During the polishing process of stainless steel, if stainless steel surface pits or polishing defects appear, it may affect the appearance and performance of the product. For such quality objections, it is very important to deal with them promptly and find out the root cause. The following is an analysis of the common causes and solutions for dealing with stainless steel polishing pits to help improve product quality.
Case Overview:
The customer complained that the surface of the purchased batch of stainless steel coils was slightly pitted during polishing.
Case Study:
By checking first, the batch of stainless steel is made of 304 material with 2B surface with a thickness of 1.0mm, all of which are first-class materials of regular large steel plants.
No surface defects can be observed on the surface of the raw material, and there are slight pits on the polished workpiece, which are densely distributed.
After sampling and analysis, the pits are irregular in shape, mainly long strips, and the size of the pits is relatively small. Through chemical analysis, Fe, Cr, and O are the main elements in the composition.
According to preliminary judgment, the possible reason for the defects is that the oxide scale produced during the annealing process is relatively thick, and there are tiny residues during the pickling process.
After the SPM leveling process, the inspectors cannot detect it with the naked eye during the finishing process but are exposed during the grinding and polishing process, forming pitting defects.
Process Result:
Minor Pit Treatment:
Use finer-grained sandpaper for secondary polishing and apply the polishing paste to improve the gloss.
Appropriately reduce the polishing pressure to ensure a uniform surface.
Severe Pit Treatment:
If the defect is deep, it needs to be repaired by local grinding and then re-polished.
If stainless steel polishing cannot be repaired it, it is recommended to replace the material or rework.
Common Causes of Pits on the Polished Surface of Stainless Steel
Raw material defects
There are tiny holes, inclusions, or flaws on the surface of the material itself, and the defects are exposed after polishing.
Solution: Strictly select high-quality stainless steel raw materials to ensure that the materials meet the standards.
Perform surface inspection and testing before the materials are put into storage.
Improper Mechanical Polishing Parameters
Polishing pressure is too high or the time is too long, resulting in uneven surface wear and pits.
Solution: Adjust the polishing machine parameters to avoid excessive polishing.
Use grinding wheels or polishing pastes of different particle sizes in stages and polish gradually.
Poor Maintenance of Polishing Equipment
Grinding wheels or polishing discs are severely worn and the surface is uneven, causing polishing pits.
Solution: Regularly check and replace consumable parts in polishing equipment.
Ensure the surface of the equipment is flat to avoid uneven friction on the workpiece.
Process Environment Problems
There are impurities or dust on the surface of the workpiece during polishing, resulting in uneven local force.
Solution: Keep the polishing environment clean to avoid dust and impurities from contaminating the workpiece.
Clean the surface before polishing to ensure that there is no oil or impurities.
Improper Control of Electrolytic or Chemical Polishing Process
Uneven current density during electrolytic polishing causes excessive dissolution in some areas.
Solution: Adjust current density to ensure uniform surface treatment.
Control chemical polishing time to avoid excessive corrosion of the workpiece surface.
The appearance of pits on the polished surface of stainless steel may be caused by many reasons, such as material problems, improper process parameter control or poor equipment maintenance. When dealing with customer quality objections, timely investigation and good communication with customers should be maintained, and effective remedial measures and preventive measures should be taken to ensure the stability of subsequent product quality.
If you have more stainless steel product polishing or quality issues, please contact us at Huaxiao Metal. We will wholeheartedly provide you with professional solutions and technical support!