JP3060687B2 - Hot steel joining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel materials on a rolling line in order to continuously perform hot rolling.

[0002]

2. Description of the Related Art Conventionally, in hot rolling of steel materials, intermittent rolling in which a heated slab is supplied one by one to a rolling line, and a slab is rolled by a rough rolling mill and a finishing rolling mill for each slab has been performed. In this method, there are many problems such as the end of the rolled material colliding with a guide or a roll of a finish rolling mill, causing flaws in the roll, and stopping the rolling work due to an increase in the number of roll changes. In addition, narrowing often occurs when the rear end of the rolled material passes through a rolling mill, so that it is necessary to take measures such as lowering the rolling speed, thereby lowering the rolling efficiency.
In addition, the leading end and the trailing end of the rolled material have large variations in product dimensions due to differences in thickness, and are more likely to be out of temperature and out of dimension than in the central portion in the longitudinal direction, and are therefore cut off as defective portions to reduce product yield. Invite.

[0003] As a method of solving the above problems,
The rear end of the preceding rolled material and the front end of the succeeding rolling mill are overlapped and joined between the rough rolling mill and the finish rolling mill, and continuous rolling is performed from rough rolling to finish rolling (finish continuous rolling). Various methods and devices have been proposed.

[0004] As one of them, Japanese Patent Publication No. 54-39195 proposes a joining method using a press machine.
In such a method, there is usually a press in which the upper mold is movable up and down and the lower mold is fixed. However, when such a press is used, the friction between the fixed lower die and the running rolled material causes the lower die to be severely worn and requires frequent replacement.

[0005] Since the time during which the lower surface of the steel material contacts the lower mold during the bonding of the steel material is long, the steel material is cooled, the temperature at the bonding interface decreases, and the bonding strength decreases. If the joining strength is not sufficient, the joint is broken at the time of finish rolling, so that continuous finishing rolling becomes impossible.

[0006] If the joint is heated with a burner to compensate for the decrease in temperature at the joint, there is a problem that the upper side of the rolled material is likely to be overheated.

A hydraulic press that moves up and down with a cylinder can be used for both the upper and lower dies. However, in this case, the time required for press contact is increased, the temperature of the steel material is reduced, and sufficient joining strength cannot be obtained. Reducing the welding time requires a large capacity hydraulic source, which is not practical.

[0008]

In order to join the preceding rolled material and the succeeding rolled material for performing the continuous continuous rolling, there is a method capable of quickly working with simple equipment and obtaining a joint having high strength. is necessary. An object of the present invention is to provide a method of overlapping and joining hot steel materials that meets such demands.

[0009]

The gist of the present invention is that "the rear end of the preceding rolled material on the hot rolling line and the front end of the succeeding rolled material are heated under a reducing atmosphere to overlap or overlap. And then heating in a reducing atmosphere and pressing the overlapped portion with a moving bed double-acting press. "

The preceding rolled material is a rolled material that travels first on a rolling line, and the succeeding rolled material is a rolled material that travels following the preceding rolled material. The hot steel material means a steel material in a hot state such as a heated steel material or a roughly rolled steel material.

The reducing atmosphere is, for example, an atmosphere of a reducing flame obtained by appropriately controlling an oxygen ratio when a combustible gas such as acetylene or propane is burned, or sealed with a reducing gas containing hydrogen gas. Means atmosphere.

The moving bed type double-acting press is a press which can vertically move up and down the molds by a single drive source.

[0013]

One of the features of the method of the present invention is that the overlap joining is carried out by a moving bed type double-acting press which can raise and lower not only the upper die but also the lower die.

FIGS. 1A and 1B show an example of a moving bed type double-acting press. FIG. 1A is a front view, and FIG. 1B is a side view.

The moving bed type double-acting press 1 has large gears 2 of rotating main shafts at both bottom ends thereof. A crankshaft 3 is provided outside the large gear 2 and a cam 4 is provided inside. Crankshaft 3
Are connected to both ends of the upper slide 6 by connecting rods 5,
At the center of the slide 6 is an adjusting screw 7. The slide 6 serves to change the rotational movement of the crankshaft 3 into a vertical movement.

An upper mold 8 is attached to the lower end of the adjusting screw 7.
Is fixed. On the other hand, a roller 9
The lower mold 10 is placed through. The lower mold 10 is moved up and down by the operation of the cam 4.

When the overlapped portion of the rolled material 11 is pressed into contact, first, the position of the upper mold 8 is adjusted with the adjusting screw 7, and when the overlapped portion comes to the press position, the electric motor 12 is pressed.
To rotate the large gear 1 of the rotating main shaft via the middle gear 14 and the small gear 13. When the large gear 1 rotates, the lower mold 10 rises by the action of the cam 4, and in synchronization with this, the upper mold 8 descends, and pressure welding is performed between these molds.

