JPH0747199B2 - Continuous casting method and its mold - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous casting method and a continuous casting mold capable of automatically controlling the taper amount, casting speed and slab width changing speed of a short side mold in continuous casting. is there.

<Conventional technology and its problems> In continuous casting, the molten steel after converter blowing is subjected to deoxidation, component adjustment, vacuum degassing, etc., and then transferred by a ladle to allow continuous casting equipment It is poured into the mold at a predetermined flow rate and then poured into the mold at a predetermined flow rate from this tundish with a dipping nozzle, and is primarily cooled by a mold having a cooling capacity to form a thin solidified shell and at a predetermined casting speed (drawing speed). ), And secondarily cooled by a spray zone to completely solidify to obtain a slab.

Here, the mold is a copper or copper alloy having good thermal conductivity on the surface in contact with molten steel, and in some cases, the contact surface of molten steel with Ni plating is used for the purpose of extending the life. There is.

Further, such a mold is provided with a cooling (water cooling) means on the outside, and further, an assembly mold in which two long-side molds and two short-side molds are assembled to form a box-shaped mold is often used. In such an assembled mold, two short side molds are movable so that a single mold can cast slabs of various widths.

On the other hand, the molten steel poured into the mold forms a thin solidified shell on the surface, but is accompanied by volume contraction during solidification, which causes a gap (air gear trap) between the side wall of the mold 4 and the solidified shell. This gap affects the formation of the solidified layer in the secondary cooling zone after the mold, and in some cases, causes the surface defect.

Further, when the thin solidified shell cannot withstand the static pressure of the molten steel, it may cause breakout (the shell breaks and the molten steel leaks), resulting in a decrease in yield.

Therefore, the state of contact between the mold and the molten steel during solidification or the state of support of the molten steel by the mold is important.

In order to cope with this, what is usually done is to use a taper mold in which the size below the mold is smaller than the size above the mold, and to adjust the taper amount to match the solidification shrinkage amount of the molten steel.

In addition to this, as means for improving the contact state between the mold and the molten steel during solidification, oscillation, that is, vibrating the mold to reduce friction seizure with molten steel during solidification, for lubrication between the mold and molten steel There is powder input.

On the other hand, as one of the measures for carrying out a multiple casting operation for the purpose of improving the production efficiency, there is a width change during casting. This is to widen or narrow the shorter side of the mold while pouring molten steel into the mold.

Then, in this case, the short side taper must be changed by moving the short side mold, but conventionally, what is practiced is to change the taper after moving the short side mold, or to change the short side mold. Is to change the taper before moving.

Here, matters to be considered regarding the width change and the taper fluctuation during the casting will be described.

It is necessary to provide a suitable short side taper according to the slab width dimension, powder type, etc., and perform width changing at an appropriate width changing speed and an appropriate casting speed. To this end, it is necessary to know the shape of molten steel in the mold during width change and the state of powder flow (contact state between molten steel and mold, etc.). Conventionally, taper, width change speed, pouring speed and mold The automatic width changing is not carried out in consideration of all the contact states between the molten steel and molten steel.For example, in order to keep the taper during the width changing constant and to give the newly set taper and width changing amount, steady casting Casting speed lower than during casting (in this case, control and reduce the amount of cooling water in the mold side wall and spray zone), and a predetermined width changing speed (contact / support state between the slab and the mold, casting speed) , A new taper and a distance between two short side mold walls (width of slab) are set by changing the width at a speed which takes into consideration the powder flow condition and the like.

Here, since the width change is performed without confirming the above-mentioned contact state, the casting speed and the width change speed during the width change are not appropriate, and further the cooling water amount is not appropriate. Therefore, various inconveniences occur during the width change.

First, if the contact is not confirmed, it causes steel leakage and breakout.

Further, the production efficiency is lowered, the heat loss and the quality are lowered due to the reduction of the casting speed (this also adversely affects the quality after changing the width when the cooling water amount exceeds the control range of the controller). If the width changing speed becomes slower than necessary, it also causes a decrease in production efficiency, heat loss and quality deterioration.

Further, it causes damage to the mold contact surface due to excessive pressing of the cast piece against the short side mold wall during width change. Next, even during the steady casting after the width change, due to unconfirmed contact, it causes leakage steel, breakout, damage to the mold, and surface defects of the slab.

Therefore, various continuous casting methods and continuous casting molds have been conventionally developed, for example, as follows.

