This document provides a description of the electropolishing procedures performed by Terra Universal. It also specifies a series of criteria for evaluating the integrity and cleanliness of the electropolished surfaces. Because these electropolishing procedures are followed on all work performed by Terra Universal, the results may be understood as indicative of standard Terra Universal electropolishing, and the specified evaluation criteria may be used as acceptance standards for work performed by Terra Universal.
Introduction
Electropolishing is a reverse plating procedure that entails the electrochemical removal of metal (including carbon, silica, iron, and other impurities) from a stainless steel surface.
Prior to electropolishing, parts are mechanically prepared to ensure optimal results. All welds are ground, deburred, and inspected to ensure that all seams are free of pockets or gaps. Finally, selected surfaces are mechanically buffed to a smooth finish.
Next, the part is fitted with electrodes, immersed in an electrolyte solution, and subjected to a direct electrical current. During this electrolytic process, the metallic surface of the the anodic part is removed ion by ion, yielding a nickel and chromium-rich surface free of microscopic “peaks” or “valleys” that could lead to metal fatigue or contamination. Optimal results depend on careful control over the current density, the precise chemical composition of the electrolytic solution, and the temperature and agitation of the bath, and the duration of current exposure.
Unlike mechanically finished stainless steel, electropolished surfaces feature no fine directional lines and hence offer less friction and surface drag. The chromium-rich surface offers excellent light reflection, yielding a bright, smooth and uniform polish.
Electropolishing Procedures
Terra Universal electropolishing is carefully controlled in each of the following areas to ensure the finest results possible.
Material Selection: Terra Universal electropolishing is performed on 304 stainless steel with either a 2B or 4 mill finish. This material standard minimizes the presence of sulfide inclusions and other subsurface contaminants and end-grain or large-grain surfaces that can produce a frosty appearance following electropolishing. Incoming material is also inspected for improper annealing, overpickling, heat scale, and directional roll marks, all of which are accentuated by electropolishing.
Precleaning and Postcleaning: For optimal results, it is important that all surfaces be uniformly exposed to the electrolyte solution, but also that provisions be made to remove all traces of the solution following electropolishing. Failure to remove the solution can result in subsequent outgassing unacceptable in a clean room environment.
Stainless steel parts intended for electropolishing are designed with these requirements in mind. All welds are carefully inspected to ensure continuous seams, free of pits or gaps where the solution could collect, and all hollow members are drilled to permit effective flushing of the solution after electropolishing.
Because the electropolishing process removes only a very thin surface layer (typically between 0.001" and 0.0001"), selected surfaces are mechanically buffed, using progressively finer grits to produce the smoothest possible finish.
Following electropolishing, all traces of the electrolyte solution are thoroughly removed from the part, and any hollow cavities are flushed to eliminate the chance of subsequent outgassing. Surfaces are then dried and buffed with a soft, non-particulating cloth.
Process Controls: The more rigorously the electropolishing process variables are controlled, the higher the quality that can be expected in the finished product.
Some of these variables are relatively easy to quantify and monitor, although some variation must be exercised in response to a given sample in order to produce the optimal results.
Electrolyte Bath: The chemistry of the bath must be constantly monitored, with special attention to the specific gravity (an indicator of water content), the acid concentration, and the metals content.
Current: A supply of clean, ripple-free DC power must be available to drive the process, as well as appropriately sized cables and connectors to the anodes and cathodes. Current density (amperes/square foot) must be carefully monitored and regulated.
For other variables, effective control depends on significant experience. Attention to these considerations, combined with close adherence to the procedures mentioned above, results in a truly superior electropolished finish.
Electrode Positioning: Electrode placement is critical to the success of the electropolishing process. Although electrode clamping of objects with a uniform geometrical shape is generally a straightforward task, irregularly shaped objects, which often contain inaccessible cavities or areas exposed to low current densities, present special challenges. Only an experienced technician, equipped with versatile electrode fittings, can ensure optimal results in these situations.
Electrolyte Temperature: Varying situations may call for varying temperatures, and heating and/or cooling during the electropolishing process may be required.
Electrolyte Agitation: Only an experienced technician possesses the knowledge of where, when and how to agitate either the electrolyte or the part in order to prevent gassing streaks, flow marks, and similar unacceptable surface anomalies.
Current Duration: The optimal duration of current exposure depends on the part size and shape. Again, only an experienced electropolisher can control this variable to produce the best results.
Performance Evaluation Parameters
Visual Inspection: The first and most obvious test of the effectiveness of the electropolishing is a close visual inspection. In a closely controlled process performed on high-quality material that is adequately prepared for electropolishing, the surface will appear uniformly brilliant, with no detectable pits, streaks, erosion, "frosting", or other anomalies.
