A method for trivalent chromium plating decorative chromium

Abstract

The present invention belongs to the technical field of metal electroplating, and specifically relates to a method for trivalent chromium decorative chromium plating. The trivalent chromium decorative chromium plating method of the present invention comprises the following steps: forming a nickel-plated workpiece after preparing a bright nickel plating layer on the workpiece; performing a first chromium plating on the nickel-plated workpiece in a first chromium plating tank to form a bottom chromium plating layer on the surface of the nickel-plated workpiece; performing a second chromium plating on the nickel-plated workpiece in a second chromium plating tank to form a surface chromium plating layer on the bottom chromium plating layer, and preparing a rare earth protective film on the surface chromium plating layer. A chromium plating solution electrolytic tank is arranged between the first chromium plating tank and the second chromium plating tank, wherein the electrolytic tank contains the same trivalent chromium plating solution as that in the chromium plating tank, and the trivalent chromium plating solution is continuously electrolyzed in the chromium plating solution electrolytic tank to reduce the concentration of nickel impurities, and the nickel-plated workpiece is immersed in the chromium plating solution electrolytic tank for cleaning after exiting the first chromium plating tank, and then chromium is plated in the second chromium plating tank. Performing trivalent chromium plating in this way can effectively avoid the contamination of the second chromium plating tank by nickel impurities, thereby forming a surface chromium plating layer of good quality.

Description

Technical Field

[0001] The invention belongs to the technical field of metal electroplating, and in particular relates to a method for plating decorative chromium with trivalent chromium. Background Art

[0002] Entering the 21st century, the application of trivalent chromium electroplating has accelerated, mainly used in decorative chromium plating. Trivalent chromium plating includes two systems: sulfate trivalent chromium plating and chloride trivalent chromium plating. The prepared coatings include trivalent chromium white chromium plating and trivalent chromium black chromium plating. The sulfate trivalent chromium plating has good performance and elegant appearance, and has been widely used in hardware, electronics and other industries. The chloride trivalent chromium white chromium plating is close to the color of stainless steel, and has low corrosion resistance, and its application is on a downward trend. The trivalent chromium black chromium plating solution is generally prepared by adding blackening agents and other ingredients to the trivalent chromium white chromium plating solution. The formula is complex, and the electroplating processes and blackening agents used by various suppliers are different. The ingredients such as additives and blackening agents have always been kept confidential, which brings a lot of difficulties to the maintenance of the plating solution. When the plating tank fails, the front-line technicians often do not know the cause and cannot eliminate it in time.

[0003] Before trivalent chromium plating, bright nickel is usually plated in a nickel plating tank. It is inevitable that nickel impurities will be brought into the trivalent chromium plating tank to contaminate the plating solution, which is also the most common problem in the maintenance of trivalent chromium plating tanks. When the nickel impurities in the trivalent chromium plating tank exceed 30 mg / L, the color of the trivalent chromium white chrome plating will be yellowish, losing the elegant appearance of the trivalent chromium white chrome plating; the brightness of the trivalent chromium black chrome plating decreases, and the plating changes from black to yellowish black after being placed for a period of time.

[0004] At present, electrolysis is usually used to reduce the content of nickel impurities in the trivalent chromium plating tank. Electroplating during the day and electrolysis at night can generally maintain the normal production of trivalent chromium plating. However, for workpieces with large water storage and large production batches, the plated parts will bring more nickel impurities into the chromium plating tank. After half a day of production, the nickel impurity content in the trivalent chromium plating tank will exceed 30 mg / L, and the quality of the coating will begin to decline. Reducing the content of nickel impurities by electrolysis will affect the production progress, and continuing production will result in more defective products. Production practice shows that the method of strengthening water washing after nickel plating still cannot effectively eliminate the pollution of nickel impurities, which has caused great trouble to the chromium plating production of electroplating manufacturers. The sodium diethyldithiocarbamate chelating precipitation method to remove nickel impurities requires a long filtration time and cannot guarantee the normal operation of production. Summary of the invention

[0005] Based on this, the present invention proposes a method for trivalent chromium decorative chromium plating, which can effectively solve the problems of yellowing and easy discoloration of the plating layer caused by the pollution of nickel impurities to the trivalent chromium decorative chromium plating tank.

[0006] The method for trivalent chromium plating decorative chromium proposed by the present invention comprises the following steps:

[0007] (1) preparing a bright nickel-plated layer on a plated workpiece to form a nickel-plated workpiece;

[0008] (2) performing a first chrome plating on the nickel-plated workpiece in a first chrome plating tank to form a bottom chrome plating layer on the surface of the nickel-plated workpiece;

[0009] (3) After the first chrome plating, the nickel-plated workpiece is directly immersed in the chrome plating solution electrolytic tank for cleaning. The cleaning time is 3 to 10 seconds to prevent the nickel-plated workpiece from bringing nickel impurities into the second chrome plating tank;

[0010] (4) After the nickel-plated workpiece is cleaned in the chrome plating solution electrolytic tank, it is directly subjected to a second chrome plating tank to form a surface chrome plating layer on the surface of the bottom chrome plating layer;

[0011] (5) using a rare earth cathode electrolysis process to electrolytically protect the trivalent chromium plating layer, thereby forming a rare earth protective film on the trivalent chromium plating layer;

[0012] The chromium plating solution electrolytic tank is arranged between the first chromium plating tank and the second chromium plating tank, the chromium plating solution electrolytic tank contains the same trivalent chromium plating solution as that in the chromium plating tank, and electrolysis is continuously performed in the chromium plating solution electrolytic tank to reduce the content of nickel impurities in the plating solution;

[0013] The rare earth cathode electrolysis process is as follows: 1-10 g / L of lanthanum acetate or praseodymium acetate, 5-50 g / L of HEDP complexing agent, 80-150 g / L of anhydrous sodium carbonate, pH of 11.5-12.5, cathode current density of 0.5-1.5 A / dm 2 , operate at room temperature, use the chrome-plated workpiece as the cathode and the stainless steel plate as the anode, and electrolyze for 10 to 30 seconds.

