The NOCOLOK International Brazing Seminar 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.
The NOCOLOK International Brazing Seminar 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.
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 Hanover, 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:
Who should attend this two-day seminar?
Watch the video of the Solvay Technical Training Seminar
Here you can find the detailed seminar program and registration.
And here the hotel booking form.
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:
Who should attend this two-day seminar?
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.
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:
Who should attend this two-day seminar?
Watch the video of the EABS Technical Training Seminar
Here you can find the detailed seminar programme and registration.
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:
Who should attend this two-day seminar?
Watch the video of the EABS Technical Training Seminar
Here you can find the detailed seminar programme and registration.
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.
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.
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…
This article provides information about the application of binder systems for NOCOLOK Flux.
Solvay offers three concepts for flux binder application:
These products can be used in water-based NOCOLOK Flux slurries to improve flux particle adhesion. This is of particular interest for fluxing of pre-formed components prior to assembly in order to reduce flux fall-off and dust formation. Binders are also helpful to pre-coat certain areas with specific flux loads. All binder mixtures can be applied on external and internal surfaces.
During the brazing cycle, these binders will completely evaporate (mostly between 350 and 400°C). When used as described below, there will neither be detrimental interactions between the binder and the flux, nor between the binder and the aluminum surfaces. Trials have shown that even at four-times the standard flux load with a binder mixture there was still no surface discoloration after brazing.
The surface areas to be coated with binder mixtures must be free of lubricants, oils, dirt, and dust. Means of application include spraying, dipping, and brushing.
All NOCOLOK Flux binder mixtures can be applied by spraying with a suitable spray gun (1.4 mm – 1.6 mm) at approximately 3 – 5 bar pressure.
The surface temperature should be at least 10°C.
When binders are used for flux application, the recommended flux load for good brazing results is the same as it is for the standard process (i.e. between 3 – 5 g/m2). The thickness of the binder coating is usually between 10 – 30 μm.
Drying can be done in air – requiring approximately 15 – 20 minutes at room temperature for the coating surface – and 50 – 60 minutes before the parts can be handled. Oven and forced convection drying is feasible too: at 50 – 80 °C, parts will dry within 5 – 20 minutes.
Please refer to the MSDS for detailed information regarding the safe handling of the product.
For all binder concepts and preparations, the mixtures should be prepared or opened immediately before consumption.
To prepare a mixture free of agglomerates and to achieve best coating results, the following procedures must be observed for either binder concepts:
If necessary, the mixtures can be passed through a sieve prior to use. This will remove any potential agglomerates.
Prior to use the flux powder in the mixture must be suspended. The thickener will prevent the flux powder from settling too fast, however, when stored for some time or diluted, the mixture must be well shaken before spraying.
The binder component is activated by oxygen from air. Once sprayed and dried, the product cannot be recycled or reused.
Any remaining flux / binder mixture should be stored in an airtight and sealed container. We recommend consuming the mixtures within one week after mixing.
Please refer to the flyer “NOCOLOK Flux Application with Binders”.
The article was written on the basis of frequently asked questions from companies which either wanted to start a new all-aluminium brazing production of heat exchangers or wanted to convert from copper and aluminium mechanical assembly design to all-aluminium brazed parts. The questions were grouped into three main categories: Equipment (emphasis on assembling process), Process (emphasis on different fluxes and fluxing methods) and Corrosion.
Specific production challenges are also presented, which are important not only to newcomers of all-aluminium brazed heat exchangers, but to established companies as well. These include typical brazing problems such as managing leaks and the basics of brazing copper to aluminium. These topics are discussed by their relevance to the brazing parameters and their role in successful brazing.
Increasing environmental concern has identified the air conditioning and refrigeration industry as one of the contributors to the greenhouse effect and ozone depletion.
Accordingly to [1] 15% of all electricity consumption in the developed world is used by the air conditioning and refrigerator industry. Increasing the efficiency of these heat transfer systems has the positive impact of decreasing electricity consumption and therefore the overall emission of CO2. The advantages of all aluminium brazed condensers in an air conditioning system are well described in [2]. For example one such case study [3] allowed for saving about 2700 USD during 6 months. The above advantages are currently well recognized by both the air conditioning manufacturers and their end users. It is our observation that the majority of the companies in the HVAC industry which have started or are about to start production of aluminium brazed heat exchangers have only limited experience with aluminium brazing; therefore providing them with maximum possible technical assistance from the supplier side is of high importance.
