INSPECTION OF THE MECHANICAL CONDITION OF THE HOISTING MACHINES IN KUZBASS MINES

V. V. Burkov, V. M. Voronchikhin, N. I. Klykov, V. A. Timofeev,
V. S. Udut

(Presented by the scientific seminar of the Department of Mining Machines, Mine Transport, and Mining Mechanics)

At the mines of Kuzbass there are in operation domestic and imported hoisting machines installed 20–25 years ago, that is, at a time when mine productivity and shaft depth were considerably smaller. These machines differ greatly in their design and operating characteristics and have unequal strength margins in the main elements of the mechanical part. Over a long period of operation, the working regime of hoisting installations has changed repeatedly (the hoisting height, terminal load, speeds, accelerations, etc., have changed). The mechanical part of some machines is substantially overloaded, and in a number of cases this leads to the failure of main shafts, gear teeth of reducers, drum shells, and other parts.

Since 1960, the Department of Mining Electromechanics, together with the Department of Applied Mechanics of the Tomsk Polytechnic Institute named after S. M. Kirov, has carried out inspections of the mechanical parts of several hoisting machines that had operated in the mines of the Kuzbassugol combine for more than 15–20 years, in order to determine their suitability for further service.

To determine the actual forces in the ropes at the drum rims, a study was made of the operating regime of the hoisting installations. Diagrams of velocity and accelerations were recorded with an MPO-2 loop oscillograph and a self-recording ammeter-voltmeter. The average terminal load and the overload coefficient of the skip were determined by weighing the useful load being hoisted and lowered. The mass of the moving parts of the hoisting installation, reduced to the radius of rope winding, was determined during free coasting from the velocity and acceleration diagram [1]. The values of maximum accelerations, acceleration jumps, possible rope slipping, and the coordinates of the points at which the ropes left the drums at various moments of the hoisting operation were found by calculation and experimentally [2].

The static forces in the ropes were determined taking into account shaft resistances and skip overloading. The static force in the ascending rope branch is

\[ F'_{\mathrm{st}} = (k_z + k')Q + Q_m + p(H_0 - x), \tag{1} \]

where \(k_z\) is the skip loading coefficient (on average \(k_z = 1.1\));

$k'$ — coefficient of mine resistances for one rope branch (for skip hoisting $k' = 0.075$, and for cage hoisting $k' = 0.1$);

$Q$ — payload, kg;

$Q_{\mathrm{m}}$ — dead load of the conveyance, kg;

$p$ — weight of 1 running m of rope, kg/m;

$H_0$ — length of the hanging rope, m;

$x$ — distance traveled by the conveyance from the start of hoisting, m.

The static force in the descending branch of the rope with an empty conveyance is

\[ F_{\mathrm{st}}'' = Q_{\mathrm{m}} + p(H_0 - H + x) - k'Q, \tag{2} \]

where $H$ is the hoisting height, m.

When there is a load, this force increases by the magnitude of the lowered load.

The difference of the static forces is

\[ F_{\mathrm{st}} = F_{\mathrm{st}}' - F_{\mathrm{st}}'' . \tag{3} \]

The dynamic forces were determined during the period of taking up rope slack (for skip hoists) and during the period of accelerated motion of the conveyances, taking into account the maximum accelerations and the greatest acceleration surges.

The maximum dynamic forces of the ascending rope branch during the period of taking up slack are

\[ F_{\mathrm{d.n}} = \frac{j_{\mathrm{n}}}{g} \left[ \varepsilon_{\mathrm{n}}(Q + Q_{\mathrm{m}}) + \frac{(GD^2)_{\mathrm{sh}}}{D_{\mathrm{sh}}^2} + p(H_0 + L_c) \right], \tag{4} \]

where $j_{\mathrm{n}}$ is the maximum acceleration during the period of taking up rope slack, m/sec²;

$g$ — acceleration of gravity, m/sec²;

$(GD^2)_{\mathrm{sh}}$ — flywheel moment of the sheave, kg/m²;

$D_{\mathrm{sh}}$ — sheave diameter, m;

$L_c$ — length of the rope strand, m.

The dynamic-load coefficient during free rope slack is

\[ \varepsilon_{\mathrm{n}} = k_{\mathrm{n}}\varepsilon_0 + \frac{g}{j_{\mathrm{n}}}(k_{\mathrm{n}} - 1) \left( \frac{k_{\mathrm{z}} + k' + n_c}{1 + n_c} + \alpha \right), \tag{5} \]

where $n_c$ is the ratio of the dead weight of the conveyance to the payload;

$\alpha$ — ratio of the weight of the hanging part of the rope to the end load.

