Surface Finishing
Overview
Process Services
Electropolishing
Processes, Properties, Advantages
The surface is critical to the appearance, function, and service life of a metal part. Treatment of metal surfaces is hence a key factor influencing the further processing and the costs of parts.
Through electrochemical polishing and deburring (electropolishing), a decisive improvement in the properties of metal surfaces is achieved, in turn leading to a lasting improvement in the stability and reliability of the treated parts.
Effect of surface treatment on the depth of the mechanically affected layer:
ground (l), honed (m), electropolished (r)
Electropolishing is an electrochemical method for removal of material from metal surfaces. The part is connected as an anode to the positive terminal of a DC power supply, provided with counter cathodes, and immersed in a material-specific electrolyte. A DC voltage is applied to the part. Under the influence of the direct current, metal is removed from the part surface. Removal occurs without loading and with a preference for areas exhibiting microroughness. The resultant surface is smooth and shiny on a microscopic scale. Macroscopic structures remain intact. Edges and corners are more strongly attacked, resulting in reliable fine and ultrafine burr removal over the entire surface.
Mechanical machining processes (such as drilling, grinding, and polishing) alter or damage the materials due to the effects of force and heat. This leads to cracks, stresses, and microstructural changes and reduces the service life of the part. Electropolishing removes these damaged surface zones, fully restoring the properties of the material.
Roughness plot for a stainless steel sheet
ground with 180 grit (top)
electropolished (bottom)
In the electropolishing of stainless steel, a continuous chromium oxide-rich oxide layer is formed on the surface, providing a passive film that protects against corrosion.
Advantages of Electropolished Surfaces
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Metal purity, chemical passivation, very high corrosion resistance
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No particles, reduced deposit formation, favorable for cleaning and sterilization
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Supports quality control (makes material and machining defects visible)
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Decorative appearance due to shiny surface
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Significantly fewer crack and stress nuclei and accordingly improved part service life
Application
Electropolished metal surfaces are used in all industries for a myriad of applications.
Metals suitable for electropolishing:
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Stainless steel
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Carbon steel
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Titanium alloys
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Cr–Co alloys
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Copper alloys
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Aluminum alloys
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Magnesium alloys
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Other metals
Electropolishing of titanium and titanium alloys
Industrial-grade electrolytes for electropolishing of titanium, titanium alloys, niobium, Nitinol, tantalum, and some chromium–cobalt alloys.
Depending on the condition of the surface, a glossy or high-gloss surface is achieved after an exposure time of about 2 minutes. Higher removal rates at tips and edges result in smoothing of the microroughness and removal of fine burrs on the surface.
The result is a metallically pure and microsmoothed surface with the highest possible corrosion resistance and passivity. Electropolishing processes are performed at temperatures between 20 °C and 50 °C. The stresses should preferably lie between 20 V and 30 V.
Electropolishing Application Example
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We would be happy to advise you on your specific surface application:
Telephone +41 44 980 30 30
Chemical deburring and polishing
Processes, Properties, Advantages
FerroChem and ChemoLux Processes
FerroChem and ChemoLux processes are used for deburring and smoothing metal surfaces. Unlike grinding and honing, these processes do not involve mechanical loading and heating of the surface. Inaccessible corners and edges can also be reached and treated highly effectively. Roughness is reduced and surface defects are eliminated, leading to improved fatigue strength behavior of the parts.
Hole in carbon steel ball bearing race before and after FerroChem treatment
Advantages of Chemical Polishing
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Reduced wear and/or better sliding properties
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More precise compliance for the mass of parts
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Increased homogeneity and adhesion of surfaces
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Improved strength of welded and soldered joints
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Elimination of crack nuclei
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Complete removal of flash, overlaps, scales and particles
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Deburring and smoothing of surfaces and edges of all surfaces wetted by the bath, even hollow spaces
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Metallically pure surfaces
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Removal of grinding and drilling burrs, even those directed inward
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Precise material removal within tight tolerances
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No damage to sensitive parts, because the process works without mechanical stress
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No thermal stress
Typical Applications for FerroChem and ChemoLux Processes
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Fixtures and appliances
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Automotive parts
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Tapes and wires
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Containers
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Turned and milled parts
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Injection nozzles
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Springs and switching elements
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Chains
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Ball bearing cage
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Needles
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Pipes
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Stamped parts
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Hydraulic and pneumatic controls
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Textile machine components
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Timepiece parts
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Toothed gears, pinions
Working Principle of the FerroChem and ChemoLux Processes
Chemical polishing results in the controlled chemical removal at the surface with a concomitant deburring and smoothing effect. For treatment, the parts are placed loosely in baskets or drums or inserted individually on racks in the process bath. For the treatment of long pipes or drilled holes, the bath liquid can be pumped through the part.
FerroChem and ChemoLux baths are chemically stable over long periods of use and enable precise control of removal over the dwell time. The removal rate is 0.5 to 4 microns per minute – depending on the hardness and composition of the material – and can be increased through movement of the liquid. The FerroChem and ChemoLux baths are characterized by their high performance and economic efficiency as well as, in comparison with conventional processes, minimal emissions.
Full-Service Provider
ElpoChem has a comprehensive offering to help your company achieve reliable processes with unwavering quality:
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Supply of process chemicals (including pre- and posttreatments) for the respective process
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Instruction and training of personnel
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Process-specific support and troubleshooting onsite
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Analysis of customer process baths in in-house lab
Chemical polishing and deburring application examples
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