JP2808633B2 - Continuous casting mold and control method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a continuous casting mold and a method of controlling the mold, and more particularly to a lower structure of the mold.

(Conventional technology and its problems) A continuous casting mold usually has a length of 600 to 1200 mm, and the inner wall of the mold is made of a material having high thermal conductivity, that is, copper or a copper alloy.

When casting is performed using such a mold, the molten steel is indirectly cooled by a cooling medium (for example, water) supplied to the inside of the mold wall, and gradually solidifies from a portion in contact with the mold wall, and a solidified shell is formed. As the thickness of the solidified shell grows to a level that can withstand the hydrostatic pressure of the internal molten steel, the solidified shell shrinks, creating voids between the mold wall and the solidified shell.

In particular, in a mold having a rectangular cross section, the slab solidified shell that is in contact with the central portion of the wide surface wall of the mold is easily swelled outward due to the internal molten steel pressure and relatively easily contacts the mold wall surface,
At the end on the wide surface side of the mold and the lower portion on the side of the sandwiching surface, voids tend to be noticeable.

This void generation significantly reduces the heat transfer efficiency from the slab to the mold wall, greatly hinders the growth of the solidified shell of the slab, causes quality defects such as surface vertical cracks due to uneven thickness of the solidified shell, and furthermore, Breakout due to breakage of the solidified shell is often a major factor. This has become a major fundamental problem of continuous casting equipment at present, and is the biggest obstacle particularly toward high-speed casting.

As a mold (apparatus) and method for preventing the generation of voids between the mold wall and the solidified shell, the mold inner wall surface (plane) is empirically inclined inward by an amount corresponding to the average solidification shrinkage of the slab in the mold. A so-called multi-tapered mold and method (Japanese Patent Application Laid-Open No. Sho 53-125932) have been proposed in which a mold and a method for fixedly holding the mold, and at least two tapered steps continuous in the casting direction are provided on the inner wall of the mold. However, if only one or two or more steps of such a mold wall are fixed and a fixedly fixed inclination (taper) is applied only, it is possible to adapt to a complicated solidification shrinkage that varies depending on various factors such as casting speed, temperature, and steel type. It is extremely difficult to bring the solidified shell into contact with the inner wall surface of the mold while maintaining an appropriate contact surface pressure, resulting in voids at the lower part of the mold wall, or conversely, severe mold wall due to intermittent contact with the solidified shell. Wear tends to occur and there are many problems of peeling of the plating layer. In addition, one or both of the two pairs of opposed mold walls are formed in two or more stages in the vertical direction, and the lower walls except for the uppermost wall are connected to the moving device, respectively. A mold provided movably in a direction (Japanese Patent Laid-Open No. 56-95451)
Has also been proposed. In this mold, the lower inner wall plate having an appropriate surface pressure between the slab and the slab is slid in the front-rear direction according to the shrinkage of the slab, thereby reducing the gap between the slab and the slab. It is devised to prevent abnormal wear of the lower inner wall plate surface due to abnormal contact with the piece. However, when normally the molten steel in the mold surface addition of mold powder as a lubricant (mixture of _{CaO-SiO 2 -CaF 2 -Na 2} O as main components base powder and carbon powder), the lower mold wall and the slab The cooling effect of the lower mold and the improvement of the lubricating effect at the same time are small because the water does not flow naturally into the gap between the upper mold and the lower mold. Therefore, the wear of the lower mold wall is not significantly improved.

On the other hand, as a method of filling the space between the mold wall and the solidified shell with a heat transfer medium and strengthening the cooling of the space, graphite, potassium chloride, calcium chloride, sodium chloride, boric acid, etc. are used as a heat transfer medium in powder form or in a powder form. Rapeseed oil and the like and supplying it to the voids in the form of a paste (Japanese Unexamined Patent Publication (Kokai) No. 55-92256), and a vegetable oil (rapeseed oil) obtained by further improving the mixture of the graphite fine particles from the viewpoint of viscosity and thermal conductivity. Etc.) with fine graphite particles of 1000 mesh or less
A method of supplying a mixed solution having 15 to 25% by volume added to voids (Japanese Patent Laid-Open No. 57-154351) has also been separately proposed. However, these heat transfer medium supply methods have a problem in that the flowability is poor, so that the details of the voids, whose shape changes every moment, cannot be reached, and the effect of the heat transfer medium cannot be sufficiently increased.

The present invention has been made in view of the above points. That is, the present invention prevents the mold cooling ability from decreasing due to the voids formed at the wide end of the mold side and the lower part on the sandwiching side, promotes and uniforms the formation of a solidified shell, or prevents excessive wear of the mold wall by improving lubrication. It is intended for.

