JP2000017325A - Walking hearth type heating furnace and method for carrying round cross sectional material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for turning a material at a suitable position in a furnace in order to achieve the decrease of uneven heat at the upper and the lower parts of a material to be heated while restraining the lowering of a furnace capacity and the increase of an equipment cost to the minimum in a walking hearth type heating furnace. SOLUTION: In the limited range of at least either one of a moving furnace hearth or a fixed furnace hearth in this walking hearth type heating furnace for a steel material, one pair or more of slopes 2 rolling down a round cross sectional material with the material dead wt., are formed and a furnace hearth in a range except the slopes is almost flattened. The shape of the slope is formed so that the length B2 in the slope horizontal direction of a side where the material steps over, is got over even in the shortest carrying pitch. Further, the length B1 of the slope on which the material rolls down, is made so as to obtain the necessary material rotation per one time. Then, the material is rolled down by laying the slope at each one time of carrying. In this way, even in the case that the interval of the material is not specially widened, the material is uniformly heated from the all surfaces in order according to the turning to decrease the uneven heat at the upper and the lower parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a walking hearth type heating furnace for steel materials such as carbon steel and stainless steel, and a method for conveying solid and hollow circular cross-sectional materials in the heating furnace.

[0002]

2. Description of the Related Art One type of continuous heating furnace is a walking hearth type, which is often used as a heating means for a relatively small-section steel material (hereinafter, referred to as a material) such as a bloom or billet. The features of this type of heating furnace are that the material is not rubbed against the hearth as in a pusher furnace because it is transported by a moving hearth, and there are no sliding flaws. The structure is simpler than a beam furnace.

On the other hand, the disadvantage is that the temperature difference in the vertical direction of the cross section perpendicular to the longitudinal direction of the material (hereinafter referred to as vertical heat deviation) tends to be large. This is because there is no heating means from the lower surface.
Generally, a gap is provided between adjacent materials during transportation so that radiant heating from the combustion gas is effectively performed.

[0004] Further, there is a method in which the movable hearth is raised at all times and a space is provided between the fixed hearth and the material by increasing the radiation below the material (Japanese Patent Laid-Open No. 57-123915). By sequentially changing the transfer start position when loading the furnace, each time the material is transferred, it is placed on the furnace floor heated by the radiant heat inside the furnace without the previous material being loaded, and the heat is transferred from there to the upper and lower (Japanese Unexamined Patent Application Publication No. 5-126472) has been implemented. Further, when the material has a circular cross-section, Japanese Unexamined Patent Publication Nos.
There is also a method of heating a material while rotating the material as disclosed in Japanese Patent No. 21110.

[0005]

The heating capacity per unit time and per unit hearth area, that is, the so-called hearth load decreases as the distance between the materials is increased in order to reduce the vertical deviation of heat. For this reason, in the walking beam type heating furnace, the heating zone and the soot transport mechanism are made independent, and the heating zone is narrowed to increase the hearth load in the heating zone. In some cases, the overall capacity is reduced to a minimum.

However, in the case of the walking hearth type heating furnace, it is difficult to make the hearths of the divided parts intersect with each other as in the walking beam type, so that most of the moving hearths are integrated in the furnace length direction. And the material spacing cannot be changed from charge to extraction. Therefore, it is necessary to give priority to either the heating capacity or the reduction in vertical deviation due to the product type.

[0007] There is also a problem with the method of reducing the vertical deviation of heat taken so far. That is, JP-A-57-123915
In the method disclosed in Japanese Unexamined Patent Application Publication No. H10-27, the range in which the material is floating from the hearth is convenient, but the portion in contact with the hearth is It is not effective and may cause a temperature difference in the longitudinal direction of the material. Also, disclosed in Japanese Patent Application Laid-Open No. 5-126472,
In the method in which the transfer start position at the time of charging the furnace is changed so that the material does not overlap the hearth on which the preceding material has been placed, the space between the materials is further increased than in the case where the transfer amount is constant, and the heating capacity is reduced.

