Determination of the economic efficiency of a radiation monitoring system for the position of the sinkhead portion of a blooming-mill stock
Abstract Generated abstract
This paper evaluates the economic justification for introducing a radiation monitoring and automated cutting system to determine the hot-top portion of blooming-mill stock at the Izhevsk Metallurgical Plant. It describes how more accurate detection of shrinkage cavities, avoidance of remelting off-gage sound metal, and earlier rejection of defective sections could reduce losses, then formulates the annual economic effect in terms of capital investment, operating costs, and savings from metal recovery and avoided downstream processing. Because production data for some savings components were not yet available, the analysis derives the minimum percentage of usable metal that must be saved for the system to meet the standard payback criterion. The calculation indicates that the planned system would be economically expedient only if it saves more than 0.88% of usable metal.
Full Text
DETERMINATION OF THE ECONOMIC EFFICIENCY OF A RADIATION CONTROL SYSTEM FOR THE LOCATION OF THE HOT-TOP PART OF A BLOOMING MILL BLOOM
V. A. BERDONOSOV, Yu. S. PROKOF’EV, L. M. DOBNER
(Presented by the scientific seminar of the Department of Economics)
The Research Institute of Introscopy has developed, for a metallurgical combine, a system of radiation control of the location of the hot-top part of a blooming-mill bloom.
In the rolling process, various defects may appear: porosity, slag inclusions, shrinkage cavities, etc. The existing technology of casting and subsequent rolling of metal on blooming mills and slabbing mills causes the predominant formation of defects of the type of shrinkage cavities and porosity in the head and bottom parts of the ingot.
Detection and removal of the hot-top part of the bloom is carried out visually by the operator; in this process, a significant portion of sound metal goes for remelting.
Thus, at the Izhevsk Metallurgical Plant, the percentage cut-off of the hot-top part of the ingot is determined as a whole by the product designation, the group of steel grades, and the ingot weight. Under selective quality control of rolled stock, according to the accepted technology, one ingot from each heat is inspected.
For inspection, from the upper bloom of the ingot a templet about 4% of the length of the sound part is cut off and subjected to macrostructure analysis. If a defect is detected, the next templet is cut off, and so on until the analysis gives a positive result. The percentage cut-off of the hot-top part of the ingots of a given heat, in the event that reject metal is detected during selective control, is established from the inspection results.
After cutting off the bottom and hot-top parts, the rolled stock is cut into a definite number of blooms in accordance with the available set of standard measured lengths for each type and cross section of rolled product.
For a number of reasons, in particular because of deviations during casting and rolling, the upper blooms may turn out to be shorter in length than required by the standard. In this case, the nonstandard portion of sound metal goes for remelting together with the reject metal.
With the introduction of the control system, it is proposed to introduce a cutting algorithm under which the remainder of the “upper” sound part of the bloom is not returned for remelting.
According to the accepted technology, quality control and rejection of metal take place after the rolling operation on the “450” mill.
A radiation quality-control system installed on the blooming mill will make it possible to detect defects already at the first operation of the technological process.
Thus, with the introduction of a radiation quality-control system for hot-rolled stock and an automatic control system for cutting, it is proposed to introduce the following changes into the process of inspection and cutting of rolled stock:
1) the position of the line for cutting off the hot-top part of the ingot will be determined by the dimensions and location of the shrinkage cavity. A more accurate determination of the boundary of the shrinkage cavity will make it possible to save a certain quantity of sound metal.
Thus, according to experimental data [1], on average the length of the hot-top part of the rolled stock, as determined by the radiation-control system, proves to be 4–5% less than the length determined on the basis of experience and visual observations;
2) with the introduction of the cutting algorithm, off-gage sound metal will not be returned for remelting;
3) it is proposed to carry out cutting and rejection of rolled stock immediately after inspection of the metal quality over the entire length of the rolled product. Hence one may expect a certain saving of funds as a result of the fact that defects are detected at the initial stage of the technological process;
4) a substantial advantage of the radiation quality-control system for hot-rolled stock being developed is the introduction of complete automation of the process of inspection and cutting of rolled stock.
