KINETIC AND ENERGETIC ANALYSIS OF GRINDERS Péter Korzenszky, Fogarasi Lajos Szent István University, Gödöllő, Hungary

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1 УПРАВЛЕНИЕ И УСТОЙЧИВО РАЗВИТИЕ 1-2/2006(14) MANAGEMENT AND SUSTAINABLE DEVELOPMENT 1-2/2006(14) KINETIC AND ENERGETIC ANALYSIS OF GRINDERS Péter Korzenszky, Fogarasi Lajos Szent István University, Gödöllő, Hungary Introduction Taking the results gained up to now, in the course of the mechanical investigations on comminuting machines (first of all impact mills) as a basis, a new measurement system was constructed. The system is suitable for investigating the states in continuous regime ranges as well between the earlier set discrete parameters as against that in the former stepped measurements. Besides the infinitely variable rotary-speed adjustment, the measurement assembly is usable and indispensable to the work on understanding better the comminution process and grounding its comminution-kinetic description. On the basis of the analysis of the experiments carried out and the conclusions drawn, a mechanically and energetically well-founded control and regulation circuit, utilizable in the practice as well, can be elaborated. The system with its present form, through using the independent parameters revealed during the investigation, is already capable of operating as a feedback regulation circuit (it may be considered a pilot-scale control device as well). Directly measured and influenced variables The performance of the mill is given as the mass flow rates of the feed (input) and/or the outflow (output) material (kg/s or t/h), which are alike in the case of the stationary running, at an actual grits fineness. The particle fineness is a datum that can be defined and given from indirect measurements (sieve analysis) effected on samples, with the knowledge of the particle-size distribution curve. Its direct measurement in the process has not been solved yet; at present it can be carried only by manual input in control program for the reference-signal creation. One of the objectives of the research is to create such a fineness-dependent physical-mechanical property which can be measured directly and to which a suitable electrical measuring transducer (transmitter) might be developed. This is allowed by the improved measurement system. The built system completed with the computer data processing is alike capable of taking the characteristics necessary for transformation of the non-stationary regime (when the input and the output material-mass flow rates are not equal and they vary as a function of time). The comminution process, besides the design of the crushing elements, the grinding chamber and the liner, is determined by the mass and the motion state of the charge (the material being instantly in the grinding chamber). The mass of charge can be determined exactly through comparing the diagrams of the input and the output masses (kg) against time. To this, the measuring system continuously detects the weight of the material to be fed namely its decreasing and the weight of the output (its accumulation) and the computer records the gained mass-time functions in a form for processing. The state of motion of the charge is a complex of the motions and collisions of the single particles that are determined by the superposed elementary interactions. For its examination, the most important dynamic parameter, besides the charge mass and the particle-size distribution by mass, is the peripheral velocity of the rotor which at once is an input property as well. The discrete records of the earlier research (carried out at some velocity i.e. rotary-speed stages several times respectively) have proved that the dynamic functions of the impact mills (mass-flow rate, grits fineness and loading torque as functions of rotary speed) have extreme values at well-defined places of which comminution-kinetic analysis is of cardinal importance and interest for us. By that measurement system in a greatly widened and increased rotary-speed range, taking continuous dynamic functions, the comminution-kinetic analysis of the significant values or value-pairs including the model creation too has been made possible. At once and only through the measuring circuit built now, it has been made possible to study the effect of the infinitely adjustable rotary speed as a control variable as well as to elaborate the mechanical and control-technical conditions of its utilization. For the kinetic examination of the load as a function of the dynamic properties of the charge, the torque developed on the rotor shaft is measured and the recorded information or torque functions are applied in the theoretical analysis of the comminution. One of the most important objectives of the research is the detailed effect analysis of the constructional, dynamic and process properties determining the energetic conditions and the efficiency (which is extremely bad at the mills) of the comminution. For that, records of large number with several constructional version, settings, material states and product fineness are required that, with the help of the measuring system built, with effective manyparameter tests, is possible. Measurement assembly The transmission of the hammer mill Zenit Jun-

Kinetic and energetic analysis of grinders 91 ior driven originally by V-belt of three stages was modified (Figure 1). To the three-phase asynchronous motor type Leroy Somer (LS132ST) of 5.

