JPH0129868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides zinc plating by irradiating X-rays on a galvanized steel sheet that has been subjected to minimum spangle treatment and adjusting the minimum spangle treatment conditions so that the diffraction intensity on a specific surface thereof is equal to or higher than a predetermined value. The present invention relates to a method for producing a minimum spangle-treated hot-dip galvanized steel sheet in which spangles on the surface of the layer are reduced.

Hot-dip galvanized steel sheets usually have large zinc crystals (spangles) on the surface, which have a negative impact on the appearance after painting. Therefore, various methods have been proposed to reduce or eliminate this spangle. For example, (1) lowering the Pb concentration in the zinc bath, (2) applying a skin pass, (3) reheating after galvanizing, and (4) adding a biphosphate aqueous solution just before solidifying the galvanized layer. Methods such as spraying are used. Among these, (1) low Pb method is difficult to operate;
The skin pass treatment (2) and reheating (3) cannot completely eliminate spangles, and currently the main method is to spray a biphosphate aqueous solution.
However, even in this minimum spangle treatment using biphosphate aqueous solution spraying, operating conditions (line speed, plate thickness, plating amount, etc.) and biphosphate aqueous solution spraying conditions (liquid concentration, air pressure, spraying position, etc.) The current situation is that the minimum spangle processing effect fluctuates depending on the situation.

Furthermore, the effectiveness of minimum spangle processing is determined visually and by the size of the spangles after etching, but visual determination can only be qualitatively determined due to individual differences and the level of skill required. In the case of etching, quick determination was not possible because sampling was performed at the exit side of the coil.

Therefore, the present invention aims to quantitatively measure the effect of minimum spangle treatment online and provide a method that can perform stable minimum spangle treatment. When the orientation of the crystal was measured, it was found that the reflection intensity of the low index plane was extremely strong in the case where the minimum spangle treatment was sufficiently performed, leading to the present invention.

As mentioned above, in the production line for hot-dip galvanized steel sheets, as a process to reduce or eliminate the pattern (spangle) of the galvanized layer,
Immediately after galvanizing, when the plating layer is still molten, a biphosphate aqueous solution is sprayed to rapidly cool it. Through this treatment, the spangles from the surface to the inside became smaller and disappeared. However, the conditions for spraying this biphosphate aqueous solution are very strict; for example,
The best spray position is just before the galvanized layer solidifies; if it is too early or late, the spangle treatment will be uneven, and the etched areas in the width direction also tend to solidify quickly. It is extremely difficult to determine the spray location and spray amount. If the amount of zinc deposited or the thickness of the plate changes, the spraying conditions will naturally change, and it takes a considerable amount of time to achieve uniform treatment. The effectiveness of the minimum spangle treatment is first judged by the size and appearance of the spangles, and since this alone is not sufficient, a sample is taken from the product and the galvanized layer is etched to determine the size and number of the spangles. This is because the minimum spangle processing conditions are changed based on the measurement results, but the above process is very time consuming.

The method of the present invention involves irradiating the minimum spangle-treated galvanized layer with X-rays online using an X-ray diffraction device, and controlling the minimum spangle treatment conditions based on the results of measuring the diffraction intensity to obtain the minimum spangle treatment effect. It is something that improves. A detailed investigation of a galvanized steel sheet that has undergone sufficient minimum spangle treatment revealed that the X-ray diffraction intensity of the galvanized layer changes depending on the degree of minimum spangle treatment, and that It was found that the reflection intensity on low-index surfaces becomes stronger, and the reflection intensity on high-index surfaces weakens or disappears.

In more detail, the reflection intensity from the (001) plane of zinc becomes extremely strong when subjected to the minimum spangle treatment, while the reflection intensity from the (101) plane, which was strong when not treated, weakens or almost disappears. Was. In this way, the reflection intensity on the (001) plane becomes stronger when the minimum spangle treatment is applied, and the reflection intensity on the (101) plane becomes weaker when the treatment is not performed or insufficiently processed. Zinc is solidified by air cooling after plating, but it is presumed that the minimum spangle treated material is rapidly cooled by spray cooling and the crystals are aligned in the (001) plane, which increases the reflection intensity of this plane.

