Zhabotin Andrey

ABSTRACT

      The mathematical model of a bulk cargo on a tape of the conveyor is developed and the analysis of influence of non-uniformity of bulk density on operating modes driving electric motors is carried out

      Raising of task

      The purpose of the present work is engineeting out of recommendations about an improvement of electric drives of transporting devices with the account granulometric structure of transported cargoes.
      For achievement of the indicated purpose following basic tasks are put:
1) To investigate operating regimes of the mechanisms;
2) To carry out the analysis of transported cargoes properties;
3) To develop the mathematical model of bulk cargo on a haul;
4) To define an actual goods traffic and character of drive loading;
5) To analyse influence granulometric cargo structure on loading on a driving electric motor shaft and its operating regimes.


       Problem and its practical tasks
      The analysis of refusals driving electric motors of mining machines has shown, that cases of the failures, which resulting electric motor in not maintainable condition, now have become frequent.
      Traditionally it is considered, that the reason of this refusal are wrong operation conditions, in particular, an overload driving electric motors. However frequent occurrences of these refusals allow to assume, that operation conditions of all mining equipment and overload capocity of driving electric motors now have essentially become complicated, in some cases, becomes insufficiently.
      Thus, misuse is only one of the reasons of these refusals occurrences. Actual problem is definition of other circumstances, which leading to electric motors failure.
      At the analysis of operation conditions of drives physical properties of trans-ported cargoes, now, are not considered. Though it is obvious, which respect to conveyors, random character of bulk density is influences on nonuniformity of loading on a driving electric motor shaft .
      In particular, for coal, value of bulk density is given in a range.
      It is obvious, the size of a range for a choice of bulk density can lead to essential divergences in values of settlement parametres of the haul when increase in length of the conveyor. Considering, that the tendency to increase in length of transportation and goods traffics now was outlined, the aligment of bulk density amount is actual.

      Analysis of researches and publications
      Modern researches have shown, that scrubbing coefficient is free-bulk cargo is function of the its particles sizes:

    1) It is known, that the form of the overhead part of a bulk cargo looks like, close to a parabolic segment. However, for convenience of productivity caculations the parabolic segment is replaced with a triangle. Therefore, in the given model it is accepted the triangular form of cargo on a haul also.




Pic. 1 - Bulk cargo on a haul.

     2) Now at haul check on lumpines consider, that cargo has the ellipse form. As a result of the conveyor vibrations cargo occupies horizontal position, as the steadiest. Thus, there are enough bases to accept, that the maximum particle of cargo has the form of an ellipse which lays on a haul horizontally.
    Therefore, it is possible to present cross-section form of cargo on a haul as isosceles triangle with the entered ellipses of the identical size.



Рiс. 2


      Using transduction of space by turn of a plane round an axis which are passing through the basis of a triangle, we will receive an equipotential triangle with the entered circles. Thus, as is known, relations of the areas of figures remain.





Рiс. 3


By geometrical calculations of the areas it is received:



     (1)
Where  Kp   –scrubbing coefficient;
         n – quantity of the entered circles located in parallel to one party of a triangle and having (each) one point of a contact with this party;
        (2)
Where В –the haul width, m;
In practice dependence from r is more often interests:


       The scrubbing coefficient for cargoes with particles of different fraction can be defined under the formula:


  Where Kpi- scrubbing coefficient, for particles of the identical fraction;
           pi - percentage of fraction.

      Researches of theoretical model have shown, that is completely defined granulometric by structure of cargo and for any bulk cargoes is in a range Кр=0,5672–0,9064. That is, unequivocal conformity to value n and r is received . Developed design procedure scrubbing Кр allows to specify value of scrubbing coefficient Кр and bulk density of transported cargo.
      The account granulometric cargo structure at conveyor calculation has shown, that at increase in length of transportation the fluctuation range capacities driving the engine considerably increases and factor of a stock of capacity accepted now it can appear insufficiently.

       Dependence ( at various values Кр) on an example of the tape conveyor, it is presented on pic. 4.





(Animation: 7 shots; 5 repetition cycles; time of scrolling of one shot - 1 second)

Рiс. 4 - Schedules of dependen N=f(L) ces at various values Кр for conveyor KLS-1600


      Where: 1 – capacity at tabular value of bulk density; 2 – capacity at Kp min; 3 – capacity at Kp max ; 4 – capacity of idling; 5 – adjusting capacity at tabular value of bulk density.


      The conclusions
      That is at achievement of critical value of length of the conveyor (Lкрит) its overload the driving electric motor is possible.

      For definition of value of critical length of the conveyor and necessary factor of a stock of capacity the driving electric motor it is necessary to consider granulometric structure of transported cargo.



LITERATURE LIST

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