Chemical nickel pretreatment method for shaft products

Abstract

The present invention provides a chemical nickel pretreatment method for shaft products, which relates to the field of electroplating processing technology. The chemical nickel pretreatment method for shaft products includes the following specific steps: chemical degreasing ‑‑ hot water washing ‑‑ water washing ‑‑ sulfuric acid + hydrofluoric acid washing ‑‑ water washing ‑‑ anodic electrolysis 1# ‑‑ water washing ‑‑ sulfuric acid + hydrofluoric acid washing ‑‑ water washing ‑‑ ultrasonic water washing ‑‑ anodic electrolysis 2# ‑‑ water washing ‑‑ activation ‑‑ water washing ‑‑ impact nickel ‑‑ water washing ‑‑ chemical nickel ‑‑ water washing ‑‑ drying ‑‑ heat treatment ‑‑ inspection and packaging; wherein the pickling adopts heated sulfuric acid. By adopting a sulfuric acid + hydrofluoric acid pickling formula, pickling twice, electrolysis twice, and combining the impact nickel process, it is ensured that the product has good bonding strength, so that the average point-like coating shedding defect is less than 0.5%, the process is stable and mature, and the reliability of the product quality is fully guaranteed. The product performance is significantly improved and the service life is greatly extended.

Description

Technical Field

[0001] The invention relates to the technical field of electroplating processing, in particular to a chemical nickel pretreatment method for shaft products. Background Art

[0002] The history of automobile development is long, and through the diligent research of countless researchers, the overall quality of automobiles has been continuously improved. As automobiles become more popular, people's requirements for automobile quality and service life are becoming higher and higher, and correspondingly, the requirements for the quality and service life of components are becoming more and more stringent and demanding.

[0003] Shaft products are the most common type of automotive parts. As the quality requirements for automotive shaft parts become higher and higher, many shaft parts have begun to be made of alloy steel, that is, C, Si, Mn, S, P, Cr, Ni, Mo, Cu and other components are added to the iron material to make alloy steel. Since alloy steel contains many of the above-mentioned metal and non-metal elements, these substances are easily oxidized in the air, forming a dense and invisible passivation layer. If the passivation layer cannot be cleaned and electroplating is performed, the subsequent electroplating layer and the alloy steel substrate will not be able to guarantee the bonding strength. The plating will bubble and fall off. Therefore, to ensure the bonding strength of the plating, the workpiece must undergo special pickling, electroplating impact nickel, and then chemical nickel tank. However, this electroplating technology is still in a blank stage in domestic mass production. Developing a stable and innovative process concept is of great significance to improving the technical level of the electroplating industry.

[0004] To this end, we have developed a new chemical nickel pre-treatment method for shaft products. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In view of the shortcomings of the existing technology, the present invention provides a chemical nickel pretreatment method for shaft products, which solves the problems of the inability to ensure the bonding strength between the electroplating layer and the alloy steel substrate, and the bubbling and shedding of the plating layer.

[0007] (2) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for chemical nickel pretreatment of shaft products, characterized in that it includes the following specific steps:

[0009] Chemical degreasing--hot water washing--water washing--sulfuric acid + hydrofluoric acid washing--water washing--anodic electrolysis 1#--water washing--sulfuric acid + hydrofluoric acid washing--water washing--ultrasonic water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging;

[0010] The pickling process uses heated sulfuric acid, and the specific configuration ratio and pickling time are as follows:

[0011]

[0012] The process components and specific processing parameters of the impact nickel process are:

[0013]

[0014] Preferably, the pickling process is divided into two times, each time lasting 1.5 minutes, and a trace amount of black ash is generated after both pickling processes.

[0015] Preferably, the trace black ash is removed by two anodic electrolysis steps.

[0016] Preferably, the concentration of the sulfuric acid is 98%.

[0017] Preferably, the concentration of the hydrofluoric acid is 40%.

[0018] Preferably, the ultrasonic washing time is 60s.

[0019] Preferably, the concentration of hydrochloric acid in the nickel impact process is 37%.

[0020] Preferably, the actual processing time of the nickel impact process is controlled within 2 minutes.

[0021] (3) Beneficial effects

[0022] The present invention provides a method for chemical nickel pretreatment of shaft products. It has the following beneficial effects:

[0023] 1. The chemical nickel pretreatment method for this shaft product adopts a sulfuric acid + hydrofluoric acid pickling formula, pickling twice, electrolysis twice, and combined with an impact nickel process to ensure that the product has good bonding strength. After repeated production practice, the average point-like plating defect is less than 0.5%. The process is completely stable and mature, fully ensuring the reliability of product quality, significantly improving product performance, and greatly extending product service life.

