Master's work
In ferrous metallurgy for heat treatment and the fuel stoves of batch-type use giving to the wares of necessary properties, thus some of them due to the compactness of location in a workshop the high productive have an index. Such indexes appeared possible due to the ассиметричного location of torch and теплоиспользующих devices (recuperators), that in turn defined a substantial defect - considerable unevenness of distribution of temperature on volume working chamber. For example, in some chamber stoves the most high temperature is observed in overhead part near-by a frontal wall, where usually produce taking temperature the thermocouple of the adjusting system, (t9, pic. 1), and the most cold area is situated in the underbody of stove - near-by a fume-collect channel (t18, pic. 1). The overfall of temperatures between these points arrives at 3000With (at the level of temperatures 1250 - 13500С) in an initial period of heating, that results in the uneven heating of bars in садке, consisting of 16 - 20 bars, to the increase of duration of heating of all садки, and, consequently, and to the increase of specific expense of fuel.
For long-term period of the industrial use of thermal stoves the row of methods of decline of unevenness of the temperature field is offered: application of swinging gas-rings; application of swinging torch, rejectable the high-speed stream of the compressed air; setting of protective wall before a fume-collect channel; setting of additional плоскопламенных gas-rings is in the lateral walls of working chamber of and other. The offered methods decided a task partly, but appeared or difficult enough in exploitation, or resulted in worsening of the use of real-estate of stove, or resulted in the loss of main dignity of thermal stoves - compactness of location in a workshop.
One of the known methods of decline of unevenness of the temperature field in stoves is the impulsive heating which consists in the continuous serve of fuel in the period of self-control of metal in the set interval of temperatures. Switching from the minimum expense of fuel (Bmin) to maximal (Bmax) carry out at the overfall of temperatures in working space of stove between hot and cold points, equal Δtк = Δtн·k, and switching from a maximal value (Bmax) to minimum (Bmin) - under reaching the set temperature in the hot point of working space of stove, where Δtн is an overfall of temperatures in hot (t9) and cold (t18) points in the moment of switching with Bmax on Bmin; Δtк is an overfall of temperatures in hot and cold points in the moment of switching with Bmin on Bmax; k is a smoothing coefficient. Switching is produced predictor, allowing to eliminate the sharp gallops of pressure in a working chamber. Dignity of the impulsive heating of thermal stoves consists in absence of necessity of some changes in the construction of stove for the receipt of the even heating, and попеременное heating of садки "long" and "short" torches assists smoothing of temperature in a working chamber. Depending on quality of management the impulsive heating the increase of the productivity and specific cost of fuel cutting is possible on 6 - 10%
Complication in realization of the impulsive heating is insufficiency of information about the temperature field of stove and heated metal, necessary for determination of moment of the timely switching of fuel. It is possible for the receipt of complete information to apply the mathematical attended zonal model of burning of fuel and heat exchange, which consists of joint decision of tasks of the non-stationary temperature fields of metal and walling-up (laying), thermal zonal balance and function of burning down of fuel. A model foresees dividing of working chamber into by volume calculation areas (pic. 1) : on a vertical line - on overhead and lower, on a horizontal - on the number of bars which are located in one row, for example, for thermal stoves with садкой of 100 т and mass of bar 5, 56 т the incurrence of areas is equal to 18.
| Picture 1 - Chart of breaking up of thermal stove on areas |
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In accordance with the chart of breaking up of well on areas (pic. 1) can be distinguished for three types of equalizations of thermal balance for overhead and bottom areas:
For extreme, near to the gas-ring, areas of 1:
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for the areas of 2 - 8:
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for the extreme distant area of 9:
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for the area of 10:
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for the areas of 11-17:
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for the area of 18:
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where and is a coefficient of burning down of fuel in an area; In is an expense of fuel; Qнр is a warmth of combustion of fuel; Vг, сг is an output of foods of combustion (gases) on unit of fuel and heat capacity of gases; tг is a gas temperature; Lд, св is an actual expense of air on unit of fuel and heat capacity of air; tв is a temperature of air; Q is power of radiation from an area in an area; a m is a metal; a g is gas; to is laying (walling-up); u is a number of area.
At the decision of task the period of heating is broken up on steps at times, the values of which are determined by the decision of internal task. From equalization of thermal balance on every step at times a gas (mixtures of foods of combustion and air) temperature is determined in every area of tru, which is used further as a border condition for the decision of non-stationary task for a bar and walling-up of stove.
The function of burning down of fuel on length of stove, difficult radiation heat exchange between foods of combustion, internal surface of the heat-resistant laying and surface of metal is taken into account in a model. The function of burning down of fuel is accepted on the basis of experimental data and can be corrected at their accumulation. For example, function of burning down for the long torch (at Bmax) of aumax and for short (at Bmin) aumin brought around to a pic. 1. Except for it, in a model a heat exchange between nearby areas and переизлучение is taken into account from overhead areas in lower one, and also heat exchange between the element of surface of the heated bar and elements of surface of nearby bars, internal surface of walling-up, gas volumes of bottom and overhead areas.
The temperature field of metal is determined by the decision of three-dimensional task of heat conductivity.At the decision of three-dimensional task of heat conductivity the sixpoint eventual non-obvious разностная chart of variable directions is used, for the decision of which the method of breaking (method of fractional steps) up, which consists in that an intricate multidimensional problem in the process of разностного decision is replaced by the great number of more simple unidimensional tasks, was used. A bar is broken up on n steps on a co-ordinate, for a thermal stove the heated bar was broken, for example, on six segments on three axes of co-ordinates.
At the decision of three-dimensional task of heat conductivity the sixpoint eventual non-obvious разностная chart of variable directions is used, for the decision of which the method of breaking (method of fractional steps) up, which consists in that an intricate multidimensional problem in the process of decision is replaced by the great number of more simple unidimensional tasks, was used. A bar is broken up on n steps on a co-ordinate, for a thermal stove the heated bar was broken, for example, on six segments on three axes of co-ordinates.
The temperature field of walling-up (laying) was determined by the decision of unidimensional task of non-stationary heat conductivity for a multi-layered wall with the border terms of III of family on internal and external surfaces on the standard method of eventual differences.
Books
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