[0014] In some embodiments, the thickness of the bottom chromium plating layer is 0.03-0.12 μm.

[0015] In some of the embodiments, the thickness ratio of the surface chromium plating layer to the bottom chromium plating layer is 1:(0.5-1.2).

[0016] In some embodiments, the content of nickel impurities in the second chromium plating tank is less than 20 mg / L.

[0017] In some of the embodiments, the chrome-plated layer is prepared by using the current trivalent chromium white chrome plating process, or by using the current trivalent chromium black chrome plating process.

[0018] In some embodiments, the trivalent chromium white chromium plating process is a Trich-9551 sulfate trivalent chromium white chromium plating process: Trich-9551 M cylinder opener 8-12 mL / L, Trich-9551 B supplement 260-300 mL / L, Trich-9551 CS conductive salt 280-320 g / L, Trich-9551 WA wetting agent 0.5-2.0 mL / L, pH range 3.4-3.8, operating temperature 50-55 ° C, cathode current density 8-15 A / dm 2 , cathode movement or slight air stirring.

[0019] In some embodiments, the trivalent chromium white chromium plating process is a Trich-6561 chloride trivalent chromium white chromium plating process: Trich-6561 aeration salt 400-450 g / L, Trich-6563 complexing agent 60-85 mL / L, Trich-6564 stabilizer 1-2 mL / L, Trich-6565 wetting agent 1-3 mL / L, pH range 2.5-3.0, operating temperature 25-36 ° C, cathode current density 8-16 A / dm 2 , medium air agitation.

[0020] In some embodiments, the trivalent chromium black chromium plating process is a Trich-7677 sulfate trivalent chromium black chromium plating process: Trich-7677 S initiator 8-12 mL / L, Trich-7677 M cylinder opener 260-300 mL / L, Trich-7677CS conductive salt 280-320 g / L, Trich-7677 C stabilizer 3.0-4.0 mL / L, Trich-7677 D toner 3.0-8.0 mL / L, Trich-7677 WA wetting agent 0.5-2.0 mL / L, pH range 3.3-3.7, operating temperature 25-40 ° C, cathode current density 8-14 A / dm 2 , cathode movement or slight air stirring.

[0021] In some of the embodiments, the chrome plating solution electrolytic cell uses a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on a side of the chrome plating solution electrolytic cell close to the exhaust port, and the cathode is arranged on a side of the chrome plating solution electrolytic cell close to the operator; the width of the cathode plate is 70% to 90% of the width of the chrome plating solution electrolytic cell, and the height of the cathode plate is 60% to 80% of the height of the chrome plating solution electrolytic cell; the cathode current density is 0.2 to 1.2 A / dm 2 , medium air agitation.

[0022] In some of the embodiments, two partitions are added in the middle of the trivalent chromium plating tank to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is the width of one hanging position parallel to the chromium plating line.

[0023] In some embodiments, when the plated workpiece is a steel workpiece, a Watt nickel pre-plated nickel layer and an acid copper plating layer are sequentially included between the steel substrate and the bright nickel plating layer from the inside to the outside. When the plated workpiece is a zinc alloy die-casting, a citrate pre-plated nickel layer, a pyrophosphate copper plating layer, and an acid copper plating layer are sequentially included between the zinc alloy substrate and the bright nickel plating layer from the inside to the outside. When the plated workpiece is an aluminum alloy part, a chemical zinc deposition layer, a citrate pre-plated nickel layer, a pyrophosphate copper plating layer, and an acid copper plating layer are sequentially included between the aluminum alloy substrate and the bright nickel plating layer from the inside to the outside.

[0024] After nickel plating and water washing, the nickel-plated workpiece enters the first cadmium plating tank. During the first chromium plating process, nickel impurities co-deposit with trivalent chromium to form a bottom chromium plating layer, which consumes most of the nickel impurities brought into the plating tank. When the nickel impurity content reaches a certain level, the amount of nickel impurities brought into the first chromium plating tank will reach a balance with the amount of nickel impurities deposited on the chromium plating layer and taken out of the plating tank. Therefore, the amount of nickel impurities brought into the chromium plating solution electrolytic tank by the nickel-plated workpiece is much less than the amount of nickel impurities brought into the first chromium plating tank. The electrode potential of nickel ions is always greater than the electrode potential of trivalent chromium ions. During electrolysis in the chromium plating solution electrolytic tank, nickel impurities are preferentially deposited on the cathode surface, and the content of nickel impurities in the chromium plating solution electrolytic tank will drop to a very low level. After being washed in the electrolysis, the nickel-plated workpiece directly enters the second chromium plating tank, and only a trace amount of nickel impurities are brought into the second chromium plating tank. The chrome plating liquid electrolytic cell cleans the plated parts during the continuous electrolysis process, and the plated parts will produce a double electrode phenomenon. However, since the current required for electrolysis is very small and the cleaning time is short, it will not have an adverse effect on the quality of the underlying chrome plating layer.

[0025] The method for trivalent chromium decorative chromium plating proposed by the present invention has at least the following beneficial effects:

[0026] 1. The method for decorative chromium plating with trivalent chromium of the present invention changes the prior art's one-time chromium plating in a trivalent chromium plating tank into two chromium platings in a first chromium plating tank and a second chromium plating tank, thereby effectively eliminating the pollution of the second chromium plating tank by nickel impurities and forming a surface chromium plating layer with good quality.

[0027] 2. In the trivalent chromium decorative chromium plating method of the present invention, a chromium plating solution electrolytic tank is arranged between the first chromium plating tank and the second chromium plating tank, and the content of nickel impurities can be fully reduced by electrolysis in the chromium plating solution electrolytic tank.

