A hydraulic support cylinder electroplating process

Abstract

This invention discloses an electroplating process for hydraulic support cylinders, relating to the field of electroplating technology. The hydraulic support cylinder workpiece undergoes a first electroplating layer, where a low-tin copper alloy with a Sn content of 8-15% is electroplated onto the outer surface of the workpiece, and polished until the outer diameter Ra < 0.2, resulting in a low-tin copper alloy plating layer. A second electroplating layer is then applied to the workpiece, where a milky white chromium plating layer is electroplated onto the low-tin copper alloy plating layer, and polished until the outer diameter Ra < 0.2, resulting in a milky white chromium plating layer. A third electroplating layer is then applied to the workpiece, where a hard chromium plating layer is electroplated onto the milky white chromium plating layer, and polished until the outer diameter Ra < 0.2, resulting in a hard chromium layer. This process improves the corrosion resistance and wear resistance of the plating layer and avoids the problem of easy peeling due to excessive hardness variations between layers.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more specifically to an electroplating process for a hydraulic support cylinder. Background Technology

[0002] There are two main electroplating processes commonly used for hydraulic support cylinders in coal mines: the first is double chromium plating (milky white chromium + hard chromium); the second is low-tin copper alloy plating + hard chromium plating.

[0003] For these two types of plating, the underlayer milky white chromium and low-tin copper alloy layer has low porosity and low hardness, and mainly serves as an anti-corrosion layer; the surface hard chromium layer has high porosity and high hardness, and mainly serves as an wear-resistant layer.

[0004] In my country's coal mine hydraulic support industry, due to the presence of large amounts of chloride and sulfate ions in the underground coal mine environment, these corrosive ions can penetrate the internal substrate through the tiny pores on the coating surface, causing numerous problems in practical applications.

[0005] 1. Because hard chrome is not resistant to Cl... - Corrosion often causes blistering in the electroplated layer;

[0006] 2. Low-tin copper alloy and hard chrome are electroplated on the outer circle of the workpiece to form a "hard-soft-hard" coating. The hardness of the iron substrate is 240-280HV, the hardness of the low-tin copper alloy is 300-400HV, and the hardness of the hard chrome is ≥800HV. The large difference in hardness between the electroplated layers creates internal stress, which can easily cause the coating to peel off and affect the normal coal mining operations of coal enterprises.

[0007] 3. The workpiece coating has high porosity and is easily corroded.

[0008] In summary, it is particularly important to find an electroplating coating suitable for the complex coal mine environment. The coating should not only have good resistance to acid and alkali corrosion and wear, but also have good adhesion between coating layers and be not easy to fall off. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a process for electroplating hydraulic support cylinders to address the shortcomings of the existing technology. The coating not only has good resistance to acid and alkali corrosion and wear, but also has good adhesion between coatings and is not easy to fall off.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0011] A process for electroplating hydraulic support cylinders includes the following steps:

[0012] A: The hydraulic support cylinder workpiece undergoes the first layer of electroplating. A layer of low-tin copper alloy with a Sn content of 8-15% is electroplated on the outer surface of the workpiece, and polished until the outer circle Ra < 0.2 to obtain the low-tin copper alloy plating layer.

[0013] B: Perform a second electroplating on the workpiece, electroplating a layer of milky white chromium on the surface of the low tin copper alloy plating, and polishing until the outer circle Ra < 0.2 to obtain the milky white chromium plating.

[0014] C: Perform a third electroplating on the workpiece, electroplating a layer of hard chromium on the surface of the milky white chromium plating, and polishing until the outer circle Ra < 0.2 to obtain the hard chromium layer.

[0015] Preferably, the hydraulic support cylinder workpiece undergoes surface pretreatment before the first layer of electroplating. The surface pretreatment includes degreasing, water washing, pickling, water washing, and activation.

[0016] Preferably, the activation solution used in the activation process has the following formulation: sodium cyanide 15-20 g / L, current density 1-2 A / dm³. 2 The temperature is room temperature.

[0017] Preferably, the thickness of the low-tin copper alloy plating is 0.030-0.040 mm, and the hardness is 300-400 HV.

[0018] Preferably, the thickness of the milky white chromium plating layer is 0.020-0.030 mm, and the hardness is 450-550 HV.

[0019] Preferably, the thickness of the hard chrome layer is 0.040-0.050 mm, and the hardness is 800-1000 HV.

[0020] Preferably, the formulation of the low-tin bronze electroplating solution in step A is: 30-50 g / L cuprous cyanide, 40-60 g / L sodium cyanide, 10-20 g / L sodium hydroxide, 20-30 g / L sodium carbonate, and 20-25 g / L sodium stannate; the electroplating temperature is 50-60℃, and the current density is 1-3 A / dm³. 2 .

