Meet us at the 5th International Congress on
“Aluminium Heat Exchanger Technologies for HVAC&R”

May 12
2017

May 16 – 17, 2017
 in Düsseldorf, Germany

 

The 5th International Congress and Exhibition on Aluminium Heat Exchanger Technologies for HVAC&R, organised by the DVS German Welding Society, will take place from 16 – 17 May, 2017 in Düsseldorf/Germany in the Radisson Blu Scandinavia Hotel.

Stringent environmental requirements for increasing energy efficiency and reducing emissions are the greatest challenges the heating, ventilation, air conditioning and refrigeration industry faces.

The 5th International Congress on “Aluminium Heat Exchanger Technologies for HVAC&R” is dedicated to these challenges.

This is a must-attend event for producers and users in the field of air conditioning and refrigeration.

 

DVS-2017

Programme and Registrationform

Download the invitation, programme and registration form

Myths about Aluminium Brazing Fluxes – Part 2

Sep 23
2016

In Myths about Aluminium Brazing Fluxes Part 1 we reported about the rumor that fluxes with a lower melting range are superior. Now we take a look to another Myths about Aluminium Brazing:

Myth – A Flux with Smaller Particle Size is More “ACTIVE” and Leaves Less Flux Residue

Some rumours have been spread that a flux with a smaller particle size leads to better brazing and results in a more pleasing post-braze appearance.

But the facts are very different. It is true that a flux with a smaller particle size covers the surfaces of the work-piece more completely. Smaller flux grains will also adhere better to those surfaces, assuming that the two fluxes to be compared indeed show a difference in particle distribution.

DSC Scans

Figure 2

As particle size decreases, the total surface area of the flux increases. This allows a higher surface area of flux to be in contact with the work-piece. During heat up, there may be more efficient energy transfer to the flux with the smaller particle size. The net result is that this would affect the kinetics of melting – how quickly the flux melts – but it does not affect the melting temperature range. This is analogous to crushed ice melting quicker than a block of ice, but both melt at the same temperature. The above figure shows the melting action of various particle size fluxes using Differential Scanning Calorimetry or DSC. As expected, all particle sizes melt at precisely the same temperature.

It is also speculated that the ability of the flux to melt and spread (activity) increases as particle size decreases. In fact, the activity of the flux is related to chemistry and phase composition, not particle size. Spreading is simply a liquid phase reaction unrelated to the particle size distribution of the solid phase.

A practical example showing how flux particle size is unrelated to brazing results is comparing NOCOLOK® Flux (X50: 2 – 6µm) used for wet fluxing with NOCOLOK® Flux Drystatic (X50: 3.5 – 25µm) used for electrostatic fluxing. Heat exchangers brazed by wet fluxing can be brazed with the same results using dry fluxing, and the only difference is the particle size of the flux. The success simply depends on applying the flux uniformly.

Finally, the appearance of the post-braze surface is only related to the initial flux loading, not particle size. Once the flux melts, it is completely liquid. In its molten state, the flux has no particles – neither large nor fine. Once the flux is liquid, it immediately spreads out and wets the surfaces. Upon cooling and solidification, the amount of flux residue and its distribution on the surface of the work-piece is related entirely to the initial flux loading, and not particle size.

It is true that particle size distribution of a flux affects slurry characteristics. A finer powder will stay longer suspended (i.e. it settles slower) than a coarser product. Material with larger grains seems to build-up more rapidly on inside surfaces of slurry tanks and spraying equipment. Regardless of the specific particle distribution of a flux, continuous agitation is necessary to prevent settling and build-up. Regular maintenance is the only way to avoid the formation of solidified material residues.

A realistic comparison of particle size distribution can only be done by measuring samples on the same equipment under exactly the same conditions.

Furthermore, we have electron microscope comparison pictures of several flux powders – showing that the grain morphology is quite similar in all products.

SEM Picture NOCOLOK© Flux Quzhou 1,000/4,000/16,000

SEM Picture NOCOLOK© Flux Quzhou 1,000/4,000/16,000

SEM Picture NOCOLOK© Flux Bad Wimpfen 1,000/4,000/16,000

SEM Picture NOCOLOK© Flux Bad Wimpfen 1,000/4,000/16,000

SEM Picture Competitor 1 1,000/4,000/16,000

SEM Picture Competitor 1 1,000/4,000/16,000

SEM Picture Competitor 2 1,000/4,000/16,000

SEM Picture Competitor 2 1,000/4,000/16,000

Myths about Aluminium Brazing Fluxes – Part 1

Aug 18
2016

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…

SECO/WARWICK Webinar:
Low Volume Cab Systems/Vacuum Purging

Mar 04
2016

Looking for alternatives of a standard aluminium brazing process with a lower level of nitrogen consumption or you are involved in the process of heat exchangers manufacturing, especially in the automotive and aftermarket, don’t miss the Webinar. SECO/WARWICK guarantee a high quality of brazing process of elements, especially for unique types of aluminium heat exchangers.

