Electropolish

Electropolishing is a surface treatment by which the metal polishing acts as an anode in an electrolytic cell, dissolving. With application of current, a polarized in the metal surface treated film, allowing the metal ions to extend accross said film is formed.

Electropolishing

Electropolishing 

Electropolishing is a surface treatment by which the metal polishing acts as an anode in an electrolytic cell, dissolving. With application of current, a polarized in the metal surface treated film, allowing the metal ions to extend accross said film is formed. Micro and macroprojections and high points of the rough surface, as burred areas are areas of higher current density than the rest of the surface, and dissolve faster, resulting in a smoother surface, level and / or the less roughness. Simultaneously, and under controlled conditions of current and temperature, comes a polishing surface.

The major advantage of stainless steel is that, as a metal  iron is readily dissolved, the contents of Chromium and Nickel at the surface increases, thus increasing corrosion resistance.

On a macroscopic scale, the contour of a surface can be considered as a series of peaks and valleys. The depth thereof and the distance between the peaks depend on the methods used to refine the surface finish.

A microscopic scale, the surface is even more complex, with small irregularities superimposed on the peaks and valleys.

In order to produce a truly smooth, both types of irregularities (gross and microscopic) must be eliminated.

Thus, the functions of an ideal polishing process can be distinguished as:

a) Smoothing: remove large-scale irregularities (greater than 1 micron size).
b) Polishing: remove small irregularities of less than one hundredth of a micron in size.

Comparison of Mechanical and Electrolytic Polishing

Comparison of Mechanical and Electrolytic Polishing

MECHANICAL POLISHING

Mechanical preparation of the surfaces may be conveniently divided into two stages:

1) Grinding: using abrasive techniques to produce a smooth, flat surface.
2) Polished: using fine abrasives on pulleys to give asmooth, shiny surface.
The investigation of the structure of the processes developed by mechanical polishing metal surfaces, states that lead to obtain a near surface severelydeformed zone. This area has different properties than the base metal and is mainly produced by a process flow; that is; under intense mechanical action of the polishing, the material of the peaks is caused to flow to fill the valleys.

This surface layer is knows as “Bielby layer”, and has a thickness of several micrometers, thickness which increases with the intensity of the grinding. The resulting structure is substantially  amorphous and contains metal oxide inclusions and basic compounds used in the polishing compounds. Therefore, it is understood that the physicochemical properties of the surface layer obtained by mechanical polishing are differnet from those of the underlying metal, leading to mechanical stresses which, under certain conditions, can lead to corrosion processes.

ELECTROPOLISHING

Electropolishing (polished electrochemical / electrolytic polishing) because it basically works, the dissolution of the metal under the current flow, a viscous layer of products of dissolution, which is slowly spreading in the electrolytic bath is formed.

The thickness of this layer is not constant, being higher in the valleys; and as its electrical resistance is higher than that of the electropolishing solution, leading to a preferential dissolution of peaks, and a leveling of the surface.

In Fig. 1 shows the diagram (a) with a cross section (a microscopic scale) of the surface at the beginning of the procedure, and in diagram (b) how then, after a while the surface treatment has dissolved and begins to “catch up”.

In this process a surface layer as in the case of mechanical polishing is not formed, since what is the metal dissolves base. The dissolved material thickness varies between 10 and 25 microns, according to the current intensity used and the exposure time.

In Fig. 2 shows a photomicrograph of a surface treated with emery 180, enlarged 50 times. In Fig. 3, the same surface, then electropolished. It clearly shows the leveling action described in the above scheme.

Fig. 4 is a microphotograph with a agnification of 50 times, of a specular surface obtained by a mechanical polishing treatment with a brush and polishing paste. Small cavities and stripes with sharp edges, which subsequently hamper the cleanup actions are clearly visible. Unlike in Fig. 5, the same electropolished surface shows no gaps with defined borders and are thereforewith this type of finish, the lower the ability to host foreign materials.

Therefore, one, although bright flat surface electropolished, will not have the dramatic aspect of mechanical polishing. However, microscopic and healthstatus is better, and you must understand that similar to a mirror surface does not necessarily imply that a microscopic level is free of imperfections that can host colonies of microorganisms
and / or initiate localized corrosion processes.

Advantages for Manufacturing Electropolished

Advantages for Manufacturing Electropolished

Focused on the manufacture of stainless steel staircases, the use of this process smooth and glossy, sanitation surfaces, due to the absence of scratches that prevent access to the products of own cleaning water treatment pool, (chlorine, various additives, leveling pH, etc.) and can become sources of contamination by microorganisms and / or initiate localized corrosion processes.

From a technical standpoint, electropolishing can treat irregularly shaped pieces (corners, interstices welding, etc.). So for example the treatment of threaded holes stair railings, where the steps are housed, is much more effective and efficient, as the work by dipping, and complete screw hole is sanitized, not just superficially. Also, when working with electropolishing bath railing tube is treated inwardly (welding, rubbing of the shaped pipe, etc.). This process prevents corrosion inside the pipe stair railings, which, not being watertight they are algo in contact with the internal surface water, untreated in the case of polished stairs.

Electropolishing can treat the edges, in the cuts, incisions, etc., for example ends of the rails, or in the case of the steps, (fixing holes slip plastic areas of the plastic tee stapling, hole land and cut shots, etc.).

Electropolishing on stainless steel can increase the corrosion resistance because the process allows to remove the surface layers formed by rolling work and polishing, leaving on the finished a layer of Chromium oxides and Nickel extremely thin and transparent surface that gives him excellent passivity in relation to many chemical reagents.

Electropolishing on stainless steel can eliminate coloration due to welding or heating, carrying out a preliminary etching with the deoxidizer-passivating, the solder is efficiently treated, removing scale, impurities and stabilizing them against chemical corrosion processes start.

Electropolishing on stainless steel allows decreasing trend in liquids and solids to adhere to the surface, improving aspects of cleaning and draining, very important aspects on all accessories from the world of pool.

In order to produce the best results, the metal should be homogeneous and free of surface defects. The defects, which are normally hidden by mechanical polishing, are disclosed; and further; are exaggerated for electropolishing (p. ex. Inclusions, casting defects, streaks, etc.).

The type of finish produced by electropolishing is totally different from that produced by the mechanical polishing. In the latter, a specular surface because it “forces” the material to provide a flat uniform and reflects light in one direction occurs.

In electropolishing, the surface is different, because although it is free of scratches and tensions, presents a three-dimensional structure that reflects light in all directions, giving it a glossy shine aspectode not so luminously mirror.

Applications

Applications

According to the characteristics of the electro process explained above, some of the potential users are:

  • Food industry in general, mainly milk, beer, wine and cold.
  • Chemical industry, plastics, mechanical.
  • Manufacturers of surgical and dental instruments, medical and hospital sector.
  • Manufacturers of machinery and components for the industry in general.
  • Manufacturers of marine accessories, cutting tools, etc.