JP3460086B2 - Cast member and method of galvanizing cast member - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast member having a plated layer made of zinc or a zinc alloy by electroplating, particularly an iron-based cast member and a zinc plating method thereof.

[0002]

2. Description of the Related Art Cast iron members such as cast iron (mouldable cast iron, ductile cast iron, alloy cast iron, etc.) and cast steel, which are iron-based cast members, are easily rusted. As one of the measures against rust, a plated layer of molten zinc or a galvanized layer is formed on the surface of the cast member by an electroplating method. Since the casting member is manufactured using a sand mold, fine irregularities are formed on the surface thereof. When the galvanized layer is formed on the cast member, when the hot dip galvanizing method is applied, the hot dip zinc adheres to the fine irregularities to form a good plated layer. For example, in a cast pipe fitting,
A 0 μm hot dip galvanized layer is formed. However, when a plated layer of molten zinc is formed on a cast member, it is extremely difficult to form a plated layer having a uniform film thickness.

Therefore, it is also practiced to form a plated layer having a uniform film thickness and a glossy surface on a cast member by an electroplating method. However, when the galvanized layer is formed by the electroplating method, since fine irregularities are formed on the surface of the casting member, it is difficult for the metal to be plated to deposit and the plating efficiency is extremely deteriorated.
Therefore, various improvement measures have been conventionally proposed for the technique of forming a zinc plating layer on a cast member by electroplating.

The method of forming the zinc plating layer by the electroplating method is roughly classified into a method using an alkaline bath and a method using an acidic bath. As the alkaline bath, a cyan bath, a zincate bath or the like has been conventionally used. Zinc plating using a cyan bath has been widely adopted because of its excellent electrodeposition property, smoothness, and flexibility of plating film. However, since a cyanide bath uses a harmful cyanide compound, a zincate method using a zincate bath has been developed from the viewpoint of environmental protection. The zincate bath is
It is an electrogalvanizing method which is a plating bath composed of zinc and sodium hydroxide, and which has excellent covering properties and can obtain good gloss.

On the other hand, for zinc plating in an acid bath,
Conventionally, sulfuric acid bath, chloride bath, etc. have been adopted. Sulfuric acid baths have been adopted by steel manufacturers for galvanizing strip steel sheets, and plating baths mainly containing zinc sulfate have been used. The chloride bath is classified into a zinc chloride ammonium bath, a zinc chloride potassium bath, and a zinc chloride ammonium-potassium bath, but the zinc chloride ammonium bath is widely adopted at present. The zinc ammonium chloride bath is a plating bath composed of zinc and ammonium chloride. The zinc chloride ammonium bath also has the advantage that the zinc plating layer adheres well to a cast member that is difficult to stick to in an alkaline bath. However, since the chloride bath contains a large amount of chlorine ions, it has a serious drawback that it is extremely corrosive to facilities such as a plating tank and a building.

[0006] As an improvement plan of the electrogalvanizing method for iron-based cast members, for example, the following have been proposed. Japanese Examined Patent Publication No. 60-13077 discloses that when cast iron or steel products are galvanized using a zincate zinc plating bath, an alkaline bath type tin plating is subjected to an undercoating treatment, and then a zincate consisting of a zincate bath is applied. Is described. The plating method disclosed in the publication uses a zincate bath for a cyanide-free bath, and when galvanizing a cast iron or steel product with a zincate bath, it is difficult to deposit the plating, so that an alkaline plating is used as a base plating treatment. It is characterized by applying bath-type tin plating.

[0007] In Japanese Patent Laid-Open No. 1-268880, in order to improve the corrosion resistance of an overhead wire fitting made of an iron-based metal material, an underground cable fitting, etc., the surface of the iron-based metal material is subjected to hot dip galvanization, There is disclosed a method of surface-treating an iron-based metal material, in which electroplating is performed on the upper surface thereof and chromate treatment is further performed thereon. The publication describes that it is preferable to use a cyan bath or a zincate bath for electrogalvanizing.

