The variety of surface processing of stainless steel broadens its application field - different surface processing makes the surface of stainless steel different, making it unique in application. Surface finishing of stainless steel is important for many reasons in architectural applications.
Corrosive environments require smooth surfaces because smooth surfaces are not prone to fouling. The deposition of dirt will rust or even cause corrosion of stainless steel.
1. The natural look of stainless steel
Stainless steel has a natural solid and radiant feel, and its natural color softly reflects the color of the surrounding environment.
2. Basic types of surface processing of stainless steel pipes
There are roughly five types of surface processing that can be used for stainless steel, and they can be combined to transform more final products. The five types are rolling surface processing, mechanical surface processing, chemical surface processing, textured surface processing, and color surface processing. There are also some dedicated surface finishes.
3. Standard Surface Finishes for Stainless Steel Tubes
Many kinds of surface finishing have been represented by numbers or other classification methods, and they have been compiled into relevant standards, such as: "British Standard BS1449" and "American Iron and Steel Institute Stainless Steel Producers Committee Standard".
4. Rolling surface processing of stainless steel tubes
There are three basic rolling surface finishes for plates and strips, which are represented by the production process of plates and strips.
No.1: After hot rolling, annealing, pickling, and descaling. The surface of the treated steel plate is dull, somewhat rough.
No.2D: Better surface finish than N0.1, but also dull surface. After cold rolling, annealing, descaling, and finally light rolling with rough surface rollers.
No.2B: This is the most commonly used in architectural applications. Except for the last light cold rolling with polishing rolls after annealing and descaling, the other processes are the same as 2D. The surface is slightly shiny and can be polished.
No.2B Bright Annealed: This is a reflective finish that is polished roll rolled and finally annealed in a controlled atmosphere. Bright annealing still maintains its reflective surface and does not produce scale.
Since no oxidation reaction occurs during the bright annealing process, no pickling and passivation treatment is required.
5. Polished surface processing of stainless steel tubes
No.3: represented by 3A and 3B.
3A: The surface is uniformly ground, and the abrasive grain size is 80~100.
3B: The rough surface is polished, and the surface has uniform straight lines. It is usually polished once on the 2A or 2B board with an abrasive belt with a particle size of 180~200.
No.4: Unidirectional surface finish, not very reflective, this finish is probably the most versatile in architectural applications. The process steps are firstly polished with coarse abrasives and finally ground with abrasives with a particle size of 180.
No.6: It is a further improvement on No.4, which is to polish No. with Tampico polishing brush in abrasive and oil medium. 4 surfaces. This surface finish is not included in "British Standard 1449", but can be found in the American Standard.
No.7: It is called bright polishing, which is to polish the surface that has been ground very finely but still has wear marks. Usually, 2A or 2B boards are used, with fiber or cloth polishing wheels and corresponding polishing pastes.
No.8: Mirror polished surface with high reflectivity, usually called mirror surface processing, because the reflected image is very clear. Continuous polishing of stainless steel with fine abrasives followed by very fine polishing pastes. In architectural applications, it should be noted that if this surface is used in a place with a large flow of people or where people often touch it, it will leave fingerprints. Of course, fingerprints can be wiped off, but sometimes it affects the appearance. Surface finishes described in "official" standards and literature are only general introductions, and samples are the most intuitive representation of the type of surface finish. Polishing or metal finishing manufacturers will provide samples of various surface finishes and users should discuss them with them.
6. Surface roughness of stainless steel pipe
The classification of rolled surface finish and polished surface finish is to describe the degree that can be achieved. Another effective way of expressing it is to measure the surface roughness. The standard method of measurement is called CLA (Center Line Average), where the gage is moved across the surface of the steel plate, recording the magnitude of the peaks and valleys. The lower the number of CLA, the smoother the surface. The results of the different grades can be seen from the surface finishes and CLA numbers in the table below.
7. Mechanical Polishing of Stainless Steel Tubes
A word of caution: We should remember that grinding with sandpaper or belts in grinding operations is essentially a buff-cutting operation, leaving very fine lines on the surface of the steel plate. We have had trouble with 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. To ensure the consistency of the surface finish, the new grinding wheel or abrasive belt should be tried on the scrap of the same composition first, so that the same sample can be compared.
8. Electrolytic Polishing of Stainless Steel Tubes
This is a metal removal process in which stainless steel acts as the anode in the electrolyte and the metal is removed from the surface when energized. The process is often used on components whose shapes are difficult to polish using 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, electropolishing will make the surface impurities more obvious, especially titanium and niobium-stabilized materials will cause differences in the weld zone due to granular impurities. Small weld scars and sharp edges can be removed by this process. The process focuses on protruding parts of the surface, preferentially dissolving them. The electropolishing process involves immersing stainless steel in a heated liquid, and the ratio of the liquid involves many proprietary technologies and patented technologies. Electropolishing works well for austenitic stainless steel.
9. Textured surface processing of stainless steel pipe
Many types of patterns can be used in stainless steel. The advantages of adding a pattern or textured surface 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 large-area decorative panels, even after stretching or tension straightening, it is difficult to make the surface completely straight, so there will be shrinkage of metal roofing materials.
②The mesh pattern can reduce the glare emitted in the sun.