Unlike mechanical buffing, which distorts the surface of the metal and may conceal the material’s true characteristics, electropolishing reveals the imperfections in the structure of the stainless steel. Electropolishing will accentuate any welding flaws, and a nonuniform appearance indicates a high volume of inclusions or a large-grained grade of stainless steel.
Micrographs: A better test of the integrity of the surface is provided by photomicrographs of the surface. Although a highly buffed (such as a No. 8 mil finish) sample and an electropolished sample may appear equally brilliant to the unaided eye, the differences between the two are apparent when they are viewed under very high magnifications. The sample micrographs below, taken at 1,000X, dramatically illustrate the smooth, featureless surface that results from electropolishing.
Before Electropolishing
This photomicrograph represents the surface of 304 stainless steel with a No. 2B mill finish before Electropolishing. Note that the etched boundaries between the grains are only partially sealed, resulting in a network of sub-surface crevices. Contaminants that lodge in these crevices are protected from contact with cleaning agents leading to subsequent migration of trapped contaminants onto the cleaned surface.
After Electropolishing
This photomicrograph represents the same No. 2B surface after Electropolishing. Note that the surface is now completely featureless on a microscopic level and has the desired noncontaminating, non-particulating and non-sticking properties.
Before Electropolishing
This photomicrograph represents a 304 stainless steel surface with a mechanically polished No. 4 mill finish before Electropolishing. Note the deep grooves, cavities, torn metal and other microscopic imperfections that entrap and retain contaminants.
After Electropolishing
This photomicrograph represents the same No. 4 finish after Electropolishing. The surface may still show some of the abrasiveproduced topography to the naked eye, but will now be microscopically featureless with the desired non-contaminating, non particulating and non-sticking properties.
ABS Plastic has very high impact strength and toughness along with excellent tensile strength and stiffness; Providing resistance to heat, most oils, acids, and alkalis.
304 stainless steel is durable and chemical resistant, making it the preferred material wherever frequent cleaning and sterilization are required.
Corian
Corian is a non-porous, stain-resistant top material that offers excellent chemical resistance and is easy to clean and disinfect
Epoxy Resin
Epoxy Resin; tested resistance to: damage from common organic compounds and volatile/non-volatile chemicals, bacteria and fungus; Heat deflection up to 325°F (167.2°C); Self-extinguishing surface; Non-absorbent and corrosion resistant; Non-reactive and low-sheen uniform finish
Non-Dissipative Laminate
Cleanroom-grade laminate is sealed along all edges to prevent particle release
Phenolic Resin
Phenolic Resin; compression molded of an organic fiber-reinforced phenolic core with an integrally cured thermoset resin surface, which is stronger than epoxy over time and not as brittle
Polypropylene
Polypropylene tops provide superior resistance to chemicals, particularly acids
Static-Dissipative Laminate
Combines the chemical- and heat-resistive properties of plastic laminate with a controlled path to ground for dissipation of static charge without voltage suppression ambiguity. This laminate has a micro-thin layer of aluminum oxide (Mohs hardness of 9; diamond = 10) integrated directly into its surface, creating an extremely hard protective layer, which provides long-term resistance to surface abrasion. This material has also been specifically tested for particle trapping (see test results below.) Each sheet used in fabrication is individually certified to meet the values set forth at below.
Corian® Top Laboratory Table, Adjustable Powder-Coated Frame, 84"W
Laboratory Tables with Corian® tops are non-porous, non-staining, easy to sterilize - ideal for processes with chemicals or biologicals. Available in several widths with adjustable powder-coated frame (shown: 84" x 30")
ErgoHeight Automatic Adjustable Work Station
ErgoHeight tables provide a 15" range of vertical motion to ensure personnel comfort without disrupting tabletop set-ups; all-stainless steel construction and sealed lifting mechanism for cleanroom use
Stainless Steel Lab Table with Backsplash
The Stainless Steel Lab Table with Backsplash features a seamless, radius cove for easy clean-up; marine-edge work surface available (shown with optional locking casters).
Epoxy Resin Laboratory Tables offer broad chemical resistance and a non-porous surface that's easy to sterilze; sturdy powder-coated steel frame supports loads up to 800 lbs. (363 kg); shown: 96"W x 30"D x 34"H.
Chemical-Resistant Cleanroom Work Station feature a polypropylene surface with powder-coated steel frame and telescoping legs: shown: 60"W x 30"D with optional drawers.
Solid-Top Stainless Steel Tables with Powder-Coated Base
Solid-top stainless steel tables with powder-coated steel base and telescoping legs (60"W model shown with optional plastic drawers).
Stainless Steel Cleanroom Tables with Perforated Tops
Stainless Steel Cleanroom Tables with Perforated Tops use 0.25”-diameter cut-outs that open up 40% of the surface for airflow (optional “C” base shown).
