WHAT HAPPENS DURING BLACK OXIDATION?
Not a conventional layered structure.
The material undergoes a transformation at the surface. The process involves a reactive transformation at the surface, whereby iron is converted into a mixed iron oxide. Consequently, there is no conventional layer formation, but rather oxidation or transformation.
Consequence:
The component dimensions do not change (provided that no alkaline or acidic etching takes place in other process steps).
THE CRUCIAL DIFFERENCE
| Optical black oxidation | Technical black oxidation | |
| Primary goal | Black finish | Functional features + black finish |
| Focus | Optics | Tribology & Surfaces |
| Process | In accordance with DIN 50938 | DIN 50938, supplemented by specific manufacturer’s standards |
| Control | Requirements set out in DIN 50938, e.g. regarding colour, abrasion resistance and freedom from stains | Advanced requirements, including non-destructive component testing |
| Process monitoring | System-specific inspection intervals | Intervals defined by the process |
| Surface | Even, deep black | Blackening depending on the alloy and the specified surface requirements |
MORE THAN JUST A SURFACE EFFECT
Goal: To extend the service life of, for example, roller bearings.
Particularly in the case of rolling bearings, the wide range of positive effects – depending on the specific application – can help to reduce, delay or prevent typical damage.
- Grey spotting
- Lubrication defects
- Spalling
- Micro-welding
- Crack formation
CRITICAL OPERATING CONDITIONS
When conditions get tough, that’s when the benefits become apparent.
Temporary insufficient lubrication
The existing burnished layer can help to reduce harmful effects.
Steel-to-steel contact
In the event of a brief breakdown of the lubricating film, the burnishing layer can help to reduce the risk of cold welding and other serious surface damage.
Extreme-pressure additives
Under certain conditions, the burnished layer can reduce or prevent undesirable reactions caused by EP additives.
THE CHALLENGING PROCESS
Technical blackening does not begin with the black colour.
Technical blackening is largely based on the requirements of traditional burnishing, but places additional demands on the metal surface and the technical implementation of the process in order to achieve the desired tribological properties.
The DEWE Brünofix approach:
Defined process control. Defined surface finish. Targeted tribological properties.