JPS59199110A - Excellent descaling method for hot cast billet - Google Patents

Abstract

PURPOSE:To strip and remove perfectly the surface scales of a high-temperature continuously-cast billet without much lowering its temperature by installing a descaling device for blowing of compressed air, etc. between a pinch roll and a flaw detector of a continuous casting line. CONSTITUTION:A continuously cast billet 5 is descaled between pinch rolls 2 and a flaw detector 3 by a descaling device 4 of compressed air, etc. blowing system. The device 4 introduces compressed air supplied from a compressed air source 43 to a nozzle holder 41 supported by a holder 42, and blows the air from many nozzles 411 on the surface of billet 5. The header 41 is rocked in the width direction of billet 5 by the rocking of the holder 42 driven by a rocking device 44, and at the same time, the compressed air is blown at >=5g/mm.<2> pressure through the nozzles 411 located at the height of <=15mm. from the surface of billet 5, and at an angle of 5-90 deg. to the upstream side in the advancing direction of billet 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for descaling thermal slabs (hereinafter referred to as slabs).

For hot charging from a continuous casting machine, direct rolling, etc., it is extremely important for quality assurance to detect and treat surface defects on the slab early prior to the rolling process. Detection of defects on the surface of slabs and hot water are often carried out using heat treatment, but since scale is formed on the surface of slabs,
The disturbance effect based on this scale reduces flaw detection accuracy, making it impossible to perform effective detection. Therefore, it becomes necessary to remove scale from the surface of the slab prior to drilling.

Conventional descaling methods include spraying high-pressure water onto the surface of the slab, a-washing, shot blasting, etc. However, the one-shot method of high-pressure water has the disadvantage that water reduces the surface finish of the slab. Furthermore, there are many factors that make it extremely difficult to apply pickling and shot blasting methods to hot processes, and they have not been put to practical use in processes other than cold processes. Particularly, in a four-continuous casting facility where the installation space is extremely small, the installation distance is -.

Therefore, it is an object of the present invention to provide a scale method that can minimize the temperature drop of the slab and exhibit sufficient scale removal performance.

The descaling method of the present invention is based on a four-continuous casting line, and a descaling device using compressed air or other gas injection is installed between the pinch roll and the hot flaw detector, and the conditions for compressed air or other gas injection are adjusted. There are certain characteristics that have been identified.

Next, the method of the present invention will be explained with reference to the drawings.

The case where compressed air is used will be explained below. In the descaling method of the present invention, as shown in FIG. 1, a descaling device 4 is provided in a four-continuous casting line 1 between a pinch roller 2 and a hot flaw detector 6. This descaling device 4
is configured as a compressed air injection type.

As shown in FIG. 2, the descaling device 4 includes a nozzle header 41, a holder 42 . Compressed air supply source 46, swing mechanism 44
made of. The nozzle header 41 extends in the width direction above the slab 5. The nozzle header 41 is a holder 42
Supported by The holder 42 is slidably supported in the width direction of the slab 5, and is moved back and forth d1 in the width direction of the slab 5 by a swinging mechanism 44 with a constant stroke. A compressed air l# supply source 46 supplies compressed air to the nozzle header 41 through the holder 42.

The nozzle header 41 has a plurality of nozzles 41=, and these nozzles 411 are installed at an angle of 5 to 90 degrees with respect to the surface of the slab on the upstream side in the traveling direction of the slab. .

Therefore, the injection angle of the compressed air also varies with respect to the surface of the slab.

The reason why the compressed air is directed upstream in the parallel direction of the slab is that peeled scale can be easily removed from the surface of the slab before deep damage occurs during heating, and the decooling property is good. The reason why the injection angle is limited to 5 to 90 degrees is that the descaling performance is significantly reduced when the injection angle is 5 degrees or less.

