JPH04160197A - Production of shaft for cylinder - Google Patents

Abstract

PURPOSE:To obtain the shaft for cylinders having excellent corrosion resistance by applying hard chrome plating on an iron shaft by using a plating bath of prescribed conditions, then baking the plating at a prescribed temp. CONSTITUTION:A hard chrome plating bath contg. 100g/l chromic anhydride and 1 to 1.5g/l sulfuric acid is prepd. The hard chrome plating is applied on the shaft consisting of the iron material by using this plating bath. The plating is then baked at 100 to 300 deg.C and is buffed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a shaft for a cylinder used in construction machinery and the like.

[Prior Art and Problems to be Solved by the Invention] Conventionally, cylinder shafts such as piston rods have been used in hydraulic machines for construction machinery such as power shovels. The shaft, on which the cylinder and the shaft slide, is required to have characteristics such as high hardness, high wear resistance, and high dimensional accuracy including surface accuracy. Therefore, cylinder shafts are usually manufactured by applying hard chrome plating to shafts made of iron-based materials.

However, unlike other electroplated layers, a plating layer formed by hard chrome plating has many defects such as cracks, pinholes, and pits even if the plating layer has a thickness of about 100 μm. Therefore, although a hard chrome-plated shaft has various excellent properties, it is susceptible to corrosion and rust. In particular, in the presence of chlorides such as sodium chloride, acids, or in a high temperature and high humidity environment, the cylinder shaft is significantly corroded due to the numerous defects described above. When the shaft corrodes, scratches occur due to sliding with the cylinder, causing oil leaks.

In order to prevent corrosion of hard chrome plated products, rust preventives are applied and allowed to penetrate into cracks and other defects, but this cannot be said to be a fundamental solution. In addition, in order to prevent corrosion of hard chrome plating, the thickness is 0.
A plating layer having a thickness of about 0.05 to 0.1 mm is formed. However, increasing the thickness of the plating layer reduces productivity.

Therefore, an object of the present invention is to provide a method for manufacturing a cylinder shaft that has excellent corrosion resistance while taking advantage of the advantages of hard chrome plating.

[Structure of the Invention] In order to achieve the above object, the inventors of the present invention have conducted extensive studies and found that baking treatment after hard chrome plating significantly improves corrosion resistance, and has completed the present invention. . That is, the present invention provides a method for manufacturing a shaft for a cylinder, in which a shaft made of an iron-based material is plated with hard chrome and then baked.

The shaft, which is the plated base material, is made of iron-based material, for example,
Low carbon steel, high carbon steel, hardened steel, high speed steel, chrome steel,
Nickel steel, nickel chromium steel, nickel chromium steel
It can be made of various materials such as molybdenum steel, stainless steel, and tungsten steel.

The shaft is typically plated with hard chrome prior to
Degreasing treatment using an organic solvent, alkali immersion, alkaline electrolytic degreasing, etc. may be carried out, and if necessary, pickling treatment with an acid such as hydrochloric acid or sulfuric acid may be carried out.

Additionally, prior to hard chrome plating, the shaft is subjected to a polishing process. The shaft can be polished by conventional methods, such as cylindrical polishing (ring buffing) with high abrasive power, vertical polishing, etc.; rough polishing such as emery buffing, belt polishing, flap wheel polishing; cotton buffing, sisal buffing, etc.
Medium polishing and final polishing, which are combinations of these, can be performed alone or in combination. Note that the intermediate polishing and final polishing may be of a closed face type, an open face type, or a unit face type.

After masking the unplated parts as necessary, the plate is subjected to etching treatment by anodic oxidation. This etching process is carried out, for example, in a chromium plating bath, a chromic acid aqueous solution, or a sulfuric acid aqueous solution at a temperature of 30 to 60°C using the shaft as an anode.
About ℃, current density about 10 to 50 A/drn', time 1
This can be carried out by electrolytic treatment under conditions of about 0 to 600 seconds. Note that instead of or in addition to the etching treatment, an acid immersion treatment in which the substrate is immersed in hydrochloric acid, sulfuric acid, or the like may be performed.

