JPH0489114A - Heating method in time of joining billets - Google Patents

Abstract

PURPOSE:To securely elevate the temperature to a target value in time of a quick heating based on an induction heating system by calculating a time to reach the target and heattreating billets based on the resultant value. CONSTITUTION:The rear end part of a preceding sheet bar 1-a and the front end part of a succeeding sheet bar 1-b are cut by a drum shear 5, both end parts are abutted on each other, then, heating is begun by an induction coil. A temperature-up curve to the target temperature is estimated by an initial temperature and a temperature-up speed of the billet, a time to reach the target temperature is calculated by this measured curve and heating is conducted based on this calculated result. When heating, however, is stopped after (t) sec. overheating may be generated by the time lag of the control system. In this way, such time lag is considered and when the time lag is tL, heating is stopped after (t-tL) and a temperature can be elevated up to the target temperature.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a heating method when joining steel pieces, and in particular, enables accurate heating to a target temperature in short-time rapid heating using an induction heating method. It's something that I'm trying to get used to.

(Prior art) Conventionally, when hot rolling steel billets, the steel billets extracted from the heating furnace were rolled one by one, but with such a method, there were the following problems: a) poor biting of the tip of the steel billet; b) ) Reduction of the rear end of the billet, c) Problems with running the tip of the billet on the runout table, and d) Dimensional defects at the tip and rear end of the billet. A continuous rolling method is being adopted in which the rear end of the preceding steel billet and the tip end of the trailing steel billet are sequentially joined together and then subjected to finish rolling on the inlet conveyance line.

Along with this, various methods for joining steel pieces have been developed, and among them, for example, the induction heating pressure welding method disclosed in Japanese Patent Application Laid-Open No. 60-244401 has been reported as a method that can complete joining in a relatively short time. There is.

In this method, as shown in FIG. 6, a solenoid type coil S is used as a heating means, and a preceding steel piece 1. After rapidly heating the joint between the rear end of -a and the tip of trailing steel piece 1-b,
Both leading and trailing steel pieces are joined by pressing both ends.

(Problem to be solved by the invention) When joining steel pieces, it is necessary to heat the joint part from 1250°C to a weldable temperature range just below the melting point, but the joining temperature should be set in a high temperature range near the upper limit. is advantageous. This is because the higher the temperature, the softer the steel pieces become, making it easier to join them by pressing. However, when the heating temperature exceeds the melting point, as shown in Figure 7, part of the joint melts and a gap is created in the joint, resulting in a uniform joint force in the width direction of the plates and a good joint surface. Therefore, it is important that the heating temperature does not exceed the melting point of the steel billet.

However, when heating is performed by setting the target temperature just below the melting point using the induction heating method described above, if the heating is stopped when the value measured by the thermometer reaches the target temperature, the heating temperature will increase due to the delay in the control system. may exceed the melting point. In other words, because the induction heating method is rapid heating,
Even a slight time lag in the control system could cause overheating.

The present invention advantageously solves the above-mentioned problems, and aims to propose a heating method that can accurately raise the temperature to a target temperature even during rapid heating using an induction heating method.

(Means for Solving the Problems) The present invention abuts the rear end of a preceding steel billet against the tip end of a trailing steel billet on the entry side of a hot finishing rolling mill, and then uses an induction heating method to In the method of joining the two by heating and pressing, when heating the butt part to the target temperature, it is necessary to predict the temperature rise curve from the initial temperature and temperature rise rate of the billet to the target temperature, and to reduce the delay in the control system. This is a heating method for joining steel billets, which involves calculating the time required to reach the target temperature, taking into account the time lag caused by the above, and performing heat treatment based on the obtained value.

This invention will be specifically explained below.

FIG. 1 schematically shows an inlet conveyance line of a finishing rolling mill incorporating a suitable joining device for carrying out the present invention.

In the figure, numbers 1-a and 1-b are respectively a leading steel piece and a trailing steel piece, 2 is a coil box, 3-a, 3-b and 3-
C is a pinch roll, 4 is a leveler, 5 is a cutting device, and 6 is a joining device. The figure shows an example in which the welding apparatus 6 performs the heating and welding process in synchronization with the running of the steel billet l, but in contrast, the heating and welding process is performed with the welding apparatus 6 stopped. In this case, the looper indicated by the broken line 7 will be used. Further, 8' is an FSB (descaler), and 9 is the first stand of the finishing mill.

In this invention, the induction heating method is not only the solenoid method as shown in FIG. It may be a method.

When an alternating magnetic field d is applied to the central region of the abutting part a of the leading and trailing steel pieces using the transverse method shown in Fig. 2, a vortex as shown in Fig. 3 is generated at the abutting part a. A current e will be induced to preferentially heat the butt contact area. In the diagram, number 10 is steel piece 1
This is an alternating magnetic field generating coil that is passed through the plate in the thickness direction to generate an alternating magnetic field, and this alternating magnetic field generating coil 10 is as follows:
A pair of cores 10-a installed with steel pieces sandwiched above and below, a coil 10-b continuously wound around these cores, and a power source 1.
It consists of 0-c.

In this invention, first, the cutting device cuts the rear end of the leading steel piece and the tip of the trailing steel piece.

After the two ends are butted together, heating and pressing are performed, but when induction heating is used for this process, because the heating is rapid, even a slight time lag in the control system can cause overheating. This caused an inconvenience.

Therefore, in this invention, the temperature increase curve to the target temperature is predicted from the initial temperature and temperature increase rate of the steel billet, the time until the target temperature is reached is calculated from this predicted curve, and heating is performed based on this calculation result. It is.

