Electropolishing

Electropolishing small and medium stainless steel components not only creates a surface that actually enhances the appearance but also provides practical advantages.

Electropolished surfaces exhibit a reduction in frictional characteristics thus liquids run off more readily, air flow is improved and powders are less likely to cling.

The process removes manufacturing contamination producing enhanced corrosion protection as a major benefit. Electropolishing is used for a wide variety of applications, not only in aerospace and medicine but also in food and agricultural hygiene such as breweries and dairies as well as for general corrosion and corrosion protective purposes.

Electropolishing is carried out in the same way as electroplating but because the component is made Anodic, instead of depositing material it is electrolytically removed. During the process three things happen, firstly high spots on the component attract a greater proportion of the current thereby removing those high spots preferentially thus smoothing out the surface resulting in a brightening of that surface, secondly much of the tarnish or contamination on the surface of the component will tend to be removed as the metal is removed (see Pickling below) further enhancing the brightening of the component, and finally, as electrolysis produces oxygen at the anode, the component gets scrubbed with free oxygen so enhancing the natural protective oxide layer which gives stainless steel it’s stainless properties.

The combination of these three events is that the electropolished component becomes cleaner, brighter and achieves its maximum stainless properties.

The success of the electropolishing process is very alloy dependant and whilst specific solution variants can be formulated to deal with other alloys, the process offered by Ashton & Moore is designed to deal with Austenitic stainless steel e.g. 316 or 304.

Pickling

Many stainless steel are fabricated, welded or cast, these manufacturing processes can impart soils and scales such as burnt on oils or carbon films or casting “crust”. These contaminants can be inert to the usual pre-cleaning methods and therefore interfere with the electropolishing process, so need to be removed by pickling with strong acids or by the use of “Pickling pastes” before the actual polishing is carried out.

Ashton & Moore do offer these pickling processes but it is worth noting that they can impart additional time and cost to the process, and frequently, these contaminants can be eliminated by good practise in the manufacturing stage.

Passivation

Although stainless and corrosion resistant steels have a natural passive film, during the manufacturing processes minute particles of steel and non ferrous metals are impacted on the surface of the component, these impurities can set up corrosion pits in the component so the passivation process is used to remove them. The process also accelerates the re-formation of the passive film which would have been removed during machining. This process does not affect the dimensional characteristics of the component.

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