, - dimensionless parameter that determines the natural frequency of oscillator oscillations in a rotating coordinate system - static torque of oscillators; - moment of inertia of the oscillator relative to the running axis; J _Ck is the moment of inertia of the oscillator relative to the axis passing through its center of mass; r is the radius of the oscillator pin; - gear ratio of the oscillator running in to the treadmill;

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