Background

The CuproBraze process is a relatively new technique for manufacturing heat exchangers, particularly automotive radiators. Developed by the International Copper Association, CuproBraze radiators have already proved themselves in US road tests, and the process is showing promise in a range of other heat exchanger products as it offers significant advantages over existing systems, according to the developers. Recognising the potential of the CuproBraze process, Seco/Warwick has marked its one hundredth anniversary by building a specialist furnace at its Development Centre in Titusville, Pennsylvania, USA, to conduct brazing trials and prototyping work on heat exchangers.

CuproBraze technology enables the manufacture of light, strong, efficient and compact heat exchangers, including oil coolers, heater cores, charge air coolers and condensers, from high strength and high conductivity copper and copper alloys. These alternative materials and technology offer several benefits over existing systems, including a 10% cost saving over conventional aluminium heat exchangers while offering better energy efficiency. Scrap levels from the CuproBraze process are low as rejects can be easily re-brazed, and less energy is required in the brazing process itself. Brazing is carried out at 300°C lower than the melting point of the materials, and the system is much less sensitive than aluminium to rapid heating and cooling cycles.

In comparison to copper/brass systems, CuproBraze has stronger brazed joints, is 35-40% lighter and is easier to recycle. In addition, the braze filler is a non toxic alloy with good wetting and adhesion with no further use for toxic lead solder in the process.

The new braze filler is an alloy of copper, tin, nickel and phosphorous with a metallic content of between 75-90% depending on the joint position and application technique. Different types of binders and braze alloys can be used for the tube to fin joints and tube to header joints, and application can be either by spraying, brushing or rolling.

The new furnace developed by Seco/Warwick highlights some other advantages of the CuproBraze process. The furnace is of a compact front loading design, and it requires a floor area of only 8x7m. However, a free working load space of 1200x1200x400mm is available, along with a larger alternative chamber size of 1500x1500x600mm. The heating system consists of a high pressure, high velocity recirculation fan passing the atmosphere over 90kW electric elements to provide the optimum flow of nitrogen atmosphere through the workload to obtain the tight temperature uniformity required for optimum brazing. At the operating temperature of below 750°C, this method of heating is the quickest way of transferring heat to the workload.

The whole process is rapid, with purging, heating and one complete cycle of cooling being achieved in 20 minutes for a single layer of radiators (16kg) or 30 minutes for a double lay (32kg). In Seco/Warwick's new furnace, the speed and accuracy of the process is ensured with a PL system responsible for temperature control sequencing and logic. Such control will achieve optimum conditions for the CuproBraze process, for which Seco/Warwick expects to see growing demand.