Mold for continuous casting (JP-A-58-145343) A thermocouple covered with an insulator is embedded in the combination of the long side and the short side of the mold to predict breakout, control the level of the molten metal, and the corner of the cast slab. The temperature distribution of the mold is grasped and the life of the mold is extended in order to control the temperature of the parts, the flow of powder, and the prevention of air gear traps.

A taper amount control method for the short side of the mold in continuous casting (JP-A-58-145344) A heat flux meter is installed on the side wall of the short side of the mold, and the inner wall of the mold and the molten steel in the mold accompanying solidification shrinkage of the molten steel in the mold In order to prevent the gap between the two, the heat flow rate according to the heat removal amount of the short side of the mold is measured, and the taper amount is controlled by this.

Method of changing slab width in continuous casting (JP-A-59-7315)
No. 4) When changing the width during casting, the parallel movement speed (short side width changing speed) and taper changing speed are specified to prevent breakout.

High-speed continuous casting method for steel (JP-A-57-202948) When changing the width during casting, the casting speed and width changing speed (short side moving speed) are specified to prevent breakout.

In the case of, the temperature is detected by a thermocouple embedded in the mold copper plate, and the heat conduction of the copper plate is very good. The temperature at which the slab and the copper plate contacted at a considerable distance (100-200 mm) from the pair did not differ much, and it was very difficult to judge that the slab contacted or did not contact the copper plate.

Therefore, when the movement of the short side taper change, which is a response to non-contact, is delayed, and the contact between the slab shell, which is the best taper (soft touch with the slab shell), and the copper plate is in a delicate state. There is a problem that is difficult to control in practice.

In the case of ,, only the correlation between the width changing speed and the taper changing speed or the casting speed and the width changing speed is specified, and the automatic control is not performed according to the actual state.

This invention was proposed in view of such circumstances, and its purpose is to maintain a proper contact state with the casting mold shell during steady casting and width change, so that the short side mold taper and Continuous casting with automatic control of pouring speed and width changing speed to prevent breakout and steel leakage, improve width changing speed and pouring speed during width changing, and reduce mold wear and cost. To provide a method and a template thereof.

<Means for Solving Problems> The continuous casting method according to the present invention, the contact state between the cast piece in the mold during casting and the inner wall surface of the short side mold, the cast piece in the mold and the short side mold inner wall surface. Detected by the detecting means for detecting by conduction / non-conduction with, input into the control system for controlling the casting operation in the mold, and the detection result and the pouring instruction information inputted prior to the control system. Based on the comparison calculation result with the casting instruction information that was input afterwards, during the steady casting and during the short side mold width change, the short side mold inner wall and the in-mold slab are kept in contact with each other. The taper amount of the short side mold is changed, or the taper amount of the short side mold is changed by changing the casting instruction information, and the casting speed is changed according to the fluctuation amount of the taper amount, and the short side mold width is being changed. If the pouring instruction information is changed to By changing the slab width changing speed while changing the taper amount of the mold, it is possible to perform casting while maintaining the proper contact state of the slab shell with the short side mold during casting and during width changing. .

Next, the continuous casting mold according to the present invention is connected to the upper and lower sides of the short side mold, respectively, and the upper side drive mechanism and the lower part capable of advancing and retracting the short side mold with respect to the in-mold slab and adjusting the taper amount thereof. It has a drive mechanism and a current-carrying (electrode plate) sensor embedded in the short-side mold so that the tip of the short-side mold can come into contact with the surface of the mold inside the mold, and the conduction between the mold inside the mold and the short-side mold inner wall. A comparatively equipped with a detection mechanism capable of detecting the non-conduction, and a control mechanism for controlling the upper drive mechanism, the lower drive mechanism and the pouring speed adjusting mechanism based on the output signal from this detection mechanism and the pouring instruction information, This is a simple configuration that enables automatic control with a highly reliable system configuration.

<Example> Hereinafter, the present invention will be described based on an illustrated example.

As shown in FIG. 1, a continuous casting mold 1 according to the present invention
Is provided with an upper drive mechanism 2, a lower drive mechanism 3, a detection mechanism 4, and a control mechanism 5.

The upper drive mechanism 2 and the lower drive mechanism 3 are connected to the upper part and the lower part of the short-side mold 1A, respectively, so that the short-side mold 1A can be moved forward and backward with respect to the in-mold casting side S and the taper amount thereof can be adjusted. ing.

The drive mechanisms 2 and 3 are composed of, for example, a motor 6 and a drive shaft 7.

