A pretreatment method for neodymium-iron-boron permanent magnets before electroplating

Abstract

The present invention discloses a pre-treatment method for NdFeB permanent magnets before electroplating, which comprises the following steps: S1, preparing a concentrated chamfering solution, where each liter of the concentrated chamfering solution is obtained by dissolving 120 - 160 g of sodium benzoate, 80 - 140 g of sodium carbonate decahydrate, 40 - 80 g of trisodium phosphate dodecahydrate, 40 - 60 mL of triethanolamine, and 10 - 20 g of sodium dodecyl sulfate in water; S2, adding abrasives into a chamfering machine, laying multiple NdFeB permanent magnet workpieces flat above the abrasives, and starting the chamfering machine for chamfering once or multiple times; S3, washing the NdFeB permanent magnet workpieces with water and then pickling them with a nitric acid solution, and washing them with water after pickling; S4, immersing the NdFeB permanent magnet workpieces in an activation solution for 30 - 90 seconds, and finally washing them with water, thus completing the pre-treatment. The present invention mainly improves the formulations of the chamfering solution and the activation solution, and the combination of the two constitutes a complete production process design scheme for the pre-treatment of TH series high-performance NdFeB permanent magnets.

Description

Technical Field

[0001] The present invention relates to the pretreatment before electroplating, and specifically refers to a method for the pretreatment before electroplating of neodymium-iron-boron permanent magnets for power motors. Background Art

[0002] Vehicle-mounted power motors are the main power output devices of new energy vehicles, undertaking the task of converting battery energy into mechanical kinetic energy. High-performance magnets are one of the core components inside. The common magnets in current high-end vehicles on the market are mainly neodymium-iron-boron permanent magnets known as the "magnetic king". Neodymium-iron-boron magnets (Nd 2 Fe 14 B) are tetragonal crystal systems with neodymium, iron, and boron as the main elements, formed by melting and flaking, hydrogen embrittlement powder making, die pressing, and vacuum sintering. They are brittle and extremely prone to rusting, and usually need to be machined and electroplated to form application products. To optimize some specific magnetic properties, some elements such as copper, nickel, carbon, heavy rare earths, etc. can be selectively added to the formula. As the substance with the largest magnetic energy product in the world, it has been gradually popularized in the power motors of new energy vehicles. Coercivity refers to the ability of a magnet to resist the return of magnetic induction intensity to zero. Objectively reflected in a power motor, the higher the coercivity, the longer the ability and lifespan of the motor to continuously output power. Therefore, the pursuit of high-coercivity magnets is a long-term demand of power motor manufacturers.

[0003] A TH series permanent magnet developed by a certain manufacturer has a coercivity Hcj≥38.5 kOe, which is the highest value in this series in the industry. It is expected to have a lifespan of more than 15 years when applied to power motors. To meet the performance requirements of high coercivity, some heavy rare earth elements such as dysprosium and terbium are added in the formula design to optimize the distribution of the Nd-rich phase along the grain boundaries, play an exchange role to separate and isolate ferromagnetic phases, and thus improve the coercivity of the product. However, currently, there are the following problems in the mass production and electroplating of this permanent magnet: 1. The brittleness of the material increases significantly. To avoid the electroplating edge effect, it is necessary to perform mechanical chamfering on the parts during pretreatment to form a smooth edge surface. During chamfering, continuous mechanical shaking and impact cause significant chipping or corner breakage of the material; 2. The material is more active and more prone to oxidation. Especially the rust-proof glue used in the machining slicing process decomposes into organic acids during chamfering, continuously oxidizing the workpiece surface and easily forming slight pits; 3. The material is more active and the production cycle time width of the activation process is relatively large, making the material prone to over-activation or defects, thus affecting the adhesion and corrosion resistance of the coating at high temperatures. The above problems will lead to an increase in the defective rate of finished products, and the cost of heavy rare earth metals such as dysprosium and terbium is extremely high (about 20,000 yuan / kg), indirectly increasing the price of this permanent magnet and the motor. Currently, commercial degreasing powder is mostly used for chamfering, and 5‰ hydrochloric acid is used as the activation solution to balance production and ensure supply, but there are still high defective rates and fluctuations in coating performance.

[0004] Therefore, in view of the edge chipping, corner breakage, rust pits and poor activation that affect the coating performance during the pretreatment of TH series permanent magnets, a new pretreatment method needs to be developed. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies of the above-mentioned background technology, and provide a pretreatment method for electroplating neodymium iron boron permanent magnets in view of the edge chipping, corner breakage, rust pits and poor activation that affect the coating performance during the pretreatment of TH series permanent magnets.

