Method for improving roughness of inner wall of micro-sized neodymium-iron-boron hollow cylindrical magnetic steel

Abstract

A method for improving the roughness of the inner wall of a small-sized neodymium-iron-boron hollow cylindrical magnetic steel, comprising the following steps: S1, putting abrasive stone and magnetic steel, and grinding and chamfering the magnetic steel; S2, pickling the magnetic steel by using pickling solution; S3, pre-plating nickel on the magnetic steel by using first plating solution, and controlling the thickness of the plating layer on the outer wall of the magnetic steel to be 0.3-0.45 μm; S4, chemically roughening the magnetic steel by using roughening solution, and controlling the roughening time to be 30-60 s; and S5, plating the magnetic steel. The present application utilizes the poor deep plating capability of nickel plating, pre-plates nickel for a short time, so that the outer wall of the magnetic steel forms a plating layer while the inner wall does not form a plating layer, and then the magnetic steel is chemically roughened, thereby improving the roughness of the inner wall of the magnetic steel while the roughness of the outer wall of the magnetic steel does not increase significantly.

Description

Technical Field

[0001] This invention relates to the technical field of magnetic materials, and more particularly to a method for improving the roughness of the inner wall of micro-sized neodymium iron boron hollow cylindrical magnets. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are used in the motor magnets of the third-generation iPad stylus. Due to the stylus's unique design, a metal shaft needs to be inserted into the magnet's inner hole. To increase the adhesion between the magnet and the matching metal shaft, the roughness of the magnet's inner wall needs to be increased, thereby increasing the adhesive area and depth. An inner wall roughness of Ra 0.8 μm or higher is required to meet the desired specifications. Simultaneously, the magnet's end face and outer wall need to be laser-engraved with characters and QR codes for automated identification and product traceability. For clear laser engraving, the magnet's outer wall needs a relatively high gloss, meaning its roughness must be as low as possible. This results in different roughness requirements for the inner and outer walls of a single magnet. Conventional processing methods cannot achieve an inner wall roughness of Ra 0.8 μm or higher while simultaneously achieving an outer wall roughness Ra < 0.6 μm. Summary of the Invention

[0003] To address the aforementioned shortcomings, this invention proposes a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets. This method utilizes the poor deep plating capability of nickel plating, involves short-time pre-plating with nickel, forming a coating on the outer wall before the inner wall forms a coating, followed by chemical roughening to increase the inner wall roughness of the magnet while the outer wall roughness does not increase significantly.

[0004] The technical solution adopted by this invention to solve the above problems is as follows: a method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets, comprising the following steps:

[0005] S1. Place the grinding stone and the magnet into the grinding stone and grind the magnet to make it chamfered;

[0006] S2. Pickling the magnets with pickling solution;

[0007] S3. The magnet is pre-plated with nickel using the first plating solution, and the thickness of the plating layer on the outer wall of the magnet is controlled to be 0.3-0.45μm;

[0008] S4. The magnet is chemically roughened using a roughening solution for 30-60 seconds.

[0009] S5. Apply a coating to the magnet.

[0010] Compared with the prior art, the advantages of the present invention are as follows:

[0011] Taking advantage of the poor deep plating capability of nickel plating, a very thin nickel layer is first plated on the outer surface of the magnet. Due to the short electroplating time, the inner wall of the magnet has not yet formed a plating layer, and the NdFeB grains on the inner wall are still exposed. Then, the magnet is subjected to chemical pickling and roughening treatment. The NdFeB grains on the inner wall are corroded by pickling, while the outer wall is not damaged due to the protection of the plating layer. Thus, the roughness of the inner hole of the magnet is improved without causing the roughness of the outer wall to increase simultaneously.

[0012] As a preferred method, the grinding stone feed amount is 100-150kg, the magnet feed amount is 15-25kg, and the grinding time is 4-8 hours. Grinding and chamfering the magnet can reduce the missing corners of the magnet; grinding and chamfering the magnet is also for better electroplating. Chamfering is a process before electroplating, which can make the product surface smoother. Grinding the right angle of the product to a certain extent reduces sharp corners, which can increase the adhesion of the electroplating layer.