2 Kinetic and energetic analysis of grinders 91 ior driven originally by V-belt of three stages was modified (Figure 1). To the three-phase asynchronous motor type Leroy Somer (LS132ST) of 5.5 kw power, with one pair of poles, a frequency converter (OMRON 3G3MV) fitted to the motor in power and load capacity as well was chosen (Figure 2). With the help of the frequency converter, the rated synchronous rotary speed of motor 3000 rpm is infinitely adjustable theoretically between 0 and 400 Hz. Arising from the design of the motor and some other reasonable parameters, it was temporarily expedient to limit the output of the frequency converter to 60 Hz that slightly higher than the rated rotary speed. Now the range to be tested will be 0 to 3600 rpm as to the motor-shaft rotary speed. However, the range for the motor rotary speed to be tested will be much wider. In the course of the experiments, the rotary speeds of the driving and the driven shafts, the power supplied by the frequency converter will be measured. With the help of the strain gauges glued on the shaft of the mill, the mechanical torque can be measured (Figure 3). To determine the mass-flow rate of the material (now cereal grains), the variation in mass of the input and output is recorded with the help of electro-tensometric dynamometers (Figure 4). The gained data are recorded by a measuring and data-acquisition device (SPIDER 8). Figure 1. Zenit Junior hammer mill The frequency converter is used in the application accordant to the instruction manual provided by OMRON. The power value is selected on the programmable transmitter (0 to 10 V = 0 to 5.5 kw) (Figure 2). To determine the mechanical torque, strain gauges were glued on the shaft of the mill. The calibration of the torque measuring circuit was carried out in static state in such a way that weights of known mass were placed at a 0.5 m distance from the shaft axis and the voltage between the bridge arms was measured. The terminals of the strain gauges were led in a groove milled in the shaft to the shaft end (Figure 3). The measurement of rotary speed was provided with the help transmitters working on reflection principle (Figure 3.b). The measurement and data-acquisition device SPIDER 8 is capable of simultaneously collecting samples 8 independent parameters (variables). The first two channels (0 and 1) are capable of receiving impulse-like quantities, the channels 6 and 7 outputs of universal transmitters (0 to 10 V; 4 to 20 ma) and full, half- and quarter bridges can be connected to the other channels (Figure 5). The schematic diagram of the measurement assembly is shown in Figure 6. Before the elaboration of the experimental project, an idle-running measurement series was also

3 92 Péter Korzenszky, Fogarasi Lajos Figure 2. Terminal connection diagram of the frequency converter type OMRON 3G3MV a.) b.) Figure 3. Torque meter assembled with slip-ring pickup Figure 4. Electro-tensometric dynamometer Hottinger PW2KRC3 Figure 5. Channel assignment of data-acquisition device SPIDER 8

4 Kinetic and energetic analysis of grinders 93 Electro-tensometric dynamometer Hottinger PW2KRC3 (Weight) Strain gauges R=120 Ω (Torque) Hammer mill Zenit Junior Reflection transmitters (Rotary speed) Frequency converter Leroy somer Typ: LS132ST OMRON 3G3MV Frequency converter (Power) Figure 6. Schematic diagram of the measurement assembly

5 94 Péter Korzenszky, Fogarasi Lajos n [1/min] Idle-runing input Rotary speed of mill shaft 1/min Rotary speed of motor shaft 1/min Torque Nm Power kw 2 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 x10 M [Nm], P [kw] Time [s] Figure 7. Evaluation of idle-running input carried out. The data from the evaluation of a test are shown in Figure 7. The rotary speed of the motor shaft has been adjusted to the 3000 rpm rated value, the rotary speed of the rotor, according to the V-belt transmission, is 3600 rpm. The higher power required by the starting can also be followed well in the preset 8 s running-up period. In the stationary range, the value of the power is 2.2 kw while, in the dynamic period (speed-up), the power has reached the 3.4 kw instantaneous value. The increasing tendency can be observed in the torque values as well but it is not of a significant degree in the case of idle running. The evaluation of the idle-running measurement raises several ideas for making more exact the later experimental presetting. Through an accurate selection of the starting boundary conditions, the process will be enabled to start in operating states different from the rated load. The incidental power peaks may be eliminated on the basis of the data gained from the test series. Literature 1. Korzenszky P., Dr. Judák E. (2005) Measurement Assembly for Energetic Analysis of Comminuters (Mérési összeállítás aprítógépek energetikai analíziséhez) Hungary Hungarian Agricultural Engineering, 18/ Petróczki K., M.H.M.Aldabbar (2006) Terménydaráló nyomatékának mérése nyúlásmérõ bélyeges nyomatékérzékelõvel XXX. MTA-AMB Kutatási és Fejlesztési Tanácskozás, Gödöllõ január Fogarasi L. Douba M. Sembery P. (1996): Grinding Cereal Grains by Hammer Mill. (Gabonafélék aprítása kalapácsos darálóval) Hungarian Agricultural Engineering No. 3 ( p. HU ISSN ) 4. Fogarasi L. Douba M. Sembery P.(1996): Relations between Surface Geometry of Hammer Mills and Energetic Parameters. (Összefüggés a kalapácsos darálók felületi kialakítása és az energetikai paraméterek között) Hungarian Agricultural Engineering No. 9 ( p. HU ISSN ) 5. Judák E. Fogarasi L. Korzenszky P.: Forgó villamos gépek hatásfok-analíziséhez mérõrendszer kifejlesztése és tesztelése terménydarálón. XXVI. K+F Tanácskozás január SZIE, Gödöllõ

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