Stainless steel machining process

The various surface treatments of stainless steel broaden its application fields-different surface treatments make the surface of stainless steel different, making it unique in its application. In construction applications, surface processing of stainless steel is important for many reasons. ​

The corrosive environment requires a smooth surface because the surface is smooth and does not easily accumulate scale. The accumulation of dirt can cause stainless steel to rust and even cause corrosion. In spacious halls, stainless steel is the most commonly used material for elevator decorative panels. Although fingerprints on the surface can be wiped off, they affect the appearance, so it is best to choose a suitable surface to prevent fingerprints from leaving. Hygienic conditions are very important in many industries, such as food processing, catering, brewing and chemical industries. In these application areas, surfaces must be easy to clean every day, and chemical cleaning agents are often used. ​

Stainless steel is the best material in this regard. In public places, the surface of stainless steel  is often scrawled with graffiti. However, one of its important features is that they can be washed away. This is a significant feature of stainless steel over aluminum. The surface of aluminum tends to leave marks, which are often difficult to remove. When cleaning the surface of stainless steel, you should clean it along the lines of the stainless steel, because some surface processing lines are one-way. Stainless steel is most suitable for use in hospitals or other areas where hygiene is critical, such as food processing, catering, brewing and chemical industries, not only because it is easy to clean every day, sometimes using chemical cleaning agents, but also because it is less likely to breed bacteria . Tests have shown that stainless steel performs the same as glass and ceramics in this regard. ​

1. The natural appearance of stainless steel Stainless steel gives people a natural strong and bright feeling, and its natural color softly reflects the color of the surrounding environment. ​​

2. Basic types of surface processing 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 categories are: rolling surface processing, mechanical surface processing, chemical surface processing, textured surface processing and colored surface processing. ​

There are also specialized surface finishes, but no matter which surface finish is specified, the following steps should be followed:

① Agree with the manufacturer on the required surface processing. It is best to prepare a sample as a standard for future mass production. ​

②When using a large area (such as composite panels, it must be ensured that the base coils or coils used are from the same batch.

③In many construction applications, such as inside elevators, although fingerprints can be wiped off, they are very unsightly. If you choose a cloth surface, it will not be so obvious. Mirror stainless steel must not be used in these sensitive areas. ​​

④The manufacturing process should be taken into consideration when selecting surface processing. For example, in order to remove weld beads, the weld may need to be ground and the original surface processing must be restored. It is difficult or even impossible for patterned boards to meet this requirement. ​

⑤For some surface processing, grinding or polishing, the texture is directional and is called one-way. If the lines are made vertical rather than horizontal when used, dirt will be less likely to adhere to it and it will be easier to clean. ​

⑥No matter what kind of finishing is used, additional process steps are required, thus increasing costs. Therefore, be careful when choosing surface processing. Therefore, relevant personnel such as architects, designers, and manufacturers need to understand the surface of cnc milling stainless steel. Through friendly cooperation and mutual exchanges, the desired results will be achieved. ​

⑦Based on our experience, we do not recommend using aluminum oxide as an abrasive unless great care is taken during use. It is best to use silicon carbide abrasives. ​

3． Standard surface processing Many types of surface processing have always been represented by numbers or other classification methods, and they have been incorporated into relevant standards, such as: “British Standard BS1449” and “American Iron and Steel Institute Stainless Steel Producers Committee Standard”. ​

4． Rolling surface processing There are three basic rolling surface processing of plates and strips, which are represented by the production process of plates and strips. No.1: Hot rolled, annealed, pickled and descaled. The surface of the treated steel plate is a dull surface and a bit rough. No.2D: Better surface processing than N0.1, but also a dull surface. After cold rolling, annealing, descaling, and finally light rolling with matte rollers. No.2B: This is the most commonly used in construction applications. Except for the last light cold rolling with a polishing roller 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 surface that is rolled with polished rollers 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 bright annealing, pickling and passivation treatments are not required. ​

5. Polished surface processing No.3: Represented by 3A and 3B. ”

3A: The surface is evenly ground and the abrasive grain size is 80~100. ​​

3B: Matte surface polishing, with uniform straight lines on the surface. It is usually polished on the 2A or 2B board with an abrasive belt with a grit of 180~200. No. 4: One-way surface processing, not very reflective, this surface processing is probably the most versatile in architectural applications. The process steps are to first polish with coarse abrasives, and finally grind with 180 grit abrasives. ​​

No.6: It is a further improvement on No.4. It is polished with Tampico polishing brush in abrasive and oil medium. 4 surfaces. This surface treatment 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 grinding marks. ​​

Usually the 2A or 2B plate is used, with a fiber or cloth polishing wheel and the corresponding polishing paste. ​​

No.8: Mirror polished surface with high reflectivity, often called mirror surface processing because the reflected image is very clear. ​ ​ Continuously polish stainless steel with fine abrasives, then polish with very fine polishing paste. ​

In architectural applications, it should be noted that such surfaces will leave fingerprints if used in areas with high traffic or where people touch them frequently. Of course, fingerprints can be wiped off, but sometimes they affect the appearance. The surface processing described in “official” standards and literature is only a general introduction, and samples can most intuitively represent the types of surface processing. Polishing or metal finishing manufacturers will provide samples of various surface finishes and users should discuss them with them. ​

