10 Dec ELECTROPOLISHING HAS A BRIGHT FUTURE
An electrochemical treatment, when related to the surfaces of metal components, conjures up a process of deposition or the application of a coating, in the eyes of most engineers. Rarely does one think that the opposite effect, namely metal removal, is also possible by electrochemical means. Probably the best example of industrial “de-plating”, as it was referred to in its infancy, is electropolishing.
To describe electropolishing simply as the reverse of electroplating is too simplistic. Reversing the polarity, and making the work-piece anodic is fundamental to the process, but any similarity to electroplating finishes there. The chemistry is a science on its own and will determine not only the polish achievable and the fixture configuration to achieve this, but also the life span of the electrolyte solution. Anopol has developed a universal electrolyte for electropolishing stainless steels, marketed under the trade name of ANOPOL 66. Various grades of stainless steel can be successfully treated, simply by varying temperature, current density and processing times.
ANOPOL 66 is used widely in the UK, mainly by companies preferring to carry out their own electropolishing in-house, rather than sub-contracting to an external source. Ireland remains by far Anopol’s best export market for this chemical, although shipments are made to a number of overseas clients, including one in USA, who takes large consignments on a regular basis.
Electropolishing is a two edged sword, insofar that the action of preferentially eroding high spots on a surface also causes preferential removal of material at the edges of a component. This is comparable to, but the reverse, to thicker deposits occurring at high current density areas on edges and corners when electroplating. The action of electropolishing, therefore, also has a deburring effect, although it must be stressed that only fine to super-fine burrs can be economically removed. Burrs, practically invisible to the naked eye, are at there most dangerous when present on implant components, which come into direct contact with a patients blood stream. The detachment of such burrs after a transplant could prove life threatening
Whilst electropolishing will produce the optimum clean and sterile finish on surgical implants, it also ensures that no micro-burrs are present on machined and the laser cut edges.
Electrochemical deburring has also been applied to the cutting edges of sharp instruments, such as scalpel blades and cutting tools in general. A precision ground edge will exhibit the finest of burrs. Removing these burrs takes seconds electrochemically, and results in the sharpest of cutting edges.
Electropolishing is indispensable when it comes to achieving a bright finish on stainless steel wire-ware. The application of conventional polishing mops is not practicable, whereas immersion electropolishing can cope with the most complex of shapes.
The function of electrochemical erosion can also be employed as an engineering tool. Screen cylinders represent important components in papermaking machinery. They vary in diameter and length and usually comprise of a stainless steel cylinder with thousands of precision machined vertical slots. The width of the slot determines the grade of paper being produced; the wider the slot, the coarser the paper. Paper making companies sometimes decide to increase the widths of slots in existing screen cylinders, which is again where electropolishing proves invaluable. Under tightly controlled treatment, all the thousands of slots can be increased in width simultaneously within extremely tight tolerances.
In stressing the functionality of an electropolished surface, one should also be aware of the decorative advantages of the process. This is demonstrated by the growing use of electropolished components in the automobile industry. Stainless steel car grilles, stone guards, bull-bars and mesh trim in general are benefiting from the aesthetically attractive finish of electropolishing, combined with improved corrosion resistance. Car manufacturers are constantly striving to use materials, which can be recycled, and electropolished stainless steel fits the bill perfectly.
Electropolished bull-bar for a 4-wheel drive vehicle
Miscellaneous electropolished wire-ware
by John Swain, Anopol Limited