[0028] 3. In the method for decorative chromium plating with trivalent chromium of the present invention, the composition of the electrolyte is the same as that of the plating solution. After the plated parts come out of the first chromium plating tank, they are directly immersed in the chromium plating solution electrolytic tank for cleaning, and then directly subjected to the second chromium plating in the second cadmium plating tank. In this process, there is no loss of trivalent chromium plating solution and no economic loss.

[0029] 4. The method for decorative chromium plating with trivalent chromium of the present invention can replace a trivalent chromium plating tank with multiple hanging positions on an existing production line with a first chromium plating tank, a chromium plating liquid electrolytic tank, and a second chromium plating tank without changing the existing trivalent chromium plating production line. The method is simple, highly operable, and can produce significant beneficial effects.

[0030] 5. The trivalent chromium decorative chromium plating method of the present invention replaces the traditional potassium dichromate cathode electrolytic protection process with a rare earth cathode electrolytic protection process, thereby eliminating the high pollution problem caused by the use of highly toxic hexavalent chromium. DETAILED DESCRIPTION

[0031] A method for trivalent chromium plating decorative chromium comprises the following steps:

[0032] (1) Pre-treat the workpiece to be plated;

[0033] (2) preparing a bottom coating on the pre-treated workpiece to be plated;

[0034] (3) preparing a bright nickel coating on the bottom coating of the plated workpiece, and forming a nickel-plated workpiece after washing;

[0035] (4) performing a first chrome plating on the nickel-plated workpiece in a first chrome plating tank to form a bottom chrome plating layer on the surface of the nickel-plated workpiece;

[0036] (5) After the first chrome plating, the nickel-plated workpiece is directly immersed in the chrome plating solution electrolytic tank for cleaning. The cleaning time is 3 to 10 seconds to prevent the nickel-plated workpiece from bringing nickel impurities into the second chrome plating tank;

[0037] (6) After the nickel-plated workpiece is cleaned in the chrome plating solution electrolytic tank, it is directly subjected to a second chrome plating in a second chrome plating tank to form a surface chrome plating layer on the surface of the bottom chrome plating layer;

[0038] (7) using a rare earth cathode electrolysis process to electrolytically protect the trivalent chromium plating layer, thereby forming a rare earth protective film on the trivalent chromium plating layer;

[0039] The chromium plating solution electrolytic tank is arranged between the first chromium plating tank and the second chromium plating tank, the chromium plating solution electrolytic tank contains the same trivalent chromium plating solution as that in the chromium plating tank, and electrolysis is continuously performed in the chromium plating solution electrolytic tank to reduce the content of nickel impurities in the plating solution;

[0040] Preferably, two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0041] The rare earth cathode electrolysis process is as follows: 1-10 g / L of lanthanum acetate or praseodymium acetate, 10-50 g / L of HEDP complexing agent, 80-150 g / L of anhydrous sodium carbonate, pH of 11.5-12.5, cathode current density of 0.5-1.5 A / dm 2 , operate at room temperature, use the chrome-plated workpiece as the cathode and the stainless steel plate as the anode, and electrolyze for 10 to 30 seconds.

[0042] Preferably, the plated workpiece includes a steel workpiece, a zinc alloy die-casting, or an aluminum alloy workpiece.

[0043] According to the current pre-treatment process, the metal workpieces are degreased, dewaxed, derusted and activated.

[0044] After pre-treatment, the steel workpiece is pre-plated with Watt nickel, acid copper, bright nickel, and trivalent chromium for decorative chromium from the inside to the outside using the current process.

[0045] After pretreatment, the zinc alloy die castings are pre-plated with citrate nickel, pyrophosphate copper, acid copper, bright nickel and trivalent chromium from the inside to the outside using the current process.

[0046] After pre-treatment of the aluminum alloy parts, the existing process is used to carry out chemical zinc deposition, citrate pre-nickel plating, pyrophosphate copper plating, acid copper plating, bright nickel plating, and trivalent chromium decorative chromium plating from the inside to the outside.

[0047] The prepared trivalent chromium decorative chromium plating layer includes a trivalent chromium base plating layer and a trivalent chromium surface plating layer. Preferably, the thickness of the base chromium plating layer is 0.03-0.12 μm, and the thickness ratio of the surface chromium plating layer to the base chromium plating layer is 1:(0.5-1.2).

[0048] Preferably, the chemical zinc deposition layer is prepared using AZIN-113 acidic aluminum zinc deposition agent produced by Guangzhou Chaobang Chemical Co., Ltd.: AZIN-113 acidic aluminum zinc deposition agent 50-250mL / L, working temperature 15-30°C, zinc deposition solution pH range 3.4-4.2, zinc deposition time 20-80s. The prepared chemical zinc deposition layer contains two components, zinc and nickel, and the mass fraction of nickel element is 8% to 20%.

[0049] Preferably, the thickness of the prepared Watt nickel pre-plated nickel layer is 0.1-1.5 μm, and the Watt nickel nickel plating process is used: 180-250 g / L nickel sulfate hexahydrate, 10-12 g / L sodium chloride, 30-35 g / L boric acid, 30-40 g / L magnesium sulfate, pH value 5-5.5, temperature 20-35 ° C, cathode current density 0.8-1.5 A / dm 2 .

[0050] Preferably, the thickness of the prepared citrate nickel plating layer is 0.5-5 μm, and the current citrate nickel plating process is used for preparation: nickel sulfate hexahydrate 90-110 g / L, sodium chloride 10-15 g / L, boric acid 20-30 g / L, sodium citrate 100-130 g / L, pH 5.0-5.8, temperature 50-60 ° C, cathode current density 1.0-1.5 A / dm 2 .