[0021] Preferably, the formula for the milky white chromium electroplating solution in step B is: 250-280 g / L chromic acid, 2.5-3.0 g / L sulfuric acid, 2-5 g / L trivalent chromium, temperature 70-72℃, and current density 24-28 A / dm³. 2 .

[0022] Preferably, the hard chromium plating solution formulation in step C is as follows: 200-220 g / L chromic acid, 2.2-3.5 g / L sulfuric acid, 2-5 g / L trivalent chromium, temperature 55-58℃, and current density 45-50 A / dm³. 2 .

[0023] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. This invention fully utilizes the advantages of Cu (acid resistance and corrosion resistance) and Cr (wear resistance), and employs a combination of three electroplating layers to reduce the porosity of the electroplating layer to 0-2 cells / dm². 2 This improves the corrosion resistance of the coating.

[0025] 2. This invention employs a composite plating process of electroplated copper-tin alloy + milky white chromium + hard chromium to control the Sn content, gradually increase the surface hardness, and ultimately effectively improve the wear resistance of the surface.

[0026] 3. As the hardness increases layer by layer, the hardness change curve becomes gentler. In particular, the hardness difference between the inner low-tin copper alloy plating layer and the iron substrate is smaller, which avoids the problems of poor adhesion and easy peeling, as well as the problem of easy peeling caused by excessive hardness changes between layers. Attached Figure Description

[0027] Figure 1 This is a diagram of the plating structure of the workpiece after electroplating in Embodiment 1 of the present invention;

[0028] Among them, 1. hydraulic support cylinder workpiece; 2. low tin copper alloy plating; 3. milky white chromium plating; 4. hard chromium plating. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the embodiments.

[0030] Example 1

[0031] A process for electroplating hydraulic support cylinders includes the following steps:

[0032] Step 1) Perform surface pretreatment on the medium carbon alloy workpiece to be electroplated: degreasing, water washing, pickling, water washing, and activation. The activation solution formula is sodium cyanide 15-20g / L, time 1-2min, current density 1-2A / dm³. 2 The temperature is room temperature.

[0033] Step 2) Perform the first electroplating on the workpiece treated in Step 1). Electroplat a layer of low-tin copper alloy with a Sn content of 8-15% on the outer surface of the workpiece and polish it until the Ra of the outer circle is less than 0.2. The thickness of the low-tin copper alloy plating layer is 0.030-0.040 mm, and the hardness is 300-400 HV. The formula of the low-tin bronze electroplating solution is: cuprous cyanide 30-50 g / L, sodium cyanide 40-60 g / L, sodium hydroxide 10-20 g / L, sodium carbonate 20-30 g / L, sodium stannate 20-25 g / L. The electroplating temperature is 50-60℃, and the current density is 1-3 A / dm³. 2 .

[0034] Step 3) Perform a second electroplating on the workpiece treated in Step 2), electroplating a layer of milky white chromium onto the surface of the low-tin copper alloy plating, and polishing until the outer diameter Ra < 0.2; the thickness of the milky white chromium plating layer is 0.020-0.030mm, and the hardness is 450-550HV. The milky white chromium electroplating solution formula is: chromic acid 250-280g / L, sulfuric acid 2.5-3.0g / L, trivalent chromium 2-5g / L, temperature 70-72℃, current density 24-28A / dm³. 2 .

[0035] Step 4) Perform a third electroplating on the workpiece treated in Step 3), electroplating a layer of hard chromium onto the surface of the milky white chromium plating, and polishing until the outer diameter Ra < 0.2; the hard chromium thickness is 0.040-0.050 mm, and the hardness is 800-1000 HV. Chromic acid 200-220 g / L, sulfuric acid 2.2-3.5 g / L, trivalent chromium 2-5 g / L, temperature 55-58℃, current density 45-50 A / dm³. 2 The final product hierarchy structure is as follows: Figure 1 As shown.

[0036] Comparative Example 1

[0037] Remove step 2), and the remaining parameters are exactly the same as in Example 1.

[0038] Comparative Example 2

[0039] Step 3 is removed, and the remaining parameters are exactly the same as in Example 1.

[0040] Salt spray resistance tests were conducted on the electroplated workpieces from Example 1 and Comparative Examples 1-2. The results are shown in Table 1 below.

