KR101981672B1 - Manufacturing method for corrosion-resistant hydraulic cylinder - Google Patents

Abstract

The present invention relates to a method for manufacturing a corrosion-proof hydraulic cylinder, minimizing generation of pores on a coating layer of a piston rod to enable the piston rod to be corrosion resistant to a working environment such as seawater. To this end, the hydraulic cylinder can be corrosion resistant by coating a surface of the piston rod with ceramic and then performing a sealing process to charge pores remaining on a coating surface.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a corrosion-resistant hydraulic cylinder,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hydraulic cylinder, and more particularly, to a method of manufacturing a corrosion-resistant hydraulic cylinder that minimizes pore generation in a piston rod coating layer so that the piston rod has corrosion resistance against working environments such as seawater. will be.

The hydraulic cylinder is a kind of important mechanical element that generates a mechanical reciprocating motion by reciprocating the piston rod from the cylinder tube using the hydraulic force generated from the hydraulic pump.

Among them, the piston rod is a member that reciprocates while maintaining airtightness along the passage provided in the rod cover of the cylinder. Therefore, the outer circumferential surface of the piston rod should not adhere to the surface of the piston rod or cause damage such as scratches, and the buffing polishing process is essentially performed.

In addition, when the outer circumferential surface of the piston rod is directly exposed to the environment such as seawater, there is a possibility that the corrosion resistance is reduced and the piston rod is easily damaged or damaged by vibration and impact.

In view of this, Japanese Patent Registration No. 10-0288499 proposes a manufacturing method of a hydraulic cylinder for seawater in which the outer periphery of the piston rod of the hydraulic cylinder is coated as a ceramic layer and a chrome layer so as to have corrosion resistance against working environment such as seawater have. However, there is a possibility that corrosion occurs due to direct contact of the seawater to the piston rod material through the pores of the ceramic and the chromium layer, and the coating of the ceramic and the chromium layer is peeled due to the growth of corrosion.

Published Patent No. 10-2006-0044092 Patent No. 10-0288499 Registration No. 10-1065059

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a corrosion-resistant hydraulic cylinder that minimizes pore generation in a piston rod coating layer so that the piston rod has corrosion resistance against a working environment such as seawater.

Other objects and advantages of the present invention will be described hereinafter and will be understood by the embodiments of the present invention. Further, objects and advantages of the present invention can be realized by the means and the combination shown in the claims.

According to an aspect of the present invention, there is provided a method of manufacturing a corrosion-

A mechanical polishing step of machining the surface of the piston rod using buffing polishing;

A ceramic coating step performed after the mechanical polishing step and performing a ceramic coating on a surface of the piston rod; And

And an electrolytic polishing step performed after the ceramic coating step and electrolytically polishing the ceramic coated surface of the piston rod,

Wherein the ceramic coating step comprises:

A bonding layer coating step of spraying a WC alloy powder in a gas phase on the surface of the piston rod to primarily coat the bonding layer,

And a ceramic layer coating step of coating the ceramic layer with the second layer by plasma spraying of zinc oxide, titanium oxide and titanium dioxide powder secondarily after coating the bonding layer.

In addition, the gas edible yarn is characterized in that it is carried out by any one of a flame spraying, an explosive spraying, and a super high-speed spraying.

Further, the gas-edible yarn is characterized in that it is carried out by ultra-high-speed spraying.

Further, the WC-based alloy powder is characterized by being one of WC-CrC-Ni, WC-Co-Cr and WC-Co.

In addition, the WC-based alloy powder has a particle size ranging from 15 to 45 mu m.

The method may further include a sealing treatment step of applying a sealing agent to the surface of the ceramic layer and performing a sealing treatment after the ceramic layer coating step.

The electrolytic polishing is performed for 1 to 9 minutes at an applied voltage between 30 and 60V.

According to the present invention, by minimizing pore generation in the piston rod coating layer, the piston rod can have corrosion resistance against the working environment such as seawater, and thus the life of the hydraulic cylinder, particularly, the piston rod can be significantly increased have.

FIG. 1 is a process diagram schematically showing a method of manufacturing a corrosion-resistant hydraulic cylinder according to the present invention,
2 is a view showing the pore ratio after the sealing treatment,
Figs. 3 and 4 are diagrams showing the ceramic coated surface of the piston rod after electrolytic polishing. Fig.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

Hereinafter, preferred embodiments of the present invention will be described in detail.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram schematically showing a manufacturing method of a corrosion-resistant hydraulic cylinder according to the present invention. FIG.

Referring to FIG. 1, a method of manufacturing a corrosion-resistant hydraulic cylinder according to the present invention comprises a mechanical polishing step S100, a ceramic coating step S200, and an electrolytic polishing step S300.

In the mechanical polishing step (S100), the surface of the piston rod is processed using buffing polishing. Specifically, buffing polishing can be performed with a buffing wheel that rotates the surface of the piston rod. For example, although not shown in the drawing, an abrasive layer is disposed on the outer circumferential surface of the buffing wheel, and the abrasive layer is formed of zinc oxide or other abrasive powder in powder form, nonwoven filaments in a powder state, The adhesive can be prepared in a mixture of 40%: 30%: 10%: 20% by volume.