(Means for Solving the Problems) In order to achieve the above object, a continuous casting mold according to the present invention is a continuous casting assembly mold having a rectangular cross section, which comprises one or both of two opposite pairs of mold walls. While forming the mold wall in two or more steps in the slab casting direction,
The downstream mold wall excluding the most upstream mold wall is divided into a plurality of cooling water guide plates in the slab width direction, and the respective cooling guide plates constituting the pair of downstream mold walls can be moved toward and away from each other. It is composed.

Further, a water supply port array and a drain port array are provided alternately on opposing surfaces of a cooling water guide plate forming a pair, which is a component of a continuous casting mold having such a configuration, and the pressures of these water supply system and drainage system are detected, In order to make the water film thickness formed between the slab and the downstream mold wall based on the detected value and the cooling water flow rate uniform in the slab width direction, the contact / separation movement of the cooling water guide plates forming the pair. Control is to be performed.

In the mold of the present invention, the downstream mold is configured to be divided in the slab width direction by using a plurality of cooling water guide plates, because the solidified shell is expanded only at the center of the wide surface, and by dividing the central part, In order to keep the gap at the end constant,
This is because when a wide cooling water guide plate is used, distortion due to thermal deformation is large, and it is impossible to equalize the gap.

In the method of controlling a mold in the present invention, the water film thickness formed between the slab and the downstream mold wall, which is uniform in the slab width direction, and the cooling water flow velocity value are not limited at all. According to our research and experiments, the water film thickness is 0.2 ~
3.0mm, if the cooling water flow rate is set in the range of 6-40m / S,
The downstream mold can have two functions of strong cooling by a high-speed water film and forced lubrication.

(Operation) According to the present invention having the above-described configuration, since the cooling guide plates constituting the downstream mold can be respectively moved, the interval between the slab and the mold wall can be controlled to be uniform in the slab width direction. .

(Examples) Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention, and shows an assembly structure in which a continuous casting mold is divided into an upstream mold 1 and a downstream mold 2 in two. Incidentally, the upstream mold 1 is usually provided with a tapered mold wall, or an opposed mold wall 2.
It has a pair of parallel mold walls. On the other hand, the downstream mold 2 is composed of, for example, a plurality of cooling water guide plates 3 having a shape similar to a strip shape shown in FIG. 2A or a turtle shape shown in FIG. Link to device 8
And the pair of mold walls can be moved toward and away from each other. In FIG. 1, reference numeral 9 denotes a spring.

FIG. 2 shows a cooling water guide plate 3 constituting the downstream mold 2 wall.
The cooling water guide plate 3 is provided with five rows of water inlets and six rows of drains alternately, and the pressure is detected by a pressure detector 7 provided in the water supply part and the drainage part. Each cooling water guide plate 3 is controlled by the cylinder 4 in accordance with the detected value.
To be able to move.

In order to prevent the cooling water from being blown up in the direction of the upstream mold 1, it is preferable that the uppermost row of the cooling water guide plates 3 is a drain port.

In addition, by forming at least one of the water supply port 5 and the drain port 6 as a slit-shaped long hole as shown in FIG. 2 (a), the water film formed between the slab 10 and the cooling water guide plate 3 is formed. A uniform flow of cooling water can be realized.

By the way, FIG. 3 measures the casting direction distribution of the overall heat transfer coefficient between the mold cooling water and the slab surface in the case of a normal mold,
It is illustrated. From this distribution, voids are likely to be generated below the mold meniscus by about 100 to 300 mm or more, and the length of the most upstream mold is 100 to 300 mm below the meniscus.
mm is effective, and the average overall heat transfer coefficient is 1000 kcal to increase the thickness of the solidified shell of the slab.
It can be seen that a downstream mold cooling capacity of at least / m ² · hr · ° C is required. Various attempts have been made to improve this, such as increasing the cooling water of the mold or increasing the pressure of the cooling water. However, there is a limit due to the formation of the voids. Therefore, the present inventors came up with the use of a high-speed water film, and as a result of intensive research, configured the mold as described above, and the water film thickness formed between the mold wall and the slab was 0.2 to 3.0 mm, If the average flow velocity of the cooling water is set in the range of 6 to 40 m / S, the fluctuation of the thickness of the water film is prevented, the thickness accuracy in the mold width direction is secured, and the enhanced cooling and forced lubrication can be performed more effectively. I found that. Hereinafter, the water film conditions will be described in detail.

The average flow velocity of the cooling water flowing out from the water supply port 5 of the cooling water guide plate 3 shown in FIG. 2 (b) is controlled to 8m / S, measured the average water layer thickness during casting, the variation width .DELTA..delta _W The results obtained are shown in FIG. As can be seen from the figure, when the average water film thickness during casting becomes 3.0 mm or more and 0.2 mm or less, the fluctuation width Δδ of the water film increases.

