Quality objection case: color difference on the stainless steel surface

Case Overview:

The customer complained that the batch of stainless steel slit coils he purchased had color differences, which had a great impact on the use.

Case Study:

It is understood that the width of this batch of strip coils varies from about 200mm, and is made of 304 material. The color difference complained by customers does exist and is relatively obvious. It is longitudinally continuous and dark, distributed on the upper surface of the steel coil. 4 out of 10 small coils There are chromatic aberrations on the surface, the width of the chromatic aberration ranges from 3mm to 10mm, and the chromatic aberration position of each small roll is different.

The customers of this batch of sub-rolls are flattened and cut into small plates of various sizes. After shearing and bending, they are made into various shells. Therefore, the surface requirements are higher. Therefore, the color difference on the material is judged as unqualified raw material and required to be returned.

Check the separate processing records, the record is that the surface of the raw materials is of good quality and has no defects, so it can basically be judged as caused during the processing.

Such dark-colored longitudinal defects cannot be erased. After inspection, they are not caused by oil pollutants. According to the traces, it can be basically judged that the processing equipment and the steel coil are caused by non-rolling direct contact.

Considering that the non-direct contact between the processing equipment and the upper surface of the steel coil is only on the side of the tension belt that establishes tension.
Check the processing records of the day, the wool felt was used when processing this batch of materials.

After inspection, the wool felt has been used for too long and accumulated a large number of stains, the surface is gray-black, and the friction with the steel plate generates heat and causes balling.

These nodules are hard and leave continuous dark-colored friction marks on the surface of stainless steel under high pressure and high friction temperature.

Process Result:

To find out the source of the problem, it was immediately required to strengthen the management of the use of wool felt. For the used wool felt, brushes were used to remove all kinds of attached dust and balls, and the unusable wool felt was scrapped.

It is required to strengthen the inspection of the winding position and impose penalties on the inadequate inspection of the winding operator.

Stainless steel, especially cold-rolled stainless steel, is different from other materials in that it has higher surface requirements. Many stainless steels are used for decorative materials or materials with high surface requirements. Therefore, inspection and protection of stainless steel surfaces are one of the first considerations for machining centers.

In the process of processing, we must intensify inspections, do not let the raw material defects pass, and do not create secondary defects to ensure that the quality of materials can meet customer requirements.

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