6. Surface roughness The classification of rolling surface processing and polished surface processing shows the degree that can be achieved. Another effective expression method is to measure surface roughness. The standard measurement method is called CLA (Centre Line Average), in which the measuring instrument moves laterally across the surface of the steel plate and records the amplitude of the peak and valley changes. The smaller the CLA number, the smoother the surface. The end result of the different grades can be seen from the surface finish and CLA numbers in the table below. ​​

Surface processing CLA, Micron 2B 0.1-0.5 2A 0.05-0.1 2D 0.4-1.0 3 3 0. 4-1.5 4 0.2-1.5 8 0.2 EP 1/2 of the basic value EP = electrolytic polishing, which can roughly reduce the range of peak and valley changes to the original value 1/2 of the surface. ​

7. Mechanical polishing

Precautions: We should remember that grinding with sandpaper or abrasive belts during grinding operations is basically a polishing cutting operation, leaving very fine lines on the surface of the steel plate. We have had trouble using alumina as an abrasive, partly due to pressure issues. Any grinding parts of the equipment, such as abrasive belts and grinding wheels, must not be used on 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 abrasive belts should be tried on scrap materials with the same composition first, so that the same samples can be compared. ​​

8. Electropolishing is a metal removal process in which stainless steel acts as an anode in an electrolyte and the metal is removed from the surface after electricity is applied. This process is often used for parts whose shapes are difficult to polish using traditional methods. This process is often used on the surface of cold-rolled steel plates because its surface is smoother than that of hot-rolled steel plates. But electrolytic polishing will make surface impurities more obvious, especially titanium and niobium-stabilized materials, which will cause differences in the weld area 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, dissolving them preferentially. The electrolytic polishing process is to immerse stainless steel in heated liquid. The proportion of the liquid involves many proprietary technologies 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 for stainless steel. The advantages of adding patterns or textured surface processing to steel plates are as follows:

① Reduce “metal roofing material shrinkage” (oil can-ning), which is a term used to describe the surface of shiny materials that does not look flat from an optical perspective. For example: even if a large-area decorative board is stretched or straightened by tension, it is difficult to make the surface completely flat, so the metal roof material will shrink. ​

②The mesh pattern can reduce glare in the sun. ​

③ If there are slight scratches and small-area indentations on the pattern plate, they will not be obvious. ​

④Increase the strength of the steel plate. ​

⑤ Provides architects with a choice. Patented patterns include cloth (used in the Ede Building in London), inlays, pearls and leather. Ripple and linear patterns are also available. Patterned surfaces are particularly suitable for interior decoration such as elevator paneling, counters, wall panels and entrances. When applying externally, consideration should be given to ensuring that the surface of stainless steel can be cleaned by rainwater and manual scouring, and to avoid dead corners where dirt and airborne impurities can easily accumulate, so as not to cause corrosion and affect the appearance. ​

10. Matte surface processing Matte 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 a polished or bright annealed steel plate. ​

11. Glass bead blasting or shot blasting For interior applications, such as the interior of elevators, hybrid surface treatments are popular. ​

This mixing process is to form a matte surface by spraying glass balls, and then cover it with a plastic film to form a polished surface, and finally form a mixed surface of polished and matte. Stainless steel sand balls 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 carbon steel. Because carbon steel particles will embed into the surface of stainless steel, it can easily cause corrosion. Ceramic balls can also be used as spray materials. ​​

12． Colored Stainless Steel The stainless steel color process was successfully developed by the International Nickel Company (INCO) in the 1970s. Many companies have licenses to use this process.

As explained before, the reason why stainless steel does not rust is because of the inert chromium oxide film on its surface. The color process uses this film to form the specified color. Because stainless steel utilizes this ever-present film, it neither fades nor requires the same regular maintenance as paint. ​

Colored stainless steel can also be shaped, even in sharp bends without any adverse effects on the color. ​​

Regarding the impact on corrosion resistance, tests show that the corrosion resistance is enhanced after using this process. This process is closely related to the operation time, and the color will change at different times. The order of color variation is brown, gold, red, purple and green. ​

A major feature of this process is that its final appearance can reflect the original surface of the material, that is: the mirror or polished surface will produce a strong metallic luster, while the color of the matte surface is matte. ​

crafting process:

This process is to soak stainless steel in a solution tank. The solution should preferably contain 250 grams of Cr2O3 per liter, or 490 grams of sulfuric acid per liter. The temperature range is 80~85°C. The soaking time depends on the color required, and the maximum is no More than 25 minutes. ​​

After rinsing the steel plate with clean cold water, it is then placed in a liquid with a concentration of 250 g/1 liter of chloric acid and 2.5 g/1 liter of phosphoric acid at room temperature for cathodic treatment. The time is about 10 minutes and the current density is 0.2 ~0.4A/dm2. ​

To prevent damage, harden immediately after coloring, rinse in hot water and dry. ​

13． Hybrid Surface Finishing Colored stainless steel can be patterned, using a proprietary technique developed that involves using a corundum abrasive belt to remove the “protruding” areas, so that the end result combines the natural beauty of the steel plate with the color of the colored pattern. ​

This kind of surface is not easy to leave fingerprints and is especially suitable for interior decoration. Polishing manufacturers can provide surface processing samples. ​

14． Etching surface processing uses a coating process to mark the pattern on the surface of the steel plate, and then immerse the steel plate in an acid solution (O-level) to etch away the uncoated parts to form a beautiful pattern on the surface of the stainless steel.