Several problems should be noticed before NdFeB permanent magnet plating

- Nov 21, 2017 -

1. Introduction

Neodymium - iron - boron magnetic material is the sieved neodymium, iron, boron ultrafine powder after mixing, pressing and sintering. According to product requirements, machining into different shapes. Due to the chemical nature of this material is more lively, easily oxidized, so the finished product needs electroplating coating process. However, the quality of the electroplated coating is closely related to its pretreatment. This pretreatment process generally includes degreasing, rust, activation and other processes. If such a pre-treatment process has not been a part of clean, will give the final plating products lurking defects, resulting in plating appear blistering, peeling and other issues arise. Defective parts of magnetic materials lose their market value and be scrapped. If a magnetic material with concealed defects once applied to the device, may be due to the failure of the machine parts on the machine caused by failure. Even have serious consequences.

2, neodymium - iron - boron magnetic material before the plating process

Neodymium-iron-boron magnetic materials are not as dense as forged metal materials. Is a microporous material. Its porosity brings many difficulties and troubles to the pre-plating process. In addition to removing alkaline, acidic materials and contaminants from the process, the biggest challenge is how to remove the dirt from the micropores.

For the less demanding low-grade magnetic materials, the pre-treatment processes used in the past are: Alkaline degreasing-washing-pickling (bleaching, neutralization) -washing-surface activation-plating. This process is simple, but it requires a higher degreasing agent, the need for neodymium - iron - boron dedicated degreasing agent, degreasing degreasing agent to the complex formula, the types of raw materials needed, the user preparation process is very trouble. And once the ratio is not appropriate, it will lapse, less practical.

Since the advent of high-power ultrasonic cleaner in industrial production, this problem will be solved. The unique cavitation effect of ultrasonic cleaning can make the alkaline and acidic substances remaining in the micropores of magnetic material get more thorough removal.

After ultrasonic cleaning, neodymium - iron - boron magnetic material pretreatment process is generally:

(1) Alkaline Degreasing - Water Bleaching - Water Bleaching - Ultrasonic Bleaching - Dilute Nitric Acid Treatment (Neutralization, Bleach) - Water Rinsing - Water Rinsing - Ultrasonic Bleaching - Activation - Plating

(2) Alkaline Degreasing - Water Rinsing - Water Rinsing - Ultrasonic Bleaching - Dilute Nitric Acid (Neutralizing and Bleaching) - Water Rinsing - Water Rinsing - Ultrasonic Bleaching - Activation - Water Rinsing - Water Rinsing - Ultrasonic Rinsing - plating

(3) ultrasonic alkaline degreasing - water rinsing - water rinsing - ultrasonic finishing - dilute nitric acid (neutralization, bleaching) treatment - water rinsing - water rinsing - ultrasonic finishing - activation treatment - water rinsing - water rinsing - ultrasonic finishing -plating

Analysis of the above three kinds of processes, the difference is that: Process (1) is characterized by: direct activation after plating. And (2)

(3) The two processes are further activated by ultrasonic cleaning after activation. The reason for using the first process is that the surface condition of the magnetic material after the activation treatment is the best and is suitable for the bonding with the plating layer. Easy to ensure the quality of plating. The reason for using 2,3 kinds of processes is that the activation solution is acidic, the residual acid in the workpiece micropores must be further removed by ultrasonic cleaning to ensure the quality of the plating.

Common to all these processes is the use of ultrasonic rinsing after basic and acidic cleaning, while process (3) uses up to four ultrasonic cleaning.

Recommended conditions for the use of technology companies (3), especially for high-grade magnetic materials with multi-pass ultrasonic cleaning more appropriate, it can well ensure the quality of electroplating products. Of course, this does not rule out the user according to their own operating habits and product targets choose a different cleaning process.

3, the choice of cleaning methods

Workpieces in the cleaning tank placed in the way and cleaning quality has a great relationship, and its placement and the workpiece size, shape, structure. In general, overlapping stacking of workpieces, or stacking too much at one time, can affect cleaning performance.

Neodymium - iron - boron magnetic materials, although different shapes, but mostly belong to small parts. It can be placed on a nylon net and cleaned in the cleaning tank. This will help to remove dirt on the surface of the workpiece and damage the water film with blind hole workpieces, which will easily cause cavitation in the blind hole. Another way is to place the workpiece directly on the tank floor (ie, ultrasonic transducer radiation plate), so that the workpiece to withstand a strong ultrasonic impact. Practice has proved that this directly on the workpiece on the floor cleaning method, the best cleaning effect, the highest efficiency.

4, the choice of power density

As we all know, ultrasonic output reaches a certain intensity can produce cavitation. Generally, the lowest power density in water should be greater than 0.3W / cm2. However, if the power density is too high and the cleaning ability is improved, it may cause mechanical damage or cavitation erosion on the surface of the workpiece. If the power density is too low, the production efficiency is too low, or even the quality of the workpiece cleaning can not meet the requirements. General mechanical processing industry with ultrasonic cleaning machine, the surface power density of 0.40 ~ 0.8W / cm2, body power density of 25W / L or so.

5, neodymium - iron - boron magnetic materials for cleaning machine performance characteristics

Neodymium - iron - boron magnetic material cleaning due to large quantities, the process of long, poor environment electroplating workshop, harsh production conditions and other factors, the performance of ultrasonic cleaning equipment require extraordinary mechanical processing industry used. The technical difficulties are:

(1) The load changes greatly. As the cleaning process by manual operation, into the tank number of the workpiece, the level of water, human factors greater randomness, the load changes are often very large. This requires ultrasonic cleaning equipment in variable load can also work stably, cleaning capacity changes can not be too large.

(2) cleaning tank shallow. Cleaning tank shallow easy to clean operation, but the low level of the ultrasonic equipment often makes the operation of large power. Individual operators tend to save energy when the discharge is not interrupted, so that equipment in a short period of no liquid run, resulting in cleaning tank plate amplitude is too large, the internal stress exceeds the fatigue strength of the material, resulting in micro-cracks in the interior of the plate, this micro-crack Once generated, under the action of ultrasonic vibration, the crack will be gradually expanded to crack the steel plate. To prevent this from happening, equipment is required to take special measures in structural design.

(3) electroplating workshop acid mist and humid environment on the impact of large equipment. Acid mist and moisture can easily erode and short-circuit ultrasonic device electronics.

In order to meet the neodymium - iron - boron magnetic materials cleaning methods and working conditions, which on the ultrasonic cleaning equipment in the structural design, material selection, manufacturing processes put forward more stringent requirements.

Article from NdFeB Industry Network

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