JPS61246386A - Improvement of corrosion resistance of plated article - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of an iron blank having a complex shape including a recess by electroplating part of the surface of the iron blank with chromium or nickel and chromium and by chemically plating the unplated part with nickel. CONSTITUTION:The surface of an iron blank having a complex shape including a recess is electroplated with chromium except the upper recess, or thick nickel electroplating and thin chromium electroplating are successively carried out when more satisfactory corrosion resistance is required. Chemical nickel plating is then carried out on the upper recess. By the chemical nickel plating, a thick nickel layer is formed on the unplated upper recess and nickel does not deposit at all on the chromium electroplated part. Thus, a plated article having improved corrosion resistance is obtd.

Description

[Detailed Description of the Invention] This invention relates to improving the corrosion resistance of the entire plated bookbinding by coating the uncoated portions of chromium plating that occur when electroplating is applied to a steel substrate with chemical nickel plating. .

BACKGROUND OF THE INVENTION Electric pottery is commonly used to improve the corrosion resistance of metal parts and to add decorative properties to them. For example, when it comes to steel products, first, the surface of the steel product is thoroughly cleaned and then subjected to electrolytic copper plating (copper bronze bath plating or copper pyrophosphate plating), and then electrolytic nickel plating (single layer plating, double layer plating) is applied. plating or three-layer plating), and then cover the product with electrochrome plating. However, due to various circumstances such as pollution problems, it has become difficult to apply copper bronze plating and copper birophosphate plating in the plating industry, and currently there is a process in which copper electroplating is omitted, that is, from steel material to electrolytic nickel plating. This led to the mass production of plated products using electrochrome plating. Although this has contributed greatly to society in terms of environmental protection and in terms of labor and resource conservation for production factories, it has become clear that there are serious drawbacks as a product. .

Metal products originally come in various shapes. Depending on the purpose of use, there are flat ones, round ones, uneven ones, and vibrator-like ones. Electro-nickel plating and electro-chrome plating can cover the entire surface of parts with relatively simple shapes, but in the case of complex parts, especially those with uneven parts, it is difficult to cover the concave parts with plating. It is well known that this is a difficult task. For this purpose, special jigs and special means are used to intentionally cover these recesses with plating for important industrial products, but equipment and labor costs increase the manufacturing costs of the products.

Therefore, such a method cannot be used in the processing of general plated products, and the recesses are left unplated.

For example, a bag nut 1 used for fastening an automobile wheel to the main body has a U-shaped cross section as shown in Fig. 1, and a screw 3 is carved into the bag-shaped inner side 2, which is open on one side and closed on the other side. ing. Although the outer surface 4 of this cap nut 1 can be easily plated, the inner surface 2 of the bag-shaped nut 1, especially the recesses such as the inner part of the screw 3, cannot be well plated.
It is in an uncovered state.

On the other hand, specifications for manufacturing plated products generally include the concept of an effective surface, and the corrosion resistance and appearance of that region are considered issues, and other regions are ignored. For example, the bag nut 1
In this case, the outer surface 4 is considered to be the effective surface. It is common knowledge that it is difficult to plate the recessed part, so designers try to avoid using the recessed valve as an effective surface as much as possible. However, if the four parts are corroded and the product is in a state of red rust from the time of delivery or first use, it becomes a problem for the product. This was hardly a problem when copper plating was applied to the steel material. This is because no red rust was observed in the recesses immediately after manufacture or during initial use. However, recently, the problem of red rust occurring in the recesses due to the removal of plated steel has come into focus.

In an attempt to solve this problem, the uncoated parts are usually coated with a rust preventive or paint after electroplating, but weak rust preventives cause rust to form immediately, and strong rust preventives However, its stickiness impairs the appearance of the product and makes it difficult to handle. Furthermore, in order to apply paint, it is necessary to mask each plated part of the plated product one by one, which is also difficult and time-consuming.

Thus, the present invention improves the overall corrosion resistance of iron materials by effectively coating the recesses of iron materials such as iron and steel materials and cast iron materials, which have complex shapes such as recesses that cannot be coated with ordinary electrochrome plating. According to the research and experiments of the present inventors, this purpose is to provide a method for improving the performance of the iron material by applying electrochromium plating or electronickel plating to a part of the surface of the iron material. It has been discovered that this can be achieved by a plating method characterized by applying electrochromium plating and applying chemical nickel plating to the non-plated areas.

