JPH0765153B2 - Wrinkle prevention method for hot-dip galvanized steel sheet - Google Patents

Description

The present invention relates to a method for preventing wrinkling of a hot-dip galvanized steel sheet.

[Prior Art and Problems to be Solved by the Invention] When alloying (iron-zinc alloy) by heat treatment after hot dip galvanizing, the temperature of the plated steel sheet immediately after alloying is 500 to 700.
The temperature is as high as ℃, and when it is conveyed through the cooling deflector roll (top roll), the plating metal in a partially molten state adheres to the deflector roll and accumulates on it, causing defects in the plated steel sheet (band). Cause.

Therefore, it is known that air and water are blown between the alloying furnace and the deflector rolls on a plated steel sheet for alloying or the like to cool it, thereby eliminating the above-mentioned difficulties.

In such a method, if the cooling method is unsuitable, wrinkles may occur continuously in the longitudinal direction of the plated steel strip, which is accompanied by drawbacks such as markedly impairing quality.

[Means for Solving the Problems] A feature of the present invention is that a hot-dip galvanized steel strip after hot dip galvanizing is subjected to a heat alloying treatment, and then the hot-dip galvannealed steel strip is heated to 250 to 400 ° C. During cooling, there is a temperature difference between the both ends and the central part in the width direction of the steel sheet, and the range of the temperature difference is such that the central part is at a temperature lower than both ends within 60 ° C., and the central part is more than both ends. A method for preventing wrinkling of a hot-dip galvanized steel sheet, which comprises cooling at a high temperature to within 30 ° C. and then conveying it through a deflector roll.

The hot-dip galvanized steel sheet is manufactured by hot-dip galvanizing, followed by heat treatment to thermally diffuse iron (steel sheet) into the plated layer to form an alloyed galvanized steel sheet containing 7 to 13% of iron. After the chemical treatment, the plated steel sheet at 450 to 600 ° C. is cooled to 200 to 450 ° C., the plated layer is solidified, and is conveyed to the next step via a cooling deflector roll (internal cooling or the like).

That is, the cooling after the alloying treatment is performed by spraying air, atomized water, a mixture of water and water, etc., as described above, to prevent the plating metal from adhering to the deflector roll, and also to cool the deflector roll. It further reliably prevents the plating metal from adhering to the surface.

However, this deflector roll has a convex shape (crown) at the center part in the roll width direction for the reason of preventing meandering of the plated steel strip.
When the coated steel strip at ~ 450 ° C is spread on the deflector roll, the central part of the plate is in strong contact with the strip, so it tends to be colder and colder than both ends.

By the way, depending on the pattern and the degree of temperature distribution in the width direction of the steel strip before winding around the deflector roll, thermal stress acts in the width direction due to uneven cooling during winding around the deflector roll as described above. The later steel strip is deformed. In extreme cases, wrinkles may occur and the product may not be produced.

Therefore, the present invention provides a method for cooling a steel strip after alloying treatment for preventing such deformation and wrinkling of the steel strip. That is, the plated steel strip at 200 to 450 ° C. after plating has a low temperature in the widthwise central portion where it is easier to cool as compared with the both end portions after leaving the deflector roll after cooling.

For this reason, when the plated steel strip is wound around the deflector roll, the central part and both end parts are strongly wound, and the parts other than the both end parts and the central part are weakly contacted with the roll. On the other hand, the central part and both ends that are in strong contact with the roll are
Since it is cooled by the rolls, shrinkage occurs in the width direction of the plated steel, and the central part and both ends that are in strong contact with the roll do not deform, but the thermal deformation concentrates between both ends of the central part where the roll contact is weak. In addition, since the central portion and both end portions are in a restrained state, the strain is large, which leads to the generation of wrinkles.

While cooling the plated steel strip after alloying treatment to 250 to 400 ° C., there is a temperature difference between both ends and the central part in the width direction of the steel strip, and the range of the temperature difference is that the central part is at both ends. 60 at lower temperatures
It is cooled so that the temperature is within ℃, and the temperature at the center is higher than both ends and within 30 ℃.