The slack coefficient [3] is

\[ k_{\mathrm{n}} = 1 + \frac{220 \cdot \Delta l_{\mathrm{n}}}{H_0 + L_c}, \tag{6} \]

where $\Delta l_{\mathrm{n}}$ is the possible magnitude of rope slack, m.

The dynamic-load coefficient at zero slack [4] is

\[ \varepsilon_0 = \left(10 + 0.93\,\frac{g}{j_{\mathrm{n}}}\right)(0.3 + 0.16\alpha). \tag{7} \]

The maximum dynamic force in the rope during the period of accelerated motion of the conveyance in the shaft is

\[ F_{\mathrm{d}} = \frac{j}{g} \left[ \varepsilon(Q + Q_{\mathrm{m}}) + \frac{(GD^2)_{\mathrm{sh}}}{D_{\mathrm{sh}}^2} + p(H_0 + L_c - x) \right], \tag{8} \]

where $j$ is the maximum acceleration, m/sec²;

The dynamic-load coefficient in this case is

\[ \varepsilon = 1+\frac{\Delta j}{j}(1+1.7\alpha), \tag{9} \]

where \(\Delta j\) is the acceleration jump, \(m/sec^{2}\).

The dynamic acceleration in the descending branch of the rope during the period of retarded motion and the difference in dynamic forces were determined by the generally known method.

To determine the maximum accelerations and acceleration jumps, the greatest and smallest starting torques were determined when switching rheostat stages [5]

\[ \gamma_{1}= \frac{ 2\gamma_{m}\dfrac{v_{0}-v}{v_{0}} \left[ \dfrac{R_{1}}{R_{n.r}} \left(\gamma_{m}+\sqrt{\gamma_{m}^{2}-1}\right) \right] }{ \left(\dfrac{v_{0}-v}{v_{0}}\right)^{2} + \left[ \dfrac{R_{1}}{R_{n.r}} \left(\gamma_{m}+\sqrt{\gamma_{m}^{2}-1}\right) \right]^{2} }, \tag{10} \]

and

\[ \gamma_{2}= \frac{ 2\gamma_{m}\dfrac{v_{0}-v}{v_{0}} \left[ \dfrac{R_{2}}{R_{n.r}} \left(\gamma_{m}+\sqrt{\gamma_{m}^{2}-1}\right) \right] }{ \left(\dfrac{v_{0}-v}{v_{0}}\right)^{2} + \left[ \dfrac{R_{2}}{R_{n.r}} \left(\gamma_{m}+\sqrt{\gamma_{m}^{2}-1}\right) \right]^{2} }, \tag{11} \]

where \(\gamma_{m}\) is the overload capacity of the motor;
\(R_{1}\) is the resistance of the rheostat stages from which the motor is switched, ohm;
\(R_{2}\) is the resistance of the rheostat stages to which the motor is switched, ohm;
\(v\) is the actual speed at the instant of switching the motor, \(m/sec\).

The rope speed corresponding to the synchronous speed of the motor is

\[ v_{0}=\frac{\pi D\cdot n_{0}}{60\cdot i}, \tag{12} \]

where \(D\) is the drum diameter, \(m\);
\(n_{0}\) is the synchronous speed of the motor, rev/min;
\(i\) is the gear ratio of the reducer.

The rated rotor resistance is

\[ R_{n.r}=\frac{U_{n.r}}{\sqrt{3}\,I_{n.r}}, \tag{13} \]

where \(U_{n.r}\) is the rated rotor voltage, \(V\);
\(I_{n.r}\) is the rated rotor current, \(A\).

The rated force of the motor on the drum shaft is

\[ F_{n}=\frac{975P_{n}\cdot i\cdot \eta_{p}}{n_{n}}\cdot\frac{2}{D}, \tag{14} \]

where \(P_{n}\) is the rated power of the motor, \(kW\);
\(n_{n}\) is the rated speed of the motor, rev/min;
\(\eta_{p}\) is the efficiency coefficient of the reducer.

The acceleration jump when switching a rheostat stage is

\[ \Delta j=\frac{\gamma_{2}-\gamma_{1}}{\mu}, \tag{15} \]

where \(\mu=\dfrac{m}{F_{n}}\) is the coefficient characterizing the moving masses.