As for the distribution of compressed air pressure, the slab is positioned within 15 mIn from the nozzle tip, and the pressure at the slab surface position is set at 5 g/min.
Set the pressure distribution to be equal to or greater than i. The reason for this limitation is that the results shown in Figure 6 were obtained by stacking tests using many different types of nozzles, such as Laval nozzles and flant nozzles, and the minimum pressure for descaling ability at the slab surface position was 5 f. This is because it was found that the value is /mx2.

This is because if the slab is moved closer to the tip of the nozzle than 15 degrees, the pressure range will expand and negative effects such as supercooling and a reduction in the surrounding effect will begin to appear.

The reason why the injection point of the compressed air is oscillated in the width direction of the slab is that a pulsating rather than a constant electric gas flow is an extremely effective method for further improving descaling performance. This is because it has become clear.

According to experiments carried out by the inventor, it was found that the compressed gas was used to reduce the scale scale and the scale that had sprung up on the surface. After shrinking and peeling off from the slab, it is removed by high-speed airflow (
blow away). At this time, a similar phenomenon occurs with fluids such as high-pressure water. However, since water has a larger density than gas, the cooling capacity is too large, and cooling progresses to the hot slab, resulting in a large difference in thermal contraction between the scale and the slab, resulting in a descaling effect. Although the temperature does not increase very much, the temperature drop of the slab is large, resulting in poor bonding. Furthermore, in the case of water, there are new problems such as processing of accumulated water droplets after descaling, problems with hot water extraction due to steam generation from water bottles, etc., and environmental deterioration.

Next, examples will be described based on the method of the present invention.

A compressed air injection type descaling device was installed immediately after the output of the pinch rolls of the hot carbon steel slabs obtained from the V-B type high-speed prefecture @ Iso, and the descaling degree was tested over a long period of time.

The preparation conditions are as follows.

Slab size: 250~270rfan thickness x 1100~11
6Ona width drawing speed: 1. O~1.7 m/min Pinch roll outlet temperature: 980~1070°C Roller apron cooling method: Mist cooling Compressed air injection conditions are as follows.

Injection angle: 45 degrees Injection distance: 15TRjn 15 + s + (b) Pressure at whom = 2 ~ from the nozzle tip
20 f/+rrri descaling results are shown in FIG.

In Figure 6, horizontal i + 111] Pneumatic pressure at 15 points from the tip of the id nozzle (g/1111112)
5, and the vertical axis indicates the degree of descaling. The degree of descaling becomes better as the number increases. Exploration/Drinking Eye Kai is 6.

In the figure, the white circle (○) indicates the case without nozzle rocking, the black circle (@) indicates the case with nozzle floating, and the boiled white circle (
○′] indicates the case where the compressed air injection method is not continuous but pulsated.

As can be seen from FIG. 3, according to the method of the present invention, a good theory scale can be obtained. Further, according to the method of the present invention, the temperature of the slab becomes 5° C. or less, the running cost is significantly reduced, and maintenance becomes better.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the method of this investigation. FIG. 2 is a schematic explanatory diagram of an apparatus for carrying out the method of the present invention. Figure 6 shows the relationship between Tabo pressure and descaling degree.Graph 1: Continuous preparation line
2: Pinch roll 6: Hot flaw detector 4: Scaling device 5: Slab 41: Nozzle/bender 42: Holder 46: Pressure air supply source 44: Concave rock structure 411: Nozzle. Patent applicant Sumitomo Metal Industries Ltd. (4 others)

Claims (3)

[Claims] (1) In a continuous casting line where the slab temperature at the exit side of the pinch rolls is 850°C or higher, a descaling device must be installed in the shadow of the pinch roll hot flaw detector, and the descaling device must be of the Laval nozzle type. The compressed gas injection method is configured such that the injection angle of the compressed gas is set at 5 to 90 degrees with respect to the surface of the slab toward the upstream side in the traveling direction of the slab, and the distribution of the compressed gas is determined by the surface position. An excellent method for descaling hot slabs, which comprises setting the pressure applied to 51/- or more. (2) The method according to claim (1), characterized in that the injection point of the compressed gas is moved in the width direction of the slab. (3) The method according to claim 11, characterized in that the injection of the compressed gas is balseized.