To explain the present invention, in the present invention, an iron material having a complicated shape such as a concave part is first subjected to electrochromium plating, or
Electrolytic nickel plating and electrochromium plating are applied to cover the surfaces other than the recesses, and then chemical nickel plating is applied to cover the uncoated parts such as recesses, thus plating the entire surface including the recesses. It became possible to coat the material to improve corrosion resistance. ~ The electrochromium plating, electrolytic nickel plating, and chemical nickel plating performed here are all performed by conventionally known methods. Apply appropriate p using a commercially available plating bath.
Plating is carried out under working conditions such as H1 current density, temperature, and time.

Generally, electrochromium plating alone does not provide sufficient corrosion resistance, so a thick electrolytic nickel plating is applied in advance and a thin electrochromium plating is applied thereon. In the case of the above-mentioned bag nuts, electrolytic nickel plating is first performed, followed by electrochromic plating, and then chemical nickel plating is performed, but when electrolytic nickel plating is performed in this way, it is usually first immersed in a semi-bright nickel plating bath that does not contain a brightening agent. After the treatment, it is preferable to perform treatment in a bright nickel plating bath containing a brightener. In the case of electrochromium plating to impart wear resistance, electrolytic nickel plating is not applied in advance. Thus, if electrochromium plating, or electronickel plating and electrochromium plating are applied, and then immediately immersed in a chemical nickel bath for plating, the chemical nickel plating bath will coat the previously unplated areas. Depending on the composition, a corrosion-resistant coating such as a nickel-phosphorus alloy or a nickel-boron alloy is deposited. That is, while chemical nickel plating can uniformly plate parts of any shape, it cannot be deposited on electrochromium plating.

Therefore, when electrolytic nickel plating and electrochromium plating are applied to an iron material that has recesses, there is no electrochromium plating coating on the recesses, and a small amount of iron material is exposed, which is thin enough to show corrosion resistance. However, by further chemical nickel plating, the exposed parts of the steel material and the thin electrolytic nickel plating can be covered with a thick chemical nickel plating. No chemical nickel deposition was observed on the electrochromium plated parts, including the effective surfaces.

In addition, it passed the corrosion resistance test by CAST test after chemical nickel plating, and during this test, no red rust was observed at all on the areas not coated with electrochromium plating and on the areas coated with chemical nickel plating.

(According to the present invention, when electrochrome plating steel products, the corrosion resistance is equivalent to that without using the conventional copper bronze plating bath or copper birophosphate plating bath. In addition, cyanide and copper are both hazardous substances stipulated in the Water Pollution Control Act, and this is extremely effective industrially because it can be done without dispersing them into the environment. It is.

Although the above description has mainly been about corrosion resistance improvement treatment for iron materials that have complex shapes that are difficult to electrochrome plate, such as recesses, the present invention is not limited to such cases; It can also be applied to relatively simple structures such as the following. In this case, the shaft portions 12 at both ends of the elongated copying roll 11 are masked with insulating paint or vinyl tape, electrochrome plating is applied only to the central portion 13 to provide wear resistance, and then the masking is removed and the shaft portions are 12 is subjected to chemical nickel plating. Conventionally, only the central portion 12 of the roll was electroplated with chrome before being delivered to the manufacturer and assembled, but this resulted in the problem of red rust forming on the shaft portion 12. However, this problem can be solved by applying chemical nickel plating to the shaft portion according to the present invention.

The present invention will be further explained with reference to Examples below, but the present invention is not limited thereto.

Example 1 (A> After performing appropriate pretreatment on 10 samples of cap nuts (length 40 as+, outer diameter 20 am, inner diameter 16 shoes) shown in Fig. 1, electrolytic nickel plating, electrochromium plating, chemical Nickel plating was carried out.The composition of the plating bath and working conditions used at that time were as follows.

Process bath composition
Working conditions Semi-bright nickel Nickel sulfate 300
9 /ρ Bath temperature 55℃ Nishilite 2N 1
rR1/41 Air stirring/I E 1
d/1 Bright nickel Nickel sulfate 300 tj
/Jl Bath temperature 55℃ Nishilite 610 5
tl/fl Air stirring 61 1d/1 # 63 15+d! /J! Julia Nickel Sulfate 3009/J) Bath Temperature 60℃n ON-MP 23g/fJn
DN-3070, 3g/II chemical nickel *
Univac HF 1 volume Bath temperature 95℃ plating Water 4 volumes 1)
84.6 "The chemical nickel bath called Univac HF is a weakly acidic high temperature type chemical nickel plating bath using sodium hypophosphite as a reducing agent, and the deposited film is a nickel-phosphorus alloy.

