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Flame brazing of aluminum is not new. In fact the very first brazed aluminum assemblies were produced using a chloride based flux and a flame as the heat source. What has changed over the years is the sophistication of the types of fluxes available and to a certain extent the alloy selection.

Introduction

However, even if one returns to the absolute basics of a flame, filler metal and flux, there remains a great deal to be learned about the fundamentals of flame brazing of aluminum. This becomes especially evident when the brazing engineer applies his techniques and equipment to NOCOLOK  ® Flux flame brazing and years of learned practice seem to fail. This is largely due to the fact that the years of acquired knowledge of flame brazing aluminum has come from corrosive chloride-based flux brazing. Unfortunately, the same techniques can not be directly applied to NOCOLOK  ® Flux flame brazing. It is therefore the intention of this article to re-familiarize the brazing engineer with the fundamentals of flame brazing aluminum and use those fundamentals to realize all the advantages of NOCOLOK  ® Flux brazing.

Flame Brazing

What is Flame Brazing?

According to the American Welding Society, brazing is the joining of metals using a molten filler metal, which on cooling forms a joint. The filler metal melting temperature is above 450 °C, but below the melting point of the metals.
Flame brazing then implies the use of a flame as the heat source to accomplish what is described above.

Flame brazing lends itself well to joining components with simple configurations such as tube-to-tube, tube-to-fitting and joints having large thermal mass differences. Since much faster heating rates are possible than in furnace brazing, flame brazing is versatile and as will be explained in more detail later, can braze some Mg containing alloys.

What is NOCOLOK ® Flux?

NOCOLOK ® flux is a white powder consisting of a mixture of potassium fluroaluminate salts of the general formula K1-3 Al‑F4-6. The flux has a defined melting point range of 565 °C to 572 °C, below the melting point of the Al-Si brazing alloy. The flux is non-corrosive and non-hygroscopic and is only very slightly soluble in water
(0.2 % to 0.4 %). The shelf and pot life of the flux is therefore indefinite. The flux does not react with Al at room temperature or at brazing temperature and only becomes reactive when molten.

Role of the Flux

Once molten the flux works by dissolving the oxide film on the Al surfaces to be joined and prevents further oxidation. The flux wets the Al surfaces and allows the filler metal to flow freely into the joints by capillary action. Upon cooling, the flux solidifies and remains on the surfaces as a thin, tightly adherent film, which need not be removed.

Joint Clearances

The recommended gap tolerances for flame brazing range from 0.1 mm to 0.15 mm. Larger gap clearances can be tolerated, but capillary action is reduced, gravity activity is increased and more filler metal may be required. Friction fits should also be avoided as this will restrict filler metal flow and result in discontinuities in the brazed joint area.

Flame Brazing

The Theory and Practice of the Flame- and Furnace-Brazing of Aluminium 

Footer-Brazing-Seminar-2018

Dates: October 9 & 10, 2018 in Hannover/Germany 

Purpose of the Seminar: 
The language of the seminar is English. It will take place in the Conference Center and laboratories of Solvay GmbH, in Hannover, Germany. It will provide information concerning the manufacturing practices commonly used for brazing operations and, in particular, will address the three fundamental aspects of the industrial-scale brazing of aluminium. These are:

  • The flame brazing of aluminium.
  • Controlled Atmosphere Brazing (CAB) of aluminium heat exchangers with non-corrosive fluxes (NOCOLOK® Flux).
  • The methodology of how to ensure that the brazing process selected is, indeed, the one that represents ‘best practice’.

Who should attend this two-day seminar? 

  • Technical staff who need to have a specific understanding of either one or both of the fine details of the technology of the brazing of aluminium with flames, and/or the NOCOLOK® furnace brazing process.
  • Design and production engineers who are fabricating, or who are intending to fabricate, aluminium pipe-work assemblies and/or condensers and/or evaporators.
  • Production Engineering Department Managers whose duties include day-to-day responsibility for the brazing of aluminium

eabs-youtube

Watch the video of the Solvay Technical Training Seminar

Here you can find the detailed seminar programme and registration.
And here the hotel booking form.

