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Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Summary

Our research activities so far have been focusing on flux blends with additives to validate lower water solubility of post braze flux residue. Another objective of this work was to allow for brazing of Al alloys with increased Mg levels using non corrosive fluxes.

First steps have been made with selected flux blends.  This paper reflects the current project status, but more work still needs to be done for further improvement.

Low flux residue solubility

It has been shown that the flux residue water solubility is reduced by combining KAlF4 with AEFs (“KAlF4 compound concept”); among them BaF2 being the most promising candidate.

Fluxes for higher Mg tolerance

Flux blends containing KAlF4 plus CsAlF4 and Li3AlF6 seem to be a promising approach to improve brazing of higher Mg containing aluminium alloys.

Aluminium coupons samples (AMAG 6951 with 0.68% Mg) for the base coupon and the angle (1.36% Mg in the joint interface) require flux loads as high as 15g/m2 for successful brazing.

Good joint formation can be achieved at 5g/m2 load on samples with 0.68% Mg content. Thus brazing of higher Mg level Al-alloys with appropriate flux mixtures at process-typical loads seems to be feasible.

Outlook

For the continuation of this project, we need to define the Mg range for real industrial aluminium heat exchanger needs. We think that this can best be done in a joint effort of HX manufacturer, Al material supplier and flux producer.


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Improved Magnesium tolerance

Mg additions to Al alloys contribute to higher strength properties. The ongoing trend in saving weight by down-gauging of Al sheet thickness requires sufficient mechanical stability. One option for the production of higher strength Al alloys is to increase the Mg content.

A disadvantage of Mg is the interaction with potas-sium fluoroamuminate fluxes during brazing, which results in poor joint formation [3] [4]. This effect, known as “flux poisoning”, is caused by the formation of high melting compounds. The addition of caesium and other metals to the flux helps to compensate to a certain degree the poisoning [6].

For the first set of laboratory brazing experiments we chose commercially available AMAG 6951 brazing sheet (0.68% Mg, 4343 clad) and clad-less AMAG angle material (0.68% Mg) to investigate the brazing performance and joint formation. In this situation the metal-to-metal interface adds up to 1.36% Mg (2 x 0.68%) in total.

Table 1 shows a list of representative flux combina-tions with NOCOLOK® types, KAlF4, Li3AlF6. CsAlF4, and AEFs.

We repeated all brazing tests with each sample three times.

Flux Type Load Fillet visual validation Comment
NOCOLOK® Cs Flux 10 g/m2 100% very small joint inconsistent seam
MD001212 LiCs24 10 g/m2 100% small joint weak seam
MD001223 LiCs43 10 g/m2 86% small joint inconsistent seam
AB039215 KAlF4/BaF2 10 g/m2 52% small joint inconsistent seam
NOCOLOK® Cs Flux 15 g/m2 100% weak seam
MD001212 LiCs24 15 g/m2 100% thicker than with NOC Cs Flux
MD001223 LiCs43 15 g/m2 100% thicker than with NOC Cs Flux
AB039215 KAlF4/BaF2 15 g/m2 98% weak seam slighly better than NOC Cs Flux

Table 1: Brazing trials: AMAG clad – AMAG clad-free angle different flux blends based on KAlF4 plus BaF2/Li3AlF6/CsAlF4

The angles from most of the AMAG specimens could be removed after brazing by pulling. Only a broken inner and outer fractured seam line was left – as can be seen below in picture 1 a.
flux_residus_part3_1
flux_residus_part3_2
flux_residus_part3_3

Picture 1: a) Photos, b) and c) SEM/EDX of NOCOLK® Cs Flux brazed sample (load 15 g/m²) Coupon 0.68% Mg, angle 0.68% Mg – angle removed by pulling

From the SEM analysis it is evident that a proper met-allurgical joint between base and angle has not been formed.

flux_residus_part3_4
flux_residus_part3_5

Picture 2: SEM/EDX analysis of aluminium ‘angle on coupon‘ brazed with KAlF4/BaF2 blend

There is flux residue present in the pulled apart fillet. This indicates that the liquid filler alloy was not capa-ble of pushing out completely the flux of the joint and it could be an explanation for the weakness of the fillet.