[0008]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 60-1307
In the alkaline bath type tin plating disclosed in Japanese Patent Publication No. 7, a potassium bath or a sodium bath using a tetravalent stannate is used. In alkaline bath type tin plating, when pure tin is used as the anode, dissolution occurs in the form of divalent stannate or tetravalent stannate. When stannous acid ions are mixed in the bath, coarse and porous precipitates are formed and a good plating layer cannot be obtained. Therefore, the anode must be dissolved as tetravalent stannic acid. For this reason,
Alkali bath type tin plating requires strict control of the plating bath, and has a drawback of high cost when a large amount of various types of members such as cast members having different shapes are plated. Further, before plating the cast member, the surface of the cast member is cleaned by shot blasting or the like, and further pickling is performed in a step before the plating step to remove oxide films and rust on the cast surface. In some cases, it may not be completely removed, and a stable quality plating layer may not be obtained by alkaline bath type tin plating.

Japanese Unexamined Patent Publication No. 1-268880 discloses that hot-dip galvanizing is performed as a base plating layer. When hot-dip galvanizing a casting member, the thickness of the plating layer is 100 to 500 μm. In addition, the film thickness tends to be non-uniform, and the smoothness of the surface of the plating layer also deteriorates. Therefore, in order to obtain an electrogalvanized layer having a uniform film thickness and excellent gloss by applying the electrogalvanized layer on the hot-dip galvanized layer, the electrogalvanized layer should have a sufficient film thickness. It will be necessary to secure it. If an attempt is made to secure a sufficient film thickness of the electrogalvanized layer, there will be disadvantages that the electroplating time becomes long, the productivity is lowered, and the cost is increased.

The object of the present invention is to improve the above-mentioned conventional drawbacks of galvanized casting members, to provide casting members excellent in gloss and corrosion resistance, and to prevent corrosion of plating equipment and buildings. That is, a casting member that can also contribute to improving the durability of plating equipment,
Particularly, it is to provide an iron-based casting member and a galvanizing method thereof.

[0011]

According to the present invention, when a plating bath used as a base treatment for a cast member is an acid bath rather than an alkaline bath, oxidation of the cast member surface that could not be removed in the pretreatment step is performed. It was made paying attention that the film and rust can be removed more reliably and the surface of the cast member can be activated. The present invention is a casting member having a zinc plating layer formed by an acidic bath as a base plating layer, and a zinc plating layer formed by an alkaline bath on the base plating layer,
It is a casting member in which the base plating layer and the plating layer formed thereon are made of the same zinc in consideration of bondability (adhesion).
Furthermore, the present invention is a casting member having a plating layer made of at least one zinc or zinc alloy on the zinc plating layer formed by the alkaline bath.

Further, the present invention is the casting member, wherein the base plating layer is a zinc plating layer formed by a chloride bath, and the zinc plating layer formed by a zincate bath is formed on the base plating layer. Further, the present invention is a casting member in which the thickness of the undercoat plating layer is 5 μm or less. In the present invention, on the uppermost galvanized layer,
It is desirable to perform a chromate treatment to further improve the corrosion resistance.

Further, according to the present invention, when a zinc alloy plating layer is formed on the zinc plating layer formed by the alkali bath, the casting layer has a zinc-nickel alloy plating layer. Is.

Further, according to the present invention, a current density of 2 to 2 is applied to a casting member.
After forming an undercoat plating layer consisting of a zinc plating layer with a chloride bath at 10 A / dm ² , and then forming a zinc plating layer with a zincate bath at a current density of ² to 10 A / dm ² on the undercoat plating layer. It is a galvanizing method, and the thickness of the underlying plating layer formed by this chloride bath is 5 μm
This is a method of galvanizing a cast member in which a galvanized layer is formed in a short time as described below.

