Flux Characteristics and Transfer Systems in Electrostatic Application – Part 3




Flux Powder Fluidization:

In an effort to develop a flux with more desirable properties for electrostatic application, the first step is to qualify criteria. In summary of the above, it is apparent that fluidization is one of them. There is standard equipment available on the market to quantify fluidization characteristics. However, when we tested these fluidity indicators, we found the fluidization ability of flux powder to be so poor that the results were meaningless unless a vibration unit was attached to the equipment. A photo of the modified installation can be found in the attachments. We combined a Binks-Sames powder fluidity indicator (AS 100 – 451 195) with a Fritsch vibration unit (L-24). The equipment consists of a fluidizing cylinder with a porous membrane on the bottom. The cylinder is mounted to a vibrator with a fixation plate. After the sample material (250 g) is placed in the cylinder, the vibration is turned on (via the vibrator control unit) and a consistent flow of dry nitrogen (via the fluidity meter control unit) is forced through the porous membrane. Depending on its potential to fluidize, the powder will start to expand until an equilibrium is reached (one minute). Measurements of the original and the fluidized height are taken at different points (see attachment).


Powder Fluidity Indicator


Indication of the locations for
the measure of the height of the
powder in both fluidized and
non fluidized condition.


Collecting powder as it comes out of the
calibrated hole.

The second parameter determined with this device is the weight of powder flowing through a small hole on the side of the cylinder (as can be seen on the picture). Similar to the above procedure, the sample is fluidized in the cylinder. The side hole is then opened for 30 seconds, and the powder flowing out is caught in a beaker and weigh.

The spray factor is a combination of the expansion factor and the powder flow. Especially in dry flux application, where the material transport depends on fluidizing properties, the spray factor presents an important relative figure for powder evaluation.

To be continued …

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Back to part 2

Flux Characteristics and Transfer Systems in Electrostatic Application – Part 2




The background of electrostatic flux application:

When controlled atmosphere brazing with non-corrosive fluxes was introduced, the only realistic method for using the flux was wet application. This strategy was supported by the physical and chemical properties of flux powder.

Non-corrosive fluxes for aluminum brazing consist of potassium fluoroaluminates (inorganic fluorides) with low water solubility. The majority of the flux products on the market are manufactured by precipitation in aqueous solution. These show a rather fine particle size distribution, i.e. from one to fifteen micrometers (1 – 15 µm) for most of the grains (50% and more) and reaching from 0.5 – 50 µm with an average particle size between four and ten micrometers (4 – 10 µm). This type of powder is ideal for slurry application, as the fine particles prevent the flux from settling too fast. Also, when sprayed on a clean surface under wettable conditions, they present a uniform, very thin and fully adhesive coating after drying. As mentioned earlier, the flux slurry needs to be agitated continuously and the concentration must be monitored in order to guarantee consistent flux loading (i.e., flux weight per surface area).

The most significant problem in wet application is waste water. With stricter requirements and limitations for trace impurities in waste water, the pressure to reduce water consumption increases. At the same time, production capacity is expanding worldwide. Waste water treatment is expensive, and some brazing operations have limited experience in this field. In addition, more and more facilities are constructed in areas where water appropriately treated for flux slurry preparation is scarce and costly.

The challenges of electrostatic flux application:

Electrostatic powder coating has been standard technology for many years, and it was only a question of time before it was also realized in flux application. The following will focus on essential flux properties and basic equipment arrangements.

Some material characteristics of non-corrosive brazing fluxes make it difficult simply to transfer the normal powder coating equipment to the fluxing area and use it there. Most powders utilized for electrostatic application are either designed with special properties or already contain them. Important elements are:

  • Particle shape and particle size distribution
  • Ability to accept and to hold electrical charge

Particle size distribution has a significant influence on the ability of a powder to fluidize and to flow. Better fluidization characteristics lead to better equipment performance. Consistent flux transfer and the ability to flow through pipes and plastic hoses is directly affected by fluidization. Additionally, it has been observed that good fluidizing material shows less tendency to build up in the equipment. Buildup can quickly result in interruptions of the flux flow. When this buildup is expelled the nozzle may release an excessive amount of flux. This excess will in turn be deposited on the surface of the part, resulting in non-uniform flux distribution. It is possible to induce charge on flux when it travels through an electrical field. However, the powder, by its chemical and physical nature, displays instantaneous charge decay when it hits the grounded heat exchanger. Therefore, the forces that adhere the flux to the part are not electrostatic forces, but are more likely Van der Waals forces. In dry flux application, the following complications have been described by users when operating conventional flux qualities:

  • Fluidizing the powder and material transport is difficult. Vibration or stirring is necessary to improve on these characteristics
  • Problems with consistency of flux flow and uniformity of applied flux
  • Adhesion of deposited flux is inferior when compared with wet application
  • High humidity causes physical adsorption of water molecules to the fine powder dust in the booth. This may result in agglomerations
  • Recovering, recycling and reusing flux requires special attention

To be continued …

Back to part 1

Forward to part 3

Flux Characteristics and Transfer Systems in Electrostatic Application – Part 1





This article summarizes some experimental results of a project on electrostatic application of non-corrosive fluxes for aluminum brazing. The objective is to qualify and quantify flux powder properties and equipment parameters with positive effect for dry flux technology.

For more than 30 years, controlled atmosphere brazing (CAB) [NOCOLOK ® Flux brazing] has been the leading technology for the manufacture of aluminum heat exchangers for the automotive industry.

The most common flux application method is by spraying an aqueous suspension. Constantly agitated flux slurries with concentrations of approximately 10 – 35% solids are pumped from tanks to fluxing booths. All aluminum surfaces involved in the brazing process are coated with the slurry, resulting in a uniform flux layer. Excess flux slurry is removed with a high-volume air blow; the excess is then collected, recycled and reused in the fluxing booth. Before going into the furnace, the heat exchangers are pre-dried in a separate drying oven to remove residual moisture.

In wet flux application, the following are critical factors and need specific observation by the user:

  • Flux slurry concentration
  • Consistency and uniformity of applied flux
  • Flux loading on heat exchangers
  • Drying step

Depending on the particular brazing operation, flux slurries may become contaminated with dust, metal particles, rust and organic compounds. The used slurry also contains the soluble portion of the flux (i.e., small levels of potassium, fluoride and aluminum), and must therefore be treated and then disposed of in accordance with environmental regulations.

Over the past five years, some users of NOCOLOK brazing technology have implemented dry flux application methods. Based on the principles of powder paint technology, an alternative application technique was introduced in the brazing industry.

The benefits of electrostatic application are directly related to the problems of wet application:

  • No need to mix slurries
  • No need to monitor slurry concentration
  • No need for a surface wettability concept (i.e., surface treatment or wetting agent)
  • No separate drying step required to remove moisture
  • No waste water effluent

Particularly when dry fluxing is used in connection with evaporative oils and lubricants, the objective is to eliminate or significantly reduce water consumption during the process.

To be continued …

Forward to part 2

Forward to part 3

Introduction of NOCOLOK® Cs Flux (SM) as Synthesized Material

What is NOCOLOK® Cs Flux (SM)? (Synthesized Material)

NOCOLOK® Cs Flux is used for brazing of aluminium alloys with higher magnesium levels. The Cs flux currently available for CAB (Controlled Atmosphere Brazing – furnace brazing) is a technical mixture (i.e. a mechanical blend) of K-Al-F flux (NOCOLOK® Flux) with Cs-Al-F flux – this product is offered under the name NOCOLOK® Cs Flux (TM): Technical Mixture. 

The new NOCOLOK® Cs Flux (SM) is a fully synthesized material – i.e. a unique and homogenous product. The Cs is completely embedded in a Cs-K-Al-F matrix during the manufacturing process.


When comparing the characteristics and application of blended Cs Flux “(TM)” with synthesized material “(SM)”, there are notable advantages of the new quality:

  • The mixture can show settling and separation in flux slurries and paints.  This is caused by differences in the density, the particle size, and the solubility of the two compounds in the blend.
  • In the new fully synthesized material – with the Cs completely incorporated in a Cs-K-Al-F matrix – the density is consistent and the particle size more uniform.  We have a homogeneous powder with improved stability in suspensions (i.e. for slurries, paints, and pastes).
  • In addition, the overall solubility is reduced when compared with the blended material.
  • There will be less settling and less separation – which means that there is  enhanced application performance with NOCOLOK® Cs Flux (SM).

