JP2662841B2 - Cast structural parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural part made of a casting, in which a galvanized layer is formed by electroplating or hot-dip coating on the surface of a base material of the structural part made of a casting, and a chromic acid-based film is formed. . In particular, the present invention is suitable for casting structural parts in which rust is likely to occur, such as many iron-based castings.

[0002] Here, castings include cast iron (plain cast iron and alloy cast iron to which Ni, Cr, Mo, Mn, etc. are added), spheroidal graphite cast iron (ductile cast iron) casting, chill casting,
This concept includes non-ferrous alloy castings in addition to iron-based castings such as malleable iron castings and steel castings.

[0003] Zinc means not only zinc but also zinc, iron, nickel, aluminum, copper, magnesium,
Refers to an alloy with manganese or the like.

[0004] Further, the cast structural component is a concept including mechanical parts such as a piston cylinder, a hose nipple, a valve casing, and a clamp, and various fittings for construction.

[0005]

BACKGROUND OF THE INVENTION Problems to be Solved by the Invention
The description will be made by taking an iron-based casting as an example, but the present invention can be applied to a casting that is likely to generate rust even if it is non-ferrous.

[0006] As a method of rust-preventing treatment of iron-based castings, it is common practice to form a galvanized layer by electroplating or hot-dip plating, and further form a calcined chromate film on the galvanized layer.

[0007] However, in the rust-preventive treatment method, in the case of an iron-based casting, the rust-preventive property is remarkably inferior to that in a case where the same rust-preventive treatment is applied to a normal steel plate. It is presumed that the casting is porous (having a large number of fine holes), the zinc plating by electroplating or hot-dip plating does not penetrate into the fine holes, and the zinc plating layer itself becomes porous.

[0008] In view of the above, the present invention provides a cast structural part having a galvanized layer formed by electroplating or hot-dip galvanizing and further having a chromic acid-based film formed thereon. It is intended to provide structural parts.

[0009]

According to the present invention, the above-mentioned object is achieved by the following constitution.

[0010] In the cast structural component, a zinc plating layer is formed on the surface of a casting base material by electroplating or hot-dip plating, and a chromic acid-based film is further formed on the zinc plating layer. The chromium trioxide and the metal salt of dihydrogen phosphate are essential components, and the lacquer is formed of an aqueous coating agent in which the ratio of the former and the latter is 9/1 to 4/6. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The means of the present invention will be described in detail below. The blending units are weight units unless otherwise specified.

(1) In the cast structural component of the present invention, a galvanized layer is formed on the surface of the base material of the cast structural component by electroplating or hot-dip plating, and a chromic acid-based film is further formed on the zinc plated layer. It is assumed that it is formed.

Here, when a zinc plating layer is formed by electroplating, it is usually performed using an acidic zinc plating bath. The acidic zinc plating bath is used because the hydrogen overvoltage is high and zinc is preferentially deposited.

The thickness of the galvanized layer is usually 1 to 10 μm in the case of electroplating, and usually 10 to 100 μm in the case of hot dip plating.

Prior to the formation of the galvanized layer,
The surface of the substrate is cleaned by a conventional method. That is, the surface is activated by removing oils and fats using an organic solvent such as trichloroethylene and trichloroethane or an aqueous detergent such as an alkaline detergent. Alternatively, the surface may be cleaned by a physical method such as shot blasting.

(2) The present invention relates to a cast structural part having the above-mentioned structure, in which chromium trioxide and metal dihydrogen phosphate (metal first phosphate) are essential components, and the mixing ratio of both is the former / The latter = 9/1 to 4/6 (preferably 7/1 to 1
/ 1), wherein the chromic acid-based coating is formed with an aqueous coating agent.

If the proportion of the metal dihydrogen phosphate is too small,
It is difficult to achieve the effect of improving the rust resistance, and if the ratio of the metal dihydrogen phosphate is excessive, the water resistance of the cured film deteriorates.

The amount of the essential components (total amount of chromium trioxide and metal dihydrogen phosphate) is 10 to 70% (preferably 40 to 60%). If it is less than 10%, it is difficult to obtain a predetermined film thickness (usually 0.1 μm), and if it exceeds 70%, the saturation solubility of both components is exceeded and precipitation is liable to occur.

Examples of the metal of the above-mentioned metal dihydrogen phosphate include calcium, aluminum, magnesium, and zinc. In addition, a part of dihydrogen phosphate may be replaced by metal monohydrogen phosphate / metal phosphate normal (about 1/2 or less in the case of water solubility, and about 1/9 or less in the case of poor solubility). .

Further, a part of the chromium trioxide may be replaced with a chromate / metal dichromate salt (such as potassium, sodium, magnesium, zinc, etc.) or dichromium trioxide (in the case of water solubility). Is about 1/2 or less, and when it is hardly soluble, about 1/9 or less).

As other components, monohydric / dihydric alcohols and surfactants are usually used.

