Electroplating process for hydraulic support oil cylinder

Abstract

The invention discloses a hydraulic support oil cylinder electroplating process, and relates to the technical field of electroplating, a hydraulic support oil cylinder workpiece is subjected to first-layer electroplating, a layer of low-tin copper alloy with the Sn content of 8-15% is electroplated on the surface of the outer circle of the workpiece, and the workpiece is polished until the outer circle Ra is smaller than 0.2, so that a low-tin copper alloy coating is obtained; second-layer electroplating is conducted on the workpiece, a layer of milky white chromium is electroplated on the surface of the low-tin copper alloy plating layer, polishing is conducted till the outer circle Ra is smaller than 0.2, and a milky white chromium plating layer is obtained; and third-layer electroplating is conducted on the workpiece, a layer of hard chromium is electroplated on the surface of the milky white chromium plating layer, polishing is conducted till the outer circle Ra is smaller than 0.2, and a hard chromium layer is obtained. The corrosion resistance and the wear resistance of the plating layer are improved, and the problem that the plating layer is easy to fall off due to overlarge hardness change between layers is also avoided.

Description

Technical Field

[0001] The invention relates to the technical field of electroplating, and in particular to an electroplating process for a hydraulic support cylinder. Background Art

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

[0003] For these two types of coatings, the base layer of milky white chromium and low-tin copper alloy has less porosity and lower hardness, and mainly plays an anti-corrosion role; the surface hard chromium layer has more porosity and higher hardness, and mainly plays a wear-resistant role.

[0004] In my country's coal mine hydraulic support industry, due to the presence of a large number of chloride ions, sulfate ions, etc. in the underground environment of coal mines, the corrosive ions enter the internal corrosive matrix through the tiny pores on the surface of the coating, so there are many problems in the actual application process:

[0005] 1. Because hard chrome is not resistant to Cl - Corrosion, blistering often occurs on the electroplating layer;

[0006] 2. Electroplating low-tin copper alloy and hard chromium on the outer circle of the workpiece to form a "hard-soft-hard" coating. The hardness of the iron matrix is ​​240-280HV, the hardness of the low-tin copper alloy is 300-400HV, and the hardness of the hard chromium is ≥800HV. The hardness difference between the electroplating layers is large, and there is internal stress, which is easy to cause the coating to fall off, affecting the normal coal mining work of the coal enterprise;

[0007] 3. The surface porosity of the workpiece coating is high and it is easily corroded.

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

[0009] The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, a hydraulic support cylinder electroplating process is provided, in which the coating not only has good properties of acid and alkali corrosion resistance and wear resistance, but also has good bonding strength between the coatings and is not easy to fall off.

[0010] In order to solve the above technical problems, the technical solution of the present invention is:

[0011] A hydraulic support cylinder electroplating process comprises the following steps:

[0012] A: The hydraulic support cylinder workpiece is electroplated for the first layer, and 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 to the outer circle Ra <0.2 to obtain a low-tin copper alloy coating;

[0013] B: Perform the second electroplating on the workpiece, electroplate a layer of milky white chromium on the surface of the low-tin copper alloy coating, and polish it to an outer circle Ra < 0.2 to obtain a milky white chromium coating;

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

[0015] Preferably, the hydraulic support cylinder workpiece is subjected to surface pretreatment before the first layer of electroplating, and the surface pretreatment includes degreasing, water washing, acid washing, water washing and activation.

[0016] Preferably, the activation solution used in the activation is formulated as follows: sodium cyanide 15-20 g / L, current density 1-2 A / dm 2 , the temperature is room temperature

[0017] Preferably, the low-tin copper alloy plating layer has a thickness of 0.030-0.040 mm and a hardness of 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 hard chrome layer has a thickness of 0.040-0.050 mm and a hardness of 800-1000 HV.

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

[0021] Preferably, the formula of the milky chromium plating solution in step B is: chromic acid 250-280g / L, sulfuric acid 2.5-3.0g / L, trivalent chromium 2-5g / L, temperature 70-72°C, current density 24-28A / dm 2 .

[0022] Preferably, the formula of the hard chrome plating solution in step C is: chromic acid 200-220g / L, sulfuric acid 2.2-3.5g / L, trivalent chromium 2-5g / L, temperature 55-58°C, current density 45-50A / dm 2 .

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

[0024] 1. The present invention gives full play to the advantages of Cu acid resistance and Cr wear resistance, and uses the combination of three electroplating layers to reduce the porosity of the electroplating layer to 0-2 / dm 2 , improve the corrosion resistance of the coating.

[0025] 2. The present invention adopts a surface treatment process of electroplating copper-tin alloy + milky white chromium + hard chromium composite plating to control the Sn content, increase the surface hardness layer by layer, and ultimately effectively improve the wear resistance of the surface.

[0026] 3. As the hardness increases layer by layer, the hardness change curve slows down, especially the hardness difference between the inner low-tin copper alloy coating and the iron substrate is smaller, which avoids the problem of poor bonding between the two and easy falling off, and also avoids the problem of easy falling off due to excessive hardness changes between layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a diagram of the coating structure of the workpiece after electroplating in Example 1 of the present invention;

[0028] Among them, 1. Hydraulic support cylinder workpiece; 2. Low-tin copper alloy plating; 3. Milky white chrome plating; 4. Hard chrome plating. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the embodiments.

[0030] Example 1

[0031] A hydraulic support cylinder electroplating process comprises the following steps:

[0032] Step 1) Pre-treat the surface of the medium carbon alloy workpiece to be electroplated: degreasing, water washing, pickling, water washing, activation, wherein the activation solution formula is sodium cyanide 15-20g / L, time 1-2min, current density 1-2A / dm 2 , the temperature is room temperature.

