What Is Electrophoresis?
Electrophoretic coating is one of the widely used anti-corrosion surface treatment technologies for sintered NdFeB and bonded NdFeB permanent magnets. It is to immerse the parts in a water-soluble electrophoretic tank, insert the positive electrode and the negative electrode in the tank at the same time, and pass a direct current between the two poles to produce an electrochemical reaction so that the water-soluble coating is evenly deposited on the parts to form an anti-corrosion coating composed of resin particles, or to form an anti-corrosion layer of a polymer.
Electrophoretic coating not only has a good bonding force with the surface of porous magnets, but also has corrosion resistance to salt spray, acid and alkali, etc., and excellent anti-corrosion performance, but poor resistance to moisture and heat. Compared with spray coating, it has the following advantages:
1 High coating utilization rate. During spraying, a large amount of spray paint is scattered, and about half of the paint is lost. After the ultrafiltration technology is used in electrophoretic coating, the coating utilization rate can reach 90%-95%.
2 Electrophoretic paint is a water-soluble paint, that does not require organic solvents, saves energy and raw materials, and reduces pollution to the environment
3 High production efficiency. After pretreatment, bonded magnet parts can be electrophoresed directly without drying, shortening the coating time.
4 The coating effect is good for complex parts. During electrophoretic coating, the electric field distribution in the electrophoretic tank liquid is used for electrodeposition. Since the deposited coating film has insulation, a uniform coating can be formed on all parts.
5 The coating quality is good, corrosion resistance is strong, and bonding strength is good.
Electrophoretic coating also has shortcomings:
1 The one-time investment cost is high, the maintenance and management of the electrophoretic tank liquid is complicated, and each process parameter needs to be carefully controlled
2 The electrophoretic coating cannot cover the defects on the surface of the magnet, such as cavities, scratches, depressions, etc., so the surface conditions of the product are required to be high 3 Hooking and unhooking require more manual labor
Classification Of Electrophoretic Coating
Put the electrophoretic coating in the electrophoretic tank, including polymer resin, organic solvent, color-suspended particles, and water, and stir them to form a uniform solution.
There are two types of electrophoretic coating: anodic coating and cathodic coating. Anodic electrophoresis uses sintered NdFeB magnets as anodes. In this method, the base metal and surface treatment film (such as phosphating film) are simultaneously precipitated and dissolved during the electrophoresis process, which reduces the corrosion resistance of the electrophoretically deposited film. Therefore, cathodic electrophoresis is used in most cases, 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 an amino-containing synthetic resin with an organic acid. The cathode electrophoretic layer uses organic acid as a neutralizer and has low toxicity. The mechanical strength of the wet paint film itself and the bonding force with the workpiece are higher than those of the anodic electrophoretic coating.
However, the cost of the cathode electrophoretic coating is high, and the electrophoretic tank liquid is acidic, which has a corrosive effect on the equipment. The cathode electrophoretic tank should be made of corrosion-resistant materials, such as stainless steel or acid-resistant plastics.