As disclosed in Japanese Patent Application Laid-Open No. Sho 60-211101, a method of placing a circular cross-section material on a slope and rotating it by its own weight is mainly performed in a walking beam furnace. There are issues like: In other words, in a walking beam furnace, the heat-resistant steel skid is installed over the entire length of the furnace regardless of the material cross-sectional shape.
By making this skid shape into a waveform with a slope in advance, it is possible to carry out rotation with little additional equipment cost, but in a walking hearth furnace, the hearth is generally refractory brick, and equipment for installing the skid is necessary. Additional costs are required.

In addition, compared to the case where the hearth is flat, the heating capacity is reduced due to the space for rotating the material on the slope. Furthermore, since there is no large space at the lower part as in a walking beam furnace, scale tends to accumulate on the slope, which increases the rolling resistance and hinders material rotation. As a problem in heat deviation, when the skid is made of heat-resistant steel, the lower portion is supported by an internal water-cooled pipe, so that the temperature of the material in contact with the skid is reduced and skid marks are generated.

[0010]

The gist of the present invention to achieve the above object is as follows. (1) In a walking hearth heating furnace having a moving hearth and a fixed-hearth for placing a material to be heated and transporting the inside of the furnace, at least either the moving hearth or the fixed hearth. A walking hearth type heating furnace characterized in that a slope for rotating a predetermined angle by rolling a circular cross-section material by its own weight is formed on a part of the mounting surface. (2) The above-mentioned (1), wherein the slope for rolling the circular cross-section material is formed with skids sufficiently narrow in width relative to the length of the material to be heated, thereby providing a space below the slope to prevent scale deposition on the slope. The heating furnace as described. (3) The slope for rolling the circular cross-section material is installed only on one of the movable hearth and the fixed hearth, and the slope portion is lowered downward so as not to come into contact with the area where the material after rotation is located during standby for transportation. The heating furnace according to the above (1) or (2), wherein the portion other than the slope portion is positioned so as to support the material at the same height as the hearth where the slope is not installed. (4) When transporting a circular section material using the heating furnace according to any one of the above (1) to (3), the relationship between the slope length and one horizontal transport distance is determined by the horizontal transport distance. When the circular cross-section material rolls down over the slope top when it is short, and the circular cross-section material rolls down when the longest horizontal transport distance is at a predetermined angle A method for transporting a material having a circular cross section in a walking hearth heating furnace, characterized in that the material is rotated only by rotation. (5) When the circular section material rotates on the slope of the hearth, the rotation is performed stepwise a plurality of times, and the sum of the rotation angles is 180 ° or more. (4) The method for conveying a circular cross-section material according to (4).

Here, the installation area of the slope for rolling the circular cross-section material is limited to a part of the material mounting surface.
It is more preferable that the content be not more than 2/20 for achieving the object of the present invention. Also, the hearth portion other than the installation of the slope portion may be provided with small irregularities or bump-shaped protrusions so that the circular cross section material does not roll on the hearth, or conversely, a flatness in which the circular cross section material easily rolls. Good. Further, the width of the skid forming the slope for rolling the circular cross-section material needs to be sufficiently narrow with respect to the length of the material to be heated. However, it is desirable that the skid width at one location be approximately 150 mm or less.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moving hearth and / or a fixed hearth of a walking hearth furnace.
Alternatively, for both, the slope for rolling the circular cross-section material by its own weight is formed in a limited area, and the remaining hearth is made substantially flat,
The amount of horizontal transfer per time is a short feed amount based on the material interval in the hearth flat part, while emphasizing heating capacity,
This is a means to reduce the vertical deviation of heat by reliably rotating the material on the slope.

First, a pair of slopes which are on the same straight line in the furnace width direction are formed in a necessary and sufficient shape and number capable of obtaining the amount of rotation of the material falling within the allowable value of the vertical deflection. The degree to which the material is radiantly heated from the surroundings becomes smaller as the upper surface becomes the largest through the side surfaces and becomes lower. for that reason,
It is difficult to eliminate the temperature difference with the side surface simply by turning over. From this, it is desirable that the total rotation angle be 180 ° or more so that the material is turned upside down while the side surface is heated in a plurality of stages at a rotation angle of about 15 ° to 120 ° at one time. . This slope installation range is arbitrary, but for example, in the case of a two-zone heating furnace consisting of a heating zone and a soaking zone, it is important that the heating capacity is emphasized in the heating zone, the hearth is flat, and the slope is provided after the soaking zone. desirable. Also,
The slope may be provided separately at a plurality of locations in the furnace.

