RU2031552C1 - Method of determination of permissible current for graphitized electrodes - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: criteria of quality of electrodes by which permissible current is determined is calculated by formula depending on bending strength, modulus of elasticity of nipples, specific resistance of electrodes, limit deviation of diameter of thread of nipple socket, limit deviation of pitch over entire length of screwing. EFFECT: increased precision of determination of permissible current for graphitized electrodes.

Description

 The invention relates to electrical engineering and can be used in the operation of graphite electrodes in arc steel furnaces.

A known method for determining the permissible current for graphitized electrodes of an arc steel furnace, consisting of sections connected by nipples, in which the specific electrical resistance of the electrode ρ _{e is} measured, which determines the permissible operating current (GOST 4426-80. Graphite electrodes and nipples (Table 9).

 The disadvantage of this method is its lack of accuracy, due to the fact that the determination is made according to one physical quantity that does not fully characterize the electrodes, - the electrical resistivity.

 A known method for determining the permissible current for graphitized electrodes in arc steel furnaces, including the measurement of the physical quantities of the reference group of electrodes, including the elastic modulus of the electrodes [1].

 The disadvantage of this method is its lack of accuracy, due to the fact that with an increase in the permissible current, thermal destruction occurs along the nipple, and not along the electrode.

(1-p) (1-T_ш·T_д.р) по которому определяют допустимый ток эксплуатации [2].A known method for determining the permissible current for graphitized electrodes of an arc steel furnace, consisting of sections connected by nipples, in which measure the electrical resistivity of the electrode ρ _e , the mechanical bending strength of the nipples σ _{ex .} pitch deviation over the entire length of screwing T _m, find the probability of unsatisfactory results acceptance tests according to the standard of individual indicators tensile strength zgib nipples p electrodes thereon define a quality criterion by the formula
K _qual =

(1-p) (1-T _ш · T _др.р ) by which the permissible operating current is determined [2].

 The disadvantage of this method is its lack of accuracy, due to the fact that the determination is made by a limited number of physical quantities that do not fully characterize the electrodes.

 The proposed method in comparison with the known will improve the accuracy of determining the permissible current for graphite electrodes.

 The essence of the proposed method lies in the fact that in the known method for determining the permissible current for graphitized electrodes of an arc steel furnace, consisting of sections connected by nipples, they measure the electrical resistivity of the electrode, the mechanical bending strength of the nipples, the maximum deviation of the diameter of the thread of the nipple socket, the maximum deviation of the pitch along the entire length of make-up, finding the probability of obtaining unsatisfactory results of acceptance tests according to the norm have individual indicators tensile strength in bending nipples, determining quality criterion electrodes, determining the criterion of quality allowable operating current.

(1-p) (1-T_ш·T_д.р) где σ_изг.н - механическая прочность на изгиб ниппеля, МПа;
ρ_э - удельное электросопротивление электродов, мкОм;
Е_н - модуль упругости ниппеля, МПа;
Р - вероятность получения неудовлетворительных результатов приемосдаточных испытаний по нормативу отдельных показателей предела прочности на изгиб ниппелей, %;
Т_ш - предельное отклонение шага при всей длине свинчивания, мм;
Т_д.р - предельное отклонение диаметра резьбы ниппельного гнезда, мм.The inventive method differs from the prototype in that the measured value is the ratio of the mechanical strength of the nipples to the product of the elastic modulus of the nipples and the electrical resistivity of the electrodes, and the quality criterion of the electrodes is found by the formula
K _qual =

(1-p) (1-T _w · T _d.r. ) where σ _ex.n - mechanical bending strength of the nipple, MPa;
ρ _e is the electrical resistivity of the electrodes, μOhm;
E _n - elastic modulus of the nipple, MPa;
P - the probability of obtaining unsatisfactory results of acceptance tests according to the standard of individual indicators of the ultimate strength in bending of nipples,%;
T _W - the maximum deviation of the pitch for the entire length of make-up, mm;
T _d.r - the maximum deviation of the diameter of the thread of the nipple socket, mm

 Improving the accuracy of the proposed method is ensured by combining in one indicator the quantities characterizing, along with electrical and mechanical properties, the elastic strength properties through the modulus of elasticity, which more fully characterizes the passage of current through the electrode into the melting space of the steelmaking furnace under conditions of dynamic mechanical loads resulting in in a number of cases, to brittle fracture of nipples as the most vulnerable part of electrodes screwed into an electrode candle.

 The use of the proposed method as a measured value of the ratio of the mechanical strength of the nipples to the product of the elastic modulus of the nipples and the electrical resistivity of the electrodes, which characterizes the passage of current through the nipple joint under conditions of significant dynamic loads, improves the accuracy of determining the allowable current for graphite electrodes.

 The main trend in modern electric steelmaking is the use of powerful large-tonnage arc steel-smelting furnaces, a distinctive feature of which are increased current and mechanical loads that change dramatically at different periods of melting. This leads to an increase in breakdowns, mainly due to the brittle fracture of nipples, and, accordingly, to an increase in their specific consumption.

 As the studies showed, the new measured value correlates with the operational stability of the electrodes when current is supplied to the melting space of an arc steel-smelting furnace under conditions of significant dynamic loads. Industrial tests of electrodes with a diameter of 610 mm with the characteristics given in the table on a DSP-100I6 furnace during electric steel smelting showed that determining the permissible current from the specified ratio reduces the specific consumption by 20% by improving the accuracy of the proposed method, which optimizes the consumption of graphite electrodes.

 The measurement of the modulus of elasticity refers to non-destructive testing methods, is performed on finished nipples and does not require additional sampling.

PRI me R. To determine the permissible current value for graphitized electrodes when they are used in DSP-100I6 arc furnaces for reference electrode groups with a diameter of 610 mm, the values of mechanical bending strength σ _iz.n and elastic modulus E _n nipples, electrical resistivity ρ _{e of the} electrodes, maximum diameter deviation are measured the threads of the nipple socket and nipple T _d.r. and the maximum deviation of the pitch along the entire length of the make-up T _sh . The elastic modulus of the nipples is measured in accordance with TU 48-12-41-91.

 According to the results of determining the mechanical bending strength of the nipples, the probability of obtaining unsatisfactory results of acceptance tests according to the standard of individual indicators of the bending strength of the nipples p. Then they find the value of the quality criterion of the electrodes according to the specified formula. Find experimentally acceptable current for the reference group. The table shows the dependence of permissible currents on the value of the quality criterion.

Depending on the quality of the electrodes received in the electric steel-smelting shop, the permissible operating current I _add on the value of the quality criterion of these electrodes, found from the indicated dependence, is determined by the previously constructed dependence (shown in the drawing).

 Using the proposed method in comparison with the known method allows more accurate determination of the permissible current during operation of the electrodes in electric arc furnaces, which ensures optimization of their consumption by operation under conditions corresponding to their properties and, accordingly, reduction of their specific consumption by approximately 20%.

Claims (1)

METHOD FOR DETERMINING allowable current of graphite electrodes of the electric arc furnace consisting of sections connected nipples, wherein the measured electrical resistivity ρ of the electrode _e, mechanical bending strength σ _izg.n nipples, deviation limit thread diameter threaded socket T _{d. p} , the maximum deviation of the step along the entire length of the make-up T _W , find the probability of obtaining unsatisfactory results of acceptance tests according to the standard of individual indicators of the flexural strength of the nipples p, determine the quality criterion of the electrodes from them, which determine the permissible operating current, which is further measured the elastic modulus of the nipples E _n , and the quality criterion of the electrodes is found by the formula

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