JPS635177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drawing control method using twin mold rollers, particularly at the start of casting, in continuous slab casting equipment, in which molten metal is injected between twin mold rollers that are close to each other, and slabs are pulled out from between both rollers. .

An outline of a conventionally known continuous casting equipment using twin mold rollers will be explained based on FIG. 1 is twin mold rollers approaching each other;
Reference numerals 2 and 3 designate a pinch roller and guide roller that extend downward from directly below both rollers 1 and constitute a slab conveyance path, and 4 designates a tundish nozzle.

In the above configuration, the molten metal 5 is injected from the nozzle 4 between both rollers 1, and both rollers 1 are rotated in the direction of arrow A to pull out the slab 6. I can't get enough _H1 . Therefore, since the volume corresponding to five parts of the molten metal is actually small, fluctuations in the molten metal level during casting are likely to occur, making continuous casting impossible, especially in high-speed casting. Therefore, it has been considered to provide a weir 7 on both rollers 1 to maintain a sufficient height _H2 of the molten metal surface during casting at a constant constant level. However, the problem here is that if the molten metal is not withdrawn before the molten metal level reaches _H2 after the injection of molten metal starts,
In order to start drawing after the hot water level reaches _H2 , the thickness of the shell 8 formed on the roller surface becomes too large because a predetermined time has elapsed in the meantime, and the thickness of the shell 8 formed on the roller surface becomes too large. This means that when the rollers 1 are sandwiched, both rollers 1 receive a strong reaction force.

Therefore, the present invention provides a drawing control method using twin mold rollers, especially at the start of casting, which eliminates such problems. In continuous slab casting equipment, which has a weir placed above these twin mold rollers, injects molten metal into the weir and pulls out the slab from between both rollers, after inserting a starter plug between the twin mold rollers, Molten metal is injected into the weir, and before the level of the molten metal stored on the starter plug reaches the predetermined height for continuous casting, when the twin mold rollers are rotated to pull out the slab, the level of the molten metal is raised. When the starter plug is located between the long side weir lower edge located on the twin mold roller, the contact time of the molten metal with the twin mold roller at any point on the surface of the injected twin mold roller is Rθ/v ₀ (R :
The radius of the twin mold rollers, θ: the center angle of the arc connecting the rolling point on the surface of the twin mold rollers and the lower edge point of the long side weir, v ₀ : the slab drawing speed in a steady state). According to this method, the unsteady shell formation at the start of casting is carried out in the same state as the steady state, so that the twin mold rollers are not subjected to a strong reaction force. Therefore, there is no need to increase the strength of the twin mold rollers and their supporting device, and it is possible to obtain slabs with excellent economic efficiency.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 2 and 3. That is, the starter plug 9 is inserted between the twin mold rollers 1, and the molten metal 5 is injected from the tundish nozzle 4 between both rollers 1 as shown in FIG. Specified height during continuous casting
Before reaching H ₂ , that is, as shown in Figure 3 A, after time t ₁ has elapsed after the injection of molten metal, the molten metal surface height reaches H _1.
When the temperature reaches 1, the twin mold roller 1 is rotated in the direction of arrow A to start pulling out. At this time, the hot water surface height H ₁ is within the range of both inner surfaces of the weir 7, and is a horizontal line connecting the longest upper edge of the shell formed by the mold roller 1 (section with solidification surface angle θ ₁ in the figure). is equal to the vertical length of the horizontal line connecting the axis O of both mold rollers 1. Further, in order to form the shell 8 in the same manner as during casting, the following conditions are satisfied.

That is, ds/dt=v ₀ (=constant) ...(a) Here, s is the wetting length, which is equal to the length along the twin mold roller surface of the shell 8 that is being formed, and t is the wetting length after pouring the molten metal. any time and v ₀
is constant at a predetermined slab drawing speed (casting speed). Therefore, the hot water level height H at any time
The rate of change of is, when wetting angle is θ, dH/dt=ds/dtcosθ=v ₀ cosθ... (b) Therefore, from s=Rθ=v ₀ t, θ=v ₀ t/R is (b ), dH/dt=v ₀ cos (v ₀ t/R) ...(c) is obtained, which can be expressed as a function of the drawing speed v ₀ , which gives the rising speed of the molten metal level. Therefore, the amount or rate of injection of molten metal can be controlled.

However, R is the radius of the twin mold roller.

When the molten metal starts to be poured and the molten metal level reaches _H1 , as mentioned above, the twin mold roller 1 is driven to start drawing, but the roller rotation speed is the same as the drawing speed of the slab. Ru. This state is shown in FIG. 3B. That is, time t ₁
The twin mold roller 1 is driven at a constant speed at a drawing speed v ₀ when the hot water level reaches H ₁ after . After the predetermined time _t2 has elapsed since the start of drawing, _the third
Between t ₁ and t ₂ in Figure A, there are cases in which the molten metal level rises proportionally, as shown by the solid line, and cases in which it rises rapidly, as shown in the dotted line. The amount of injection into is controlled to be greater than the amount of extraction.