Next, the method of transporting the material is such that, even when the horizontal conveying distance of the moving hearth is the shortest, the moving hearth is placed on the slope that rolls over the top of the slope, and even when the moving distance is longest, After turning on the slope, it is necessary to rotate by the required angle.

In order to prevent scale from accumulating on the slope and increasing the rolling resistance, the slope is a skid sufficiently narrower than the furnace width, and the slope other than the skid is a space. This makes it easier for the scale on the skid to fall into the space on both sides of the skid and prevents the scale from being deposited, thereby preventing an increase in the rolling resistance of the skid and maintaining a stable rotation of the material for a long time.

The skid is desirably made of steel from the viewpoint of durability. However, in order to suppress skid marks, the skid is installed only on one of the movable hearth and the fixed hearth, and the material is skid during standby. And so as not to touch directly. At this time, the hearth flat portion has the same height as the hearth where the skid is not installed, and the material is supported by both the movable hearth and the fixed hearth. However, if there is a risk of sagging of the material because the skid does not support the material, keep the vertical distance between the skid and the material below a certain value, and if the material sags a certain amount, touch the skid and The sag is prevented from progressing, and the moving hearth is moved up and down to support the material at regular intervals.

[0017]

Next, the present invention will be described with reference to the drawings. In addition, although each drawing shows an example in which the slope is installed on the movable hearth, the same applies to the case where the slope is installed on the fixed hearth. FIG.
An embodiment of the first aspect of the present invention is shown in FIG. The illustrated walking hearth type heating furnace is an upper two-zone type comprising a heating zone 3 and a soaking zone 4, and a circular section material 5 is lifted by a lifting device 6 of a movable hearth 1 installed at the lower part of the furnace, and is conveyed in a horizontal direction. Device 7
, The paper is sequentially and intermittently conveyed from left to right in the figure.

In such a heating furnace, a plurality of slopes 2 for rotating the material 5 are arranged downstream of the soaking zone 4 of the moving hearth 1, and the other hearths are made substantially flat. However, when the material conveyance pitch is limited or when the material easily rolls during conveyance, the hearth of the flat portion may have a small waveform, or a bumper-shaped skid may be provided in some places.

FIG. 2 shows an embodiment of the carrying method according to the present invention. Although the shape of the slope 2 shown in FIG. 2 is slightly changed from that of the first step to that of the second step and thereafter, all may be the same or different one by one as long as certain conditions are satisfied. In FIG. 2, the slope height H ₁ is set so that when the moving hearth is retreating at the lower limit, the moving hearth is at the lower limit and the adjacent fixed hearth does not interfere with the material. Lower than the height of The horizontal distance B ₂ slopes side across skid material is to exceed a slope top in the shortest transport distance. On the other hand, the horizontal distance B _{1 of the} slope on the material rotation side of the skid is combined with the horizontal transport distance P for one cycle to set a condition that a rolling distance L at a target rotation angle on the slope is obtained. The groove bottom of the slope 2 is formed in an arc having a radius R, and the material is gently stopped after the material has rolled down the slope to avoid a strong collision with the next slope.

In consideration of the above points, the angle θ _{1 of the} slope on the rotating side of the material of the skid and the angle θ ₂ of the slope on the side on which the material of the skid straddles are appropriately determined. In FIG. 2, a: a state in which the material has reached the side of the first skid, b: a state in which the material is at the bottom of the skid groove after rotation, c: a state in which the material is conveyed one time and is above the slope, and d: a state in which the material is above the slope. Each state is shown in a state of being conveyed once and rolling down the slope to reach the skid groove bottom.