In the present invention, the reason for forming the zinc plating layer in the acidic bath as the base plating layer is as follows.
Conventionally, a method using a cyan bath or a chloride bath has been adopted as a method for galvanizing an iron-based casting member.
However, it is preferable not to use the cyan bath as much as possible because it takes care of harmful substances and causes environmental problems as described above. On the other hand, the acid bath does not use harmful substances unlike the cyan bath, and therefore there is little risk of causing problems in environmental protection. Also, if you use an acidic bath as the base plating bath,
The effect of further activating the surface of the iron-based casting member and promoting the deposition of the galvanized layer occurs. However, as described above, zinc plating using a chloride bath, which is one of the acidic baths, is superior in the adhesiveness of the plating layer to a material to be plated having fine irregularities on its surface, such as a cast member. However, since it contains a large amount of chlorine ions, it has a major drawback of accelerating the corrosion of plating equipment such as plating tanks and steel frames of buildings. The present inventor, as a zinc member for casting members, particularly iron-based casting members, after forming a base plating layer by a chloride bath which is an acid bath in a short time, on the base plating layer by this chloride bath, alkali It has been found that when a dense zinc plating layer is formed by a zincate bath, which is a bath, the gloss and corrosion resistance of the plating layer of a cast member can be obtained with properties equivalent to those of a conventional cyan bath or chloride bath. In addition, 1 with the conventional zincate bath
It was found that the efficiency of the plating time can be improved as compared with the case of forming a galvanized layer.

In the present invention, the reason why the thickness of the undercoat plating layer formed by the chloride bath is limited to 5 μm or less is as follows. Generally, a casting member, particularly an iron casting member, is manufactured by using a sand mold, and thus has fine irregularities on its surface. After coating these fine irregularities with a zinc plating layer in a chloride bath that surely forms the base plating in a short time, in order to efficiently form the zinc plating layer in the zincate bath on this base plating layer, the base plating The thickness of the galvanized layer is 5 μm or less, preferably 1 to 3 μm. Substrate zinc plating by chloride bath is 2-10A / d
A galvanized layer of 1 to 5 μm can be formed with a current density of about m ^{2 and} a short plating time of 2 to 5 minutes. In the case of performing plating such that the thickness of the base plating layer with a chloride bath exceeds 5 μm, a plating bath with a large capacity is required, and further, the plating time becomes long,
This is because it will promote corrosion of plating equipment and buildings.

In the present invention, an iron-based casting member is suitable as the casting member. As the material of the cast member, cast iron (normal cast iron, ductile cast iron, malleable cast iron, other alloy cast iron), cast steel and the like can be applied. Products of iron-based casting members to which the present invention can be applied include pipe members such as pipe joints and valves, automobile castings, machine parts, building members, ornaments, and the like.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Example 1) When a cast member was electrogalvanized for a predetermined time to form a zinc plating layer by a Hull cell test, the relationship between the current density and the plating film thickness was tested. The cast member used in this test is a cast iron plate-shaped sample manufactured by using a sand mold, and its dimensions are 90 mm in length, 70 mm in width, and 4 mm in thickness. Further, the galvanized layer is formed on this casting member by (A) a plating method using only a chloride bath for 5 minutes, (B) a plating method using only a zincate bath for 5 minutes, (C) )
Three methods were tested: a plating method in which a base plating with a chloride bath was performed for 2.5 minutes, and then a plating with a zincate bath was performed for 2.5 minutes on the base plating layer. In addition,
The surface of the plate-shaped cast member was cleaned by shot blasting, pickling, etc. as a pretreatment for plating.

The composition of the plating bath used in Example 1 is shown in Table 1.
Table 2 shows the plating conditions such as the plating time. After the Hull cell test was performed, the film thickness of the plating layer of the plate-shaped sample was measured, and the fluorescent X-rays were measured at five points 15 mm apart on the straight line from the left end where the current value was highest. It was measured using a line micropart thickness meter.