[0051] Preferably, the thickness of the prepared pyrophosphate copper plating layer is 8-15 μm, and it is prepared by the pyrophosphate copper plating process of Chaobang Chemical: 60-70 g / L of copper pyrophosphate, 280-320 g / L of potassium pyrophosphate, 2-3 mL / L of ammonia water, 3-5 mL / L of GAFFA PC-1287 pyrophosphate gloss agent, pH value 8.2-8.8, temperature 50-60°C, cathode current density 0.6-1.2 A / dm 2 , medium air agitation.

[0052] Preferably, the thickness of the prepared acid copper coating is 8-20 μm, and it is prepared by the acid copper plating process of Chaobang Chemical: 180-220 g / L of copper sulfate pentahydrate, 60-80 g / L of sulfuric acid, 40-100 mg / L of chloride ions, 3-8 mL / L of GAFFA M-8000Mu cylinder opener, 0.3-0.6 mL / L of GAFFA M-8000A main light agent, 0.1-0.3 mL / L of GAFFA M-8000B auxiliary light agent, temperature 18-30 ° C, cathode current density 0.5-3.0 A / dm 2 , strong and uniform air stirring.

[0053] Preferably, the prepared bright nickel coating has a thickness of 1 to 10 μm and is prepared using the bright nickel plating process of Chaobang Chemical: 240 to 280 g / L of nickel sulfate hexahydrate, 45 to 60 g / L of nickel chloride hexahydrate, 40 to 50 g / L of boric acid, 15 to 30 mL / L of NINFEA SC-260 bright nickel softener, 0.3 to 0.7 mL / L of NINFEA AS-250 bright nickel auxiliary, 0.4 to 0.8 mL / L of NINFEA 8003 bright nickel main brightener, 0.5 to 1.5 mL / L of NINFEA NI-35 bright nickel wetting agent, pH value 4.2 to 4.8, temperature 55 to 60°C, cathode current density 3 to 6 A / dm 2 , medium air agitation.

[0054] The trivalent chromium decorative chromium plating includes a trivalent chromium white chromium plating process and a trivalent chromium black chromium plating process.

[0055] Preferably, the trivalent chromium white chromium plating process is the Trich-9551 sulfate trivalent chromium white chromium plating process of Chaobang Chemical: Trich-9551 M cylinder opener 8-12mL / L, Trich-9551 B supplementer 260-300mL / L, Trich-9551 CS conductive salt 280-320g / L, Trich-9551 WA wetting agent 0.5-2.0mL / L, pH range 3.4-3.8, operating temperature 50-55°C, cathode current density 8-15A / dm 2 , cathode movement or slight air stirring.

[0056] In the second chrome plating tank, the mass concentration of nickel impurities is required to be less than 20 mg / L.

[0057] Preferably, the trivalent chromium white chromium plating process is the Trich-6561 chloride trivalent chromium white chromium plating process of Chaobang Chemical: Trich-6561 opening salt 400-450g / L, Trich-6563 complexing agent 60-85mL / L, Trich-6564 stabilizer 1-2mL / L, Trich-6565 wetting agent 1-3mL / L, pH value 2.5-3.0, operating temperature 25-36°C, cathode current density 8-16A / dm 2 , medium air agitation.

[0058] In the second chrome plating tank, the mass concentration of nickel impurities is required to be less than 20 mg / L.

[0059] Preferably, the trivalent chromium black chromium plating process is the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical: Trich-7677 S initiator 8-12mL / L, Trich-7677 M cylinder opener 260-300mL / L, Trich-7677 CS conductive salt 280-320g / L, Trich-7677 C stabilizer 3.0-4.0mL / L, Trich-7677 D toner 3.0-8.0mL / L, Trich-7677 WA wetting agent 0.5-2.0mL / L, pH value 3.3-3.7, operating temperature 25-40°C, cathode current density 8-14A / dm 2 , cathode movement or slight air stirring.

[0060] In the second chrome plating tank, the mass concentration of nickel impurities is required to be less than 20 mg / L.

[0061] Preferably, the chrome plating solution electrolytic cell uses a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chrome plating solution electrolytic cell close to the exhaust port, and the cathode is arranged on the side of the chrome plating solution electrolytic cell close to the operator; the width of the cathode plate is 70% to 90% of the width of the chrome plating solution electrolytic cell, and the height of the cathode plate is 60% to 80% of the height of the chrome plating solution electrolytic cell; the cathode current density is 0.2 to 1.2 A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0062] Example 1

[0063] The trivalent chromium plating of steel parts is white chromium, and the Watt nickel pre-plating layer, the acid copper plating layer, the bright nickel plating layer, the trivalent chromium bottom white chromium plating layer, the trivalent chromium surface white chromium plating layer, and the rare earth protective film are prepared from the inside to the outside. The thickness of the Watt nickel pre-plating layer is 0.3 μm, the thickness of the acid copper plating layer is 12 μm, the thickness of the bright nickel plating layer is 7 μm, the thickness of the bottom white chromium plating layer is 0.08 μm, and the thickness of the surface white chromium plating layer is 0.08 μm.

[0064] Two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0065] The specific steps are as follows:

[0066] 1. Pretreatment: chemical degreasing → water washing → rust removal → water washing → cathode electrolytic degreasing → water washing → anode electrolytic degreasing → activation → water washing.

[0067] 2. Pre-plating with Watt nickel: After pre-treatment of steel parts, a Watt nickel pre-plating layer is prepared according to the Watt nickel plating process and then washed with water.

[0068] The nickel plating process of Watt Nickel is as follows: 220 g / L nickel sulfate hexahydrate, 12 g / L sodium chloride, 30 g / L boric acid, 35 g / L magnesium sulfate, pH = 5.2, temperature 30°C, cathode current density 1.2 A / dm 2 .

[0069] 3. Acid copper plating: After the steel parts are pre-plated with Watt nickel, the acid copper plating process of Chaobang Chemical is used to prepare the acid copper plating layer, and then washed with water.

