JPH02307652A - Method for controlling crown in thin continuous casting - Google Patents

Abstract

PURPOSE:To produce a thin cast billet having the objective projecting crown at good accuracy by measuring the profile of the thin cast billet sent out from drum gap and adjusting the flow rate of cooling water based on the measuring result. CONSTITUTION:The molten metal 4 poured in pouring basin part 3 is rapidly cooled and solidified on circumferential surfaces of the cooling drum 1a, 1b to make this the solidified shells and welded and integrated with the drum gap 5 and sent out as the thin cast billet 6. The thickness of the thin cast billet 6 is measured in the lateral direction to detect the profile of the thin cast billet 6. This detection result is inputted to a computing element 10, and by comparing with the reference information and operating, the flow rate of the cooling water corresponding to the crown rate of the thin cast billet 6 during production is calculated. By this calculated value, a flow rate adjusting value 13 disposed on the way of a water supplying pipe 12 for supplying the cooling water 11 is adjusted. The cooling water 11 having the flow rate adjusted in such a manner is guided into the cooling drums 1a, 1b to control the crown of the thin cast billet 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of continuously casting a thin-walled slab to make the profile of the thin-walled slab into a convex crown suitable for cold rolling.

[Conventional technology]

BACKGROUND ART Recently, a method of directly manufacturing a thin slab having a thickness of several mm, which is close to the final shape, from molten metal such as molten steel has been attracting attention. When this continuous casting method is used, there is no need for a multi-step hot rolling process unlike in the case of slabs manufactured using conventional continuous casting machines, so that the process and equipment can be simplified.

Figure 3 shows the equipment configuration of the twin-drum method, which is known as one of the continuous casting methods (Japanese Patent Application Laid-Open No. 60-137
(See Publication No. 562). In this system, a pair of cooling drums 1a, 1b rotating in opposite directions are partitioned at both ends in the axial direction of the drums by side weirs 2a and 2b.
A hot water reservoir 3 is formed. By injecting the molten metal 4 into this sump 3 and removing heat from the molten metal 4 through the cooling drums la, lb, the respective cooling drums la,
A solidified shell is formed around the periphery of lb. The solidified shell is
Cooling drum la while growing.

As the drums 1 and b rotate, the drum gap shifts to the drum gap 5.

The solidified shells formed on the surfaces of the respective cooling drums 1a, 1b are pressed and integrated in the drum gap 5, and are carried out as a thin slab 6 from between the cooling drums 1a, 1b.

The thin slab 6 is directly sent to a cold rolling process and rolled to a predetermined size. In order to increase the rolling effect in this cold rolling process, it is preferable that the slab fed into the cold rolling mill has a cross-sectional shape with a convex crown. Therefore, it is conceivable to attach crowns corresponding to the profile of the thin slab 6 to the cooling drums la and lb, as shown in FIG. 4.

[Problem to be solved by the invention]

However, the initial crown is placed on the cooling drum la.

1b, the amount of heat removed to the cooling drum changes depending on the thickness of the slab to be cast, resulting in a problem that the crown shape of the resulting slab changes depending on the plate thickness. As a means to solve this problem, it is possible to prepare a cooling drum that can obtain an appropriate slab crown shape for each plate thickness.

However, this method requires enormous equipment costs;
Moreover, since it becomes complicated to replace the cooling drum for each thickness of the cast plate, a problem remains in the actual production process.

Furthermore, casting with an inappropriate initial crown drum causes uneven reduction edges to be added to the solidified shell in the drum gap, causing surface cracks.

In other words, the solidification shelves a and 7b formed by the circumferential surfaces of the cooling drums la and lb, which have concave crowns corresponding to the convex crowns of the target slab, grow into a curved state along the cooling drum la and lb laundries. are doing. The drum gap 5 is wide at the center of the cooling drums la and lb, and unsolidified molten metal 8 remains between the solidification shelves a and 7b.

When the solidification shelves a, 7b are pressed together and integrated in this state, the rolling blade applied to the solidification shelves a, 7b at the center of the cooling drums la, lb becomes extremely small.

Then, since the rolling blades acting on the solidification shelves a and 7b move along the axial direction of the cooling drums la and lb, scratches, wrinkles, etc. occur on the surface of the obtained thin slab 6, and the surface quality deteriorates. .