[0013] As a preferred method, the pickling solution is nitric acid with a concentration of 2%-2.5%, the pickling time is 150-240 seconds, and the weight of the magnet is 4-5 kg. The pickling solution removes the residual black ash and rust on the surface of the magnet.

[0014] As a preferred embodiment, the first plating solution consists of the following components: 280-350 g / L nickel sulfate, 40-60 g / L nickel chloride, and 40-60 g / L boric acid. The pH value of the first plating solution is 3.8-4.4, the pre-plating temperature is 47-53℃, and the pre-plating is carried out by electroplating. The electroplating current is 45-55 A, and the electroplating time is 200-300 s. If the pre-plating time is extended, a very thin nickel layer will be formed on the inner wall of the magnet, which will protect the grains to some extent. As a result, the improvement effect on the roughness of the inner wall of the magnet after the subsequent steps are completed is also poor.

[0015] As a preferred option, the roughening solution consists of the following components: 2% nitric acid and 1.5% sulfuric acid. The roughening time is 30-60 seconds. The chemical roughening achieves the effect of etching the inner wall of the magnet. If the roughening time is too long, it will over-corrode the outer surface of the magnet, resulting in poor appearance. If the roughening time is too short, the effect of etching the inner wall will not be achieved.

[0016] As a preferred embodiment, step S5 includes:

[0017] S5.1. Electroplating the magnet with nickel base using the first plating solution;

[0018] S5.2, Electroplating copper onto the magnet using a second plating solution;

[0019] S5.3. Electroplating nickel onto the magnet using the first plating solution;

[0020] S5.4. Electroless nickel plating is performed on the magnet using a third plating solution.

[0021] To protect the magnets from oxidation and corrosion and to enhance their appearance, they need to be coated.

[0022] As a preferred option, in step S5.1, the temperature for electroplating the base nickel is 47-53℃, the electroplating current for electroplating the base nickel is 45-55A, and the electroplating time for electroplating the base nickel is 2400-3600s. Because the copper plating layer does not have sufficient adhesion, while the NdFeB after nickel plating has good adhesion, the adhesion of nickel plating followed by copper plating is improved. Therefore, it is still necessary to plate a layer of nickel to ensure the adhesion of the NdFeB substrate.

[0023] As a preferred embodiment, in step S5.2, the second plating solution is composed of the following components: 35-60 g / L copper pyrophosphate and 240-360 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.2-8.8, the electroplating temperature of copper is 47-53℃, the electroplating current of copper is 20-30A, and the electroplating time of copper is 3600-4800s. Copper plating can result in fewer defects in the coating, no shielding effect on the magnetism of the magnet, good uniformity of plating, low edge effect, and minimal change in the shape of the magnet due to the coating.

[0024] As a preferred option, in step S5.3, the electroplating temperature of the nickel plating surface is 47-53℃, the electroplating current of the nickel plating surface is 18-25A, and the electroplating time of the nickel plating surface is 3600-4800s. This plating design is more conducive to the salt spray corrosion resistance index of NdFeB components meeting customer needs, and can achieve the salt spray index 24 hours after laser engraving.

[0025] As a preferred option, in step S5.4, the third plating solution consists of the following components: a nickel concentration of 4.0-4.8 g / L, a pH value of 4.2-4.8, a chemical nickel plating temperature of 80-86℃, and a chemical nickel plating time of 1800-2400 s. Chemical nickel plating is a process that uses chemical reduction to form a nickel layer on the surface of a substrate without the need for an external current. It forms a relatively thin nickel layer on the surface of the magnet. Compared with electroplated nickel, chemical nickel has higher hardness and excellent wear resistance, ensuring that the characters and QR codes can be clearly identified after laser engraving. Attached Figure Description

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods:

[0027] Figure 1 Box plot of internal hole roughness data for each electroplating process;

[0028] Figure 2(a) shows the appearance of the magnet end face in Example 1;

[0029] Figure 2(b) is a side view of the magnet in Example 1;

[0030] Figure 3(a) shows the appearance of the magnet end face in Example 2;

[0031] Figure 3(b) is a side view of the magnet in Example 2;