NOCOLOK® Cs Flux (SM) is on stock at our Wimpfen facility and available right away. 

Worldwide Registration

For a number of years, more and more countries are converting their existing chemical regulations or are implementing new regulations. In many cases, these regulations ​c​an be considered as an adaption of the European REACH Regulation. A registration of chemical substances or reaction masses is required, including comprehensive material data sets and risk assessment. 

Solvay appreciates and supports these new product safety initiatives.
As a consequence, however, this leads to that in order to fulfill all regulatory requirements new products can only be introduced stepwise to other countries.

NOCOLOK® Cs Flux (SM) has already been successfully registered according to the European REACH Regulation and can be used without restriction within the European Union. Please also refer to our Safety Data Sheet, which is available on request. Registration for other countries/regions will be done successive. For more information, please contact our local sales offices.​



Flux Pastes – Part 2

Go to Flux Pastes – Part 1


NOCOLOK® flux and brazing pastes offer numerous advantages that distinguish them from other products.

1. Solvent system
Use of systems miscible with water and glycols

  • Equipment and facilities used for paste application can be easily cleaned with water
  • If required, the setting or adjustment of viscosities is possible with certain glycols


2. Variable viscosity
Depending on requirements, the pastes can be produced in a wide viscosity range and with different solids contents.

  • Flux pastes
    Possible viscosity range 500 – 50,000 mPa·s
    Flux content 5 – 60 %
    Variable flux content at constant viscosity 15 – 30 %
  • Brazing pastes
    Possible viscosity range 1,000 – 80,000 mPa·s
    Flux content 15 – 40 %
    Plummet content 15 – 45 %


3. Minimum precipitation of the pastes

  • Low settling behaviour of the contained solids even after several weeks of storage
  • Simple agitation, homogenisation is – if necessary – possible


4. Very good adhesion

  • Marginal running during application of the paste, even on vertical surfaces
  • By use in multi-chamber tubes, there is no leakage during transport, storage or processing

Comparison of vertical adhesion of brazing pastes

Above is a conventional brazing paste; Below NOCOLOK® brazing paste after 15, 45 and 75 minutes

5. Residue-free solvent system

  • Evaporation and removal of the glycol carrier system from the surfaces takes place at below 200 °C
  • The complete solvent content of the pastes comes off in the first third of the brazing cycle
  • Consequently, the removal of the glycol carrier system is possible in the drying phase or in the degreasing furnace before the brazing process

The resulting emissions are thus removed in good time before the brazing process by appropriate channelling of the waste gases. Therefore, the actual brazing process is not affected.

Differental Thermo Analysis (DTA) of NOCOLOK® Flux Paste – Representative Sample

At just under 200 °C, the organic solvent have decomposed without residue.


Available packaging forms

  • Plastic container 1 kg
  • Plastic buckets 5, 10, 15 or 20 kg
  • Optional: Plastic drums 60 or 200 kg

Go back to Flux Pastes – Part 1

For more information please download the brochure






Flux Pastes – Part 1


  • Flux Pastes are mainly used inside B-tubes and folded tubes, in order to provide a line of flux on a cladded surface. These paste formulations are available in FG (fine grade) version, the N version (“new” – i.e. with adjusted rheology and re-mixing characteristics) and UV version (ultraviolet sensitive pigments for special application monitoring).
  • Metalized Flux Pastes (Brazing Pastes) are often used manifolds/tubes or blocks/manifolds or header/tubes or in any place there is need for joint formation with additional filler metal (usually used to compensate for challenging design situations or for larger tollerances on stamped parts).
  • Ultra Flux Paste is used inside B-tubes and folded tubes, in order to provide a line of flux on a cladded surface (more “sticky” than glycol family “028”).

NOCOLOK® Flux Pastes

NOCOLOK® flux and brazing pastes command a maximum variety of options in flux and brazing alloy powder applications.

Consequently, NOCOLOK® flux pastes can be individually adapted according to respective technical requirements and the brazing processes used.

