·Table of Contents
·Methods and Instrumentation
Creation of Means of the Control of Magnetic permeability of Heterogeneous Substances and Materials
Dnepropetrovsk State University, Nauchni-Lane str. 13, Dniepropetrovsk,Ukraine
State Agrarian University, Voroshilov str., 25, Dniepropetrovsk, Ukraine
Many low-magnetic heterogeneous substances and materials are characterized by good correlation of their magnetic penetrability and phisico-mechanical parameters. However, their non-destroying control is hampered by the influence of some preventive factors (anisotropy of properties, variability of electric conductivity, curving of the controlled surface, etc.), which lower the reliability of information. The authors have held the work on creating the means of non-destroyed express-control of magnetic penetrability of such heterogeneous substances as iron-ore raw materials on different stages of extraction and treatment, as well as composition materials based on polyamide phenilon filled with carbonyl nickel.
Iron-ore raw materials whose quality is defined by magnetite contents are most often found as pieces of ore (average diameter 100-200 mm) , crushed ore (sized 30 mm ) ,pulp (mechanical mixture of water and crumbled ore sized 0,5 mm). As an object of electromagnetic control, iron-ore raw materials represent the low-magnetic (m£
2 - 8), low-conductive environs with strong anisotropy of properties, which significantly hampers the processes of defining their magnetic penetrability. In order to improve the accuracy of control, the decrease of preventive factors influence (anisotropy of properties, curving of the controlled surface, variability of ore-pieces` size, segregation processes in iron-ore pulp) is expedient to be held on the stage of obtaining primary information by means of inductive dator's; suppression of these factors must be presupposed in the dators` construction.
At controlling iron-ore pieces these are the anisotropy of properties and random distributed curving of the controlled surface which are the most hampering factors whose influence cannot be suppressed simultaneously which the help of the known means. In order to lower the influences of these factors, the parametric inductive dator's were elaborated ; they allow to reach the rejection of properties anisotropy by creating the field with strict axial symmetry within the contact zone, and surface relief influence is compensated by dator's geometry change. Such dators` contain three spools two measuring ones and a compensating one which changes its situation relatively to measuring ones depending on the controlled surface relief, and the stability of dator`s initial inductively is provided. A mathematical model is elaborated, based on row inductivities account method by Tailer and allowing to optimize the dator's constructive parameters with the error not exceeding 2,5 % . For poor low-magnetic ores there is elaborated the dator with one measuring spool, ferrous concentrator of the magnetic field and mobile core with variable area of cutting whose situation relatively to the concentrator depends on the controlled surface relief. Here, the stability of dator's initial inductivity is provided by the stability of magnetic conductor's magnetic resistance with no dependence on mobile core's situation. For dators with variable geometry sized 70 mm in diameter, comparative error from the influence of cavities at the controlled surface up to
±9 mm does not exceed 0,1%, from magnetic anisotropy - 1%.
At controlling magnetite's contents in explosive slits, dynamic error is the major one occurring due to the random deviation of dator's axis from normal in the process of its movement along the cam surface of the slit's side. In order to lower the dynamic error, there is elaborated the dator constituing of three spools with ferrous pivoted magnetic conductors situated in the plane normal to the slit's cutting, fan-shaped under equal acute angles. Such a dator has the error not exceeding 0,15 % at axis's deviation from normal at the angle of ±18. The dator with dynamic error correction is used at slit gadget of a device for explosive slit's magnetic carotage.
Controlling magnetite contents in crumbled ore-mass is significantly hampered with strong anisotropy of properties. In this case, dator's construction represented by three spools (Helmgoltz rings) with orthogonally situated axes is optimal. Automatic commutation of spools with their further integrity allows to average the values of dator's inductivity as to orthogonal directions of ore-mass control. Fort ore sized 30 mm, the comparative error from anisotropy influence does not exceed 1,5 %.
At statistic measurements of magnetite contents in iron-ore pulp, the major source of errors is the influence of segregation processes on dator's impedance, which reveals in constant change of inductivity. In order to lower the error there is elaborated a construction of two parallel cylinder spools whose sizes and distances are chosen so as to provide for the homogenity of the magnetic field along the axis. The technique of constructing such dators lies in optimization of spools' height and distance between them. Dator's inductivity change for 30 min is stated to make no more than 0,018 %.