[0006] The technical solution of the present invention is as follows: a pretreatment method for electroplating neodymium iron boron permanent magnets, characterized by comprising the following steps:

[0007] S1. Prepare concentrated chamfering liquid. Each liter of concentrated chamfering liquid is obtained by dissolving 120 - 160 g of sodium benzoate, 80 - 140 g of sodium carbonate decahydrate, 40 - 80 g of trisodium phosphate dodecahydrate, 40 - 60 mL of triethanolamine, and 10 - 20 g of sodium dodecyl sulfate in water;

[0008] S2. Add abrasive into the chamfering machine, lay multiple neodymium iron boron permanent magnet workpieces flat above the abrasive, start the chamfering machine for multiple chamfering operations. Before each chamfering, add water and concentrated chamfering liquid into the chamfering machine according to a volume ratio of (18 - 23):1. The water and concentrated chamfering liquid form chamfering liquid to immerse all neodymium iron boron permanent magnet workpieces;

[0009] S3. Wash the neodymium iron boron permanent magnet workpieces with water and then pickle them with a 0.1% - 0.2% nitric acid solution by mass fraction. After pickling, wash them with water;

[0010] S4. Immerse the neodymium iron boron permanent magnet workpieces in the activation liquid for 30 - 90 seconds. Each liter of activation liquid is obtained by dissolving 7 - 10 g of ammonium chloride and 3 - 5 g of oxalic acid in water. Finally, wash them with water, and the pretreatment is completed.

[0011] Preferably, in step S2, the abrasive includes spherical brown fused alumina A, columnar brown fused alumina B, triangular plastic stone C, and conical plastic stone D added according to a mass ratio of (3 - 4):1:(3 - 4):(1 - 2).

[0012] Further, in step S2, the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single spherical brown fused alumina A, the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single columnar brown fused alumina B, the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single triangular plastic stone C, and the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single conical plastic stone D are all 1:(0.2 - 0.4).

[0013] Preferably, in step S2, the mass ratio of all neodymium iron boron permanent magnet workpieces in the chamfering machine to all the abrasive is 1:(3 - 4).

[0014] Preferably, in step S2, the liquid level of the chamfering liquid is 5-8 cm higher than that of the NdFeB permanent magnet workpiece.

[0015] Preferably, in step S2, when the number of chamfering times is two, the first chamfering time is 80-100 minutes and the second chamfering time is 50-70 minutes.

[0016] Preferably, in step S1, each liter of the concentrated chamfering liquid is obtained by dissolving 135-145 g of sodium benzoate, 90-125 g of sodium carbonate decahydrate, 50-70 g of trisodium phosphate dodecahydrate, 50-55 mL of triethanolamine, and 12-15 g of sodium dodecyl sulfate in water.

[0017] Preferably, in step S3, the pickling time is 60-80 seconds.

[0018] Preferably, in step S3, pickling is carried out with a nitric acid solution having a mass fraction of 0.2%.

[0019] Preferably, in step S2, the mass ratio of spherical brown fused alumina A, columnar brown fused alumina B, triangular plastic abrasive C, and conical plastic abrasive D = 4:1:3:2;

[0020] The mass ratio of all NdFeB permanent magnet workpieces to all abrasives in the chamfering machine is 1:3.

[0021] Preferably, in step S4, each liter of the activation liquid is obtained by dissolving 8-9 g of ammonium chloride and 4-4.5 g of oxalic acid in water.

[0022] In the present invention, the chamfering liquid formulation has the following advantages:

[0023] a. As a common preservative, sodium benzoate can effectively reduce the influence of mold on rare earth elements. At the same time, hydrolysis has weak alkalinity and lipophilicity, and can also protect the corrosion and oxidation of rare earth metals, playing a certain auxiliary role in the degreasing effect of surfactants.

[0024] Main reaction equation: C 6 H 5 COONa + H 2 O → C 6 H 5 COOH + NaOH.

[0025] b. As a weak alkaline salt, sodium carbonate has a certain saponification ability to decompose grease. At the same time, it easily absorbs carbon dioxide in the air and undergoes a hydrolysis reaction to form sodium bicarbonate. The generated sodium bicarbonate has a certain buffering effect on the pH value of the solution, stabilizing the pH value of the chamfering liquid between 8.5-10.2, enabling the saponification reaction to proceed smoothly.