[0070] The acid copper plating process is as follows: 200 g / L of copper sulfate pentahydrate, 70 g / L of sulfuric acid, 70 mg / L of chloride ions, 5 mL / L of GAFFA M-8000Mu opener, 0.5 mL / L of GAFFA M-8000A main light agent, 0.2 mL / L of GAFFA M-8000B auxiliary light agent, temperature 25°C, cathode current density 2.0 A / dm 2 , strong and uniform air stirring.

[0071] 4. Bright nickel plating: After the steel parts are plated with acid copper, the bright nickel plating process of Chaobang Chemical is used to prepare a bright nickel plating layer, and then washed with water to form nickel-plated parts.

[0072] The bright nickel plating process is as follows: 260 g / L nickel sulfate hexahydrate, 55 g / L nickel chloride hexahydrate, 45 g / L boric acid, 20 mL / L NINFEA SC-260 bright nickel softener, 0.5 mL / L NINFEA AS-250 bright nickel auxiliary, 0.6 mL / L NINFEA 8003 bright nickel main brightener, 1.0 mL / L NINFEA NI-35 bright nickel wetting agent, pH = 4.5, temperature 58°C, cathode current density 4 A / dm 2 , medium air agitation.

[0073] 5. First trivalent chromium plating: The nickel-plated workpiece adopts the sulfate trivalent chromium white chromium plating process to prepare the bottom white chromium plating layer in the first chromium plating tank.

[0074] 6. Second trivalent chromium plating: After the first chromium plating, the nickel-plated workpiece is directly immersed in the chromium plating solution electrolytic tank for cleaning, and then directly prepared in the second chromium plating tank for the surface white chromium plating layer and washed with water.

[0075] The sulfate white chromium plating process is the Trich-9551 sulfate trivalent chromium white chromium plating process of Chaobang Chemical: Trich-9551 M cylinder opener 10mL / L, Trich-9551 B supplementer 300mL / L, Trich-9551 CS conductive salt 280g / L, Trich-9551 WA wetting agent 0.5mL / L, pH=3.6, operating temperature 52°C, cathode current density 10A / dm 2, cathode movement or slight air stirring.

[0076] In the second chrome plating tank, the mass concentration of nickel impurities is 1 mg / L.

[0077] The product was plated in the first chrome plating tank for 1.5 min, washed in the chrome plating solution electrolytic tank for 6 s, and plated in the second chrome plating tank for 1.5 min.

[0078] Two partitions are added in the middle of the trivalent chromium plating tank to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0079] The chromium plating bath adopts a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chromium plating bath close to the exhaust port, and the cathode is arranged on the side of the chromium plating bath close to the operator; the width of the cathode plate is 80% of the width of the chromium plating bath, and the height of the cathode plate is 70% of the height of the chromium plating bath; the cathode current density is 1A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0080] 7. Rare earth electrolytic protection: The trivalent chromium plating layer is electrolytically protected by a rare earth cathode electrolytic process to form a rare earth protective film on the trivalent chromium plating layer.

[0081] The rare earth cathode electrolysis process is: lanthanum acetate 6g / L, HEDP complexing agent 30g / L, anhydrous sodium carbonate 100g / L, pH=12, cathode current density 1A / dm 2 , operate at room temperature, use the chrome-plated workpiece as cathode and the stainless steel plate as anode, electrolyze for 15s, then wash with water and dry.

[0082] Example 2

[0083] The trivalent chromium plating of steel parts is white chromium, and the Watt nickel pre-plating layer, the acid copper plating layer, the bright nickel plating layer, the trivalent chromium bottom white chromium plating layer, the trivalent chromium surface white chromium plating layer, and the rare earth protective film are prepared from the inside to the outside. The thickness of the Watt nickel pre-plating layer is 0.5 μm, the thickness of the acid copper plating layer is 15 μm, the thickness of the bright nickel plating layer is 5 μm, the thickness of the bottom white chromium plating layer is 0.12 μm, and the thickness of the surface white chromium plating layer is 0.12 μm.

[0084] Two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0085] The specific steps are as follows:

[0086] 1. Pretreatment: chemical degreasing → water washing → rust removal → water washing → cathode electrolytic degreasing → water washing → anode electrolytic degreasing → activation → water washing.

[0087] 2. Pre-plating with Watts nickel: After pre-treatment of the steel parts, a Watts nickel pre-plating layer is prepared according to the Watts nickel plating process as described in Example 1, and then washed with water.

[0088] 3. Acid copper plating: After the steel parts are pre-plated with Watt nickel, an acid copper plating layer is prepared according to the acid copper plating process described in Example 1, and then washed with water.

[0089] 4. Bright nickel plating: After the steel parts are plated with acid copper, a bright nickel plating layer is prepared according to the bright nickel plating process described in Example 1, and then washed with water to form a nickel-plated part.

[0090] 5. First trivalent chromium plating: The nickel-plated workpiece adopts chloride trivalent chromium white chromium plating process to prepare the bottom white chromium plating layer in the first chromium plating tank.

[0091] 6. Second trivalent chromium plating: After the first chromium plating, the nickel-plated parts are directly immersed in the chromium plating solution electrolytic tank for cleaning, and then directly prepared in the second chromium plating tank for the surface white chromium plating layer and washed with water.

[0092] The trivalent chromium chloride white chromium plating process is the Trich-6561 trivalent chromium chloride white chromium plating process of Chaobang Chemical: Trich-6561 opening salt 420g / L, Trich-6563 complexing agent 70mL / L, Trich-6564 stabilizer 1.5mL / L, Trich-6565 wetting agent 2mL / L, pH=2.8, operating temperature 28°C, cathode current density 10A / dm 2 , medium air agitation.

[0093] In the second chrome plating tank, the mass concentration of nickel impurities is 3 mg / L.

[0094] The product was plated in the first chrome plating tank for 1 min, washed in the chrome plating solution electrolytic tank for 6 s, and plated in the second chrome plating tank for 1 min.

