Discussion on the pretreatment of the hottest magn

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Discussion on several problems of pretreatment of magnetic materials before electroplating

1 Preface

neodymium iron boron magnetic materials are formed by mixing, pressing and sintering the screened ultrafine neodymium, iron and boron powders. According to the requirements of product use, it is machined into different shapes. Due to the active chemical properties of this material, it is easy to be oxidized, so its finished products need to be electroplated and coated. However, the quality of electroplating coating is closely related to its pretreatment. This pretreatment process generally includes degreasing, derusting, activation and other processes. If one part of this pretreatment process is not handled cleanly, it will bring latent defects to the final electroplating product, resulting in blistering, peeling and other problems of the electroplating layer. Defective magnetic material parts will lose market value and be scrapped. Once the magnetic material parts with hidden defects are applied to the equipment, the failure of the whole machine may be caused by the unqualified parts. Even cause serious consequences

2. Treatment process before electroplating of neodymium iron boron magnetic materials

neodymium iron boron magnetic materials are not as dense as wrought metal materials. It is a microporous material. Its porosity brings many difficulties and troubles to the pretreatment of electroplating. In addition to removing the alkaline and acidic substances on the surface of the workpiece and the dirt brought in by the processing process, the biggest difficulty is how to remove the dirt in the micropores

for low-grade magnetic materials with low general requirements, the previous pretreatment process is: alkaline degreasing - water washing - acid pickling (bleaching, neutralization) - water washing - surface activation - electroplating. Although this process is simple, it has high requirements for degreaser, which requires neodymium iron boron special degreaser. The formula of this degreaser is complex, and there are many kinds of raw materials required, so the user's preparation process is very troublesome. And once the ratio is improper, it will be ineffective and less practical

since the advent of high-power ultrasonic cleaning machines in industrial production, this problem has been solved. The unique cavitation effect of ultrasonic cleaning can completely remove the alkaline and acidic substances remaining in the micropores of magnetic materials

after ultrasonic cleaning, The pretreatment process of neodymium iron boron magnetic materials is generally:

(1) alkaline degreasing - water bleaching - water bleaching - ultrasonic fine bleaching - dilute nitric acid treatment (neutralization and bleaching) - water rinsing - water rinsing - ultrasonic fine bleaching - activation treatment - electroplating

(2) alkaline degreasing - water rinsing - water rinsing - ultrasonic fine bleaching - dilute nitric acid (neutralization and bleaching) Treatment - water rinsing - water rinsing - ultrasonic fine bleaching - activation treatment - water rinsing - water rinsing - ultrasonic fine bleaching - electroplating

(3) ultrasonic alkaline degreasing - water rinsing - water rinsing - ultrasonic fine bleaching - dilute nitric acid (neutralization, bleaching) treatment - water rinsing - Ultrasonic fine bleaching - activation treatment - water rinsing - water rinsing - ultrasonic fine bleaching - electroplating

analyze the above three processes, The difference lies in: process (1) is characterized by direct electroplating after activation treatment. And (2) and (3) the two processes further use ultrasonic fine rinsing after activation treatment. The reason for using the first process is that the surface condition of the magnetic material workpiece after activation treatment is the best, which is very suitable for the combination with the electroplated coating. Easy to ensure electroplating quality. The reason for using 2 or 3 processes is that the activation solution is acidic, and the residual acidic substances in the pores of the workpiece must be further removed by ultrasonic cleaning to ensure the electroplating quality

the common point of these processes is that ultrasonic fine rinsing is used after alkaline cleaning and acid cleaning. Process (3) uses up to four ultrasonic cleaning

we recommend qualified enterprises to adopt process (3), especially for high-grade magnetic materials, multi-pass ultrasonic cleaning is more suitable, which can well ensure the quality of electroplating products. Of course, it does not rule out that users choose different cleaning processes according to their own operating habits and product objects

3. Selection of cleaning mode

the placement mode of the workpiece in the cleaning tank has a great relationship with the cleaning quality, and its placement mode is also related to the size, shape and structure of the workpiece. Generally speaking, the overlapping stacking of workpieces or excessive stacking at one time will affect the cleaning effect

Although neodymium iron boron magnetic materials have different shapes, they are mostly small parts. It can be placed on nylon and cleaned by shaking in the cleaning tank, which will help the dirt on the surface of the workpiece fall off, and it is also conducive to the destruction of the water film of the workpiece with blind holes, making it easy to produce cavitation effect in the blind holes. Another placement method is to directly lay the workpiece on the bottom plate of the cleaning tank (that is, the radiation plate of the ultrasonic transducer), so that the workpiece can withstand strong ultrasonic impact. Practice has proved that this method of directly placing the workpiece on the bottom plate for cleaning has the best cleaning effect and the highest efficiency. In order to adapt to this cleaning method, Beijing Jinxing ultrasonic equipment Technology Co., Ltd. specially designed and manufactured a shallow groove flat bottom ultrasonic cleaning machine, which is popular in the magnetic material industry

4. Selection of power density

as we all know, cavitation can only occur when the ultrasonic output reaches a certain intensity. 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 corrosion on the surface of the workpiece. If the power density is too small, the production efficiency is too low, and even the workpiece cleaning quality cannot meet the requirements. Generally, ultrasonic cleaning machines are used in the machining industry, with an area power density of 0.40 ~ 0.8w/cm2 and a volume power density of about 25W/L. The area power density of the special ultrasonic cleaning machine for neodymium iron boron magnetic materials manufactured by Beijing Jinxing ultrasonic equipment Technology Co., Ltd. is about 0.6w/cm2, and the volume power density is about 100W/L