As the reason, it is estimated that when the average water film thickness becomes 0.2 mm or less, a local water film break occurs, the cooling water guide plate 3 is further thermally deformed, and the fluctuation width Δδ of the water film increases. Is done. In addition, the thickness deviation Δd of the cast slab solidified shell is also shown in FIG.
It shows the same tendency as δ, and it is preferable to set the average water film thickness in the range of 0.2 to 3.0 mm in order to make the thickness of the solidified shell uniform. Although not shown, the tendency shown in FIG. 4 was the same when the cooling water flow rate was changed within the range of 6 to 40 m / S.

Next, the average water film thickness was set to 0.5 mm, and the average flow rate of the cooling water was changed in the range of 1 to 100 m / S. Shown in the figure.
As can be seen from the figure, if the average flow velocity of the cooling water is less than 6 m / S, the water temperature of the water film rises, causing bubbles to be generated, and the cooling capacity becomes insufficient. In addition, even if the average flow velocity of the cooling water is 40 m / S or more, the heat transfer coefficient does not increase so much, and the equipment becomes large to flow a large amount of the cooling water, so the average flow velocity of the cooling water is 6 to 40 m / S. It is preferable to be in the range of S. The above tendency was the same when the average film thickness of the water film was changed in the range of 0.2 to 3.0 mm.

Next, the results of experiments performed to confirm the effects of the present invention will be described.

A 50-ton low-carbon aluminum killed steel was cast under a casting condition of 4 m / min using a continuous casting machine equipped with a two-stage continuous casting mold shown in FIG. 1 to produce a slab having a thickness of 105 mm and a width of 1050 mm. . The length of the upstream mold used at this time was 350 mm (250 mm below the meniscus), and the downstream mold had a strip-shaped cooling water guide plate (width: 100 mm, length: 5 mm) shown in FIG.
22 pieces (50 mm) (2 pieces on the wide side of the mold and 1 piece on the side between the molds) × 2}. Details of the water supply port and drain port of the cooling water guide plate are as follows.

Water inlet: 1.5mm high x 12mm wide Drain outlet: 2.2mm high x 12mm wide Spacing between water inlet and drain: 2mm Horizontal pitch between water inlet and drain: 14mm With water inlet and drain rows Interval: 50 mm During casting, the average water film thickness of the water film was maintained at 0.5 mm, and casting was performed with the cooling water flow rate in the range of 10 to 15 m / S.

As a result, the thickness of the solidified shell was ensured even at a casting speed of 4 m / min, and there was no wear on the downstream mold wall and no increase in frictional force.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent the mold cooling ability from being deteriorated due to the voids formed at the end of the mold on the wide surface side and the lower portion of the sandwiched surface, and to promote and uniformize the formation of the solidified shell. The improved lubrication prevents severe wear of the mold wall. That is, high-speed casting of 4 m / min or more can be stably performed.

[Brief description of the drawings]

FIG. 1 is a drawing showing an embodiment of the mold of the present invention, FIG. 2 is an explanatory view of a cooling water guide plate, (a) is a front view showing the first embodiment, and (b) is a second embodiment. Front view showing the main part of
(C) is a cross-sectional side view, FIG. 3 is a drawing showing the distribution of the overall heat transfer coefficient between the mold cooling water and the slab surface in the casting direction, and FIG. 4 is an average water film thickness and water film. Thickness variation Δδ
FIG. 5 is a graph showing the relationship between the thickness deviation Δd of the slab solidified shell and the fifth example.
The figure shows the relationship between the average cooling water flow velocity and the overall heat transfer coefficient between the mold cooling water and the slab surface. 1 is an upstream mold, 2 is a downstream mold, 3 is a cooling water guide plate, 4 is a cylinder, 5 is a water supply port, 6 is a drain port, and 7 is a pressure detector.

Continuation of front page (56) References JP-A-47-16331 (JP, A) JP-A-63-26246 (JP, A) JP-B-46-3922 (JP, B1) (58) Fields investigated (Int) .Cl. ⁶ , DB name) B22D 11/04 B22D 11/124

Claims (2)

(57) [Claims] In a continuous casting assembly mold having a rectangular cross section, one or both of two opposing mold walls are formed in two or more steps in a slab casting direction. The downstream mold wall excluding the upstream mold wall is divided into a plurality of cooling water guide plates in the slab width direction, and the respective cooling guide plates constituting the pair of downstream mold walls can be moved toward and away from each other. A mold for continuous casting, characterized in that it is constituted. 2. A cooling water guide plate comprising a pair of cooling water guide plates constituting a continuous casting mold according to claim 1. , And based on the detected value, the water film thickness formed between the slab and the downstream mold wall, and the respective cooling water guide plates forming the pair to make the cooling water flow velocity uniform in the slab width direction. A method for controlling a casting mold for continuous casting, comprising: