New Member of the NOCOLOK®-Team Worldwide

Rüdiger Funke is a new member of the NOCOLOK® Team since October 1st, 2014.

Rüdiger Funke is 46 years old and a trained merchant. His professional career began in the 80's at Brenntag and in 1990 he moved to Helm in Hamburg. After an intermediate employ at the Harke group in the Hamburg branch, Rüdiger Funke came to Flux GmbH in Garbsen in 2001, becoming a partner in 2009. Since October 2014 he is head of the new NOCOLOK® Business Unit at Solvay (see article below).

Rüdiger Funke is married and loves to cook. To balance his activities at work he likes to jog and travelling is also one of his hobbies.

ruediger.funke@solvay.com

We Need Your Support

We like to inform and request your support in defeating Work Item 2642 “Standard Test Method for Engine Coolant Stagnation in Flux-Brazed Aluminium Heat Exchangers” (in subcomittee D15.21).

This proposal intends to indirectly task all heat exchanger manufactures to quanitfy the amount of flux present in a heat exchanger, as opposed to using laboratory methods to test the performace of coolants unders varying flux loads.

We ask that you please join ASTM Subcommittee “D15.21 Extended Long Life Coolants” immediately to cast your vote against this proposal. We do no believe the voices of those who manufacture heat exchangers are being adequately represented in ASTM. As a result of this proposal, you may be forced to change how you manufacture your heat exchangers to compete for business.

More informations about ASTM

We believe the test proposal in Work Item 2642 itself:

• is not scientifically sound
• is not repeatable
• does not cover “coolant fluid” to “Aluminium surface” to “flux” ratio
• does not represent the population of heat exchanger products
• makes assumption that the potassium (K) threshold levels of 125 (mg/L) as representing the data population threshold for requireing this test.
• fails in Precision and Bias
• does not adequately represent manufacturers of heat exchangers

We ask that you vote against this work item so it does not move forward as currenty proposed.

EABS Seminar in Hannover

Since 2001, the annual Aluminium Brazing Seminar of EABS (European Association of Brazing and Soldering) and Solvay brings many interested participants from the industry together.

On September 9th and 10th, 2014, the focus was again on flame brazing and furnace brazing of aluminium. Theory and practice are equally important during this technical training.

More than 25 people enjoyed an informative two-day seminar with many demonstrations on the fundamentals of aluminium brazing.

Technical Article Flux Residue Part 1

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

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, such as 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).

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.

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 potassium 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 fluoroaluminates 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 analysed for K, Al and F.

The data achieved form these experiments is illustrated in figure 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.

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)