However, in case of the blend MD001212 LiCs24 with load 15g/m2 the joint structure is thorough as can be seen in picture 3 a).

flux_residus_part3_6

Picture 3: Microstructures of the brazed joints
a) Flux MD001212, load 15g/m2
b) Flux MD001223, load 15g/m2

It is worth mentioning when connecting blocks are brazed to condenser manifolds often a high load of manually applied flux is used in order to overcome the high Mg content in the block material. For such a case using the mixture MD001212 would allow for having quite high Mg content in the block material, which can be required by the designers of condens-ers.

The total concentration of 1.36% Mg (joint interface) is probably too high, because for most brazing applica-tions, a flux load of 15g/m2 is impractical. Thus, we decided to reduce the level of Mg in our samples to half – i.e. to 0.68% – by switching to an AA1050 (Al 99.5%) angle. We also reduced the flux load to a more process-typical level of 5g/m². The results are listed in table 2:

Flux Type Load Fillet visual validation Comment
MD001212 LiCs24 5 g/m2 100% good seam
NOCOLOK® Cs 5 g/m2 87% small joint

Table 2: Brazing tests AMAG coupon (0.68% Mg)/Al99.5 angle

The structure of the joint cross section below (picture 4) obtained with flux MD001212 LiCs24 shows good quality.

flux_residus_part3_7

Picture 4:Joint cross sections of alloys containing 0.68% Mg brazed with MD001212 LiCs24, load 5g/m2

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Reduced Flux Residue Solubility

The water solubility of standard NOCOLOK® Flux is 4.5 g/l, whereas for post-braze flux residue (pbr) it is 2.7 g/l. Post-braze residue of NOCOLOK® Li Flux shows a solubility of 2.2 g/l [1].

In the periodic table of chemical elements the group I fluorides have a reasonable low solubility (LiF: 2.7g/l [20°C]), but their Al-F-complexes much lower (Li3AlF6: 1.1g/l , K2LiAlF6: 0.3g/l with about 183 mg F-/l, K3AlF6: 2g/l), the group II fluorides (Alkaline Earth Fluorides “AEF”) show very low solubility (MgF2: 0.13g/l, CaF2: 0.016g/l, SrF2: 0.12g/l [25°C], BaF2: 0.12g/l [25°C]) [5]. Based on the facts of the dissolution behaviour of NOCOLOK® Li and the much lower solubility of the AEFs, we started investigating combinations of potas-sium fluoroaluminate fluxes with selected AEFs to combine the brazing characteristics of NOCOLOK® type flux with the very low solubility of AEF.

NOCOLOK® Flux consists of potassium fluoroalumi-nates with a specific ratio of KAlF4 and K2AlF5. Each of these compounds has different solubility. The combination of the (pure) compounds with different AEFs was of our main interest. We melted and pulverized the flux blends, dissolved them in a defined amount of DI-water and analyzed for K, Al and F.

The data achieved form these experiments is illus-trated in figure 1:

Flux-Residue-dia-1

Fig. 1: Solubility of flux blends – melted and pulverized
(lines are used to illustrate differences of the blends)

Considering minor statistical variations, the results look quite reasonable, with the blend of NOCOLOK® Li/BaF2 showing the lowest K value. This observation can be explained by the low solubility of NOCOLOK® Li Flux. Of more relevance is the actual post-braze solubility (flux residue) on brazed Al surfaces. Interactions of base material and molten filler metal may have a more complex chemical impact on the solubility behaviour

The results from coupon brazing under laboratory conditions and the solubility of the flux residue can be seen in figure 2.

Flux-Residue-dia-2

Fig. 2: Post-braze fluoride solubility of selected flux/ AEF combinations on Al coupons
(lines are used to illustrate differences of the blends)

Among the combination of NOCOLOK® type fluxes with diverse AEF additions, KAlF4/BaF2 shows the lowest residue F– solubility, i.e. 4mg/l. All our laboratory brazing tests with the samples showed the same good results like with standard NOCOLOK® Flux.

Corrosion comparison tests will be subject for future investigations.

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance

Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann

We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Abstract

 

For more than 30 years, potassium fluoroaluminates (NOCOLOK®) fluxes are already successfully used in controlled atmosphere brazing (CAB) of aluminium heat exchangers. Residues of these so-called non-corrosive fluxes have very low – but evident – solubility in water [1] [2]. In the discussion about corrosion of CAB produced aluminium heat exchangers, the flux residue solubility is an important parameter. There are concerns that – in addition to several other factors – fluoride ions (F–) potentially released from dissolved residue play a role in aluminium corrosion.