[0041] Table 1

[0042]

[0043] The workpieces in the above acetic acid spray test were observed every 24 hours. In Example 1, the coating remained intact until 668 hours, but a rust spot appeared on the side of the coating at 692 hours. In Comparative Example 1, the coating remained intact until 216 hours, with no rust on the front at 240 hours, but two minor rust spots appeared on the back. After 264 hours, there was no obvious rust on the front, but multiple rust spots appeared on the back. In Comparative Example 2, the coating remained intact after 208 hours, but a large amount of bluish-black chromium corrosion products appeared after 233 hours, with no red rust observed. After 256 hours, a large amount of bluish-black chromium corrosion products appeared, with no red rust observed. After 301 hours, localized red rust appeared. The three-layer coating structure of low-tin copper alloy + milky white chromium + hard chromium can withstand 668 hours of AASS (acetic acid spray test), and the level 10 coating does not rust.

[0044] The adhesion between the plating layer and the substrate was tested on the workpieces after electroplating in Example 1 and Comparative Examples 1-2. The results are shown in Table 2 below:

[0045] Table 2

[0046]

[0047] The surface treatment method for electroplating copper-tin alloy + milky white chromium + hard chromium composite plating of hydraulic support cylinders provided in this embodiment fully utilizes the advantages of Cu's acid resistance, corrosion resistance, and Cr's wear resistance. By using the combination of three electroplating layers, the porosity of the electroplating layer is reduced to 0-2 porosities / dm². 2 This process improves the corrosion resistance of the coating. Furthermore, the use of a composite plating process of electroplated copper-tin alloy + milky white chromium + hard chromium increases the Sn content, gradually increasing surface hardness layer by layer, ultimately effectively improving the surface's wear resistance. Finally, due to the gradual increase in hardness layer by layer, the hardness change curve becomes gentler, especially with a smaller hardness difference between the inner low-tin copper alloy plating layer and the iron substrate. The electroplating process physically bonds the chemically similar composite plating layers, resulting in a reasonable hardness distribution. This ensures the bonding strength between the electroplated layers, avoiding problems such as poor bonding and easy detachment, as well as excessive hardness variations between layers that could lead to easy detachment.

[0048] It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A process for electroplating hydraulic support cylinders, characterized in that, Includes the following steps: A: The hydraulic support cylinder workpiece undergoes the first layer of electroplating. A layer of low-tin copper alloy with a Sn content of 8-15% is electroplated on the outer surface of the workpiece, and polished until the outer circle Ra < 0.2 to obtain the low-tin copper alloy plating layer. B: Perform a second electroplating on the workpiece, electroplating a layer of milky white chromium on the surface of the low tin copper alloy plating, and polishing until the outer circle Ra < 0.2 to obtain the milky white chromium plating. C: Perform a third electroplating on the workpiece, electroplating a layer of hard chromium on the surface of the milky white chromium plating, and polishing until the outer circle Ra < 0.2 to obtain the hard chromium layer; The formula for the low-tin bronze electroplating solution is as follows: cuprous cyanide 30-50 g / L, sodium cyanide 40-60 g / L, sodium hydroxide 10-20 g / L, sodium carbonate 20-30 g / L, sodium stannate 20-25 g / L. The electroplating temperature is 50-60℃, and the current density is 1-3 A / dm³. 2 ; The formula for the milky white chromium electroplating solution is as follows: chromic acid 250-280 g / L, sulfuric acid 2.5-3.0 g / L, trivalent chromium 2-5 g / L, temperature 70-72℃, and current density 24-28 A / dm³. 2 ; The hard chrome plating solution formula is as follows: chromic acid 200-220 g / L, sulfuric acid 2.2-3.5 g / L, trivalent chromium 2-5 g / L, temperature 55-58℃, and current density 45-50 A / dm³. 2 .

2. The electroplating process for a hydraulic support cylinder as described in claim 1, characterized in that: Before the first layer of electroplating, the hydraulic support cylinder workpiece undergoes surface pretreatment, which includes degreasing, water washing, pickling, water washing, and activation.

3. The electroplating process for a hydraulic support cylinder as described in claim 2, characterized in that, The activation solution used in the activation process has the following formula: sodium cyanide 15-20 g / L, current density 1-2 A / dm³. 2 The temperature is room temperature.

4. The electroplating process for a hydraulic support cylinder as described in claim 1, characterized in that: The thickness of the low-tin copper alloy plating is 0.030-0.040 mm, and the hardness is 300-400 HV.

5. The electroplating process for a hydraulic support cylinder as described in claim 1, characterized in that: The thickness of the milky white chromium plating is 0.020-0.030 mm, and the hardness is 450-550 HV.

6. The electroplating process for a hydraulic support cylinder as described in claim 1, characterized in that: The thickness of the hard chrome layer is 0.040-0.050 mm, and the hardness is 800-1000 HV.

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