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Specifications for automotive coolants of European car manufacturers differ from those of U.S. car manufacturers. In Europe, especially, the performance concerning the protection of engine materials against cavitation-corrosion is outlined in a series of specifications. Each car manufacturer had developed his own house test. Later on, Forschungsvereinigung für Verbrennungskraftmaschinen (FVV), a federation of German car manufacturers in cooperation with the Technical High School at Darmstadt, had investigated the correlation of cavitation and corrosion properties in engines and test rigs. This so-called FVV test was published in 1977. The main parts of this text consist of (1) an ultrasonic swinger with a frequency of 20 KHz and an amplitude of 40 μm and (2) a circulation test.
The FVV test is done in two steps: At first, samples containing 10, 20, and 50% of antifreeze in water with 10° German hardness are prepared. From each sample, the cavitation rate on two different test specimens cut out of the cylinder head and motor block materials is determined in mg/h at 55°C as at this temperature the cavitation rate has its maximum. In a second step, a 20% aqueous solution of antifreeze is circulated in the shown test rig for 168 h between 75°C in the cooling vessel and 95°C in the heating vessel. The cavitation rate of this so aged antifreeze is compared to that of a non-aged one at the same concentration of 20%. It was soon found that the correlation to practice was not sufficient in all cases and further research was done by Motor-Turbinen Union, Friedrichshafen, a common affiliate of Daimler-Benz and MAN (MTU). They have developed a special cavitation chamber with a mechanical actuator. This test equipment is installed into the circulation test of FVV. The metal coupons for the dynamic samples are made from the material of the liners, those for the static samples from the material of the crank-case or the cylinder head. Thus it is possible to run different combinations of materials within one test run. Usually in both tests, FVV and MTU, metal coupons are placed in the circuit additionally. Conditions of circulation test according to FVV and to MTU are identical.
Test results obtained from the MTU-cavitation test are the weight losses of the specimens (dynamic and static sample) of the cavitation chamber and those of the metal coupons. A comparison of the results of both rigs show that the MTU test is more critical for evaluating the performance of preventing cavitation in engines, as shown by the weight losses of metal specimen in the chamber and on the swinger. The weight losses of the metal coupons that are showing the corrosion rate are similar in both tests. Further tests cover the behavior of antifreezes in the presence of hot surfaces (HF Test) using different metals and alloys with lower antifreeze concentrations down to 15 %. Different circulating tests and simulated performance tests with electrical heated engine blocks and radiators make possible the evaluation of newly developed additive systems and antifreeze blends.
coolants, corrosion, cavitation
Chemist, BASF AG, ESB/AK-G 100, Ludwigshafen,
Engineer, BASF AG, TEW Technical Prufstand L544, Ludwigshafen,