(Function) The temperature rise curve can be predicted as follows, for example.

As shown in Figure 4, the target temperature is θF ("c), the initial temperature is θ+("c), the plate temperature t+(s) after the start of heating is θ2('C), and further tz(s). The plate temperature after is θ
3 (''C), the time t required to reach the target temperature after (tl+tz) has elapsed from the start of heating is expressed by the following equation.

However, A and B are expressed by the following formula.

t.

B - θ2 However, if the heating is stopped after the above t seconds, there is still a risk of overheating due to the time lag of the control system.

Therefore, in the present invention, such a time lag is taken into consideration, and if the time lag is tL, heating is stopped after (11 L), and thus the temperature can be accurately raised to the target temperature.

Above, we have explained the case where the temperature rise curve is estimated from the temperature measurement data after heating. However, according to the preset method described next, the time required to reach the target temperature can be determined without measuring the temperature as described above. can be detected.

That is, the application type crab W (W) Specific heat of the steel billet: C (J/N-g) Density of the steel billet: ρ (g/cm3) Thickness of the steel billet: D (mm), and initial temperature of the steel billet: θ+("c) Target temperature after heating: θF("C) Then, the time t to reach the target temperature is calculated by the following formula, where a
, az are expressed as constants.

It goes without saying that even in this preset method, it is necessary to take time lag into account.

This preset method has the advantage that it is only necessary to measure the initial temperature, and there is no need to measure the temperature after heating starts.

The heating and pressing treatments include: i) stopping the heating when the temperature of the part to be joined reaches the target temperature, and then pressing; ii) once the temperature of the part to be joined reaches the welding temperature; There are various methods that can be considered, such as a method in which pressing is started while heating continues (however, the melting temperature of the steel billet is not exceeded), and a method in which the steel billets are pressed together from the beginning and the contact area is heated at the same time. However, in the present invention, any method may be used, and method iii) is particularly effective.

This is because before hot finish rolling, the billet is still 1
Since the steel pieces are in a high temperature state of about 000 to 1100°C, the joining of the steel pieces will progress to some extent even with mere pressing, but if heating is applied while performing such pressing treatment, the joining will be effectively promoted. This is because it can be expected to shorten the bonding time and reduce the amount of power input required for heating.

The above-mentioned pressing process can be easily carried out using pinch rolls provided front and back to sandwich the abutting portions of the ends of the steel piece, and a pressing force of about 3 to 5 kg/mm2 is sufficient.

(Example) Example 1 Using the welding apparatus shown in FIG. 1 above, steel pieces were joined in the following manner.

The steel pieces used in the experiment were leading steel piece 1-a and trailing steel piece 1.
-b are both low carbon steel sheet bars with a thickness of 30 mm and a width of 1000 mm.

Now, the rear end of the leading sheet par 1-a and the leading end of the trailing sheet par 1-b are cut by the drum shear 5.
After the two ends were brought together, heating was started using the solenoid induction coil shown in FIG. The heating conditions at this time were as follows, and the heating time was estimated according to the method shown in FIG. 4 above.

・Injection type crab 2000 kW ・Target temperature θF; 1300°C ・First temperature measurement time: t, : 0.5s ・Second temperature measurement time t2: 1s At this time ・Initial temperature θ, : 1000°C・Plate temperature θz after t: 1040°C・Plate temperature θ after t2: 1120°C.

Therefore, from equations (2) and (3) above, A and B are respectively A=26.2 B = -1020, and therefore, from equation (1), t = 2.2.

Note that the time lag jt specific to the control system: o, 5s knee (
t −t L) = 1.7 s Therefore, the current supply was cut off 1.7 s after the second temperature measurement.

As a result, the plate temperature reached 1290''C after a few seconds, and the plate was heated to the target temperature.

(Effects of the Invention) Thus, according to the present invention, even when the induction heating method, which is rapid heating, is used as the heating method for the steel billet,
The temperature can be accurately raised to the target temperature, and there is no risk of overheating.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the inlet conveyance line of a finishing rolling mill incorporating a heating and joining device suitable for carrying out the present invention. FIG. 2 is a schematic diagram of a transverse type induction heating device. Figure 3 is a diagram showing the flow of eddy currents induced by the transverse method, Figure 4 is an explanatory diagram of how to predict a temperature rise curve based on temperature measurement data, and Figure 5 is a diagram showing the flow of eddy currents induced by the transverse method. Fig. 6 is a schematic diagram of a solenoid-type induction heating device; Fig. 7 is a diagram showing a state in which a part of the joint surface has melted due to overheating. 1-a... Leading steel piece 1-b... Trailing steel piece 2.
・・Coil box 3-a, 3-b, 3-c=・Via %D −/l
z4...Reherer-5 cutting device 6...Joining device 7...Louver 8...FS
B 9... First stand 10... Alternating magnetic field generating coil 10-a... Core 10-b... Coil 1
0-c...Power supply fO-0 core Fig. 4 Fig. 5 hU ft! 8! Between i (S) Figure 6 Figure 7 Fusion 1-11t

Claims (1)

[Claims] 1. On the entry side of a hot finishing rolling mill, the rear end of the leading steel billet and the tip end of the trailing steel billet are butted together, and then heated and pressed using an induction heating method. In the method of joining both, when heating the above butt part to the target temperature, the temperature increase curve from the initial temperature and temperature increase rate of the steel billet to the target temperature is predicted, and the time lag due to the delay of the control system is taken into account. A heating method for joining steel billets, characterized in that the time required to reach a target temperature is calculated, and heat treatment is performed based on the obtained value.