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Over the last few decades, aluminium has largely replaced copper and copper-brass as the material of choice in car radiators. But the Copper Development Association (sponsored by the copper and brass industries of the USA) is fighting back. In this paper they explore some of the new technologies that may see the reintroduction of copper and brass as the materials of choice for automotive heat exchangers. And, reading between the lines, that could have substantial implications for the development of highly efficient intercoolers as well.....
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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 aluminium 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, non-optimised 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 aluminium radiators because their copper and brass components are much thinner than the components in their aluminium 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 about 500,000km of service. Researchers are confident that brazed copper-brass models will last 800,000km or more (8,000 hours). In comparison, soldered copper-brass radiators in the US average 120,000 - 130,000km, although one model, the Nippondenso NSR, has lasted the equivalent of 320,000km.
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.
No-Flux Brazing
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 aluminium fins and tubes, the figures are 0.005 inches and 0.016 inches, respectively. Thinner copper-brass metal leads to lower air side pressure drop than in comparable aluminium 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. 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.
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, very limited attacks were found in brazed joints between tubes and fins. Soldered joints, on the other hand, suffered severe corrosion.
Electrophoretic Coating
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 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.
The first electropaints were made in 1958 to prime car bodies. Developed in the US 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.
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.
Claimed Advantages
In addition to lower weight and smaller size, brazed copper-brass radiators have many other advantages.
As base metals for radiators, copper and brass require fewer manufacturing steps. Thus, brazed copper-brass radiators can be produced more easily and at less cost than comparable aluminium radiators. And since the brazed copper-brass models can be brazed without flux (which is not the case with aluminium radiators), their cost can be reduced even further. In contrast to the huge multi-million dollar capital investment required when aluminium radiators were first introduced, brazed copper-brass radiators can be built with minor retooling of existing production lines.
- Higher Operational Performance
Wind tunnel tests confirm the lower air side pressure drop in brazed copper-brass radiators compared to aluminium radiators. Overall performance can be strengthened by utilizing innovative fin and tube designs.
For consumers, brazed copper-brass radiators mean longer life than conventional copper-brass radiators, in addition to higher quality. In laboratory cycle testing, they have shown the capacity to last the equivalent of ten years.
As one of the most recycled metals in the world, copper has had a well-established reclamation infrastructure in place for generations. The metal from recycled radiators can be used directly for producing free-cutting brass. With brazed radiators, copper's recyclability will be even greater. Since they are made without lead/tin solder, the radiators will be significantly easier to remelt. In fact, the recycled copper will be pure enough to fabricate directly into new radiator tube strip. Owing to their silicon content, brazed aluminium radiators can only be recycled into less critical casting alloy.
Brazed Copper-Brass vs. Brazed Aluminium
| Radiator Core: |
Brazed Aluminium |
Brazed Copper-Brass I
Lower air
pressure drop,
same size, heavier |
Brazed Copper-Brass II
Same air
pressure drop,
smaller, slightly heavier |
Brazed Copper-Brass III
Same air
pressure & coolant
pressure drop,
smaller & lighter |
| Header Width, inches |
17.01 |
17.01 |
17.01 |
15.55 |
| Tube Length, inches |
21.65 |
21.65 |
19.10 |
19.90 |
| Fin Thickness, inches |
0.0045 |
0.0015 |
0.0015 |
0.0015 |
| Tube Wall Thickness |
0.0150 |
0.005 |
0.005 |
0.004 |
| Dry Core Weight, pounds |
3.68 |
4.18 |
3.95 |
3.43 |
| Wet Core Weight, pounds |
4.50 |
5.13 |
4.79 |
4.16 |
| Coolant Pressure Drop, pounds per square inch |
0.69 |
0.48 |
0.42 |
0.69 |
| Air Pressure Drop, inches of water |
1.24 |
0.87 |
1.24 |
1.24 |
Brazed Copper-Brass I,which is made with conventional technology, has the same frontal area and 30% lower air pressure drop, but is slightly heavier.