A theoretical option to address this point is the development of virtually insoluble flux. More realistic, however, will be fluxes with less soluble residues than the current compositions.

Some commercialised NOCOLOK® derivates, like NOCOLOK® Li Flux show already reduced solubility when compared to the standard product [1]. While investigating the chemical possibilities for further minimising the residue solubility and the release of F- ions, we have developed NOCOLOK® variants in combination with selected inorganic fluorides.

During this R&D project we also looked closely at the brazing properties of the new fluxes – with a focus on their performance for brazing of aluminium alloys with higher magnesium level. The current maximum magnesium range suitable for CAB with standard NOCOLOK® Flux is approximately 0.3%. Some improvement can be seen when using caesium-containing NOCOLOK® formulations (up to 0.5% Mg) [3] [4]. Some of the new fluxes we developed for further reduced residue solubility surprisingly show higher magnesium tolerance. This article summarizes the results of our laboratory work related to the development of fluxes with further reduced residue fluorides solubility and improved magnesium tolerance.

Basic experimental laboratory procedures

 

1. Lab brazing and alloy specimen setup
For experimental lab furnace brazing we used standard CAB brazing profile and 25 by 25 mm clad sheet coupons (single side) with angle on top. In case of the Mg topic an AMAG (Austria Metal AG) clad alloy (6951/4343) was brazed with an AMAG clad-less angle. Fluxing was done manually (flux load weight on precision scale, drops of isopropanol and homogenous spreading).

Test coupon

2. Solubility data generation
Coupon (3003/4343) with Al angle (Al 99.5%) were manually coated with a dedicated amount of flux blend and brazed as described in point 1. Brazed samples were placed in PET bottles and a defined quantity of demineralised water was added. Daily visual control and air exposure (by opening and closing the lid) was done.

PET-Flasche_klar

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

In recent years, the topic of what to do with wastewater from fluxing operations has gained a lot of attention in light of heightened environmental awareness and compliance. Years ago, wastewater from cleaning slurry booths, waste flux slurries etc. were simply diluted and dumped down the drain. Some manufacturers are still following this practice, but it is become less and less common. Today, the heat exchanger manufacturers are faced with what to do with wastewater more and more.

Some manufacturers collect the waste slurries and effluent from cleaning out the fluxing stations and allow the flux to settle out. The water phase is then decanted and collected until a sufficient volume is collected. At that point, a waste disposal company is called in to collect and treat the contaminated water. This is an expensive, but in many cases a necessary option. If the collected water is relatively clean and not contaminated with oil, it may be reused to top up flux slurries. The only problem here is that one must be certain that there are no other contaminants in the wastewater other than flux ions. If there are other contaminants (and there almost certainly will be), tests should be performed to ensure that these will not in any way interfere with the brazing process.

Solvay Fluor also developed a continuous process to reuse and recycle wastewater in a fluxing operation. It is based on the principles described above, only in a continuous fashion:
Lauzon, D.C., Swidersky, H.W., “Methods for Eliminating Wastewater from Flux Slurries in Non-Corrosive Flux Brazing”, VTMS 2001-01-1764, pp 649-654, 2001.

Dumping
With continuous use, a flux slurry will eventually become contaminated. So far, there is no data that correlates the level of accumulated contaminants with poor brazing. Therefore, it is better to be on the safe side rather than wait till the number of rejects rise due to a contaminated or dirty slurry. It is therefore recommended that a slurry should be dumped when there is visual evidence of contamination. If there is an oil slick floating on top of the slurry in the reservoir or when it is discolored, the slurry should be dumped and replaced with fresh slurry. Alternatively, to avoid misjudging the quality of slurry visually, the slurry could be dumped at regular intervals, especially if the manufacturer knows that the cleanliness of the heat exchangers entering the fluxing booth is not ideal. Experience will dictate how often the slurry should be dumped.

Note however that some heat exchanger manufacturers almost never dump their flux slurries or if they do it might be only once per year. This is only the case when the heat exchangers are very well degreased prior to entering the fluxing booth and efforts are made to avoid undue contamination of the slurry. Simply keeping the cover closed on the slurry tank reservoir will keep out airborne contaminants and lengthen the slurry life.

