JPH01237057A - Belt deformation preventing method for twin belt caster - Google Patents

Abstract

PURPOSE:To reduce the permanent deformation of a lower belt and to improve the quality of the cast billet surface by subjecting the following protection plate to internal chilling in the front material of a cast billet after starting a casting by covering the protection plate to the molten metal feeding part of a lower belt. CONSTITUTION:In order to reduce the thermal load at casting starting time, a protection plate 22 is covered on a lower driving pulley 5. One end of this protection plate 22 is linked to a dummy bar head 21 and the other end is suspended from a lower driving pulley 5 in order to secure the specified length. When casting is started and a molten metal 11 is stored in specified amt. by the dummy bar head 21, the protection plate 22 is pulled out together with the dummy bar. Thereafter, the protection plate 22 cast in a cast billet is revoked by being cut as the front material of the cast billet. The cast billet is thus cooled uniformly and the quality of the cast billet surface can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing belt deformation in a twin belt caster.

[Conventional technology and its issues]

As is well known, the -a twin belt caster is constructed as follows. That is, as shown in Fig. 5, which shows a conceptual diagram of twin casters, the main part of the twin belt caster 1 is sandwiched between the upper and lower belts 2.3 and the ears of these belts 2.3, and runs parallel to each other. The pair of dam blocks 6, the lower drive pulley 4 and upper tension pulley 8 for the upper belt, the lower drive pulley 175 and lower tension pulley 9 for the lower belt, and the belt 2.3 are tensioned in the longitudinal direction. Belt tension device 10.
10 and a dam block guide 7.

Then, the molten metal 11 is supplied to the hot water supply part A of the twin belt caster 1 through the hot water supply gutter (see Figure 1), cooled by the primary cooling spray zone (see Figure 1) of the twin belt caster L, and then turned into a slab. It is designed to cast 12.

Here, when the molten metal 11 is supplied to the hot water supply section A, the upper and lower belts 2.degree. 3 are thermally deformed due to severe thermal load.

That is, the water-cooled upper and lower belts 2 and 3 (hereinafter referred to as
When the lower belt 3 (which will be described simply as a belt) comes into contact with the molten metal 11 at a high temperature (for example, about 1550°C in the case of molten steel), a temperature difference occurs in the belt in the thickness direction and in the plane, and the sixth Thermal deformation 1 as shown in the figure
3 occurs. In addition, in Fig. 6, X is the elongation in the longitudinal direction,
Y is the elongation in the width direction, Wl is the width of the slab 12, and F is the belt tensile force.

This thermal deformation 13 occurs as follows. In other words, the surface of the water-cooled belt that contacts the molten metal [11] is approximately 100 to 200°C hotter than the water-cooled surface on the back of the belt. The portion that does not come into contact with the molten metal 11 is generated in order to restrain the thermal expansion of the portion that comes into contact with the molten metal 11.

Therefore, due to such belt deformation (and fluctuation), the slab 12 is subjected to external force at the early stage of solidification, that is, at the stage where the solidified shell is thin (for example, about 2 - ugliness), resulting in cracks, dents, and, in particularly severe conditions, local fractures. This results in a decrease in the quality of the surface of the slab.

In order to solve this problem, in the prior art, for example, in Japanese Patent Application Laid-Open No. 50-89218, the belt is stretched in the longitudinal direction to yield the cold frame f, thereby reducing the central heat affected zone (in FIG. We have proposed a method of giving elongation in the X direction to deformation 13). Also, JP-A-59-
In order to perform slow cooling, Japanese Patent No. 174254 proposes a method of forming a sprayed coating of alumina or the like on the surface of the belt (the surface in contact with the molten metal).

However, although these proposals are effective in preventing thermal deformation of the belt that occurs during stable pouring, they are not effective in preventing thermal deformation of the lower belt 3 at the start of casting when molten metal is supplied using a dummy bar. Not necessarily valid.

That is, the present inventors analyzed the thermal deformation of the belt in detail, and as shown in the graph shown in Figure 4, where the vertical axis represents the amount of belt deformation and the horizontal axis represents the time from the start of casting.
They discovered that thermal deformation of the belt appears periodically with each rotation of the belt, and that a relatively large deformation occurs at the start of casting, which becomes permanent deformation and is repeated every rotation. This phenomenon is thought to be due to the fact that the residual stress inherent in the belt during belt manufacture manifests itself in the degree of thermal deformation of the belt depending on the degree of thermal load.