[0032] Figure 4(a) shows the appearance of the magnet end face in Example 3;

[0033] Figure 4(b) is a side view of the magnet in Example 3;

[0034] Figure 5(a) shows the appearance of the magnet end face in Example 4;

[0035] Figure 5(b) is a side view of the magnet in Example 4;

[0036] Figure 6(a) shows the appearance of the magnet end face in Example 5;

[0037] Figure 6(b) is a side view of the magnet in Example 5;

[0038] Figure 7(a) shows the appearance of the magnet end face in Example 6;

[0039] Figure 7(b) is a side view of the magnet in Example 6;

[0040] Figure 8(a) shows the appearance of the magnet end face in Example 7;

[0041] Figure 8(b) is a side view of the magnet in Example 7;

[0042] Figure 9(a) is an appearance view of the magnet end face in Example 8;

[0043] Figure 9(b) is a side view of the magnet in Example 8. Specific implementation methods

[0044] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0045] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0046] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0047] In the following embodiments, the magnets are D4.5×D1.4×4.5mm in size, are hollow cylindrical structures with tiny apertures, and have a 56H performance rating.

[0048] Example 1 is a conventional electroplating process.

[0049] Example 1

[0050] As shown in Figures 2(a) and 2(b), a method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets includes the following steps:

[0051] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0052] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0053] S3. Apply a coating to the magnet;

[0054] S3.1. Electroplating nickel base onto the magnet using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The electroplating temperature is 49°C. The electroplating current is 50 A. The electroplating time is 3600 s.

[0055] S3.2. Electroplating copper onto the magnet using a second plating solution, the second plating solution being composed of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate, the pH value of the second plating solution being 8.4, the electroplating temperature of the copper plating being 50°C, the electroplating current of the copper plating being 20 A, and the electroplating time of the copper plating being 4200 s.

[0056] S3.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature is 50°C, the electroplating current is 20A, and the electroplating time is 4800s.

[0057] S3.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.5, electroless nickel plating temperature 82°C, and electroless nickel plating time 2400 s.

[0058] The average roughness of the outer diameter of the magnet after treatment in this embodiment is 0.397 μm, and the average roughness of the inner diameter is 0.463 μm, with no abnormalities in appearance.

[0059] Compared with Example 1, Examples 2 to 5 added the steps of pre-plating nickel on the outer wall of the magnet and chemical roughening on the inner wall. In the examples, the parameters for chamfering, pickling, base nickel plating, copper plating, surface nickel plating, and chemical nickel plating were kept the same. Only the experimental parameters for the pre-plating nickel and chemical roughening steps were varied within the range required by the method of the present invention.

[0060] Example 2

[0061] As shown in Figures 3(a) and 3(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0062] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0063] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0064] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 200 s. The thickness of the outer wall plating layer is approximately 0.3 μm.

[0065] S4. The magnet is pickled and roughened by a roughening solution consisting of 2% nitric acid and 1.5% sulfuric acid, and the roughening time is 30 seconds.

[0066] S5. Apply a coating to the magnet;

[0067] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 49°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0068] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 50°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0069] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 50°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0070] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 83°C, and electroless nickel plating time 2400 s.

[0071] The average roughness of the outer diameter of the magnet after processing in this embodiment is 0.423 μm, and the average roughness of the inner diameter is 0.963 μm, with no abnormalities in appearance.

[0072] Example 3

[0073] As shown in Figures 4(a) and 4(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0074] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0075] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0076] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 200 s. The thickness of the outer wall plating layer is approximately 0.3 μm.

[0077] S4. The magnet is pickled and roughened using a roughening solution, which consists of the following components: 2% nitric acid and 1.5% sulfuric acid. The roughening time is 60 seconds.

[0078] S5. Apply a coating to the magnet;

[0079] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 49°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0080] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 50°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0081] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 50°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0082] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 84°C, and electroless nickel plating time 2400 s.

[0083] The average roughness of the outer diameter of the magnet after treatment in this embodiment is 0.564 μm, the average roughness of the inner diameter is 1.228 μm, and there are no abnormalities in appearance.