Thus, the total amount of the expected saving, to be taken into account in determining the annual economic effect, consists of three principal elements:
\[ Э_{\Sigma}=Э_1+Э_2+Э_3, \tag{1} \]
where \(Э_{\Sigma}\) is the total amount of the expected saving;
\(Э_1\) is the magnitude of the expected saving of sound metal as a result of accurate determination of the boundary of the shrinkage cavity;
\(Э_2\) is the magnitude of the expected saving of sound metal due to introduction of the rolled-stock cutting algorithm;
\(Э_3\) is the magnitude of the expected saving of funds as a result of rejecting defective metal at the initial stage of the technological process.
In view of the fact that, at the design stage of the radiation quality-control system for hot-rolled stock, the initial data needed to calculate the first two components of the total annual effect are lacking, at present a narrower problem is posed: to determine the minimum percentage saving of sound metal that ensures payback of the system within a period not exceeding the standard payback period.
The absolute magnitude of the expected economic effect is determined by the formula
\[ Д=Э_{\Sigma}-W_{\text{п.п}}, \tag{2} \]
\[ W_{\text{п.п}}=C_c+E_{\text{н}}K_c, \tag{3} \]
where \(Э_{\Sigma}\) is the magnitude of the expected saving due to introduction of the radiation quality-control system for hot-rolled stock;
\(W_{\text{п.п}}\) is the annual reduced costs due to the development, introduction, and operation of the control system;
\(C_c\) is the annual current expenses due to operation of the system;
\(K_c\) — total capital investment in the control system;
\(E_n\) — standard coefficient of comparative economic efficiency, 0.15.
The amount of total capital investment in the radiation-control system is determined as the sum of the cost of the control computer, the cost of developing the mechanical part, the cost of all automation of the system, the cost of the radiation head and isotope, and the cost of developing and manufacturing the tooling and installing the system.
The amount of annual current expenses is determined by the formula
\[ C_c = C_z + C_a + C_r + C_e + C_{\mathrm{tool}}, \tag{4} \]
where \(C_c\) — total annual current expenses;
\(C_z\) — annual wages of the maintenance personnel;
\(C_a\) — equipment depreciation;
\(C_r\) — costs for current repair of the installation;
\(C_e\) — costs for electric power;
\(C_{\mathrm{tool}}\) — costs associated with operation of the tooling.
- Wage costs are determined by the formula
\[ C_z = S_{\mathrm{hour}} \cdot P \cdot K_q \cdot K_p \cdot K_n \cdot K_g \cdot \mu_p, \tag{5} \]
where \(S_{\mathrm{hour}}\) — hourly wage rate of the maintenance personnel;
\(P\) — number of personnel servicing the radiation-control system;
\(K_q\) — percentage determining the size of the bonus and additional-payment fund;
\(K_n\) — percentage of contributions to the social-insurance fund;
\(K_g\) — actual working-time fund;
\(\mu_p\) — coefficient taking into account the degree of employment of the maintenance personnel (1);
\(K_p\) — district coefficient.
- The annual depreciation fund is determined by the formula
\[ C_a = \frac{Ts_c \cdot ad}{100} + \frac{Ts_{\mathrm{is}}}{T_{\mathrm{rep}}}, \tag{6} \]
where \(Ts_c\) — price of the control system without the isotope and tooling;
\(ad\) — percentage of depreciation deductions;
\(Ts_{\mathrm{is}}\) — price of the isotope;
\(T_{\mathrm{rep}}\) — period for amortizing the cost of the isotope.
- The amount of expenses for current repair of the system per year is taken, approximately, as equal to the annual deductions for major repair
\[ C_r = \frac{H \cdot C_a}{100}, \tag{7} \]
where \(H\) — standard rate of annual deductions for major repair.
