JPS6137917A - Method for controlling uniform heating of steel material - Google Patents

Abstract

PURPOSE:To heat uniformly a steel material without generating unevenness of temps. by heating locally the low-temp. zone of the steel material before the steel material is charged into an induction heating furnace to make the temp. distribution uniform. CONSTITUTION:The temps. of a material B drawn out from a combustion furnace A in the lengthwise and widthwise directions are measured by a radiation thermometer C while the material is conveyed on a table, and the measured results are inputted to an arithmetic unit D. The requisite temp. and specified uniformity of temps. of the material B when the material is taken out from an induction heating furnace F are inputted to the arithmetic unit D, and the amt. of heat to be afforded and heating time necessary for leveling the temps. of the local low-temp. zone of the material B are calculated from said measured results. The low-temp. zone of the material B is locally heated by an induction heating coil E on the basis of the calculated values to make the temp. distribution uniform. Then the material B is introduced into the induction heating furnace F, and rapidly heated.

Description

[Detailed Description of the Invention] (Industrial Application Field) When rolling steel materials, it is necessary to soak the material to a high temperature, and the technical content described in this specification regarding such soaking temperature increase control is The purpose of the present invention is to propose the development result of achieving a predetermined uniform heating in a short period of time by using the minimum amount of heat input.

[Conventional technology]

When heating steel materials, attempts have been made to shorten the heating time by combining an induction heating furnace with a conventional general atmosphere furnace, that is, a combustion furnace.

In this case, the temperature difference between the surface of the steel material and the circular part can be easily eliminated by holding it for a while after induction heating, but the temperature distribution on the surface of the steel material is 1. Temperature unevenness that is inevitable in combustion furnace heating However, it is brought in after being subjected to induction heating.

This temperature unevenness is mainly due to the fact that the temperature of the contact area with the skid, which is the steel support equipment in the combustion furnace, is difficult to rise compared to other parts. Such temperature unevenness, which is typified by the formation of skid marks, can hardly be eliminated by short-term rapid heating using induction heating.

(Problems to be Solved by the Invention) As mentioned above, even if the steel extracted from the combustion furnace is directly charged into the induction heating furnace, due to the temperature unevenness caused by the heating of the combustion furnace, the induction heating furnace The problem of this invention is that it is difficult to uniformly heat the steel material due to the temperature rise in the steel material.

(Means for Solving the Problems) This invention provides a temperature distribution on the surface of the steel material before charging it into the induction heating furnace, when the steel material is sequentially passed through a combustion furnace and an induction heating furnace and uniformly heated to a predetermined temperature. □ From the measured values, calculate the amount of heat input and heating time required to equalize the temperature in the local low temperature area, and apply local heating to the low temperature area based on the obtained results, 1. A method for controlling temperature increase in soaking steel material, which is characterized in that after the temperature distribution is made uniform, rapid heating is performed using an induction heating furnace.

FIG. 1 is a soaking temperature increase control system diagram according to the present invention,
A is a combustion furnace, B is a steel material, C is a temperature measuring device consisting of a radiation thermometer, and D is an arithmetic unit connected to a host process computer (not shown). Further, E is an auxiliary heating means, and in this example, an induction heating coil is used. Then, it is heated in an Fld induction heating furnace.

While the steel material B extracted from the combustion furnace A is being transported on the table, the surface temperature in the longitudinal direction and the -□ width direction is measured with a radiation thermometer C, and the measurement results are input into the computer. . Specifications such as the dimensions and standards of the material to be heated are entered in advance from the host process computer into the computer, and this data includes the required heating temperature and predetermined soaking temperature of 11 degrees when extracting from the induction heating furnace, as well as product specifications. , shall be determined based on operability, etc., and shall be included. Based on the satisfactory heating temperature and processing time, the necessary amount of heat increase in the local low temperature region of the material is calculated using the method described below, and the auxiliary heating means E performs local heating.

Regarding the calculation of the required heat increase amount, Figure 2 (a) shows the temperature distribution in the longitudinal direction of the steel material extracted from the combustion furnace.

In Fig. 2), the steel material extracted from the combustion furnace at Vc shows the temperature increase behavior with respect to the treatment time Δt for local heating by auxiliary means and soaking until the end of induction heating. In Fig. 2(b), when the time required for local heating to compensate for the temperature difference between the high temperature region (a) and the low temperature region (b) is Δt0 (<c), the high temperature region (surface temperature) of the steel material (A) Temperature Tn [Concerning the temperature after heating in the induction heating furnace as Tn/, it is sufficient to raise the temperature in a time of (Δt - Δ1.), so the required power input is calculated using the following formula 1 formula %
) is determined.

In addition, the temperature in the high temperature range (a) while heating the low temperature range (b)! "The drop Tl (I~...) can be calculated from 'T□ (I~7,)=f (slab thickness t, atmospheric temperature θ, slab surface temperature θ8...).

Here, the cylinder 1 temperature range (
If the allowable temperature difference between E) and the low humidity region (E) is Δθ2, then the temperature T after local heating in the low temperature region 5 (B) is calculated from the amount of heat raised by the input power Q to reach the high temperature region (E). is determined. Therefore, the surface temperature T of the local low temperature area (b) immediately after extraction from the combustion furnace increases by Δθ8, and after extraction from the induction heating furnace...Δθ
, it is sufficient to raise the temperature within the time period Δt□. Although there are no particular restrictions on Δt0, it is desirable to set it to a value as small as possible in order to achieve the intended purpose.