[0084] Example 4

[0085] As shown in Figures 5(a) and 5(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0086] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0087] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0088] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 300 s. The thickness of the outer wall plating layer is approximately 0.45 μm.

[0089] S4. The magnet is pickled and roughened by a roughening solution consisting of 2% nitric acid and 1.5% sulfuric acid, and the roughening time is 30 seconds.

[0090] S5. Apply a coating to the magnet;

[0091] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 49°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0092] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 50°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0093] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 51°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0094] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 84°C, and electroless nickel plating time 2400 s.

[0095] The average roughness of the outer diameter of the magnet after treatment in this embodiment is 0.510 μm, and the average roughness of the inner diameter is 0.901 μm, with no abnormalities in appearance.

[0096] Example 5

[0097] As shown in Figures 6(a) and 6(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0098] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0099] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0100] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 300 s. The thickness of the outer wall plating layer is approximately 0.45 μm.

[0101] S4. The magnet is pickled and roughened using a roughening solution, which consists of the following components: 2% nitric acid and 1.5% sulfuric acid. The roughening time is 60 seconds.

[0102] S5. Apply a coating to the magnet;

[0103] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 50°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0104] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 50°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0105] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 51°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0106] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 83°C, and electroless nickel plating time 2400 s.

[0107] The average roughness of the outer diameter of the magnet after processing in this embodiment is 0.551 μm, and the average roughness of the inner diameter is 1.034 μm. There are no abnormalities in appearance.

[0108] Compared with Example 1, Example 6 adds the steps of pre-plating nickel on the outer wall of the magnet and chemical roughening on the inner wall. In the examples, the parameters for chamfering, pickling, base nickel plating, copper plating, surface nickel plating, and chemical nickel plating are kept the same. Compared with Examples 2 to 5, the experimental parameters for pre-plating nickel in Example 6 are varied within the range required by the method of the present invention, while the experimental parameters for chemical roughening are varied beyond the range required by the method of the present invention.

[0109] Example 6

[0110] As shown in Figures 7(a) and 7(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0111] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0112] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0113] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 200 s. The thickness of the outer wall plating layer is approximately 0.3 μm.

[0114] S4. The magnet is pickled and roughened by a roughening solution consisting of 2% nitric acid and 1.5% sulfuric acid, and the roughening time is 90 seconds.

[0115] S5. Apply a coating to the magnet;

[0116] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 50°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0117] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 51°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0118] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 50°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0119] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 83°C, and electroless nickel plating time 2400 s.

[0120] In this embodiment, the average roughness of the outer diameter of the magnet after treatment is 0.636 μm, the average roughness of the inner diameter is 1.556 μm, and white spots appear on the surface.

[0121] Example 7

[0122] As shown in Figures 8(a) and 8(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0123] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0124] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0125] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 300 s. The thickness of the outer wall plating layer is approximately 0.45 μm.

[0126] S4. The magnet is pickled and roughened by a roughening solution consisting of 2% nitric acid and 1.5% sulfuric acid, and the roughening time is 90 seconds.

[0127] S5. Apply a coating to the magnet;

[0128] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 50°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0129] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 50°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0130] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 50°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0131] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 83°C, and electroless nickel plating time 2400 s.

[0132] In this embodiment, the average roughness of the outer diameter of the magnet after treatment is 0.597 μm, the average roughness of the inner diameter is 1.319 μm, and white spots appear on the surface.

[0133] Compared to Example 1, Example 8 adds the steps of pre-plating nickel on the outer wall of the magnet and chemical roughening on the inner wall. In Example 8, the parameters for chamfering, pickling, base nickel plating, copper plating, surface nickel plating, and chemical nickel plating are kept consistent. Compared to Examples 2 to 5, the experimental parameters for the pre-plating nickel and chemical roughening steps in Example 8 are varied beyond the range required by the method of the present invention.

[0134] Example 8

[0135] As shown in Figures 9(a) and 9(b), a method for improving the inner wall roughness of micro-sized NdFeB hollow cylindrical magnets includes the following steps:

[0136] S1. Put in 120kg of grinding stone and 20kg of magnet, grind and chamfer the magnet for 6 hours;

[0137] S2. Pickle the magnet with a 2% nitric acid pickling solution. The pickling weight of the magnet is 4.5 kg, and the pickling time is 200 s.

