Electrolytic polishing of stainless steel uses the workpiece to be polished as the anode, the insoluble metal as the cathode, the two poles are immersed in the electrolytic cell at the same time, and the direct current is applied to generate selective anode dissolution, and the surface of the workpiece is gradually leveled, so as to increase the surface brightness of the workpiece. Effect. In actual operation, there are often common problems such as spots in the electrochemical polishing of stainless steel due to various reasons. How to solve it? Here are some common problems and solutions:

The surface of stainless steel is white, black and yellow

⑴The surface is whitish. The whitening of the surface of the parts is mainly caused by the subsequent operation, and the main reason is the drying process in the oven.

The analysis is as follows: the temperature of the parts in the oven is too high, the airflow is not smooth, the air moisture in the oven and the moisture on the surface of the parts cannot be discharged well, and a layer of whitish light blue air is formed on the surface of the parts under high temperature conditions. fog.

In order to improve this problem, the oven temperature should be controlled at 80±2℃, and an oven with a better gas circulation system should be used.

(2) The surface is black. This kind of bad phenomenon mainly occurs in the place where the parts are in contact with the hanger, which is mainly caused by the hanger.

The analysis is as follows: ① EP parts are blackened: when the EP of the last part is completed, the parts need to be removed from the hanger in 10% dilute nitric acid. After the parts are removed, the hanger needs to be cleaned in DI water before continuing. Make the next part; if the hanger is not cleaned or not cleaned, then when the next part is in the EP, the place where the part contacts the hanger will turn black: the nitric acid reacts with the part through an electrochemical reaction during the electrolysis process. Strong corrosion and burns (blackening) occur on the surface of the parts.

Because nitric acid is a strong oxidizing acid, it is highly corrosive to metals such as steel and copper. By means of electrochemical reaction to accelerate the destruction of the surface of the part, in order to avoid such problems, the fixture must be cleaned.

② Blackening of passivation parts: EP is not required, only the surface of parts that need passivation is blackened because the parts are excessively corroded in the passivation acid solution; after long-term passivation of the passivation acid solution, the oxidizing ability will be reduced. At this time, the passivation effect on the parts has been reduced, and the parts will corrode in the acid solution and make the surface black.

Therefore, the passivation acid must be regularly maintained and replaced, and different passivation processes should be selected according to parts of different materials.

⑶ surface yellowing

This kind of bad phenomenon mainly occurs in the place where the part is in contact with the fixture. When the contact area between the part and the anode plate of the hanger is relatively small, the contact point will generate relatively high temperature and heat during EP, and the contact surface will not be in contact with each other. To the electrolytic polishing solution to cool down, so there is a slight burn----yellowing;

Improvement method: mainly by reasonably improving the contacts of the fixture, or adjusting the EP parameters.

There are pits on the surface of stainless steel (over-corrosion points)

At present, the pitting on the surface of the workpiece is the problem of stainless steel electropolishing. This phenomenon is affected by many factors; the more direct factors are: uneven current density distribution, poor gas escape, electrolyte composition deviation.

(1) The flow density distribution is uneven. The main factors are as follows:

① The fixture structure leads to uneven current density distribution when the workpiece is in EP. Improve the fixture structure to make the contact between the fixture and the workpiece more balanced and even, and try to increase the contact area between the fixture and the workpiece under the condition that the fixture print is qualified.

② The specific gravity of the electrolytic polishing solution decreases or exceeds the maximum value. Each electrolyte has a different specific gravity range. If the specific gravity is lower than the smaller value, it means that the water content in the electrolyte increases, and the increase of water is likely to cause pitting; the specific gravity exceeds the minimum value. The maximum value of the required range is likely to cause the current density to be too large locally, the current distribution is uneven, and the workpiece is partially corroded and pitted. The specific gravity of phosphoric acid: 1.70; the specific gravity of concentrated sulfuric acid: 1.84; the specific gravity of water: 1; the reason for the increase of electrolyte moisture: the electrolyte will generate water during the production process, and the fixture will carry part of the water into the tank. Adjust the specific gravity of the electrolyte to the maximum range, and the moisture on the fixture and the workpiece must be dried before EP.

③ If the temperature is too high, the conductivity of the electrolyte can be improved and the surface brightness of the workpiece can be increased, but it is easy to cause uneven current density distribution and pitting. Adjust the temperature to the maximum temperature range.

(2) The workpiece is not cleaned during degreasing and cleaning, and there is oil residue on the workpiece. Pockmarks will appear in the place where there is oil pollution during EP.

⑶ The material problem of the workpiece. Different types of electrolytes should be used for different workpiece materials, but sometimes the grain structure of the post material will also cause the workpiece to appear pitted during the EP process. Try to choose the best material to process the workpiece.

⑷Reworked parts. After the first EP, the parts need to be mechanically polished and thrown back for EP due to some local appearance problems. The workpiece is prone to pitting during the second EP. In order to avoid the second generation of pitting, the second EP must correspondingly reduce the time and current size.

⑸ Gas escape is not smooth. The main reason is that the angle of the fixture on the workpiece is unreasonable, the direction of the hole of the workpiece is as high as possible, and the fixture is adjusted to an appropriate angle, so that the gas generated by the workpiece is easily emitted during EP.

⑹The EP time is too long.

According to the material of the workpiece and the roughness of the surface of the workpiece, the EP time of each workpiece is also different. When the EP of the workpiece reaches the required time, it will stop immediately. Because electrolytic polishing is a microscopic leveling effect, when the surface of the workpiece reaches a microscopic level of brightness, the surface of the part will stop oxidation, resulting in over-corrosion and pitting.

⑺The current is too large. When the part is in EP, if the current passing through the part is too large, the dissolved state of the surface of the part is greater than the oxidation state of the surface of the part, then the surface of the part will be excessively corroded, resulting in corrosion points. Therefore, when the part is in EP, it is necessary to select the appropriate current (according to the material, surface area of the part, and the current density required by the electrolyte).

⑻ The roughness of the front surface of the part EP. The pretreatment process before the EP of the part is very important for the EP, especially the roughness of the hole wall and the surface of the part. For the ideal EP effect, the roughness before EP should be controlled at Ra5-10. between.

Hongchang stainless steel surface treatment material research and development and production, stainless steel pickling passivation paste, stainless steel passivation solution, stainless steel electrolytic polishing solution, copper pickling solution, stainless steel pickling passivation solution, stainless steel pickling passivation agent, Tel: 0550- 7093728 Mobile: 18175233777 Contact: Miss Yang