A large number of detection mechanisms 4 are provided in the short side mold 1A, and the tip surface is flush with the surface of the copper plate 1B, and an electrode plate sensor 8 that can contact the surface of the casting side S in the mold, a power supply 9, an ammeter 10 and an alarm Wiring 12 that has 11 and connects the electrode plate sensor 8 and the upper end of the copper plate 1B
Consists of.

The detection mechanism 4A in which the electrode plate sensor 8A is embedded in the upper part of the copper plate 1B via the insulator is used for molten steel overflow, and the electrode plate sensors 8B and 8C are embedded in the substantially central part and the lower part of the copper plate 1B, or the electrode plate sensor 8D. Detection mechanism with the copper plate 1B attached to the bottom surface
4B, 4C or 4D is for detecting contact / non-contact between the cast piece in the mold and the inner wall of the short piece mold.

The output of the ammeter 10 is input to the control mechanism 5.

The control mechanism 5 has a microcomputer MC and has a drive mechanism.
The mold position information from the position detectors 13 and 14 of the position 2 and 3 is the position converter.
Input via 15,16. Further, the casting instruction information 17 and the short side mold taper dimension setting value 18 by the instruction of the main computer are input.

From the microcomputer MC, the upper drive controller 19, the lower drive controller 20, the pouring speed controller 21, the contact abnormality alarm 22,
Output to the short side mold taper display 23, casting speed controller 21
Drives the pinch roll driving device 24.

In the above-described configuration, the contact state is detected, and based on the detection result, the casting instruction information that was input in advance and the casting instruction information that was input afterward, the short side mold taper amount during casting , Automatic control of casting speed and slab width changing speed.

The detection pitch of the detection mechanism is And

Next, these control amounts will be described.

Short piece mold taper amount This is the best taper when the inner wall of the mold and the slab are in the soft touch state.The factors that cause the taper amount to change are the molten steel temperature, the type and amount of powder, the slab width, the casting speed, and the molten metal level inside the mold Levels (which also vary with injection rate, casting speed, slab width and thickness, width change rate).

Therefore, when the taper amount is small, non-contact between the inner wall of the mold and the slab leads to non-uniform shell due to insufficient cooling and steel breakout.

When the taper amount is large, the cast shell becomes non-uniform due to breakout due to increased cast pull resistance, mold wear, and abnormal vibration of the mold.

Casting speed This is the speed at which the slab is pulled out from the mold, but if it is too large, it causes internal defects (cracks and segregation) in the slab, fluctuations in the width of the slab, breakout, and surface defects. If it is too small, it will cause seizure in the mold and decrease in production efficiency.

Width change speed This is because the wall of the short piece mold is narrowed as the width of the slab changes.
It is the moving speed when expanding, but for example, when changing from wide to narrow, if it is too large, it does not follow breakout due to increase in slab drawing resistance, steel leakage, mold wear, oscillation, which causes surface defects. .

If it is too small, it will cause seizure in the mold and decrease in production efficiency. In particular, the casting speed during width change is important. in this case,
The casting speed is made lower than the casting speed during steady casting.

Next, the control method will be described in detail.

A taper amount T ₁ is given to the microcomputer MC before casting. Therefore, the taper amount at this time is However, h ₁ : Upper drive point height h ₂ : Lower drive point height Wp ₁ : Upper drive point width direction position Wp ₂ : Lower drive point width direction position, and the taper amount of the other short side mold also differs Can be expressed in the same way. Note that one of the short-side molds will be described below.

When the taper amount T ₁ is given, the microcomputer MC calculates the difference | T ₁ −T ₀ | = | ΔT ₁ | from the previously set taper amount T _0, and drives it via the controllers 19 and 20. The taper amount T ₁ is displayed on the display 23 while the mechanisms 2 and 3 are driven.

Here, for example, when ΔT ₁ is positive, the lower part of the short-side mold 1A is advanced, and when ΔT ₁ is negative, the upper part is advanced.

The mold moving time is Becomes

However, R: Number of rotations of the motor 6 (rpm) i: Reduction ratio when the drive shaft rotates via the transmission mechanism due to rotation of the motor S: Pitch of drive shaft (mm) Furthermore, Wp ₁ and Wp ₂ are Detected by the position detectors 13 and 14, converted into output signals by the position converters 15 and 16 and input to the microcomputer MC.

Before pouring, pouring instruction information 17 is given to the microcomputer MC. This information 17 includes the slab width, the slab thickness, the molten steel temperature, the molten steel component, the molten steel injection amount, the molten metal level, the casting speed, the mold cooling water amount, the powder type, the powder amount, and the mold oscillating amount.