Alcohols are presumed to have an effect of reducing and polymerizing chromic acid. Specifically, alcohols include ethyl alcohol, isopropyl alcohol, isobutyl alcohol, cellosolve (monovalent), ethylene glycol, diethylene glycol, and polyethylene glycol (molecular weight). 200 to 600) can be used. The blending amount of the alcohol varies depending on the kind and blending amount of the essential blending component, but is usually 1 to 10%.

The surfactant has an effect of improving the leveling property of the coating film, and a fluorine-based surfactant is preferably used. The amount is usually 0.01 to 0.1%.

(3) The chromic acid-based film is formed by applying the water-based film agent of the above requirements on the galvanized layer and curing by heating.

The coating method is not particularly limited, but is performed by a dipping impregnation method or a spray method. Moreover, you may apply repeatedly, if needed.

The conditions for heat curing are usually from 100 to 400
C. x 5-120 min. If the heating temperature is lower than 100 ° C., the water resistance is inferior. If the heating temperature is higher than 400 ° C., the occurrence of cracks in the film increases, and the film properties may be deteriorated.

The thickness of the chromic acid-based coating is usually 0.05
To 10 μm (preferably 0.1 to 5 μm). 0.05μ
If it is less than m, the effects on heat resistance, hardness, corrosion resistance, etc. cannot be sufficiently obtained. If it exceeds 10 μm, deterioration of the film quality due to accumulation of internal stress of the film and time for film deposition are required, and uniformity of the film is problematic. Tends to occur.

[0028]

The cast structural part of the present invention is characterized in that a galvanized layer is formed on the surface of a base material by electroplating or hot-dip plating, and a chromic acid-based film is formed on the galvanized layer. In the following, the chromic acid-based film is
It is characterized by being formed of an aqueous coating agent in which chromium trioxide and metal dihydrogen phosphate are essential components and the mixing ratio of the two is former / latter = 9/1 to 4/6. As supported by the examples described below, it is possible to obtain a structural part made of a casting with significantly improved corrosion resistance.

The reason is presumed to be as follows.

A zinc layer is formed on a casting by electroplating or hot-dip galvanizing to become a sacrificial anode electrochemically, electrochemical corrosion protection is performed, and the porosity of the casting (porosity) itself and the zinc plating layer resulting therefrom are utilized. And slightly soluble phosphoric acid
It is thought that the permeation and filling with the chromic acid complex compound results in electrochemical corrosion protection due to passivation of chromium.

The corrosion resistance of the chromic acid-based coating is such that the resulting coating is glassy and is coated with good adhesion, so that the contact between the base metal and air and moisture is cut off and the supply of oxygen is blocked. Remains and is slightly soluble by heat curing, so that hexavalent chromium is replenished to the metal surface over time over a long period of time to promote the passivation by hexavalent chromium. It is thought that they can be obtained in a synergistic manner.

[0032]

EXAMPLES Hereinafter, examples performed together with comparative examples to confirm the effects of the present invention will be described.

(1) Casting structural parts on which a galvanized layer is formed (object to be coated: 20 cm × 5 cm φ piston cylinder,
(Made of gray cast iron) is immersed and coated in a water-based coating agent having the composition shown in Tables 1 and 2 prepared in advance, and after lifting, centrifugal drying (800 rpm × 30 seconds), and coating under the conditions shown. Was cured by heating.

In Examples 1 to 7 and Comparative Examples 1 to 7, electroplating was performed in the following zinc plating bath (chloride bath) and conditions.

ZnCl ₂ .7H ₂ O 30 g / L NH ₄ Cl 200 g / L Brightener 31.5 ml /
L pH 5 Temperature 25 ° C. Current Density 2 A / dm ² Plating Layer Thickness 5 μm Further, in Example 8, hot-dip plating was performed at an immersion temperature of 450 ° C. to a plating thickness of 30 μm.

(2) The following items were tested for each of the structural parts thus obtained. From the test results shown in Tables 1 and 2, it can be seen that the respective examples which are the cast structural parts of the present invention have significantly improved corrosion resistance and surface hardness as compared with the comparative examples.

Salt spray test: heat resistance test (200 degrees × 5)
h) Thereafter, the measurement was performed according to JIS Z 2371.

[0038]

[Table 1]

* 1) "Floraldo FC-95" Sumitomo 3
M company

[0040]

[Table 2]

* 1) "Floraldo FC-95" Sumitomo 3
* 2) Nonionic surfactant manufactured by NOF Corporation * 3) Nonionic surfactant manufactured by Diamond Shamrock

Claims (1)

(57) [Claims] 1. A cast structural component comprising: a galvanized layer formed by electroplating or hot-dip plating on a surface of a cast base material; and a chromic acid-based film formed on the galvanized layer. The chromic acid-based film contains chromium trioxide and metal dihydrogen phosphate as essential components, and the mixing ratio of both is the former / the latter =
A casting-made structural part characterized by being formed of an aqueous coating agent of 9/1 to 4/6.