[0095] The chromium plating bath adopts a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chromium plating bath close to the exhaust port, and the cathode is arranged on the side of the chromium plating bath close to the operator; the width of the cathode plate is 80% of the width of the chromium plating bath, and the height of the cathode plate is 70% of the height of the chromium plating bath; the cathode current density is 1A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0096] 7. Rare earth electrolytic protection: The trivalent chromium plating layer is electrolytically protected by a rare earth cathode electrolytic process to form a rare earth protective film on the trivalent chromium plating layer.

[0097] The rare earth cathode electrolysis process is prepared as follows: praseodymium acetate 3g / L, HEDP complexing agent 15g / L, anhydrous sodium carbonate 120g / L, pH = 12, cathode current density 1A / dm 2 , operate at room temperature, use the chrome-plated workpiece as cathode and the stainless steel plate as anode, electrolyze for 20 seconds, then wash with water and dry.

[0098] Example 3

[0099] The trivalent chromium black chromium plating of steel parts is carried out by sequentially preparing a Watt nickel pre-plating layer, an acid copper plating layer, a bright nickel plating layer, a trivalent chromium bottom black chromium plating layer, and a trivalent chromium top black chromium plating layer from the inside to the outside. The thickness of the Watt nickel pre-plating layer is 0.5 μm, the thickness of the acid copper plating layer is 12 μm, the thickness of the bright nickel plating layer is 7 μm, the thickness of the bottom black chromium plating layer is 0.07 μm, and the thickness of the top black chromium plating layer is 0.07 μm.

[0100] Two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0101] The specific steps are as follows:

[0102] 1. Pretreatment: chemical degreasing → water washing → rust removal → water washing → cathode electrolytic degreasing → water washing → anode electrolytic degreasing → activation → water washing.

[0103] 2. Pre-plating with Watts nickel: After pre-treatment of the steel parts, a Watts nickel pre-plating layer is prepared according to the Watts nickel plating process as described in Example 1, and then washed with water.

[0104] 3. Acid copper plating: After the steel parts are pre-plated with Watt nickel, an acid copper plating layer is prepared according to the acid copper plating process described in Example 1, and then washed with water.

[0105] 4. Bright nickel plating: After the steel parts are plated with acid copper, a bright nickel plating layer is prepared according to the bright nickel plating process described in Example 1, and then washed with water to form a nickel-plated part.

[0106] 5. First trivalent chromium plating: The nickel-plated workpiece adopts the sulfate trivalent chromium black chromium plating process to prepare the bottom black chromium plating layer in the first chromium plating tank.

[0107] 6. Second trivalent chromium plating: After the first chromium plating, the nickel-plated workpiece is directly immersed in the chromium plating solution electrolytic tank for cleaning, and then directly prepared in the second chromium plating tank for the surface black chromium plating layer and washed with water.

[0108] The sulfate trivalent chromium black chromium plating process is the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical: Trich-7677 S initiator 10mL / L, Trich-7677 M cylinder opener 280mL / L, Trich-7677 CS conductive salt 280g / L, Trich-7677 C stabilizer 3.0mL / L, Trich-7677 D toner 4.0mL / L, Trich-7677 WA wetting agent 0.5mL / L, pH=3.5, operating temperature 30°C, cathode current density 10A / dm 2 , cathode movement or slight air stirring.

[0109] In the second chrome plating tank, the mass concentration of nickel impurities is 5 mg / L.

[0110] The product was plated in the first chrome plating tank for 2 minutes, washed in the chrome plating solution electrolytic tank for 6 seconds, and plated in the second chrome plating tank for 2 minutes.

[0111] The chromium plating bath adopts a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chromium plating bath close to the exhaust port, and the cathode is arranged on the side of the chromium plating bath close to the operator; the width of the cathode plate is 80% of the width of the chromium plating bath, and the height of the cathode plate is 70% of the height of the chromium plating bath; the cathode current density is 1A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0112] 7. Rare earth electrolytic protection: The trivalent chromium plating layer is electrolytically protected by a rare earth cathode electrolytic process to form a rare earth protective film on the trivalent chromium plating layer.

[0113] The rare earth cathode electrolysis process is as follows: 5 g / L praseodymium acetate, 25 g / L HEDP complexing agent, 120 g / L anhydrous sodium carbonate, pH = 12.5, cathode current density 1 A / dm 2 , operate at room temperature, use the chrome-plated workpiece as cathode and the stainless steel plate as anode, electrolyze for 18s, then wash with water and dry.

[0114] Example 4

[0115] The zinc alloy die casting is plated with trivalent chromium and white chromium, and a citrate pre-plated nickel layer, a pyrophosphate copper layer, an acid copper layer, a bright nickel layer, a trivalent chromium bottom layer white chromium layer, a trivalent chromium top layer white chromium layer, and a rare earth protective film are prepared from the inside to the outside. The thickness of the citrate pre-plated nickel layer is 1 μm, the thickness of the pyrophosphate copper layer is 12 μm, the thickness of the acid copper layer is 15 μm, the thickness of the bright nickel layer is 5 μm, the thickness of the bottom layer white chromium layer is 0.12 μm, and the thickness of the top layer white chromium layer is 0.12 μm.

[0116] Two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0117] The specific steps are as follows:

[0118] 1. Pretreatment: chemical dewaxing → water washing → ultrasonic dewaxing → water washing → chemical degreasing → water washing → acid salt activation → water washing.

[0119] 2. Citrate pre-nickel plating: After pre-treatment of zinc alloy die castings, the pre-nickel plating layer is prepared using the current citrate nickel plating process and then washed with water.

[0120] The citrate nickel plating process is as follows: nickel sulfate hexahydrate 100 g / L, sodium chloride 12 g / L, boric acid 25 g / L, sodium citrate 120 g / L, pH = 5.5, temperature 55 ° C, cathode current density 1.2 A / dm 2 .