FIG. 2 shows the operation curve of the mold of the moving bed type double-acting press. The horizontal axis represents the rotation angle of the large gear 2, and the vertical axis represents the position in the height direction. As shown in the figure, the upper mold and the lower mold rapidly approach each other at a rotation angle of about 180 °, and press the steel material from above and below. Accordingly, the time during which the mold comes into contact with the steel material is short, so that the decrease in the temperature of the rolled material is reduced, and the wear of the mold is reduced. If the gap when the upper and lower dies are closest to each other with the adjusting screw 7 is appropriately adjusted according to the thickness and the rolling reduction of the rolled material, sufficient bonding strength can be obtained by one pressing operation. Can be

Another feature of the method of the present invention is that heating at the time of joining is performed in a reducing atmosphere. An oxide film (scale) is formed on the surface of the hot steel material in the previous heating and rolling processes, and it is generally considered that this scale must be completely removed before joining. However, if the bonding is performed in a reducing atmosphere, descaling is not always essential. For example, if the bonding surface is heated by using a reducing flame, the oxide film on the bonding surface is reduced and removed at the same time, and the bonding can be performed with sufficient strength by pressing immediately thereafter. Regarding the method of joining hot steel materials in a reducing atmosphere, the present applicant has previously filed Japanese Patent Application No. Hei.
A patent application has been filed as 2553.

In the method of the present invention, the heating in the reducing atmosphere may be performed before overlapping the materials to be joined.
It may be performed after overlapping. The former is desirable in order to more completely remove the oxide film, but the oxide film on the joint surface can be removed by heating in a reducing atmosphere even after the superposition.

[0021]

[Example] A 30 mm thick, 1220 mm wide, 2,000 mm long plain steel plate was used as a test material, pressed by a moving bed type composite press according to the method of the present invention, and this was finish-rolled to investigate the state of fracture. did. The plate before pressing is the one with the scale attached.

The test conditions and test results are as follows.

(1) Joining method A direct-fired reduction burner of φ60 mm is used at a pitch of 150 mm in the plate width direction.
The rear end of one of the plates of the above size (preceding rolled material) and the front end of the other one (post-rolled material) are arranged in a heating device arranged in a row.
Heated to 1100 ° C. The combustion conditions of the burner were set to an air ratio (m) using coke oven gas as fuel.

After the temperature was raised to the above-mentioned temperature, both ends were overlapped by 100 mm, and immediately pressed by a moving bed type double-acting press as shown in FIG. 1 for 0.5 seconds. The rolling reduction at this time was set to 50% (the thickness of the overlapped portion was reduced from 60 mm to 30 mm).

(2) Finish Rolling The rolling was performed at a rolling temperature of 1000 ° C. using a 7-stand tandem rolling mill (work roll diameter: 770 to 660 mm) at an initial draft of 55% and an initial rolling speed of 48 mm / min.

(3) Test Results As a result of performing the above test seven times, the finish rolling was all performed smoothly, and there was no trouble such as breakage of the joint. From this result, it can be inferred that the temperature of the rolled material at the time of joining hardly decreases, and the joint has sufficient strength.

For comparison, a lower mold fixed type press was used, the other conditions were the same as above, and pressure welding was performed, and finish rolling was performed in the same manner. The joint broke between the two. This is because the temperature of the rolled material was lowered before joining because the contact time with the lower mold was long, and sufficient joining strength could not be obtained.

[0028]

According to the method of the present invention, hot steel materials can be relatively easily and reliably overlapped and joined. The equipment used is not too complicated and can be easily integrated into existing rolling lines. By securing high joining strength by this method, highly efficient finish continuous rolling can be realized.

[Brief description of the drawings]

FIG. 1 is a view showing a moving bed type composite press used in the method of the present invention, wherein (a) is a front view and (b) is a side view.

FIG. 2 is an operation curve diagram of an upper die and a lower die of the moving bed type double-acting press.

[Explanation of symbols]

1: moving bed double-acting press 2: large rotating spindle gear 3: crankshaft 4: cam 5: connecting rod 6: slide 7:
Adjustment screw, 8: Upper mold, 9: Roller, 10: Lower mold 11: Rolled material, 12: Electric motor, 13: Small gear, 14: Medium gear

Continuation of front page (56) References JP-A-60-244407 (JP, A) JP-A-5-57306 (JP, A) JP-A-5-15902 (JP, A) JP-A-6-71306 (JP, A) JP-A-5-50111 (JP, A) JP-A-60-244406 (JP, A) JP-A-4-200907 (JP, A) JP-A-4-200984 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B21B 15/00 B21B 1/26 B23K 20/00 340 B23K 20/14 B30B 1/26

Claims (1)

(57) [Claims] The present invention is characterized in that a rear end portion of a preceding rolled material and a front end portion of a succeeding rolled material on a hot rolling line are overlapped by being heated in a reducing atmosphere, or heated in a reducing atmosphere after being overlapped. A method for joining hot-rolled steel materials, wherein the overlapped portions are pressed by a moving-bed double-acting press.