March 2000

CuproBraze® Copper/Brass Radiators in Production

Copper Applications in Automotive Area

By Konrad J. A. Kundig, Ph.D.

Combination of Light Weight, High Strength,Unmatched Heat Transfer Returns Copper to an important Automotive Market

Automotive radiators have undergone numerous technological changes over the past 100 years, although none of these changes are more obvious than the metals from which the radiator is constructed. In the copper/brass radiator, the radiator's fins are made from nearly pure copper and the tubes and header tanks are made from brass. In an aluminum radiator, all components are made from an aluminum alloy.

Once, copper/brass dominated the market in both passenger vehicles and trucks; today, aluminum is used for radiators in most new cars, while copper/brass maintains a strong position in the trucks and aftermarket radiators for vehicles of all types. Here is a brief chronology of the changes that have taken place:

1900s-1970: Copper/Brass 100%, Aluminum Zero

Radiators came into being when cars and trucks were first equipped with water-cooled engines. Radiators were needed to keep the water or coolant in the engine from overheating. Copper was used for the original radiators because of the metal's excellent thermal conductivity. This physical property dictates the rate at which a radiator can transfer heat: higher conductivity = faster cooling = higher efficiency, etc. Among copper's other attributes that made it the natural choice for radiators are the metal's high natural corrosion resistance and the ease with which it can be fabricated and repaired. In addition, copper/brass radiators can be removed from scrapped vehicles and recycled to form other copper alloys such brasses and bronzes.

Until the early 1970s, copper/brass radiators were installed in all new cars and trucks worldwide. There was no good reason to use else because nothing else could compete with copper/brass's many advantages.

1970-1990s: Aluminum Gains, but Copper/Brass Still Leads Market

The radiator environment changed in the 1970s, when Volkswagen decided to convert their vehicles from an air-cooled engine to a lightweight water-cooled powerplant. In the wake of the world oil crisis and urgent calls for ways to reduce fuel consumption, major automobile manufacturers in Europe and the U.S. began making cars and trucks with lighter materials.

For radiators and other heat exchangers (heater cores, oil coolers, air-conditioners), the lighter material chosen was aluminum. Aluminum has only one-third of copper's thermal conductivity, but it is also only one-third as dense as copper/brass. In its raw state, aluminum is also less expensive than copper. (This fact applies as ingot produced by aluminum refineries. It is not, however, necessarily true when the metal is in form of radiator strip.) These qualities—along with dire, albeit unrealized predictions by commodity analysts that copper/brass would be in short supply in the 1980s—created a wave of enthusiasm for something "new."

As a result, aluminum gradually replaced copper/brass as the metal for radiators in new cars. Copper/brass continued to maintain a majority of the overall radiator market since it dominates the truck sector and retains more than 80% of the replacement market. That situation continues into the new century.

1990: New Copper/Brass Technology Development Begins

As aluminum grew in acceptance by automakers, the copper/brass industry began looking at ways to improve its once dominant product. Sale of copper and brass strip to radiator manufacturers does, after all, constitute an important market accounting for approximately 200,000 metric tons of copper annually.

There was obviously room for improvement in the traditional copper/brass product. In addition to being too heavy for modern automotive designs, the radiators tended to fail at the weakest points in their fabrication, where lead-tin solder joins the various components. The lead-tin solder itself was seen as an environmental shortcoming even though it was completely recycled along with the rest of the radiator.

Once aluminum radiators had been in service for several years, however, they began to manifest a number of disadvantages. When corroded or damaged, for example, aluminum radiators proved to be far more costly to repair than copper/brass radiators. As a result, they were simply replaced, placing a cost burden on the consumer.

Also, the aluminum alloy used for radiator strip is weaker and less forgiving than brass of stresses caused by vibration. As a result, many aluminum radiators began to exhibit cracks, particularly those caused by metal fatigue, at the points where the radiators were mounted to the automobile frame. Moreover, aluminum radiators were found to be particularly prone to coolant-side, pinhole corrosion. When this occurs, the radiator is irreparable. The industry's "fix" to this vexing shortcoming was to utilize complex coolants (neé antifreeze) containing corrosion inhibitors. Copper/brass does not require such inhibitors in the coolant, which is one reason why copper/brass radiators remain a practical choice in tropical or developing countries, where the most readily available "coolant" is still ordinary water.

Finally, while aluminum radiators could be recycled, the aluminum-alloy in them could not be re-processed to manufacture new radiator strip or other products in which high formability would be required. As a result, discarded aluminum radiators were down-cycled into less demanding applications such as castings. Aluminum and copper/brass radiators are therefore equally recyclable in one sense, although the recycling of copper/brass radiators—which yields valuable brasses and bronzes—holds clear economic advantages.

Challenges Met, Enter CuproBraze

Industry experts recognized that a new copper/brass radiator would have to offer the light weight of aluminum while avoiding the disadvantages (weak solder joints, lead-containing solder) of traditional designs. Another challenge was that much of the production capacity for new-car radiators had switched to furnaces designed for aluminum radiators. A way had to be found that would utilize these furnaces for the manufacture of copper/brass radiators and thus avoid the natural reluctance of industry to invest in new equipment.

