JPS63235014A - Preventing method for scale indentation flaw - Google Patents

Abstract

PURPOSE:To de-scale before rolling and to prevent the titled flaw by injecting highly pressurized water mixed with prescribed particle size of impacting materials on a heated slab by a specified pressure. CONSTITUTION:The slab 2 heated to a required temp. by a heating furnace 1 is conveyed to a mill on a conveying table 3. At this time, the highly pressurized water mixed by 2-15vol.% with the impacting material consisting of particules having diameter of 250-1400mum by 10-50wt.% to the total weight and remaining particles having diameters below 250mum is injected to the surface of the slab 2 by a pressure range of 100-700Kg/cm<2> just before a rough mill 4. By this method, the residual local scale are eliminated to obtain the product wholly free from the titled flaw.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for preventing scale intrusion flaws occurring on the surface of a slab during rolling in a hot rolling line.

(Prior Art and its Problems) Scale grows in a slab heated in a heating furnace and during transportation to a rolling mill. If the slab with this scale is rolled as it is, the scale will be pushed in, causing surface defects on the product. For example, in a continuous hot rolling mill, a descaling device is installed just before rough rolling and before the finish rolling mill row. It is often installed and descaled.

As this descaling method, conventionally, 100kg/cff
A common method is to spray high-pressure water of around 100 ml of water onto the slab, but depending on the material of the slab, it is difficult to completely remove scale.

Therefore, when scale intrusion flaws occur, they are dealt with by cutting down or, in the case of thick steel plates, by cleaning the product surface, but these methods have poor yields and increase the number of man-hours on the product, making production difficult. The problem was that it was inefficient.

The present invention has been made in view of such problems, and it is an object of the present invention to provide a method that can remove scale as completely as possible before rolling to prevent indentation defects in a rolling mill.

(Means for solving the problem) For example, the occurrence of scale loss in a hot strip can be reduced to 0.
．． It is said to be around 4% to 0.9%, of which 1
Approximately 0% is in the heating furnace.

On the other hand, the scale is 300 μm to 400 μm in an oxidizing atmosphere furnace.
The thickness is about μm.

Therefore, in order to prevent scale intrusion flaws in a rolling mill, it is advantageous to roll the slab with zero scale remaining on the entire surface of the slab in order to eliminate scale intrusion flaws.

Therefore, in the present invention, as a method for this purpose, an impact material is mixed into high-pressure water and sprayed before rolling. It is important to note that the particle size of the impact material used at this time is small and that no leakage occurs over the entire surface.

On the other hand, it is also necessary to eliminate local residue by increasing the impact force.

That is, in the present invention, the heated slab has a grain size of 25
100 to 700 kg of high-pressure water mixed with 10 to 50% by weight of particles with a diameter of 0 to 1400 μm, and the remainder being 2% to 15% by volume of impact material consisting of particles with a particle size of less than 250 μm.
This is a method for preventing scale intrusion defects, which involves spraying at a pressure of /cnl.More specifically, by covering the slab surface when heating the slab, the growth of scale during heating is suppressed, and the scale is easily removed. This is a method for preventing scale intrusion flaws, the gist of which is to inject high-pressure water mixed with the above-mentioned impact material so as to be able to remove the above-mentioned impact material.

In the present invention, the particle size and blending ratio of the impact material are limited as described above for the following reason.

In order to efficiently remove scale, it is necessary to have (1) an impact force and (2) apply an impact to the entire surface without leaking, and the particle size composition is determined to satisfy these requirements.

In addition, the reason for setting the contamination rate in high-pressure water to 2% to 15% is 2.
If it is less than 30%, scale removal will be incomplete, and if it exceeds 30%, post-treatment of the impact material will become difficult.

Furthermore, the pressure of high-pressure water was set to 100 to 700 kg/c+I [because if it is less than 100 kg/ccd, sufficient scale removal effect cannot be obtained, and if it exceeds 700 kg/ctA, equipment wear and maintenance problems may occur. This is because

Therefore, by carrying out the method of the present invention, it is possible to eliminate local scale residues and to manufacture products (thick steel plates or hot-rolled steel plates) without any indentation flaws.

