Regarding the Polishing Technology of Stainless Steel The various surface treatments of stainless steel broaden its application scope. Different surface treatments give stainless steel different surface appearances, endowing it with unique characteristics in various applications. In the field of architectural applications, the surface treatment of stainless steel is important for many reasons. I. Basic Types of Surface Treatments There are roughly five types of surface treatments that can be applied to stainless steel. They can be used in combination to create a greater variety of final products. The five types are: 1. Rolled Surface Treatment 2. Mechanical Surface Treatment 3. Chemical Surface Treatment 4. Embossed Surface Treatment and Colored Surface Treatment There are also some specialized surface treatments. However, no matter which surface treatment is specified, the following steps should be followed: 1. Discuss with the manufacturer the required surface treatment. It is best to prepare a sample as a standard for future mass production. 2. When used over a large area, such as for composite plates, it is necessary to ensure that the base coils or strips used are from the same batch. 3. When choosing a surface treatment, the manufacturing process should be considered. For example, to remove welding beads, the weld seam may need to be ground, and the original surface treatment should be restored. Embossed plates can hardly or even cannot meet this requirement. 4. For some surface treatments, the grinding or polishing lines are directional, which is called unidirectional. If these lines are made vertical instead of horizontal during use, dirt is less likely to adhere to the surface, and it is easier to clean. II. Rolled Surface Treatment There are three basic rolled surface treatments for plates and strips, which are represented by the production processes of plates and strips. No.1: After hot rolling, annealing, pickling, and descaling. The surface of the treated steel plate is a dull surface, which is a bit rough. No.2D: Better than the No.1 surface treatment, it is also a dull surface. After cold rolling, annealing, descaling, and finally lightly rolling with a matte roller. No.2B: This is the most commonly used in architectural applications. Except that a final light cold rolling is carried out with a polishing roller after annealing and descaling, the other processes are the same as those of No.2D. The surface is slightly shiny and can be polished. No.2B Bright Annealing: This is a reflective surface, rolled with a polishing roller and finally annealed in a controlled atmosphere. Bright annealing maintains its reflective surface and does not produce scale. Since no oxidation reaction occurs during the bright annealing process, there is no need for pickling and passivation treatment. III. Polished Surface Treatment No.3: Represented by 3A and 3B. 3A: The surface is uniformly ground with an abrasive grain size of 80-100. 3B: Matte polishing, with uniform straight lines on the surface, usually achieved by a single polishing on a No.2A or No.2B plate with an abrasive belt of grain size 180-200. No.4: Unidirectional surface treatment, with low reflectivity. This surface treatment is probably the most widely used in architectural applications. The process steps are to first polish with a coarse abrasive and finally grind with an abrasive of grain size 180. No.6: It is a further improvement of No.4, which is to polish the No.4 surface with a Tampico polishing brush in an abrasive and oil medium. This surface treatment is not included in "British Standard 1449", but can be found in American standards. No.7: Known as bright polishing, it is to polish the surface that has been ground very finely but still has grinding marks. Usually, No.2A or No.2B plates are used, with a fiber or cloth polishing wheel and the corresponding polishing compound. No.8: Mirror-polished surface, with a high reflectivity, usually called a mirror surface treatment, because the reflected image is very clear. Continuously polish the stainless steel with a fine abrasive and then polish it with a very fine polishing compound. In architectural applications, it should be noted that if this surface is used in places with a large flow of people or places that are frequently touched, fingerprints will be left. Of course, the fingerprints can be wiped off, but sometimes it affects the appearance. IV. Surface Roughness The classification of rolled surface treatment and polished surface treatment describes the achievable degree. Another effective way to represent it is to measure the surface roughness. The standard measurement method is called CLA (Center Line Average). The measuring instrument moves transversely on the surface of the steel plate and records the amplitude of the peaks and valleys. The smaller the CLA number, the smoother the surface. From the surface treatments and CLA numbers in the following table, the final results of different grades can be seen. V. Mechanical Polishing Points for Attention: We should keep in mind that the grinding operation with sandpaper or abrasive belts is basically a polishing and cutting operation, leaving very fine lines on the surface of the steel plate. We have encountered problems when using aluminum oxide as an abrasive, partly due to the pressure problem. Any grinding parts of the equipment, such as abrasive belts and grinding wheels, must never be used for other non-stainless steel materials before use. Because this will contaminate the surface of the stainless steel. VI. Electrolytic Polishing This is a metal removal process. In this process, stainless steel serves as the anode in the electrolyte, and the metal is removed from the surface layer after electrification. This process is usually used for the processing of components because their shapes are difficult to be polished by traditional methods. The process is often used for the surface of cold-rolled steel plates because their surface is smoother than that of hot-rolled steel plates. However, electrolytic polishing will make the impurities on the surface more obvious, especially for materials stabilized by titanium and niobium, which will show differences in the weld zone due to granular impurities. Small welding scars and sharp edges can be removed through this process. This process focuses on the protruding parts of the surface and preferentially dissolves them. The electrolytic polishing process is to immerse the stainless steel in a heated liquid, and the proportion of the liquid involves many proprietary and patented technologies. Austenitic stainless steel has a very good electrolytic polishing effect. VII. Embossed Surface Treatment There are many types of patterns that can be applied to stainless steel. The advantages of giving the steel plate an embossed or patterned surface treatment are as follows: 1) Reduce "oil can-ning", a term used to describe the surface of shiny materials, which is optically uneven. For example, for large-area decorative plates, it is very difficult to make the surface completely flat even after stretch leveling or tension leveling, so oil can-ning will occur. 2) The embossed pattern can reduce the glare in the sunlight. 3) Slight scratches and small-area dents on the embossed plate are less obvious. 4) Increase the strength of the steel plate. 5) Provide architects with more choices. Patented patterns include cloth patterns (used for the Ed Building in London), inlaid patterns, pearl-like and leather patterns. Corrugated and linear patterns can also be used. The embossed surface is particularly suitable for interior decoration, such as elevator panels, counters, wall panels, and entrances. When used externally, it should be considered to enable the stainless steel to be cleaned by rainwater and manual scrubbing, avoiding dead corners where dirt and airborne impurities are likely to accumulate, so as to prevent corrosion and affect the appearance. VIII. Matte Surface Treatment Matte surface treatment is one of the most commonly used surface treatments. It is to polish the surface of the polished or bright-annealed steel plate with a nylon grinding belt or brush.