JPS5817243B2 - Operating method in reheating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a reheating furnace.

In recent years, as part of energy-saving measures, continuous cast steel slabs are cut into specified dimensions using a continuous casting machine, and the resulting slabs (approximately 800°C) are loaded into a reheating furnace as hot slabs without cooling. So-called hot charge rolling is being carried out.

However, in this case, the temperature at which the hot slab is charged into the reheating furnace is
The temperature difference varies depending on the elapsed time after continuous casting and the slab dimensions, etc., and the temperature difference is usually between 300 and 650 degrees Celsius.The heated slabs with these temperature differences are heated in multiple reheating furnaces operated with the same heat pattern. This was extremely uneconomical from the point of view of effective use of energy, since reheating was performed based on the slab with the lowest temperature as a standard, which resulted in applying more heat than necessary to the high-temperature slab.

The present invention has been made in view of the above-mentioned problems, and will be described below based on the drawings showing one embodiment of the present invention.

First, as shown in the flowchart in Figure 1, a rolling schedule including slab dimensions, slab heating temperature, etc. is determined taking into consideration the manufacturing specification conditions of the product, and based on the rolling schedule, hot slab slabs to be sequentially supplied to the reheating furnace are determined. In addition to estimating the number of slabs to be charged and the pitch at which the warm slabs loaded into the reheating furnace will be extracted from the reheating furnace, the above estimated values and the cutting time of the slabs in the continuous casting machine are estimated. Based on the estimated value, the track time from the time when the slab is cut in the continuous casting machine until it is charged into the reheating furnace is determined.

Next, we ascertain the above track time and the temperature at the time of cutting each hot slab that cuts the continuously cast steel slabs cast by the continuous casting machine, and use the following heat transfer calculation to load the hot slabs into the reheating furnace. The temperature θin at the time of input is calculated.

In other words, it is shown in the above equation 0 based on the cutting time of the hot slab slab in the continuous casting machine calculated in the above order, the hot slab temperature at that time, the charging time of the hot slab slab to the reheating furnace, and the slab dimensions. The charging temperature θin of the hot slab into the reheating furnace is calculated based on the heat transfer equation.

Here, θ (t, X): Material temperature t Elapsed time from cutting the varnish slab Single slab thickness Initial condition θ (O,
: Slab temperature and boundary conditions at the end of continuous casting (i) Slab center (11) Slab surface, where ε: Emissivity with the atmosphere θair : By substituting the ambient temperature into the heat transfer equation shown in equation 0 above, the slab reheating furnace is obtained. The charging temperature θin is determined by:

Here, tin is the elapsed time from cutting the slab to charging it into the reheating furnace.

Furthermore, we collect the hot slabs whose charging temperature θ group to the reheating furnace obtained by the above formula A heat pattern for each reheating furnace for heating each slab group to the required rolling temperature is determined.

Furthermore, by measuring the actual surface temperature of the hot slab before charging into the reheating furnace and estimating the average charging temperature of the hot slab, the temperature of the reheating furnace operated under each heat pattern as described above can be estimated. A reheating furnace having a heat pattern corresponding to the average charging temperature is selected from among the reheating furnaces, each hot slab is charged therein, and heated to a required rolling temperature.

Note that the above-mentioned average charging temperature of hot slabs refers to the temperature difference between the surface temperature and center temperature of each hot slab that changes over time. It refers to the average temperature seen from the overall temperature, and estimation of the average temperature from the surface temperature of these warm slabs is obtained from the relationship between the surface temperature and the average temperature determined by heat transfer calculation.

In other words, the temperature of a slab cut by a continuous casting machine decreases over time, but in the heat transfer equations
,,H9t, the relationship between the surface temperature and the average temperature can be obtained. Figure 2 is an example of this, and shows the relationship between the surface temperature and the slab average temperature after heating slabs of different thicknesses to 800°C. The relationship was determined using a heat transfer equation.

As mentioned above, by actually measuring the slab surface temperature for each slab and estimating the slab average temperature using heat transfer calculations, it is possible to determine which heat pattern to charge each slab into the reheating furnace. This is done to more completely heat each slab to the target temperature.

In other words, based on the estimated temperature at the time of charging the slabs determined by heat transfer calculation, a group of slabs that approximate the estimated temperature are directly charged into a reheating furnace set to a heat pattern corresponding to the estimated temperature. Although it seems possible to heat the slab to the target heating temperature even if the slab is cut, in reality, calculations are difficult due to troubles that occur during transportation of the slab from the time the slab is cut until it is charged into the reheating furnace. This is because there are some slabs that do not fit into the street.

As described above, according to the method of the present invention, the number of hot slabs to be supplied to the reheating furnace is determined based on a predetermined rolling schedule, and each hot slab is successively supplied in order to correspond to the number of slabs. After calculating the temperature at the time of charging the hot slab into the reheating furnace by taking into account the temperature at the time of cutting in the casting machine and the elapsed time from cutting the slab to charging the reheating furnace, The warm slabs are collected to have similar temperatures and divided into the same number of hot slab groups as the number of reheating furnaces, and each of these warm slab groups is heated to the required rolling temperature using the reheating furnace. After determining the heat pattern and actually measuring the surface temperature of each hot slab before charging into the reheating furnace, the average charging temperature of the hot slab is estimated, and each hot slab is adjusted to the charging average temperature. Since the hot slabs are charged separately into a reheating furnace with a heat pattern corresponding to the required rolling temperature and heated to the required rolling temperature, the warm slabs are not heated more than necessary and the required and minimum fuel consumption is used. This invention enables the operation of a reheating furnace, which is effective in saving energy, and can also contribute to reducing product costs.

[Brief explanation of drawings]

FIG. 1 is a flowchart for carrying out the method of the present invention, and FIG. 2 is a diagram showing the relationship between slab surface temperature and average temperature.

Claims (1)

[Claims] 1. When reheating the hot slab obtained from the continuous cast steel slab cast by a continuous casting machine and supplying it to the rolling mill without cooling, the hot slab for the continuous cast steel slab is reheated and supplied to the rolling mill based on a predetermined rolling schedule. In addition to determining the number of slabs, the temperature at the time of cutting and the elapsed time up to the time of charging are calculated to calculate the hot slab charging temperature, and the warm slabs whose charging temperature is approximate are collected and reheated. The hot slab slabs are divided into the same number of hot slab groups as the number of furnaces, and heat patterns of multiple reheating furnaces are set to heat each hot slab group to the required rolling temperature. Estimating the charging average temperature of the warm slab by performing surface temperature measurement,
A method of operating a reheating furnace, comprising charging a warm slab into the reheating furnace set to a heat pattern corresponding to the average charging temperature.