If the cooling temperature of the above-mentioned plated steel strip exceeds 400 ° C, the plating metal may adhere to the roll surface even if the cooling temperature of the deflector roll is lowered. This is not preferable because it lowers the plate speed and prolongs the cooling time, which lowers the productivity.

After cooling after alloying treatment, there is a temperature distribution in the width direction of the plated steel strip during contact with the deflector roll, and when the central part is cooled to a temperature higher than both ends and the temperature difference exceeds 30 ° C, both ends are centered. It becomes a shape in which the central part is elongated by contracting relatively from the part. When the deflector roll is contacted in this state, both ends are strongly contacted with the roll and are further cooled and contracted. On the other hand, although the central portion comes into contact with the roll due to the roll crown, the intermediate portion between the central portion and both ends does not come into contact with the roll, so that this portion is in a state of being further extended as compared with the central portion and both end portions. In this state, because it is wound around a roll and subjected to bending stress, wrinkle flaws occur at a point 200-400 mm from both ends. In order to prevent this, it is effective to cool the central part so that the temperature is higher than both ends and the temperature difference is within 30 ° C., or to make both ends have a higher temperature than the central part. However, if the temperature difference between both ends of the central part exceeds 60 ° C and the temperature difference between the both ends exceeds the yield point of the steel strip due to thermal stress, the deformation of both ends becomes large and wrinkles occur.

Here, the both end portions mean a portion at the center of at most 50 mm from both ends of the steel strip.

Wrinkles can be prevented by controlling the temperature distribution in the width direction of the steel strip as described above. A cooling method for controlling this temperature distribution is as shown in FIG. 2 described later. Arrangement of nozzles for blowing air or atomized water in the width direction is made dense or dense, or as shown in Fig. 3, the nozzles are evenly arranged and a movable shield plate in the width direction is installed between the nozzle and the steel strip. Is a practical and effective method, and one example thereof will be described with reference to the drawings.

FIG. 1 is an overall view of a cooling device. In FIG. 1, 1 is a galvanized steel sheet after alloying treatment, 2 is a deflector roll, 3 is an alloying furnace, 4 is a nozzle for blowing cooling air or atomized water. In such cooling, in the nozzle header 4 as shown in FIG. 2, the blowout holes 5 are densely arranged in the center and both sides are roughly arranged, and cooling in the width direction of the plated steel strip 1 is performed as described above. is there. Further, as shown in FIG. 3, the blow-out holes 5 of the nozzle 4 are uniform, but a shield plate 6 for shutting off air and atomized water on both sides is arranged in accordance with the width of the steel strip 1 and movable by a drive unit 7. The steel strip 1 is cooled in the width direction as described above.

[Examples] Next, examples of the present invention will be given together with comparative examples.

[Effects of the Invention] By doing so, excellent effects such as reliably preventing wrinkling of the hot-dip galvanized steel sheet and significantly improving the quality can be obtained.

[Brief description of drawings]

FIG. 1 is an overall explanatory view showing a cooling state of an alloyed galvanized steel strip, and FIGS. 2 and 3 are explanatory views showing an example of cooling by a nozzle. 1 ... Galvanized steel strip, 2 ... Deflector roll 3 ... Alloying furnace, 4 ... Cooling nozzle 5 ... Blowing hole, 6 ... Shield plate 7 ... Drive device

Claims (1)

[Claims] 1. A hot-dip galvanized steel strip after hot-dip galvanizing is subjected to heat alloying treatment, and then, when the hot-dip galvanized steel strip is cooled to 250 to 400 ° C., both end portions in the width direction of the steel sheet. And the central part have a temperature difference, and the range of the temperature difference is such that the central part is cooler than both ends at 60 ° C. and the central part is hotter than both ends within 30 ° C., and then cooled. A method for preventing wrinkling of a hot-dip galvanized steel sheet, characterized by transporting it through a deflector roll.