(B) Next, for another 10 bag nut samples (A
> was carried out in the same manner. However, instead of chemical nickel plating, the following chemical nickel plating (2) was used. This deposited film is a nickel-boron alloy.

Nickel sulfate 30 97M Sodium citrate 10 9/j Sodium succinate 20
g/l sodium acetate 20 g/j diethylborazane 3 d/1 methanol
50 d/j stabilizer 0.
01g/j working conditions were pH 6-7 and temperature 65°C.

(C) For comparison, ten other bag nut samples were subjected to electrolytic nickel plating and electrochromium plating in the same manner as in (A), but chemical nickel plating was not performed.

(D) Also for comparison, another bag nut sample 10
After copper plating was carried out using the following bath composition and working conditions, electrolytic nickel plating and electrochromium plating were carried out as in (A).

(Chemical nickel plating was not performed.) Pre-brightened copper plating bath composition Working conditions
100g/j @ Temperature 70℃ Sodium cyanide 120〃 Current density 3A/da2 Sodium hydroxide 30nP, R, Sodium carbonate using electrolytic method
15〃 Rosselle salt 45〃 Rodankali 8 〃 Ten bag nut samples as shown in Fig. 1 were added to the above (A).
The samples were plated as shown in (D) above, and the average values of film thicknesses (μ) obtained by each plating process for each sample were as follows. Of course, in the treatments (A) to (B) according to the present invention, the inside of the bag nut was also coated uniformly, but for the sake of comparison, treatments (C) to (D)
In this treatment, the inside of the bag nut was not coated.

BCD Pre-bright copper plating ---8 Semi-bright nickel plating 12 16 16 16 Bright nickel plating 10 12 15
12 units 1 1
1 1 Electrochrome plating 0.25 0.
25 0,25 0.25 Chemical nickel plating l2--
− Chemical nickel plating ■ 2 −
-Next, 10 samples each of the above (A) to (D)-
) A plating corrosion resistance test was conducted according to JIS H8502 (1977) GC. At that time, each sample was exposed to an atmosphere in which a solution of cupric chloride added to a vinegar-based sodium chloride solution was sprayed for a certain period of time using a CASS test device to test the rusting state. The results are shown in rating numbers, with the highest being 10 (A) to (D).
For each sample, the effective surface (outer surface of the bag nut) had a rating number of 9 or higher and was passed. However, in the case of Comparative Example C, the entire inside of the bag nut was covered with red ta, and in the case of (D), patina was observed in some of the samples.
In the cases of (A) and (B) according to the present invention, neither red rust nor patina was observed at all.

Example 2 Copy roll as shown in Figure 2 (the center part has a diameter of 12111 mm)
1I, length 300m, both end shafts have a diameter of 6 shoes, length 1
5) The shaft portion 12 of 11 was masked with an insulating paint, and the remaining center roll portion 13 was electroplated with chromium in the bath used in Example 1 to obtain a chromium plating film with a thickness of 10 μm. Then, the masking was removed using an organic solvent, alkali cleaning was performed using a commercially available metal cleaning agent, and after activation using a 5% sulfuric acid bath, chemical nickel plating was performed using the chemical nickel plating bath of Example 1. A chemical nickel plating film with a thickness of 2 μm was formed on the shaft portion 12 .

Along with the sample obtained in this way, a sample without chemical nickel plating was made for comparison, and both were JIS
When subjected to a salt spray test using H8502, red rust was already observed on the shaft portion of the sample without chemical nickel plating after 8 hours, but the sample treated with the present invention showed 72.
No rust was observed even after the passage of time.

[Brief explanation of drawings]

Figures 1 a, b, c, and d are a left side view, a front view, a sectional view, and a right side view of the cap nut used in Example 1 of the present invention, and Figures 2 a and b are the same side 2 FIG. 2 is a front view and a side view of a copying roll used in FIG. DESCRIPTION OF SYMBOLS 1... Bag nut, 2... Bag-like inside, 3... Thread part, 4... Outer surface, 11... Roll for copying, 12
...Both end shaft parts, 13...Central roll part.

Claims (1)

[Claims] A method for improving the corrosion resistance of plated products, characterized by applying electrochromium plating or electronickel plating and electrochromium plating to a part of the surface of an iron material, and applying chemical nickel plating to the unplated parts.