JPH0729207B2 - Belt of belt type continuous casting machine - Google Patents

Description

Description: (Field of industrial application) Efficiently avoiding slab cracking by improving welded joints of belts in a belt type continuous casting machine in which continuous metal casting is performed, in particular, molds are formed using endless belts The following are the results of the development.

(Prior Art) In recent years, a belt-type continuous casting machine using an endless belt has been developed, and its application has been particularly widened to a steel whose surface quality is strictly required.

Normally, joining of endless belts is performed by welding such as TIG welding and submerged arc welding. Further, in order to increase the strength of the belt welded portion, laser welding of the belt disclosed in JP-A-60-9555 is used. When continuous casting of steel was carried out in such an endless twin-belt continuous casting machine, it was often experienced that lateral cracks over the entire width of the slab corresponding to the belt weld occur. In this case, the belt uses cold rolled steel strip (SPCC) with a thickness of 1.5 mm,
Welding is by TIG welding as an example.

(Problems to be solved by the invention) In order to eliminate lateral cracks that occur in a slab obtained by a belt-type continuous casting machine by improving the care method after welding of a belt welded portion, various investigations have been made on a care method after welding. went.

Based on the results of this investigation, it is an object of the present invention to realize belt type continuous casting without lateral cracking.

(Means for Solving Problems) The present invention relates to a belt of a belt-type continuous casting machine in which an endless belt is formed by welding ends in a longitudinal direction of a thin steel plate, in which a welded joint is a belt thickness near a welded portion. A belt of a belt-type continuous casting machine, characterized in that the deviation is 50 μm or less, and the surface roughness of the welded portion is Hmax ≦ 15 μm, Hrms ≦ 1.8 μm.

After conducting various studies on the care to be applied to the welded part, it was found that the difference between the maximum and minimum values of the total thickness of the belt at the welded part, that is, the thickness deviation and the surface roughness are factors that affect the occurrence of cracks in the slab Then, the conditions for eliminating the crack generation were studied.

After welding the belt, baby sander, #
A 40 belt grinder and a # 320 belt grinder were used.

The baby sander is a handy type work machine that grinds by rotating the disk-shaped grinding part.The belt grinder is a work that is used for grinding and grinding work by attaching a grinding belt to the belt grinding machine. In the machine, the base material of the abrasive belt was hard rubber containing wire, the abrasive materials were zirconia and alumina, and two kinds of abrasive particle sizes, # 40 and # 320, were used.

After measuring the thickness deviation and the surface roughness in the welded portion that has undergone the above maintenance, molten steel was cast by the vertical twin-belt continuous casting machine shown in FIG. 1 and the molten steel was associated with cracks on the surface of the slab. .

The vertical twin-belt type continuous casting machine uses belts 4 and 4'opposed to each other to support rolls 1,2,3 and 1 ', 2', respectively.
It is supported by 3'and is driven in synchronization with the withdrawal of the cast piece 8.

The belts 4,4 'are back-cooled by a cooling medium (usually water) from the cooling pad indicated by the numbers 6,6', which heats the molten metal or slab and promotes its solidification.

As the belts 4 and 4 ', thin steel plates having a thickness of 1 to 2 mm are usually used, and end portions 7 in the longitudinal direction of the steel plates are joined together to form an endless belt as shown in FIG. There is.

FIG. 3 shows the thickness deviation of the welded portions of the belts 4 and 4'depending on the care method and the cracking condition of the slab using the belts.

It can be seen from FIG. 3 that large cracks occur when the thickness deviation exceeds 50 μm. However, the baby sander finish causes small cracks even at 50 μm or less.

Here, a large crack means a crack having a crack width of 1 mm or more, and a small crack means a crack having a crack width of less than 1 mm.
In both cases, it becomes a surface defect and a starting point of breakage during rolling, which hinders the subsequent steps.

Therefore, the surface roughness of the weld maintenance part was investigated. Roughness is the maximum value Hmax of surface irregularities measured by a surface roughness meter,
The unevenness was evaluated by H root mean square. Hrms is the 4th
Using the symbols shown in the figure Is. Fig. 5 shows Hmax and Hrms depending on the maintenance method, but in the experiment shown in Fig. 3, no cracks occurred. # 320 With belt grinder finishing, Hmax = 9 to 15 µm, Hrms = 0.9 ~
1.8 μm, which means that the limit value at which cracking does not occur is H
It is considered that max ≦ 15 μm and Hrms ≦ 1.8 μm.

(Operation) Based on the knowledge that the maintenance after welding performed on the welded portion of the belt in the above belt type continuous casting machine influences the presence or absence of lateral cracking of the slab, the belt thickness deviation is 50 μm or less, By setting the surface roughness to Hmax ≤ 15 μm and Hrms ≤ 1.8 μm, it is possible to properly avoid the occurrence of lateral cracks in the slab, but when the thickness deviation and surface roughness deviate from the above conditions, It cannot be reliably prevented.

(Example) A twin-belt vertical continuous casting machine shown in FIG.
We cast low-carbon aluminum-killed steel with a width of 00 mm and medium carbon steel with C: 0.10%.

The belt used was a 1.5 mm thick SPCC thin steel plate, TIG welding was performed to make it endless, and the # 320 belt grinder was used to care for the welded part and finished as shown in Fig. 6. The thickness deviation of the belt is 45 μm and the surface roughness is Hmax: 10 μ
m, Hrms: 1.8 μm.

As for the slab, neither low carbon aluminum killed steel nor medium carbon steel, which is highly susceptible to cracking, did not crack and was good.

(Effect of the Invention) A sound slab surface can be obtained even at a belt welded portion of a belt type continuous casting machine.

[Brief description of drawings]

FIG. 1 is a perspective view showing a twin belt type vertical continuous casting machine, and FIG.
FIG. 3 is a perspective view showing an endless belt, FIG. 3 is a graph showing a relationship between a belt thickness deviation of a welded portion and a degree of cracking of a slab according to a care method of a belt welded portion, FIG. 4 is a definition diagram showing a surface roughness, FIG. 5 is a graph showing the surface roughness of the belt welded part according to the care method, and FIG. 6 is a sectional view of the welded part of the belt. 4,4 ′ …… Endless belt 5,5 ′ …… Short side mold 6,6 ′ …… Cooling pad 7 …… Belt weld (end in the belt longitudinal direction) 8 …… Slab

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saburo Moriwaki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Tomoaki Kimura 3-1-1 Sachimachi Hitachi, Ibaraki Stock Association Hitachi, Ltd.Hitachi factory

Claims (1)

[Claims] 1. A belt of a belt type continuous casting machine, wherein an endless belt is formed by welding longitudinal ends of a thin steel sheet, wherein a welded joint has a belt thickness deviation in the vicinity of the welded portion of 50 μm or less, and a welded portion. A belt of a belt-type continuous casting machine, which has a surface roughness of Hmax ≤ 15 μm, Hrms ≤ 1.8 μm and has a welded surface texture.