The surface of an electropolished stainless steel piece is intended to be smooth and highly reflective. For this to happen, the surface condition and the process controls have to be perfect.
The surface condition:
Less than perfect Electropolishing will be the result of base metal, which includes carbon steel inclusions, non-metallic inclusions, roll marks, excessive cold working, improper pickling or annealing or base metal with a grain size to large. Imperfections of this nature can be inherent in the stainless steel as it is received from the mill. Electropolishing will revel these flaws.
The final result of Electropolishing stainless steel is the directly affected by the degree of process control. A super fine, consistent finish is only available through control. Within the industry, there are companies that employ very few controls, if any. The result is a product with inconsistent quality, and the output is totally unpredictable. The control that is employed is a function of both technology and skill.
It begins with the electrolyte being at the exact temperature required and that this temperature is maintained and/or adjusted throughout the process. As well as the temperature, is the chemistry of the acidic base. The factor’s that must be taken into account with the chemistry is specific gravity of the electrolyte, the concentration of acid and the metals content. The entire process must be driven by a clean, ripple-free supply of DC power and cables connected to the anode and cathode must be large enough to eliminate any voltage drop and to maintain the correct current density.
The “art” part, or the skill of the operator comes when shaping the cathode to polish in inaccessible areas, tight corners and in areas where there is low current density. As important, is the operators’ knowledge of when and how to agitate either the electrolyte or the part to make sure there are no gassing marks or any other imperfections, which are undesirable.
Because the polishing process does not mechanically interfere with the surface of the part, the resulting finish shows the true granular structure of the underlying metal. Electropolishing stainless steel provides both a mirror-like finish and a surface with mechanical integrity. Alternatively, mechanical polishing leaves behind a thin layer of disturbed material and the part will not have the same properties throughout.
Differences between surfaces polished mechanically and electrically
Mechanical polishing yields a surface which has scratches, embedded abrasives and debris. Conversely, metal subjected to Electropolishing is free of any disfiguring features, the real crystalline structure of the metal shows through. Even burnishing or lapping cannot approach the finish revealed by Electropolishing, although these processes may decrease the roughness and enhance the reflectivity of the surface, but, under microscopic examination, embedded material is still there.
The Electropolishing of stainless steel is the chosen surface of many industries that need absolute cleanliness in their processing plants. Their components are sent to New England Electropolishing for complete, flawless polishing.