[0138] S3. The magnet is pre-plated with nickel using a first plating solution. The first plating solution consists of the following components: 300 g / L nickel sulfate, 45 g / L nickel chloride, and 50 g / L boric acid. The pH value of the first plating solution is 4.2. The temperature of the pre-plating is 50°C. The pre-plating is carried out by electroplating. The electroplating current is 50 A. The electroplating time is 400 s. The thickness of the outer wall plating layer is approximately 0.6 μm.

[0139] S4. The magnet is pickled and roughened by a roughening solution consisting of 2% nitric acid and 1.5% sulfuric acid, and the roughening time is 90 seconds.

[0140] S5. Apply a coating to the magnet;

[0141] S5.1. Electroplating nickel base onto the magnet using a first plating solution, wherein the temperature for electroplating the nickel base is 50°C, the electroplating current for electroplating the nickel base is 50A, and the electroplating time for electroplating the nickel base is 3600s.

[0142] S5.2. The magnet is electroplated with copper using a second plating solution, which consists of the following components: 50 g / L copper pyrophosphate and 300 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.4. The electroplating temperature of the copper is 51°C. The electroplating current of the copper is 20 A. The electroplating time of the copper is 4200 s.

[0143] S5.3. Electroplating nickel onto the magnet using the first plating solution, wherein the electroplating temperature of the nickel plating surface is 50°C, the electroplating current of the nickel plating surface is 20A, and the electroplating time of the nickel plating surface is 4800s.

[0144] S5.4. The magnet is electroless nickel plated using a third plating solution, the third plating solution being composed of the following components: nickel concentration 4.4 g / L, pH value 4.4, electroless nickel plating temperature 83°C, and electroless nickel plating time 2400 s.

[0145] The average roughness of the outer diameter of the magnet after treatment in this embodiment is 0.582 μm, the average roughness of the inner diameter is 0.823 μm, and a slight white spot abnormality appears on the surface.

[0146] label Electroplating parameters Mean outer diameter roughness Mean inner diameter roughness Example 1 Conventional electroplating 0.397μm 0.463μm Example 2 Pre-plating nickel for 200 seconds + roughening for 30 seconds 0.423μm 0.963μm Example 3 Pre-plating nickel for 200 seconds + roughening for 60 seconds 0.564μm 1.228μm Example 4 Pre-plating nickel for 300 seconds + roughening for 30 seconds 0.510μm 0.901μm Example 5 Pre-plating nickel for 300 seconds + roughening for 60 seconds 0.551μm 1.034μm Example 6 Pre-plating nickel for 200 seconds + roughening for 90 seconds 0.636μm 1.556μm Example 7 Pre-plating nickel for 300 seconds + roughening for 90 seconds 0.597μm 1.319μm Example 8 Pre-plating nickel 400s + roughening 90s 0.582μm 0.823μm

[0147] The average inner and outer diameter roughness values ​​of the eight sets of embodiments are shown in the table above. Of the eight sets of embodiments described above, Embodiment 1 uses a conventional electroplating process, while Embodiments 2 to 8, compared to Embodiment 1, add pre-plating of nickel on the outer wall of the magnet and chemical roughening steps. A selection of embodiments were chosen for comparison. To eliminate other interfering factors in the experiment, the parameters for chamfering, pickling, base nickel plating, copper plating, surface nickel plating, and chemical nickel plating were kept consistent in all eight sets of embodiments; only the experimental parameters for the pre-plating nickel and chemical roughening steps changed.

