JPH0610183A - Method for improving the corrosion resistance of piston rods - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the corrosion resistance of a hard chromium plated piston rod at low cost. [Structure] By buffing the surface of a piston rod plated with hard chrome, a plastic fluidized layer having a microcrack width of 0.2 μm or less opened on the surface is formed at a depth of 0.2 μm or more from the surface of the plated layer. This plastic fluidized layer prevents outside air and moisture from penetrating into the substrate due to defects such as microcracks and pinholes generated in the hard chrome plating layer, so that the substrate is prevented from rusting by the outside air and moisture. Therefore, the corrosion resistance of the piston rod can be improved at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the corrosion resistance of a piston rod used in a fluid pressure cylinder such as a hydraulic cylinder or a pneumatic cylinder, a hydraulic shock absorber or a gas spring.

[0002]

2. Description of the Related Art Conventionally, the surface of a piston rod used in this type of equipment is plated with hard chrome to improve wear resistance.

[0003]

However, the hard chrome plating film formed on the surface of the piston rod has defects such as microcracks and pinholes due to residual stress. The base material of the piston rod rusts due to the outside air and moisture,
There were problems such as reduced product value and oil leakage due to damage to the sealing surface due to rust when the piston rod slides. The present invention has been made to solve the above problems, and an object thereof is to provide a method for improving the corrosion resistance of a piston rod in which corrosion resistance is improved by preventing rusting of the base material.

[0004]

In order to achieve the above object, the present invention buffs the surface of a piston rod plated with hard chrome so that the surface of the plated layer has a depth of 0.2 μm or more. A plastic fluidized bed having an open microcrack width of 0.2 μm or less is formed.

[0005]

With the above structure, the plastic fluidized layer prevents the outside air and water from penetrating into the substrate due to defects such as microcracks and pinholes generated in the hard chrome plated layer.
It is possible to prevent the base body from rusting due to outside air or water, and it is possible to improve the corrosion resistance of the piston rod at low cost.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. After degreasing the piston rod made of chromium molybdenum steel (SCM435H), a base polishing step is performed as a pre-step. First, # 320 the surface of the piston rod.
Ring buff # 600 ring buff # 100
Polishing is performed using a No. 0 ring buff.

Next, in order to perform an etching treatment, the piston rod was immersed as an anode in a plating bath containing chromic anhydride: 224 g / l, sulfuric acid: 2.5 g / l, and trivalent chromium: 1.5 g / l. Etching is performed for 4 minutes at a current density of 35 A / dm ² . In order to perform hard chrome plating after the etching treatment, the piston rod is immersed in a plating bath containing the above-mentioned bath components as a cathode, and hard chrome plating is performed at a current density of 35 A / dm ² and a plating bath temperature of 50 ° C.

On the other hand, after the hard chrome plating is applied as described above, the piston rod is left to stand in the air heated to 180 ° C. for 5 hours to perform the baking treatment. The reason for performing the baking treatment is that the piston rod plated with hard chromium generates a large amount of hydrogen in the plating layer, and this hydrogen diffuses and penetrates into the crystal grain boundaries of the base material to cause brittle hardening of the base material. As a result, the base material may crack. Further, since the hydrogen storage amount reaches a peak when the plating film thickness is 10 μm or less, by heating the piston rod within a range not exceeding the tempering temperature of the base material and performing baking treatment,
The storage hydrogen is released from the plated layer.

When the baking process is completed as described above, a finishing process is performed to form a plastic fluidized layer on the plated surface. First, No. 600 emery (SiO ₂ adhered to paper), cloth buff with compressive chromium oxide (rough abrasive grain) abrasive cloth, cloth buff with compressive chromium oxide (medium abrasive grain) compressive cloth, buff with chromium oxide (fine abrasive grain) compressive cloth. , 5 kinds of buffs prepared by compressing chromium oxide (ultrafine abrasive grains) on the cloth buff, and performing the finishing process in 5 steps by using these buffs sequentially, the depth of the plating layer from 0 A plastic fluidized bed having a microcrack width of 0.2 μm or less, which was opened to the surface, was formed at a thickness of 0.2 μm or more.

For comparison, piston rods (those plated with hard chrome by the above method) which were not subjected to the finishing process were also manufactured, and the corrosion resistance of these piston rods was evaluated by the following accelerated test method. As a test method, in order to make the conventional salt spray test JIS Z2371 even more severe, the temperature was always 50 ° C., and the salt solution JIS K81
50 is a high temperature seawater spray test in which seawater JISK2510 is changed, and the results are shown in Table 1 below.

[0011]

[Table 1]

As is clear from Table 1, the piston rod not subjected to the finishing process has a latency No. R and N8 and rusting were remarkable, and after 96 hours, it was R and N3, whereas in the piston rod finished with this invention, R and N1 were still after 96 hours.
At 0, no rusting was observed and the effect could be confirmed.

[0013]

As described in detail above, according to the present invention, the surface of the piston rod plated with hard chrome is finished by buffing so that the depth from the surface is 0.2 μm.
m or more, the width of the microcracks opened on the surface is 0.2
A plastic fluidized layer having a thickness of μm or less is formed. This plastic fluidized layer prevents external air and moisture from penetrating to the substrate due to defects such as microcracks and pinholes generated in the hard chrome plating layer. It is possible to reliably prevent the base material from rusting due to outside air or moisture. As a result, it is possible to solve the problems that the product value of the piston rod is reduced due to rusting of the base material, and the seal surface is damaged due to rust when the piston rod slides, causing oil leakage. Further, since it is only necessary to buff the surface of the piston rod plated with hard chrome, the corrosion resistance of the piston rod can be improved at low cost.

Claims (1)

[Claims] 1. A plastic fluidized layer having a depth of 0.2 μm or more and a microcrack width of 0.2 μm or less opened on the surface of the plated layer by buffing the surface of a piston rod plated with hard chromium. A method for improving the corrosion resistance of a piston rod, characterized by being formed.