What to do with the used flux slurry is treated covered under wastewater.

Flux Recovery – Recycle and reuse?
Around the flux slurry preparation station or around the perimeter of the fluxing booth, there will inevitably be some flux on the floor. The inclination is to sweep up this flux and throw it into the flux slurry reservoir or back into the flux drum. This action should be avoided at all costs. Any flux that falls on the floor should be disposed of promptly. The reason is that there are too many contaminants in a manufacturing environment that can affect brazing or cause other damage. Cigarette butts, paper clips, dust, dirt, oil, paper and so on can all have very damaging effects to the flux delivery system and on the brazed products. If the flux is on the floor, dispose of it and do not reuse it.

Spilled Flux

Flux powder on the plant floor should be collected by vacuum cleaners equipped with high efficiency particulate air (HEPA) filters, dedicated central vacuum systems or a wet vacuum system. Avoid sweeping and the use of compressed air. Small wet spills may be mopped up. To remove large spills the floor should be hosed down with water. Waste and contaminated water must be disposed of in accordance with local regulations.

De-ionized (DI) or reverse osmosis (RO) water is recommended to make up the flux slurries. This is to avoid long-term accumulation of mineral deposits in the flux delivery system that can cause blockage of nozzles and/or inadvertently drop on the heat exchanger. Furthermore, local plant or city water may contain ppm levels of contaminants such as chloride and copper that are detrimental with respect to corrosion performance. Other contaminants may also be present which can affect brazing. Furthermore, to avoid any seasonal variations in water quality, to avoid variations in water quality between manufacturing locations and so on, it is highly recommended that DI or RO water is used to make us flux slurries.

Water analysis recommended

In general, it is difficult to comment on potential effects of trace impurities in the flux slurry water without knowing more details about the character of the contamination. There may be only very little influence on the brazing results even with 1,000 μScm-1 conductivity. However, it is necessary to perform a chemical analysis of the water for further evaluation in each case.

The use of de-ionized water has always been recommended to prevent scale build up in the flux delivery system. Reverse osmosis (RO) water is also used successfully. There are no recommendations on conductivity or maximum hardness values (except those related to the calcium levels as listed below). The only reference Solvay Fluor can provide is the conductivity of the de-ionized water used at our Technical Services and Analytical Department in Hanover, which is below 0.2 μScm-1.

As far as we know, no scientific study was yet conducted to determine water quality requirements for aluminum brazing. In collaboration with Alcan, Solvay Fluor has established guidelines for maximum impurity limits for water quality based on contamination which might interfere with brazing or cause discoloration of the brazed parts:

[table id=3 /]

For Chloride a maximum of 0.02% is specified (corrosion problems). Based on experiences at some customer locations with post braze odor in the past, Sulfates should be below 0.02%. Phosphates can cause problems with post braze odor too, due to the potential formation of PH3. Silicates are known to interfere with flux activity. Borates and Silicates can cause black spots on post braze flux residue.

Residual hydrocarbons on all aluminum surfaces should be limited to the lowest level possible, due to the potential formation of carbonaceous residue and the long term corrosion problems caused by this residue. The same applies to all other carbon containing trace impurities in the system.

Most of the above information refers to flux and flux slurry contamination. However, it also relates to other additives and chemicals in the process, particularly when those additives cannot be,- or are not-, removed from the fluxed component prior to reaching brazing temperature.

The general appearance of NOCOLOK® brazed parts can range from relatively bright to light grey depending on the flux loading and furnace dew-point. When either is increased excessively over recommended levels, the appearance moves towards the grey colour. The flux residue usually can not be seen by the naked eye, however, it is visible under a microscope at 50x magnification. Higher magnification SEM views of the flux residue are shown in the pictures below.

SEM photomicrographs of NOCOLOK flux residue

SEM photomicrographs of NOCOLOK flux residue

The pictures on the left are typical of a tunnel furnace brazed surface, needle-like in structure possibly including the odd flat platelet. The pictures identified M-70323 are typical of a furnace atmosphere containing higher than recommended levels of O2 specifically during the cooling cycle in a batch furnace. The morphology is almost 100% flat platelets. This surface has been reported to have better corrosion resistance in service.

