BMW 3 series E30

Since 1983-1994 of release

Repair and car operation

14.43. Metal corrosion

THE GENERAL DATA

Approximately 70 % of cost of the car are defined by a body condition. And it, in turn, depends on, whether the car has visited failure and, the main thing, from degree of its corrosion damages.

The reasons causing accelerated corrosion, are subdivided on two groups and connected:

– With constructive or technological features of concrete models;
– With external influences.

It is possible to carry to the first group:

– Occurrence of high pressure and vibrations of metal of a body;
– Presence of "pockets" in bearing sections of bodies;
– Use of thin metal sheet (0,7–0,8 mm);
– Use of metal with the impurity increasing speed of corrosion;
– Presence of concentrates of corrosion in a kind молдингов and other ornaments.

External influences concern:

– Sulphurous connections, dioxide of carbon and the chlorides containing in environment;
– The salt solutions applied to struggle against ice.

Under our conditions the greatest influence is rendered by various salt solutions as lead to formation of current-carrying "bridges" between body details, as a rule, having different electric potential. It causes most быстротекуший a kind of destruction of metal – electrochemical corrosion. An essence that all cars have the single-wire electroscheme, and, hence, on a body currents from one consumer to another "walk".

Let's not go deep further into the theory, having left its experts in the field of corrosion, and it is reversible to practical questions. These results are based on use during examination of three types of the devices, allowing to estimate:

– Change of a thickness of "live" metal, that is not подвергшегося to corrosion influence;
– Degree of erosion of metal from the inside, better to say, its degree разрыхления or destructions by oxides;
– A thickness of cosmetic layers (a paint, шпатлевки) that allows to define, whether there was a body under repair and attempts it to hide.

Results of examinations which are spent by experts, allow to draw following conclusions:

1. In the conditions of our region speed of penetration of corrosion in metal for cars with winter operation makes – 0,2 mm year and 0,1 mm in a year for the cars which were not seeing salts.

2. Corrosion in the zones which were exposed кузовному to repair, and absolutely quickly if this repair was made with use of welding or the soldering as electrochemical steams from diverse metals are created especially quickly develops. For buying the car, in particular a foreign car, it is essentially important. After all knowingly economical Europeans practically always sell even slightly beaten car (the truth, having received the insurance) for nothing – $1-2 thousand. For how many them then перепродают in our markets, the reader, probably, knows also itself. But if to you has had the luck to find out a latent defect before purchase fulfilment, know that real cost of such motor vehicle on 25–50 % more low, than at the unbeaten. It is impossible to forget that sooner or later you will sell the car, and without experts expensive purchases are done now only by very naive people.

3. Most quickly there is a corrosion process in the cars maintained in the winter and stored in garages, especially warm, without preliminary dissolution of salts by flowing water. We underline, not washings off, namely dissolution. Those who believe very are mistaken that, washing away a strong stream the bottom part of the car, they do a good deed. Salts are easily dissolved and without a strong pressure, and here sheetings from a powerful stream quickly enough "come unstuck" from metal, sag, creating only protection illusion. In formed between metal and the sagged mastic cavities corrosion develops much faster, than on open metal.

The inquiry

Extremely it is not recommended to wash the car with hot water as because of different temperature expansion sheetings getting warm first of all "slip" from metal, forming a negative effect.

Those who believes are not right that the a sheeting more thickly, the better. All very much the other way. The main thing that in a covering there were no ruptures that is why it is necessary for updating regularly.

In summary – a practical advice. From two cars what is younger"is better not, and on what process of destruction of metal has not got on depth more than 0,4-0,5 mm. In this case any processing it is impossible to prevent formation of holes in one and a half-two year. And on the contrary, even the old car possessing from the beginning of operation by reliable protection, will serve as early as more many years. Under our conditions in a foreign car it is possible to repair the engine and a running gear, but is economically inexpedient to repair strongly rotted through body.