The casting is started, that is, molten steel is poured into the mold from a tandem (not shown) above the mold.

Therefore, the taper amount at this time is T ₁ , the casting speed is V _c1 , and the pinch roll (not shown) rotation speed is P ₁ .

During the casting, the detection mechanisms 4A to 4D detect the contact state between the slab and the inner wall of the mold, and give it to the microcomputer MC.

As a result, in the case of non-contact, since no current flows, an abnormality alarm is issued by a signal from the microcomputer MC.

Further, according to the result of (3), when there is no contact, the microcomputer gives a pushing amount ΔT ₂ (a constant value in the microcomputer).
Similar to, the taper fluctuates to T ₂ . (T ₁ <T ₂ ) If non-contact is not resolved, repeat this.

Next, since the taper became T ₂ , the casting speed V _c1
To V _c2 (V _c1 > V _c2 ). This is ΔT from the microcomputer
₂ is given to the controller 21 and the rotational speed P ₁ of the pinch roll is changed to P ₂ (P ₁ > P ₂ ), but the taper fluctuation amount (eg ΔT ₂ ) and the pinch roll are calculated in advance by a calculation formula. obtained relation between the standard rotational speed P ₀ of previously determined constants kp, executes _{ΔT 2 = P / kp P 2} = P o + ΔT 2.

Next, during casting, new casting instruction information 17 'is input. As a result, the taper T ₂ changes and becomes T ₃ .

The amount of taper variation | ΔT ₃ | is calculated by multiplying the difference between each piece of information 17 and 17 'by a constant k determined in advance.

Hereinafter, the same as the above is repeated.

As described above, the taper amount and the casting speed are automatically controlled by the contact state between the inner wall of the mold and the slab and the fluctuation of the casting instruction information during the steady casting.

Next, changing the width of the slab during casting will be described.

In FIG. 1, it is decided to change the upper width of the slab from W ₁ to W ₃ and the lower width from W ₂ to W ₄ .

Previously obtained relationship between the motor rotational speed R and the width exchange rate V _w, previously determined constant kw.

Next, the width change of both short piece molds is started at a speed V _w .

Then, as with the rotational speed of the pinch rolls from P ₃
Change to P ₄ and change casting speed from V _c3 to V _c4 . (P _3>
P ₄ , V _c3 > V _c4 ) That is, And | ΔT ₄ | = | P ₀ / kp ′ | P ₄ = P ₀ + | ΔT ₄ |.

Since the casting speed is changed from V _c3 to V _c4 , the casting instruction information changes to 17 ″, and the same operation is performed to change the taper from T ₃ to T ₄ (T ₃ <T ₄ ).

 Further, during the width change, the above items 1 to 3 are continuously performed.

From the above, the slab width change during casting can be performed while checking the contact status, so there is no need to reduce the width change speed (constant),
The taper amount and the casting speed during the width change of the slab are automatically controlled.

Next, a case where the width changing speed during changing the width of the cast piece during casting is changed will be described.

While changing the width at the width changing speed V _m , the casting instruction information was changed to 17, so the same change calculation as above was performed, and the casting speed was changed from V _c4 to V _c5 and the pinch roll speed was set to P. ₅ to P
Change to ₆ and taper from T ₄ to T ₅ .

The width change speed variation amount | ΔV _m | is also calculated by the comparison calculation as described above.

Change V _m to V _m ′ by | ΔV _m |.

From the above, the taper amount, the casting speed and the width changing speed are automatically controlled while maintaining the correlation.

<Specific Examples> Inventive Method Components (0.06% C, 0.2% Si, 0.3% Mn, 0.015% P, 0.01% S)
Slab size 220mm (thickness) × 1200m at casting temperature 1570 ℃
m (width), short side mold taper 4.2mm (taper) / 750mm on one side
(Short piece mold height) During casting at a casting speed of 1.4 m / min, the width change to change the slab width to 1300 mm was performed for 3 minutes at a short piece mold moving speed of 35 mm / min, and the taper (4.6 mm / 750 mm) simultaneously changed. The casting speed at this time was reduced to 1.0 m / min. The detection mechanism was arranged as shown in FIG.

