JPS6144200A - Production of steel sheet galvanized on one side - Google Patents

Abstract

PURPOSE:To produce a titled steel sheet having the non-plated surface cleaned uniformly by a short period of treatment by subjecting the steel sheet to washing and drying after galvanizing one side thereof then anodizing the same under specific conditions in a specific electrolytic pickling liquid. CONSTITUTION:The surface of the steel sheet after plating is washed to remove the plating liquid and is once dried in the stage of pickling electrolytically the non-plated surface of the steel sheet after galvanizing the one side thereof. The surface is then anodized in an aq. soln. contg. 1 or >=2 kinds among the sulfate or phosphate of Na, K, Li, Mg and Al and having 4-13pH under the conditions of <=2.5m/sec relative speed of the steel sheet and the aq. soln. and >=20A/dm<2> anode current density. The non-plated surface is thus cleaned in several seconds. The steel sheet is thereafter polished and is then washed and dried, by which the steel sheet is made into the product.

Description

[Detailed Description of the Invention] <Industrial Application Fields> Is the present invention one-sided zinc-based? The present invention relates to a method for manufacturing a galvanized steel sheet.

<Prior art and its problems> In recent years, the use of K, zinc-based 1t% plated steel sheets has been increasing in order to prevent corrosion of automobile bodies caused by antifreeze agents sprayed on roads. In this case, steel plates plated on both sides have problems with weldability and appearance after painting, so steel plates plated on only one side are often used. , cold-rolled steel sheets and excellent rolling properties are required.

But zinc-based? I! In the production of plating steel sheets,
Since an acid bath such as a sulfuric acid bath or a chloride bath is used as a plating bath, acid corrosion of the non-plated surface is unavoidable.As a result, the non-plated surface becomes dirty due to the accumulation of acid-insoluble vinegar and the precipitation of impurities. This often causes streak-like unevenness and deterioration of chemical conversion properties. Furthermore, plating precipitation on non-plated surfaces due to the plating current passing around is also often a cause of deterioration in chemical conversion treatment properties.

Deterioration of chemical conversion treatment property means that uniform phosphate crystals are not formed and K
, some parts may have a non-crystalline part called suke,
It may cause uneven coarse crystals. This is an important problem in terms of quality because it causes deterioration in corrosion resistance and adhesion after it is applied, or causes non-uniformity in appearance. Therefore, as a countermeasure to this problem, after plating, electrolysis is performed in an acid or salt aqueous solution using the non-plated surface as an anode. So-called electrolytic pickling is performed.

For example, if we take Na2504 aqueous solution as an example,
Chemical effects due to 82 SO4 generated on the surface of the steel plate and occur simultaneously. The combination of the physical effects of the two gases provides an excellent cleaning effect on the surface of the steel plate. However, in the plating line for steel plate strips, only one or two electrolytic pickling tanks are actually installed, and the unplated surface is uniformly cleaned during the short period of a few seconds or less that passes through this tank. It was difficult to do so.

That is, in some cases, the removal of dirt was insufficient in general, or the dirt and cleaned parts were mixed in spots.

This phenomenon occurs when alloy plating such as Zn-Xl is performed, and elements more harmful than Fe are deposited on the Fe surface during plating.
When the non-plated surface is in such a state, which is particularly prone to staining, the chemical conversion treatment properties are inferior to those without electrolytic pickling in terms of uniformity, and are extremely large. This is a problem.

(Objective of the Invention) In view of the above-mentioned current situation, the object of the present invention is to obtain an electrolytically pickled surface that is uniformly cleaned even with a short treatment of a few seconds or less, thereby providing a non-oxidizing surface with excellent chemical conversion treatability. An object of the present invention is to provide a method for manufacturing a zinc-based single-sided electroplated steel sheet having a plated surface.

(Structure of the Invention) According to the present invention, after applying zinc-based electroplating to one side of a steel sheet, when electrolytically pickling the non-plated surface, the non-plated surface of the steel sheet after plating is washed with water to remove the plating solution. , once dried, and then Na, K, Li, Mg
In an aqueous solution with a pH of 4 to 13 containing one or more of sulfates or phosphates of Al, the relative velocity between the W4 plate and the liquid is 2.5 ■/sea or less, and the anode current density, The above objective can be achieved by anodizing 20^/d intestine 2 or more. Furthermore, if the non-plated surface is polished with an abrasive after one electrolytic treatment, the chemical conversion treatment properties can be made uniform and good.

The method for electrolytic pickling of zinc-based single-sided electroplated steel sheets of the present invention will be described in detail below.

Electrolytic pickling in the present invention must be performed after plating, washing the non-plated surface with water, removing the plating solution, and drying it once. This is because washing with water alone will not allow the plating solution to absorb onto the surface of the steel sheet. This is because the IIL acid is not completely removed and a passive film is not formed in the areas where the M acid remains, so electrolytic pickling often results in over-etching. This phenomenon is particularly likely to occur with phosphorous-added steel, which is susceptible to etching.After washing with water, the surface is once dried, and in the process, the remaining free soap reacts with the steel plate surface, forming a uniform passive film over the entire surface. Therefore, uniform etching can be performed in the subsequent electrolytic pickling.

