JP2000061656A - Billet joining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve joining strength between a preceding billet and succeeding billet by forming the end part of the billet into an engageable shape before the billet is hot-rolled by a continuous type rolling mill as a base stock for wire rod or steel bar having a round or square cross section and rolling the formed end parts by a four-roll rolling mill in an overlapped or fitted state mutually thereby engaging them. SOLUTION: In the end part of a billet heated by a heating furnace 1, its top end part is worked into an inverse triangular shape and its tail end is worked into a triangular shape respectively by a press device 4, and surface scales are removed by a descaling device 6. Thereafter, the top end of a succeeding billet is rapidly sent by a pinch roll 5, overlapped and engaged with the end part of a preceding billet mutually, then the end parts of both billets are storngly rolled down by two four-roll rolling mills 7a, 7b in this state. In this case, a roll arrangement or joining surface position is adjusted so that the width direction of a joining surface is rolled by a rolling roll from both sides. Successively, an actual rolling operation is executed, that is, rough rolling and finish rolling or the like are successively executed to form a wire rod or bar stock as a product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of joining end portions of a heated billet to each other as a pre-stage of continuous hot rolling of a raw material for producing a wire rod or a steel bar.

[0002]

2. Description of the Related Art A continuously cast billet is cut into a predetermined length according to the dimensions of a heating furnace before being heated. Then, the billet heated in the heating furnace is sequentially sent to a hot rolling line starting from the row of rough rolling mills and rolled to be a target wire rod or steel bar.

At this time, when the material (billet) enters the rolling mill, the tip of the material hits the guide or the rolling roll, and when the tail end of the material comes out of the rolling mill, the shape of the tail end and Depending on the rolling conditions etc., narrowing may occur and rolling troubles such as roll damage may occur.

In order to avoid such rolling troubles,
Continuous hot rolling is performed by joining the longitudinal ends of the billet (the leading end of the trailing member and the tail end of the preceding member) to each other. As a conventional method for joining billets, as described in JP-A-53-7559, a method of welding and joining the ends of the billet by flash butt welding, and JP-A-61-238482. As described, a method in which the ends of the billet are inserted into the metal tube from both sides, the two are connected, and the whole is directly rolled on a rolling line to join the billet.
As described in Japanese Patent No. 141303, the ends of the billets to be joined are reduced in thickness by press molding so that they can be engaged with each other, and then the ends are superposed and pressed together in the direction of superposition to join them. Methods etc. have been proposed.

[0005]

However, in the joining by the above welding, a wide space for installing a welding line and a welding apparatus is required, and the welding apparatus itself is expensive. However, there is a problem that it is required to move the billet in synchronization with the movement.

Further, after the welding and joining, post-processes such as deburring of the welded portion and shaping of the deformed portion are required, and post-treatment equipment other than the welding device is also required. Further, the joining method using the above metal pipe has the following problems. That is, since the rough rolling process, which is the first rolling process of the rolling line, is performed by the two-roll rolling mill, the two rolling rolls are joined in the rolling direction, but the pressure is not applied in the direction orthogonal to the rolling direction. No bonding or weak bonding strength. Therefore, there is a problem that the joining strength required in continuous rolling is not secured and rolling trouble occurs at the joining portion, which causes a decrease in yield.

Further, the above-mentioned method of overlapping the formed end portions and press-contacting each other has no problem in the plate rolling without the width expansion, but in the bar steel rolling with the width expansion, the boundary surface between the preceding material and the following material is However, there is a problem that the bonding strength is weakened because the metal flows of the are different.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a billet joining method suitable for joining billets having a round cross section or a square cross section.

[0009]

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is a continuous rolling mill in which a billet having a round cross section or a square cross section is used as a material for wire rods and steel bars. Before hot rolling, in the billet joining method of joining the longitudinal ends of the billet heated,
Billet joining, characterized in that the ends of the billets to be joined are formed into shapes that can be engaged, and the formed ends are overlapped or fitted together and rolled by a 4-roll rolling machine to join them. It provides a method.

Here, the molding of the ends of the billets to be joined into a shape that can be engaged with each other means that the ends of the billets to be joined can be fitted to each other (including fitting by overlapping). Say.

Next, the invention described in claim 2 is characterized in that, in contrast to the structure described in claim 1, the area reduction rate of the rolling by the above four-roll rolling mill is set to 30% or more. is there.