- Determination of the amount of annual expenses for electric power
\[ C_e = N_d \cdot K_n \cdot K_p \cdot t_{\mathrm{chk}} \cdot P_g \cdot S, \tag{8} \]
where \(N_d\) — power consumed;
\(K_n\) — motor load factor with respect to power;
\(K_p\) — losses in the plant network;
\(t_{\mathrm{chk}}\) — calculated time for radiographic inspection of one product. This time is determined by the speed of movement of the rolled product according to the technological process and by the length of the rolled product.
\(P_g\) — annual program of products being inspected radiographically;
\(S\) — cost of 1 kWh of electric power.
- Determination of the amount of costs due to the operation of the equipment:
\[ C_{\mathrm{eq}}=\frac{C_{\mathrm{eq}}\cdot \alpha_{\mathrm{eq}}}{100}, \tag{9} \]
where \(C_{\mathrm{eq}}\) is the cost of the equipment;
\(\alpha_{\mathrm{eq}}\) is the annual percentage of depreciation deductions.
The annual reduced costs due to the development, introduction, and operation of the radiation-control system will be economically justified only if the projected control system ensures the receipt of a quite definite saving of sound metal exceeding these costs:
\[ E_1+E_2+E_3>C_c+E_n\cdot K_c. \tag{10} \]
At present it is not possible to calculate the first two elements of the annual economic effect, since the system has not been introduced into production. As for the value \(E_3\), the saving from detecting rejects at the initial stage of the technological process, it can be determined from data of the Izhevsk Metallurgical Plant.
At present, quality control of the products of the Blooming mill is carried out only after the operations of scarfing and rolling on the 450 mill. According to plant data, 0.5–1% of the total amount of metal is rejected in this case. After introduction of the radiation-control system for rolled-product quality, it is intended to detect rejected sections of metal immediately after rolling on the blooming mill.
In this case it is possible to save the funds expended on scarfing and rolling (on the 450 mill) of rejected metal.
The amount of annual saving for this factor is determined by the formula
\[ E_3=\sum_{i=1}^{k}\cdot S_{\mathrm{proc}}\cdot \delta_{\mathrm{rej}}\cdot P_g, \tag{11} \]
where \(k\) is the number of operations in the technological process between the rolling operation on the blooming mill and the control operation;
\(S_{\mathrm{proc}}\) is the cost of processing 1 t of metal at each operation;
\(\delta_{\mathrm{rej}}\) is the percentage of rejected metal (0.5–1);
\(P_g\) is the annual program for metal output.
The minimum value of metal saving at which the control system being developed will be economically justified can be obtained from the following equality:
\[ E_1+E_2+E_3=C_c+E_n\cdot K_c \tag{12} \]
or
\[ E_1+E_2=C_c+E_nK_c-E_3. \tag{13} \]
From this equality we obtain a formula for determining the minimum percentage saving of annual metal, \(\Delta q\), upon exceeding which the projected system ensures the receipt of an economic effect:
\[ \Delta q=\frac{(C_c+E_nK_c)-E_3}{P_g\cdot C_{\mathrm{avg.m}}}\cdot 100, \tag{14} \]
where \(C_{\mathrm{avg.m}}\) is the weighted-average shop cost of 1 t of sound metal;
\(P_g\) is the annual output program of sound metal.
Calculations showed that the application at the Izhevsk Metallurgical Plant of the planned system of radiation control of the quality of hot-rolled products and automatic control of cutting will be economically expedient only if it ensures a saving of usable metal of more than 0.88%.
Otherwise, the system will prove uneconomical.
REFERENCES
- I. Kogler. Gamma flaw detection of hot blooms for shrinkage cavities. Ferrous Metals, 11, 12, 1968.
- Report of the Scientific Research Institute of EI No. 19/70, Tomsk, 1970.