Quality heating of the steel charge to be rolled into seamless tubes in the rotating-hearth furnace requires continuous operation of the pilger mill. Interruption of the charging schedule leads to ...impaired charge heating process. Prolonged heating time causes a rise in the charge temperature above the limit values, and that in turn brings to a larger quantity of scale formed on the charge surface. Final result is loss of metal and overheating of the charge accompanied by increased fuel consumption and lower furnace productivity.
Taking statistically-documentary basis as a starting point and applying adequate mathematical methods, numerical functional relations between total annual production and single production expenses, ...i.e. average total production expenses are defined. Functional relation between both of them with different number of employees compared to the average number of employees in the analysed period of time is also defined.
The paper deals with the production of seamless steel tubes at the Sisak Steel Works in Sisak, Croatia since 1992, i.e. during the war and the postwar years. Due to operation at a greatly reduced ...capacity the steel mill and the rolling mill have faced major financial losses. Based on those negative experiences a way of overcoming the current state of affairs in steel production has been sought. The cost of specific energy consumption is analysed in respect to its share in the selling price of the product for the purpose of predicting the terms of operational profitability and reducing the financial losses caused by occasional drops in the production rate below the profit-making level.
Providing a correct thermal regime the consumption of heat is reduced as well as the loss of steel because of its surface oxidation. Using the data about the steel charge and the furnace working ...space geometry and particular requests in connection with the temperature of the charge and the decrease of the rotating hearth furnace heating capacity, the temperature of gases combustion and the inside walls surface along the working space of the furnace are defined by a calculating method. Calculated parameters are used as the initial parameters for the charge heating in working conditions. The steel oxidizing loss as well as the influence of the oxidizing loss on the total heat consumption in the furnace are defined by a calculating method and by direct measuring too. Having the insight of the steel oxidizing loss is a presumption for a more complete heating control as to ensure high quality products of a seamless pipes rolling mill.
The heating operation of the rotating-hearth furnace involving semi-finished steel products was analysed, and specific heat consumption was determined as a function of furnace productivity. The aim ...was to find out how a change in productivity, which is not accompanied by a modification of the thermal regime, can affect the heating quality and surface oxidation of products.
In many cases, due to the complicated conditions of heat exchange in the furnace chamber and the shape of the heated metal, heating conditions cannot be determined by means of traditional analytical ...calculations but must be found out experimentally. For that reason, a mathematical model of the heating process for a steel charge having an octagonal cross-section will be constructed on the basis of finite element analysis. Transient heat conduction analysis and thermal stress analysis will be performed in order to determine the allowable heating rate with regard to temperature distribution within the structure and the distribution of induced stresses and deformations. The latter are due to the heat transferred from the combustion gases and furnace lining by radiation as well as to the forced convection of combustion gases to the charge. The model will be verified with the help of experimental results obtained by temperature measurements of die main parameters of heating conditions.
The heating operation of the rotating-hearth furnace involving semi-finished steel products was analysed, and specific heat consumption was determined as a function of furnace productivity. The aim ...was to find out how a change in productivity, which is not accompanied by a modification of the thermal regime, can affect the heating quality and surface oxidation of products.
On the basis the geometrical characteristics of radiation from the furnace lining to metal, as well as defined temperature regime in the rotary-hearth reheating furnace, the requisite temperature of ...lining and heating metal along the working space of the furnace were calculated. Calculation results, consequently and the calculation scheme, were verified by the temperature measurements of lining and heating metal.
Operating data for two pusher-type furnaces, old and new, of approximately identical length but having different longitudinal profiles were analysed. The old furnace had a partly inclined ...longitudinal profile and the new one had a rectangular longitudinal profile. Results of analysis showed a higher rate of specific fuel consumption for the old furnace than for the new one. To reduce the difference a possibility was considered of building in an air-preheating recuperator instead of relocating the burners and altering the longitudinal profile of the old furnace. Results of quantification demonstrated that by building a recuperator into the old furnace specific fuel consumption would greatly diminish and would become comparable to that of the new furnace.
