JPH03128149A - Twin roll type continuous casting machine - Google Patents

Abstract

PURPOSE:To reliese rapid heat conduction with a cooling roll at the time of solidifying molten metal and to prevent crack in longitudinal direction of a cast slab by forming projecting parts having suitable pitch and height on surface of the cooling roll according to surface tension of molten metal. CONSTITUTION:The molten metal 6 is supplied into pouring basin part formed between one pair or horizontal cooling rolls 1 and solidified shell formed by cooling is drawn between the cooling rolls to obtain the cast slab. In the above twin roll type continuous casting machine, on the surface of cooling roll 1, the projecting parts 9 having the necessary pitch P (mm) and the necessary height G (mm) are formed. Then, to radius of curvature R (mm) formed with the surface tension of molten metal 6 stuck between the adjacent projecting parts 9, 9, the above P and G are set so as to satisfy the condition of P<2R and G>=R-{R<2>-(P/2)<2>}<0.5>+0.05, respectively. By this method, the molten metal does not contact with recessed parts 10 on the surface of cooling roll 1 to form are gap 11 (g) having >= about 0.05mm. Then, heat transfer rate at the initial stage between the molten metal 6 and the cooling roll 1 is lowered to reliese the rapid heat conduction and the crack in the longitudinal direction of cast slab is not developed.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a twin roll continuous casting machine.

[Prior Art] Conventionally, as this type of twin roll type continuous casting machine, for example, there is one described in Japanese Patent Application Laid-Open No. 83-242445, and this is as shown in FIG. A refractory tundish 2 capable of containing molten metal 6 is installed above a gap t between a pair of cooling rolls 1 which are horizontally and parallelly arranged and further have side weirs 7 at both ends thereof. There is a pouring hole 3 at the bottom of 2 for regulating the flow rate with the required hole diameter.
A suitable number of holes are bored in the width direction of the slab, and a guide nozzle 4 made of refractory is provided on the lower surface side of the bottom of the tundish 2, and each pouring nozzle hole 5 of the guide nozzle 4 communicates with each pouring hole 3. The molten metal 6 in the tundish 2 is supplied to the gap t through the guide nozzle 4 to form a sump 13, and the molten metal B is cooled while rotating both rolls 1. The formed solidified shell 12 is separated from the gap t.
The slab 8 is formed by continuously drawing it out from the slab. Note that the guide nozzle 4 may be immersed in the hot water reservoir 13.

[Problem to be solved by the invention] In the twin roll continuous casting machine as described above, the cooling roll L
The surface is usually cut using a lathe, and the roughness of the surface is approximately 7n based on the JIS standard, that is, the height of the unevenness on the surface of the cooling roll 1 or G- as shown in Figure 4.5. The pitch of the unevenness is suppressed to about 1.6 μ (microns), and the pitch of the unevenness produced by feeding the cutting tool of the lathe in the axial direction is about P-0.1 to 0.2111+s.

Therefore, the height G1 and the pitch P of the unevenness on the surface of the cooling roll 1 are each quite small, and the molten metal 6 comes into close contact with the surface of the cooling roll 1, so that during casting, the molten metal 6 does not cool When the entire surface of roll 1 contacts, no air gap is formed and the molten metal 6 (solidified shell) and cooling roll L
The initial heat transfer coefficient α between α'=lO' v/rrr・
℃, heat is rapidly removed from the molten metal 6, and the gradient of thermal strain becomes large between the surface side of the molten metal 6 in contact with the cooling roll l and the inner side. When the gradient of thermal strain becomes large, tensile stress and compressive stress coexist in the molten metal 6 that is solidifying, and as a result, there is a problem that cracks occur in the longitudinal direction of the slab 8, and this tendency This became more noticeable as the slab 8 became wider.

In view of these circumstances, the present invention aims to provide a twin-roll continuous casting machine that can alleviate rapid heat removal during solidification of molten metal and prevent cracks in the longitudinal direction of the slab.

[Means for Solving the Problems] The present invention includes a pair of horizontal cooling rolls, supplies molten metal to a sump formed between the cooling rolls, and cools the molten metal with the cooling rolls. In a twin-roll continuous casting machine in which the formed solidified shell is pulled out from between the cooling rolls to form a slab, convex portions with a required pitch P [eml and a required height G (am) are formed on the cooling roll surface. If the radius of curvature formed by the surface tension of the molten metal adhering between adjacent convex parts is R (++m), then the pitch P and height G of the convex parts are P<2R, respectively. [Function] Therefore, when casting is performed using a cooling roll having convex portions of height G and pitch P formed on the surface, the molten metal is supported by the tops of the convex portions due to surface tension, and does not come into contact with the surface of the concave portions. First, there is a gap of 0.05+Ila between the surface of the recess and the molten metal.
Since an air gap with a gap of + or more is formed,
The initial heat transfer coefficient α' between the cooling roll with convex portions and the molten metal (solidified shell) is 10' v/rr?・The temperature is below ℃, the sudden heat loss during solidification of molten metal is alleviated, and cracks do not occur in the longitudinal direction of the slab.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Figures 1 and 2 show an embodiment of the present invention, in which a convex portion 9 with a height G (mm) continuous in the roll circumferential direction is formed on the surface of a cooling roll 1 made of copper, which has low wettability with respect to molten metal 6. , are formed in the shape of an enemy so that the pitch is P [mm] in the direction of the roll axis.