[0026] Main reaction equation: Na 2 CO 3+CO 2 +H 2 O → NaHCO 3 。

[0027] c. As an inorganic degreasing agent, trisodium phosphate hydrolyzes to a strong alkaline, has a certain saponification ability and a role in buffering the pH value. At the same time, trisodium phosphate also has an emulsifying effect, is highly soluble in water, has good water washability and can make saponified salts easier to wash off from the workpiece surface.

[0028] Main reaction equation: Na 3 PO 4 +H 2 O → NaOH + Na 2 HPO 4

[0029] Na 2 HPO 4 +H 2 O → NaOH + NaH 2 PO 4

[0030] NaH 2 PO 4 +H 2 O → NaOH + H 3 PO 4 。

[0031] d. Under the weak alkaline environment formed by the above solutes and the vibration chamfering conditions, triethanolamine reacts with a small amount of organic glue and a large amount of oleic acid left in the previous machining and slicing process to form triethanolamine lipid compounds, which adhere to the material surface to form a good corrosion inhibitor, protecting the workpiece from oxidation and corrosion, thus reducing the risk of rust pits on the workpiece surface. At the same time, these lipid compounds are more easily removed in ultrasonic cleaning. Finally, the influence of the corrosion medium brought by the previous machining and slicing process is effectively avoided.

[0032] e. Sodium dodecyl sulfate, as an anionic surfactant and at the same time as a foaming agent and wetting agent, expands the contact surface between the chamfering liquid and the workpiece, so that each substance in the chamfering liquid can better wet the workpiece surface, enabling the workpiece to be better acted on. At the same time, sodium dodecyl sulfate has a good cleaning effect on the solid grease left by the upstream process.

[0033] The abrasives in the chamfering machine are obtained by combining spherical brown fused alumina A, columnar brown fused alumina B, triangular plastic stone C, and conical plastic stone D. The principle of using these four abrasives in combination is that brown fused alumina abrasives have a relatively high hardness, which can chamfer the edges and corners of the workpiece, enabling the edges and corners of the process to form a considerable arc surface and avoiding the edge effect of subsequent electroplating. The plastic stone abrasives have a relatively low hardness, which can flatten the slight grinding wheel marks left on the surface of the workpiece in the upstream process, making the surface smoother and without obvious visible uneven surfaces. At the same time, it also plays a certain buffering role in the gravity collision between workpieces during the vibration process. There is also no chemical reaction between the abrasives of this formula and the chamfering liquid of the present invention to contaminate the workpiece.

[0034] All four abrasives are commercially available products:

[0035] Brown fused alumina is smelted at high temperature with bauxite and anthracite as the main raw materials, with 94% - 95% alumina, ≤1.5% silica, ≤3.0% titanium oxide, and other trace metal oxides. The Mohs hardness is 9.0 - 9.2, and the density is about 3.85 g / cm 3 。

[0036] Plastic stone is formed by casting with polyamide fiber, plus a little brown fused alumina sand and alumina sand, and the density is about 1.46 - 1.52 g / cm 3 。

[0037] In the present invention, the activation liquid formula has the following advantages:

[0038] a. Oxalic acid is a dibasic weak acid that does not completely ionize hydrogen ions in water. As the number of activated workpieces increases, resulting in continuous consumption of hydrogen ions, the ionization continuously shifts forward to supplement the acidity and maintain the hydrogen ion concentration from fluctuating significantly with consumption. The oxalic acid concentration in the present invention is 3 - 5 g / L, and the pH of the activation liquid can be stabilized at about 1.5 for a long time, so that the activation state of the workpiece will not have obvious fluctuations. At the same time, the low acidity also makes the allowable range of activation time wider, avoiding over-corrosion.

[0039] Main reaction equations: HOOCCOOH → HOOCCOO - +H+

[0040] HOOCCOO - →OOCCOO 2- +H +

[0041] R+H + →R 2+ +H 2 ↑。

[0042] b. Ammonium chloride is a strong acid and weak base salt. Its solution is weakly acidic after hydrolysis. However, its hydrolysis is inhibited after mixing with oxalic acid. It also inhibits the excessive ionization of oxalic acid and controls the fluctuation of hydrogen ion concentration of the solution. It is a good pH stabilizer. The residue after activation is mixed in the workpiece and does not affect the subsequent electroplating process.

[0043] Main reaction equation: NH 4 Cl+H 2 O→NH 3 ·H 2 O+HCl.

[0044] The beneficial effects of the present invention are:

[0045] 1. Prepare the concentrated chamfering liquid first, and add water to prepare the chamfering liquid at any time as needed, which is convenient and quick.

