INTRODUCTION

The coal industry faces the complex of issues of its technical re-equipment, an important place takes the transportation systems improvement, which ensure the product delivery from the production place (lava) to the place of processing, storage and lifting to the surface. Such situation creates high demands on conveyors specifications. In particular, to such question as stock up on bandwidth. The powerful high-performance belt conveyors creation, which are highly technical and economic, is possible only on the basis of deep theoretical and experimental research and by improving the methods of calculating the basic parameters and design elements. Belt conveyors as the most economical, efficient and reliable form of transport in bulk are widespread in our country and abroad. They are the primary means of continuous transport in coal mines, but, as it is known from experience of exploitation, utilization conveyor and time performance because of the uneven acting on their coal cargo is still very low and ranges between 0,28-0, 75. This leads to additional costs of electricity and conveyors equipment and hence to raise the cost of coal transportation. Currently, with increasing of conveyors length and their performance issues a particular importance takes smooth start of belt conveyor [1]. This work is dedicated will to this issue.

1 THEME’S ACTUALITY

The questions of starting modes of belt conveyors involved domestic and foreign scientists: a corresponding member of USSR A.O. Spivakovsky [1], prof. V.G. Dmitriev [10], prof. I.G. Shtockman [11], prof. B.A. Kuznetsov, N.Y. Bilichenko, L.G. Shahmeyster [9], E. H. Zavgorodny, V.I. Leskevich, V.M. Nazarenko.

Underutilization of belt conveyors leads to unnecessary costs of electricity, reduces the work time of belts and rollers, and consequently raise the cost of coal transportation. For the effective conveyor transport functioning it is necessary to ensure the maximum filling of the tape. But the mountain freight is uneven due to the extraction equipment downtime. As a result there are difficulties with filling of load-bearing body of the belt conveyor. If you reduce the speed of the belt, you are decreasing the length of the path, while transports certain amount of coal. By reducing the speed of the tape in certain time moments, we increase the belts work life. As it is known band is 60% of the belt conveyors, and by extending the life of the tape for at least a couple of months, we will receive significant economic effect.

The index of specific power consumption per unit mass of cargo transportion does not reflect the actual energy efficiency of drive systems for variable loading conveyor performance. When you start the resulting tension in the belt conveyor are growing and efforts in conveyor components are increasing, these changes may lead to unstable work of the drive drum, such as partial or full slips. Stalemate is unacceptable for many reasons: the intensive wear of the lining of the drum and the lower mantle strip, heating the drum, the sharp decline in the clutch, which finds it difficult to start the conveyor and its further normal operation. This can cause accidents and even fire, which is unacceptable in the Donbass mines, as it results not only in material damage, but also leads to losses of many lives. From the above it is follows that the theme of this work is topical.

2 COMMUNICATION OF WORK WITH SCIENTIFIC PROGRAMS, PLANS, THEMES

Qualification master’s work was carried out during 2009-2010 years according to scientific directions of the chair «Gornozavodsky transport and logistics» of Donetsk National Technical University

3 PURPOSE AND RESEARCH TASKS

Objective: To create and to select rational parameters of belt conveyor soft start, which will allow to increase the efficiency of belt lines use, to maximize the lifespan of other moving parts belt conveyor, to reduce energy costs for transportation of the material.

To achieve this goal it is necessary to solve the following main tasks:

1. Analyze the various methods and constructive schemes;
2. Create a mathematical model for the soft start of asynchronous motor;
3. To establish the degree of relationship between dynamic process of the engine and belt line;
4. To substantiate the optimal parameters of belt conveyor launch;

Object of research is the belt conveyor, which serves as the primary mean of continuous transport in coal mines. In this work we provided a brief overview of the literature to the topic, explored questions of calculation of transients during the start-up of conveyor, dynamic tension, the ways of definition of tension in the tape during the start of conveyor. The different methods of belt conveyor start-up control: rheostatic regulation, regulation of the stator windings voltage feeding, frequency regulation, the mathematical model of asynchronous motor.

4 THE SCIENTIFIC NOVELTY

The scientific novelty of the work consists in modeling of the belt conveyer start-up processes that will allow to determine a rational value of drive acceleration time, providing the fastest start-up with minimal dynamic effort of the belt.

5 PRACTICAL IMPORTANCE OF THE RECEIVED RESULTS

Program algorithm was created, it shows on the schedule more natural mechanical characteristic of induction motor, which takes into account the displacement of the magnetic flux in the rotor, that leads to the torque increas. Modeling of the belt conveyer processes which take place during the start-up process will determine rational values of transmission acceleration time, providing the fastest start-up with minimum dynamic efforts in the tape.

