Electrophoresis

The electrophoretic coating is to immerse the parts in a water-soluble electrophoresis bath, insert the anode and cathode electrodes into the bath at the same time, and apply a direct current between the two electrodes to produce an electrochemical reaction, so that the water-soluble paint is evenly deposited on the parts, forming an anti-corrosion coating composed of resin particles, or a high-molecular polymer anti-corrosion layer.

Electrophoretic coating not only has good bonding force with porous magnet surface, but also has corrosion resistance such as salt spray, acid, and alkali resistance. 

Compared with spray coating, it has the following advantages:

1. High coating utilization rate. During the spraying process, a large amount of spray paint is scattered, and about half of the paint is lost. However, the use of ultrafiltration technology in electrophoretic coating can make the paint utilization rate reach 90%-95%.

2. Electrophoretic paint is water-soluble paint, no organic solvent is needed, energy and raw materials are saved, and environmental pollution is reduced.

3. High production efficiency. After pretreatment, the bonded magnet parts can be electrophoresed directly without drying, shortening the coating time.

4. Good coating effect for complex parts. Electrophoretic coating relies on the distribution of the electric field in the electrophoresis bath for electrodeposition. Since the deposited coating film is insulating, a uniform coating can be formed on all parts of the part.

5. The coating quality is good, the corrosion resistance is strong, and the bonding force is good.

Electrophoretic coating also has disadvantages:

1. The one-time investment cost is high, the maintenance and management of the electrophoresis bath is complicated, and various process parameters need to be carefully controlled.

2. Electrophoretic coating cannot cover up the defects of the magnet surface, such as cavities, scratches, dents, etc., so the surface conditions of the product are relatively high.

3. Hooking and unhooking require more manual labor.

Classification of electrophoretic coating

Put the electrophoretic paint in the electrophoresis tank, including polymer resin, organic solvent, color suspended particles and water, etc., and stir them to form a uniform solution.

Electrophoretic coating has two types: anode coating and cathode coating. Anodic electrophoresis uses a sintered NdFeB magnet as the anode. In this way, the base metal and surface treatment film (such as phosphating film) are precipitated and dissolved at the same time during the electrophoresis process, which reduces the corrosion resistance of the electrophoretic deposited film. Therefore, in most cases Cathodic electrophoresis is used, that is, sintered NdFeB is used as the cathode, and cationic electrophoretic paint is used. This paint is a water-soluble coating formed by neutralizing synthetic resins containing amino groups with organic acids.

The cathodic electrophoresis layer uses organic acid as a neutralizer, which has low toxicity. The mechanical strength of the wet paint film itself and the bonding force with the workpiece are higher than that of the anode electrophoretic coating. However, the cost of cathodic electrophoretic coating is high, and the electrophoresis bath is acidic, which has a corrosive effect on equipment. The cathodic electrophoresis tank should be made of corrosion-resistant materials, such as stainless steel or acid-resistant plastics.

The process flow of electrophoretic coating is mainly divided into three parts: surface pretreatment, electrophoresis and drying and curing.

Smooth and clean surface is the basis of high-quality electrophoretic coating, and the purpose of surface treatment is to create good surface conditions. The electrophoretic coating process is a complex chemical change process. As the coating is continuously deposited on the surface of the magnet, the composition of the electrophoresis tank is constantly changing. The solid components, the pH value of the electrophoresis tank, temperature, electrophoresis voltage, Electrode spacing, etc.