Cleanroom ErgoHeight Laminate Work Station
The laminate tops are bonded to a 1.25" high-density epoxy bonded fiber core. Standard color is non-glare white.
OpenTop Perforated Top
Hidden reinforcements minimize dead spots, add strength, and eliminate deflection without dead spaces whereas conventional perforated tops rely on “blank out” support panels, which create turbulence in cleanroom laminar flow.
Clean and Durable Powder Coat Finish
Terra’s signature white powder coat finish provides a high quality, durable barrier to protect against corrosion, plus a clean and attractive aesthetic. The advanced heat-fused formulation exceeds ASTM and ISO paint standards to resist chipping, scratching, fading, and wearing.
UL-Tested Cleanroom Workbenches for Highest Quality and Safety
Ensuring the safety of your personnel and equipment is essential. UL is recognized around the world as the leader in product safety testing and certification. Terra’s cleanroom workbenches are tested by UL to meet the strictest safety and stability standards.
Arrange Accessories to Suit Needs
Customize your cleanroom workstation with drawer and shelf systems to add clean, convenient storage where you need it. Cantilever shelves can be adjusted to any height. Mix and match 3”, 6”, and 12”H drawer systems.
Workstations and Tables
Stainless Steel, Solid-Top Workstation
Heavy Duty Electropolished 304-Grade Stainless Steel Work Station
Chemical Resistant, Epoxy-Resin Top Work Station
ErgoHeight Adjustable Bench, 304 SS Top, 36"W x 30"D
Corian® Top Laboratory Table, Adjustable Powder-Coated Frame, 84"W
Solid stainless steel top with a power-coated stainless steel base and telescoping legs | 1751-00 displayedStainless Steel, Solid-Top WorkstationSolid-top stainless steel tables with powder-coated steel base and telescoping legs (60"W model shown).
Electropolished 304-stainless steel cleanroom table with continuous seam welds; durable, all-welded work station for critical processes | 9603-07 displayedHeavy Duty Electropolished 304-Grade Stainless Steel Work StationFully welded, ultra-clean, electropolished 304-grade stainless steel work station for sterile, aseptic environments.
Work station with epoxy-resin top resists common organic compounds and solventsChemical Resistant, Epoxy-Resin Top Work StationEpoxy-resin top work station resists common organic compounds, acids and solvents.
ErgoHeight adjustable tables include heavy-duty stainless steel top and frame for lateral stability and cleanroom compatibility (Shown: 60"W model) | 3504-02A displayedErgoHeight Adjustable Bench, 304 SS Top, 36"W x 30"DErgoHeight tables provide a 15" range of vertical motion; all-stainless steel construction and sealed lifting mechanism ensure cleanroom compatibility, and heavy-duty frames enhances lateral stability.
Laboratory Tables with Corian® tops are non-porous, non-staining, easy to sterilize | 2903-38 displayedCorian® Top Laboratory Table, Adjustable Powder-Coated Frame, 84"WLaboratory Tables with Corian® tops are non-porous, non-staining, easy to sterilize - ideal for processes with chemicals or biologicals. Available in several widths with adjustable powder-coated frame (shown: 84" x 30")
Polypropylene top resists a broad range of chemicals, including most acids. Powder-coated steel base includes telescoping legs | 1522-00 displayedChemical-Resistant Table: Polypropylene Top, Powder-Coated Steel FrameChemical-Resistant Cleanroom Work Station feature a polypropylene surface with powder-coated steel frame and telescoping legs: shown: 60"W x 30"D with optional drawers.
The Stainless Steel Lab Table with Backsplash features a seamless, radius cove for easy clean-up | 9607-02 displayedStainless Steel Lab Table with BacksplashThe Stainless Steel Lab Table with Backsplash features a seamless, radius cove for easy clean-up; marine-edge work surface available (shown with optional locking casters).
Sealed laminate top design is compatible with Class 100/ISO 5 cleanrooms | 1722-00-E | 1728-00-E displayedCleanroom ErgoHeight Laminate Work StationThe laminate tops are bonded to a 1.25" high-density epoxy bonded fiber core. Standard color is non-glare white.
Lightweight polypropylene surface resists a wide range of acids and other caustic chemicals | 1522-00-E displayedErgoHeight Adjustable Polypropylene Work StationCustom work surfaces with cut-outs or perforations are available to accommodate other equipment.
Customize your cleanroom workstation with drawer and shelf systems to add clean, convenient storage where you need it. | 1752-00 displayedArrange Accessories to Suit NeedsCustomize your cleanroom workstation with drawer and shelf systems to add clean, convenient storage where you need it. Cantilever shelves can be adjusted to any height. Mix and match 3”, 6”, and 12”H drawer systems.