Electropolishing
Sandblastring with glass pearls
Pickling and pasivization
Mechanical processing
Design

Electropolishing

Reasons for electropolishing of metals

The surface finish of a metal component will determine its appearance, function and service life. Electropolishing improves the crucial metallic surface properties considerably.

The Process Principle

Electropolishing is, in principle, a reversal of the electroplating process. Metal is removed by applying a dc current to the anodically connected work piece submerged in a special acid electrolyte. Removal takes place without inducing stress and preferentially affects the surface micro-roughness. The surface becomes smooth and bright, with burrs, edges and corners being removed.

What Materials can be Electropolished?

All kinds of chromium-nickel steel.

Electropolished surfaces are distinguished by:

Free from burrs, fragments and particles
Improved corrosion resistance and durability
Reduced friction and wear
Easier cleaning, reduced bacterial growth
Reduced pumping times to achieve high vacuum
Reduced radioactive contamination
Improved adhesion of plating deposits
Optimum reflectivity
Bright and decorative
Chemically passive

The Process Results

Electropolished and mechanically produced metal surfaces have fundamental differences. Mechanical operations such as lathing, drilling, grinding and polishing will all adversely affect the structure and properties of the material surface. 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 structure can be affected to a depth of 50 microns.In contrast to this, electropolishing will removed metal from the component without any mechanical, thermal or chemical transformation. Electropolishing will eliminate damaged surface layers and allow the original properties of the material to be fully utilised again.

Applications

The processes and the electropolished surfaces produced by these processes have been employed in practically all fields of engineering and industry:

Food and beverage industries
Electrical and electronic engineering
Machine and tool manufacturing
Textile and paper industries
Automotive and vehicle manufacturing
Aviation and aerospace engineering
Nuclear research and nuclear industry
Vacuum and cryogenic engineering
Ornaments and fancy metal shapes
Architecture and interior decoration
Household and catering equipment
Medical-technical products

Sandblasting with glass pearls

Pickling and pasivization

Why the pickling of metals?

Pickling cleans and restores the corrosion resistance of components manufactured from stainless steel and thus considerably influences their service life and usefulness.

The corrosion resistance of stainless steel is primarily based upon the presence of at least 13% chromium in the alloy. In combination with oxygen, the chromium forms a dense layer of chromic oxide which is chemically resistant and protects the surface against corrosion.

Unfortunately, every mechanical treatment will damage the surface layer by contamination with ferritic matter, e.g. by changes to the microstructure. In addition, any heat treatment, such as annealing and welding, will lead to scaling and discolouration. These aspects not only diminish the visual appearance of the components, but in particular reduce their corrosion resistance.

A dense passive layer of chromic oxide can only form on a metallically pure surface. Professionally pickled stainless-steel surfaces and welding seams:

are metallically pure and free of scaling and discolouration
have full corrosion resistance
have a decorative satin metallic appearance

How to Pickle

Depending upon size and shape, the components that are to be pickled are either immersed in a pickling bath or the pickle solution is applied to their surface. The process is allowed to take effect at least for a few minutes, but also up to a few hours at room temperature. Afterwards the pieces are fully rinsed with water.

The active chemicals consist of mixed acids that cause a removal of the surface layer of the component from 1 to 3 microns. Discolouration, ferritic matter and surface contamination are preferentially attacked and removed. The final passive film is formed while rinsing with water and upon exposure to air.

The environment

All processes used by BIOTECHNIK pay due consideration to the relevant health and safety issues as well as the safe disposal of wastewater.