Zn Flux – The Alternative Flux for Corrosion Protection
All heat exchanger manufacturers currently using zinc-coated tubes or zinc-coated brazing sheet and extrusions for corrosion protection are invited to consider NOCOLOK® Zn Flux as an alternative.
How does NOCOLOK® Zn Flux work?
The flux – a fine white powder with the chemical formula KZnF3 – is manufactured by Solvay Fluor similarly to standard NOCOLOK® Flux in a water-based batch process. Thus this material has a distinguished and uniquely homogeneous composition. Coating methods for the new product include slurry-based spraying, dipping, and painting, or electrostatic spraying for aluminium surfaces where zinc diffusion layers are required.
NOCOLOK® Zn Flux is a so-called “reactive” flux, i.e. the compound becomes active only at brazing temperature when it is in contact with aluminium. Pure KZnF3 without contact to aluminium decomposes at temperatures above 700°C. But when in contact with an aluminium substrate, this material initiates a series of reactions beginning at around 565°C. At first, a NOCOLOK®-type flux is liberated together with elemental zinc from the KZnF3 and the aluminium surface according to the following equation:
6 KZnF3 + 4 Al 3 KAlF4 + K3AlF6 + 6 Zn
The flux then dissolves the oxides present on the aluminium.
Once the Al/Si eutectic melting point is reached at 577°C, the filler alloy (supplied from a clad layer by one of the base components) starts to gradually liquefy until the maximum brazing temperature is reached. During this entire period the elemental zinc, which is formed by the NOCOLOK® Zn Flux, diffuses into the surface of the base component, thus creating a zinc diffusion layer – as is also known from zinc sprayed surfaces.
The coating process for NOCOLOK® Zn Flux on aluminium components can be adjusted to provide exactly the same diffusion profiles as in zinc flame spraying. Furthermore, this material allows the modification of precise zinc levels in a much more controlled manner, because the handling of a fine powder provides increased flexibility.
Tests confirm the good results
Successful brazing is feasible with a NOCOLOK® Zn Flux load of just 3 – 5 g/m2 – Another step to reduce overall flux consumption – because this material provides flux and zinc at the same time. Well defined physical and chemical product properties are essential performance factors. The melting behaviour and compatibility with appropriate coating binder systems were researched by Solvay and further developed and optimised in joint projects with our customers.
Currently, the main fields of application for NOCOLOK® Zn Flux are the production of automotive condensers and next generation evaporators. The compound therefore is used together with cladded brazing sheet.
Watch the brazing process as an animated video:
Dear,Currently we are using Zinc Coated tubes for making MF Condensers, what will happen if i use the Zn-Flux on already Zinc Coated tube. Would it give some extra benefit or not?
NOCOLOK Zn Flux is developed as an alternative to Zn arc spray coated tubes. The usage of Zn Flux on a Zn coated tube would not provide additional benefit. I would rather expect some negative effect because the overall Zn level will get too high.