Reinigingsonderzoek met waterige (alkalische) oplossingen - VeMet

SUMMARY
High temperature vacuum brazing is a clean and environmental friendly joining technique capable
of joining similar and dissimilar materials and constructions which can not easily be joint by
e.g. welding.
Good quality brazings have mechanical properties comparable to weldings. However, a clean
surface before brazing is necessary. Nowadays, new regulations restrict or even forbid the use of
CFK based cleaning methods, which, in the past gave good results. To maintain high temperature
vacuum brazing as a clean and environmental joining technique new cleaning methods will
have to be introduced. Water based Alkaline solutions is one of the possibilities. Therefore,
NIL-TC1-A initiated a project to investigate he possibilities of water based alkaline solutions
for the cleaning of carbon steel, austenitic stainless steel and copper. Final aim of the project
was to set up a draft proposal for a guideline to develop and/or optimise a cleaning procedure,
using environmental friendly cleaning methods. The materials were machined and subjected to a
deep draw process, using appropriate fluids. As cleaning fluids, silicate free, water based solutions
were used. High alkaline (pH = 13) for C-steel and stainless steel and neutral with surface
active additives for copper. As a reference, degreasing in cyclohexane was also performed.
Since ageing has a negative influence on the cleanibility, also aged surfaces were cleaned. The
surfaces of the materials were characterised by XPS, an indirect method using testing fluids for
the determination of the surface energy and in a brazing test.
XPS was used to determine a value for the surface, contamination as a C/Me ratio. A higher
ratio indicates a higher contamination.
The indirect method for determining the surface energies was used as a quick and easy
method to determine the surface cleanliness and for the optimisation of the cleaning procedure.
The brazing test was used as reference to get an indication of the expected brazing result.
The samples were mainly inspected for discoloration.
The results can be summarised as follows:
In general, cutting fluids can easily be removed in both the unaged and aged condition.
Standard procedure is sufficient.
Deep draw fluids however are more difficult to remove. As for cutting fluids, simple agitation
is enough to remove the fluids, for deep drawn products, ultrasonic consistent cleaning
is necessary. And even then, not always all is removed. In the case of copper, a more alkaline
solution will be required.
The indirect method using testing fluids for the determination of the surface energy proved
to be ver useful. The method can be used to monitor the cleaning process. Comparing the
XPS-results and the indirect method shows that up to a certain degree of degreasing both
methods can be used. Above a certain level of cleanness the indirect method is not applicable
to distinguish anymore. However, the fluids used have a limited range between 44-30 mN/m.
Using fluids with higher values (up to 58 mN/m) may be better. Finally, a cleaning procedure
for the optimisation or the introduction of a cleaning procedure is suggested.
Adoption the cleaning procedure is expected to enhance the acceptance of water based alkaline
solutions in cleaning, thereby reducing the emission of hydrocarbon to the atmosphere.
ECN-CX--01-088 7