Electropolishing Key to Fighting Contamination

Mention the term electropolishing and most people get an image of a bright, reflective metal surface- whether it is found on a diner wall, behind the scenes of an operating room or in the form of a laboratory instrument. While it is true that electropolishing has long been used to shine up many metals, especially stainless steel, the reason may be much more than image. 

Electropolishing (also known as electrochemical polishing or electrolytic polishing) is critical to reducing contaminants in equipment used in industries that touch peoples’ health. These industries include food and beverages, cosmetics and  -- perhaps most critical -- pharmaceuticals and biotechnology. During the normal course of alloy fabrication, bending, grinding, machining and other normal processes change the metal surfaces significantly. These alterations take the form of burrs, scales and tooling marks. Without treatment these surface imperfections can be a focal point for infection or metal contamination.  

Electropolishing removes this surface material from metal. It deburrs and polishes metal parts. This is particularly useful when applied to objects of complex shape, such as the storage and pressurized tanks used in the pharmaceutical and biotechnology industries. Electropolishing may also be used in place of the abrasive fine polishing in microstructural preparation. Through electropolishing, an alloy fabrication professional can achieve as much as a 50 percent improvement in the average roughness height.

Smoother, cleaner surfaces
Electropolishing occurs through the electrolytic removal of metal in a highly ionic solution by means of an electric potential and current. In this process, the work piece is typically immersed in a temperature-controlled bath of electrolyte. It is then connected to the positive terminal of a DC power supply, while the negative terminal is attached to the cathode. A current passes from the anode, where metal on the surface is oxidized and dissolved in the electrolyte, to the cathode. At the cathode, a reduction reaction occurs.  

 During microfinishing, surface metal on the work piece is greatly reduced, leaving the part much smoother both visually and measurably by a profilometer. Generally speaking, Ra surfaces are improved by 50 percent (e.g., a 14 Ra finish becomes a 7 Ra finish).

A Beneficial Process
Highly sophisticated surface analysis reveals the many benefits that are derived from the fine surface finishing achieved through electropolishing. In general, it is much better to restore a metal surface than to coat a defect. Electropolishing has proven itself to be a critical step in alloy fabrication, a step that is best performed by superior crafts people employed by superior vendors and service providers. 

American Alloy Fabricators, Inc. partners with leading pharmaceutical and biotech companies to design and fabricate process equipment used in their research and production facilities. For more information on our wide range of products and services, contact American Alloy Fabricator, Inc., at 610-635-0205 or via the Web at http://www.americanalloyfab.com/contact.html.

Meeting a Pharmaceutical Need through Surface Finishing

American Alloy Fabricators has recently solved a problem for one of the world’s top pharma companies. We designed and fabricated for them custom pressure vessels, which are designed to grow vaccines.  Several factors affect the growth rates of vaccine cells, such as nutrition and temperature. Another is the “cleanability” of the growth containers’ surface: If the cells are in an environment that is too sterile, then they cannot survive.  Therefore, the surface finish of the tanks is critical.
 
Our vessels were chosen because their Ra measure (“average roughness”) passed the customer’s in-house testing, and that is a testimony to American Alloy Fabricators.

Three Categories of Surface Roughness
The roughness of a surface can be measured in these basic ways:
•    Statistical descriptors  – the average behavior of the surface height
•    Extreme value descriptors — measures of isolated events, such as the maximum peak height (Rp), the maximum valley height (Rv) and the maximum peak-to-valley height (Rmax).
 
The Ra measure is defined as the average value of the departures from its centerline through a prescribed sampling length. It is widely considered to give a good general description of the height variations in the surface.
 
A profilometer is typically used to measure surface roughness — the small surface variations in vertical stylus displacement as a function of position. A typical profilometer can measure small vertical feature anywhere from 10 nanometers to 1.0 millimeter. The height position of the profilometer’s diamond stylus produces an analog signal that ranges from 20 nanometers to 25 µm. The horizontal resolution is controlled by the scan speed and the data signal sampling rate.
 
Surface Finish
Until recently, measuring and specifying surface finish has been somewhat speculative. The differing standards among equipment manufacturers have created a great deal of confusion and misunderstanding throughout the pharmaceutical and biotechnology industries. Increasingly stringent specifications for surface finish are now being demanded on all items of process equipment, and many suppliers of valves and pipe work are quantifying the surface roughness of their product. The specification of grit reference cannot be equated to a consistent surface finish. Variables affecting the final finish are grit size, tool load, condition of tool, feed rate, traverse rate condition of metal to be polished and lubricant used, if any.
 
For precise and consistent results, surface finish should be specified in a range or maximum level of roughness average (Ra, which is defined above). Ra is normally expressed in micrometers (microns) or microinches. Micron or microinch values that express surface finish
as Ra are interchangeable with those values identified as centerline average (CLA), or arithmetic average. Measured values expressed as root mean square (RMS) will read approximately 11 percent higher than values expressed in Ra (microinches x 1.11 = RMS). American Alloy Fabricators, Inc., uses a profilometer to measure surface roughness. Surface finish can then be described by using Ra.
 
The increasing purity requirements in the pharmaceutical and biotechnology industries require surface finishes that meet BPE standards. With the advent of ASME/BPE, the pharmaceutical and biotechnology industries finally have a standard that can be universally applied.
 
Our client received the vessels from us in 14 weeks, and they have delivered excellent results. For more information on mechanical polishing for your biotech or pharmaceutical company, contact American Alloy Fabricators at 610-635-0205 or via the Web at
http://www.americanalloyfab.com/contact.html.

We are American Alloy Fabricators, Inc.

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