Here, when the 4-roll rolling mill is constituted by a plurality of passes, the above-mentioned area reduction rate means a total area reduction rate in all the plurality of passes. The present invention is based on the finding that if the joints between billet ends are pressure-welded by four-roll rolling, the joints are rolled and joined by a four-roll rolling machine based on the finding that the width is not widened like plate rolling. To do.

FIG. 1 shows the examination of the width-spreading characteristics when the two-roll rolling and the four-roll rolling are performed on the joint between billets in the strip steel rolling. Figure 1
Among them, A is due to 2-roll rolling and B is due to 4-roll rolling.

Here, the width expansion ratio in FIG.
(Width after rolling / width before rolling). As can be seen from FIG. 1, the two-roll rolling is accompanied by the width expansion, but it is understood that the four-roll rolling can suppress the width expansion. On the contrary, the narrowed width improves the bonding strength.

For example, in the conventional method of connecting with a metal tube and then performing two-roll rolling in a rough rolling step, as shown in FIG. 2, even if pressed in the rolling direction, it is in the direction orthogonal to the rolling direction. As a result, a gap D is formed between the metal tube 50 and the billet 51, so that the joint strength decreases. Reference numeral 52
Indicates a rolling down device. On the other hand, when four-roll rolling is performed, the width is not spread due to simultaneous rolling from four directions.
On the contrary, since the width is narrowed, a strong pressure is applied to the entire peripheral surface, so that the welding can be performed with the joining strength required for continuous rolling.

Further, in this case, since the joint surface is formed into the same shape as the front and rear cross-sections, no special device for post-treatment such as shaping treatment is required, and the billet joining treatment can be continuously rolled. .

That is, since the material rolled by the four-roll rolling machine is directly sent to the ordinary rolling line, the rough rolling machine train is connected by the amount of rolling by the four-roll rolling machine for joining. It is possible to make it shorter, and even if new billet joining equipment is added, the increase in the overall line length will be small.

Further, in the rolling by the 4-roll rolling machine for joining, regardless of the number of passes, by setting the area reduction rate of the entire 4-roll rolling to 30% or more, it is possible to carry out rolling continuously. Since it has been confirmed that the bonding strength can be reliably ensured (see FIG. 8 described later), in the present invention, the surface reduction rate in the 4-roll rolling mill is set to 30% or more.

The upper limit of the surface reduction rate is naturally determined by the roll pass design. That is, it is common knowledge of rolling to perform rolling in a range where biting out from the roll to be rolled does not occur, and from this viewpoint, the upper limit of the area reduction rate is regulated.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 3, the equipment of this embodiment includes a heating furnace 1, a billet joining equipment 2, and a continuous hot rolling mill train 3 (only a rough rolling mill train is shown in FIG. 3) from the upstream side. Are arranged.

The billet joining equipment 2 of this embodiment comprises a pressing device 4, a pinch roll 5, a descaling device 6 and a 4-roll rolling mill train 7. The pressing device 4 is a device for processing the end portion of the billet 10 from the heating furnace 1. As shown in FIGS. 4 and 5, the tip portion of the billet 10 is crushed on the lower side to have a cross-section Δ shape (see FIG. 5), the tail end is pressed so that the upper side is crushed and processed into a ∇-shaped cross section (see FIG. 4), and the tail end of the preceding material 10 and the tip of the following material 10 are overlapped. It is formed into a shape that engages with.

The 4-roll rolling mill train 7 is composed of two passes, the first roll 7a is arranged in a cross shape, and the second roll 7b is arranged in an X shape with a 45 ° inclination. (See Figure 6).

In the above equipment, 1000 to 11 in the heating furnace 1
The end portion of the billet 10 heated to 00 ° C. is processed by the pressing device 4 into a ▽ shape at the front end and a Δ shape at the rear end, and then the surface scale is removed by the descaling device 6, and then the succeeding material 10 is formed. The leading edge of the material is fast-forwarded with a pinch roll 5
After overlapping and engaging with the end of No. 0, as it is, as shown in FIG. 6, two 4-roll rolling mills 7a, 7
It is strongly reduced at b.

In FIG. 6, reference numeral 11 indicates a rolling roll, and 1
0 indicates a billet. The alternate long and short dash line shows the shape of the billet 10 before rolling, and the symbol C shows the joint surface between the billet ends.

Here, as shown in FIG. 6 (a), in order to ensure reliable joining, a rolling roll 11 (vertical roll in FIG. 6 (a)) having a first pass in the width direction of the joining surface C is used. It is preferable to adjust the roll arrangement or the position of the joint surface between the billet ends so that the rolling is performed from both sides.