Regarding the pitch P C1n) of the convex portions 9, the radius of curvature of the surface of the molten metal 6 due to the surface tension γ when the molten metal 6 adheres between adjacent convex portions 9.9 is R [mm] (=
-= 1.72 open; however, Fp is 0.0 with the relative pressure of the menicus obtained empirically. OIKg/
cj ), the condition for supporting the molten metal 6 by the convex portion 9 without contacting the surface of the concave portion 10 of the cooling roll l is P<2R.

Further, the molten metal corresponds to the pitch P of the convex portions 9, and the relationship between the pitch P and the sinking ah is as shown in FIG.

Here, the initial heat transfer coefficient α (#lO
'w/rr?・℃) can be reduced to about 1/lo or less,
The air gap 11 to be provided between the surface of the cooling roll 1 and the molten metal 6 in FIG. If the gap is Q (mm), the heat transfer coefficient of air during casting is K (w/rr+"・℃), and the initial heat transfer coefficient in this case is α' [V/bo・℃], then -6X10" S (m) -0.06[關]:0.05[關]

Therefore, the height G [+nm] of the convex portion 9 is G−
h+lJ Next, the operation of the above embodiment will be explained.

Pitch P (beat) of convex portions 9 formed on the surface of the cooling roll 1
When the cooling roll 1 is used to perform casting, the molten metal 6 forms convex portions extending linearly in the circumferential direction of the roll due to surface tension. It is supported on the top of 9,
The surface of the recess 10 does not touch the surface of the recess 10 and the molten metal 6
An air gap 11 having a gap 9 of 0.05+nm or more is formed between the two.

For this reason, as shown in FIG.
' is 10' w/rr? ℃ or less, the rapid heat removal during solidification of the molten metal 6 is alleviated, the gradient of thermal strain becomes small, and cracks do not occur in the longitudinal direction of the slab 8.

Below, we will discuss the actual tests and their results.

Casting is carried out using a cooling roll 1 whose pitch P of the convex portions 9 is set to P-0,6a+ll (<2R-3,44), while casting is performed using a cooling roll 1 whose surface roughness has been cut as a finishing symbol as in the past. As a result, cracks occurred in the slab 8 in the longitudinal direction with the conventional cooling roll I, whereas no cracks occurred in the slab 8 with the cooling roll I in which the convex portions 9 were formed.

In this way, by setting the pitch P and height G of the convex portions 9 formed on the surface of the cooling roll 1 to desired values, it is possible to control the amount of heat removed during solidification of the molten metal 6, and the amount of heat removed from the slab 8 can be controlled. It can be used to prevent cracking.

In the above embodiment, the cooling roll itself was made of copper, but it is also possible to form an air gap using a metal other than copper, and rapid heat removal relaxation during solidification of molten steel is possible.

In addition, if the cooling roll is made of a material that has a high wettability on its surface and cannot form an air gap,
The surface of the cooling roll may be coated (plated, etc.) with a metal that does not oxidize or remains less susceptible to molten steel even if oxidized (for example, gold, platinum, Ni1Cr and its alloys, etc.).

Further, regarding the convex portions, convex portions having a height of G [mm] that are continuous in the roll axis direction may be formed on the surface of the cooling roll so as to have a pitch P (mm) in the roll circumferential direction.

Furthermore, the shape of the convex portion is not limited to a circular shape, but may be a thread shape with a pitch P, or a pyramid shape with a height G, and the pyramid-shaped convex portion is formed in the roll axis direction and the roll circumferential direction, respectively. Place it with a pinch P, and support the molten steel by the apex of each convex part! 7.

[Effects of the Invention] As explained above, the twin-roll continuous caster of the present invention has the advantage of being able to alleviate rapid heat removal during solidification of molten steel and preventing cracking in the longitudinal direction of the slab. It can have a great effect.

[Brief explanation of the drawing]

Fig. 1 is an enlarged sectional view of the main part of an embodiment of the present invention (corresponding to part I in Fig. 2), Fig. 2 is an overall plan view of a cooling roll in an embodiment of the invention, and Fig. 3 is a convex Fig. 4 is an enlarged sectional view of the main part showing the conventional example (corresponding to section ■ in Fig. 5), Fig. 5 is the overall plane of the conventional cooling roll. 6 are overall side views showing a conventional example. 1 is a cooling roll, 6 is a molten metal, 9 is a convex part, IO is a concave part, 11 is an air gap, 12 is a solidified shell, 13 is a sump,
G is the height, P is the pitch, R is the rate radius, and 9 is the gap. B・Ste P mm) Fig. 4 Fig. 5 ■

Claims (1)

[Claims] 1) A solidified shell formed by providing a pair of horizontal cooling rolls, supplying molten metal to a sump formed between the cooling rolls, and cooling the molten metal with the cooling rolls. In a twin-roll continuous casting machine that forms a slab by drawing it from between the cooling rolls, a required pitch P [m
m] with a required height G [mm], and if the radius of curvature formed by the surface tension of the molten metal adhering between adjacent protrusions is R [mm], then the radius of curvature of the protrusion is Pitch P
, height G are set to satisfy the following conditions: P<2R and ▲There are mathematical formulas, chemical formulas, tables, etc.▼.