[0046] 2. Chamfering fluid can reduce the probability of rust pits, edge collapse and corner chipping in the chamfering process of permanent magnets. The principle is that the workpiece is fully emulsified and wetted in a stable weak alkaline environment. Even if there is a small amount of oleic acid residue brought by upstream machining, it can react with it to form a stable lipid corrosion inhibition compound and an oxidation diaphragm to protect the workpiece, reducing the risk of rust. At the same time, the use of mixed chamfering stones with appropriate proportions and materials can not only ensure the chamfering effect, but also reduce the proportion of corner chipping and edge chipping caused by "hard collision", alleviating the risk of rust point expansion.

[0047] 3. Oxalic acid and ammonium chloride are used as activators, the pH is stable and excessive or poor corrosion can be avoided, avoiding large fluctuations in activation effect caused by production cycle time, thereby creating the risk of insufficient corrosion resistance and adhesion of subsequent coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The process flow chart of the present invention is

[0049] Figure 2 Schematic diagram of the abrasive shape of the present invention DETAILED DESCRIPTION

[0050] The following specific examples further illustrate the present invention in detail. The pharmaceutical raw materials and abrasives used in the following examples are all commercially available products.

[0051] The components of the concentrated chamfering fluid can be industrial grade, including:

[0052] Triethanolamine is a colorless or slightly yellow viscous liquid with a relative density (water = 1) of 1.12 and an effective content of ≥99%;

[0053] Sodium dodecyl sulfate is in powder form, with an active matter content of ≥94%, a relative density (water = 1) of 1.09, and a pH value of 1% aqueous solution between 8.2-8.5;

[0054] Sodium benzoate, sodium carbonate decahydrate, and trisodium phosphate dodecahydrate are all white crystalline powders with an active ingredient ≥ 98%.

[0055] The spherical brown corundum A and columnar brown corundum B in the abrasive are made of brown corundum (provided by Huzhou Dongao Grinding Machinery Co., Ltd.), and their shapes are as follows: Figure 2 As shown in the upper and lower figures on the left:

[0056] Brown corundum is made of bauxite and anthracite as the main raw materials through high temperature smelting, with 94%~95% aluminum oxide, ≤1.5% silicon dioxide, ≤3.0% titanium oxide, and other trace metal oxides. Mohs hardness is 9.0~9.2, density is about 3.85g / cm 3 .

[0057] The triangular plastic stone C and the conical plastic stone D in the abrasive are made of plastic stone (provided by Dongguan Tianqi Grinding Technology Co., Ltd.), and their shapes are as follows: Figure 2 As shown in the upper and lower figures on the right side:

[0058] Plastic stone is made of polyamide fiber, a little brown corundum sand and alumina sand, and is cast through a mold. The density is about 1.46~1.52 g / cm 3 .

[0059] The NdFeB permanent magnet workpiece in this embodiment is:

[0060] The dimensions are in the shape of a rectangular parallelepiped: (40±3) mm×(40±3) mm×(8±1) mm.

[0061] Example 1

[0062] like Figure 1 As shown, the present embodiment provides a NdFeB permanent magnet electroplating pretreatment method, comprising the following steps:

[0063] S1. Prepare concentrated chamfering liquid (taking 1 liter of chamfering concentrated liquid as an example)

[0064] 135g sodium benzoate [C 7 H 5 NaO 2 ], 90g sodium carbonate decahydrate [Na 2 CO 3 10H 2 O] and 50 g of trisodium phosphate dodecahydrate [Na 3 PO 4 12H 2 O] After fully mixing, add into 800 mL of water and stir until completely dissolved;

[0065] Add 55 mL of triethanolamine and 12 g of sodium dodecyl sulfate, and stir slowly for several times to reduce the foaming of the solution. Make up the water to 1 liter. The preparation of the chamfering concentrate is completed and stored in an opaque plastic bucket for later use.

[0066] S2. Chamfering process (taking 40 kg of workpieces as an example for chamfering)

[0067] Place the flat-bottomed curved-mouth vibrating chamfering machine on a flat ground, and add abrasives into the chamfering machine. For example, Figure 2 the abrasives shown are obtained by mixing 48 kg of spherical brown fused alumina A, 12 kg of columnar brown fused alumina B, 36 kg of triangular plastic stone C, and 24 kg of conical plastic stone D (the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single spherical brown fused alumina A, a single columnar brown fused alumina B, a single triangular plastic stone C, and a single conical plastic stone D is all 1:0.2 - 0.4). Start the chamfering machine and vibrate it at an appropriate frequency for 2 - 3 minutes to make the abrasives evenly distributed in the chamfering machine;