The electrolytic pickling solution contains Na, K, Li, Kg, Al
The main component is at least one sulfate or phosphate of . Since the deposition potential of the metal ions mentioned above is higher than the hydrogen reduction potential, metal deposition does not occur in aqueous electrolysis.
For this reason, it is easy to maintain the metal ion concentration in the bath and maintenance of the cathode, and the acid produced on the anode and the alkali produced on the cathode are balanced in equivalence, making it easy to maintain the bath pH. This is because it is suitable.

Also, I chose Vt salt or phosphate.

These aqueous electrolysis systems do not generate harmful gases, and F
This is because the cleaning power of the e-side is strong. Ij1 compound, fluoride or nitric acid I'! ! etc. may generate toxic gases such as halogen gas and NOx, and carbonates, borates, and ammonium
Salts and the like are not preferred because they have poor acid-dissolving power.

The pl of the electrolytic bath needs to be 4-13. The reason for this is that if the pH of the bath is less than 4 or more than 13, Zn, which is an amphoteric metal, will dissolve on the plated surface, even for a short time, and this will cause problems such as appearance, corrosion resistance, etc. This is because it causes deterioration of the above.

Furthermore, in the present invention, the relative velocity between the steel plate and the electrolyte is
．． Defined as 5a/sea or less. The reason for this is that if the relative speed is too high, the acid generated on the non-plated surface will quickly separate from the Fe surface, reducing the pickling power and making it impossible to uniformly clean the Fe surface in a short period of time. This is because it becomes difficult.

Figure tjS1 shows the non-plated side of a steel sheet coated with Zn-old alloy on one side.
7) shows the relative velocity of the steel plate and the liquid when subjected to anodic electrolysis treatment and the r:JJ ratio of the appearance after electrolysis. TrtM
The previous non-plated surface was stained light brown due to smut and Ni precipitation. When this is anodic electrolyzed for a short time of 1.5 to 2.0 seconds, which corresponds to actual operation on a line, the appearance of the surface after electrolysis is strongly influenced by the relative speed of the steel plate and the liquid, and the appearance is 2.5 seconds. It can be seen that the surface is uniformly cleaned when the temperature is less than /see.

As mentioned above, an uneven surface always causes uneven chemical conversion treatment, so it must be avoided in conclusion 4, and for this purpose, controlling the relative velocity of the steel plate and the liquid is extremely important. It can be said.

In addition, in the present invention, electrolytic treatment must be performed at a current density of 2 OA/dm2 or more. 7 shows the relationship between anode current density and surface whiteness (measured with a color difference meter) when anodic electrolysis is performed on the 7th surface. There are two types of baths: Ha H2PO4 and Na2 SO4, both of which are lOOg/m and the pH is 21 to 6-7.
! I! I got an F. Also, the amount of electricity is all 100 coulombs/d.
unified to m2.

From this result, the whiteness, which is an index of surface cleanliness, is affected by the current density even if electrolyzed with the same amount of electricity, and it is 20A/d.
■It can be seen that 2 or more indicates a high level. L5A/d
It is thought that the reason why the cleaning effect decreases below s2 is because the disfiguring film is not completely destroyed or because the stirring force at the interface due to the generation of 02 gas decreases.

The processing properties of the non-plated surface treated under the above conditions are excellent in themselves, but they can be further improved by subsequent grinding with an abrasive material. This is MI
This is because B provides a more active surface state B. As the abrasive material, a brush containing abrasive grains such as SiC or ^1203, Scotch Brite, or a grinding belt can be used.

In the present invention, zinc-based N,% plating refers to Zn13 and Zn13
Including alloy plating such as n-11i, Zn-Fe, etc., as well as those to which other elements such as C and Co are added.
It is plated with an acidic solution in a sulfur bath, a chloride bath, or a mixed bath. Horizontal, vertical, or radial cells are used for electrolytic cleaning, and the liquid temperature ranges from room temperature to 70°C.
It can be arbitrarily selected between ℃. The bath temperature is preferably about 50 g/1 or more, although it cannot be said to be exact because the cleaning efficiency of the non-plated surface varies slightly depending on the type of chemical used, and the electrical conductivity varies.

Further, during electrolysis, 11JI can clean the non-plated surface even in a short time of several seconds or less, for example, one second.

After electrolytic treatment, or after further Kenfu treatment, the steel plate is washed with water, dried, and made into a product.

(Example) Examples of the present invention will be specifically described below.

A phosphorous-added steel plate (P content: 0.1%) with a thickness of 0.7 mm was subjected to single-sided ZII-old alloy plating using a horizontal plating bath under primary conditions.