In order to solve the above-mentioned problems, the inventors of the present invention have devised a means for manufacturing thin slabs with a predetermined convex crown by varying the heat extraction capacity or the reduction blade of the cooling drums la and lb in the axial direction. Developed and patent application No. 1983i381, patent application No. 1983-
No. 16148, Japanese Patent Application No. 63-45509, etc. The cooling drum proposed in Japanese Patent Application No. 63-9381 divides the internal space of the drum into a plurality of sections in the axial direction, and adjusts the flow rate and/or temperature of cooling water supplied to each section. The cooling drum proposed in Japanese Patent Application No. 63-16148 controls the cross-sectional shape of the thin slab by moving a movable ram built into the drum in the direction of the thin slab. Furthermore, in the cooling drum disclosed in Japanese Patent Application No. 63-45509, the heat removal ability is adjusted in the axial direction by means of depressions and heat insulating material provided on the circumferential surface of the drum.

By these means, the thin slab 6 sent out from the drum gap 5 has a convex crown required for cold rolling. However, the means proposed in Japanese Patent Application No. 63-9381, Japanese Patent Application No. 63-16148, etc. complicate the internal structure of the cooling drum, making maintenance and management of the equipment troublesome. In addition, in the proposal of Japanese Patent Application No. 63-45509, the amount of change in cooling capacity in the direction of the drum axis is uniquely determined by the density and size of the depressions and the thickness of the insulation material, and the necessary convexity is determined according to the width of the plate. A crown is attached to the thin slab 6, or the thin slab 6 changes slightly depending on the casting conditions.
It is unsuitable for controlling the crown of the machine with high precision.

The present invention is based on the knowledge that the flow rate of cooling water supplied to the cooling drum affects the crown of the slab, and the present invention detects the profile of the cast slab and adjusts the cooling water according to the profile. The purpose is to manufacture thin slabs with a target convex crown in a simple manner and with high accuracy by adjusting the flow rate.

[Means to solve the problem]

In order to achieve the objective, the crown control method of the present invention has the following advantages: When continuously casting thin slabs by rapidly cooling and solidifying molten metal supplied to the surfaces of a pair of cooling drums, The present invention is characterized in that the profile of the thin-walled slab being sent out is measured, and the flow rate of cooling water supplied to the cooling drum is adjusted based on the measurement results.

[Effect]

The present inventors have been conducting test operations of a continuous casting machine with the equipment configuration shown in Figure 3, with the aim of commercializing the twin-drum method, and in the process, the cooling water supplied to the cooling drum has been tested. It was found that the flow rate of the thin-walled slab affected the profile of the thin-walled slab.

FIG. 2 shows the cooling water flow rate expressed in relation to the thickness and crown amount of the cast thin slab. In addition, in Fig. 2, 2 thin-walled slabs are made from molten steel of stainless steel 5US304 composition at a temperature of 150 [11 tl] using a cooling drum with an initial crown of 400 ALm.
The case of casting at a casting speed of 5 to 80 m/min is shown.

As is clear from FIG. 2, when thin slabs of the same plate thickness are cast, as the flow rate of cooling water increases, the crown of the resulting slab becomes larger on the convex side. Furthermore, when the flow rate of cooling water is kept constant, as the thickness of the slab increases, the amount of crown decreases, sometimes resulting in a negative crown.

The reason why the crown amount changes depending on the plate thickness and the flow rate of cooling water is as follows.

In other words, during casting, the cooling drum receives a heat load due to contact with molten steel, and the Cu and N1 constituting the surface layer of the drum are
The plated portion expands thermally and generally exhibits a deformation as shown in FIG. This thermal deformation tends to increase as the heat load of 1-kur on the drum increases, that is, as the plate thickness increases, and as the cooling capacity of the drum decreases, that is, as the amount of cooling water decreases.

For this reason, it is thought that the crown amount of the slab changes depending on the plate thickness and the flow rate of cooling water.

Therefore, the present invention utilizes this relationship between the crown pot, plate thickness, and cooling water flow rate to attach a predetermined crown l required according to the plate thickness of the thin slab. That is, the profile of the thin slab sent out from the drum gap is measured, and if the amount of crown is insufficient, the flow rate of cooling water is increased. Conversely, if the crown is too large, the flow rate of cooling water is reduced to maintain the convex crown within an appropriate range. In this way, the amount of crown can be easily adjusted by changing the flow rate of cooling water, making it possible to operate using a normal cooling drum, and controlling the crown, which varies slightly depending on casting conditions, online. I can do it.

Further, the required amount of crown varies depending on the thickness of the thin slab and the reduction rate in the cold rolling process. Therefore, when using the cooling drums la and lb shown in Fig. 4, the target crown amount is set according to the plate thickness, rolling reduction, etc., and the cooling drum la and lb with a concave crown corresponding to the crown amount are set. It becomes necessary to use it. In this point,
According to the present invention, thin slabs with various crowns can be manufactured using the same equipment by keeping the flow rate of cooling water constant corresponding to the target crown amount.