[0068] Lay 40 kg of neodymium iron boron permanent magnet workpieces evenly above the abrasives, add 120 L of water and 6 L of the chamfering concentrate prepared in step S1 into the chamfering machine. The water and the chamfering concentrate form a chamfering liquid that submerges the workpieces by 5 - 8 cm. Set the frequency of the chamfering machine to 36 Hz, start the chamfering machine for the first chamfering, and the chamfering time is 90 minutes;

[0069] After the first chamfering is completed, drain the turbid chamfering liquid, add 120 L of water and 6 L of the chamfering concentrate again for the second chamfering. The chamfering time is 60 minutes. After the chamfering is completed, take out the workpieces to prepare for the next process.

[0070] S3. Pickling process

[0071] Mount the chamfered workpieces on the fixture for water washing, and enter the pickling station. The pickling uses nitric acid with a mass concentration of 0.2%, and the pickling time is 60 seconds. After completion, wash twice with water to prepare for the next process;

[0072] S4. Activation process

[0073] Immerse the neodymium iron boron permanent magnet workpieces in 200 liters of activation liquid for 30 - 90 seconds (each liter of activation liquid is obtained by dissolving 9 g of ammonium chloride and 4.5 g of oxalic acid in water, and the pH value of the activation liquid is about 1.5). Finally, perform two water washes to complete all the pretreatment processes for electroplating.

[0074] Perform the electroplating process on the workpieces after the pretreatment according to the design of the product coating, mostly galvanizing or nickel - copper - nickel plating. In this embodiment, it is the galvanizing process.

[0075] Example 2

[0076] Such as Figure 1As shown, a pre-treatment method for electroplating a neodymium-iron-boron permanent magnet provided in this embodiment includes the following steps:

[0077] S1. Prepare concentrated chamfering liquid (taking 1 liter of concentrated chamfering liquid as an example)

[0078] Put 145 g of sodium benzoate [C 7 H 5 NaO 2 , 125 g of sodium carbonate decahydrate [Na 2 CO 3 ·10H 2 O] and 70 g of trisodium phosphate dodecahydrate [Na 3 PO 4 ·12H 2 O] into a container, fully mix them, then add 800 mL of water, and stir until completely dissolved;

[0079] Then add 50 mL of triethanolamine and 15 g of sodium dodecyl sulfate, stir slowly for a few times to reduce the foaming of the solution, and add water to make up to 1 liter. The preparation of the concentrated chamfering liquid is completed, and it is filled into an opaque plastic bucket for standby.

[0080] S2. Chamfering process (taking chamfering 40 kg of workpieces as an example)

[0081] Place the flat-bottomed curved-mouth vibrating chamfering machine on a flat ground, add abrasives into the chamfering machine. The abrasives are obtained by mixing 50 kg of spherical brown fused alumina A, 15 kg of columnar brown fused alumina B, 50 kg of triangular plastic stone C, and 15 kg of conical plastic stone D (the volume ratios of a single neodymium-iron-boron permanent magnet workpiece to a single spherical brown fused alumina A, a single columnar brown fused alumina B, a single triangular plastic stone C, and a single conical plastic stone D all satisfy 1:0.2 - 0.4). Start the chamfering machine and vibrate it at an appropriate frequency for 2 - 3 minutes to make the abrasives evenly distributed in the chamfering machine;

[0082] Evenly lay 40 kg of neodymium-iron-boron permanent magnet workpieces above the abrasives, add 120 L of water and 6.2 L of the chamfering concentrated liquid prepared in step S1 into the chamfering machine. The water and the concentrated chamfering liquid form a chamfering liquid that submerges the workpieces by 5 - 8 cm. Set the frequency of the chamfering machine to 36 Hz, start the chamfering machine for the first chamfering, and the chamfering time is 100 minutes;

[0083] After the first chamfering is completed, drain the turbid chamfering liquid, add 120 L of water and 6.2 L of chamfering concentrated liquid again for secondary chamfering. The chamfering time is 50 minutes. After chamfering is completed, take out the workpieces to prepare for the next process.

[0084] S3. Pickling process

[0085] The chamfered workpiece is mounted on a fixture for water washing and then enters the pickling station. The pickling uses nitric acid with a mass concentration of 0.2%, and the pickling time is 80 seconds. After that, it is washed twice with water to prepare for the next process.