The composition of the chrome plating bath is not particularly limited, and any conventional plating bath can be used. The plating bath may be, for example, a Sargent bath containing chromic anhydride CrO3 and sulfuric acid; a silicofluoride bath containing sodium fluorosilicate, potassium fluorosilicate, etc. in addition to chromic anhydride CrO3 and sulfuric acid. Further, the chromium plating bath may contain at least one component such as hydrofluorosilicic acid, ammonium fluoride, strontium sulfate, citric acid, tartaric acid, oxalic acid, and formic acid. The plating bath usually contains 0.1 trivalent chromium.
It often contains about 3 g/l.

The ratio of chromic anhydride and sulfuric acid in a plating bath, for example, a Sargent bath, is usually chromic anhydride:sulfuric acid -10
0: about 0.8 to 1.5 (g/l). In order to improve corrosion resistance, the amount of sulfuric acid per 100 g/j of chromic acid anhydride is 1.0 to 1.5 g/j, preferably 1.
．． 02~1.3g/! .

More preferably, it is about 1.05 to 1.25 g/l. As the amount of sulfuric acid decreases, the covering power improves, but
Corrosion resistance tends to decrease, and as the amount of sulfuric acid increases, corrosion resistance improves, but adhesion and uniformity of the plating layer tend to decrease. The plating bath may be a high concentration bath, a standard bath, or a low concentration bath, and the chromic anhydride concentration is usually 100 to 400 g/l, preferably 150 to 350 g/l.
g/j.

More preferably, it is about 200 to 300 g/l.

In hard chrome plating, lead alloy, iron, or the like can be used as an anode, arranged as appropriate, and an auxiliary cathode, a shielding plate, etc. can be used to make the plating layer uniform.

Plating conditions can be selected depending on the bath composition, etc., and are usually
The plating temperature is about 20-70°C, preferably about 40-65°C, and the current density is about 10-100 A/d m', preferably about 30-60 A/d m'. Further, the plating time can be selected depending on the bath temperature, current efficiency, desired plating film thickness, etc.

The thickness of the hard chrome plating layer is 10 to 300 μm, preferably 30 to 250 μm, and more preferably 40 to 20 μm.
It is about 0 μm. Even with such a thin film thickness, corrosion resistance can be improved. Note that, according to microscopic observation, as described above, the hard chromium plating layer has many cracks, pinholes, etc. that cause corrosion.

Then, the plated object subjected to the hard chrome plating is subjected to a baking treatment. This baking treatment significantly improves corrosion resistance. Baking temperature is usually 100
The temperature is approximately 300°C to 300°C, preferably 150 to 250°C, more preferably 160 to 230°C. If the baking temperature is less than 100℃, it will take a long time to improve the corrosion resistance.
If it exceeds 300°C, the temperature becomes excessive and workability tends to decrease. The baking time can be selected, for example, from 30 minutes to 12 hours, preferably from 1 to 8 hours, depending on the baking temperature. Further, when the shaft is made of hardened steel, baking is preferably performed at a temperature that does not exceed the tempering temperature of the iron base material. After baking process,
Plating products are usually slowly cooled.

After the baking process, the plated product is subjected to a buffing process. Corrosion resistance can be improved by subjecting the plated product to a buffing process. This buff finish is
This can be performed in the same manner as the polishing step described above. A preferred method is to polish by applying a large polishing force, and then perform a fine buff finish in sequence. Especially #400-1000
After performing ring buffing of about 100 ml, it is preferable to perform cotton buffing or sisal buffing using an abrasive of about #240 to 600, followed by oven sisal buffing. When buffing is performed using this method, a large abrasive force is applied by the ring buff, and the protrusions of the plating layer are not only cut away by the cotton buff or sisal buff, but also plastically deformed and the plating layer is damaged. Corrosion resistance improves, probably because openings such as cracks are closed and smoothed.