Webinar date: 3PM CET, March 22, 2016

Visit the Website of SECO/WARWICK for details

Flame Brazing Technology – Part 4

Feb 29
2016

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

Jan 29
2016

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…

Flame Brazing Technology – Part 2

Dec 21
2015

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…

Flame Brazing Technology – Part 1

Nov 30
2015

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…

NOCOLOK® App 3.0

Aug 06
2015


The NOCOLOK® app has received a facelift. Straightforward design, ease of use, adaptation to the current branding – the NOCOLOK® App has been thoroughly revised and in the handling improved.

All NOCOLOK® products and tools are easy to find, as are the packaging and packaging options. Calculators for flux load and flux slurry assist by speedy calculation of amounts and concentrations. A real reference book for all technical terms is the NOCOLOK® Encyclopaedia. New are the topics flux paints and pastes. The update is automatically displayed – upload the new version of NOCOLOK® app on your smartphone.

nocolok-app

You don’t know the NOCOLOK® app yet?
Then it’s time you did!

iOs

qr_nocolok_ios


Android

qr_nocolok_android

 

 

 

Flux Paints and Pastes – Part 2

Jul 27
2015

Part: 1: Flux Paints and Pastes – Part 1

Flux and Braze Paste Characteristics

The purpose of flux and/or braze pastes is to provide an initial or supplemental volume of flux and/or filler metal in the form of a viscous liquid at or near the interface of two components:

  • Folded tube seams
  • Tube to header joints
  • Connector tube to manifolds
  • End caps
  • Blocks and fittings
  • Flame braze joints

Viscosity

Flux and braze pastes exhibit pseudoplastic viscosity, meaning to have shear thinning behavior. As the shear stress is increased, the viscosity decreases, but the relationship is not linear. When the shear stress decreases, the viscosity increases, again non-linearly. Other factors affecting viscosity are solids content and temperature. Generally speaking, as the temperature increases, the viscosity decreases. Conversely, as the solids content increases, the viscosity also increases. These dependences illustrate the importance of quoting the parameters under which the viscosity is measured.

The graph below shows the effect of temperature on viscosity:

gf_Temperature_viscosity_1_RGB

Note that at each temperature, a double curve is shown representing two sets of measurements: one curve shows the decrease in viscosity as the shear rate is increased and the other curve shows the increase in viscosity as the shear rate is decreased. This mirrored behavior as the shear rate is increased or decreased perfectly illustrates the pseudoplastic behavior.

The following curves show both: – the effect of temperature, and – solids content on viscosity:

gf_Temperature_viscosity_2_RGB
These properties allow a bead of flux paste to be dispensed on the surface of a folded tube consistently and continuously at line speeds ranging from 30 m/min to 120 m/min.
braze-paste

Influence of Carrier on Volatilization Behavior

Since the carrier is a main ingredient, the carrier burn off temperature must be considered.

Below are 3 TGA curves showing burn-off temperature of 3 different paste formulations:

Glycol based carrier

Glycol based carrier – burn off at 180°C @ 10°C/min

 

Acrylate based carrier

Acrylate based carrier – burn off at 400°C @ 10°C/min

Polybutene based carrier

Polybutene based carrier – burn off at 425°C @ 10°C/min

 

Delivery Systems and Recommendations

When designing a flux delivery system, choosing the right delivery pump is just as important. Below is a list of pros and cons for the associated pumps.

Diaphragm Pump

  • Low cost, low maintenance
  • High flow
  • Generally used for low viscosity fluids
  • Pulsation, viscosity sensitive
  • Poor flow metering

Air Over Liquid (Pressure Vessel)

  • Low cost, low maintenance
  • Temperature sensitive
  • Viscosity sensitive
  • Poor flow metering

Rotary/Gear Pump

  • High viscous liquids
  • Metered dosing
  • Pulsation
  • Does not handle solids

Rotor-Stator Pumps

  • High viscous liquids
  • No pulsation
  • Precision metering
  • Not viscosity sensitive
  • Highest cost

Rotor-stator pumps are the pumps of choice because of their ability to deliver a constant volume of material without pulsation over a range of flow rates. The best example of this is in the localized dispensing of a continuous bead/stripe in folded tube mills where speeds can range from 20 m/min to 120 m/min.

In lower demanding applications where precision dispensing and flow control is not so critical, for example in tube to header fluxing, the lower cost options (air over liquid, diaphragm pumps) are more than adequate.

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