The pinch roll 5 also serves to apply a pushing force to the trailing material so that the billets do not separate from each other during the rolling. Further, the rolling-down pattern in the two 4-roll rolling mills 7a and 7b is, for example, as shown in FIG.
From 0φ to 100φ, set a strong reduction of about 55%.

Then, the actual rolling operation is performed, that is, the rough rolling and the finish rolling are sequentially carried out to obtain a wire rod or a steel bar as a product. The following effects are brought about by the above operation. Since the billets are continuously supplied to the rolling line, the loss time between billets is eliminated in the rolling operation, so that the efficiency is improved. Higher rolling troubles are reduced in the tip and tail portions, improving the operating rate. For this reason, the front end and the tail end of the rolled material are generally cut and discarded as defective portions, but the defective portions are suppressed from occurring and the yield is improved.

In particular, in this embodiment, the joining strength required for continuous rolling is reliably ensured between the billets and the width is not widened in the vicinity of the joining portion. That is, continuous rolling can be reliably performed, and rolling trouble at the billet end can be reliably suppressed. Since the equipment space is small, the billet joining equipment can be installed inexpensively by modifying the existing equipment.

In addition, the equipment does not require a post-treatment device such as a welding machine or a deburring device after joining, and thus the investment can be inexpensive. Here, in the above-described embodiment, the case where the 4-roll rolling mill 7 is configured with two passes is described as an example, but one pass may be used or three passes.
It may be more than the pass.

Further, the processing shape of the billet end is not limited to the above-mentioned shape, and may be any other shape as long as the ends can be formed into a shape capable of engaging with each other. For example, the billet 10 may be formed into a shape as shown in FIG. 7, and the ends of the billet 10 may be fitted to each other to be engaged with each other, and 4-roll rolling may be performed as they are.

[0031]

EXAMPLE An experiment was conducted on the relationship between the area reduction rate in the above four-roll rolling and the rate of occurrence of defective bonding in the subsequent rolling operation, and the results shown in FIG. 8 were obtained.

The number of passes of four-roll rolling is performed in three ways, one to three, respectively, and the area reduction rate is represented by the total area reduction rate of the entire four-roll rolling mill train. As can be seen from FIG. 8, when the total area reduction rate by 4-roll rolling is 30% or more regardless of the number of passes, the defective joint occurrence rate becomes almost zero, and continuous rolling can be performed on the joined portion. It is understood that sufficient bonding strength can be obtained.

[0033]

As described above, when the billet joining method of the present invention is adopted, a joining strength of a predetermined value or more is secured for joining billets as raw materials for wire rods and steel bars with inexpensive equipment. It This has the effect of suppressing rolling troubles due to defective joints, leading to an improvement in the yield of continuous hot rolling for wire rods and steel bars.

At this time, if the invention described in claim 2 is adopted, there is an effect that the joining strength required for continuous rolling is surely secured.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a surface reduction rate and a width expansion.

FIG. 2 is a diagram showing a state of pressure welding using a metal tube.

FIG. 3 is a diagram showing a facility layout according to the embodiment of the present invention.

FIG. 4 is a view showing a processed shape of a billet tip portion,
(A) shows a side view and (b) shows a front view.

FIG. 5 is a view showing a processed shape of a billet tail end portion,
(A) shows a front view and (b) shows a side view.

FIG. 6 is a diagram showing rolling by a 4-roll rolling mill according to an embodiment of the present invention, in which (a) is the first unit and (b) is 2 units.
Show the table.

FIG. 7 is a side view showing another example of processing the billet end portion.

FIG. 8 is a diagram showing a relationship between a surface reduction rate and a bonding failure occurrence rate.

[Explanation of symbols]

1 heating furnace 2 Billet joining equipment 4 Press equipment 5 pinch rolls 6 Descaling device 7 4-roll mill 10 billets 11 rolling rolls

Claims (2)

[Claims] 1. A billet joining method for joining longitudinal ends of heated billets to each other before hot rolling a billet having a round cross section or a square cross section as a wire / bar stock material by a continuous rolling mill, Billet joining, characterized in that the ends of the billets to be joined are formed into shapes that can be engaged, and the formed ends are overlapped or fitted together and rolled by a 4-roll rolling machine to join them. Method. 2. The billet joining method according to claim 1, wherein the reduction rate of rolling by the four-roll rolling mill is set to 30% or more.