Created inductive dators are distinguished by low weight and size, they are used in small field devices of express controlling magnetite contents in ore on different stages of the technological process of extraction and treatment of iron-ore raw materials. The work of these devices is based upon the autogenerative technique characterized by low apparatus expenses. In order to heighten the method's accuracy and to provide for good sensitivity to the controlled parameter at low frequences, there were held the investigations on synthesizing convertors and invertors of impedance on the basis of the combined operational scheme. There are created the devices for scaling the inductive dator's reactance with multiplying coefficient of 400, which allowed to provide for stable work of measuring autogenerators with resonant circuit within the frequences' rage of 100-180 Hz , their inductive branch was represented by dators with proper inductivity of 1-5 mHz. Here, applying convertors of positive impedance allowed to significantly lower the weight and size of low-frequency inductive dators.
Increase of dator's sensitivity to the controlled parameter is quite easily held by compensating its initial impedance with the entering impedance of the negative convertor. Comparative sensitivity then grows proportionally to the degree of compensation. Increase of absolute dator's impedance increment is reached by means of successive joining the current convertors of the negative impedance. Increase of sensitivity is explained by simultaneous growth of dator's impedance increment and the compensation of its initial value. Practically, there was obtained the increase of absolute dator's inductivity increment by 80 times.
Convertor of negative active resistance linked up to fluctuating circuit, at the condition of self-excitement makes the autofluctuating system which can be used to create low-frequency measuring autogenerators. Rejection of anisotropy of properties and curving of the controlled surface is held by means of inductive parametric dator with variable geometry. The device weighs 2 kg. Modified variants are the devices of indicator type weighing 1,2 kg (OKM-3) and 0,5 kg (OKM-4). The range of defining the mass per cent of magnetite makes from 2 to 50 abs % with average quadratic error 1,0-1,5 abs % depending on geological type of ore. OKMC-6 type device is distinguished by improved exploitation properties: ability to work with built-in graduation drawings; maximum average quadratic error of 0,9 abs %; device's weight of 0,25 kg; power from built-in accumulators.
Defining magnetite contents in explosive slits is held by carotage device of OKMC - 1K type. Caroted slits are 30 m deep, from 190 to 250 mm in diameter. Average quadratic error does not exceed 1,5 abs % within the magnetite contents range up to 50 abs %. The device weighs 2,8 kg, the slit gadget weighs 1,6 kg.
Controlling magnetite contents in crumbled ore is held by means of OKM-5 type device where properties anisotropy rejection is provided by a dator represented by a set of spools creating the homogeneous magnetic field within the control zone with tension vector changing its direction in expanse. The range of defining magnetite mass per cent is from 2 to 35 abs. % with average quadratic error of 1-1,2 abs. % the device weighs 4,3 kg.
OKMC - 3P type devise allows to define magnetite contents in iron-ore pulp specimen from classifier drain of enrichment plant within the range of 5 to 30 abs. % with average quadratic error of 0,6 abs.%. Dator's structure allows to reject the influence of segregation processes.
Industrial tests and further exploitation of devices showed quit a high efficiency of the chosen ways of rejecting the hampering factors, proved the expediency of applying the autogenerative method at creating portative devices, the use of applying impedance transformers for improvement of sensitivity and accuracy of measuring devices. The specific exploitation feature of OKM seria is the absence of necessity of special test preparation before measuring (sides' polishing, crumbling, wearing, drying, weighing, ets.), which significantly shortens the time of defining the magnetite mass per cent compared to the traditional testing, improves the control productivity.
Investigations held also allowed to create the means of express-control of strength characteristics of composition materials based on polyamide phenilon filled with low-disperse carbonile nickel, whose percentage gives good correlation with the magnetic sensitivity of the material and makes strengthening effect on the polymer. The latest reveals itself in the increase of hardness, shock strength, fluidity limit at compression, and the decrease of volumous wear. Decrease of wear intensity is conditioned by the presence of carbon in carbonile nicel; carbon takes the role of hard lubrication in the conditions of dry friction. In order to control the composition material's magnetic sensitivity, autogenerative measuring devices are created with applying impedance convertors allowing to define the percentage of carbonile nickel within the range from 0,1 to 20 %. This gave the opportunity to measure the strength characteristics of the materials without their destruction.