The task fell to the International Copper Association, Ltd. (ICA), and, in earlier years, to ICA's predecessor, the International Copper Research Association, Ltd., INCRA.) By the early 1990s, engineers had identified new technology that would make producing a lighter, stronger, more durable copper/brass radiator possible. The key to success was a new brazing technology called CuproBraze.

The CuproBraze® radiator (on left) can be made smaller and more compact than aluminum models having comparable performance. The CuproBraze® radiator can be made smaller and more compact than aluminum models having comparable performance.
As its name implies, the CuproBraze process makes use of brazing in place of traditional soldering to join copper and brass radiator components. Brazing uses alloys that are considerably stronger than conventional lead-tin solders. Brazing alloys are commonly applied in the form of a paste containing a protective flux, followed by heating the assembly to be joined in a furnace. Brazing alloys contain no lead.

Because brazed joints are stronger than soldered ones, it became possible to make the metal itself thinner than that used for conventional copper/brass radiators. This improvement led to a further advantage in that thin cross-sections resulted in even higher heat transfer. In all, CuproBraze radiators can be:

  • Stronger
  • Lighter
  • More corrosion resistant
  • More efficient, and therefore potentially smaller

than their aluminum counterparts, depending on the priority assigned to the various properties. Additional benefits to the automotive OEM include lower air-side pressure drop, less parasitic engine loss (and therefore better fuel economy), as well as lower cooling module costs.

Advantages of the CuproBraze® Process over the Nocolok® Process

The CuproBraze process itself offers significant cost advantages to manufacturers. These advantages are apparent when the CuproBraze process is compared with the Nocolok process that is commonly used to make aluminum radiators:

  • CuproBraze technology is ideal for heat transfer applications such as radiators (shown here), oil coolers, heaters, charge air coolers and condensers. The brazing time needed for the CuproBraze process is about half that for the Nocolok process even though both processes operate at about 600°C (1112°F). This is possible because the margin between the brazing temperature for copper/brass radiators and the melting point of brass is more than 300°C (540°F), while the corresponding difference for aluminum radiator alloys is only 30°C-40°C (54-72°F). The brazing temperature for aluminum radiators must therefore be raised slowly and carefully in order to avoid overshooting the melting point at any part of the radiators. This precaution is not necessary for copper-brass radiators because an overshoot of a few tens of degrees would not cause problems in either copper or brass. The doubled hourly output of the CuproBraze process resulting from this technical advantage means savings to the manufacturer in both capital and labor. CuproBraze technology is ideal for heat transfer applications such as radiators (on right ), oil coolers, heaters, charge air coolers and condensers.
  • Experience has shown that the CuproBraze process's scrap rate is considerably lower than that experience with Nocolok. Again, this benefit results from the larger temperature margin that is possible with copper/brass.
  • Any leaks in newly manufactured CuproBraze radiators can be repaired simply and effectively by adding additional brazing paste and recycling the unit through the brazing furnace. Leaks in installed radiators can be repairs just as easily. Aluminum radiators cannot readily be repaired, if at all, in this manner.
  • The energy consumption in the CuproBraze process is considerably lower than Nocolok because the specific heat of copper is only 40% that of aluminum.
  • Copper and brass are easier to form and fabricate than aluminum radiator strip. This property reduces tool wear and maintenance costs in the manufacture of raw materials.
  • The cost for making radiators with the CuproBraze process is fully competitive with the cost of making radiators with the Nocolok process.

And finally,

  • The CuproBraze process can be carried out in Nocolok furnaces, thereby eliminating the need for additional capital investment.

CuproBraze Production Begins in Pittsburgh

Universal Auto Radiator Manufacturing Company (UAR), Pittsburgh, is producing the first commercial CuproBraze radiators in configurations that fit more than 90 models of American, European and Japanese cars and trucks.

The automotive industry appears to be pleased with the new copper/brass products. Having three to four times the life of soldered models, CuproBraze radiators have successfully endured more than 140,000 miles in road testing. "We have no reported failures," says UAR's president, Peter Rossin. "This technology is impressive in strength."

A radiator capable of lasting 100,000 miles has long been sought by Detroit's Big Three. Now, CuproBraze makes attaining that goal possible, and not just for radiators.

"We see great potential for other heat transfer applications," says Mr. Rossin. "Oil coolers, heater cores, charge air coolers, condensers and other applications are all possibilities for CuproBraze."

Worldwide, more than 80 independent projects involving CuproBraze technology are currently underway. Products are initially being offered to (and are currently available in) the radiator aftermarket, where copper/brass retains a strong position. In addition, CuproBraze charge-air coolers have been accepted for production by one major diesel engine manufacturer. Testing by auto manufacturers is proceeding, and it may not be long before copper/brass radiators can once again be found in original equipment vehicles.

For further information, please contact the International Copper Association, Ltd. at Anthony Lea.

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