[Means to solve the problem]

Therefore, the present invention was created in order to prevent such thermal deformation of the belt at the start of casting. A twin belt caster consisting of a pair of dam blocks sandwiched in parallel and a hot water supply gutter for supplying molten metal between these belts.
A method for preventing belt deformation of a twin-belt caster, which is characterized in that a protective plate is placed over the hot water supply part of the lower heald and casting is started, and then the protective plate is cast around the front material of the slab. be.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of the present invention will be explained in detail with reference to embodiments shown in the accompanying drawings. Fig. 1 is a conceptual diagram of the embodiment of the present invention at the start of casting, Fig. 2 is a conceptual diagram of Fig. 1 at the time of stable casting, and Fig. 3 is a graph of the thermal deformation state of the belt according to this embodiment. .

Note that the same parts as those in the conventional example shown in FIG. 5 are indicated by the same reference numerals, and the explanation thereof will be omitted.

In FIGS. 1 and 2, the molten metal 11 is supplied from the small tundish 14. Molten metal is supplied to the hot water supply section A of the twin belt caster 1 via 1l15, and casting starts.

In addition, in Fig. 1 and Fig. 2, 16.16 is for driving,
17. a first cooling nozzle wound around the lower pulleys 4 and 5;
17... is a second cooling water nozzle that is provided on the upper surface of the upper and lower belts 2.3 and spouts cooling water toward the belt and in the belt running direction, 18° 18... collects cooling water 19 is a back-up roll, and 20 is a dam block cooling chamber.

Here, at the start of casting, the upper and lower belts 2.3
Insert the dummy bar head 21 between them, store the required amount of molten gold, and pull out the dummy bar downstream.
At this time, the molten metal 11 flows down from the small tundish 14 onto the lower belt 3 due to the head difference between the hot water supply gutter 15 and the hot water supply section A of the lower belt 3, but the belt may be coated with lubricant. Even if a sprayed layer of , alumina or the like is formed, the molten metal TI&ll directly collides with the lower belt 3, resulting in a large thermal load being applied to the belt. Therefore, permanent deformation occurs in the lower belt 3 at the start of casting.

Therefore, in this embodiment, a protection plate 22 is placed over the lower drive pulley 5 in order to reduce the thermal load at the start of casting. One end of this protection plate 22 is connected to the dummy bar head 21, and the other end is allowed to hang down from the lower drive pulley 5 to ensure a predetermined length. The protection plate 22 is made of a plate made of non-ferrous metal, glass fiber, etc., or cloth-like, with a thickness of about 0.5 to 0.8 m, and is made of a flexible material that follows the bending of the belt. The width is wider than the waterfall width of the small tandaitsu 14 and smaller than the width between the dam blocks 6.
Considering ~4 m/in2 and approximately 30 seconds until the storage amount is secured by the dummy bar head 21, it is sufficient to have a length of 1.5 to 2 m or more and 3 m.

Then, when casting is started and a predetermined amount of molten metal 11 is stored in the dummy bar head 21, the protection plate 22 is pulled out together with the dummy bar.

After that, the protection plate 22 cast into the slab 12
The front material (4 to 5 m) is cut and discarded.

(Effects of the Invention) According to the present invention, since the protection plate is used on the lower belt, the thermal shock caused by hot water supply at the start of casting is alleviated, so that permanent deformation of the lower belt is reduced. This is shown in the graph of FIG. 3, and as is clear from comparing the thermal deformation between the graph of FIG. 3 and the graph of FIG. 4, the amount of thermal deformation has been significantly reduced.

As a result, the slab can be cooled uniformly and the quality of the slab surface can be improved. Furthermore, since the protective plate is cut and discarded as a front material of the slab, it does not have any adverse effect on the slab that is manufactured into a product.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the embodiment of the present invention at the start of casting, Fig. 2 is a conceptual diagram of Fig. 1 at the time of stable casting, and Fig. 3 is a conceptual diagram of the embodiment of the present invention at the time of stable casting.
The figure is a graph of the thermal deformation state of the belt according to this embodiment, FIG. 4 is a graph of the thermal deformation state of the belt according to the conventional example, FIG. 5 is a conceptual diagram of a general twin belt caster, and FIG. 6 is an explanatory diagram of belt thermal deformation. show. 1... Twin belt caster, 2, 3... Upper and lower belts, 6... Dam block, 11... Molten metal,
12... Slab, 15... Hot water supply gutter, 22... Protective plate, A... Hot water supply section. Agent Patent Attorney Masanobu Kato (1 idiot) Figure 16

Claims (1)

[Claims] (1) Slightly inclined upper and lower belts, a pair of parallel dam blocks sandwiched between the ears of these belts, and a water supply gutter for supplying molten metal between these belts. The twin belt caster is characterized in that, after a protective plate is placed over the hot water supply part of the lower belt and casting is started, the protective plate is cast around the front material of the slab. A method to prevent belt deformation of twin belt casters.