Brazed Copper Brass Radiators Design Innovations
Low Weight, Low Cost, Long Life
Over the next few years, new copper-brass car and truck radiators that could last ten years will debut in the automotive industry. They are fully competitive with today’s aluminum counterparts.
Based on technological advances and design innovations developed with research funding from the International Copper Association (ICA), these radiators are 35%-40% lower in weight compared to traditional, nonoptimized copper-brass radiators, and correspondingly lower in material costs.
They have lower weight because they are manufactured with far less material in their fins and tubes than previous models, and because the heavy lead-base solder traditionally used in copper-brass radiators is replaced with a very small amount of light brazing alloy.
The brazed copper brass radiators also provide 30% or more lower air side pressure drop than aluminum radiators because their copper and brass components are much thinner than the components in their aluminum counterparts.
Now in testing by major auto and radiator manufacturers, brazed copper-brass prototypes have lasted over 6,000 hours without failure in laboratory durability tests. This equals 300,000 miles of service. Researchers are confident that brazed copper-brass models will last 500,000 miles or more (8,000 hours).
In comparison, soldered copper-brass radiators in the U.S. average 75,000-80,000 miles, although one model, the Nippondenso NSR, has lasted the equivalent of 200,000 miles.
Brazed copper-brass radiators can be tailored to fit the diverse cooling requirements of the world’s automakers.
Equally important, they can be made in existing aluminum brazing furnaces. To produce them, manufacturers don’t have to invest large sums of money in new equipment.
To bring brazed copper-brass radiators to market, the ICA is continuing its research and tests in cooperation with the worldwide copper industry. Its findings and related technical assistance are available without charge for use by automakers and radiator manufacturers worldwide.
The New Worldwide Standard
To develop brazed copper-brass radiators, the worldwide copper industry has taken advantage of several technologies that can be utilized in their manufacture. Chief among them are no-flux brazing and electrophoretic coating.
Cross section of brazed copper fin to brass tube wall Cross section of brazed copper fin to brass tube wall
Brazing gives copper-brass radiators a mechanical strength in fin, tube and header joints that is far superior to soldered copper-brass models. With new designs, the radiators can be strengthened further.
Brazed copper brass radiators also use thinner fin and tube material. Brazed copper fins are 0.002 inches thick or less; brazed brass tubes are 0.005 inches thick. For most aluminum fins and tubes, the figures are 0.005 inches and 0.016 inches, respectively.
Thinner Brazed Copper Brass Radiators metal leads to lower air side pressure drop than in comparable aluminum radiators. This translates to more efficient radiators, lower cooling module costs, less parasitic engine losses and greater fuel economy.
The brazing of copper-brass radiators uses a non-toxic, low temperature melting alloy that works well in either a conventional vacuum brazing furnace that is back filled with nitrogen, or in a CAB furnace (an electrically heated furnace containing a nitrogen atmosphere). A typical temperature for the brazing is 620°C-635°C.
Based on the CuNiSnP system, the new alloy is composed of 75% copper, 5% nickel, 15% tin, and 5% phosphorus.
As with other alloys in this system, it is self-fluxing. Thus, no flux is required for its application, no lead or other dangerous material is in the brazing material and rinsing after brazing isn’t needed.
After brazing, the brazed copper-brass joints are significantly stronger than the solder metal and do not suffer from galvanic corrosion. Developed for this process, anneal-resistant header, fin and tube materials assure the strength of the radiator cores.
To make brazed copper-brass radiators, little or no change is needed in fin rolling, tube welding, or the drawing of header plates. The tube ends are reformed on line as part of the core assembly.
If brazing paste is used to make the tube to header joints, it is added to the outside of the header with specially designed equipment. The tubes are coated with paste that is rapidly dried.
Side support design to allow axial expansion Side support design to allow axial expansion
For the proper brazing paste, the powder is mixed with a specially designed binder. Tubes and fins are stacked into cores that can be handled as easily as solder-coated cores.
Other potential coating methods for tube to header joints include:
spraying of braze powder;
preplacing braze alloy from wire-type rings and clips;
applying molten braze alloy directly to the tube strip before or after welding.
As expected, the brazed cores are two to three times stronger in torsion and tension than soldered cores. The corrosion properties of the base metal and joints are also important. During lengthy exposure to road environment pollutants (REP+ sulfide tests), very limited attacks were found in brazed joints between tubes and fins. Soldered joints, on the other hand, suffered severe corrosion.
Widely used for auto components, electrophoretic coating enhances a radiator’s external corrosion protection by providing an even distribution of paint throughout the entire radiator. Conventional spray painting is largely cosmetic in comparison and actually accelerates corrosion. Most important, E-coating allows for the use of much thinner fin material.
Extensive laboratory corrosion testing by ICA of electrophoretically coated brazed copper-brass radiators has shown their corrosion resistance to be excellent, even within seams and on sharp edges. In addition, heat transfer is affected very little or not at all.
Samples of automotive radiator cores:Samples of automotive radiator cores:
• left is electrophoretically coated
• right is conventionally spray painted
The first electropaints were made in 1958 to prime car bodies. Developed in the U.S. and Europe, these paints are now used worldwide almost to the total exclusion of other priming systems – for seat frames, wheels, brake shoes, rocket-box covers, seat belt anchors, chassis sub-frames, suspension systems, clutch assemblies, petrol tanks, etc. Most truck cabs are also primed by this method, as are many tractor cabs and other agricultural equipment.
The four most commonly available E-coating paints for radiators are H976-80 and H976-100 from ICI Electrocoat (England), a unit of ICI Autocolor, and Powercron 643/501 and 643/506 from PPG Industries (U.S.).
During electrophoretic coating, a thin film of paint, one-half to one-third the thickness of paint applied by conventional methods, builds around the radiator causing an electrical insulation that restricts further build-up. Known as “throwing power,” this property allows for the coating of all relatively inaccessible areas, including the dense inner core.
After electrophoretic coating, the paint film is baked in an oven at a curing temperature of 150°C-177°. The development of low-temperature curing has made this form of coating applicable to radiators fitted with plastic tanks and gaskets.
The electrophoretic coating process has other benefits. It is highly automated, so it can be easily integrated with other production operations. It is also highly efficient. Paint utilization is between 95%-99% compared to 30%-50% for spray painting. And it is environmentally friendly. Being water-borne, not solvent-borne, the paints used are fire and explosion proof.