In the above structure, the material is set at the slope pitch W
By transporting with a shorter transport distance P, the material is placed on the slope and rolls down to the groove bottom. The material stop position coincides with the center of the arc at the bottom of the groove if the rotation is smooth after placing on the first slope. Therefore, by selecting the conditions of the slope shape, the number of slopes, and the transport pitch, the rotation angle per rotation and the total rotation angle can be optimized according to the material conditions. By rotating the material in this way and heating the outer surface several times, the material cross section is also heated evenly from multiple directions, reducing uneven heat in the vertical direction.It is necessary to increase the transport amount to increase the material spacing. Disappears.

Next, a second embodiment will be described with reference to FIGS.
This will be described with reference to FIG. The slope 2 is a skid, which is sufficiently narrower than the length of the material 5 as shown in FIG.
By doing so, most of the lower part of the slope can be made a space, and the oxide scale falling from the material 5 is prevented from accumulating on the slope to increase the rolling resistance. Can be maintained over time. Further, as shown in FIG. 2, by increasing only the H ₂ from the hearth of the groove bottom height of the skid, suppressing the influence of the scale deposition even in the material stops after rotation, be long-term stability of the stop position Can be.

Next, a third embodiment will be described with reference to FIGS. 3, 4, and 5. FIG. If the skid is made of steel,
It is common to install the skid 2 on a cooling pipe 9 which also serves as a support structure below the surface of the hearth 1 to cool the skid, as described in the above, for the durability of the skid. Therefore, the temperature of the skid is lower than that of a flat part of the hearth made of a firebrick or the like, and when the material comes into contact with the skid, the temperature is lowered by heat conduction, and a skid mark is generated. In order to prevent this, as shown in FIG. 4, the material 5 is supported on the adjacent fixed hearth 8 at the time of conveyance standby,
The moving hearth 1 is lowered so that the skid 2 does not contact the material. However, since the material bends at high temperatures due to creep, the flat part of the hearth has the same hearth height as the adjacent fixed hearth side as shown in FIG. 5 (a), and supports the entire length of the material to reduce creep deflection. To prevent. Since the material rotates in the skid portion, the direction due to creep differs in direction from the viewpoint of the material for each rotation, and the deflection is dispersed and does not accumulate.

FIGS. 5A, 5B, 5C, and 5D show the states of material transport. (A) is a conveyance standby state. At this time, the skid 2 portion of the movable hearth 1 lowers the groove bottom portion where the material 5 is located after the rotation, and a space is provided between the skid and the material so that the two do not directly contact. The top of the skid 2 may be slightly higher than the height of the fixed hearth 8. Next, (b) shows a state where the moving hearth 1 has been lowered once and then retreated. The top of the first slope skid is located between the material on the most extraction side of the hearth plateau and the following material. (C) is a state in which the moving hearth is raised. At this time, the material is placed on the slope, rolls down, rotates, and stops at the groove bottom. (D) shows a state in which the movable hearth has moved forward, and the material placed on the groove bottom further moves forward by one transfer amount. Thereafter, the movable hearth 1 descends and returns to the state shown in FIG.

[0025]

In the walking hearth type heating furnace, the slope for rolling down the circular cross-section material is set in a limited area, and the relationship between the slope length and the horizontal conveyance distance is determined. Even when the horizontal conveyance distance is shortest, the circular cross-section material is used. Is designed to be placed on the slope that rolls over the top of the slope, and that even when the transport distance in the horizontal direction is longest, the circular cross-section material is rotated by a predetermined angle after being placed on the slope that rolls down. In the method of the present invention, since it is not necessary to increase the material interval in order to reduce the vertical deviation of heat, it is possible to eliminate a decrease in the heating capacity as compared with the case where the material intervals in all the furnaces are increased. Further, according to the apparatus of the present invention, the degree of freedom of the horizontal transfer amount is large and the equipment cost can be significantly reduced as compared with the case where a slope for rotating the material is installed over the entire length of the furnace. Further, when a steel skid is used, the length of a water cooling tube supporting the skid can be shortened to minimize cooling water loss.