Maximum acceleration of the hoisting system

\[ j=\frac{\gamma_2-\gamma_{\mathrm{st}}}{\mu}, \tag{16} \]

where \(\gamma_{\mathrm{st}}=\dfrac{F_{\mathrm{st}}}{F_{\mathrm{n}}}\) is the ratio of the static load on the motor to the normal force.

The results of calculations for determining the maximum accelerations and acceleration jumps for the skip hoisting installation of the “Kapitalnaya-1” mine are given in Table 1, and the motor starting diagrams and acceleration diagrams for this same installation are shown in Figs. 1 and 2.

Table 1

Calculated values of accelerations and acceleration jumps during motor starting of the skip hoist of the “Kapitalnaya-1” mine of the Osinnikugol Trust

Note. \(v_0=4.33\) m/s; \(R_{\mathrm{n.-r.}}=0.67\) ohm; \(j_{\mathrm{st}}=0.835\); \(\mu=0.52\); \(j=1.40\) m/s²; \(\Delta j=1.24\) m/s²; \(j_{\mathrm{n}}=0.32\) m/s².

The correctness of the calculation and the quality of installation of the metal rheostat have a significant effect on increasing the service life of the mechanical part of the hoisting installation. However, the investigations carried out have shown that, in many hoisting installations, the resistances of sections of different phases of the rotor rheostat are not equal to one another. On skip hoist No. 14 of mine No. 5–7 of the Anzherougol Trust, the asymmetry of individual sections of different phases of the rheostat reaches 40–55%; on the western skip hoist of mine No. 9/15 of the same trust, 44–57%; and on the cage hoist of the Fizkulturnik mine, 114%. This circumstance leads to an asymmetrical load on individual motor phases, to deterioration of its mechanical characteristics, and to reduced reliability of operation during the starting and stopping periods of the hoisting machine. In addition, in most hoisting installations the resistances of the rotor-rheostat sections do not correspond to the calculated data obtained by the method set forth in the “Temporary Instructions for the Inspection, Adjustment, and Testing of Mine Hoisting Installations with Asynchronous Drives.” In the Anzherougol Trust, on the western skip hoist of mine No. 9/15, the actual resistances of individual rheostat sections differ from the calculated ones by \(\pm 50\%\); on the eastern skip hoist of the same mine, by \(\pm 23\%\); on the cage hoist of mine No. 2, by \(\pm 30\%\); and on the cage hoist of the Fizkulturnik mine, by \(\pm 60\%\). A similar picture is also observed at other mines of Kuzbass.

The adjustment of magnetic stations likewise often does not correspond to the technical data of the motor, the specified operating mode, and the actual resistances of the rheostat stages. This leads to the fact that, at the moment the drive is switched on in hoisting installations, large impact loads arise. For example, on the Eastern skip hoist of the 9/15 mine, with the rheostat resistance fully inserted into the rotor circuit, the magnitude of the torque developed by the motor was equal to 48% of the nominal motor torque; on the cage hoist of the Fizkulturnik mine—56%; and on the cage hoist of Mine No. 2—45%. In many hoisting installations, large accelerations occurred during the period of taking up the slack in the rope (the skip hoist of the S. M. Kirov mine of the Leninugol trust, the Northern skip hoist of the Koksovaya No. 1 mine of the Prokopyevskugol trust, etc.).

Fig. 1. Starting diagram of the drive motor of the skip hoist of the “Kapitalnaya-1” mine of the “Osinnikugol” trust

Large and uneven jumps in acceleration occurred during the period of accelerated motion of the conveyances (the Southern skip hoist of the “Koksovaya-1” mine of the “Prokopyevskugol” trust, the skip hoist of the “Kapitalnaya-1” mine of the Osinnikugol trust, etc.). As a result of the above-mentioned causes, large forces arise on the rim of the rope winding, which leads to breakage of drums, reducer teeth, and premature wear of hoisting ropes.

Fig. 2. Diagrams of accelerations (1) and decelerations (2) of the skip hoisting installation of the “Kapitalnaya-1” mine of the “Osinnikugol” trust

To prevent such phenomena, the rheostat steps must be selected and the magnetic station adjusted so that the acceleration at the moment the machine starts does not exceed \(0.3\text{–}0.35\ \mathrm{m/sec^2}\), and the largest acceleration jumps during the starting period do not exceed \(0.6\text{–}0.7\ \mathrm{m/sec^2}\). These considerations must be taken into account when developing a method for calculating metallic rheostats for asynchronous hoisting motors.

