Stainless steel, as well as many other types of metal, often undergoes additional processing, through which it is possible not only to make the steel surface aesthetic, but also to give the metal the necessary quality characteristics necessary for the appropriate operating conditions. Processing can be as stainless steel billets, and finished parts / products. Most often stainless alloys are finished using three basic methods – etching, polishing and grinding.
This technology refers to chemical methods. It allows qualitatively remove a number of defects from steel surfaces. First of all, etching of stainless steel is carried out after its treatment by methods of plastic deformation and welding / melting. It is etching that makes it possible to remove the color of escape from such steel and give it a homogeneous shine, as well as provides an update of the so-called passive layer, which protects the stainless alloy type from possible negative consequences after the action of too high temperatures.
The process of etching stainless steel in industrial workshops is carried out in an environment of acid and alkaline solutions. In case of acid etching of steel is carried out in two stages. First, the metal is treated with sulfuric acid, and then with nitric acid composition. The alkaline etching method implies placing the workpiece into caustic soda solution. It decomposes the film formed by oxides on the metal surface rather quickly. Its structure does not change in any way.
In addition to the methods described above, to give a dull stainless steel shine and fill in its surface layer of chromium “burned” in the welding process, you can use a special etching paste. This method is well suited for self etching at home. At the same time, utmost care should be taken, because such pastes, in addition to nitric and hydrofluoric acid, also contain highly aggressive chlorides and hydrochloric acid.
Before using the paste, steel work surfaces undergo preliminary preparation – thoroughly cleaned, degreased and washed with heated water. The paste is smeared with plastic/rubber blades or smeared with brushes with lint resistant to acidic media. The pickling compound is kept on metal for 10/60 minutes. It is washed off with plain water. If there are significant amounts of work, stainless steel is etched with special sprays, which are fed with the appropriate spray nozzles jet type.
Stainless steel is satin-finished by two mechanical methods – grinding and polishing. Grinding with power tools helps to remove roughness very quickly and to smooth out smaller defects. Welded joints are most often ground. They are machined using Bulgarian saws with abrasive grinding or paddle grinding wheels. Apart from bell saws, pneumatic band files and standard band grinders can be used as grinding tools. As a rule, satin-finishing of stainless steel starts with coarse grinding wheels/sandpaper belts (grain 180). After that, they are replaced by working attachments with 320 grains and then with 600 grains. Finishing involves polishing with dense felt circles/stripes.
Manual satin polishing is more time consuming and labor intensive. This method is relevant for single or periodic works of small volume. In this case, hand grind sheets, special grinders and felt are used.
In industrial workshops and home workshops for metal satin, often used automated lathes on work shafts which are fixed special circles. For these purposes, even the simplest modification of the lathe with low power will be suitable. Machines are relevant only when the size, weight and shape of the workpiece allow you to grind it with a circle fixed to the shaft of the machine.
Other methods: chrome plating, funneling, painting
With chrome plating you can solve several problems at once. First, to give the products an aesthetic look. Secondly, you can additionally protect the steel from various mechanical influences (blows, scratches, abrasion, etc.). Thirdly, a layer of chromium significantly increases the resistance of steel to rust. It is only possible to achieve a high-quality chrome plating result under industrial conditions. This requires not only knowing the technology of chrome plating, but also have at hand the right equipment with a full set of consumables.
On the other hand, the funneling that gives the stainless steel its specific appearance can be carried out in both production and home workshops. The funeral is done in three ways: acid treatment, treatment by alkaline solutions, thermal treatment.
We should not forget about such a method of treatment of stainless steel as traditional painting. Stainless steel is painted with different compositions with the help of rollers, brushes and spray guns. Modern paints give the metal the desired color and additionally protect it from corrosion.