A star Steyr 1491 / 280 / k29 / 6×4 dump truck found antifreeze leakage at the rear end of the engine water outlet pipe just after driving 3000 km. After disassembly, it was seen that the inner wall of the water outlet pipe was full of needle holes, and there was another honeycomb hole group at the rear end. The depth had penetrated the water outlet pipe, resulting in antifreeze leakage. The water pipe joint removed later also has the above needle hole.
This is an obvious case of metal pitting. That is, when metal parts contact with liquid and have relative movement, a damage phenomenon occurs on the surface of parts. It is characterized by pitting or needle like holes in a specific area of metal parts, and honeycomb hole groups in severe cases. Pitting corrosion is a special corrosion phenomenon, which is not only caused by mechanical movement, but also related to the physical and chemical properties of antifreeze. Improper use and maintenance will also aggravate the destructive effect of cavitation erosion.
Steyr engines mostly adopt supercharging technology, with high compression ratio and large average effective pressure. Under normal working conditions, the pump impeller continuously pumps antifreeze into the cylinder block. The continuity of antifreeze is damaged due to the vibration of the engine and the instability of its speed. The antifreeze close to the surface of engine parts is easy to produce bubbles
(1) Select antifreeze correctly. The primary condition for cavitation is that there are a large number of bubbles in the liquid. There are many reasons for bubbles, but the improper selection of antifreeze is a main factor. Therefore, the antifreeze must be selected correctly according to the operating instructions.
The engine of Steyr adopts a closed forced circulation water cooling system. This structure makes the coolant difficult to evaporate and is suitable for the recycling of antifreeze. Considering the working environment of Steyr, it is required to use antifreeze without phosphate and with borax as anti-corrosion additive. Ethylene glycol has certain corrosive effect on metal materials. Borax or Triethanolamine phosphate and other additives must be added to prevent it from corroding the metal of engine cooling system. Silicate type heavy load four seasons long-term antifreeze recommended in the operation manual of Steyr WD615 Series diesel engine has good performance and can meet the needs of Steyr vehicles.
(2) Adopt correct operation methods. During normal operation of the engine, ensure that the temperature of cooling water is between 80-85 ℃, and the mechanical loss of the engine is the least. When the cooling water temperature is between 40-60 ℃, the diesel engine is most prone to cavitation. If the temperature is too low, the engine power decreases and the wear intensifies. In addition, when the working process of diesel engine is rough and the explosive pressure rise rate per unit crankshaft angle increases, cavitation corrosion is easy to occur.
(3) Maintain and repair correctly. After using the antifreeze for a period of time, the internal additives are continuously consumed and precipitated, and the anti-corrosion effect is continuously reduced, which is prone to cavitation. The storage life of ethylene glycol is limited, and it will degenerate into corrosive acid after two or three years. After mixing air or other impurities into the antifreeze, it will also aggravate the generation of cavitation.
Steyr engines require the use of long-term antifreeze throughout the year. The following table lists the replacement requirements of such antifreeze.
The cooling system is an important part of the engine. Ignoring its role will not only affect the power and fuel economy of the engine, but also shorten the service time of the engine. Therefore, the use and maintenance of engine coolant must be strengthened to improve the reliability and service life of the engine.
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