The ceramic coating step (S200) is performed after the mechanical polishing step (S100), and ceramic coating is performed on the surface of the piston rod. The ceramic coating step (S200) is a main process that imparts the features of the present invention.

The ceramic coating step S200 is performed in three steps including a bonding layer coating step S210, a ceramic layer coating step S212, and a sealing processing step S214.

In the bonding layer coating step (S210), the bonding layer is primarily coated by gas-spraying the WC-based alloy powder on the surface of the piston rod.

The gas edible yarn can be carried out by any one of a flame spraying, an explosion spraying, and a super high-speed spraying. Preferably, the gas-edible yarn can be carried out with a super-high-speed spray.

The WC-based alloy powder may be any one of WC-CrC-Ni, WC-Co-Cr and WC-Co, and the WC-based alloy powder preferably has a particle size of 40 탆 or less.

In the step of coating the ceramic layer (S212), zinc oxide, titanium oxide and titanium dioxide powder are secondarily sprayed by plasma after the bonding layer coating, and then the ceramic layer is coated with the second layer.

The sealing treatment step S214 is performed after the ceramic layer coating step S212, and a sealing agent is applied to the surface of the ceramic layer to perform a sealing treatment.

The sealing treatment step (S214) is a process which is important for ensuring corrosion resistance as a process of filling the pores remaining on the coating surface after performing the ceramic coating on the surface of the piston rod.

In the electrolytic polishing step S300, the ceramic coating surface of the piston rod is electrolytically polished after the ceramic coating step S200. When the surface is subjected to electrolytic polishing, the effect of surface gloss can be provided by partially removing and flattening the strained layer formed on the surface.

Ceramic coating

The hydraulic cylinder consists of piston rod, piston, cylinder head, cylinder shell, and various parts. The cylinder operates by using hydraulic energy by connecting each part. In particular, surface damage to the piston rod causes corrosion of the material and damage to the seal, which can lead to a reduction in the hydraulic cylinder operating aging rate.

The fundamental cause of corrosion was corrosion of the seawater due to direct contact with the piston rod material through the pores of the piston rod ceramic coating, and the ceramic coating peeled due to corrosion growth.

To solve this problem, in the present invention, a ceramic coating is applied to the surface of the piston rod, and then a sealing treatment is further performed so as to fill the pores remaining on the coating surface, so that the hydraulic cylinder piston rod has corrosion resistance.

The ceramic coating consists of three layers: a bonding layer coating, a ceramic layer coating and a sealing treatment. Compared to chrome plating or nickel plating, the ceramic coating has excellent corrosion resistance, scratch resistance, abrasion resistance, impact resistance and durability.

The bonding layer coating is carried out by gas-phase spraying, preferably ultra-high-speed spraying, the WC-based alloy powder onto the surface of the piston rod. Here, the WC-based alloy powder may be any one of WC-CrC-Ni, WC-Co-Cr and WC-Co. The following Table 1 shows the chemical composition of the WC-based alloy powder.

[Table 1]

The warrior is divided into a gas-type spray gun and an electric spray gun depending on the purpose and characteristics of use. Gas type spray can be divided into flame spray, explosion spray, and high speed spray, and electric spray can be divided into arc spray, plasma spray, and line width spray laser spray.

In the bonding layer coating, in the present invention, high velocity oxygen fuel (HVOF) is applied in order to improve the bonding strength of the coating film. JP-5000 is a typical spraying method, and uses a hypersonic jet flow heating and acceleration energy from a rocket combustion chamber, which is discharged at a high pressure of 13 bar at a speed of 2100 m / s or higher. At this time, Thereby softening and accelerating the sprayed material to form an extremely dense high-density film. Therefore, when applied to a piston rod, it is possible to obtain a coating film having an excellent adhesive force while preventing oxidation of the piston rod base material. As described above, by applying the super fast spraying method to the coating of the bonding layer, the generation rate of pores can be significantly reduced.

Table 2 compares the characteristics of plasma spraying and super-high-speed spraying. In the case of plasma spraying, the pore rate is 1 to 3%, and in the case of super-high-speed spraying, have.

[Table 2]

In addition, conventionally, a ceramic ceramic material such as aluminum oxide and titanium oxide is coated as a ceramic coating material. Since the existing aluminum oxide-based coating material particles are thick, the deposition of the coating is well formed during plasma spraying, while the frequency of pores is relatively high and the pore size is relatively large.

In order to compensate for this, materials that are thin and have minimal pore generation were examined. The particle size of the powder used for plasma spraying is a very important factor in the spraying operation. For example, when the particle size is large, a large amount of melting heat energy is required, and the time required for the molten oil is required. Therefore, the intensity of the flame and the gas flow rate must be controlled according to the particle size.