Furthermore, when applying the method of the present invention, if the slab in the heating furnace is covered to prevent oxygen from entering and to suppress the growth of scale during heating, it will be relatively easy to remove scale.

(Example) Hereinafter, the method of the present invention will be explained based on the schematic explanatory diagram shown in FIG.

In the drawings, reference numeral 1 denotes a heating furnace, and a slab 2 that has been heated to a required degree in this heating furnace 1 is transported on a transport table 3 to a rolling mill. At this time, high-pressure water mixed with impact material is sprayed onto the surface of the slab 2 immediately before the rough rolling mill 4. Then, it is carried into the rough rolling mill 4 and rough rolled,
Thereafter, it is sequentially rolled and reaches the finishing rolling mill 5. Immediately before this finish rolling mill 5, high pressure water is further injected and finish rolling is carried out. In the figure, 6 is a nozzle that sprays high-pressure water mixed with the impact material, 7 is a high-pressure water generator that supplies this nozzle, and 8 is a tank for the impact material.

Thick steel plate 250 is produced in this manner and under the conditions shown below.
0 ton was rolled, and products with plate thicknesses of 4 to 150 Tsuru were manufactured and their surface conditions were inspected.

Part 1) Conditions for manufacturing thick plate materials Before charging the slab 2 into the heating furnace 1, a cover 9 made of a steel plate (one fin thick) having the shape shown in FIG. 2 was placed on its upper surface.

In addition, for thin slabs (50 mm thick), in order to reduce the temperature drop from charging to rolling, we use a slab with a concave part 91 as shown in Fig. 3, and the concave part 91 is insulated. The one with the material was used.

At this time, the cover 9 was removed before spraying high-pressure water mixed with impact material immediately before the rough rolling mill 4.

Further, experiments were also conducted in the case where the cover 9 was removed after exiting the heating furnace 1, and in the case where the cover was not placed.

In addition, in this example, the pressure of high-pressure water was changed as shown in the table below, and the grain size of the iron sand constituting the impact material was 250 μm or less, and the mixing ratio of sand for blasting (diameter 250I1 m to 1400 μm) was changed to make the impact material on both sides. I sprayed it.

After cooling on the cooling bed, both sides were inspected on an inspection table.

Part 2) Conditions for manufacturing hot-rolled materials As shown in Figure 1 above, hot-rolled materials are manufactured using exactly the same method on the rough rolling mill, with only high-pressure water used in the subsequent rolling mills, and finishing mills. It was cooled by passing through a tube and then wound up.

Note that surface flaws were inspected by visual inspection after unwinding on the slitter line.

The results are shown in the table below.

As is clear from the table above, the invention examples (111113 to 8 and 10) had significantly reduced occurrence of indentation defects compared to the comparative example (1.2) and the conventional example (9).

In this example, only the top surface is covered, but the bottom surface is subjected to its own weight by the table roll during transportation, and cracks occur in the scale due to vibration, making it easier to remove, so impact material is mixed in. This is because the scale could be removed using only high-pressure water.

(Effects of the Invention) As explained above, the present invention provides an impact material in which 10 to 50% by weight of particles with a particle size of 250 to 1400 μm are added to the heated slab, and the remainder is made up of particles with a particle size of less than 250 μm. High-pressure water mixed with 2% to 15% by volume of
Since it is injected at a pressure of 0.00 kg/cJ, scale can be removed as completely as possible before rolling, preventing scale intrusion defects, and improving manufacturing efficiency and product yield. Moreover, the above-mentioned effects are further improved by covering the slab with a cover during heating.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the method of the present invention, and FIGS. 2 and 3 are perspective views showing an example of a cover. 1 is a heating furnace, 2 is a slab, 6 is a nozzle, 7 is a high pressure lengthening generator, and 8 is a tank.

Claims (2)

[Claims] (1) Particle size of 250 to 1400μ is added to the heated slab.
10 to 50% by weight of the total particles, and the remainder has a particle size of 25%.
Impact material consisting of particles less than 0 μm in a volume ratio of 2% to 15%
A method for preventing scale intrusion defects, characterized by spraying high-pressure water mixed with 100% to 700kg/cm^2. (2) The method for preventing scale intrusion flaws according to claim 1, characterized in that the surface of the slab is covered when the slab is heated.