Here, the input power Q to raise the temperature by Δθ8 is determined as follows.

・In the case of fc using an induction coil, f(Δ1. plate thickness t, dissipated heat R1 physical properties, temperature difference Δθ8.・
...)・When using direct flame f(Δt0. Plate thickness t, physical properties, flame temperature, temperature difference Δθ
8...) The reason why an induction heating coil is used as the auxiliary heating means E in Figure 1 is because when temperature unevenness occurs as shown in Figure 2 (a) above, it can be used to heat only that part. This is because it is convenient. That is, as shown in FIG. 8, the coils are arranged in the longitudinal direction of the steel material So, S2. The coil is divided into sections like s8...sn, and the coil corresponding to the local low temperature region (b) is selectively used.

In addition, the auxiliary heating means E can heat one local area Hiko combustion 2...°
A burner may be used. In this case, as shown in FIG. 4, the nozzle N serves as a combustion burner with fuel gas G and zero oxygen.
Alternatively, air is supplied and appropriate heating is applied to the location corresponding to the skid portion. Furthermore, such a heat treatment can be carried out at any time after extraction from the combustion furnace and temperature measurement, so the auxiliary heating means E does not necessarily have to be arranged independently of the induction heating furnace. That is, in the induction heating furnace shown in FIG. Local heating may be carried out in combination with heating.

However, in the case of Fig. 5, there is a disadvantage that the position where local heating is possible in the width direction of the steel material is limited. This can be easily solved by selecting according to the situation where the coldest point occurs.

(Function) Here, Fig. 6 shows the trend of the surface temperature of steel materials in two longitudinal directions when high-temperature heating of steel materials, especially when a combustion furnace and an induction heating furnace are used together. The state immediately after extraction from the induction heating furnace is shown in the lower and upper rows. Due to so-called uneven heating, a temperature difference Δθ occurs between the high temperature region (a) and the local low temperature region (b) on the surface of the steel material when it is extracted from the combustion furnace. Therefore, the temperature difference Δθ is hardly eliminated even after extraction through temperature raising in an induction heating furnace. In contrast, in this invention, after understanding the above trends through actual measurements, we
Then, local heating is applied to reduce the temperature difference to the allowable l···temperature difference (Δθ5), as shown in (b)′ in the lower part of Figure 7.
The temperature rise is controlled and then induction heating is applied to uniformly heat the steel material. Here, the temperature can be soaked and raised to a predetermined high temperature K within an allowable temperature difference Δθ' in a short time using an induction heating furnace.

(Example) Fig. 8 illustrates an example of a specific application of the method for controlling the soaking temperature increase of steel materials according to the present invention. Changes in temperature (a),
In addition, the transitions of the local low-temperature region (b) are shown separately using broken lines.

In this example, the temperature range (a) corresponds to the skid middle part, and the temperature range (b) corresponds to the skid contact part, and it is extracted from the combustion furnace that the difference in average temperature in the thickness direction of each plate Δt is 60°C. It was detected by measurement at the point in time. This handling takes 2 minutes and during this time each temperature range (a) (b)
In both cases, the temperature will drop slightly when left to cool.

If the average temperature in the thickness direction of the plate is increased by 25°C in the required heating time of 70 seconds by local heating using an induction heating coil in the temperature range (B)), the temperature range 1" (A)
The above temperature range was 15° C. at the completion of local heating due to the temperature drop due to cooling. In other words, the temperature range (A) decreased by 20°C, and the temperature range (A) increased by 25°C. Then, after 1 minute of handling, it is charged into an induction furnace and heated to 1260℃.
When the sample was rapidly heated to a soaking temperature of fc1□ for 80 minutes and then soaked for 5 minutes, the above temperature range was further reduced to 5 to 10°C.

In the above-mentioned embodiments, a case where soaking and holding is performed after induction heating has been described, but it goes without saying that such soaking and holding can be omitted. 1 (Effects of the Invention) According to the present invention, the influence of temperature unevenness, which is inevitable in heating in a combustion furnace, is advantageously eliminated by applying local heating prior to soaking in an induction heating furnace. Due to the particularly rapid heating to high temperatures, uniform heating is achieved with an effective shortening of the heating time required by the furnace.

[Brief explanation of the drawing]

Fig. 1 is a diagram of a soaking temperature increase control system suitable for carrying out the present invention. Fig. 2 (a) and (b) are temperature distribution diagrams in the longitudinal direction of the steel material during extraction from the combustion furnace and according to the present invention. Figure 8, Figure 4, and Figure 5 are explanatory diagrams of specific heating procedures for local temperature low temperature regions. and a graph showing the surface temperature distribution during extraction from an induction heating furnace. Figure 7 is a graph showing the temperature change due to temperature increase control according to the present invention. Figure 8 is a graph showing the temperature change when temperature increase control was performed according to the present invention. It is a figure showing the temperature history of the steel material at the time.

Claims (1)

[Scope of Claims] 1. When passing steel material sequentially through a combustion furnace and an induction heating furnace and soaking it to a predetermined temperature, the temperature distribution on the surface of the steel material is measured before charging into the induction heating furnace; From the values, calculate the input heat amount and heating time required to equalize the temperature in the local low-temperature area; Based on the obtained results, apply local heating to the low-temperature area to make the temperature distribution uniform. , followed by rapid heating using an induction heating furnace.