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Fasteners used in marine diesel engines
Compared with machinery in other industries, although ships do not have the harsh environment test of high temperature, high pressure and strong corrosion, the corrosion of sea water, salt spray and water fog cannot be underestimated. This is the external environment that ships and diesel engine fasteners must withstand. The following types of fasteners are called important fasteners by industry insiders.
Important bolts refer to the connecting bolts of marine diesel engines and other equipment that bear dynamic loads. Such as diesel engine cylinder head bolts, connecting rod bolts, main bearing bolts, connecting bolts of the combined piston, through bolts and anchor bolts, and flange connecting bolts in the shaft system. These bolts must not only ensure the connection and tightening of the parts, but also bear the load of the machine during operation; therefore, the quality of these bolts will directly affect the safe rotation of the diesel engine. The force of bolts is complicated. In addition to tensile and shear forces, they also bear periodic actions such as inertial force, impact force, and vibration. In order to ensure the safe and reliable operation of the machine, the bolts are required to have the following properties:
1. Sufficient strength, fatigue strength, proper hardness;
2. Good toughness, plasticity, and manufacturability;
3. Higher hardenability and lower notch sensitivity, should have cushion resistance at high temperatures, and should have corrosion resistance in seawater salt spray corrosive media.
The materials commonly used in the manufacture of important bolts are 40Cr, 35CrMoA, 40CrNi and 45# steel.
The commonly used heat treatment method is quenching and tempering treatment, so that it can obtain better comprehensive mechanical properties.
40Cr, 35CrMoA, 40CrNi, etc. are mostly used for important bolt materials for medium and high-speed marine diesel engines; 40, 45, 40Cr, etc. are mostly used for important bolt materials for large low-speed marine diesel engines.