Process and Issue of Treatment to Magnet Material before Coating
The bismuth-iron-boron magnetic material is obtained by mixing, pressing and sintering the ultrafine powder of bismuth, iron and boron after sieving. Machined into different shapes according to product application requirements. Because the material is chemically active and easily "oxidized", its finished product needs to be electroplated. However, the quality of the electroplating coating is closely related to its pretreatment. This pretreatment process generally includes processes such as degreasing, rust removal, and activation. If such a pre-treatment process is not cleaned in a way, it will bring latent defects to the final electroplating product, causing problems such as foaming and peeling of the plating layer. Defective magnetic material parts will lose their marketing value and be scrapped. If a magnetic material part with a concealed defect is applied to the equipment, it may cause the whole machine to malfunction due to the failure of the unqualified part. Even serious consequences.
Treatment process of bismuth-iron-boron magnetic material before electroplating
Niobium-iron-boron magnetic materials are not as dense as forged metal materials. It is a microporous material. Its porosity brings many difficulties and troubles to the pre-plating treatment. In addition to removing the alkaline, acidic substances and dirt from the surface of the workpiece, the biggest difficulty is how to remove the dirt from the micropores.
For low-grade magnetic materials that are generally not demanding, the pre-treatment processes used in the past are: alkaline degreasing - water washing - pickling (bleaching, neutralization) - water washing - surface activation - electroplating. Although the process is simple, it has high requirements for degreasing agents, and it requires a degreasing and degreasing agent for strontium-iron-boron. This degreasing and degreasing agent has a complicated formula and requires many kinds of raw materials. The user preparation process is very trouble. And once the ratio is improper, it will fail and the utility will be poor.
This problem has been solved since the advent of high-power ultrasonic cleaners in industrial production. The unique cavitation effect of ultrasonic cleaning enables the alkaline and acidic substances remaining in the micropores of magnetic materials to be completely removed.
After ultrasonic cleaning, the pretreatment process of the bismuth-iron-boron magnetic material is generally:
(1) Alkaline degreasing - water bleaching - water bleaching - ultrasonic fine bleaching - dilute nitric acid treatment (neutralization, 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, bleaching) treatment - water rinsing - water rinsing - ultrasonic fine bleaching - activation treatment - water rinsing - water rinsing - ultrasonic fine bleaching - plating
(3) Ultrasonic alkaline degreasing - water rinsing - water rinsing - ultrasonic fine bleaching - dilute nitric acid (neutralization, bleaching) treatment - water rinsing - water rinsing - ultrasonic fine bleaching - activation treatment - water rinsing - water rinsing - ultrasonic fine bleaching -plating
The above three processes are analyzed, and the difference is that the process (1) is characterized by direct electroplating after activation treatment. However, the two processes (2) and (3) were further subjected to ultrasonic fine rinsing after the activation treatment. The reason for using the first process is that the surface condition of the magnetic material workpiece after the activation treatment is optimal and is suitable for combination with the plating layer. It is easy to guarantee the quality of plating. The reason for using 2 or 3 processes is that the activation solution is acidic, and the residual acidic substances in the micropores of the workpiece must be further removed by ultrasonic cleaning to ensure the plating quality.
Common to these processes is the use of ultrasonic fine rinses after alkaline and acid cleaning, and the process (3) uses up to four ultrasonic cleanings.
We recommend qualified companies to adopt the process (3), especially for multi-grade ultrasonic cleaning of high-grade magnetic materials, which can guarantee the quality of electroplating products. Of course, it is not excluded here that the user selects different cleaning processes according to his own operating habits and product objects.
Choice of cleaning method
The placement of the workpiece in the cleaning tank has a great relationship with the cleaning quality, and its placement is related to the size, shape and structure of the workpiece. In general, overlapping stacks between workpieces, or too many stacks at a time, can affect the cleaning effect.
Although the Nd-Fe-B magnetic materials vary in shape, they are mostly small parts. It can be placed on the nylon mesh and shaken in the cleaning tank, which helps the dirt on the surface of the workpiece to fall off, and is also conducive to the destruction of the water film with the blind hole workpiece, which makes the cavitation effect easy in the blind hole. Another way of placing the workpiece is to directly level the workpiece on the bottom of the cleaning tank (that is, the ultrasonic transducer radiant panel) to subject the workpiece to strong ultrasonic shock. 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 type ultrasonic cleaning machine, which is favored by the magnetic material industry.