As described above, there is a good correlation between the X-ray diffraction intensity and the quality of the minimum spangle processing effect, and this correlation will be explained below. Now, I _P1 is the diffraction intensity of the (001) plane obtained by the zinc powder method, I _B1 is its background value, I _P2 is the diffraction intensity of the (001) plane of the minimum spangled galvanized steel sheet, and I _B2 is its background value. As a value, the X-ray diffraction intensity was measured for samples that had undergone sufficient minimum spangle processing, samples that had undergone insufficient or no minimum spangle processing, and (I _P2 -
When the value of I _B2 )/(I _P1 − I _B1 ) was calculated, the value of the above formula was found to be
If the sample shows a value of 300 or more, and the minimum spangle treatment is insufficient or not done, the above formula value is 10 to 60.
Only the degree was shown, and a clear difference was observed. Therefore, in the method of the present invention, the above formula value is determined by measuring the X-ray diffraction intensity of the galvanized layer, and the results are fed back to the minimum spangle treatment conditions to control the treatment so as to increase its effectiveness. In the present invention, the above formula value is limited to 300 or more because a minimum spangle treated steel sheet exhibiting a value of 300 or more can be obtained with a good spangle treatment over the entire length in the coil width direction and length direction. It is.

The spangle processing line according to the method of the present invention will be explained with reference to the attached drawings. The cold-rolled strip 2 unwound from the payoff reel 1 is heated in an annealing soaking furnace 3 to burn off oil and fat on the surface of the steel sheet. It is then annealed and softened, then cooled to a temperature suitable for plating, passed through the snout section 4 maintained in a non-oxidizing atmosphere, and introduced into a zinc bath 6 filled in a plating bath 5 for plating. Excess zinc is removed from the plated strip 2 by a gas wiping mechanism 7, and the amount of plating is adjusted to the target amount. 8 is a minimum spangle processing device, by which the galvanized layer is rapidly cooled.
Processing is performed to reduce or eliminate spangles. The degree of this treatment is continuously measured by the X-ray diffraction device 9, and the spangle treatment conditions are changed and adjusted according to the above formula value, and this operation is repeated to operate the line under the optimum treatment conditions. The galvanized steel sheet subjected to the minimum spangle treatment in this controlled manner is given the required mechanical properties in the skin pass mill 10, treated in the chemical conversion treatment equipment 11, and then wound onto the tension reel 12.

Example A galvanized steel sheet with a zinc coating amount of 280 g/m ² was manufactured on a line for manufacturing hot-dip galvanized steel sheets as shown in the attached drawings, and subjected to minimum spangle treatment. At that time, immediately after online minimum spangle processing, the (001)
Measure the diffraction intensity of the surface, and set the minimum spangle processing conditions until the formula value of (I _P2 − I _B2 )/(I _P1 − I _B1 ) is 350 ~
I managed to keep it within the range of 600. It was confirmed that the minimum spangle-treated galvanized steel sheet obtained in this way had a good minimum spangle treatment over the entire width and length of the coil, and a homogeneous product was continuously obtained. Ta.

Online quality control using this X-ray diffraction method has already been used to control the degree of alloying in the alloying treatment of hot-dip galvanized steel sheets, but in addition to determining the effectiveness of the minimum spangle treatment of the present invention, it is also used in the zinc phosphate treatment process. It can also be used to control the quality of zinc phosphate crystals.

[Brief explanation of drawings]

The attached drawing is a diagram of a production line for hot-dip galvanized steel sheets equipped with an X-ray diffraction device for detecting the treatment effect immediately after the minimum spangle treatment device. Explanation of symbols 1... Payoff reel, 2... Strip, 3... Annealing soaking furnace, 4... Snout, 5
... plating tank, 6 ... zinc bath, 7 ... gas wiping mechanism, 8 ... minimum spangle processing device,
9...X-ray diffraction device, 10...Skin pass mill,
11...Chemical conversion treatment equipment, 12...Tension reel.

Claims (1)

[Claims] 1. When producing a hot-dip galvanized steel sheet by subjecting a hot-dip galvanized steel strip to a minimum spangle treatment, the minimum spangle-treated galvanized steel sheet is irradiated with characteristic X-rays. Continuously measure the X-ray diffraction intensity of the (001) crystal plane of zinc in the galvanized layer, and adjust the minimum spangle processing conditions so that the value of I _P2 − I _B2 / I _P1 − I _B1 is 300 or more. A method for producing a minimum spangled hot-dip galvanized steel sheet. (In the above equation, I _P1 is the diffraction intensity of the (001) plane obtained by the zinc powder method, I _B1 is its background value, I _P2 is the diffraction intensity of the (001) plane of the minimum spangled galvanized steel sheet, and I _B2 is the its background value)