Electrophoretic surface treatment of sintered NdFeB (classify technological process)
In the previous introduction of NdFeB surface treatment, the introduction of electrophoresis is less. Today, we will introduce the classification and process flow of sintered NdFeB surface treatment.
Classification of electrophoretic coatings
There are two kinds of electrophoretic coating: anode coating and cathode coating. In anode electrophoresis, sintered NdFeB magnet is used as anode. In this way, the base metal and surface treatment film (such as phosphating film) are precipitated and dissolved at the same time during electrophoresis, which reduces the corrosion resistance of Electrodeposited film. Therefore, in most cases, cathode electrophoresis is used, that is, sintered NdFeB is used as cathode, and cation type electrodeposition paint is used. The paint is a water-soluble coating made of organic acid and synthetic resin containing amino group.
Organic acid is used as neutralizer in cathodic electrophoresis layer, which is less toxic. The mechanical strength of the wet film and its adhesion to the workpiece are higher than that of the anode electrophoretic coating. However, the cost of cathodic electrophoretic coating is high, and the bath solution is acidic, which has corrosive effect on the equipment. The cathode electrophoresis tank shall be made of corrosion-resistant materials, such as stainless steel or acid resistant plastic.
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Process flow of sintered NdFeB electrophoretic coating
The process flow of electrophoretic coating is as follows, which is mainly divided into three parts: surface pretreatment, electrophoresis and dry curing. The specific process flow is roughcast - degreasing - water washing - pore sealing treatment - water washing - phosphating - water washing - electrophoresis - water washing - dry curing.
The smooth and clean surface is the basis of high quality electrophoretic coating. The purpose of surface treatment is to create good surface conditions. The process of electrophoretic coating is a complex chemical change process. With the continuous deposition of coating onto the surface of magnet, the composition of electrophoretic bath also changes constantly. It is necessary to strictly control the solid component, pH value, temperature, electrophoretic voltage, electrode spacing, etc.