Brazed Copper-Brass II, also made with conventional technology, has the same air pressure drop as the brazed aluminium model, but is smaller in size.
But Brazed Copper-Brass III, which is made with advanced technology and has the same air pressure and coolant pressure drop as the brazed aluminium radiator, combines a smaller frontal area and thinner tube walls to achieve distinct advantages in both size and weight. All four radiator cores have same cooling capacity (168,000 BTU/hr) and fin depth. Their weights include fin and tube material only.
- Superior Energy Efficiency
Brazed copper-brass radiators are almost three times more energy efficient than aluminium radiators. This can be seen most readily by looking at each metal's energy consumption, both as primary metal and as recycled scrap.
Energy values for aluminium are fairly consistent except in one or two instances where estimates are based on hydro electricity, where no losses are reported. A normal value for aluminium is 75 MWh/t for producing primary metal and 5 MWh/t for recycling clean scrap. For copper, the figure depends on several factors - the quality of ore, type of energy used and losses involved - but a reasonable value for a typical 0.5% copper ore is 30 MWh/t for producing primary metal and 3 MWh/t for recycling clean scrap. Specifically applied to car and truck radiators, copper's energy efficiency is even greater because of its high recycled metal content.
Design Innovations
In addition to technologies, the ICA has harnessed a number of design innovations to enhance the effectiveness of brazed copper-brass radiators. Chief among them are the following:
- Reformed Tube-Header Joint
The brazed tube to header joints in brazed copper-brass radiators must be redesigned to eliminate tube distortion in the header joint during brazing. Since the tubes heat faster than the header, the tube sides can buckle inwards, causing a gap that will not fill with brazing alloy. One approach for reducing the possibility of distortion is to use oval or round ferrules in the header and reshaped tube ends. In general, brazing requires very close tolerance fits, and reforming the tube ends helps to control the tolerance between the tube and header.
With round or oval tube ends it is possible to use a tube-touching concept. In this design, the ferrules in the header can be placed so that the radii of the tubes are in contact. The depth of the fins thus becomes smaller. Any loss in air side performance is limited because the total fin area is efficiently used when the tubes touch.
To eliminate thermal stress in tubes, headers and tube-header joints resulting from rigidly attached conventional side supports, a new side assembly has been designed to allow for axial core expansion.
Other Technologies
Laser-welded brass tubes that are competitive with the thinnest lockseam or high frequency welded tubes have shown promise for advanced copper-brass radiators. As a process, laser welding can be easily integrated into current lock-seam tube manufacturing operations with minimal modifications in existing equipment.
Laser welding also permits new tube designs. One innovation is a one-row radiator in place of a standard two-row design. The two edges of a piece of brass strip are welded into a centre support structure that yields a one-unit tube with two equally sized water passages. The "twin" tube helps to overcome constraints on wall thickness and the weight of conventional welded brass tubes. Laser-welded twin tubes may be manufactured with depths of 30 mm or more.
To ensure the overall strength and durability of brazed copper-brass radiators, three new alloys have been developed. These are in addition to the basic brazing alloy, OK 600.
- First is an anneal-resistant fin material that maintains the strength of fins after brazing. Strong fins are required because they support the tubes. Soft fins couldn't resist the pressure in tubes that can lead to bulging. The new fin material also provides 92% conductivity after brazing and is environmentally safer because it doesn't contain cadmium.
- Second is an anneal-resistant tube alloy (ISO# C664429) that retains its fine grain structure after brazing. The fine grain structure is needed to provide ductility and fatigue strength in the brazed radiator core. The new tube material welds and forms as easily as conventional tube brass.
- Third is a brass header alloy modified to be anneal resistant. In addition to having forming characteristics equal to or better than conventional brass header material, this new alloy retains its original structure after brazing.
http://automotive.copper.org
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