Next, FIGS. 4A and 4B show other embodiments of the present invention, which will be described below. In other words, before the hot water level reaches H ₁ ,
t ₁ ′ hours after starting injection of molten metal (however, t ₁ ′<t ₁ )
In this case, the drawing speed v is controlled to be gradually increased without suddenly increasing it to the casting speed _v0 . Therefore, the conditions for forming the shell 8 to be the same as the state during casting are the same as in the previous example, ds/dt=v ₀ (=constant)...(a)', and The rate of change of the surface height H is dH/dt=v ₀ cos(v ₀ t/R)...(c)'.

Next, after time t ₁ ′ has elapsed, drawing is started, and during the time t ₁ ′ → t ₂ until the height of the molten metal reaches H ₂ ,
The goal is to bring the initial drawing speed v as close as possible to the steady state drawing speed, that is, the casting speed _v0 , and in order to prevent the melt level from falling during this time, q(t)>v・As......(d) ' Must. However, q(t) is the injection speed of the molten metal, and As is the cross-sectional area of the slab to be drawn.

Furthermore, it is necessary to limit the injection rate q(t) so that the height of the hot water level in the weir does not approach H ₂ rapidly, and for that purpose, Q(t)=∫ ^t _t1 ′{q(t) -v(t)・As}dt+Q ₁
′
……(e)′ holds true, so Q(t)−Q ₁ ′/Q ₂ −Q ₁ ′<t−t ₁ ′/t ₂ −t ₁ ′×
The injection rate q(t) may be controlled so as to satisfy F(t)...(f)'. However, F(t) should be selected based on the shape of the part where the molten metal accumulates in the weir, the controllability of the injection rate q(t), etc.

Here, as shown in FIG. 5, Q(t) is the amount of hot water accumulated at an arbitrary time t, and Q ₁ ' and Q ₂ are the amounts of hot water accumulated at times t ₁ ' and t ₂ , respectively.
In addition, after the predetermined time t ₂ has elapsed, the hot water level height H ₂
In order to always maintain the following, the injection rate q(t) is kept constant so that q(t)= _v0 ·As...(g)'.

As described above, according to the drawing control method using the twin mold rollers of the present invention, the twin mold rollers are rotated before the level of the molten metal stored on the starter plug reaches a predetermined height during continuous casting. When the slab is pulled out, if the molten metal surface is between the starter plug and the lower edge of the long side weir located on the twin mold roller, the molten metal at any point on the surface of the twin mold roller that has been injected will reach the twin mold roller. _The contact _time of Since the drawing speed is controlled so that the shell formed on the roller surface in the pool before drawing starts is the same as during casting, the thickness of the shell does not increase at the start of drawing, and Twin mold rollers are not subjected to strong reaction force. Therefore, there is no need to increase the strength of the twin mold rollers and their supporting device, and it is possible to obtain slabs with excellent economic efficiency.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of continuous casting equipment using twin mold rollers, Figs. 2 to 5 show an embodiment of the present invention, Fig. 2 is a schematic longitudinal cross-sectional view, and Fig. 3 is a schematic diagram of a continuous casting equipment using twin mold rollers. A graph showing the relationship between the elapsed time after pouring, the height of the hot water level, and the drawing speed of the slab, Figure 4 is a graph showing another example of Figure 3, and Figure 5 is a schematic diagram showing the state of the amount of stored hot water. FIG. 1... Twin mold roller, 5... Molten metal, 6
...Slab, 7...Weir, 8...Ciel, 9...Starter plug.

Claims (1)

[Claims] 1. Continuous slab casting equipment that has a pair of twin mold rollers that are placed close to each other and a weir that is placed above these twin mold rollers, and that injects molten metal into the weir and pulls out the slab from between the two rollers. After inserting the starter plug between the twin mold rollers, molten metal is injected into the weir, and before the level of the molten metal stored on the starter plug reaches a predetermined height during continuous casting, the twin mold rollers When the slab is pulled out by rotating the molten metal, if the molten metal surface is between the starter plug and the lower edge of the long side weir located on the twin mold roller, the molten metal at any point on the surface of the injected twin mold roller The contact time with the twin mold roller is Rθ/v ₀ (R: radius of the twin mold roller, θ: central angle of the arc connecting the rolling point on the surface of the twin mold roller and the lower edge point of the long side weir, v ₀ : steady A drawing control method using twin mold rollers, particularly at the start of casting, characterized in that the drawing speed is controlled so that the drawing speed at