[0033] Step 2), the workpiece treated in step 1) is subjected to a 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 to an outer circle Ra <0.2; wherein the thickness of the low-tin copper alloy coating is 0.030-0.040mm, the hardness is 300-400HV, the formula of the low-tin bronze electroplating solution is: 30-50g / L of cuprous cyanide, 40-60g / L of sodium cyanide, 10-20g / L of sodium hydroxide, 20-30g / L of sodium carbonate, 20-25g / L of sodium stannate, the electroplating temperature is 50-60°C, the current density is 1-3A / dm 2 .

[0034] Step 3), the workpiece treated in step 2) is subjected to a second layer of electroplating, a layer of opalescent chromium is electroplated on the surface of the low-tin copper alloy coating, and polished to an outer diameter Ra < 0.2; the thickness of the opalescent chromium coating is 0.020-0.030mm, and the hardness is 450-550HV. The formula of the opalescent chromium plating solution 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 / dm 2 .

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

[0036] Comparative Example 1

[0037] Step 2) is removed, and the remaining parameters are exactly the same as those in Example 1.

[0038] Comparative Example 2

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

[0040] The salt spray resistance test was carried out on the electroplated workpieces in Example 1 and Comparative Examples 1-2, and the results are shown in Table 1 below:

[0041] Table 1

[0042]

[0043] The workpieces in the above acetate spray test were observed every 24 hours. The workpiece in Example 1 was well coated until 668 hours, and a rust spot appeared on the side of the coating at 692 hours; the workpiece in Comparative Example 1 was well coated until 216 hours, no rust on the front at 240 hours, 2 slight rust spots appeared on the back, no obvious rust on the front after 264 hours, and multiple rust spots appeared on the back; the workpiece in Comparative Example 2 was well coated after 208 hours, a large amount of blue-black chromium layer corrosion products appeared after 233 hours, no red rust was seen, a large amount of blue-black chromium layer corrosion products appeared after 256 hours, no red rust was seen, and red rust appeared locally after 301 hours. The three-layer coating structure of low-tin copper alloy + milky white chromium + hard chromium can withstand AASS (acetate spray test) for 668 hours, and the ten-level coating will not rust.

[0044] The bonding strength between the coating and the substrate was tested by electroplating the workpieces 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 the hydraulic support cylinder electroplating copper-tin alloy + milky white chromium + hard chromium composite plating provided in this embodiment gives full play to the advantages of Cu acid resistance and Cr wear resistance, and uses the combination of three electroplating layers to reduce the porosity of the electroplating layer to 0-2 pcs / dm 2 , improve the corrosion resistance of the coating; in addition, the electroplating copper-tin alloy + milky white chromium + hard chromium composite plating surface treatment process is adopted to increase the Sn content, increase the surface hardness layer by layer, and finally effectively improve the wear resistance of the surface; finally, due to the gradual increase of hardness layer by layer, the hardness change curve slows down, especially the hardness difference between the inner layer low-tin copper alloy coating and the iron matrix is ​​smaller, and the composite coating with similar chemical properties is physically combined through the electroplating process, and the hardness is reasonably distributed, which ensures the bonding strength between the electroplated layers, avoids the problem of poor bonding strength and easy falling off between the two, and also avoids the problem of easy falling off due to excessive hardness changes between layers.

[0048] It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

Claims

1. A hydraulic support cylinder electroplating process, characterized in that: The following steps are involved: A: The first layer of electroplating is performed on the hydraulic support cylinder workpiece. 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 to an outer circle Ra < 0.2 to obtain a low-tin copper alloy coating; B: Perform the second electroplating on the workpiece, electroplate a layer of milky white chromium on the surface of the low-tin copper alloy coating, and polish it to an outer circle Ra < 0.2 to obtain a milky white chromium coating; C: Perform the third electroplating on the workpiece, electroplate a layer of hard chrome on the surface of the milky white chrome plating layer, and polish it to the outer circle Ra<0.2 to obtain a hard chrome layer.

2. The electroplating process for the hydraulic support cylinder according to claim 1, characterized in that: Before the first layer of electroplating, the hydraulic support cylinder workpiece is subjected to surface pretreatment, wherein the surface pretreatment includes degreasing, water washing, pickling, water washing and activation.

3. A hydraulic support cylinder electroplating process as claimed in claim 2, characterized in that: The activation solution used in the activation process is formulated as follows: sodium cyanide 15-20 g / L, current density 1-2 A / dm 2 , the temperature is room temperature.

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

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

6. The electroplating process for the hydraulic support cylinder according to claim 1, characterized in that: The hard chromium layer has a thickness of 0.040-0.050 mm and a hardness of 800-1000 HV.

7. The electroplating process for the hydraulic support cylinder according to claim 1, characterized in that: The formula of the low-tin bronze electroplating solution in step A is: 30-50g / L cuprous cyanide, 40-60g / L sodium cyanide, 10-20g / L sodium hydroxide, 20-30g / L sodium carbonate, 20-25g / L sodium stannate, the electroplating temperature is 50-60°C, the current density is 1-3A / dm 2 .

8. The electroplating process for the hydraulic support cylinder according to claim 1, characterized in that: The formula of the milky chromium plating solution in step B is: chromic acid 250-280g / L, sulfuric acid 2.5-3.0g / L, trivalent chromium 2-5g / L, temperature 70-72°C, current density 24-28A / dm 2 .

9. The electroplating process for the hydraulic support cylinder according to claim 1, characterized in that: The formula of hard chrome plating solution in step C is: chromic acid 200-220g / L, sulfuric acid 2.2-3.5g / L, trivalent chromium 2-5g / L, temperature 55-58℃, current density 45-50A / dm 2 .

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