The condition of the main shaft, drums, and reducer was checked by careful external inspection, measurement of worn elements, and ultrasonic flaw detection.

Because many mines lack information on the materials from which the main mechanical units of the hoisting machines were made, metal samples were taken from the corresponding parts, specimens were prepared, and mechanical tests, chemical analysis, and metallographic analysis were carried out. The results of these tests made it possible to establish the grade of steel and its principal mechanical characteristics (hardness, yield point, tensile strength, etc.).

Verification calculations for strength and durability were performed on the basis of the resultant loads in the rope branches during various periods of hoist operation, the actual dimensions of the parts, and the number of load cycles since the machine was put into service. The safety margin of the mechanical parts of the machine was determined from the maximum stresses, the yield point, and the fatigue limit of the material. The safety margin under emergency loads was determined from the breaking force of the rope.

The investigations carried out showed that, despite long service, many old hoisting machines in the mines of Kuzbass are in satisfactory condition and can be used for further operation (for example, the skip-hoist machines of the S. M. Kirov mine of the Leninu-gol trust, the cage-hoist machine of mine 5–7 of the Anzherougol trust, the skip hoist of mine 5–6 of the Prokopyevskugol trust, and others). However, at some mines accident-free operation of the hoisting machines cannot be guaranteed (for example, the cage and Southern skip-hoist machines of the Koksovaya-1 mine of the Prokopyevskugol trust). In individual cases, further operation of hoisting machines is possible only under certain conditions. For approximately five years, operation of the skip-hoist machine of the Kapitalnaya-1 mine is permissible if the drum shell is replaced and dampers are installed on the braking device, or if a separate drive is provided for the service brake and the safety brake—in order to avoid the superposition of braking torques during safety braking; at the Northern skip hoist of the Koksovaya-1 mine of the Prokopyevskugol trust, it is necessary to replace the reducer, increase the rigidity of the drums, use a thicker lining, and replace it in good time; at the single-cage hoisting installation of the Kapitalnaya-1 mine and at many others, it is necessary to change the resistance of the rheostat steps in order to reduce accelerations and acceleration jumps; at the 15-bis cage hoist of mine 9/15 of the Anzherougol trust, it is necessary to limit the terminal load.

It should be noted that liquid rheostats produce the most favorable dynamic operating conditions for hoisting machines. An example is the cage-hoisting installation of mine 5/7 of the Anzherougol trust. The mechanical part of hoisting machines equipped with a drive according to the G–D system had remained in good condition by the time of inspection; for example, skip hoist No. 7 at the same mine. Po-

A positive influence on the operation of the ropes and the elements of the mechanical part of hoisting machines is exerted by spring connecting couplings between the drive motor and the reduction gear, for example on the skip hoist of the Chertinskaya-1 mine of the Belovougol trust.

To avoid the harmful consequences of rope slack, it is necessary to adjust the length of the ropes in a timely manner and to introduce continuous automatic monitoring of emergency and operational slack.

Particular attention should be paid to checking the position of the lower bearing shells of the three-bearing main shafts, since exceeding the calculated clearances at the middle support may cause the development of high stresses, which will lead to shaft breakage.

During biennial inspections, ultrasonic flaw detection should be carried out on critical parts of the mechanical part of hoisting machines; and every five years, the mechanical part of hoisting machines should be checked according to the method described above, in order to determine the continued serviceability of the principal assemblies. These measures will make it possible to eliminate major accidents and injuries at hoisting installations.

REFERENCES

1. I. A. Balashov. Experimental determination of the reduced mass in an ore hoisting installation. In: Mining and Geology. Scientific Transactions of the Novocherkassk, Tomsk, Central Asian, and Kharkov Industrial Institutes. “Sovetskaya Nauka,” 1940.

2. N. I. Klykov. Monitoring rope slack in hoisting installations. Kolyma, No. 1, 1960.

3. V. V. Georgievskaya. The influence of rope slack on dynamic forces in it (second stage). Applied Mechanics of the Academy of Sciences of the Ukrainian SSR, vol. 2, issue 2, 1956.

4. F. V. Florinskii. Dynamics of a Mine Hoisting Rope. Ugletekhizdat, 1955.

5. V. D. Petunov. Operation and design of an asynchronous drive for mine hoisting machines. Dissertation for the degree of Candidate of Technical Sciences. Manuscript. Scientific and Technical Library of the Tomsk Polytechnic Institute, 1958.