A method for high-precision plating of cadmium layer with high aspect ratio deep hole structure

Abstract

The present invention belongs to the field of surface treatment and discloses a method for high-precision plating of a cadmium layer with a deep hole structure having a high aspect ratio, comprising the following steps: cleaning excess material from the surface of a product; electrochemically degreasing the product; weakly corroding the electrochemically degreased product; neutralizing the weakly corroded product; plating cadmium on the neutralized product; performing dimensional inspection on a position where the product requires dimensional inspection; photochemically treating the product after measurement; and passivating the photochemically treated product; wherein during the cadmium plating, the temperature of the cadmium plating solution is 15°C to 40°C. The solution composition is 140g / L~180g / L sodium cyanide, 30g / L~50g / L cadmium oxide, 15g / L~25g / L sodium hydroxide, 30g / L~50g / L ammonium sulfate, and 0.5g / L~1.5g / L nickel sulfate; the electroplating method adopts repeated alternation of impact current / normal current; the cadmium layer obtained by this method has uniform thickness, and any plane is tested multiple times using three coordinates. The measured values are all within the tolerance range of 0.003mm, and the coating adhesion and appearance meet the use requirements.

Description

Technical Field

[0001] The invention relates to the field of surface treatment, and in particular to a method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure. Background Art

[0002] Due to the slow flow of solution within deep-hole structures, the coating thickness increases in a stepped pattern, decreasing toward the center of the hole, sometimes even without a film. According to navigation standard HB5036, which states: "There are no requirements for the cadmium coating where the hole depth is greater than one hole diameter, and no requirements for the cadmium coating where the hole depth is less than one hole diameter," there are no requirements for the cadmium coating thickness within the holes of deep-hole structures. In recent years, aircraft flight safety requirements have tightened controls on the cadmium coating thickness of faulty gear parts. These products involve aspect ratios as high as 8:1, requiring uniform thickness for both inner and outer diameters and inner and outer splines. This requires seven measurements of the same plane using three-dimensional coordinates with a tolerance of 0.003mm, a significant challenge that has prevented the production of qualified products and delayed their delivery. Finding a high-precision cadmium coating method for deep-hole structures with high aspect ratios is an urgent and imperative task. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for high-precision plating of a cadmium layer in a deep hole structure with a high aspect ratio, so as to meet the current processing requirements of products with deep hole structures.

[0004] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0005] A method for high-precision plating of a cadmium layer in a deep hole structure with a high aspect ratio comprises the following steps:

[0006] Step 1: Clean the excess material on the surface of the product;

[0007] Step 2, electrochemically degreasing the product;

[0008] Step 3, subjecting the electrochemically degreased product to weak corrosion;

[0009] Step 4, neutralizing the weakly corroded product;

[0010] Step 5, plating cadmium on the neutralized product;

[0011] Step 6: Perform dimensional inspection on the product at the required dimensional inspection position;

[0012] Step 7, photochemically treating the measured product;

[0013] Step 8: passivate the photochemical product.

[0014] Furthermore, during the electrochemical degreasing in step 2, the solution composition is: sodium hydroxide 20g / L~40g / L, sodium carbonate 20g / L~40g / L, trisodium phosphate 20g / L~50g / L, sodium silicate 2g / L~5g / L, temperature: 60℃~95℃, current density: 5A / dm 2 ~10A / dm 2 , time: cathode 2min ~ 3min, anode 3min ~ 5min, after electrochemical degreasing, the water film continuity check is 30s without rupture and the degreasing is qualified, otherwise, degreasing shall be repeated.

[0015] Furthermore, during the weak corrosion in step 3, the solution composition is: hydrochloric acid 100g / L to 150g / L, temperature: room temperature, time: 0.5min to 1min.

[0016] Furthermore, during the neutralization treatment in step 4, the solution composition is: 30g / L to 60g / L of sodium carbonate, the temperature is room temperature, and the time is within 1 minute.

[0017] Furthermore, during the cadmium plating in step 5, the solution temperature is 15°C to 40°C, the solution composition is 140g / L to 180g / L sodium cyanide, 30g / L to 50g / L cadmium oxide, 15g / L to 25g / L sodium hydroxide, 30g / L to 50g / L ammonium sulfate, 0.5g / L to 1.5g / L nickel sulfate, and the impact current density is 14A / dm 2 ~20A / dm 2 , the normal current density is 8A / dm 2 ~11A / dm 2 , apply impulse current for 20s, take out the product and brush it, check the bonding strength of the coating, then continue to apply impulse current for 20s, and then apply normal current electroplating for 20s. This 40s is a cycle, and multiple cycles are performed in total.