[0020]

[Table 1]

[0021]

[Table 2]

FIG. 1 shows the relationship between the current density and the film thickness of the plating layer obtained in Example 1. In FIG. 1, a curve a shows a case where only a chloride bath is used, a curve b shows a case where only a zincate bath is used, and a curve c shows a case where a chloride plating bath is used to form an underplating layer and then the zincate bath is applied to this undercoating layer. The change when galvanizing is used is shown. As is clear from FIG. 1, the growth rate of the plating layer is best in the method using only the chloride bath (curve a), followed by the method using the chloride bath followed by the zincate bath (curve c), and then The order is the method using only the zincate bath (curve b). As described above, if an attempt is made to form a galvanized layer using only a chloride bath, the scale of equipment such as a plating tank must be increased, and corrosion of the plating equipment is expanded by chlorine ions. Therefore, as shown by curve c, after using the chloride bath,
If a plating method using a zincate bath and a plating method using this chloride bath to shorten the plating time as much as possible are used, the plating method will be compared to the plating method using only the chloride bath as shown in the curve a. It is possible to form a galvanized layer having a desired film thickness on a cast member without significantly reducing efficiency.

(Embodiment 2) A malleable cast iron pipe fitting (2-inch elbow) 1 shown in FIG. 2 is galvanized (first layer) using a chloride bath which is an acid bath as a base plating layer for a predetermined time. After the application, zinc plating (second layer) using a zincate bath was applied on the base plating layer for a predetermined time (Sample Nos. 1 and 2 shown in Table 4). Then, the appearance of the plating layer surface after the color chromate treatment on the zinc plating layer by the zincate bath, which is the second layer, that is, the state of sticking, gloss, and burning was evaluated. As a comparative example,
Similarly, when the malleable cast iron pipe fitting (2 inch elbow) 1 shown in FIG. 2 was galvanized for 20 minutes only with a chloride bath to form a plating film thickness of 17 μm on the outer surface 1a (see Table 4). The sample No. 3) and the case where the zinc plating using only the zincate bath was applied for 20 minutes to form a plating film thickness of 9 μm on the outer surface portion 1a (Sample No. 4 shown in Table 4), the galvanized layer was colored. The condition of throwing power, gloss, and burning after the chromate treatment was evaluated. The conditions of the chloride bath and the zincate bath at this time are as shown in Table 3. The current density and the plating time, which are the plating conditions at this time, are as shown in Table 4.

[0024]

[Table 3]

Table 4 shows the evaluation results of the appearance. In addition, among the evaluation items of appearance shown in Table 4, the throwing power is the length in which the galvanized layer is normally formed in the depth direction of the inner surface portion 1b from the pipe end portion of the pipe joint elbow 1 shown in FIG. A is shown. Similarly, gloss refers to the result of visual evaluation as to whether or not there is unevenness in the gloss of the plating layer applied to the outer surface 1a of the pipe fitting 1 (○ indicates no unevenness, Δ indicates unevenness 1).
Indicates that more than one place has occurred). Similarly, the term “burnt” indicates the result of evaluating whether or not a rough plating layer is formed on the corners 1c of the pipe end of the pipe joint elbow 1 (○ indicates no burnt, Δ indicates burnt. Has occurred in one or more places).

From the results of Example 2 shown in Table 4, the following was clarified. 1) As in Sample Nos. 1 and 2 which are examples of the present invention, after forming a zinc plating layer by a chloride bath as a base plating layer on the surface of a casting member, a zinc plating layer by a zincate bath was formed on the base plating layer. In this case, the throwing power is the same as when only the chloride bath is used, and the occurrence of gloss and burn is the same as when only the zincate bath is used, but it is better than when only the chloride bath is used. .

2) As shown in Sample No. 2, even if the thickness of the zinc plating layer as the base plating layer is 3 μm, the clinging and gloss conditions do not deteriorate, and no burns occur. .

[0028]

[Table 4]

(Embodiment 3) A pipe joint 1 (Sample Nos. 1, 2, 3, and 4) obtained by electrogalvanizing according to Embodiment 2 and further subjecting the zinc plating layer to chromate treatment,
A corrosion resistance test was conducted. In this corrosion resistance test, the state of rust generation on the outer surface portion 1a and the inner surface portion 1b after 72 hours was evaluated. In addition, as the corrosion resistance test, a salt spray test (salt water concentration: 5%, in-tank atmosphere temperature: 35 ° C.) was performed. The results are shown in Table 5.