Comparative method composition (0.05% C, 0.2% Si, 0.2% Mn, 0.020% P, 0.015% S)
Steel at a casting temperature of 1570 ℃, slab dimensions 220mm × 1200mm, taper (4.2mm / 750mm), casting speed 1.4mm / min. During casting, changing the slab width to 1300mm changes the mold moving speed 18mm / min. For 8 minutes. In this case, unlike the method of the present invention, the taper (4.6 mm / 750 m
changed to m). The casting speed at this time was reduced to 0.6 m / min.
No contact between the inner wall of the short side mold and the slab was detected during steady casting and width change.

From the results of the above, the method of the present invention, while confirming the contact state between the slab and the mold inner wall during width changing, can perform width changing and taper change at the same time, and increase the width changing speed and casting speed. As a result, it has become clear that the following effects occur.

(A) Steel leaks, breakouts, and defective slabs are eliminated,
Yield can be improved.

(B) Since the good taper, the amount of cooling water, and the casting speed are appropriate, the quality of the cast piece is improved.

(C) Since the casting speed and the width changing speed can be increased, the productivity is improved.

(D) Since the casting speed and the width changing speed can be increased, the heat loss of the slab can be prevented.

(E) Wear of the mold can be reduced.

Furthermore, the above-mentioned effects can be expected even during steady casting.

In addition, in the above-mentioned Example, only one charge was compared,
In the comparative method that does not detect the contact state, breakout and steel leakage are inevitable if a few charges are carried out.

<Effects of the Invention> As described above, according to the continuous casting method of the present invention, the contact state between the molten steel in the mold and the inner wall of the mold during solidification is detected using a detector, and steady casting due to fluctuations in casting conditions is performed. The short side mold taper during medium and width changing and automatic control of the casting speed and width changing speed can prevent steel leaks, breakouts, defective slabs, and the width changing speed and casting during width changing. The speed can be improved. As a result, yield improvement, quality improvement, productivity improvement, and heat loss prevention can be achieved. Further, the wear of the mold is reduced, and the cost can be reduced.

Further, the continuous casting mold according to the present invention exhibits the above-mentioned effects with a relatively simple structure.

[Brief description of drawings]

1 and 2 are an overall schematic view showing a continuous casting mold according to the present invention, a perspective view, FIG. 3 and FIG. 4 are a partial sectional schematic view and a schematic view showing a detection mechanism. 1 ... Continuous casting mold, 1A, 1B ... Short side mold, 2 ... Upper drive mechanism, 3 ... Lower drive mechanism, 4,4A, 4B, 4C, 4D ... Detection mechanism, 5 ... Control mechanism, 6 ... motor, 7 ... driving shaft, 8,8A, 8B, 8C, 8D ... electrode plate sensor, 9 ... power supply, 1
0 …… ammeter, 11 …… alarm, 12 …… wiring, 13,14 …… position detector, 15,16 …… position converter, 17 …… casting instruction information, 18 …… short side mold taper dimension Set value, 19 ... Upper drive controller, 20 ... Lower drive controller, 21 ... Pouring speed controller, 22 ... Contact abnormality alarm, 23 ... Short side mold taper display, 24 ... Pinch Roll drive device.

Claims (2)

[Claims] 1. A continuous casting method using a continuous casting mold in which the short side mold is movable, in which the contact state between the cast piece in the mold and the short side mold inner wall surface during casting is Detected by the detection means for detecting by conduction / non-conduction with the inner wall surface of the mold, input into the control system that controls the casting operation in the mold, and the detection result and the casting that is input prior to the control system. Based on the comparison calculation result of the instruction information and the casting instruction information that was input afterwards, the inner wall of the short side mold and the in-mold slab maintain contact with each other during steady casting and during changing of the short side mold width. To change the taper amount of the short side mold, or to change the taper amount of the short side mold by changing the casting instruction information, and change the casting speed according to the amount of change in the taper amount If the pouring instruction information is changed during the replacement, the pouring speed And a continuous casting method, characterized in that the slab width changing speed is changed while changing the taper amount of the short side mold. 2. A continuous casting mold in which a short side mold is movable, which are respectively connected to the upper and lower sides of the short side mold and which can move the short side mold forward and backward with respect to a cast piece in the mold and its taper amount. An upper drive mechanism and a lower drive mechanism that can be adjusted, and has an energization sensor that is embedded in the short side mold so that the tip can contact the surface of the in-mold slab, and the in-mold slab and the short side A detection mechanism that can detect conduction / non-conduction with the inner wall of the mold, and a control mechanism that controls the upper drive mechanism, the lower drive mechanism, and the pouring speed adjustment mechanism based on the output signal from this detection mechanism and the pouring instruction information. A continuous casting mold comprising: