JPS631379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for continuous annealing of thin strips, such as tin blanks, in a continuous annealing line.

(Prior art) Tin plate blanks are manufactured on a continuous annealing line equipped with a skin-pass rolling mill.The continuous annealing line, which is a feature of the continuous annealing line, can be fully utilized to achieve a uniform length of material. In addition to obtaining a uniform product across the board,
In terms of operation, it is important to consistently operate under specified operating conditions.

The strip to be continuously annealed is connected to the next stage strip by lap welding to form a continuous strip, which is annealed in a continuous annealing furnace at a predetermined thermal cycle, and then temper rolled in a temper rolling mill. administered.

By the way, this welded joint is one of the causes of flaws in the rolls of the temper rolling mill, so in order to avoid this, before the welded joint passes through the temper rolling mill, the upper and lower rolls must be Measures are taken to prevent the weld from coming into contact with the roll by opening the gap between the rolls, or to reduce the rolling force of the roll.

For this reason, the range of several meters before and after the welded joint is different from other parts in terms of material and becomes a non-conforming area. It has not yet been possible to manufacture a product with uniform material over the years.

This problem is caused by the fact that the strip is relatively thick.
In the case of cold-rolled steel sheets used for so-called automotive steel sheets, lubricants are generally used during temper rolling, so roll defects due to welds are less likely to occur, and rolling can be performed under constant rolling conditions over the entire length. In the case of a thin tin plate having a thickness of, for example, 0.35 mm or less, temper rolling is performed without lubrication (dry), and roll defects are likely to occur.

For this reason, in temper rolling, when the welded joint passes through the temper rolling mill, it is necessary to take measures such as opening the mill (opening the space between the upper and lower rolls). , a thin strip about 10 meters in front and behind it will not produce the desired product. On the other hand, if mill-opening is not done, the rolls will be flawed and the roll flaws will be printed on subsequent thin strips, resulting in very long stretches of reject material.

(Object of the Invention) The present invention was developed as a result of various studies in view of the above-mentioned circumstances, and proposes a continuous annealing method for thin strips that does not produce mismatched parts in welded joints.

(Structure and operation of the invention) The present invention has a plate thickness of 0.35 mm at the entrance side of the continuous annealing line.
When connecting thin strips of mm or less and processing them continuously, the thickness of the lap welded joint is
By keeping the thickness within 130% of the thickness of the thin strip, the heating, soaking, and cooling effects in the continuous annealing line are no different from those in other parts, and furthermore, roll defects can occur even during temper rolling. It has been found that the material is uniform over the entire length of the strip, including the area immediately adjacent to the welded joint, and that the same temper rolling as for other parts can be carried out.

The present invention has been made based on this knowledge, and will be explained in detail below.

FIG. 1 shows the line along which a thin strip is continuously annealed in one embodiment of the invention.

In the drawing, reference numerals 1-1 and 1-2 are payoff reels, from which thin strips, such as original tin plate 2, are sent out. 3 is a welding device equipped with a welding part thickness reduction mechanism, 4 is a cleaning device, 5 is an entrance looper, and 6 is a continuous annealing furnace, which is provided with a heating zone, a soaking zone, an overaging zone, and a cooling zone. . Reference numeral 7 indicates an exit looper, and 8 indicates a temper rolling mill, two of which are provided in series in this embodiment. 9 is a refinement section, 10-1, 1
0-2 is a tension reel.

Incidentally, the relationship between the occurrence of roll flaws and the thickness ratio of the welded joint was investigated when a thin strip was continuously annealed and then temper-rolled in a temper-rolling mill.
Note that the welded joint plate thickness ratio is the ratio of the welded part plate thickness to the base metal plate thickness.

This investigation was conducted on thin strips with a thickness of 0.25 to 0.35 mm, and the thickness of the welded joint was reduced using a pressure roll or an energized pressure roll to change the welded joint thickness ratio. Then, the thin strip was continuously annealed at 630°C for 25 seconds, and the pressure adjustment rate was 0.8 to 1.2.
Roll flaws that occurred on the rolls were examined when the rolls were temper rolled at 10%. The results are shown in FIG. In the figure, a is an example of a rolling force of 200 tons, and b is an example of a plate thickness of 0.28 mm by dry temper rolling, with a rolling force of 800 tons. The weld thickness ratio is expressed as weld thickness/base metal thickness.

When temper rolling the welded joint from this,
It has been found that when the plate thickness ratio of the welded joint is 130% or less, the occurrence of roll flaws is suppressed regardless of the rolling force. It has also been found that in this case, a desired degree of thermal refinement can be obtained from the vicinity of the welded joint, and a uniform material can be obtained.

From the above, in the present invention, when welding and connecting thin strips on the entrance side of a continuous annealing furnace, the thickness of the welded joint is set to 130% of the thickness of the thin strip.
The following shall apply. Details of the welding device 3 for making such welded connections will be described with reference to FIG.

The thin strip 2 is welded to the next thin strip 2-1 by the welding electrode 11, and then the first pressure roll 12 and the second pressure roll 1 provided at the rear are welded.
In Step 3, reduce the thickness of the welded joint. The method for reducing the thickness of the welded joint is not limited to the above-mentioned method. For example, the first pressure roll 12 may be provided with an energizing mechanism to apply pressure while applying a heating effect.

The welded thin strip 2 is cleaned by a cleaning device 4, passed through an entrance looper 5,
It is heated in a continuous annealing furnace 6 to a predetermined temperature, e.g.
soaked at a temperature of 600-650°C, then cooled to an overaging temperature, e.g. 300-500°C, if necessary;
Either an over-aging treatment is performed, or the material is cooled to a temperature at which oxidation does not occur even when exposed to the atmosphere without performing an over-aging treatment.

(Effect of the invention) In the present invention, the skin pass rolling mill 8 performs skin pass rolling at a predetermined pressure adjustment rate according to the degree of temper rolling, but even when the welded joint is temper rolled, the welded joint Since the thickness of the thin strip 2 is set to 130% or less of the plate thickness of the thin strip 2, the welded joint can be temper-rolled in the same manner as other parts without generating roll flaws.

Therefore, a uniform material can be obtained over the entire length except for the welded joint, and there are no mismatched parts.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a continuous annealing line in which an embodiment of the present invention is carried out, FIG. 2 is a diagram of the plate thickness ratio of the welded joint and roll flaws, and FIG. 3 is an explanatory diagram of the welding apparatus. 3: Welding device, 6: Continuous annealing furnace, 11: Welding electrode, 12: First reduction roll, 13: Second reduction roll.

Claims (1)

[Claims] 1 In a continuous annealing line equipped with a temper rolling mill, thin strips with a thickness of 0.35 mm or less are connected by welding and continuously annealed, and the thickness of the welded joint of the thin strip is 130 mm
A continuous annealing method for a thin strip, which is characterized by successive annealing after reducing the thickness to less than %, followed by skin pass rolling.