INFLUENCE OF THE SIZE OF THE GAP ON THE SPEED OF CREVICE CORROSION OF AUTOMOTIVE EQUIPMENT
Introduction. Structural and operational factors contribute to the formation of gaps and gaps in agricultural machines and automotive equipment: the presence of welding, threaded, riveting and other types of connections, bends of sheet materials, insufficient sealing between the gasket materials and metal when fasteners are loosened, peeling film of paint and anticorrosive material, corrosion products, contamination of parts, and others. Slots are formed in the thread itself, at the outer ends of fasteners, at the joints of the elements being connected, etc. There is always a gap or gap between the connected parts, where there is an increased capillary condensation of moisture, various contaminants are fixed and crevice corrosion develops. As a result, the anode sections of the surface of the slit joint that are located inside are destroyed, and the outer sections, characterized by free access of oxygen, are cathodes. The liquid is always present in the gaps, since its evaporation from the cracks is very slow. This leads to limited oxygen access, which determines the nature of the anode and cathode reactions: in a neutral environment, the intensity of the anode process in the gap increases, and the cathode process decreases. This is due to the fact that the anode processes occur at more negative potential values, due to the limited access of oxygen to the gap. Moisture in crevices dries longer in comparison with the open surface, so corrosion processes in crevices are intense and depend on the size of the gap. Crevice corrosion is hidden, which makes it difficult to detect it in a timely manner and take measures to neutralize it. This leads to significant metal losses and a decrease in the mechanical strength of the machines. In connection with the above, research on this topic is relevant and in demand in the agro-industrial and motor transport industry. Оbject. The object of research is the rate of crevice corrosion in elements of agricultural machinery and automotive equipment, depending on the size of the gap or gap. Materials and methods. The studies were conducted at room temperature (20-22°C) using cells from two experimental samples made of 08kp steel with a size of 30 × 100×0,8 mm with different gaps, placed in corrosive media, which served as a 3% solution of table salt and a medium that simulates the operating conditions of cars. The volume of solutions in chemical glasses with a capacity of 800 ml was kept constant at the level of 700 ml. The required size of the gap between the samples in the cell was regulated using spacers of various thicknesses. The medium that simulates the operating conditions of cars was prepared based on the concentration of active ions of the main components of road surface pollution, in mg-EQ/l: chlorides 22,00-26,00; ammonium 0,25-0,55; nitrates 5,00-7,00; sulfates 5,18-5,82. To do this, in one liter of distilled water was dissolved: 1,404 g of sodium chloride NaCl, 0,0068 g of ammonia water NH4OH, 0,051 g of sodium nitrate NaNO3 and 0,3905 g of sodium sulfate Na2SO4. The mass of the dissolved ingredients is determined from the condition of the maximum content of the main components of pollution on the road surface. Sampling of road surface contamination was carried out from November to March 2013-2014 and 2014-2015 years on the 20th day of each month, starting from November to March, inclusive. The rate of corrosion was estimated by the gravitational method based on the mass loss of samples sustained for 48 hours in the test medium. Results and conclusion. Studies have shown that the most dangerous, from the point of view of corrosion, are gaps between 0,2 and 0,9 mm. this is Explained by the fact that in gaps of this size, dirt, dust and other contaminants always accumulate, which are hygroscopic and retain moisture, limiting the possibility of access of passivating substances available in the liquid to the gap. Growths appear on the edges of