[0030]

[Table 5]

As is clear from Table 5, sample Nos. 1 and 2 which are examples of the present invention and sample Nos. 3 and 4 which are comparative examples,
No rust was found on the outer surface 1a on which the plated layer was normally formed even after 72 hours. Sample number 4
Then, after 72 hours had elapsed, rust occurred on the inner surface portion 1b. This is because galvanization of the zincate bath alone results in extremely poor throwing power. That is, in the present invention,
It was clarified that almost the same corrosion resistance as that of the conventional galvanized layer by the chloride bath can be obtained.

In the sample Nos. 1 and 2 of the above-mentioned embodiment, the zinc plating layer having the thickness of 8.5 μm and 3.0 μm was formed by the chloride bath as the base plating layer of the pipe joint 1. In the above, if the thickness of the undercoat layer is 5 μm or less, preferably 1 to 3 μm, the effect as the undercoat layer on the casting member can be sufficiently achieved. Further, in the present invention, the zinc plating layer (or zinc alloy plating layer) formed on the base plating layer using an alkaline bath such as a zincate bath is a plating layer for ensuring the thickness of the plating layer. , A desired plating film thickness according to each casting member, for example, 5 to 15
It is preferable to form the film with a thickness of about μm.

Example 4 With respect to the cast iron plate-shaped sample which was subjected to the Hull cell test in Example 1 above, the relationship between the gloss of the plating surface and the current density was examined for the result of galvanizing in each plating bath. I tried. The plating conditions at this time are the same as those described in Tables 1 and 2 above. The result is shown in FIG. In FIG. 3, column C (chlorination bath + zincate bath) showing the plating method shows that the zinc plating layer is formed on the undercoating layer after the undercoating zinc plating by the chloride bath according to the present invention. The following shows the plating method. The gloss of the plating layer surface was evaluated by visual inspection.

As is apparent from FIG. 3, in the zinc plating method (A) using only the chloride bath, the current density was 1 A / d.
The plating layer was formed at m ² or more, but the plating surface had a poor gloss. In the zinc plating method (B) using only the zincate bath, the current density is 9 A / dm ²
Through the above steps, a plated layer having excellent gloss was formed. On the other hand, in the method (C) of forming a zinc plating layer as a base by a chloride bath and then forming a zinc plating layer by a zincate bath on the base plating layer according to the present invention, a chloride bath, a zincate It was possible to form a galvanized layer having excellent gloss at a current density of 2 A / dm ² or more in both baths. In the visual evaluation of the gloss, the plating layer with poor gloss indicates that gloss is present, but uneven gloss is observed, and the plating layer with excellent gloss is glossy and uneven gloss occurs. Indicates that not.

According to the fourth embodiment, when a zinc plating layer is formed on the ground plating layer after the zinc plating is formed on the ground plating layer by galvanizing, the chloride bath and the zincate bath both have a current density of 2 A / A. It can be said that a galvanized layer having excellent gloss can be formed by plating at dm ² or more. If the current density is too high, burns may occur at the corners of the cast member, so that the current density is 2 to 10 in both the chloride bath and the zincate bath.
A / dm ² is recommended. In an actual plating line, the current density of an automobile casting member is 2 to 8 A / d in both the chloride bath and the zincate bath by the method (C) of the present invention.
When galvanizing was performed so as to be m ² , a cast member having excellent gloss could be obtained.

In the present invention, a known chromate treatment may be applied to the uppermost galvanized layer to further improve the corrosion resistance of the cast member. Further, as a concrete casting member to which the present invention is applied, a malleable cast iron pipe joint which is an iron casting member has been described, but the present invention is an iron pipe member other than the pipe joint, such as a valve or a cast iron pipe. , Castings for automobiles, castings for machinery, castings for construction,
It can be applied to non-ferrous cast members as well as decorative members.