[0121] 3. Pyrophosphate copper plating: The pyrophosphate copper plating layer is prepared on the citrate pre-nickel plating layer using the pyrophosphate copper plating process of Chaobang Chemical.

[0122] The pyrophosphate copper plating process is as follows: 65 g / L copper pyrophosphate, 300 g / L potassium pyrophosphate, 2.5 mL / L ammonia water, 4 mL / L GAFFAPC-1287 pyrophosphate brightener, pH=8.5, temperature 55°C, cathode current density 1 A / dm 2 , medium air agitation.

[0123] 4. Acid copper plating: an acid copper plating layer is prepared on the pyrophosphate copper plating layer according to the acid copper plating process described in Example 1, and then washed with water.

[0124] 5. Bright nickel plating: a bright nickel plating layer is prepared on the acid copper plating layer according to the bright nickel plating process described in Example 1, and then washed with water to form a nickel-plated workpiece.

[0125] 6. First trivalent chromium plating: The nickel-plated workpiece adopts the sulfate trivalent chromium white chromium plating process to prepare the bottom white chromium plating layer in the first chromium plating tank.

[0126] 7. Second trivalent chromium plating: After the first chromium plating, the nickel-plated workpiece is directly immersed in the chromium plating solution electrolytic tank for cleaning, and then directly prepared in the second chromium plating tank for the surface white chromium plating layer and washed with water.

[0127] The sulfate trivalent chromium white chromium plating process is the Trich-9551 sulfate trivalent chromium white chromium plating process of Chaobang Chemical: Trich-9551 M cylinder opener 10mL / L, Trich-9551 B supplement 270mL / L, Trich-9551 CS conductive salt 290g / L, Trich-9551 WA wetting agent 0.5mL / L, pH=3.6, operating temperature 50°C, cathode current density 12A / dm 2 , cathode movement or slight air stirring.

[0128] In the second chrome plating tank, the mass concentration of nickel impurities is 6 mg / L.

[0129] The product was plated in the first chrome plating tank for 2 minutes, washed in the chrome plating solution electrolytic tank for 8 seconds, and plated in the second chrome plating tank for 2 minutes.

[0130] The chromium plating bath adopts a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chromium plating bath close to the exhaust port, and the cathode is arranged on the side of the chromium plating bath close to the operator; the width of the cathode plate is 80% of the width of the chromium plating bath, and the height of the cathode plate is 70% of the height of the chromium plating bath; the cathode current density is 1A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0131] 8. A rare earth cathode electrolysis process is used to electrolytically protect the trivalent chromium plating layer, and a rare earth protective film is formed on the trivalent chromium plating layer.

[0132] The rare earth cathode electrolysis process is as follows: praseodymium acetate 8g / L, HEDP complexing agent 40g / L, anhydrous sodium carbonate 120g / L, pH = 12.2, cathode current density 1A / dm 2 , operate at room temperature, use the chrome-plated workpiece as cathode and the stainless steel plate as anode, electrolyze for 25 seconds, then wash with water and dry.

[0133] Example 5

[0134] Aluminum alloy parts are plated with trivalent chromium and black chromium, and chemical zinc deposition layer, citrate pre-nickel plating layer, pyrophosphate copper plating layer, acid copper plating layer, bright nickel plating layer, trivalent chromium bottom black chromium plating layer, trivalent chromium surface black chromium plating layer, and rare earth protective film are prepared in sequence from the inside to the outside. The thickness of the citrate nickel plating layer is 3μm, the thickness of the pyrophosphate copper plating layer is 12μm, the thickness of the acid copper plating layer is 12μm, the thickness of the bright nickel plating layer is 8μm, the thickness of the bottom black chromium plating layer is 0.1μm, and the thickness of the surface black chromium plating layer is 0.1μm.

[0135] Two partitions are added in the middle of the trivalent chromium plating tank on the original production line to separate the chromium plating tank into a first chromium plating tank, a chromium plating solution electrolytic tank, and a second chromium plating tank; the width of the chromium plating solution electrolytic tank is parallel to the width of one hanging position of the chromium plating line.

[0136] The specific steps are as follows:

[0137] 1. Pretreatment: chemical dewaxing → water washing → ultrasonic dewaxing → water washing → slag discharge → water washing → chemical degreasing → water washing → acid salt activation → water washing.

[0138] 2. Chemical zinc precipitation: first chemical zinc precipitation → water washing → zinc removal → water washing → second chemical zinc precipitation → water washing.

[0139] After the aluminum alloy parts are pre-treated, the chemical zinc deposition layer is prepared using Chaobang Chemical's AZIN-113 acidic aluminum zinc deposition agent: AZIN-113 acidic aluminum zinc deposition agent 150mL / L, working temperature 25℃, zinc deposition solution pH=3.8, zinc deposition time 60s. The prepared chemical zinc deposition layer contains two components, zinc and nickel, with a mass fraction of nickel of 12%.

[0140] 3. Citrate pre-nickel plating: After chemical zinc deposition on the aluminum alloy part, a pre-nickel plating layer is prepared according to the same citrate nickel plating process as in Example 4, and then washed with water.

[0141] 4. Pyrophosphate copper plating: A copper plating layer is prepared on the citrate pre-nickel plating layer according to the same pyrophosphate copper plating process as in Example 4.

[0142] 5. Acid copper plating: prepare an acid copper plating layer on the pyrophosphate copper plating layer according to the acid copper plating process described in Example 1, and wash with water.

[0143] 6. Bright nickel plating: After the steel parts are plated with acid copper, a bright nickel plating layer is prepared according to the bright nickel plating process described in Example 1, and then washed with water to form a nickel-plated part.

[0144] 7. First trivalent chromium plating: The nickel-plated parts adopt the sulfate trivalent chromium black chromium plating process to prepare the bottom black chromium plating layer in the first chromium plating tank.

[0145] 8. Second trivalent chromium plating: After the first chromium plating, the nickel-plated parts are directly immersed in the chromium plating solution electrolytic tank for cleaning, and then the surface black chromium plating layer is directly prepared in the second chromium plating tank and washed with water.

