Electropolishing

The electro-polishing, also called electro-polishing, one of the subtractive manufacturing processes. More specifically, it is assigned to the electrochemical removal process with external power source. In this case, in a specially adapted to the material metal is electrolyte removed anodic, that is, the metal work piece forms the anode in an electrochemical cell.

Plasma polishing is similar to the method of electrolytic polishing, but works with ecologically valid than acceptable salt solutions. An important difference is the much higher voltage results in a plasma film around the workpiece, and therefore, a different mechanism of action leads to the removal.

Electrolytes - Active pairings

The electrolytes used are different depending on the metals to be machined. Today usual electrolytes are often mixtures of mineral acids and water and in some cases alcohols. Mixtures of phosphoric acid and sulfuric acid are used for the electropolishing of stainless steels and steels and aluminum alloys. Brass and copper can be edited in a mixture of phosphoric acid and alcohols.

% Phosphoric acid and 35 weight - - For most stainless steels is aged, aqueous electrolytes containing 45 wt % sulfuric acid at temperatures can be 50 to 65 ° C. and current densities in excess of 5 A / dm ² use. Mixtures of 55 wt - % phosphoric acid and 35 wt - % sulfuric acid and are also suitable for the electropolishing of aluminum. For copper and brasses to aqueous electrolytes are prepared from 50 wt - % phosphoric acid and 30 wt - % alcohol, such as 2-propanol.

Furthermore, the electrolytic baths often added surfactants. The electrolytes are hazardous substances in most cases. Accordingly, expert handling of the substances is necessary in order to avoid health and environmental damage.

Today, no longer in use because of the Perchlorsäureanteils electrolytes for the most common metals have the following composition:

• One part perchloric acid ( concentrated), a part of butyl cellosolve ( for buffering ) and seven parts of ethanol ( to the dissociation to keep low) with voltage of 45 V and a current density of 0.3 A / cm ² or part of ortho- phosphoric acid
• A portion of perchloric acid ( concentrated), a portion of glycerol with a portion of ethanol in the current density of 0.1 to 0.2 A / cm ².

Electrochemical machining

The removal takes place mostly with DC instead, but the use of pulsed currents takes place. The workpiece is connected as anode. Industrially current densities are applied, which allows removal in the transpassive range of current density -voltage curve. This has the result that not only metal is removed, but also the oxygen on the anode, the workpiece is formed.

Method

The surface roughness is reduced by electropolishing. Is this the goal of the processing can be spoken of electrochemical smoothing. Editing lowers the micro-roughness of the metallic surfaces. Asperities are removed faster than roughness valleys, as in the electropolishing in mineral acid mixtures before the surface forms a transportlimitierende polishing layer, which favors the removal of asperities. The Nanorauheit is also reduced. In this case, is electrochemically polished. The gloss is a result of roughness in the range of fractions of the wavelength of visible light. Retained in the macro range structures. Edges and corners can be more reduced, resulting in a Feinstentgratung the entire surface area. Therefore, the method can also be used for the electrochemical deburring.

Preparation

Before electropolishing, the metal workpieces are cleaned and degreased. An electrolytic or electrochemical etching may be required. Also parts are necessary, mechanically processed before editing. They are ground, sanded or polished, for example.

Scope

Electropolishing is for decorative purposes, for example for facade panels and jewelery applied. It is used in pipe and tank. Similarly, electro-polished in medical technology, because with the electropolishing decreases the Keimanhaftungsvermögen. Surgical instruments, but also implants such as stents (stents ) are processed in such a way. Also samples for material tests are electropolished. This type of electro- chemical surface treatment takes place both in sheets, large containers such as tanks, pipe lines and the like in the food and chemical industries as well as in micro-technology. Most often chromium and chromium -nickel steels, especially stainless electropolished. The reason for this situation lies in the fact that highly polished surfaces such steels are much more resistant to corrosion than untreated in fact. Microscopic point of view is reduced by such treatment the surface considerably, environmental influences, in turn, offers less options for attack. As examples may be mentioned here, the locations of sewage treatment plants and the chemical industry, but also in the maritime sector is often resorted. In addition, be used, for example in the high vacuum industry often electropolished recipients and connecting pieces to keep the surface and thus the amount of adherent adsorbates as low as possible. In aircraft, the electrochemical removal is used for lightweight construction in order to reduce the thickness of the aluminum sheets partially.

Materials

Editing can be a variety of metallic materials. Especially common is the process in stainless steels.