〔Example〕

FIG. 1 schematically shows the continuous casting equipment used in this example. In addition, in the figure, parts corresponding to the members shown in FIG. 3 are indicated by the same reference numerals.

The molten metal 4 injected into the sump 3 is cooled by a cooling drum la,
As in the case of FIG. 3, the solidified shell is rapidly cooled and solidified on the circumferential surface of the drum, is pressed and integrated in the drum gap 5, and is sent out as a thin slab 6. In this embodiment, the thickness of the thin slab 6 is measured in the width direction using a thickness gage 9, and the profile of the thin slab 6 is detected. This detection result is manually input to the computing unit 10 as a detection signal a.

In the calculator 10, the relationship between the round tooth, the plate thickness, and the cooling water flow, as shown in FIG. The flow rate of cooling water corresponding to the amount of crown of the thin slab 6 inside is calculated.

The calculated value is output as a control signal C, and the cooling drum la
The cooling water 11 is manually supplied to a flow rate regulating valve 13 provided in the middle of a water supply pipe 12 that feeds the cooling water 11 into the inside of the .

By casting the thin slab 6 while introducing the thus adjusted amount of cooling water 11 into the cooling drums la, lb, the crown of the thin slab 6 is controlled. In addition, since the convex crown of the thin-walled slab 6 can be determined from the profile immediately after casting and the amount of crown can be controlled online, the effect of fluctuations in casting conditions on the profile of the thin-walled slab 6 can be offset while A product with constant shape characteristics can be obtained.

The specific operating conditions are shown below. Molten stainless steel having a composition of S'US304 and a temperature of 1500° C. was poured into the sump 3, and a thin slab 6 having a target thickness of 2 mm and a width of 1000 mm was cast at a casting speed of 80 m/min. At this time, the target crown amount was set to 40μm, and the reference waterfall basin for cooling water was set to 2.
It was set to 500 A/min.

While the casting of the thin slab 6 was continued, the crown amount sometimes decreased to 20 μm due to a slight change in the casting conditions. Therefore, in order to counteract the decrease in crown amount,
The flow rate of cooling water 11 was temporarily increased. As a result, the amount of crown of the thin slab 6 sent out from the drum gap 5 after a few seconds was within the target value ±5 μm. Furthermore, when the amount of crown increased, the flow rate of the cooling water 11 was temporarily reduced to actively form the crown. As a result, the crown amount of the thin slab 6 will change to ± the target value after a few seconds.
It returned to the range of 5 μm.

When the amount of crown of the cast thin slab 6 was precisely measured after cooling, it was found that the percentage of the amount of crown within the range of 5 μm above the target value was as high as 100% in the steady portion.

When this thin slab 6 was sent to the subsequent cold rolling process and rolled, it was rolled into the final shape without any rolling defects.

〔Effect of the invention〕

As explained above, the present invention requires a device that can perform online crown control while measuring the profile of the thin slab sent out from the drum gap of the cooling drum, and that also incorporates a special mechanism. A normal cooling drum is used without Furthermore, even when attaching a different convex crown to a thin slab, the desired amount of crown can be obtained by simply changing the flow rate of cooling water. Therefore, it becomes possible to easily and accurately manufacture a thin slab having a convex crown, which is required to improve cold rolling efficiency. As described above, the present invention is very effective in bringing twin-drum continuous casting to an industrial production level.

[Brief explanation of drawings]

FIG. 1 shows an example of the equipment configuration used to carry out the present invention, and FIG. 2 is a graph showing the influence of the amount of cooling water on the amount of crown of a thin slab. On the other hand, Fig. 3 shows a conventional twin-drum type continuous casting equipment, Fig. 4 is a diagram for explaining the problems when casting a thin slab with a convex crown, and Fig. 5 shows a cooling system. FIG. 3 is a diagram showing thermal deformation of a drum. □ la, lb: cooling drum 2a, 2b: side weir 3: pool 4: molten metal 5 Ni drum gap 6: thin slab 7a, 7b: solidified shell
8: Unsolidified molten metal 9: Thickness gauge 10:
Computing unit 11: Cooling water 12: Water supply pipe 13:
Flow rate adjustment valve a: Detection signal 2 type information
C: Control signal patent applicant Nippon Steel Corporation-' (and one other person) Agent □ Masu Kobori” (Ten 7)
f) lft,,46

Claims (1)

[Claims] 1. When continuously casting thin slabs by rapidly cooling and solidifying the molten metal supplied to the surfaces of a pair of cooling drums, measure the profile of the thin slabs sent out from the drum gap of the cooling drums, and measure the measurement results. 1. A crown control method in continuous casting of thin materials, the method comprising adjusting the flow rate of cooling water supplied to the cooling drum based on the following.