[0146] The sulfate trivalent chromium black chromium plating process is the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical: Trich-7677 S initiator 10mL / L, Trich-7677 M cylinder opener 270mL / L, Trich-7677 CS conductive salt 290g / L, Trich-7677 C stabilizer 3.3mL / L, Trich-7677 D toner 4mL / L, Trich-7677 WA wetting agent 0.5mL / L, pH=3.4, operating temperature 40°C, cathode current density 12A / dm 2 , cathode movement or slight air stirring.

[0147] In the second chrome plating tank, the mass concentration of nickel impurities is 8 mg / L.

[0148] The product was plated in the first chrome plating tank for 2.5 min, washed in the chrome plating solution electrolytic tank for 10 s, and plated in the second chrome plating tank for 2.5 min.

[0149] The chromium plating bath adopts a sulfate trivalent chromium plating anode plate as an anode and a stainless steel plate as a cathode; the anode is arranged on the side of the chromium plating bath close to the exhaust port, and the cathode is arranged on the side of the chromium plating bath close to the operator; the width of the cathode plate is 80% of the width of the chromium plating bath, and the height of the cathode plate is 70% of the height of the chromium plating bath; the cathode current density is 1A / dm 2 , with moderate air agitation, the electrolysis is continued.

[0150] 9. A rare earth cathode electrolysis process is used to electrolytically protect the trivalent chromium plating layer, and a rare earth protective film is formed on the trivalent chromium plating layer.

[0151] The rare earth cathode electrolysis process is prepared as follows: 6 g / L praseodymium acetate, 30 g / L HEDP complexing agent, 120 g / L anhydrous sodium carbonate, pH = 12.2, cathode current density 1 A / dm 2 , operate at room temperature, use the chrome-plated workpiece as cathode and the stainless steel plate as anode, electrolyze for 30 seconds, then wash with water and dry.

[0152] Test Example 1

[0153] In this test example, the samples prepared in Examples 1 to 5 were subjected to corrosion resistance tests, and neutral salt spray tests were performed according to GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test", and the test results are shown in Table 1. As can be seen from Table 1, the trivalent chromium decorative chrome plating layer prepared by the technical solution of the present invention has high corrosion resistance.

[0154] Table 1 Neutral salt spray test results of samples prepared by the present invention

[0155]

[0156] Test Example 2

[0157] In this test example, the coating bonding strength of the samples prepared in Examples 1 to 5 was tested by the thermal shock method according to JB 2111-1977 "Method for testing the bonding strength of metal coatings". The plated parts were placed in a heating furnace and heated to 190°C for 30 minutes. After being taken out, they were placed in water at room temperature and suddenly cooled. The coating did not blister or fall off. The test shows that the coating structure prepared by the present invention has good bonding strength.

[0158] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for trivalent chromium plating decorative chromium, characterized in that: The method for trivalent chromium plating decorative chromium comprises the following steps: (1) preparing a bright nickel-plated layer on a plated workpiece to form a nickel-plated workpiece; (2) performing a first chrome plating on the nickel-plated workpiece in a first chrome plating tank to form a bottom chrome plating layer on the surface of the nickel-plated workpiece; (3) After the first chrome plating, the nickel-plated workpiece is directly immersed in the chrome plating solution electrolytic tank for cleaning. The cleaning time is 5 to 10 seconds to prevent the nickel-plated workpiece from bringing nickel impurities into the second chrome plating tank; (4) After the nickel-plated workpiece is cleaned in the chrome plating solution electrolytic tank, it is directly subjected to a second chrome plating tank, thereby forming a surface chrome plating layer on the surface of the bottom chrome plating layer; (5) using a rare earth cathode electrolysis process to electrolytically protect the trivalent chromium plating layer, thereby forming a rare earth protective film on the trivalent chromium plating layer; The chromium plating solution electrolytic tank is arranged between the first chromium plating tank and the second chromium plating tank, the chromium plating solution electrolytic tank contains the same trivalent chromium plating solution as that in the chromium plating tank, and electrolysis is continuously performed in the chromium plating solution electrolytic tank to reduce the content of nickel impurities in the plating solution; The rare earth cathode electrolysis process is as follows: 1-10 g / L of lanthanum acetate or praseodymium acetate, 5-50 g / L of HEDP complexing agent, 80-150 g / L of anhydrous sodium carbonate, pH of 11.5-12.5, cathode current density of 0.5-1.5 A / dm 2 , operate at room temperature, use the chrome-plated workpiece as the cathode and the stainless steel plate as the anode, and electrolyze for 10 to 30 seconds.

2. The method for trivalent chromium decorative chromium plating according to claim 1, characterized in that: The thickness of the bottom chromium plating layer is 0.03-0.12 μm; the thickness ratio of the surface chromium plating layer to the bottom chromium plating layer is 1:(0.5-1.2).

3. The method for trivalent chromium decorative chromium plating according to claim 1, characterized in that: The content of nickel impurities in the second chromium plating tank is less than 20 mg / L.

4. The method for trivalent chromium decorative chromium plating according to claim 1, characterized in that: The chrome plating layer is prepared by using the current trivalent chromium white chrome plating process, or by using the current trivalent chromium black chrome plating process.

5. The method for trivalent chromium decorative chromium plating according to claim 4, characterized in that: The trivalent chromium white chromium plating process is a Trich-9551 sulfate trivalent chromium white chromium plating process: Trich-9551 M cylinder opener 8-12 mL / L, Trich-9551 B supplementer 260-300 mL / L, Trich-9551 CS conductive salt 280-320 g / L, Trich-9551 WA wetting agent 0.5-2.0 mL / L, pH range 3.4-3.8, operating temperature 50-55°C, cathode current density 8-15 A / dm 2 , cathode movement or slight air stirring.

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