The Theory and Practice of the Flame- and Furnace-Brazing of Aluminium 

 
26081-Footer-Brazing-Seminar-2017
 

Dates: September 5 & 6, 2017 in Hannover/Germany 

 
Purpose of the Seminar: 
The language of the seminar is English. It will take place in the Conference Center and laboratories of Solvay GmbH, in Hannover, Germany. It will provide information concerning the manufacturing practices commonly used for brazing operations and, in particular, will address the three fundamental aspects of the industrial-scale brazing of aluminium. These are:

  • The flame brazing of aluminium.
  • Controlled Atmosphere Brazing (CAB) of aluminium heat exchangers with non-corrosive fluxes (NOCOLOK® Flux).
  • The methodology of how to ensure that the brazing process selected is, indeed, the one that represents ‘best practice’.

Who should attend this two-day seminar? 

  • Technical staff who need to have a specific understanding of either one or both of the fine details of the technology of the brazing of aluminium with flames, and/or the NOCOLOK® furnace brazing process.
  • Design and production engineers who are fabricating, or who are intending to fabricate, aluminium pipe-work assemblies and/or condensers and/or evaporators.
  • Production Engineering Department Managers whose duties include day-to-day responsibility for the brazing of aluminium

eabs-youtube

Watch the video of the EABS Technical Training Seminar

Here you can find the detailed seminar programme and registration.

The Theory and Practice of the Flame- and Furnace-Brazing of Aluminium 

 

Dates: September 6 & 7, 2016 in Hannover/Germany 

 

Brazing Seminar NOCOLOK

 

Purpose of the Seminar: 

This technical training seminar will be presented in the English language at the Conference Centre and laboratories of Solvay GmbH, in Hannover, Germany. It will provide information concerning the manufacturing practices commonly used for brazing operations and, in particular, will address the three fundamental aspects of the industrial-scale brazing of aluminium. These are:

  • The flame brazing of aluminium.
  • Controlled Atmosphere Brazing (CAB) of aluminium heat exchangers with non-corrosive fluxes (NOCOLOK® Flux).
  • The methodology of how to ensure that the brazing process selected is, indeed, the one that represents ‘best practice’.

Who should attend this two-day seminar? 

  • Technical staff who need to have a specific understanding of either one or both of the fine details of the technology of the brazing of aluminium with flames, and/or the NOCOLOK® furnace brazing process.
  • Design and production engineers who are fabricating, or who are intending to fabricate, aluminium pipe-work assemblies and/or condensers and/or evaporators.
  • Production Engineering Department Managers whose duties include day-to-day responsibility for the brazing of aluminium

eabs-youtube

Watch the video of the EABS Technical Training Seminar

Here you can find the detailed seminar programme and registration.

U‐shape brazing alloys with flux integrated into material

u-rings-picture

Advantages

  • Reduced labor cost
  • Reduced waste
  • No post-braze cleaning
  • Flexible design
  • Multiple applications
  • Ideal geometry for feeding
  • No hidden flux voids
  • Precise control of alloy and flux

 

Ideal for Preforms

  • Unlimited preform options
  • Flux flows unobstructed

u-rings-drawing

NON‐CORROSIVE FLUX

No post braze cleaning required, reducing the environmental impact associated with waste water

treatment

LESS CONTAMINATION

there are no powders leaching out to contaminate assembly equipment. The flux we deposit in the

channel stays in the channel.

Microsoft PowerPoint - HPa Flame brazing.pptx

Download the brochure.

To be continued…

Selecting the Correct Flux –WHAT?
The first requirement of an Aluminium brazing is to be chemically effective.
Fluxes are categorized as active (corrosive) and inert (noncorrosive).

