As a rule, burnishing produces an even, black to black-brown surface coating on objects made from ferrous materials (cast iron, unalloyed and alloyed steel) in order to give the workpieces an attractive appearance and increase their resistance to corrosion, while largely maintaining their dimensional accuracy.
The objects are dipped in a boiling (130-140 °C) alkali-oxidising solution. The process is carried out in the Rohde factory in Göttingen.
|Characteristics and Composition of Burnishing|
|Preferred applications||To increase resistance to corrosion while preponderant maintaining dimensional stability in the steel machine parts|
|Approximate chemical composition||Iron (II-III)-oxide|
|Weight per unit area||approx. 4.5-6.5 g/m2|
|Inherent colour of the protective layer||brown-black – black, depends among other things on the quality of the material and surface treatment|
|Adhesion||very good, deformation stability|
|Resistance to corrosion, subsequent treatment||approx. 24-48 h in condensation water constant atmosphere; not recommendable for parts with high exposure to corrosive factors.If there is no additional lacquer or similar coating, the items are usually oiled as subsequent treatment.|
|See also DIN 50 938 for further details|
|Maximum workable size of item|
|Burnishing of machine parts||1000||350||350|