The cylinder shaft obtained in this way can withstand harsh conditions even if there are cracks in the plating layer.
For example, it does not corrode even when subjected to a salt spray test. In addition, when evaluating corrosion resistance by an accelerated test, the plated product may be heated to about 400° C. and subjected to the above-mentioned salt spray test.

The present invention can be suitably applied to various cylinder shafts, for example, construction machine cylinder shafts, especially piston rods.

[Effects of the Invention] According to the manufacturing method of the present invention, a cylinder shaft having excellent corrosion resistance can be obtained despite being plated with hard chrome.

[Examples] The present invention will be described in more detail below based on Examples.

Example 1 Rod 4 made of low carbon steel (SC) with an outer diameter of 75nvnφ
．． 3. The rod was degreased, ring buffed with #320, ring buffed with #600, and ring buffed with #11000, and then etched in a plating bath with the following composition using the rod as an anode. The etching conditions were a current density of 35 A/d m' and a time of 4 minutes.

Plating bath composition Chromic anhydride: 224 g/l Sulfuric acid: 2.5 g/j Trivalent chromium: 1.5 g/j Hard chromium plating was then performed using the above plating bath under the following conditions.

Plating bath temperature = 50°C Current density: 35A/drn The obtained hard chrome plated product was baked at a temperature of 180°C for 5 hours,
After slow cooling, it was subjected to a finishing buffing process to produce a piston rod plated with hard chrome. The finishing buffing was carried out in the following order: ring buff No. 11000, cotton buff No. 1320, cotton buff No. 400, and open sisal buff.

Example 2 A piston rod was produced in the same manner as in Example 1 except that the baking temperature was 160°C.

Example 3 A piston rod was produced in the same manner as in Example 1 except that the baking temperature was 230°C.

Example 4 The composition of the plating bath was 224 g/l of chromic anhydride.

A piston rod was produced in the same manner as in Example 1, except that the amount of sulfuric acid was 2.3 g/l and the amount of trivalent chromium was 1.5 g/l.

Example 5 Example 1 except that ring buffing of No. 8600 was performed instead of ring buffing of No. 11000 in the finishing buffing process.
A piston rod was produced in the same manner.

Comparative Example 1 Same as Example 1 without baking treatment,
A piston rod was made.

Comparative Example 2 The composition of the plating bath was 224 g/l of chromic anhydride and 1 liter of sulfuric acid.
．． 9g/j and trivalent chromium 1. A piston rod was produced in the same manner as in Example 1, with a concentration of 5 g/l and without baking.

The corrosion resistance of the piston rods obtained in each Example and Comparative Example was evaluated by the following accelerated test method.

First, 48 hours after plating, the piston rod was
After heating to 0° C. and cooling, it was subjected to a salt spray test according to JIS Z2371, and the degree of corrosion after 8 hours was evaluated using the following criteria.

Excellent: No red rust Good = 5-10% red rust Acceptable: 10-20% red rust Impossible = 30% or more red rust The results are shown in the table.

From the table, the piston rods obtained in Examples 1 to 5 have significantly higher corrosion resistance than the piston rods obtained in Comparative Examples 1 and 2. In addition, the piston rods obtained in Examples 1 to 5 did not develop red rust even when subjected to a 100-hour salt water spray test.

Patent applicant: Kowa Industries Co., Ltd.

Claims (1)

[Claims] 1. A method for manufacturing a shaft for a cylinder, which comprises applying hard chrome plating to a shaft made of an iron-based material and then baking the shaft. 2. The amount of sulfuric acid is 1.0 per 100 g/l of chromic acid anhydride.
2. The method of manufacturing a cylinder shaft according to claim 1, wherein the hard chromium plating is carried out in a plating bath of ~1.5 g/l. 3. The method for manufacturing a cylinder shaft according to claim 1, wherein the baking is followed by buffing. 4. Claim 1, wherein the baking temperature is 100 to 300°C.
Method of manufacturing the cylinder shaft described.