[0086] S4. Activation process

[0087] The neodymium iron boron permanent magnet workpiece is immersed in 200 liters of activation solution for 30 - 90 seconds (each liter of activation solution is obtained by dissolving 8g of ammonium chloride and 4g of oxalic acid in water, and the pH value of the activation solution is about 1.5). Finally, it is washed twice with water to complete all the pretreatment processes for electroplating.

[0088] The workpiece after pretreatment is electroplated according to the design of the product coating, mostly with zinc plating or nickel - copper - nickel plating. In this embodiment, it is a zinc plating process.

[0089] Example 3

[0090] As Figure 1 shown, a pretreatment method for electroplating neodymium iron boron permanent magnets provided in this embodiment includes the following steps:

[0091] S1. Preparation of concentrated chamfering solution (taking 1 liter of concentrated chamfering solution as an example)

[0092] 120g of sodium benzoate [C 7 H 5 NaO 2 , 140g of sodium carbonate decahydrate [Na 2 CO 3 ·10H 2 O], and 40g of trisodium phosphate dodecahydrate [Na 3 PO 4 ·12H 2 O] are fully mixed and then added to 800 mL of water, and stirred until completely dissolved;

[0093] Then 60 mL of triethanolamine and 10g of sodium dodecyl sulfate are added and slowly stirred a few times to reduce the foaming of the solution, and water is added to make up to 1 liter. The preparation of the concentrated chamfering solution is completed and it is filled into an opaque plastic bucket for standby.

[0094] S2. Chamfering process (taking chamfering 40 kg of workpieces as an example)

[0095] Place the flat-bottomed curved-mouth vibrating chamfering machine on a flat ground, add abrasives into the chamfering machine. The abrasives are obtained by mixing 60 kg of spherical brown fused alumina A, 18 kg of columnar brown fused alumina B, 54 kg of triangular plastic stone C, and 20 kg of conical plastic stone D (the volume ratio of a single neodymium iron boron permanent magnet workpiece to a single spherical brown fused alumina A, a single columnar brown fused alumina B, a single triangular plastic stone C, and a single conical plastic stone D all satisfies 1:0.2 - 0.4). Turn on the chamfering machine and vibrate it at an appropriate frequency for 2 - 3 minutes to make the abrasives evenly distributed in the chamfering machine;

[0096] Evenly lay 40 kg of neodymium iron boron permanent magnet workpieces on top of the abrasives, add 120 L of water and 5.5 L of the chamfering concentrate prepared in step S1 into the chamfering machine. The water and the concentrated chamfering liquid form a chamfering liquid that submerges the workpieces by 5 - 8 cm. Set the frequency of the chamfering machine to 36 Hz, start the chamfering machine for the first chamfering, and the chamfering time is 80 minutes;

[0097] After the first chamfering is completed, drain the turbid chamfering liquid, add 120 L of water and 5.5 L of the chamfering concentrate again for secondary chamfering. The chamfering time is 70 minutes. After chamfering is completed, take out the workpieces to prepare for the next process.

[0098] S3. Pickling process

[0099] Mount the chamfered workpieces on a fixture for water washing, enter the pickling station. The pickling uses nitric acid with a mass concentration of 0.2%, and the pickling time is 70 seconds. After completion, wash twice with water to prepare for the next process;

[0100] S4. Activation process

[0101] Immerse the neodymium iron boron permanent magnet workpieces in 200 liters of activation liquid for 30 - 90 seconds (each liter of activation liquid is obtained by dissolving 7 g of ammonium chloride and 3 g of oxalic acid in water, and the pH value of the activation liquid is about 1.5). Finally, perform two water washes to complete all the pretreatment processes for electroplating.

[0102] Perform the electroplating process on the workpieces after the pretreatment according to the design of the product coating, mostly galvanizing or nickel - copper - nickel plating. In this embodiment, it is the nickel - copper - nickel plating process. Example 4

[0103] As Figure 1 shown, a neodymium iron boron permanent magnet electroplating pretreatment method provided in this embodiment includes the following steps:

[0104] S1. Prepare the concentrated chamfering liquid (taking 1 liter of concentrated chamfering liquid as an example)

[0105] Put 160 g of sodium benzoate [C 7 H 5 NaO 2 , 80 g of sodium carbonate decahydrate [Na2 CO 3 ·10H 2 O] and 80 g of trisodium phosphate dodecahydrate [Na 3 PO 4 ·12H 2 O] are fully mixed and then added to 800 mL of water, and stirred until completely dissolved;

[0106] Then add 40 mL of triethanolamine and 20 g of sodium dodecyl sulfate, and stir slowly several times to reduce the foaming of the solution. Add water to make up to 1 liter. The concentrated chamfering liquid is prepared and filled into an opaque plastic bucket for standby.