[0018] Furthermore, during the dimensional inspection in step 6, the inner and outer surfaces of the product are measured more than 7 times using three-coordinate measurement, and the measurement value tolerance is less than 0.003mm.

[0019] Furthermore, during the photochemical treatment in step 7, the solution composition is 150 g / L to 260 g / L of chromic anhydride and 5 g / L to 10 g / L of sulfuric acid, the temperature is room temperature, and the time is 3 s to 5 s.

[0020] Furthermore, during the passivation in step 8, the solution composition is 150 g / L to 250 g / L of sodium dichromate and 8 g / L to 16 g / L of sulfuric acid, the temperature is room temperature, and the time is 5 s to 15 s.

[0021] Compared with the prior art, the present invention has the following technical features:

[0022] This method uses a repeated alternating electroplating method of impulse current / normal current to achieve high-precision plating of the cadmium layer in a deep hole structure with a high aspect ratio. After plating using this method, the inner and outer surfaces of the product are measured more than 7 times using three-coordinate measurement. The measured values meet the requirements of 0.008mm to 0.012mm, and the tolerance is less than 0.003mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the product to be processed in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a method for high-precision plating of a cadmium layer on a deep hole structure with a high aspect ratio, thereby achieving uniform plating of the cadmium layer on products with a high aspect ratio deep hole structure (for example, an aspect ratio of not less than 8:1); and enabling any plane after plating to be repeatedly inspected using three coordinates, with the measurement values all being within a tolerance range of 0.003 mm.

[0025] A method for high-precision plating of a cadmium layer in a deep hole structure with a high aspect ratio comprises the following steps:

[0026] Step 1: Clean excess material from the product surface.

[0027] Step 2: Electrochemically degrease the product.

[0028] When performing electrochemical degreasing, the solution composition is: sodium hydroxide 20g / L~40g / L, sodium carbonate 20g / L~40g / L, trisodium phosphate 20g / L~50g / L, sodium silicate 2g / L~5g / L, temperature: 60℃~95℃, current density: 5A / dm 2 ~10A / dm 2 Time: 2min~3min for cathode, 3min~5min for anode. After electrochemical degreasing, if the water film continuity check is not broken for 30s, the degreasing is qualified. Otherwise, degreasing should be repeated. This step can effectively remove oil and other substances generated during the product processing.

[0029] Step 3: subject the electrochemically degreased product to weak corrosion.

[0030] During the weak corrosion treatment, the solution composition is: hydrochloric acid 100g / L to 150g / L, the temperature is room temperature, such as 25 degrees Celsius, and the time is 0.5 minutes to 1 minute. This step activates the product surface with hydrochloric acid, making the cadmium layer on the product surface more bonded.

[0031] Step 4: neutralize the weakly corroded product.

[0032] During the neutralization treatment, the solution composition is: 30g / L to 60g / L sodium carbonate, the temperature is: room temperature, and the time is: within 1 minute. This step uses sodium carbonate to neutralize the hydrochloric acid remaining on the surface of the product to prevent the hydrochloric acid from causing rust on the product surface.

[0033] Step 5: cadmium plating is performed on the neutralized product.

[0034] During cadmium plating, the solution temperature is 15°C to 40°C, the solution composition is 140g / L to 180g / L sodium cyanide, 30g / L to 50g / L cadmium oxide, 15g / L to 25g / L sodium hydroxide, 30g / L to 50g / L ammonium sulfate, 0.5g / L to 1.5g / L nickel sulfate, and the impact current density is 14A / dm 2 ~20A / dm 2 , the normal current density is 8A / dm 2 ~11A / dm 2 After applying the impulse current for 20 seconds, the product is removed and brushed to check the coating adhesion. If the adhesion meets the preset requirements, the product is placed in the solution and the impulse current is continued for 20 seconds, followed by the normal current electroplating for 20 seconds. This 40-second cycle is repeated multiple times. This step uses the impulse current repeated alternating electroplating method to achieve high-precision plating of the cadmium layer with a high aspect ratio and deep hole structure. Using this method of cadmium plating, the thickness of the cadmium layer is highly uniform.

[0035] Step 6: Perform dimensional inspection on the product at the required dimensional inspection location.

[0036] Use three coordinates to measure the inner and outer surfaces of the product more than 7 times respectively. When the measured values meet the range of 0.008mm to 0.012mm and the tolerance is less than 0.003mm, proceed to the next step.

[0037] Step 7: photochemically test the measured product.

[0038] During photochemical treatment, the solution composition is 150g / L to 260g / L of chromic anhydride and 5g / L to 10g / L of sulfuric acid. The temperature is room temperature and the treatment time is 3s to 5s. This step can improve the corrosion resistance of the cadmium layer.

[0039] Step 8: passivate the photochemical product.