Fluoride base fluxes → NON‐CORROSIVE
The fluxes leave the white gritty residue on the part. These fluxes include the higher temperature potassium
aluminium fluoride and the lower activated cesium aluminium fluoride Fluoride flux residues is tightly adhered to aluminium surface, relatively insoluble, not necessary to be removed. Fluoride flux operates by melting, spreading and dissolving of aluminium oxide layer.

Active fluxes ‐ Chloride base fluxes → CORROSIVE
The appearance of the part after brazing is bright and shiny. The chloride post braze residues must be removed by water washing or chemical treatment, to prevent the occurrence of electrolytic corrosion. These fluxes require a significant exposure to hot water to remove the corrosive flux residues. Attention must be given to the outside of the assembly and to any residues that have migrated to the inside of the part.
Chloride flux is reported to work penetrating aluminium oxides at weak points and breaking up the oxide/aluminium bond.

Selecting the Correct Flux –WHY?
Effect of Mg content on mechanical properties and braze ability of Al‐alloys.

Microsoft PowerPoint - HPa Flame brazing.pptx

0,3‐0,6% Σ(Mg+Cu)% -> 2% cesium flux
0,6‐0,9% Σ(Mg+Cu)% -> 6‐10% cesium flux
0,9‐2% Σ(Mg+Cu)% -> 100% cesium flux
>2% Σ(Mg+Cu)% -> 726/0726 pastes

Correct filler metal / Correct flux
Fluxes must be thermally matched to the melting phase of the braze filler base metal.

Microsoft PowerPoint - HPa Flame brazing.pptx

CORROSIVE flux paste for the flame brazing of aluminium materials
Al‐FLUX 0726/2zG – Flux Paste
• As the active component of Corrosive‐Flux‐Paste, AL‐Flux 0726 contains a mixture of LiCl,
NaCl, KCl, inorganic‐ and complex‐ fluorides.
• Organic carrier systems are used to prepare a wide range of pastes for the flame brazing of
aluminium materials.
• Al‐Flux 0726 Flux Paste is typically applied by dispensing and brushing for flame brazing. No
component mixing is required. Products are supplied as ready to use products, requiring short
remixing

Download product information.

NON‐CORROSIVE Flux Paste for the flame brazing of aluminium materials
NOCOLOK® 028/55 Cs2 ‐ Flux Paste
NOCOLOK® 028/55 Cs3 ‐ Flux Paste
NOCOLOK® 028 CsD ‐ Flux Paste
From low‐temperature brazing (450°C) to the brazing of high‐strength aluminium alloys.

Download product information.

To be continued…

Aluminium joining – Brazing ‐ Flux function



What is brazing?
Brazing is the joining of metals using a molten filler metal. On melting, the filler metal spreads between the closely fitted surfaces, forms a fillet around the joint and on cooling forms a metallurgical bond. By technical definition ‘brazing’ is a joining process in which the filler metal melting temperature is above 450°C, but below the melting point of the metals to be joined.


Aluminium brazing ‐ How does it work?
An aluminium oxide layer is formed instantly on aluminium in the presence of oxygen. This oxide layer has to be removed before brazing and the formation of a new oxide layer has to be prevented. The oxide layer is chemically dissolved by a FLUX.

 

use_of_flux

Aluminium joining – Flame Brazing



Flame (torch) brazing of aluminium involves locally applied heat typically generated by a slightly reducing oxy‐acetylene or oxy‐natural gas flame. (Gas mixture is preferred as it is cheaper and more comfortable).
Care must be taken to ensure even heat distribution. As with other aluminium brazing processes, close temperature control is important – it`must be closely monitored as there is no colour change in the aluminium to indicate temperature.


Flamebrazing1


Flamebrazing2

 

Aluminium joining – Basic Requirements


CORRECT FLUX / CORRECT FILLER METAL / CORRECT DIFFUSION OF FILLER METAL
The first requirement of an Aluminium brazing is to be chemically effective.
Fluxes are categorized as active (corrosive) and inert (noncorrosive)

CORRECT BRAZING TEMPERATURE
Between liquidus and solidus of filler metal
Decide how to manage the small thermal window between the melting temperature of the brazing filler metal and thermal damage to the base metals

BRAZING THROUGH CAPILARITY / RIGHT GAP OF THE BRAZING JOINT
Apart from the selection of flux and filler metal, important process parameters are the cleanliness and proper geometrical alignment of the individual components.