In general, the powder used for thermal spraying should be selected so that the thermal stress caused by the thermal expansion difference between the base material and the sprayed layer is minimized because the thermal expansion coefficient and the thermal conductivity are similar to the base material used.

In the present invention, zinc oxide and titanium dioxide powder are used as a ceramic coating material.

Zinc oxide acts as a passive layer that blocks oxygen entering the metal, thereby preventing rusting.

Titanium dioxide is physically and chemically very stable and has high hiding power, so it is often used as a white pigment. And is also widely used for ceramics having high refractive index because of high refractive index. And has characteristics of photocatalytic property and superhydrophilic property. Titanium dioxide plays a role of air purification, antibacterial action, harmful substance decomposition, pollution prevention function, and discoloration prevention function. This titanium dioxide serves to ensure that the coating layer is surely covered around the piston rod.

Here, when zinc oxide and titanium dioxide are mixed and used, it is preferable that the mixing ratio thereof is such that 95 to 98% of zinc oxide and 2 to 5% of titanium dioxide are mixed.

When the mixing ratio of zinc oxide is less than 95 to 98%, the coating of zinc oxide often breaks down in an environment of high temperature and the like, so that the rust prevention effect of the piston rod may be deteriorated.

Plasma spraying is a coating method in which plasma is sprayed at high temperature and high speed to momentarily melt a coating material to closely contact a spraying material to form a coating. When the particle size is small, it has a merit that the pore ratio is lowered and the corrosion resistance is strengthened by spraying more finely than when the particle size is large. Therefore, the size of the powder was set to be 40 mu m or less, preferably 37.49 mu m on average.

Further, in the present invention, a ceramic coating is performed on the surface of the piston rod, and a sealing treatment is performed to fill the pores remaining on the coating surface.

The sealing agent used AP, EP-100, which is suitable for ceramic coating, and after the ceramic coating, the first sealing treatment was performed, and as the final standard of the product, the secondary sealing treatment was added after polishing and polishing, Respectively. The coating pore ratio before the sealing treatment was 2.88%, but it was confirmed to be 1.04% after the sealing treatment as shown in FIG.

Preferably, the application of the sealing agent can be carried out at 100 to 200 ° C.

Electrolytic polishing

Electrolytic polishing is performed by connecting a workpiece to the (+) electrode by the anodic dissolution process using an electrochemical reaction and connecting a tool to the (-) electrode and using the metal elution on the surface of the anode, Corrosion resistance and so on. Electrolytic polishing is known to exhibit excellent resistance to corrosion by removing impurities and deformation layers on the surface, that is, substances causing corrosion.

In the present invention, phosphoric acid or a phosphoric acid and a sulfuric acid electrolytic solution were used. When phosphoric acid electrolytes were used, surface changes were observed under the conditions of 60 ° C, 30V, 0.512A / cm 2 with time (3 min, 6 min, 9 min) with 172 ml of phosphoric acid + 28 ml of water. 152 ml + sulfuric acid (48 ml) was observed under the conditions of 60 ° C, 30 V, and 0.512 A / cm 2 over time (9 minutes, 18 minutes).

As a result, in FIG. 3, the surface gloss effect was confirmed with time in the phosphoric acid electrolyte. In the phosphoric acid + sulfuric acid electrolyte of FIG. 4, the surface improvement was not confirmed until 18 minutes, . It is considered that the selective effect of electrolytic polishing is more actively promoted in the same electrolytic solution as the voltage is increased, so that the polishing effect is exhibited.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

Claims (7)

A mechanical polishing step of machining the surface of the piston rod using buffing polishing;
A ceramic coating step performed after the mechanical polishing step and performing a ceramic coating on a surface of the piston rod; And
And an electrolytic polishing step performed after the ceramic coating step and electrolytically polishing the ceramic coated surface of the piston rod,
Wherein the ceramic coating step comprises:
A bonding layer coating step of spraying a WC alloy powder in a gas phase on the surface of the piston rod to primarily coat the bonding layer,
And a ceramic layer coating step of secondarily coating the ceramic layer by plasma spraying of zinc oxide, titanium oxide, and titanium dioxide powder in a second order after coating the bonding layer. The method according to claim 1,
Wherein the gas-edible yarn is carried out by any one of a flame spraying, an explosive spraying, and an ultrahigh-speed spraying. The method according to claim 1,
Wherein the gas-edible yarn is carried out by ultra-high-speed spraying. The method according to claim 1,
Wherein the WC-based alloy powder is one of WC-CrC-Ni, WC-Co-Cr, and WC-Co. 5. The method of claim 4,
Wherein the WC-based alloy powder has a particle size in the range of 15 to 45 mu m. The method according to claim 1,
Further comprising a sealing treatment step of applying a sealing agent to the surface of the ceramic layer and performing a sealing treatment after the ceramic layer coating step. The method according to claim 1,
Wherein the electrolytic polishing is performed for 1 to 9 minutes at an applied voltage between 30 and 60V.

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