Surface processing of stainless steel

6. Surface roughness

The classification of rolled surface processing and polished surface processing is an indication of the degree that can be achieved, and another effective way to express it is to measure surface roughness. The standard measurement method is called CLA (Centerline Average). The measuring instrument moves laterally on the surface of the steel plate to record the peak and valley changes. The smaller the CLA number, the smoother the surface. The final results of different grades can be seen from the surface finish and CLA number in the table below.

Surface finish CLA, micron

2B 0.1-0.5

2A 0.05-0.1

2D 0.4-1.0

3 0.4-1.5

4 0.2-1.5

8 0.2

1/2 of EP basic value

EP=Electropolishing, which can roughly reduce the range of peak and valley changes to 1/2 of the original surface.

7. Mechanical polishing

Precautions:

We should remember that the grinding with sandpaper or belt in the grinding operation is basically a polishing and cutting operation, leaving very fine lines on the surface of the steel plate.

We have had trouble using alumina as an abrasive, partly because of pressure issues.

Any grinding parts of the equipment, such as abrasive belts and grinding wheels, must not be used for other non-stainless steel materials before use. Because this will contaminate the stainless steel surface.

In order to ensure the consistency of surface processing, new grinding wheels or belts should be tried on waste materials with the same composition first, so that the same products can be compared.

8. Electrolytic polishing

This is a metal removal process, in which stainless steel is used as the anode in the electrolyte, and the metal is removed from the surface after power is applied.

This process is usually used for the processing of parts, because their shape is difficult to polish with traditional methods.

This process is often used on the surface of cold-rolled steel sheets because the surface is smoother than that of hot-rolled steel sheets.

However, electrolytic polishing will make the surface impurities more obvious, especially the titanium and niobium stabilized materials will cause differences in the weld zone due to particulate impurities.

Small weld scars and sharp edges can be removed by this process. This process focuses on the protruding parts on the surface and preferentially dissolves them.

The electrolytic polishing process involves immersing stainless steel in a heated liquid. The ratio of the liquid involves many proprietary and patented technologies.

The electrolytic polishing effect of austenitic stainless steel is very good.

9. Textured surface processing

There are many types of patterns that can be used in stainless steel.

The advantages of adding patterns or netting surface processing to the steel plate are as follows:

①Reduce “oil can-ning”, which is a term used to describe the surface of bright materials, which is not flat from an optical point of view. For example, for large-area decorative panels, even after stretching straightening or tension straightening, it is difficult to make the surface completely flat, and thus the metal roofing material will shrink.

②The net pattern can reduce the glare in the sun.

③If the tread plate has slight scratches and small area indentations, it is not obvious.

④Increase the strength of the steel plate.

⑤Provides a choice for architects.

Patented patterns include cloth patterns (used in Ed Building in London), inlay patterns, pearl patterns and leather patterns. Wave and line patterns can also be used.

The patterned surface is particularly suitable for interior decoration, such as elevator panels, counters, wall panels and entrances.

In external applications, consideration should be given to enabling the stainless steel to be cleaned by rain and manual washing to avoid dead spots where dirt and airborne impurities are easy to gather, so as not to cause corrosion and affect the appearance.

10. Rough surface processing

The rough surface processing is one of the most commonly used surface processing. It is polished with a nylon abrasive belt or brush on the surface of the polished or bright annealed steel plate.

11. Spray glass balls or shot peening

For internal applications, such as the interior of elevators, mixed surface processing is very popular.

This mixing process is to form a matte surface by spraying glass balls, and then through a masking treatment, covering with a plastic film, processing into a polished surface, and finally forming a polished and matte mixed surface.

Stainless steel sand shots can also be used in similar processes.

The glass balls or pellets to be used must not be used on other materials in advance, especially on carbon steel. Because carbon steel particles will be embedded in the surface of stainless steel, it is easy to cause corrosion.

Ceramic balls can also be used as spray materials.