To be continued…

Making fire from water is a seemingly insoluble contradiction – but in 2014 the project will hit the markets.

Instead of propane or acetylene, hydrogen is burnt, which in turn is produced from water in an electrolyzer. Also, the oxygen for the combustion arises from the chemical decomposition. The portable unit requires a standard 220 volt outlet and plenty of water. Therefore, no pressure cylinders for fuel gas and oxygen are required.

Safe-Flame

In addition, the flame burns much more smoothly and the hot spot is located outside of the burner head. The first tests, brazing aluminum, have been completed successfully.

The Safe Flame project is supported by the EU and actively supported by 11 partners, including EABS (The European Association for Brazing and Soldering).

Solvay supporting EABS technical awareness days for the joining of aluminium and copper piping in the huge global HVACR market. These will commence in January 2014 and run through out the year and will include ALL flames for brazing Al/Al, Al/Cu and Cu/Cu together with appropriate brazing alloys and fluxes.

For further information either contact Solvay or EABS.

Safe-Flame-Logo

A video and more information can be found on Euronews.com

euronews-video

The European Association for Brazing and soldering — EABS for short — together with experts from Solvay Fluor, holds technical training seminars in which the theory and practice of flame and furnace aluminium brazing are communicated in detail.

40 interested participants from all over the world gather for the two day seminar in Hannover, Germany: technical staff, design and production engineers as well as production engineering managers.

EABS Seminar

More information about the seminar.

Brazing aluminium to copper is common in the refrigeration industry where copper tubes are brazed to aluminium roll-bond panels or tubes. To join aluminium and copper using brazing technology and standard NOCOLOK® Flux, flame brazing would be applicable (as well as using a low-melting flux with a low-melting filler metal). It is very similar to brazing aluminium to aluminium, but some precautions are necessary.

However, when copper is brazed to aluminium and the heating process takes too long, the copper will diffuse into the aluminium at the joints. A low melting Al-Cu alloy (Al-Cu33 eutectic temperature 548°C) is thus formatted, and this could lead to erosion by perforation.

Therefore, during the brazing process, the flame should never be directly applied to the joint, because the heat should be transferred by conduction through the parts to be brazed. As soon as the filler metal begins to melt, the flame must be quickly removed.

A second issue with brazing copper to aluminium is that the aluminium has a much lower melting point than copper (Al: app. 650°C; and Cu: above 1000°C). Therefore, the flame is usually directed on the copper. Nevertheless, once the heat transferred from the copper to the aluminium reaches the melting range of aluminium, it will start to burn down very fast, while the copper is still taking the heat. The formation of the above mentioned low melting Al-Cu alloy accelerates the destruction of the aluminium components.

Consequently, flame Brazing of aluminium to copper is a delicate process and requires some experience. But it is used by many companies for large scale production. But it is next to impossible in furnace brazing. There are no conventional furnace designs which will cool quickly enough to halt the continual formation of the aluminium-copper eutectic. For this reason, brazing copper to aluminium in a furnace is not practiced.

There are three different ways to provide (or generate) filler metal in flame brazing of aluminium to copper.

  • Use of Al-Si filler alloy (Al-Si 12 – AA4047). Standard procedure like in flame brazing of aluminium to aluminium – just a little bit faster to avoid burn-through.
  • Rely on the formation of Al-Cu alloy during the brazing cycle. If this method is used, a support provided by a thin Stainless Steel tube along the interior joint area can provide additional structural integrity.
  • A pre-heated copper tube is inserted very fast into an aluminium tube. The mechanical energy released will generate additional heat. Abrasion of surface oxide by the inserted tube promotes the formation of Al-Cu filler alloy. This process works with and without flux (however, results are better with flux).