JPH04238647A - Method for oscillating mold in continuous casting - Google Patents

Abstract

PURPOSE:To prevent restricting break-out and to reduce oscillation mark in the case of continuously casting a material having low heat conductivity and low strength at a high speed by using an assembling mold. CONSTITUTION:As an oscillating method for the mold for continuous casting, the mold is lowered at the same constant speed as the drawing seed of a cast slab and successively at every one vibration in the vertical direction of the mold and at the time of ascending the mold, a pair of opposed mold faces are retreated to separate them from the cast slab and the mold face retreated to separate during lowering the mold is returned back.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold vibration method for continuous casting of steel, nonferrous metals (copper, aluminum), etc. by vertically vibrating the mold.

0002

[Prior Art] Generally, when molten metal is continuously cast by vertically vibrating a mold, when the mold is rising with respect to the slab being pulled out, a tensile force is applied to the solidified shell in the mold, causing solidification. Shell breaks easily. On the other hand, when the mold is descending, a compressive force acts on the solidified shell, and oscillation marks are generated on the surface of the solidified shell.

In the former case, insect-eaten defects (bleed) occur on the surface of the slab, and in severe cases, this can lead to a major accident called a restraining breakout. In the latter case, if the oscillation mark becomes too deep, cracks along the mark, accumulation of inclusions, and solute segregation are likely to occur.
Before rolling the slab, it is necessary to shave the surface of the slab. In response to such problems, Japanese Patent Application Laid-Open No. 57-47558,
A method has been proposed in which the above-mentioned problems are simultaneously solved by lowering the mold speed VX at the same speed as the casting speed VR, then lowering it at a speed more than twice VR, and then rapidly raising it back to the original position. ing.

0004

However, when steel with very low thermal conductivity is cast, or when cast at high speed, the solidified shell becomes hot and the tensile strength of the shell becomes very low. Therefore, the effect of increasing the thickness of the solidified shell by setting VX = VR when the mold is lowered as in the conventional method is very small, and if the mold is raised rapidly when the mold is raised, the solidified shell will break and a restraining breakout will occur. It becomes easier to do.

[0005] Furthermore, the effect that the oscillation mark becomes shallower by setting VX = VR occurs when there is no fluctuation in the hot water level. If there is a fluctuation in the melt level, the actual casting speed at the meniscus will be VR - Vm (Vm: fluid level fluctuation speed), and under casting conditions such as Vm ≠ 0, VX =
Even if controlled so that VR is achieved, the mold and casting speeds are not actually constant. Therefore, there is a problem in that even if the oscillation mark depth becomes shallower on average, it varies greatly.

An object of the present invention is to provide a mold vibration method that prevents restrictive breakout and stably makes oscillation marks shallow even when a material with low thermal conductivity and low strength is continuously cast at high speed. That's true.

[0007]

[Means for Solving the Problems] That is, the present invention aims to continuously cast molten metal by vertically vibrating an assembled mold, and to move the mold at a speed equal to the drawing speed of the slab for each vibration. Continuous casting, characterized in that when the mold is lowered, at least a pair of opposing mold surfaces are moved back and away from the slab when the mold is raised, and while the mold is lowered, the mold surfaces that have been moved back and away are returned to their original positions. This is a mold vibration method.

[0008]

[Function] When the mold is raised and the mold is moved back and away from the slab, the thickness of the liquid lubricant film existing between the mold and the slab increases, and therefore the frictional force decreases in inverse proportion to the thickness. It turns out. As a result, the tensile force acting on the solidified shell is also reduced, and breakage of the shell can be prevented.

[0009] Furthermore, even if the mold is lowered at VX = VR and the lowering speed of the solidified shell in the meniscus portion and the lowering speed of the mold are not substantially equal, once the mold is lowered, By gradually returning the mold surface that has retreated from the slab to its original position, the compressive force acting on the solidified shell can be maintained in a state extremely close to zero. As a result, the depth of the oscillation mark becomes shallower and less variable than when the oscillation mark is controlled simply by setting VX = VR without retreating and separating the mold surface.

0010

EXAMPLE FIG. 1 shows the movement of a mold when the present invention is practiced. Cast steel is S20C, slab size is 110 x 400
Continuous casting was carried out under the following conditions: the casting speed VR was 1.2 m/min, the frequency f was 100 cpm, the mold vertical amplitude S was 6 mm, and the receding amount da of the long sides of the mold was 0.5 mm. For comparison, casting was also performed with da=0 mm. In the case of comparison, the vibration conditions were determined so as to satisfy the following equations, Equations 1 and 2 proposed in Japanese Patent Laid-Open No. 57-47558. However, VR and S were the same as the conditions of the present invention.

Equation 1 t1 = (0.9-0.4 ・λ0.5)/f Number 2 f=60VR (0.9-0.4 ・λ0.5)/S Here, λ is the thermal conductivity (cal/cm・s・℃)=0.0
7, t1 is the falling time at which VX = VR.

From now on, the frequency f of the comparative example is 132 cpm.
becomes. The results are shown in Table 1. In the case of the present invention, the oscillation mark depth was lower than that of the comparative example (conventional method), even though the mold descending time was longer (acting in the direction of deepening the oscillation mark depth). The depth is shallower and the variation is smaller than that of the conventional method. On the other hand, in the case of the present invention, even though the rising speed of the mold is the same, the occurrence rate of restraint breakout does not occur at all in the case of the present invention.

[0013]As described above, it can be said that the problems of the conventional method have been almost solved by the present invention.

[0014]

[Effects of the Invention] By preventing the occurrence of restrictive breakouts, the stability of continuous casting operations is ensured, and as a result, productivity can be expected to increase. In addition, since the depth of the oscillation marks on the surface of the slab becomes very shallow, maintenance-free rolling is possible for special steels that require surface treatment before rolling the slab.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of mold vibration conditions when the present invention is implemented.

Claims (1)

[Claims] Claim 1: When continuously casting molten metal by vertically vibrating the assembled mold, the mold is lowered at a speed equal to the drawing speed of the slab for each vibration, and then when the mold is raised, at least A mold vibration method in continuous casting, characterized in that a pair of opposing mold surfaces are moved back and away from the slab, and while the mold is descending, the mold surfaces that have been moved back and away are returned to their original positions.