Automotive Radiators

The recent history of the passenger car radiator is well known - the conventional wisdom is that aluminum has largely taken this market. The trend started in Western Europe, has moved forward in the United States and has more recently taken hold with Japanese automobile producers. Aluminum penetration in original equipment in terms of tons of material consumed in 1995 is shown in Table 1, below. It is as high as 77% in Western Europe and is at 29% in Japan. Worldwide, on the basis of weight, 52% of radiator material consumed for original equipment is aluminum. But aluminum penetration in the large aftermarket is only about 10% as shown in Table 2. Overall, as shown on Table 3, contrary to the conventional wisdom, the copper/brass radiator still accounts for two-thirds of the total tonnage of radiator material consumed worldwide. Also shown here is the changing market share for the two material systems in the 1991 to 1995 period. Copper/brass radiator tonnage had decreased by 4.6% in five years and aluminum has captured all of the growth in consumption of radiator material as the worldwide auto industry grew.

We must conclude though that copper/brass radiators will be a significant factor in scrap in all sectors of the world for some time to come.The copper/brass radiator, despite the spectacular success of the aluminum system, still consumes about two thirds of the total tonnage of radiator material due to its continued but decreasing use in new automobiles and its advantages and dominance in the aftermarket and in trucks, heavy off-road and industrial equipment.

At this meeting, where the audience is clearly representative of and interested in the copper industry, a digression to examine just why the industry lost a large share, possibly 100,000 tons per year, to a competitive material system, is appropriate. Again, the conventional wisdom is that the copper/brass system is too heavy and too expensive compared to aluminum. After all, everyone knows that the density of copper is more than three times that of aluminum and that on the LME or Comex markets, copper has consistently been more expensive than aluminum. Those facts would seem to explain the success of the automotive aluminum radiator. But the real reasons for the success of the aluminum radiator are, first, the strong, 25-year development effort of the aluminum industry and, secondly, the total neglect in that same period on the part of the copper industry for its product. We had 100% of the market and did not believe that situation could be changed.

But the copper/brass radiator was too heavy - not because the laws of physics dictated that it be, but because no effort to improve design to take advantage of superior mechanical properties and thermal conductivity had been expended. More recently, in tests conducted at Penn State University on three generations of the new brazed copper/brass radiator, CuproBraze radiators were shown to be fully competitive with the brazed aluminum. These data are shown in the table below.

CuproBrazeI, designed to have the same frontal area as the aluminum radiator, has 30% lower air pressure drop but is slightly heavier. CuproBrazeII has the same air pressure as the brazed aluminum model, but is smaller in size. CuproBrazeIII combines a smaller frontal area and thinner tube walls to achieve distinct advantages in both size and weight. All four of these radiator cores have the same cooling capacity (168,000 BTU/hr) and fin depth. Their weights include fin and tube material only. This work has shown conclusively that a much lighter copper/brass radiator is possible. In addition to replacing the lead solder by a brazed joining system, tube touching design and compact core designs were among a number of innovations that reduced the weight of the copper/brass system.

It has only been in the last ten years, long after the aluminum system had its foothold on the market, that any serious thought was given to improving the joining system used in the manufacture of the copper/brass system; after all, the lead-tin solder is heavy, it tended to fail by creep at the tube-to-header joints causing leaks, and it was vulnerable to corrosion on the coolant side. This was known as "blooming" corrosion because of the voluminous lead corrosion product that often resulted in tube blockage. Environmental concerns about lead in the air in manufacturing plants and radiator repair shops also posed problems. And corrosion of the copper fins in industrial environments was another problem that required attention if the system were to be competitive.

The cost issue is nowhere near as large as the difference in copper cathode and aluminum ingot prices would suggest, because radiators are made from strip materials, not from cathode or ingot. The aluminum tube strip is a complex composite of two or three layers; these provide structural support, a brazing alloy layer and often a sacrificial inner layer to control coolant-side corrosion. The brass tube and copper fin materials are simple homogenous materials.

Consequently, the copper/brass radiator strip materials have actually been less costly than the aluminum strip, as shown below.

That left the joining and corrosion issues. In 1988, the International Copper Association launched an effort to develop an entirely new copper/brass radiator system that substituted brazed construction for the lead-tin solder. An electrophoretic coating system for external corrosion protection familiar to the auto industry, cost effective, and having negligible impact on heat transfer, was developed and proved effective in on-the-road tests. A laser welding system for production of brass tube was developed. The brazing alloy is a self-fluxing Cu-Ni-Sn-P alloy not relying on silver or other expensive materials. Brazing is done on this copper system using no flux and at the same temperature the aluminum radiator is brazed allowing brazing furnaces now used for aluminum radiators to be used for the new brazed copper/brass radiator. New anneal-resistant brass and copper fin alloys were developed.

Original equipment and aftermarket radiator manufacturers all over the world are involved in testing this new system. At long last the copper industry is addressing this market with the hard work and creative thinking required for success. Assuming the industry has the patience and capacity for follow through required, the picture some ten years from now could be that the new copper/brass system has recaptured some of the lost market share and has established an equilibrium with its aluminum competition in original equipment automobile radiators. This would further assure that copper/brass radiators would continue to be a component of the scrap stream. But this new radiator, showing up in the scrap stream possibly 15 or so years from now, will be a different product. It will be lead-free and will thus be a more versatile scrap product not limited to use in copper alloy castings as is the present copper/brass radiator.