[0148] As can be seen from the surface roughness results of the above eight specific embodiments, under conventional nickel plating processes, the surface roughness of the magnet after electroplating is generally within 0.5 μm. However, the technical solution of this patent can significantly improve the inner wall roughness without significantly increasing the outer wall roughness. In Examples 2 to 5, the pre-plating nickel stage uses a current of 45-55 A for 200-300 s, and the chemical roughening stage uses a roughening solution with a concentration of 2%-2.5% nitric acid and 1%-1.5% sulfuric acid for 30-60 s. This can improve the inner wall roughness to Ra 0.8 μm or higher without affecting the appearance and outer wall roughness of the magnet. Examples 6 and 7 extended the roughening time, leading to excessive corrosion of the magnet by the roughening solution, resulting in white spot abnormalities on the magnet's appearance. Example 8 extended the pre-nickel plating time, which resulted in a very thin nickel layer being deposited inside the magnet, thus protecting the grains to some extent. Therefore, even with the extended chemical roughening time, the roughness improvement was not significant. On the contrary, the extended roughening time caused slight white spot abnormalities on the magnet's appearance.

[0149] Depend on Figure 1 As shown, after grinding, chamfering, and pickling, the inner hole roughness of the magnet decreased from 0.558 to 0.515. After pre-plating with nickel, the average inner hole roughness of the magnet was 0.520 μm, which was not significantly different from that before pre-plating. After chemical roughening, the inner hole roughness of the magnet increased significantly to 1.229. After electroplating, the inner hole roughness of the magnet decreased from 1.229 to 1.047. By adding the chemical roughening step, the inner hole roughness of the magnet was improved.

[0150] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above methods. Any non-substantial improvements made using the technical solution of the present invention, or the direct application of the concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets, characterized in that, Includes the following steps: S1. Place the grinding stone and the magnet into the grinding stone and grind the magnet to make it chamfered; S2. Pickling the magnets with pickling solution; S3. The magnet is pre-plated with nickel using the first plating solution, and the thickness of the plating layer on the outer wall of the magnet is controlled to be 0.3-0.45μm; S4. The magnet is chemically roughened by a roughening solution for 30-60 seconds. The roughening solution consists of 2% nitric acid and 1.5% sulfuric acid. S5. Apply a coating to the magnet.

2. The method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 1, characterized in that, In step S1, the amount of grinding stone is 100-150kg, the amount of magnet is 15-25kg, and the grinding time is 4-8 hours.

3. The method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 1, characterized in that, In step S2, the pickling solution is nitric acid with a concentration of 2%-2.5%, the pickling time is 150-240s, and the weight of the magnet is 4-5kg.

4. The method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 1, characterized in that, In step S3, the first plating solution is composed of the following components: nickel sulfate 280-350 g / L, nickel chloride 40-60 g / L, and boric acid 40-60 g / L. The pH value of the first plating solution is 3.8-4.

4. The temperature of the pre-plating nickel is 47-53°C. The pre-plating nickel is carried out by electroplating. The electroplating current of the pre-plating nickel is 45-55 A, and the electroplating time of the pre-plating nickel is 200-300 s.

5. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 1, characterized in that, Step S5 includes: S5.

1. Electroplating the magnet with nickel base using the first plating solution; S5.2, Electroplating copper onto the magnet using a second plating solution; S5.

3. Electroplating nickel onto the magnet using the first plating solution; S5.

4. Electroless nickel plating is performed on the magnet using a third plating solution.

6. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 5, characterized in that, In step S5.1, the temperature for electroplating the base nickel is 47-53℃, the electroplating current for electroplating the base nickel is 45-55A, and the electroplating time for electroplating the base nickel is 2400-3600s.

7. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 5, characterized in that, In step S5.2, the second plating solution is composed of the following components: 35-60 g / L copper pyrophosphate and 240-360 g / L potassium pyrophosphate. The pH value of the second plating solution is 8.2-8.

8. The electroplating temperature of the copper plating is 47-53℃. The electroplating current of the copper plating is 20-30A. The electroplating time of the copper plating is 3600-4800s.

8. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 5, characterized in that, In step S5.3, the electroplating temperature of the nickel plating surface is 47-53℃, the electroplating current of the nickel plating surface is 18-25A, and the electroplating time of the nickel plating surface is 3600-4800s.

9. A method for improving the inner wall roughness of micro-sized neodymium iron boron hollow cylindrical magnets according to claim 5, characterized in that, In step S5.4, the third plating solution is composed of the following components: nickel concentration of 4.0-4.8 g / L, pH value of 4.2-4.8, electroless nickel plating temperature of 80-86℃, and electroless nickel plating time of 1800-2400 s.

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