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Recently, the appeals number of individuals and legal entities for establishment disturbances causes in internal combustion engines has increased in the Kharkiv Research Institute of Forensic Examinations. Analyzing the conclusions of performed expert research it was established that one of the main disturbances causes of internal combustion engines is the turning of plain bearings (bearing brass) of crankshaft. Conditions for metals jawing, scratching and grabbing are created during the start-up or turning of the plain bearing when oil does not contact details or while transient operating modes of the engine when the thickness of layer oil is less critical and the surfaces are in contact. This leads to a significant increase of friction surfaces temperature and the destruction of the oil film on. At the same time, the forces acting in the places of actual contact cause stresses exceeding metal yield strength; this leads to the fact that metal plastic deformations occur in thin surface layers, while surface adsorbed oxidizing, gas films and contaminants are destroyed. Simultaneously, the smoothing of irregularities on friction surfaces occurs, thereby their area actual contact is significantly increased. When the friction surfaces close together, interatomic gravities of metals arise, and in the large area of factual contact, metal bonds are formed, similar to interatomic bonds in a continuous metal; this leads to the metal adhesion. This results in a sharp increase of the friction coefficient and intense adhesive deterioration of the rubbing details. It should be noted that provided information can be used by forensic autotechnician experts while research disturbances causes of internal combustion engines. |
