Guide to NOCOLOK® Flux by Solvay Fluor: Aluminium brazing – Seven Steps to Success

The properties of the materials involved make brazing the preferred choice for joining aluminium – especially when economic factors are taken into account. Aluminium brazing [aluminium-brazing.com /nocolok/ aluminiumbrazing.php] is, however, a complex application with several challenges along the road to success. A new user guide by Solvay Fluor sets out seven golden rules to achieve success – rules based on many years of experience in the use of NOCOLOK Flux as fluxing agent and flux/binder system.

The seven golden rules of aluminium brazing:

1. Choose the right alloys:
Solvay Fluor has published a tabulated listing of suitable and classified aluminium alloys on its aluminium brazing website. Most alloys of the 1xxx and 3xxx series are suitable for brazing with non-corrosive fluxes.

2. Clean the surfaces
Dust and dirt, condensates, lubricants, grease and oils must be thoroughly removed. If the metal surfaces are poorly prepared, the brazing flux cannot be applied properly and will not spread evenly. The flow of filler alloy will thus be restricted. This results in incomplete joints. One of the most important process steps is therefore: Always clean the components of all oil and grease. This can be done by using water-based, chemical or thermal cleaning techniques. Thermal cleaning makes use of evaporative lubricants. For best results with water-based cleaners, use a mixture of water, tensides, cleaning agents and active ingredients.

3. Remove the oxide layer
Success in aluminium bonding depends on removing the oxide layer. Molten NOCOLOK Flux penetrates the oxide layer, removing it very effectively. The metal surface is cleaned by the flux, leaving an ideally prepared surface for the filler alloy – the actual bonding material. It is therefore obviously vital that flux is spread across all active brazing surfaces.

4. Choose the right flux and the right filler alloy
When brazing with NOCOLOK Flux a typical filler alloy comprises an alloy of aluminium and silicon (Al-Si). There are various different filler alloys available: in the case of furnace brazing for example, filler alloys with ~ 7.5% Si (AA4343) and others with ~ 10% Si (AA4045) are used.

5. Select the appropriate capillary size (gap)
The work pieces to be joined by aluminium brazing must have the right small spacing to one another. Only the correct gap guarantees the movement of molten filler alloy by capillary action. Rule of thumb: molten filler alloy can flow but it can’t jump. The space determines the strength of capillary action and ultimately the quality of the join.

6. Apply sufficient amounts of flux
As a general rule, the recommended amount of flux is 5 grams per square meter, uniformly distributed on all active brazing surfaces. Manufacturers of heat exchangers quickly gain on experience how much flux is necessary for the specific component designs. One tip: if the right amount of flux is applied, the surfaces look like that of a dusty car. To find out exactly how much flux is needed, check out the “Successful Aluminium Brazing – A Guide” (available as a PDF) or contact our NOCOLOK experts.

7. Heat metal components evenly
An essential factor in controlled atmosphere brazing is even temperature distribution of 600°C across all components to be joined. Controlled heating helps to ensure uniform temperature distribution and thus consistent bonding. Caution: Too slow heating may dry out the flux, reducing its effectiveness. There must be sufficient molten flux present when the filler alloy reaches its melting point. The rule is to make the heating cycle as short as possible while still achieving stable temperature distribution.

Detailed tips available as download

All those who take the above golden rules to heart will enjoy successful aluminium brazing with NOCOLOK Flux from Solvay Fluor as the brazing flux/binder system of choice. For more details and a host of technical and application details, the market leader for non-corrosive fluxing agents has put together a free PDF download. The guide provides advice on how to select materials, temperatures, markers, fluxing agents and filler alloys – and how to make best use of them.

About Solvay ( http://www.solvay.com )

Solvay is an international industrial Group active in Chemistry. It offers a broad range of products and solutions that contribute to improving quality of life. The Group is headquartered in Brussels and employs about 17,000 people in 40 countries. In 2009, its consolidated sales amounted to EUR 8,5 billion. Solvay Fluor combines all fluorochemicals activities of the international Solvay Group. The Solvay Fluor plants in Bad Wimpfen, Germany and Onsan, South Korea produce NOCOLOK Flux and flux/binder systems for aluminium brazing applications.

Press contact:

Solvay Fluor GmbH
Werner Schmitt
Hans-Böckler-Allee 20
30173 Hannover
Tel.: +49(0)511 857-0
E-Mail: werner.schmitt@solvay.com

This release was published on openPR.