This is a Re-Post of Blog article by Garrett Hanrahan of ANCORP
Before you determine whether or not to specify
an EP (electropolish) finish on a custom-fabricated vacuum component or chamber,
it helps to know what electropolishing can and cannot do for you in the context
of your vacuum application.
What EP Can Do
Enhance Component Cleanliness
The concentrated acidic solution baths used in
EP thoroughly clean a component by removing contaminants that can be introduced
during fabrication (dust, debris, lubricants, fingerprints, etc.) Moreover, the
surface of a stainless-steel component is rendered smoother after undergoing
EP, meaning the resultant surface is easier to sterilize repeatedly over the
life of the component.
Prolong Component Life
The EP process passivates stainless-steel
components by removing iron from the surface and enhancing the concentration of
chromium and nickel and that same surface. As a result, electropolished parts
are less susceptible to corrosion over time.
Improve Aesthetic Quality
Electropolishing stainless steel concentrates
chromium at the component’s surface and smooths out microscopic peaks and
valleys in the material. When the EP process is performed after the component
has been adequately polished by mechanical means beforehand, the result is a
bright, smooth, mirror-like finish that is uniform across the entire component.
Additionally, electropolishing can polish areas of a component that would
otherwise be inaccessible by other polishing methods due to component geometry.
What EP Cannot Do
It Will Not Achieve Exceptionally Smooth Surface Finishes On Its Own
The EP process serves to improve the surface finish that is already there, but it can only do so much. If you EP a rough, non-uniform, non-polished surface, the results will be neither aesthetically pleasing nor particularly beneficial to the component’s vacuum performance. EP works best when done after the component has been given a uniform finish by some mechanical means (e.g. glass-bead blasted, machine-polished). The mechanical method employed will be determined by the surface finish specification and vacuum-performance benefits you hope to achieve post-EP.
It Will Not Drastically Improve Pump-Down Time
The notion that rougher stainless-steel surfaces out-gas more than comparably smoother surfaces has been refuted by several studies. When it comes to pump-down time, the main benefit to be achieved through electropolishing is the reduction of a component’s surface area at a microscopic level. This reduction in surface area allows water vapor to be more readily evacuated from the component’s surface. At high-vacuum and ultra-high vacuum pressure levels, water vapor becomes the primary gas load within a vacuum system. If a vacuum component is specified to be baked out prior to installation, then the pump-down benefits of electropolishing become even more negligible since the bake-out process will remove most of the water vapor.
================================================================
IES Technical Sales is a high technology field sales representation and distribution company located in Danvers, MA. Contact Us to learn more about ANCORP or for general inquiries about vacuum, thin-film, temperature, fluid handling, and related metrology.