Possible NOCOLOK<sup>®</sup> Flux brazing paste variations:

  • NOCOLOK® Flux Standard
  • NOCOLOK® Cs Flux
  • NOCOLOK® Li Flux

Alloy powder:

In combination with the various flux powders, NOCOLOK® brazing pastes can contain different brazing alloy according to the application requirements:

AlSi12     AL104 (DIN EN 1044)     AA 4047

AlSi10     AL103 (DIN EN 1044)     AA 4045

AlSi7,5     AL102 (DIN EN 1044)    AA 4343

The grain size of the brazing powder can be adapted to all corresponding applications.

Application Areas for NOCOLOK® Flux and Brazing Pastes

  • Production of multi-chamber tubes
  • Use as B-pipe flux paste
  • Furnace brazing
  • Flame brazing


Go to Flux Pastes – Part 2

For more information please download the brochure

Myths about Aluminium Brazing Fluxes – Part 1


Myth – Fluxes With a Lower Melting Range are Superior

There are claims that a lower melting point flux is better for brazing (i.e. melting between 550 and 560°C – approximately 10 – 15°C below conventional fluxes). The idea here is to try to fool the engineer by illustrating the merits of “early” flux melting, and thus “prolonged” flux action. However, the facts are very different.

As soon as the flux begins to melt, one of the components of the flux – KAlF4 – begins progressively evaporating, with a vapour pressure determined to be 0.08 mbar at 600°C. Evaporation of KAlF4 causes the flux melt to change composition, and it begins to dry out. Given enough time, it is possible for the flux melt to completely dry out before reaching the maximum peak brazing temperature.

A good brazing flux only needs to be available just before filler metal melting. The following table describes what happens at brazing temperature:

Myths on Brazing Flux

Table 1

As soon as the flux melts, it begins to dissolve the oxide layer, and this solvating process continues until the oxide is removed, even if the filler alloy has melted. The above table shows that even if the period of flux activity would be limited only to the time between complete flux melting and the lower brazing range of AA 4045, it is still adequate. The authors thus consider a flux melting range between 560 and 575°C as the most suitable for aluminium brazing with Al-Si filler alloys.

One should not completely dismiss the point made about “prolonged” fluxing action with lower melting point fluxes. However, once again, all the information must be examined. It has been shown that with an increase in the K2AlF5 content, the flux will start to melt at a lower temperature so that the flux will work at a lower temperature. However, even if KAlF4 evaporation is ignored increasing the K2AlF5 content eventually prevents the flux from spreading smoothly, and therefore affects the efficiency of the flux.

Merely lowering the melting point does not in itself create a better brazing flux.

Table 2

Table 2


Figure 1

Figure 1


To be continued…

New NOCOLOK® Packaging Brochure now available!

This new brochure shows the different packaging types available for our NOCOLOK® product range including Powders, Pastes and Paints and Liquids.

Any special package request?
Don’t hesitate to contact us!

Download NOCOLOK Packaging

NOCOLOK Packaging

Flame Brazing Technology – Part 4


What is critical

Have a clean surface (free of dust, grease)
Heat the joint evenly to brazing Temperature
Choose the right brazing alloy for the job (Mg content !)
Select the appropriate flux to remove the oxide skin from the faying surfaces of the joint
Use a capillary gap of the appropriate size

ALUMINIUM BRAZING – Correct brazing temperature

Melting point of copper 1084°C
Copper‐phosphorus alloy

  • Elgalin Cu87 657°C ‐ 687°C
  • Elgalin Cu93 710°C – 820°C

Abbildung 4-1

No flux necessary
Brazing temperature is below the melting
point of base material

Melting point of aluminium 630‐660°C
Aluminium‐Silicon alloy

  • AlSi12 577°C – 585°C

Abbildung 4-2

Flux is necessary
Brazing temperature is very near the
melting point of base material

ALUMINIUM BRAZING – Correct brazing temperature ‐ flame

Acetylene + O2 3170°C
Propane + O2 2830°C
Natural gas + O2 2780°C

Abbildung 4-3

Acetylene + compressed air 2300°C
Propane + compressed air 1900°C
Natural gas + compressed air 1850°C

Abbildung 4-4


CAPILLARITY – right gap of the brazing joint

Capillary action works with gap between 0.05 and 0.2mm

Abbildung 4-5Preciseness is essential for Al brazing.

Flame Brazing Technology – Part 3


U‐shape brazing alloys with flux integrated into material



  • 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



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



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…