[0024] 2. The chemical nickel pretreatment method for shaft products, by adopting a brand-new production process, fills the gap in the domestic mass production of this electroplating technology, while also improving the stability of the production process, ensuring the high performance and high quality of automotive parts; it promotes the steady development of high quality in the automotive industry and is of great significance to the improvement of the technical level of the electroplating industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Example 1:

[0028] This embodiment provides a method for chemical nickel pretreatment of shaft products, and the specific process flow is as follows:

[0029] Chemical degreasing--hot water washing--water washing--anodic electrolysis 1#--water washing--hydrochloric acid washing (3min)--water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging;

[0030] Conventional hydrochloric acid is used for pickling, and the specific configuration ratio and pickling time are as follows:

[0031] Hydrochloric acid (37%) 400-600 mL / L;

[0032] Temperature: normal temperature;

[0033] Time 2-4 minutes (3 minutes during production);

[0034] The process components and specific processing parameters of the impact nickel process are:

[0035]

[0036] According to the above process flow, the processed products are tested and 10-30% of the finished products have point-like coating shedding. The point-like coating shedding mainly exists at the top, where there is no coating. It is rarely found after plating. After heat treatment and full inspection, a large proportion of such defects are found, indicating that after heat treatment, the coating is not firmly bonded and falls off. After more than ten batches of tests, one batch that has not been impacted with nickel has a defect rate of more than 80%; the batch that has been impacted with nickel has a defect rate of between 15-30%. After analysis, due to this defect Basically near the hanging hole (teeth), the preliminary analysis showed that the hanging teeth "grabbed" the current, and the impact nickel was not plated there; after the test was hung and the impact nickel came out, after careful inspection, it was found that the impact nickel layer was not plated. 5 products were taken from the middle (the lowest current point) and 4 corners, and the thickness of the impact nickel film at the places prone to falling off near the hanging hole was measured. The result was between 0.5-1um, indicating that it was not that the impact nickel was not plated, but that the bonding between the impact nickel layer and the substrate was not strong, causing the subsequent chemical nickel layer to fall off. The temperature was raised to 50℃, and other factors remained unchanged. The test was carried out, but there was no obvious improvement.

[0037] Example 2:

[0038] This embodiment provides a method for chemical nickel pretreatment of shaft products. Based on the first embodiment, the pickling formula is changed and nickel impact is used for priming. Since the corrosion ability of heated sulfuric acid aqueous solution to metal substrates is greater than that of hydrochloric acid (or heated hydrochloric acid) aqueous solution (hydrochloric acid aqueous solution has a greater ability to remove rust and oxide layers than sulfuric acid aqueous solution), sulfuric acid is used for pickling in the experiment. The specific process flow is as follows:

[0039] Chemical degreasing--hot water washing--water washing--anodic electrolysis 1#--water washing--sulphuric acid washing (3 min)--water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging;

[0040] The pickling process uses heated sulfuric acid, and the specific configuration ratio and pickling time are as follows:

[0041] Sulfuric acid (98%) 13% (volume ratio V / V);

[0042] Temperature 45-55℃;

[0043] Time 2-4 minutes (3 minutes during production);

[0044] The process components and specific processing parameters of the impact nickel process are:

[0045]

[0046] According to the above process flow, after many tests, it was found that 5-10% of the finished product would have a point-like coating peeling phenomenon. Obviously, there has been a great improvement, but the proportion is still high during normal mass production, and the process still needs to be optimized. After comparison, it was found that sulfuric acid washing is significantly better than hydrochloric acid washing.

[0047] Example 3:

[0048] This embodiment provides a method for chemical nickel pretreatment of shaft products. Based on the second embodiment, the pickling formula is changed and nickel impact primer is used.

[0049] In Example 2, due to the strong corrosion of sulfuric acid on the substrate, it was found during production that after pickling, there was a thin layer of black ash on the surface of the product that could be removed with a single wipe of the finger. However, even after the subsequent anodic electrolysis 2# (the main function of which is to remove ash), the black ash could not be completely removed, which would also affect the bonding strength. A pickling time of 3 minutes is effective because the main components of black ash are non-metallic elements, which are mainly carbon, silicon, sulfur, and phosphorus. The sulfur and phosphorus contents are very low and have little impact, while the carbon and silicon contents are relatively high. The silicon content is even slightly higher than the carbon content. Therefore, the silicon content in black ash is theoretically higher than the carbon content. Carbon only reacts with concentrated sulfuric acid and concentrated nitric acid. It is obviously impossible to use concentrated sulfuric acid and concentrated nitric acid. Carbon ash can only be removed by anodic electrolysis; while silicon can react with hydrofluoric acid and be volatilized and removed:

[0050] Si+2HF=SiF2↑+H2↑

[0051] The effect of silicon on the bonding strength is eliminated. Hydrofluoric acid is a weak acid and has a low dissolution rate for metals. Therefore, a small amount of hydrofluoric acid (3% (V / V)) is added to the sulfuric acid solution for testing. The specific process flow is as follows:

[0052] Chemical degreasing--hot water washing--water washing--anodic electrolysis 1#--water washing--sulphuric acid + hydrofluoric acid washing (3min)--water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging;

[0053] The pickling process uses heated sulfuric acid, and the specific configuration ratio and pickling time are as follows:

[0054]

[0055] The process components and specific processing parameters of the impact nickel process are:

[0056]

[0057]

[0058] According to the above process flow, after many tests, it was found that 2-5% of the finished products would have point-like coating peeling phenomenon, which was fundamentally improved. Through summary, it was found that after the pickling was changed to heated sulfuric acid solution and a small amount of hydrofluoric acid was added, the problem was effectively solved, but there is still room for improvement.

[0059] Example 4:

[0060] This embodiment provides a method for chemical nickel pretreatment of shaft products. Based on the third embodiment, the process flow is changed to use impact nickel primer. The 3-minute pickling is divided into two times. The trace black ash generated in the two times is electrolytically removed in two times. To ensure thorough cleaning, an ultrasonic water washing is added before the anodic electrolysis 2# to remove most of the black ash. The remaining trace amount is electrolytically removed by the anodic electrolysis 2#.

[0061] The specific process is as follows:

[0062] Chemical degreasing--hot water washing--water washing--sulfuric acid + hydrofluoric acid washing (1.5 min)--water washing--anodic electrolysis 1#--water washing--sulfuric acid + hydrofluoric acid washing (1.5 min)--water washing--ultrasonic water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging;

[0063] The pickling process uses heated sulfuric acid, and the specific configuration ratio and pickling time are as follows:

[0064]

[0065] The process components and specific processing parameters of the impact nickel process are:

[0066]

[0067]

[0068] According to the above process flow, sulfuric acid washing is carried out twice, each time in the same tank, each time for 1.5 minutes, and the total time is 3 minutes. After the first 1.5-minute acid washing, the ash is basically removed by electrolysis in the anode electrolysis 1#, and then it enters the sulfuric acid washing for 1.5 minutes, and then enters the ultrasonic water washing for 60 seconds to remove most of the black ash. The remaining trace black ash is thoroughly removed by electrolysis in the anode electrolysis 2#, and then flows backward according to the process flow;

[0069] According to the above process flow, after many tests, it was found that only less than 1% of the finished product had point-like coating shedding phenomenon, and the process was finalized and applied to normal production.

[0070] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Chemical nickel pretreatment method for shaft products, characterized in that: The specific steps include: Chemical degreasing--hot water washing--water washing--sulfuric acid + hydrofluoric acid washing--water washing--anodic electrolysis 1#--water washing--sulfuric acid + hydrofluoric acid washing--water washing--ultrasonic water washing--anodic electrolysis 2#--water washing--activation--water washing--impact nickel--water washing--chemical nickel--water washing--drying--heat treatment--inspection and packaging; The pickling process uses heated sulfuric acid, and the specific configuration ratio and pickling time are as follows: The process components and specific processing parameters of the impact nickel process are:

2. The chemical nickel pretreatment method for shaft products according to claim 1, characterized in that: The pickling process is divided into two times, each time for 1.5 minutes, and a trace amount of black ash is generated after both pickling processes.

3. The chemical nickel pretreatment method for shaft products according to claim 2, characterized in that: The trace black ash is removed by two anodic electrolysis steps.

4. The chemical nickel pretreatment method for shaft products according to claim 1, characterized in that: The concentration of the sulfuric acid is 98%.

5. The chemical nickel pretreatment method for shaft products according to claim 1, characterized in that: The concentration of the hydrofluoric acid is 40%.

6. The chemical nickel pretreatment method for shaft products according to claim 1, characterized in that: The ultrasonic washing time is 60s.

7. The chemical nickel pretreatment method for shaft products according to claim 1, characterized in that: The concentration of hydrochloric acid in the nickel impact process is 37%.

8. The chemical nickel pretreatment method for shaft products according to claim 7, characterized in that: The actual processing time of the nickel impact process is controlled within 2 minutes.

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