JPH04350193A - Undustrial chrome plating method - Google Patents

Abstract

PURPOSE:To offer a method of industrial chrome plating having high corrosion resistance. CONSTITUTION:The primer chrome plating 3 is applied by using a hydrosilicofluoric acid-base chrome plating bath as a plating bath and the top chrome plating 5 is applied by laminate plating on the primer chrome plating 3 by using a hydrosilicofluoric acid-base chrome plating bath in which methane- sulfonic acid is added so as to be 2-10g/l conc.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying industrial chromium plating with excellent wear resistance and corrosion resistance to metal surfaces.

0002

[Prior art] Chrome plating has excellent wear resistance (
High hardness and low coefficient of friction. ), it is widely used as industrial chrome plating.

0003

[Problems to be Solved by the Invention] However, chromium plating has poor corrosion resistance. This is because there are countless cracks in the plating layer that reach the substrate.

That is, regardless of the film thickness, industrial chrome plating showed corrosion of the base metal in a relatively short period of time in a salt spray test, and could not withstand use in a corrosive environment.

[0005] An object of the present invention is to provide a new industrial chromium plating method that has both excellent corrosion resistance and wear resistance.

[0006]

[Means for Solving the Problems] The industrial chromium plating method of the present invention solves the above problems by the following configuration.

[0007] Using a fluorosilicic acid-based chromium plating bath,
The method is characterized in that a base chromium plating is applied, and two or more layers of upper chromium plating are laminated on the base chrome plating from a fluorosilicic acid chromium plating bath to which methanesulfonic acid is added at a concentration of 2 to 10 g/l. Industrial chrome plating method.

[0008]

[Detailed explanation of means]

(i) The industrial chromium plating method of the present invention includes the first step of laminating a base chromium plating and two or more layers of upper chromium plating using a hydrofluorosilicic acid (hexafluorosilicic acid) chromium plating bath. It shall be a configuration requirement.

[0009] Here, the silicofluoric acid-based chromium plating bath is basically an aqueous solution of chromic anhydride, sulfuric acid, and silicofluoride. Here, silicofluoride refers to hydrofluorosilicic acid,
These include sodium silicofluoride and potassium silicofluoride.

(2) The thickness of the base chromium plating and the upper layer plating must be 8 μm or more, preferably 10 μm or more. If it is less than 8 μm, the desired high corrosion resistance cannot be obtained. Although the upper limit of the film thickness is not particularly limited, sufficient corrosion resistance can be obtained with a thickness of 20 μm or less.

(ii) The present invention provides the above upper layer plating,
Methanesulfonic acid (CH3SO3H) from 2 to 10
The second component is that the plating is carried out in a fluorosilicic acid-based chromium plating bath to which the plating solution is added at a concentration of g/l, preferably 3 to 8 g/l.

[0012] If the amount of methanesulfonic acid added is less than 2 g/l, the desired high corrosion resistance cannot be obtained;
If it exceeds 0 g/l, the gloss of the plating will decrease, which is not preferable.

[0013]

[Actions and effects of the invention] The industrial chromium plating of the present invention is
As shown in the examples below, the above structure exhibits a high degree of corrosion resistance. That is, the plating film formed by the method of the present invention is resistant to salt spray tests and exposure to corrosive environments.
It has the ability to completely prevent corrosion of base metals.

[0014] Film thickness of conventional industrial chrome plating is 20 μm
In contrast, industrial chromium plating with a film thickness of 20 μm produced by the method of the present invention shows no red rust even after 300 hours of salt spray testing.

The reason for exhibiting such high corrosion resistance is presumed to be as follows.

[0016] The present inventors have developed a chromium plating layer electrodeposited from a conventional silicofluoric acid-based chromium plating bath and a chromium plating layer electrodeposited from a silicofluoric acid-based chromium plating bath to which methanesulfonic acid was added. When compared through a diffraction test, it was discovered that both plating layers had different crystal orientations. That is, a chromium plating layer electrodeposited from a conventional fluorosilicic acid-based chromium plating bath shows three peaks in the plane of Miller indices (110), (200), and (211) in X-ray diffraction, especially in the (110) plane. ) and (200) planes, and (211) planes showed a weak peak. On the other hand, the plating layer electrodeposited from a fluorosilicic acid-based chromium plating bath containing methanesulfonic acid was (
The peak for the (110) plane completely disappeared, and only the peaks for the (200) and (211) planes were shown, with a particularly strong peak for the (211) plane. This crystal orientation was not observed in conventionally known chromium plating layers, and it was confirmed that this was a new chromium plating.

[0017] By stacking chromium plating layers having different crystal orientations, the present inventors prevented cracks existing in the chromium plating layer from penetrating into the base material, thereby creating a chromium plate without cracks reaching the base material. They came up with the idea that it could be plated, and as a result of intensive research, they arrived at the present invention, which realizes industrial chrome plating that exhibits a high degree of corrosion resistance. Such effects of the present invention can be obtained only when the above-mentioned constituent requirements are satisfied. That is, even if a Sargent bath is used instead of a hydrosilicic acid-based chromium plating bath, such an effect cannot be obtained. Also, even if the order of base plating and top layer plating is reversed,
Experiments have confirmed that even if a bath containing methanesulfonic acid is used, the effect of high corrosion resistance cannot be obtained.