[0107] S2. Chamfering process (taking a 40 kg workpiece for chamfering as an example)

[0108] Place the flat-bottomed curved-mouth vibrating chamfering machine on a flat ground, and add abrasives into the chamfering machine. The abrasives are obtained by mixing 60 kg of spherical brown fused alumina A, 15 kg of columnar brown fused alumina B, 50 kg of triangular plastic stone C, and 20 kg of conical plastic stone D (the volume ratios of a single neodymium iron boron permanent magnet workpiece to a single spherical brown fused alumina A, a single columnar brown fused alumina B, a single triangular plastic stone C, and a single conical plastic stone D all meet 1:0.2 - 0.4). Start the chamfering machine and vibrate it at an appropriate frequency for 2 - 3 minutes to make the abrasives evenly distributed in the chamfering machine;

[0109] Evenly lay 40 kg of neodymium iron boron permanent magnet workpieces above the abrasives, add 120 L of water and 6.6 L of the chamfering concentrated liquid prepared in step S1 into the chamfering machine. The water and the concentrated chamfering liquid form a chamfering liquid to submerge the workpieces by 5 - 8 cm. Set the frequency of the chamfering machine to 36 Hz, start the chamfering machine for the first chamfering, and the chamfering time is 100 minutes;

[0110] After the first chamfering is completed, drain the turbid chamfering liquid, add 120 L of water and 6.6 L of the chamfering concentrated liquid again for the second chamfering. The chamfering time is 70 minutes. After the chamfering is completed, take out the workpieces to prepare for the next process.

[0111] S3. Pickling process

[0112] Hang the chamfered workpieces on the fixture and wash them with water, then enter the pickling station. The pickling uses nitric acid with a mass concentration of 0.2%, and the pickling time is 60 seconds. After that, wash them twice with water to prepare for the next process;

[0113] S4. Activation process

[0114] Immerse the neodymium iron boron permanent magnet workpieces in 200 liters of activation liquid for 30 - 90 seconds (each liter of activation liquid is obtained by dissolving 10 g of ammonium chloride and 5 g of oxalic acid in water, and the pH value of the activation liquid is about 1.5). Finally, wash them twice with water to complete all the pretreatment processes of electroplating.

[0115] The pre-treated workpieces are subjected to an electroplating process according to the design of the product coating, mostly galvanizing or nickel-copper-nickel plating. In this embodiment, it is the nickel-copper-nickel plating process.

[0116] Comparative example

[0117] S1. Chamfering process (taking a 40 kg workpiece for chamfering as an example)

[0118] Place the flat-bottomed curved-mouth vibrating chamfering machine on a flat ground, add abrasives into the chamfering machine. The abrasives are obtained by mixing 70 kg of square brown fused alumina, 30 kg of rhombic brown fused alumina, and 40 kg of spherical brown fused alumina. Turn on the chamfering machine and vibrate it at an appropriate frequency for 2 - 3 minutes to make the abrasives evenly distributed in the chamfering machine;

[0119] Evenly lay the 40 kg workpiece above the abrasives, add 120 L of water and 15 kg of commercial degreasing powder into the chamfering machine. The water and commercial degreasing powder form a chamfering liquid to submerge the workpiece. Set the frequency of the chamfering machine to 36 Hz, start the chamfering machine for the first chamfering, and the chamfering time is 120 minutes;

[0120] After the first chamfering is completed, drain the turbid chamfering liquid, add 120 L of water and 15 kg of commercial degreasing powder again for secondary chamfering. The chamfering time is 60 minutes. After chamfering is completed, take out the workpiece to prepare for the next process.

[0121] S2. Pickling process

[0122] Hang the chamfered workpiece on a fixture for water washing, then enter the pickling station for pickling. After completion, wash it twice with water to prepare for the next process;

[0123] S3. Activation process

[0124] Immerse the neodymium iron boron permanent magnet workpiece in 200 liters of hydrochloric acid with a mass fraction of 0.5% for 30 - 90 seconds, and finally wash it twice with water to complete all the pre-treatment processes of electroplating.

[0125] The pre-treated workpieces are subjected to an electroplating process according to the design definition of the product coating. In this comparative example, it is the galvanizing process.

[0126] Performance test

[0127] According to the production control standards of permanent magnet products, count the number of chipped edges, missing corners, and rust pits generated on the chamfered workpieces for the electroplated products obtained from the above examples and comparative examples, and conduct multi-batch inspections on the coating adhesion and corrosion resistance of the finished products. Count the number of unqualified batches. Finally, the qualified rate optimization status of the finished products can be evaluated. The data is shown in Table 1 below. Count the number of defective products based on 500 pieces per tank.