Other flux residue properties are as follows:

a) Residue Thickness

Typically 1–2 microns. This can vary depending on flux coating weight prior to brazing.

b) Hardness

The residue hardness is about 4 on the Mohs scale.

c) Adhesion

No measurable loss has been found in circulation tests with freon or glycol type coolants using recommended flux loading. However there are reports that some detachment may occur where higher than recommended flux loading is used, particularly where molten flux pooled in downside areas.

d) Wettability

The post-braze flux residue has a hydrophilic (wetting) surface, however that wettability decreases with time.

e) Corrosion Resistance

The presence of flux residue on the part surface mildly increases corrosion resistance under normal conditions.

f) Solubility

Solubility of flux residue is influenced by the method of measurement. A typical value are between 1.2 and 3.0 g/l with Al, F and K ion concentrations approaching the stoichiometry of the compound KAlF4 .

g) Post-Braze Odour

There is a slight odour from minute amounts of H2S immediately after brazing. It disappears within a short time. If objectionable, the odour may be eliminated by rinsing the part with water.

h) Post-Treatment

The flux residue provides a good base for coatings. However, thicker residues resulting from higher than recommended flux loading can result in the poor or non-adhesion of wet or dry powder paint coatings.

NOCOLOK® Flux residue is not easily removed from the surface of brazed parts. Mechanical abrasion, such as wire brushing or grit blasting, can be used to clean off heavier flux residues from “robust” joints. No practical chemical cleaning solution has been found. Boric acid and nitric acid solutions at higher temperature will partually remove the residues, however the times required (~ 1 hour) and the dangerous fuming with nitric acid preclude their use. Basically, the best procedure is to flux the product properly so that there is no visible after-braze residues and therefore no flux removal required.

Based on currently available information, there is no simple cleaning method for flux residues by washing or dissolving – i.e. there is no suitable solvent or chemical solution – without attacking (corroding) the substrate material as well.

Mechanical Cleaning
Usually, removal of flux residue can only be done by mechanical means. From solid surfaces and from robust joints, as well as from Stainless Steel fixtures, the flux residues can be mechanically removed by sand or grit blasting. Wire brushing is a second alternative for flux residue removal. We recommend using Stainless Steel wire brushes for cleaning. Rotating SS-wire brushed are suitable too – provided the surface areas are accessible. Brushes made from copper and brass should only be used when the cleaned surfaces are not exposed to any subsequent welding or brazing cycle any more, because copper traces from the brush (even dust particles) in contact with aluminum can cause severe erosion problems.

Chemical Cleaning

Flux residue has a slightly higher solubility in strong alkalis and some acids. But in many cases the base materials (aluminum or Stainless Steel) will be attacked (corroded) by these chemicals too.

A solution of hot boric acid (10 to 15%, 75 – 80°C) can be used to remove some of the flux residue from brazed assemblies. Aluminum dissolution by boric acid is relatively moderate. The immersion time necessary to remove the bulk of residues varies from 10 to 30 minutes. But even then the flux residue removal will not be 100% successful.

Handling (preparation and usage) and discharging (waste disposal) of such chemical solutions can be problematic and expensive – due to their corrosive properties and the subsequently necessary waste water treatment. Considerations for health, safety and environment must be in accordance with the Safety Data Sheets.

Ultrasonic cleaning

Ultrasonic treatment may be effective in removing flux residues, provided that the parts to be cleaned fit into the ultra sonic dipping bath. A detergent (cleaning agent) can be added to the solution to improve the cleaning activity. The use of Antarox BL 225 for ultrasonic cleaning treatment is probably feasible. However, when there are any other additional chemicals mixed with the Antarox-containing cleaning solution (particularly when adding acids or alkalis) their compatibility with Antarox must be verified.

There are commercial solutions available for ultrasonic cleaning of Stainless Steel. More information on this subject is available from suppliers for industrial cleaning chemicals.

Summary

Flux residue from NOCOLOK Flux can only be removed by mechanical means, i.e. using wire brushes or grit/ sand blasting. This is a very difficult and laborious procedure – and a very dirty one (dust formation!). Local exhaust and ventilation is needed in the work area where the parts are cleaned. There is no suitable solvent to take off the flux residue without corroding the base materials.