Further, in the present invention, a zinc plating layer having a desired film thickness of at least one layer using an alkaline bath or an acid bath is further provided on the zinc plating layer (second layer) using the above alkaline bath. Alternatively, a plating layer made of zinc alloy may be formed to further improve the corrosion resistance. As this zinc alloy, it is preferable to adopt a zinc-nickel (Zn-Ni) alloy. Zinc as the outermost layer of the plating layer
When the plating layer made of a nickel alloy is formed, it is possible to obtain a casting member exhibiting sufficient corrosion resistance without performing chromate treatment on the plating layer serving as the outermost layer. The zinc-nickel alloy plating layer can be formed by a known electroplating method using a chloride bath or a sulfuric acid bath. When the nickel content of the plating layer is 5 to 20% by weight, preferably 10 to 20% by weight, the corrosion resistance of the plating layer can be further improved.

The acidic bath used in the present invention may be a sulfuric acid bath in addition to the chloride bath, and the alkaline bath may be a zincate bath or a cyanide bath.

[0039]

The present invention described above has the following effects. 1) Since the base plating layer is formed in an acid bath, the surface of the iron-based casting member is activated in this acid bath, so that the deposition of plating is further promoted on the surface of the casting member having minute irregularities. It 2) The base zinc plating layer can be formed to a plating film thickness of 1 to 5 μm in a short plating time of about 2 to 5 minutes even when a chloride bath, which is one of the acidic baths, is used. , By applying a zinc plating layer having a desired film thickness by a zincate bath on the zinc plating layer formed by this chloride bath,
A cast member having excellent corrosion resistance and uniform gloss can be efficiently obtained. 3) As described in 2) above, the zinc plating time using the chloride bath can be shortened to 2 to 5 minutes, and the scale of the plating bath of the chloride bath can be minimized. Therefore, even if a plating bath using a chloride bath is used, the corrosion of the plating equipment and the building due to chlorine ions can be suppressed to a low level, and the plating equipment can be used for a long time without renewing.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between current density and plating film thickness for each plating bath when an electrogalvanized layer was formed on a cast member by the Hull cell test.

FIG. 2 is a schematic view of a pipe joint showing an example of an iron-based cast member according to the present invention.

FIG. 3 is a diagram for explaining the relationship between the current density and the gloss of the plating layer in each plating bath when an electrogalvanized layer is formed on a cast member by the Hull cell test.

[Explanation of symbols]

1: Pipe joint 1a: Outer surface part 1b: Inner surface part 1c: Corner part

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-350198 (JP, A) JP-A-3-53096 (JP, A) JP-A-59-145792 (JP, A) JP-A-59- 129792 (JP, A) JP 62-33793 (JP, A) JP 57-149498 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 5/00-7 / 12

Claims (7)

(57) [Claims] 1. A casting member comprising a zinc plating layer formed by an acidic bath as a base plating layer, and a zinc plating layer formed by an alkaline bath on the base plating layer. 2. A zinc plating layer formed by an acid bath as a base plating layer, a zinc plating layer formed by an alkali bath on the base plating layer, and at least 1 on a zinc plating layer formed by the alkali bath. A casting member having a plating layer made of zinc or a zinc alloy having at least one layer. 3. The base plating layer is a zinc plating layer formed by a chloride bath, and the zinc plating layer formed on the base plating layer is a zinc plating layer formed by a zincate bath. The casting member according to claim 1 or 2. 4. The casting member according to claim 1, wherein the film thickness of the base plating layer is 5 μm or less. 5. The casting member according to claim 2, wherein the zinc alloy is a zinc-nickel alloy. 6. A casting member having a current density of ^{2 to} 10 A / dm ²
After forming a base plating layer consisting of a zinc plating layer in a chloride bath, a current density of 2 to 10 A is applied on the base plating layer.
A method for galvanizing a cast member, which comprises forming a galvanized layer with a zincate bath at / dm ² . 7. The casting member according to claim 6, wherein the base plating layer formed by the chloride bath is a zinc plating layer having a current density of ² to 10 A / dm ² and a film thickness of 5 μm or less. Galvanizing method.