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Technical Paper

Electrocoating of Car Radiators - A Way to Improve Corrosion Resistance

External corrosion of automotive heat exchangers, mainly radiators, has in recent years become a problem in some cases. The reasons for the corrosion attacks are a combination of air pollution on one side and road salting or tropical marine climate on the other. This paper deals with actions taken to improve the corrosion resistance of copper/brass radiators. Rapid corrosion of the tubes due to dezincification which gave early radiator leakages was solved by introducing arsenic and phosphorous containing brass qualities (1). Corrosion of fins and solder has been tackled by different types of coatings (2, 3). Copper strips that are zinc coated before the fin production are a new product for large scale application (4). Solder coated strips have been used since many years but are expensive and heavy. Organic coatings applied on complete radiators have been tested for a couple of years. The black painting that is normally used on radiators does not give any corrosion prevention.
Technical Paper

Corrosion and Corrosion Protection of Automotive Heat Exchangers - Comparison between Copper/Brass and Aluminium

Demands on longer life time, lower weight, mixing of different materials and last but not least changed corrosion conditions due to pollution and climate conditions have made the corrosion behaviour both externally and internally of automotive heat exchangers more important in recent years. This paper presents our experiences from both field and laboratory tests of copper/brass and aluminium radiators together with some literature results. The main part is dealing with external corrosion. Comments are given on the influence of material properties, production methods and ways of protection. In the case of copper/brass results, from trials and use of an improved corrosion protection with a special type of lacquer are presented. In conclusion, it is stated that the competing materials mentioned, show different characters from a corrosion point of view.
Technical Paper

Recycling of Copper/Brass Radiators

Scrap is an important source of copper. Of the total consumption of copper in the western world 1993, 12 473 000 t, the scrap content was 4 697 000 t or 38%. This is much more than the production of the largest copper mine. The use of scrap has long traditions. The metal can, with a fracture of the energy used for the original production, be refined to high purity. Heat exchangers in scrapped cars are in many cases removed together with other valuable parts before the shredding operation. Copper is also separated during the treatment of the shredded car. It is important to avoid mixture of copper and steel. Today standard copper/brass radiator joined with lead/tin solder can be used for production of lead containing casting or extrusion ingots. If the metal is too mixed up a new refining can be done which gives as result pure metals. Lead free copper/brass radiators are likely to be used more and more. Soft solder based on tin alloyed with copper, silver, antimony is one option.
Technical Paper

New Joining Methods for Copper/Brass Heat Exchangers

The copper industry has during the last couple of years developed two new joining techniques for copper/brass heat exchangers. The results are promising and they are likely to find industrial applications very soon. Laser welding can use a modified ordinary lock seam tube mill together with the laser. The welding speed can be at least the same as during normal lock seam tube production and the wall thickness as thin as the thinnest used in lock seam tubes. Results from laser welding of a new tube profile, “double tubes”, is also presented. Brazing instead of soldering is possible as new materials for brazing now are available. A cheap, non toxid low temperature brazing alloy based on the CuSnNiP system has been developed. Brazing can be done using a fluxless paste made from atomized powder. Both vacuum and inert gas furnaces can be utilized.
Technical Paper

Corrosion of Copper/Brass Radiators - Corrosion Mechanisms - Prevention Actions

The demands for longer lifetimes of cars have meant that the durability of radiators has also become more important, particularly with regard to the resistance to external corrosion due to environmental pollution. In this paper corrosion mechanisms, as well as some preventive measures for copper/brass radiators, are discussed. The radiator is constructed basically of solder–coated flat brass tubes and copper fins. The tubes and fins are joined together with tinllead solder. Bimetallic contact points in joints and also pores and scratches are exposed to corrosive chloride and sulfur compounds. This can initiatiate corrosion damage, if corrosion prevention measures have not been taken into consideration. Experiments have been made to evaluate the risks of bimetallic corrosion between copper, some brass alloys and soldering alloys on radiators. Experiments are based on electrochemical methods.