6 THE CALCULATION AND ANALYSIS OF MECHANICAL CHARACTERISTICS THE ASYNCHRONOUS MOTOR

We can assume approximately uniform distribution of resistances along the length of the conveyor

The Scheme of the conveyor is shown in Fig.6.1

Fig. 6.1 – The distribution of resistances along the length of the conveyor

the tractions force Fт the determined by the moment of asynchronous motor M(w), and depend from speed of rotation of billow of motor w:

(6.1)

One of the main characteristics of the mechanical characteristics n2 = f(М) – the dependence of the frequency of rotation from the moment of the motor shaft is described by the equation:

(6.2)

The with of increasing load on the shaft slip S increases, and frequency of rotation of rotor goes down on 5...10%, i.e. the mechanical characteristic n = f (M) AM is rigid. The change of direction of rotation of rotor АM - the reversirovanie - by switching any two wires three-phase system, which supplies engine. The torque asynchronous motor of the speed curve is expressed by mechanical asynchronous motor.The torque is proportional to the square of the phase voltage U1ф and depends on the slip S, i. е.

(6.3)

where m1 - the number of phases of stator; – the active, inductive resistance of stator winding and rotor winding resistance shown, S – the nominal slip, р – the number of pair of poles, f – frequency of network, U1 – the phase voltage.

Of the critical sliding sizes Sкр and starting moment Мп the depend on the resistance of the rotor circuit, thus moment Мп increases with increasing, reaching Мmax at – resulted resistance of starting rheostat, used in AM with the slip-ring motors to reduce the starting current, increases of starting moment, the ensure a smooth start and speed control of rotor.

The refined of construct a mechanical characteristic M = f (S) three-phase asynchronous motor with squirrel cage type 4А160М4У3, voltage 220/380 В, the frequency of rotation 1465 оb/min. The parameters of equivalent circuit of the engine: The ability shifting of engine a = 2,3, multipleness of starting moment Мп/Мн = 1,0, the sliding Sн = 0,023.

To obtain the data necessary for constructing the mechanical characteristics of the engine torque using formula:

(6.4)

The moment starting of engine Мп = Мном = 121 Н•м.

The moment maximal of engine Ммах = a Мном = 2,3•121 = 278 Н•м.

The sliding of critical Sкр = 0,158/(0,521+0,892)=0,112.

By changing the sliding S from 0 and from 1,0 the build the mechanical characteristic of motor, shown in Fig.6.2

Fig 6.2 – The mechanical characteristics of the engine 4А160М4У3 (Animation: volume - 28,2 KB, size - 509x388; number of frames - 5, the delay between frames - 50 ms delay between the last and first frames - 100 ms, the number of repetition cycles - 5)

The mechanical characteristics of the engine the constructed in Fig.6.2 the substantially different values starting torque motor, due to the reduced active resistance of the rotor, which greatly increases the smooth running conveyor belt and control the rotor speed.

The total traction conveyor W0, the consists of the resistance movement of unladen and laden conveyor branch:

W0= k (Wгр+Wпор),

где: k – the generalized coefficient taking into account the additional concentrated resistance;

Wгр – the resistance movement in the cargo branch;

Wпор – the resistance movement in the empty branches;

The total traction conveyor W0:

W0= 1.3 (70000-5250)=84000 Н.

Along with the systems that have only the items that are in the rotational motion, sometimes encountered with systems moving steadily. In this case, instead of the equation of moments is necessary to consider the equation of forces acting on the system.

In the forward motion driving force F always balanced by the force of resistance machine Fc and inertial force occur with the change of speed. If the body mass m is expressed in kilograms, and the rate of V - in meters per second, the force of inertia, as well as other actors in a working machine, measured in Newtons.

In line with the equation of equilibrium of forces in the progressive movement is written as:

(6.5)

It is assumed that body weight is a constant, which is valid for a large number of industrial machinery.

The full equation for the characteristics of the motor acceleration V(t):

(6.6)

To implement the regime of effective start it is necessary to use technical devices, which ensure a smooth motor torque increase over the time to a value corresponding to the pick-up of the band, which followed by a transfer of the engine to the nominal mode.

CONCLUSION

As a result of research work has been collected and studied materials on issues related to the theme of the master's work. A mathematical model is developed in such way that that, apart from the torque it also takes into account the forces of inertia and resistance forces, which will provide a more accurate motor starting characteristics. By varying such parameters as voltage, frequency and speed we get a variety of mechanical characteristics of the engine. Options of voltage, in it’s turn, are calculated according to the T - shaped pattern, G - shaped scheme requires specification of a coefficient representing of the voltage ratio U1 to EMF in the stator, but it is very little differs from unity. And when calculating the error of measurement is to be 2 - 5%. At this stage a graph of speed versus time for starting the belt conveyor is being developed, which will in future allow to choose the best settings for smooth start-up of the conveyor and the actual conditions of it’s use.

LIST OF USED LITERATURE

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TOP

At writing of the given abstract a master’s work has not been finished yet. Date of the work’s final end is on December, 1st, 2010. Full text of work and materials on a theme can be received from the author or her supervisor after the named date.