5. Performance characteristics of special cleaning machine for neodymium iron boron magnetic materials

the cleaning of neodymium iron boron magnetic materials has special requirements for the performance of ultrasonic cleaning equipment due to factors such as large batch, long process, harsh environment in electroplating workshop, harsh production conditions and so on. Its technical difficulties lie in:

(1) large load changes. Because the cleaning process depends on manual operation, the number of workpieces put into the tank, the water level and human factors are random, and the load changes are often great. This requires that the ultrasonic cleaning equipment can work stably under variable load, and the cleaning capacity cannot change too much

(2) the cleaning tank is shallow. The shallow cleaning tank is convenient for cleaning operation, but 5. The low liquid level of the guide post deformation compensation algorithm often makes the ultrasonic equipment run with excessive power. Individual operators try to save time and often do not cut off power when draining liquid, so that the equipment operates without liquid in a short time, resulting in excessive vibration amplitude of the steel plate of the cleaning tank, internal stress exceeding the fatigue strength of the material, and micro cracks are generated in the steel plate. Once such micro cracks are generated, under the action of ultrasonic vibration, the cracks will gradually expand and cause the steel plate to crack. In order to avoid this situation, special measures are required in the structural design of the equipment

(3) the acid mist atmosphere and humid environment in the electroplating workshop have a great impact on the equipment. Acid mist and humidity can easily cause corrosion and short circuit of electronic components of ultrasonic equipment

in order to adapt to the cleaning methods and working conditions of neodymium iron boron magnetic materials, more strict requirements are put forward for the structural design, material selection and manufacturing process of ultrasonic cleaning equipment

the following describes the characteristics of the special ultrasonic cleaning machine for neodymium iron boron magnetic materials manufactured by Beijing Jinxing ultrasonic equipment Technology Co., Ltd

5.1 structure of equipment

Beijing Jinxing ultrasonic equipment Technology Co., Ltd. has designed and manufactured an ultrasonic cleaning machine for neodymium iron boron magnetic materials according to the characteristics and needs of users

5.1.1 structural characteristics of the equipment size and external structure

the height of the ultrasonic cleaning machine for neodymium iron boron magnetic materials is 800 mm, which is particularly suitable for manual operation. It can reduce the labor intensity of operators. There are four casters under the equipment, which are flexible and convenient to move, suitable for users to use one machine for multiple purposes. The water outlet is arc-shaped, unobstructed, suitable for small workpieces, which are discharged and blocked with water. The total depth of the cleaning tank is 200mm. It not only saves water, but also facilitates the replacement and discharge of water thickness of ultrasonic transmitting panel

ultrasonic transmitting plate is the bottom plate of cleaning tank. Jinxing ultrasonic equipment Technology Co., Ltd. adopts 3mm stainless steel plate. Its thickness is directly proportional to the cavitation corrosion resistance and service life of the equipment (generally, the bottom plate of the ultrasonic cleaning machine of the self-excited power supply is mostly 1.5mm thick). Venus products can use a thicker bottom plate, thanks to its excellent transducer and generator (power supply) manufacturing technology in its goal of building a core guarantee base for the research, production and production of key materials for national defense and aerospace industry number of ultrasonic heads

the nominal power of the ultrasonic cleaning machine of Jinxing ultrasonic company is not equal to its power capacity. It is named to ensure the maximum use of power by users. Table 1 shows the power capacity of various types of ultrasonic cleaning machines produced by the company

power capacity table of ultrasonic cleaner 1

equipment model nominal power (kw) number of ultrasonic heads * actual power capacity

jxd-10 1.015 1.5

jxd-15 1.5202.0

jxd-20 2.0282.8

jxd-25 2.5323.2

jxd-30 3.0404.0

* each ultrasonic head is 100w

in the process of equipment manufacturing, each ultrasonic head must be strictly screened and tested, Try to ensure the consistency of the performance of multiple ultrasonic heads. The increase of ultrasonic head not only increases the power capacity of the whole machine, but also makes the sound field in the cleaning tank more uniform without blind spots. In addition, the load of each ultrasonic head is left with margin, which will prolong the service life of the equipment power switch:

usually, the power switch of ultrasonic is set on the panel of ultrasonic generator. In order to prevent the ultrasonic generator from being affected by damp and corrosive atmosphere and keep the ultrasonic generator away from the cleaning tank, Jinxing company has configured a long-range waterproof button switch for this special cleaning machine, which is extremely convenient to use

5.1.2 the performance of the special cleaning machine is really positive. 1 key operation characteristics: ultrasonic generator power supply:

the ultrasonic generator produced by Jinxing company adopts the internationally advanced high-power IGBT module, which belongs to "other excitation" power supply. The so-called "alternative excitation" means that the ultrasonic generator has a complete and independent drive control circuit and protection system. Suitable for long-time continuous work, high stability and reliability ultrasonic head bonding material:

Jinxing company adopts imported high-quality metal glue as the adhesive of ultrasonic head. With good bonding process and transducer manufacturing process, the ultrasonic head will never fall off under normal use conditions, thus ensuring the long-term use of the equipment frequency sweeping device

generally, the frequency of ultrasonic cleaning machine belongs to a fixed value, such as 20khz 28KHz. 33khz, etc. The ultrasonic cleaning machine produced by Jinxing also adds a frequency sweeping device

the advantages of adding frequency sweeping device are:

(1) the working frequency of the transducer is not fixed, but changes within a certain frequency range, which increases the uniformity of the sound field and is conducive to the improvement of the cleaning force. The "dead point" was not cleaned

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