[0128] Table 1

[0129]

[0130] As can be seen from Table 1 above, the adhesion and corrosion resistance of the products of the present invention are good, greatly reducing the probabilities of product edge chipping, corner breakage and rust pits. Compared with the comparative example, the overall defective rate of the surface-treated electroplated parts of the present invention has been reduced from 16% to 1.6 - 1.8%, which not only ensures the product supply but also indirectly reduces the production cost.

Claims

1. A pretreatment method for NdFeB permanent magnets before electroplating, characterized in that, the NdFeB permanent magnet is a TH series permanent magnet, and the method includes the following steps: S1. Prepare a concentrated chamfering solution. Each liter of the concentrated chamfering solution is obtained by dissolving 120 - 160 g of sodium benzoate, 80 - 140 g of sodium carbonate decahydrate, 40 - 80 g of trisodium phosphate dodecahydrate, 40 - 60 mL of triethanolamine, and 10 - 20 g of sodium dodecyl sulfate in water; S2. Add abrasives into the chamfering machine. The abrasives include spherical brown fused alumina A, columnar brown fused alumina B, triangular plastic stone C, and conical plastic stone D added in a mass ratio of (3 - 4):1:(3 - 4):(1 - 2). The volume ratio of a single NdFeB permanent magnet workpiece to a single spherical brown fused alumina A, the volume ratio of a single NdFeB permanent magnet workpiece to a single columnar brown fused alumina B, the volume ratio of a single NdFeB permanent magnet workpiece to a single triangular plastic stone C, and the volume ratio of a single NdFeB permanent magnet workpiece to a single conical plastic stone D are all 1:(0.2 - 0.4); Lay multiple NdFeB permanent magnet workpieces flat above the abrasives. The mass ratio of all NdFeB permanent magnet workpieces to all abrasives in the chamfering machine is 1:(3 - 4). Start the chamfering machine for one or more chamfering operations. Before each chamfering, add water and the concentrated chamfering solution into the chamfering machine in a volume ratio of (18 - 23):

1. The water and the concentrated chamfering solution form a chamfering solution to immerse all NdFeB permanent magnet workpieces; S3. After washing the NdFeB permanent magnet workpieces with water, pickle them with a nitric acid solution with a mass fraction of 0.1% - 0.2%, and then wash them with water after pickling; S4. Immerse the NdFeB permanent magnet workpieces in the activation solution for 30 - 90 seconds. Each liter of the activation solution is obtained by dissolving 7 - 10 g of ammonium chloride and 3 - 5 g of oxalic acid in water, and finally wash them with water. The pretreatment is completed.

2. The pretreatment method for NdFeB permanent magnets before electroplating according to claim 1, characterized in that, in step S2, the liquid level of the chamfering solution is 5 - 8 cm higher than the NdFeB permanent magnet workpieces.

3. The pretreatment method for NdFeB permanent magnets before electroplating according to claim 1, characterized in that, in step S2, when the number of chamfering operations is two, the first chamfering time is 80 - 100 minutes and the second chamfering time is 50 - 70 minutes.

4. The pretreatment method for NdFeB permanent magnets before electroplating according to claim 1, characterized in that, in step S1, each liter of the concentrated chamfering solution is obtained by dissolving 135 - 145 g of sodium benzoate, 90 - 125 g of sodium carbonate decahydrate, 50 - 70 g of trisodium phosphate dodecahydrate, 50 - 55 mL of triethanolamine, and 12 - 15 g of sodium dodecyl sulfate in water.

5. The pretreatment method for NdFeB permanent magnets before electroplating according to claim 1, characterized in that, in step S3, pickle with a nitric acid solution with a mass fraction of 0.2%.

6. The pretreatment method for NdFeB permanent magnets before electroplating according to claim 1, characterized in that, in step S2, the mass ratio of spherical brown fused alumina A, columnar brown fused alumina B, triangular plastic stone C, and conical plastic stone D = 4:1:3:2; the mass ratio of all NdFeB permanent magnet workpieces to all abrasives in the chamfering machine is 1:

3.

7. The pretreatment method of neodymium iron boron permanent magnet before electroplating according to claim 1, characterized in that, in step S4, each liter of the activation solution is obtained by dissolving 8-9 g of ammonium chloride and 4-4.5 g of oxalic acid in water.

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