WHAT IS ELECTROPOLISHING AND HOW DOES IT WORK ?

Electropolishing is an electrochemical method of modifying the surface of a material. To make things simple, it is the reverse of plating. Typically, it is done in a tank that is filled with an electrolyte solution. On the sides of the tank are stainless steel cathodes with an anode bar in the center of the tank to which parts can be connected. When the correct tooling is applied and proper current and run time is set the electropolishing process begins.


WHAT MATERIALS CAN BE ELECTROPOLISHED ?

Almost any metal can be electropolished but the majority in the UK are austenitic stainless steels. 


ADVANTAGES

SURFACE ENHANCEMENT

During the electropolishing process the high points in the material are attacked first. In other words, the "peaks" of the material are depleted more rapidly than the low areas or "valleys". As a result, the surface roughness is reduced. We have experienced in some cases, surface finishes improved by up to 50%. You should note that a "normal" electropolish run can result in 0.0001" to 0.0004" material removal. The most important thing to remember is the better the surface you start with, the better you can expect after electropolishing.

A smoother surface means less area for particulates to be trapped. It is also thought that the smoother surface restricts impurities from attaching themselves to a processed surface as well.

Smoother ( Ra, Rms, Rmax ) finishes are very important to many industries and applications. Manufacturers of high purity gas systems, high vacuum chambers, and surgical instruments have benefited from a smoother, electropolished surface.

 
CORROSION RESISTANCE / PASSIVATION

Corrosion resistance is greatly enhanced by the electropolishing process. Iron and or iron oxide usually exists on the surface of stainless steel. This is especially true when a machine or fabricating operation is performed on a surface. The iron or as it is sometimes referred to as "free iron" gets dissolved during the electropolishing process. At the same time a chromium- rich layer is formed on the surface.

Surface analysists have shown chromium to be present on a electropolished surface along with nickel and carbon. Some refer to this as a nichrome oxide, since nickel, chromium, carbon, and iron are usually formed in the make up of nichrome.

It is our belief that electropolishing has many advantages over standard passivation. Standard passivation mearly dissolves the free iron from the surface. The evidence of chromium is not as great as in an electropolished surface.

In our system, after the electropolishing procedure is performed we then go to a passivation process. The passivation solution or "nitric acid" solution attacks free iron without attacking the chromium oxide or base metal. Areas such as tapped holes or crevices that might not have been exposed to the electropolishing process are now passivated.

 
COSMETIC BENEFITS

The electropolishing process usually results in the brightening of stainless steel. It is believed that since the process leaves a chromium rich layer on the surface it gives the illusion of chrome plating. Remember though, that the condition of the material will dictate the final finish after electropolishing. Scars, scratches and imperfections might still be present after electropolishing. Good or bad, the electropolishing process is a great developer. Since you are removing 0.0001" to 0.0004" of material, it sometimes exposes imperfections in the base metal.

The electropolishing process can only enhance the material given. Typically, the better mechanical finish you can produce, the better material you can provide, the better the results after electropolishing.

 
OTHER ADVANTAGES

In many tests, it has been found that electropolishing is a great method for removing hydrogen from stainless steel. This is of extreme importance in counteracting metal fatigue due to hydrogen embrittlement.

It is very difficult for bacteria to grow on or in an environment free of hydrogen. Many people in the food service and Bio-med industries believe this, and have used electropolishing on their food handling machinery and surgical tools.

Other advantages and benefits include descaling and stress relieving. Some have been said to have used the process for adhesion improvement. Many have used electropolishing as a deburring application.

So, as you can see, electropolishing has many advantages and a wide range of uses and applications.