POLIGRATElectropolishing

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The Process Principle

The surface finish of a metal component can determine its appearance, function and service life.

The type of surface finish will therefore deter-mine the cost benefit ratio. Electrochemical polishing and deburring (electropolishing) improves, like no other method of surface finishing, a number of crucial metallic surface properties. High quality functional surface finishes to meet differing demands can be obtained by an uncomplicated and cost-effective operation.

For over 30 years POLIGRAT has been developing and supplying high performance electropolishing processes, which have been employed in industries all over the world.

POLIGRAT processes for electrochemical polishing and deburring represent in principle a reversal of the electroplating process. Metal is removed by applying d.c. to the anodically connected workpiece, sub-merged in a special electrolyte. Removal takes place without inducing stress and affects preferentially the surface texture or micro-roughness.The surface becomes smooth and bright on a microscopic scale. This is therefore referred to as „electropol-ishing“. The structure on the macroscopic scale remains unaltered, but is smoothed and rounded on the surface irrespective ofshape and form. Edges and corners are removed preferentially, resulting in a reliable fine and super-fine deburring of the total surface area (electrochemical deburring).

The results can be repeated with a high degree of precision so that components with tight tolerances can also be treated in safety.

Electropolishing releases oxygen on the surface of the component. There is there-fore no danger of hydrogen embrittlement.

The Process Results

Electropolished and mechanically produced metal surfaces have fundamental differences

Mechanical operations like machining, drill-ing, grinding and polishing detrimentally af-fect the structure of the layers of the mate-rial at the surface and modify their properties unfavourably.

High temperatures and severe deformation during manufacturing lead to fissures, mod-ifications to structure, crystalline damage, and stresses in these areas. Contamination resulting from tool abrasion and contact with coolants can lead to corrosion and wear. Dependent upon the degree of the manufacturing forces applied the surface can be altered to a depth of 50 microns.In contrast to this, electropolishing removes metal from the component without mechan-ical, thermal or chemical transformation. Electropolishing eliminates damaged sur-face layers and allows the original proper-ties of the material to be fully utilised.

Surface of a filter plate in material 1.4301 (304S15) magnified 50 times

A screen cylinder in CrNi-steel electropolished for the purpose of fine deburring and smoothing of the surface

Influence of surface treatment on the depth of the mechanically modified layerMaterial: Chrome-nickel steel 18/8A ground B honed C electropolished

1 Austenite2 Austenite and cold formed ferrite3 Cold formed ferrite4 Cold formed ferrite and formed austenite5 Formed austenite6 Heavily formed grain with oxidized inclusions7 Various oxides

acc. to J. Wulff, The Metallurgy of Surface Finish, Cambridge/Mass.

Electron beam perforatef Roughly deburring by grinding Electropolished 10 minutes

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Electropolishing brings out the characteristic properties of the material to full effect

A combination of desirable technical features can be obtained in one operation which is not possible with any other type of surface preparation process.

Electropolished surfaces are:

– Metallically clean and free from stress– Smooth and free from microscopic cracks

– Minimized in respect of their absolute surface area

– Chemically passive

– Free from burrs, fragments, particles and gas occlusions

– Bright and decorative

Electropolished surfaces are distinguished by:

– Improved corrosion resistance and durability

– Reduced friction and wear

– Easier cleaning, reduced build-up of products on the surface, reduced bacteria growth

– Reduced radioactive contamination and improved decontamination behaviour

– Prevention of catalytic wall reaction

– Reduced pumping times to achieve high vacuum

– Improved high frequency conductivity

– Improved adhesion of plating deposits

– Optimum welding and soldering conditions

– Optimum reflectivity

– Particle freeness and pyrogenical soundness

– Quality control aid for exposing manufac-turing and material faults

CrNi-steel surfaces after various treatments1 Blasted with aluminium oxide2 Ground to a 180 grit finish

(see surface roughness diagram A)3 Surface n (previously IIIC)4 Electropolished

(see surface roughness diagram B)

Electropolished stainless steel tubes

Record of surface roughness measurements on a stainless steel sheetA Ground to a 180 grit finishB Electropolishing with about 40 microns metal

removal

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The Areas of Application

The POLIGRAT processes and the electropolished surfaces produced by these processes have been employed for a wide range of varying applications in practically all fields of engineering and industry:

