The causes that cause accelerated corrosion are divided into two groups and are related:
- with design or technological features of specific models;
- with external influences.
The first group includes:
- the occurrence of high stresses and vibrations of the body metal;
- Availability "pockets" in load-bearing sections of bodies;
- use of thin sheet metal (0.7–0.8 mm);
- the use of metal with impurities that increase the rate of corrosion;
- the presence of corrosion concentrates in the form of moldings and other decorations.
External influences include:
- sulfur compounds, carbon dioxide and chlorides contained in the environment;
- saline solutions used to combat ice.
Under our conditions, various salt solutions have the greatest impact, as they lead to the formation of conductive "bridges" between body parts, as a rule, having different electrical potential. This causes the fastest type of metal destruction - electrochemical corrosion. The bottom line is that all cars have a single-wire electrical circuit, and, therefore, on the body "walk" currents from one consumer to another.
We will not delve further into the theory, leaving it to specialists in the field of corrosion, and turn to practical issues. These results are based on the use of three types of instruments during the examination, which make it possible to evaluate:
- thickness change "alive" metal, that is, not exposed to corrosion;
- the degree of erosion of the metal from the inside, in other words, the degree of its loosening or destruction by oxides;
- thickness of cosmetic layers (paints, putties), which allows you to determine whether the body was under repair and attempts to hide it.
The results of the examinations carried out by experts allow us to draw the following conclusions:
1. Under the conditions of our region, the rate of corrosion penetration into metal for cars with winter operation is 0.2 mm per year and 0.1 mm per year for cars that have not seen salt.
2. Corrosion develops especially rapidly in areas subjected to body repairs, and very quickly if this repair was carried out using welding or soldering, since electrochemical pairs are created from dissimilar metals. For those who buy a car, especially a foreign car, this is fundamentally important. After all, it is not in vain that thrifty Europeans almost always sell even a slightly broken car (true, getting insurance) for nothing - $ 1-2 thousand. For how much they are then resold in our markets, the reader, apparently, knows himself. But if you were lucky enough to discover a hidden defect before making a purchase, you should know that the real cost of such a car is 25-50% lower than that of an unbeaten one. We must not forget that sooner or later you will sell a car, and without experts, expensive purchases are now made only by very naive people.
3. The most rapid process of corrosion occurs in cars operated in winter and stored in garages, especially warm ones, without preliminary dissolution of salts with running water. We emphasize not flushing, namely dissolution. Those who believe that by washing out the lower part of the car with a strong jet, they are doing a good deed are very mistaken. Salts dissolve easily and without strong pressure, but protective coatings from a powerful jet rather quickly "come off" from metal, sag, creating only the illusion of protection. In the cavities formed between the metal and the sagging mastic, corrosion develops much faster than on open metal.
It is highly not recommended to wash the car with hot water, because due to different thermal expansion, protective coatings that warm up first of all "slide down" with metal, forming a negative effect.
Those who believe that the thicker the protective coating, the better, are wrong. Everything is just the opposite. The main thing is that there are no gaps in the coating, and therefore it must be updated regularly.
Finally, some practical advice. Of two cars, the better is not the one that "younger", and the one on which the process of destruction of the metal did not penetrate to a depth of more than 0.4–0.5 mm. In this case, no treatment can prevent the formation of holes in one and a half to two years. And vice versa, even an old car that has reliable protection from the beginning of operation will last for many more years. Under our conditions, it is possible to repair the engine and chassis in a foreign car, but it is not economically feasible to repair a heavily rotten body.