(1) Bath M1 composition NiSO46H20250g/cost Zn
SO47H2O130g/1 Na2 S04 40g/x (2)
Bath pH 1,6 (3) Bath temperature 60°C (4) Current density 50 A/d++2 (5) Plating time 15 sec (6) Plating weight 20 g/m fJ
Perform electrolytic pickling on the non-plated surface under the conditions shown in the tJ1 table,
Then, it was washed with water and dried.

In addition, some of the samples were subjected to Scotchbrite polishing after electrolytic pickling, followed by washing with water and drying.

Thereafter, the presence or absence of stains and unevenness on the non-plated surface was visually determined, and the whiteness (W) was measured using a color difference meter as an index of surface cleanliness, and the amount of NI deposited was analyzed using chemical analysis. Also, visually compare the presence or absence of dirt and unevenness on the plating surface1.
I judged it.

Thereafter, a chemical conversion treatment was performed by a dipping method using a phosphate treatment solution (Bonderai) #3030 manufactured by Nippon Barker Rising. The chemical conversion coating was visually inspected and observed with a scanning electron microscope to give a 2f rating based on its uniformity, crystal density, presence of scratches, etc., and the amount of chemical deposition was also used for non-plated surfaces. These results are shown in Table 1.

The non-plated surface shown in Comparative Example 6, in which no electrolytic treatment was performed after plating, had low whiteness due to contamination, a large amount of NI deposited, and poor chemical conversion treatment properties.

However, the electrolytically treated products shown in the examples of the present invention have improved surface cleanliness as shown by an increase in whiteness and a significant decrease in the amount of lli+ deposited, and are also excellent in chemical conversion treatment properties. .

On the other hand, the pH of the bath is WA&! Comparative example 1 exceeding I]
and No. 2, the chemical conversion treatment property of the plated surface was poor.

In addition, Comparative Examples 3 to 3 are outside the scope of the present invention due to the relative speed of the steel plate and bath, current density, plating, drying after wood washing, and drying up to electrolysis, etc.
No. 5 had poor chemical conversion treatment properties on the non-plated surface. It should be noted that the reason why the amount of chemical conversion coating in these comparative examples is larger than that in the examples is due to coarsening of the chemical conversion coating crystals.

(Effects of the Invention) From the above, it can be seen that the method of the present invention very effectively improves the chemical conversion treatability of non-plated surfaces even with a very short treatment time of 1 to 1.5 seconds. K. If a polishing treatment is performed after the above-mentioned electrolytic pickling treatment, even better chemical primordial properties can be obtained on the non-plated surface.

[Brief explanation of the drawing]

':JSf diagram is a graph showing the relationship between the relative speed of the m plate and the solution and the surface appearance after electrolysis when a non-plated steel sheet coated with a Zn--Ni alloy on one side is subjected to anodic electrolysis treatment in an aqueous l1a2 SO4 solution. FIG. 2 is a graph showing the relationship between current density and surface whiteness when the non-plated surface of the same single-sided plated steel sheet as in FIG. 1 is subjected to anodic electrolysis treatment. FIG.
m/5ac) FIG, 2 t J v& (A/drr?) Procedure-1IT1
1 official document (spontaneous) Special, Office Commissioner Shiga AWJ Kei 60 years 1
Name of former °82゜ departure J Method for manufacturing zinc-based single-sided electroplated steel sheet 3, Person making amendment 1 Relationship with the matter Patent applicant address 1-1-2 Kitahonmachi-dori, Chuo-ku, Kobe, Hyogo Prefecture
No. 8 Name (125) Kawasaki Steel Corporation 4 Agent
1011s8as4-44c+a Address: 3-2-2 Iwakicho, Chiyoda-ku, Tokyo Column 6 of Detailed Description of the Invention J of the specification and page 15 of the specification of contents of the amendment are amended as shown in the attached sheet.

Claims (2)

[Claims] (1) After applying zinc-based electroplating to one side of a steel plate, when electrolytically pickling the non-plated side, after plating, the steel plate surface is washed with water to remove the plating solution, dried once, and then Na , K, Li, Mg, Al, pH 4 ~ containing one or more of sulfates or phosphates.
In the aqueous solution of No. 13, the relative velocity between the steel plate and the liquid was set to 2.5 m/s.
A method for manufacturing a zinc-based single-sided electroplated steel sheet, characterized by anodizing at an anodic current density of 20 A/dm^2 or higher, with an anodic current density of 20 A/dm^2 or higher. (2) After applying zinc-based electroplating to one side of a steel plate, when electrolytically pickling the non-plated side, after plating, the steel plate surface is washed with water to remove the plating solution, dried once, and then Na , K, Li, Mg, Al, pH 4 ~ containing one or more of sulfates or phosphates.
In the aqueous solution of No. 13, the relative velocity between the steel plate and the liquid was set to 2.5 m/s.
A method for manufacturing a zinc-based single-sided electroplated steel sheet, which comprises performing anodization at an anodic current density of 20 A/dm^2 or higher, and then polishing the non-plated surface.