– Chemical, bio-chemical, pharmaceutical industries

– Food and beverage industries– Electrical and electronic engineering– Plant and equipment manufacture– Machine and tool manufacturing– Precision engineering and associated

equipment– Textile and paper industry– Car and vehicle manufacturing– Aviation and aerospace engineering– Nuclear research and nuclear industry– Vacuum and cryogenic engineering– Ornaments and fancy metal goods– Architecture and interior decoration– Household and kitchen equipment

POLIGRAT offers special processes, electrolytes arid equipment for a wide range of materials, components and processing objectives.

POLIGRAT processes are suitable for treating:

– Austenitic and ferritic chrome and chrome-nickel steels

– Tool steels, mild steel and special steels– Copper and copper alloys– Aluminium and aluminium alloys– Nickel and nickel based alloys

(Monel, Hastelloy, Inconel etc.)– Magnetic alloys– Chrome cobalt alloys

The POLIGRAT processes can be employed in POLIGRAT plant virtually irrespective of the size and shape of the component requiring treatment.

POLIGRAT electropolishing plant consists of:

– a rectifier as the source of electrical current and

– an electropolishing tank fitted with electrical control gear for maintaining consistent processing conditions.

The plant is available for either manual or automatic operation.

– Mass produced small components can be electropolished in barrelling plant.

– Large fabrications up to several meters long are electropolished by immersion in a tank.

– Wire, strip and chain can be processed continuously on a reel to reel basis which can be integrated into a plating line.

– Tubes and pipes can be internally electropolished on special purpose plant.

– Large containers and large surface area fabrications can be electropolished by the moving cathode method or by a mobile pad system (POLITEC Process) which can be used on site without necessitating dismantling. In this way a limited rectifier output capacity can be utilised to process a large surface area.

Elctropolished contact strips in bronze, German silver, beryllium bronze, brass and copper. Process objective: fine deburring and improved plating deposition

Stainless stell valve body, internally electropolished to produce an extremely clean, partical free surface

POLIGRAT effluent treatment plant

The Range of Our Supplies and Services

POLIGRAT delivers answers to problems and supplies turn-key equipment

POLIGRAT is in a position to establish the optimum technical and cost-effective methods for treating production components and thereby ensure consistent electropolishing results under continuous production conditions.

The basis for this is the supply of the com-plete plant package, tailored to suit the process criteria, and incorporating equipment for the pre- and post-treatments; the supply of electrolytes; the training of operatives; the provision of technical services and advice on engineering applications.

POLIGRAT

offers a sub-contract facility for electropol-ishing customer components and fabrica-tions employing expert application of the POLIGRAT processes.

The Environment

Safety of application, the health and safety of operatives and the simple treatment of resulting effluent waste waters are essential features of the POLIGRAT processes.

POLIGRAT builds and delivers complete and inexpensive compact processing units for the treatment of waste waters. They are designed to suit the particular specific process, are safe in operation, and require minimal maintenance.

Fully automated POLIGRAT plant type EK 3500 AS for electropolishing stainless steel drums for spin dryers, inclusive of pre- and post-treatment equipment

POLIGRAT GmbH

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Continual monitoring on the basis of electrolyte samples taken from customers’ tanks is a part of POLIGRAT’s comprehen-sive service to clients. Consultation with process and equipment engineers ensures consistent high quality finishes.

Side by side with this service, new electro-lytes and processes are developed in a modern, well equipped laboratory in order to maintain the high technical standard of the POLIGRAT processes.

In the Engineering-Application Department, process trials are carried out using indus-trial plants so as to establish the working parameters for a specific client’s require-ments.

The development of electropolishing plant is carried out in close co-operation between the Design Drawing Office, Equipment Con-struction Engineering and the Engineering-Application Department.

Customer Service and Development

D-81829 MünchenValentin-Linhof-Straße 19

D-81805 MünchenP.O. Box 82 05 80

Phone +49 / (0) 89 / 42778-0Fax +49 / (0) 89 / 42778-309

e-mail: info@poligrat.dewww.poligrat.de