[0040] During passivation, the solution composition is 150g / L to 250g / L sodium dichromate and 8g / L to 16g / L sulfuric acid, the temperature is room temperature, and the time is 5s to 15s. This step can further improve the corrosion resistance of the cadmium layer.

[0041] The present invention will be further described below in conjunction with the embodiments:

[0042] Example 1:

[0043] For gear fault parts with a length-to-diameter ratio of 8:1, cadmium plating is required. The thickness of the cadmium layer on the inner and outer diameters and inner and outer splines is required to reach 0.008mm to 0.012mm, and the same plane needs to be measured 7 times using three-coordinate measurement with a tolerance of 0.003mm.

[0044] Step 1, Cleaning: Clean the excess material on the surface of the faulty gear.

[0045] Dimension measurement before plating: The inner diameter and inner and outer splines are measured before plating. The actual measured values and required values are shown in Table 1 below.

[0046] Table 1 Pre-plating measured values and pre-plating required values

[0047]

[0048]

[0049] Step 2, electrochemical degreasing: Place the gear parts that meet the pre-plating size requirements in an electrochemical degreasing solution of 30g / L sodium hydroxide, 35g / L sodium carbonate, 45g / L trisodium phosphate, and 3g / L sodium silicate, at a temperature of 65°C and a part area of 5dm 2 , current: 40A, time: cathode 2min, anodic 3min. After electrochemical degreasing, check the water film continuity for 30s without rupture.

[0050] Step 3, weak corrosion: immerse the faulty gear part in a weak corrosion solution of 120g / L hydrochloric acid, temperature: room temperature, time: 1 minute.

[0051] Step 4, neutralization treatment: immerse the faulty gear part in 45g / L sodium carbonate, temperature: room temperature, time: 45s.

[0052] Step 5, cadmium plating: Place the gear faulty part in 160g / L sodium cyanide, 45g / L cadmium oxide, 20g / L sodium hydroxide, 45g / L ammonium sulfate, 1g / L nickel sulfate solution at 30°C and impulse current 19A / dm 2 , electroplating time: 20s, take out the parts, brush and check the bonding strength; impulse current 20A / dm 2 , electroplating time: 20s, normal current 11A / dm 2 , plating time: 20s; impulse current 17A / dm 2 , electroplating time: 20s, normal current 9.5A / dm 2 , plating time: 20s; impulse current 14A / dm 2 , electroplating time: 20s, normal current 8A / dm 2 , plating time: 20s; impulse current 13A / dm 2, electroplating time: 20s, normal current 9.5A / dm 2 , electroplating time: 20s; during this period, there is no need to take it out for brushing and bonding inspection, turn off the power, and take out the gear fault part.

[0053] Step 6, dimensional inspection after plating: First, use the inside diameter micrometer, outside diameter micrometer, sample ring φ50.5, roller φ3.0, internal spline M size measuring tool, and internal spline M size to conduct a basic inspection of the gear fault parts. After the measurement is qualified, use the three coordinates to conduct 7 inspections on the inner diameter position required by the design drawing. All measured values meet the post-plating dimensional requirements. The actual measured values and required values are shown in the following table.

[0054] Table 2 Post-plating measured values and post-plating required values

[0055]

[0056]

[0057] Step 7, photochemical treatment: Place the faulty gear part in a photochemical solution of 200g / L chromic anhydride and 6g / L sulfuric acid at room temperature for 4s.

[0058] Step 8, passivation: Place the faulty gear part in a passivation solution of 200g / L sodium dichromate and 10g / L sulfuric acid, temperature: room temperature, time: 10s.

[0059] Inspection: Visual inspection shows that the faulty gear part is golden yellow with rainbow color, and the plating is uniform, fine and firmly bonded.

[0060] Example 2:

[0061] The steps of this embodiment are basically the same as those of embodiment 1, except that:

[0062] In this embodiment, the electrochemical degreasing in step 2 is performed with the following parameters: sodium hydroxide 20 g / L, sodium carbonate 20 g / L, trisodium phosphate 20 g / L, sodium silicate 2 g / L, temperature 60°C, current density 5 A / dm 2 , time: cathode 2min, anode 3min;

[0063] When performing weak corrosion in step 3, the parameters selected are: hydrochloric acid 100g / L, temperature: 25°C; time: 0.5min;

[0064] During the neutralization treatment in step 4, the selected parameters are: sodium carbonate 30 g / L, temperature: 25°C, time: 1 min;

[0065] When cadmium plating is performed in step 5, the selected parameters are: solution temperature is 15°C, solution composition is 140g / L, 30g / L, 15g / L sodium hydroxide, 30g / L ammonium sulfate, 0.5g / L nickel sulfate, and the impact current density is 14A / dm 2 ~20A / dm 2 , the normal current density is 8A / dm 2 ~11A / dm 2 ; A total of 5 cycles were performed;

[0066] During step 7, the parameters selected are: chromic anhydride 150 g / L, sulfuric acid 5 g / L, temperature: 25°C, time: 3 s;

[0067] When passivation is performed in step 8, the parameters selected are: solution composition: sodium dichromate 150g / L, sulfuric acid 8g / L, time: 5s.

