ELECTROPOLISHING : ACHIEVING PERFECTION WITH STAINLESS STEEL

Stainless steel is very time consuming to polish manually, and most of us are familiar with the rust stains which appear when it is neglected for even a short time. Marine grade stainless steel is a mixture of about 70% ordinary steel, mixed with chrome, nickel and molybdenum. This alloy depends on the chrome molecules combining with oxygen to form a thin layer of chrome oxide on the surface. Any scratches in this layer expose mild steel molecules, which then rust. Polishing tends to smear the relatively soft chrome over the surface, protecting the substructure. There remains a fair amount of free iron at the surface, both from within the material as well as from the tools used to machine, mill or form the finished item.

Stainless steel used in raw water plumbing or exhaust systems relies on the oxide film to prevent the chrome / nickel from using the steel molecules as anodes, and quite literally eating itself away. Stagnant seawater quickly becomes oxygen depleted and corrosion sets in as the oxide film breaks down. In order to maximise the corrosion resistance of stainless steel, it is vital to remove scratches, any mild steel molecules at the surface and to create as thick an oxide layer as possible.

Electroplishing is the opposite of electroplating. The item to be polished is connected to a very high amperage electrical current, while immersed in a hot acid bath. There are also cathodes in the bath, so the cleat or turnbuckle becomes the anode, and the surface molecules are removed. Mild steel molecules are easiest to lift off, so they are preferentially removed, leaving behind a surface of pure chrome nickel. High spots are also removed first, smoothing the surface to a mirror finish on a microscopic scale, with an oxide film thickened many times over on the chrome rich surface layer. Depending on the size of the object, this process takes up to 10 minutes – only a small fraction of the time required to polish manually, with far superior results. The process is also valuable as an early warning system, as microscopic cracks or porosity become clearly visible, however the prime purpose remains the long-lasting surface which has become the standard polishing system used by professionals worldwide.

Palma Engineering is proud to announce the opening of the first Electropolishing plant in the Balearics.