JPH04138844A - Solid lubricated casting method having excellent quality in cast slab - Google Patents

Abstract

PURPOSE:To stably execute a casting at high velocity by thickening the thickness at mold edge parts to center part of the mold to casting direction and the transverse direction of lining ceramic pieces on the whole surface of inner wall in the mold and executing solid lubrication with small ceramic pieces to the edge parts while slow cooling it. CONSTITUTION:Major sides 1 of the mold and minute sides 2 of the mold are made of copper or apply plating, etc., to the copper. The thickness of small ceramic pieces 3 is varied to the whole surface of inner wall in this mold step by step or in continuous-state along the casting direction. At the same time, besides the casting direction, the thickness thereof at the mold edge parts is thicker than that at the mold center part to the transverse direction of the mold so as to slowly cool the edge parts. By varying the thickness thereof along the casting direction and thickening that at the mold edge parts to that at the center part to the transverse direction, shrinking deformation caused by quick cooling at edge parts in a cast slab or uneven cooling between the center part and the edge parts, is eliminated. By this method, the solid lubricated casting is stably executed at high velocity and surface flaw, bleed flaw, transverse crack, pin hole, slag inclusion, deformation, etc., of the cast slab, is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] Generally, in continuous casting, the solidified shell cooled by the mold is quickly moved down the inner wall surface of the mold, and the solidified shell is sequentially grown to achieve sound solidification. is important.

In order to ensure this healthy solidification, a surface protection material is added to the upper part of the mold to prevent air oxidation of the molten metal and to lubricate the solidified shell and the inner wall surface of the mold with melting powder to prevent seizure and breakage of the solidified shell. It is prevented. In addition, in order to cool the mold and extend its lifespan, as well as to slowly cool the molten metal or solidified shell, a low thermal conductivity material is pasted to the lower end or halfway of the mold, including the solidification start point. Publication No. 58-173061, JP-A-61-195
This method has been proposed in Publication No. 742, etc. In addition, in order to extend the life of the mold, it is proposed in JP-A-58-13445 that a wear-resistant material such as ceramics or stainless metal be applied to the inner wall surface of the mold, including the vicinity of the lower end of the mold. is being put into practical use.

[Problems to be Solved by the Invention] However, the above-mentioned lubrication by the melt of molten balata using the surface protection material does not ensure uniformity of the molten powder flowing between the mold and the solidified shell. This results in the formation of a solidified shell or non-uniformity. As a result, the solidified shell may seize into the mold, break, or cause surface flaws due to the entrainment of powder. In addition, the above-mentioned Japanese Patent Application Laid-Open No. 58-1730
In the molds proposed in JP-A No. 61 and JP-A No. 61-195742, solidification starts from the surface of the molten metal. Therefore, problems such as the need for molten powder, oscillation marks, and powder entrainment remain unsolved.

In addition, no matter what mold is used, the ends of the slab and the vicinity thereof are cooled more strongly than the center, so the edges of the slab shrink and deform, leaving oscillation marks. Lateral cracks may occur. Furthermore, if the mold end and its vicinity are cooled too strongly, the solidified shell at the end and its vicinity will shrink and separate from the mold, causing more molten powder to flow into this gap, causing problems such as pinholes, etc. There are also points.

The purpose of the present invention is to address these conventional drawbacks such as shrinkage deformation of the ends of slabs, transverse cracks along oscillation marks caused by this shrinkage deformation, pinholes, slits, and shell breakage due to excessive inflow of molten powder. The object of the present invention is to provide a solid lubrication casting method that solves the above problems.

[Means for Solving the Problems] The casting method of the present invention changes the thickness of small pieces of ceramic on the entire inner wall of the mold stepwise or continuously along the casting direction, and also changes the thickness in the width direction of the mold in addition to the casting direction. The mold is characterized in that the end portions of the mold are thicker than the center portion of the mold, and the end portions are slowly cooled while solid lubrication is provided by small pieces of ceramic.

In solid lubrication casting, in which small pieces of ceramic are attached to the entire inner wall of a mold, the solidification start point below the molten metal surface is made uniform around the entire inner wall of the mold, and the solidified shell that grows from the solidification start point is pulled out in a rigid state all around. That is important.

Even if you simply stick ceramics on the inner wall and perform solid lubrication casting, if the solidification at the edges and center of the mold does not approximate a uniform state, the solidification start point and the growing solidified shell will become uneven in the casting direction. When the slab is pulled out, the drawing resistance becomes uneven, leading to breakage of the brittle initial solidified shell and inhibition of growth of the solidified shell.

Moreover, since it is a solid lubricant, there is no inflow of molten powder, which may cause the end of the slab to shrink and deform, or become a large air cap, which may lead to subsequent heat removal from the solidified shell or defects.
This causes re-melting of the solidified shell and causes bleat defects or breakouts at the ends of the slab.