[0018]

[Example] Examples carried out to confirm the effects of the present invention will be explained.

The following fluorosilicic acid-based chromium plating bath was used as the base plating bath.

[0020]
Fluorosilicic acid bath Chromic anhydride
CrO3 2
50 g/l sulfuric acid
H2 SO4
1 g/l Potassium silicofluoride K2 SiF6
3 g/l Plating bath similar to the above A bath to which 3 g/l of methanesulfonic acid (CH3SO3H) was added was used as the upper layer plating bath.

[0021] A mild steel plate (100 x 50 x 1 mm) was used as a test piece, and a film thickness of 10 μm was formed at a bath temperature of 55° C. and a current density of 40 A/dm2 under electrolytic conditions using the above-mentioned base plating bath. A base chromium plating was applied, and an upper layer plating with a thickness of 10 μm was applied thereon under the same electrolytic conditions using the bath for upper layer plating described above.

[0022] ■ Using the plated test piece chromium plated by the method of the present invention, ASTM-B117 (JIS
-Z-2371), no red rust was observed even after 300 hours of spraying.
The rating number (hereinafter abbreviated as "RN") indicating the degree of corrosion was 10.

[0023] Furthermore, a combined cycle corrosion test was conducted using this plated test piece.

The test conditions were one cycle consisting of a 4-hour salt spray test at a temperature of 50° C. and a 20-hour humidity test at a temperature of 50° C. and a relative humidity of 95%.

Even after 10 cycles of this combined cycle corrosion test, no red rust was observed, and the RN was 10.

■ Also, the surface hardness of this test piece was determined by ASTM
- When a Vickers hardness test was conducted according to the method of B578 (JIS-Z-2251), the Vickers hardness was Hv. 1
100, showing higher hardness than conventionally known industrial chrome plating.

[0027]

[Comparative Example 1] In order to confirm the superiority of the effects of the present invention, the following comparative test was conducted.

Using the known fluorosilicic acid-based chromium plating bath used for the base plating in the examples, a known industrial chromium plating with a film thickness of 20 μm was applied to the same test piece as in the examples under the same electrolytic conditions. When a salt water spray test similar to that in the example was conducted using a plated test piece, it was observed that red rust occurred after 1 hour of spraying, and after 300 hours of spraying, the entire surface was covered with red rust, and the RN was 1. Ta.

Note that the RN was 3 after 10 cycles of the same combined cycle corrosion test as in the example. Also, Vickers hardness is Hv. It was 900.

[0030]

[Comparative Example 2] The order of the upper layer plating bath and base plating bath in the above example was reversed, and the methanesulfonic acid addition bath was used for base plating, and the conventional fluorosilicic acid-based chromium plating bath was used for upper layer plating. When the same salt water spray test as in the example was conducted using a plated test piece subjected to the same electrolytic conditions as in the example, red rust was observed after 24 hours of spraying time, and the RN was 4 after 300 hours. there were.

Further, the RN was 3 after 10 cycles of the same combined cycle corrosion test as in the example.

[0032]

[Comparative Example 3] Instead of the fluorosilicic acid-based chromium plating bath in the example, the following Sargent bath was used as a base plating bath, and 6 g/l of methanesulfonic acid was added to the same Sargent bath for upper layer plating. Laminated plating was performed using the same electrolytic conditions as in the example to prepare a plating test piece, and the same salt spray test as above was conducted. After 24 hours of spraying, red rust was observed, and 30
RN after 0 hours was 6. Further, the RN was 6 after 10 cycles of the same combined cycle corrosion test as in the example.

Sargent Bath Chromic Anhydride
CrO3 250
g/l sulfuric acid
H2 SO4
2.5 g/l

[0034]

[Comparative Example 4] Two-layer plating with a 10 μm thick plating layer was performed using only a methanesulfonic acid-added fluorosilicic acid chromium plating bath similar to the upper layer plating bath in the example, and a salt water spray test was conducted. However, the spray time is 7.
After 2 hours, red rust was observed, and after 300 hours, the RN was 7.
Met.

[Brief explanation of drawings]

FIG. 1 is a model diagram of a plating film formed by the chromium plating method of the present invention.

[Explanation of symbols]

1. Plated object, 3 Base chrome plating film, 5 Upper layer chrome plating film.

Claims (1)

[Claims] Claim 1: A fluorosilicic acid-based chromium plated with a base chromium plating using a fluorosilicic acid-based chromium plating bath, and methanesulfonic acid added to the base chromium plating at a concentration of 2 to 10 g/l. An industrial chrome plating method characterized by laminating two or more upper chrome plating layers from a plating bath.