[0068] Example 3:

[0069] The steps of this embodiment are basically the same as those of embodiment 1, except that:

[0070] In this embodiment, the electrochemical degreasing in step 2 is performed with the following parameters: sodium hydroxide 40 g / L, sodium carbonate 40 g / L, trisodium phosphate 50 g / L, sodium silicate 5 g / L, temperature 95°C, current density 10 A / dm 2 , time: cathode 3min, anode 5min;

[0071] When performing weak corrosion in step 3, the selected parameters are: hydrochloric acid 150g / L, temperature: 25°C; time: 1min;

[0072] During the neutralization treatment in step 4, the selected parameters are: sodium carbonate 60g / L, temperature: 25°C, time: 1min;

[0073] In step 5, when cadmium plating is performed, the selected parameters are: solution temperature is 40°C, solution composition is 180g / L sodium cyanide, 50g / L cadmium oxide, 25g / L sodium hydroxide, 50g / L ammonium sulfate, 1.5g / L nickel sulfate, and impulse current density is 14A / dm 2 ~20A / dm 2 , the normal current density is 8A / dm 2 ~11A / dm 2 , a total of 6 cycles;

[0074] During the chemical reaction in step 7, the selected parameters are: chromic anhydride 260 g / L, sulfuric acid 10 g / L, temperature: 25°C, time: 5 s;

[0075] When passivation is performed in step 8, the parameters selected are: solution composition: sodium dichromate 250g / L, sulfuric acid 16g / L, time: 15s.

[0076] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for high-precision plating of a cadmium layer in a deep hole structure with a high aspect ratio, characterized in that: The following steps are included: Step 1: Clean the excess material on the surface of the product; Step 2, electrochemically degreasing the product; Step 3, subjecting the electrochemically degreased product to weak corrosion; Step 4, neutralizing the weakly corroded product; Step 5, plating cadmium on the neutralized product; Step 6: Perform dimensional inspection on the product at the required dimensional inspection position; Step 7, photochemically treating the measured product; Step 8, passivating the photochemical product; During the cadmium plating in step 5, the solution temperature is 15°C to 40°C, the solution composition is 140g / L to 180g / L sodium cyanide, 30g / L to 50g / L cadmium oxide, 15g / L to 25g / L sodium hydroxide, 30g / L to 50g / L ammonium sulfate, 0.5g / L to 1.5g / L nickel sulfate, and the impact current density is 14 A / dm 2 ~20A / dm 2 , the normal current density is 8A / dm 2 ~11A / dm 2 , apply impulse current for 20s, take out the product and brush it, check the bonding strength of the coating, then continue to apply impulse current for 20s, and then apply normal current electroplating for 20s. This 40s is a cycle, and multiple cycles are performed in total.

2. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During electrochemical degreasing in step 2, the solution composition is: sodium hydroxide 20g / L~40g / L, sodium carbonate 20g / L~40g / L, trisodium phosphate 20g / L~50g / L, sodium silicate 2g / L~5g / L, temperature: 60℃~95℃, current density: 5A / dm 2 ~10A / dm 2 Time: cathode 2min~3min, anode 3min~5min. After electrochemical degreasing, if the water film continuity check is not broken for 30s, the degreasing is qualified, otherwise, degreasing should be repeated.

3. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During the weak corrosion in step 3, the solution composition is: hydrochloric acid 100g / L~150g / L, temperature: room temperature, time: 0.5min~1min.

4. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During the neutralization treatment in step 4, the solution composition is: 30g / L to 60g / L of sodium carbonate, the temperature is room temperature, and the time is within 1 minute.

5. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During the dimensional inspection in step 6, the three-coordinate system is used to measure the inner and outer surfaces of the product more than 7 times, and the measurement value tolerance is less than 0.003mm.

6. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During the photochemical treatment in step 7, the solution composition is 150 g / L to 260 g / L of chromic anhydride and 5 g / L to 10 g / L of sulfuric acid, the temperature is room temperature, and the time is 3 s to 5 s.

7. The method for high-precision plating of a cadmium layer with a high aspect ratio deep hole structure according to claim 1, characterized in that: During the passivation in step 8, the solution composition is 150g / L to 250g / L of sodium dichromate and 8g / L to 16g / L of sulfuric acid, the temperature is room temperature, and the time is 5s to 15s.

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