This article was written on the basis of our contacts with such companies having an aim to offer some assistance to all newcomers and companies facing some troubles with their new type of production.
In most cases, the first question from a company that wants to start a new aluminium brazing activity is: “What kind of furnace should I buy?”
It is a complex issue which mainly depends on size of the products, its diversity and overall planned production volume. The general principles for the choice of the brazing furnace are shown in Fig. 1. It should be pointed out that the furnace manufacturers will make a brazing furnace customized to particular requirements of a given client.
Fig. 1: Basic principles for brazing furnace choice
In many cases the companies which are starting production of all aluminium brazed heat exchangers have been producing copper brazed heat exchangers. Therefore the natural question is: ”Can I use the same equipment which is used for copper units?”
The straight forward answer is: No! Aluminium requires high precision for assembling (recommended gap size is 0.1 to 0.15mm), which is hardly ever achieved for brazing copper parts. Also one should remember that any copper contamination on aluminium can cause catastrophic brazing failures (holes).
The process of component assembly can be done on a simple manual stacker or on machines with varying degrees of automation through to fully automated units. The level of automation should be mainly determined by the planned production volume, but also other factors such as local labour costs should also be considered.
Basic requirements for a manual assembling unit:
The process of the part assembly is invariably connected with fixtures; these are the steel elements which hold the parts together during brazing and then removed after brazing. The most frequently asked question is: ”What should be the design of the brazing frames/fixtures?”
Basically there are rigid and elastic designs which allow for some expansion when the core is heated. For larger cores elastic design is preferred. This type of fixture is reusable, also known as a permanent fixture and can go through the brazing cycle several hundred times. Apart from that we could use single usage fixtures, known as disposable fixtures and these include steel wire and steel bands. The multi-use fixtures must be made of stainless steel and in most cases the single use fixtures are usually made of ordinary low carbon steel.
Fig. 2: Example of rigid and elastic fixtures
When designing the length of the fixture (distance marked in red as Ls in fig. 2, one must remember thatthere is a difference in thermal expansion coefficient between aluminium and steel. To compensate for this, the following assumption is made: The length of the steel fixture at brazing temperature must be equal to the nominal width of the aluminium exchanger at brazing temperature. On this basis, an equation can be used describing the linear change of dimensions with temperature.
Ls(1 + αstΔt) = Lo(1 + αalΔt)
Where:
Ls – length of steel fixture,
αst – thermal expansion coefficient for the fixture material,
αal – thermal expansion coefficient for aluminium,
Δt – Increase of the part temperature during brazing,
Lo – Nominal width of the part.
As an example, for a part having width of 900 mm and nominal tube spacing of 8 mm, solving this equation and taking into account the fact that after assembly there must be some pressure exerted by the fixture on the part, the length of the fixture should be 907.5 mm and the fin height 8.08 mm. The longer steel fixture is compensated by the increased fin height. It also means that after assembly the part will have a slightly barrel-like shape (bowed out at the sides).
The question: ”What final checks are required for brazed parts?”is also connected to equipment purchases. All brazed parts must be checked for leak tightness. The most simple method is the so called “under water test”. In this case the part is pressurized with air and lowered into a water bath to look for bubbles. However some end users require more accurate and reliable methods. In the automotive industry it is common to check condensers for leaks with high pressure and extremely sensitive helium leak detection devices.
Each product should be accepted by the end user. In every case the scope of acceptance tests should be agreed to between the manufacturer and the end users. Typical tests include burst pressure, thermal cycling and of course standard ones for heat transfer efficiency and pressure drop. As a general rule it can be said that all aluminium parts should meet all the requirements applied to copper/brass parts.
1. Hans W. Swidersky, “Brazed Aluminium Heat Ex-changers for the Refrigeration and Air Conditioning Industry”, APT Aluminium News, 1-2009
2. Bjørn Vestergaard, “Brazed Aluminium Heat Ex-changers – Ask for the inexpensive features”, Seminar “Aluminium Process-Technology for HVACR Industry” Vienna, March 21st-23rd, 2007
3. Case Study – Harris County Sheriff’s Building, “Carrier Turn to the Experts” 2006 Carrier Corporation 05/06 04-811-10206
Will be continued…
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.