Further, by making the slope for rolling the circular section material a skid sufficiently narrow in width relative to the length of the material to be heated,
The function of suppressing the scale deposition on the rolling slope and rotating the circular section material can be exhibited for a long period of time. Furthermore, by lowering the hearth on the skid installation side relative to the other hearth so that the skid does not touch the material to be heated, the skid marks on the material are reduced and the temperature is uniform in the longitudinal direction. Can be

[Brief description of the drawings]

FIG. 1 is a schematic view showing a walking hearth furnace according to an embodiment of the present invention, in which a slope for rolling a material having a circular cross section is provided in a uniform tropical zone.

FIG. 2 is a diagram showing a relationship between a shape of a slope on which a circular cross-section material is rolled and a horizontal conveying distance according to the present invention.

FIG. 3 is an explanatory view of a supporting example of a steel skid employed in the present invention.

FIG. 4 is an explanatory view in a case where a skid is installed on a moving hearth in an example in which the skid and the material to be heated are prevented from touching during standby.

FIGS. 5A and 5B are explanatory views of the transfer method of the present invention in which the skid and the material to be heated are prevented from touching during standby; FIG. 5A illustrates a case where the moving hearth is at the standby position; FIG. (C) when the moving hearth is in the raised position,
(D) shows the case where the moving hearth is at the forward position.

[Explanation of symbols]

1: Moving hearth 2: Slope or skid 3: Heating zone 4: Uniform tropical zone 5: Heated material 6: Moving hearth lifting / lowering device 7: Moving hearth horizontal transfer device 8: Fixed hearth 9: Skid support water-cooling pipe 10: moving hearth hearth frame 11: fixed hearth hearth frame 12: water-cooled tube support frame H _1: from hearth to skid groove bottom: height H ₂ of from the furnace floor to skid top Height B ₁ : Horizontal distance of the slope on the rotating side of the material of the skid B ₂ : Horizontal distance of the slope on the side on which the material of the skid straddles W: Pitch of the skid P: Horizontal distance of material transport per turn L: On one slope Rolling distance of material R: radius of arc at bottom of skid groove

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuru Ishizaki 4-3-1 Funato, Itabashi-ku, Tokyo F-term in Nippon Steel Corporation Tokyo Works (reference) 4K034 AA03 AA06 BA03 BA06 BA08 CA01 DB02 DB04 EA15 EB23 EB24 4K050 AA01 BA02 CA09 CA13 CD02 CG13 CG16 CG27

Claims (5)

[Claims] 1. A walking hearth heating furnace in which a moving hearth and a fixed hearth for placing a material to be heated and transporting the inside of the furnace are arranged. A walking hearth-type heating furnace, wherein a slope for rotating a predetermined angle by rolling a circular cross-section material by its own weight is formed on a part of one of the mounting surfaces. 2. A space under a slope is formed by forming a slope for rolling a material having a circular cross section with a skid having a width sufficiently small with respect to the length of a material to be heated, thereby preventing scale deposition on the slope. The heating furnace according to 1. 3. A slope for rolling a material having a circular cross section is provided only on one of a movable hearth and a fixed hearth, and the slope portion does not come into contact with an area where the material after rotation is located during standby for transportation. The heating furnace according to claim 1 or 2, wherein a portion other than the slope portion is located below and has a positional relationship of supporting the material at the same height as the hearth where the slope is not installed. 4. When conveying a material having a circular cross section using the heating furnace according to any one of claims 1 to 3, the relationship between the slope length and a single horizontal conveying distance is determined by determining the maximum horizontal conveying distance. When the circular section material rolls over the top of the slope when it is short, it should be placed on the slope where it rolls down, and when the horizontal transport distance is the longest, the circular section material rolls on the slope on which it rolls down. A method for transporting a material having a circular cross section in a walking hearth heating furnace, characterized in that the material is rotated. 5. When the circular section material rotates on the slope of the hearth, the rotation is performed stepwise a plurality of times,
5. The method according to claim 4, wherein the sum of the rotation angles is 180 [deg.] Or more.