The various surface processing of stainless steel has broadened its application field.
Different surface processing makes the surface different and also makes the stainless steel unique in application.
In the field of architectural applications, there are many reasons why the surface processing of stainless steel is important.
Basic types of stainless steel surface processing
There are roughly five types of surface processing that can be used for stainless steel. They can be used in combination to transform more final products.
The five categories are:
- Rolled surface processing
- Mechanical surface processing
- Chemical surface processing
- Textured surface processing
- Color surface processing
There are also some special surface processing, however, no matter what kind of surface processing you choose, the following steps should be followed:
- Negotiate the required surface processing with the manufacturer. It is much better to prepare a sample as the standard for future mass production.
- In case of large-scale use (such as composite plate), it must be ensured that the base roll plate or roll material used is from the same batch.
- The manufacturing process should be considered when selecting the surface processing. For example, in order to remove the welding beads, the weld seam may need to be ground, and the original surface processing must be restored. The pattern plate is difficult or even unable to meet this requirement.
- For some surface processing, grinding or polishing, the texture is directional, which is called unidirectional. If this kind of texture is used vertically instead of horizontally, dirt will not be easily attached to it, and it will be easy to clean.
Rolling surface processing
There are three basic rolling surface processing for plates and strips, which are represented by the production process of plates and strips.
- 1: After hot rolling, annealing, pickling and descaling, the surface of the treated steel plate is dull surface and a bit rough.
- 2D: It is better than N0.1 surface processing, but also has a dull surface. After cold rolling, annealing, descaling, and finally light rolling with a mat roll.
- 2B: This is the most commonly used in architectural applications. Except for the last mild cold rolling with a polishing roller after annealing and descaling, the other processes are the same as 2D. The surface is slightly shiny, which can be polished.
- 2b Bright annealing: This is a reflective surface, rolled by a polishing roller and finally annealed in a controlled atmosphere. Bright annealing still retains its reflective surface and does not produce oxide scale. Since no oxidation reaction occurs during bright annealing, so no further acid pickling and passivation treatment is required.
Polished surface processing
No.3: It is represented by 3A and 3B.
- 3A: The surface is uniformly ground, and the particle size of the abrasive is 80～
- 3B: Rough polishing with uniform straight lines on the surface. It is usually made by polishing abrasive belt with a particle size of 180 to 200 on a 2A or 2B plate.
No.4: Unidirectional surface processing with poor reflexivity.
This kind of surface processing is probably the most widely used in architectural applications. The processing steps are firstly polishing with coarse abrasive, and then grinding with abrasive with a particle size of 180.
No.5: It is a further improvement of No.4, which is used to polish No.4 surface with Tampico polishing brush in abrasive and oil medium. This surface processing is not available in “British Standard 1449”, but can be found in American standards.
No.6: It is called bright polishing, which is used to polish the surface that has been finely ground but still has wear scars.
2A or 2B board is usually used as well as fiber or cloth polishing wheel and the corresponding polishing paste.
No.7: Mirror polishing surface, with high reflectivity, is usually called mirror surface processing, because of it’s clear image reflections. Stainless steel is continuously polished with a fine abrasive and then polished with a very fine polishing paste.
It should be noted in architectural applications that this kind of surface will leave fingerprints if it is used in places with large flow of people or where people often touch. Fingerprints can, of course, be wiped off, but they sometimes affect aesthetics.
The classification of rolled surface processing and polished surface processing is to explain the extent to which it can be achieved.
Another effective expression method is to measure the surface roughness.
The standard measuring method is called CLA (Central Line Average). Use a measuring instrument to move laterally on the surface of the steel plate, and record the change in peak and valley. The smaller the CLA number, the smoother the surface. The final results of different grades can be seen from the surface processing and CLA numbers in the table below.
Note: We should keep in mind that the grinding with abrasive paper or belt during the grinding operation 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 because of pressure problems. Any abrasive parts of the equipment, such as abrasive belts and wheels, must not be used on other non-stainless steel materials before use. Because this will contaminate the stainless steel surface.
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 the current is applied.
This process is commonly used for machining parts because their shapes are difficult to polish by using conventional methods.
The process is often used on the surface of cold-rolled steel sheet because its surface is smoother than that of hot-rolled steel sheet.
However, electrolytic polishing will make the surface impurities more obvious, especially the stabilized materials like Titanium and Niobium, will cause differences in the welding zone due to granular impurities.
Small welding scars and sharp edges can be removed by this technique. This technique mainly focuses on the protrusions on the surface and preferentially dissolves them. The electrolytic polishing process is to immerse stainless steel in a heated liquid, and the proportion of the liquid involves many proprietary and patented technologies. Electrolytic polishing of austenitic stainless steel works well.
Textured surface processing
There are many types of patterns that can be used on stainless steel. The advantages of making the steel plate with patterned or textured surface processing are as follows:
1) Reduce “oil can-ning”. This word 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 boards. It is difficult to completely straighten the surface even after stretching and straightening. As a result, oil can-ning will happen.
2) The textured pattern can reduce the glare emitted in the sun.
3) It is not obvious if there are slight scratches and small area indentations on the pattern plate.
4) Increase the strength of the steel sheet.
5) Provide architects with a choice. Patented patterns include linen (for the Ed Building in London), mosaic patterns, pearl 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. For external applications, consideration should be given to enabling the stainless steel to be cleaned by rain and manual flushing. Avoid dead corners that are easy to collect dirt and airborne impurities, so as not to cause corrosion and affect aesthetics.
Rough surface processing
Rough surface processing is one of the most commonly used surface processing. It is used to polish the surface of the steel plate after polishing or bright annealing with a nylon abrasive belt or brush.