In addition, in a flume, cracks occur inside near the surface layer when the initially solidified shell shrinks and deforms due to rapid cooling of the end of the slab, resulting in defects.

Therefore, when performing solid lubrication casting, the present invention changes the thickness of small pieces of ceramic on the entire inner wall of the mold stepwise or continuously along the casting direction, and also changes the thickness in the width direction of the mold in addition to the casting direction. The ends of the mold are made thicker than the center of the mold, and the ends are slowly cooled.

By changing the thickness stepwise or continuously along the casting direction and making the thickness in the width direction thicker at the ends of the mold than at the center, rapid cooling of the ends of the slab or cooling of the center and ends is achieved. Shrinkage deformation of the solidified shell due to non-uniformity is eliminated.

By eliminating the shrinkage deformation at the end of the slab and its vicinity, the initial solidification start point is uniformly formed all around the mold, making it possible to pull out the solidified shell that has grown from the solidification start point in a rigid state around the entire circumference. Become. Stiffness can cause the brittle initial solidified shell to be easily pulled out and peeled off in spite of solid lubrication, and the solidified shell can gradually grow.

Furthermore, shrinkage deformation can be eliminated by eliminating the air cap between the lining ceramics and the solidified shell of the slab, and the subsequent heat removal of the solidified shell is improved, eliminating re-melting of the solidified shell and preventing bleed defects or breakouts caused by the ends of the slab. etc. can be prevented.

In addition, in bloom, rapid cooling of the ends of the slab is prevented, which eliminates shrinkage deformation of the initially solidified shell (defects caused by cracking inside near the surface layer, which is a problem during conventional casting).

This enables stable continuous casting even with solid lubrication, as well as high-speed casting.

Here, the mold used is made of copper or has a plated copper surface. The thickness of this mold changes stepwise or continuously along the casting direction, and the thickness of the ceramic piece at the end of the mold is 0.3 to 3.0 mm thicker in the width direction than the center of the mold. If the difference in thickness of the ceramic pieces exceeds 3.0 mm, the ceramic pieces will be cooled too slowly, and due to insufficient heat removal, the solidified shell will grow slowly and the solidified shell strength will decrease, causing the slab to break. On the other hand, if the thickness is less than 0.3 mm, it becomes difficult to slowly cool the mold end, and it is impossible to prevent bleed defects, lateral cracks, pinholes, grooves, deformation of the slab, etc. Further, the mold end includes the vicinity thereof, and the thickness thereof increases toward the mold end. Note that the mold end and its vicinity account for 20 to 40% of the entire mold width, and if it exceeds 40%, uniform cooling of the entire mold width cannot be achieved.

[Example] Next, mold size 290 x 290.250 x 98
Table 1 shows the results of casting under conditions in which a 120 mm thick ceramic heat insulating part was provided at the upper end of the mold and the thickness of the mold was changed in the width direction. A comparison is shown in Figure 1.

1 is a long piece of the mold, and 2 is a short piece of the mold made of copper or plated copper. Ceramic pieces 3 or, for example, an organic adhesive mixed with copper or aluminum powder are attached to the inner wall surfaces of the long piece 1 and the short piece 2 of the mold. Further, in the mold of the present invention, as shown on the left side of the mold structure in FIG. 1, the thickness of the ceramic piece 3 is increased toward one side of the mold end.

In this way, the present invention can even out the mold inner wall surface temperature from 200 to 210 degrees Celsius in the mold width direction as shown in Figure 1, so compared to Comparative Examples Scratches, horizontal splits, pinholes, rough edges,
Good results were obtained with no deformation of the slab.

[Effects of the Invention] As described above, by using the solid lubrication casting method of the present invention, the temperature of the inner wall surface of the mold can be made uniform in the width direction of the mold, so solid lubrication casting can be realized stably and at high speed. This is an excellent casting method that does not cause surface flaws, bleed flaws, horizontal cracks, pinholes, rough edges, or deformation of slabs.

[Brief explanation of the drawing]

FIG. 1 shows the lining diagram and mold inner wall surface temperature of the present invention in which the ceramic thickness is varied in the mold width direction and a comparative example in which the ceramic thickness is the same. 1.- long piece of mold, 2... short piece of mold, 3.
...Ceramics cantilever permit applicant representative

Claims (1)

[Claims] 1. The thickness of the lining ceramic piece on the entire inner wall of the mold is changed stepwise or continuously along the casting direction, and the thickness in the width direction of the mold is changed from the center of the mold to the edge of the mold. A solid lubrication casting method with excellent slab quality, characterized by thickening the slab, slowly cooling the edges, and applying solid lubrication using small pieces of ceramic.