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HOW STEEL IS PROTECTED

From rental to color.

Sergey KANUNNIKOV, Anton CHUIKIN

Even the most fashionable paint is designed not only to please the eye, but to protect what is beneath it - metal. But this is the last line of defense against corrosion, and the first is still being prepared at a metallurgical plant. Let's walk along the chain from the deep rear to the front edge. Our front is VAZ 2110, at times we will look back at Samara and Lada occupying the flanks.

Post number 1. The first guardian of metal - zinc. On the "top ten" they cover half (by weight) of the body "iron". Why does zinc protect metal from wings, doors, floors (and, inappropriately, buckets) from corrosion?

Let's digress to deal with galvanizing, zinc metals and so on. - remember how corrosion proceeds. Let's say a drop of rain water gets on bare steel - it has the role of an electrolyte. Iron, as a base metal with a relatively low electric potential, gives off positively charged ions to an electrically conductive medium (the very same drop). The released electrons are absorbed during the oxidation reaction. Thus, an anode appears that loses metal ions and a cathode that receives electrons. Together they form a microelement with a closed current loop. The result of the process is the formation of oxides of the starting metal.

But is it possible to give another metal instead of iron instead of iron? The role of the so-called sacrificial coating was entrusted to relatively cheap and technologically advanced zinc. Its potential is even lower than that of iron, that is, it is oxidized more easily. Imagine our drop on a galvanized steel sheet. Initially, zinc acts as a mechanical protection, and if its layer is damaged to iron, it becomes an anode. Losing its ions, zinc saves steel. Simply put, it corrodes instead of iron.

The model of this process is familiar to all more or less experienced motorists. Remember how an aluminum alloy brake drum soups on a steel hub: here is the cathode, anode and oxides, and corrosion products. Steel remains almost unscathed thanks to aluminum, which, like zinc, has a lower electric potential.

We have zinc protection appeared for the first time on "Samara". About 10% of its parts were made of zincmetal - steel coated with a thickness of 15-17 microns based on epoxy resins and zinc powder. The composition was applied at a metallurgical plant, zincmetal withstood stamping and welding. However, since the zinc in the resin was weighed in the form of separate particles, and did not cover the iron with a continuous layer, its protective potential was not fully used. According to VAZ, in salt fog, the material withstood from 40 to 120 hours before the appearance of foci of corrosion.

With the birth of the “tenth” family, metallurgical plants in Lysva and Lipetsk have mastered a more modern, technologically advanced and durable coating that reliably provides 120-hour salt resistance. Over 30 parts, including floor panels, body side panels, rear wheel arches, trunk lid and door panels, are made of ETs-1 steel, on which zinc is deposited on one side with an electrochemical method of 10-15 microns. When stamping, the sheet is oriented so that the non-ferrous metal is turned from the inside of the body panel: after welding, the body is straightened, and a thin layer of zinc will not withstand such a rough effect. From the ETs-2 - steel with double-sided galvanized steel - they make the rear part of the floor, its cross-members and connectors, internal hood panels and trunk lids.

The mudguard of the engine, the radiator frame, the battery pad, the gas tank flap cover and some other elements are made of HZ-2 - hot dip galvanized steel (zinc is applied on both sides, dipping iron into the melt).

The front fenders, the radiator frame and its cross member, and other Samar parts that were previously made from zinc metal are now galvanized. At VAZ news - 2123 and 1119 - non-ferrous metal is supposed to protect already 65% ​​of parts. Models of the older generation will survive their century without zinc …

Soil work. Even before welding, acrylic adhesive mastics capable of conducting electric current are applied to some parts. They provide sealing for welds. Places of flanging (joints without welding) are protected with one-component epoxy glue.

After welding, the body is degreased in several stages. If there are foci of corrosion, they are treated with compounds based on lactic or salicylic acid. Preparing a springboard for the soil, the body of the future car is phosphated - covered with salt solutions, then washed several times. The quality of processing and washing is checked by … measuring the conductivity of the water flowing from the body.

Then the following line of defense is built: the body is lowered into a bath with a capacity of 120–130 m3, where special soil is applied electrolytically.

“Tens”, “Samaras” and part of the “sixes” are primed using cataphoresis, the rest of the models are anaphoresis. The difference is not only and not so much that the “plus” in the first case is fed to the bath, the “minus” - to the body, and in the second - vice versa. Polarity is just a matter of technology, allowing the use of much more advanced durable soils. Tests in salt fog showed: a body covered with modern anaphoretic soil used for processing “Lada” can withstand 275 hours until the first foci of corrosion and 700 hours after cataphoresis.

"Lada", alas, is not destined to become more persistent - they do not intend to use cataphoresis for them.

At the forefront. After priming, future cars are thoroughly washed with partial immersion. Then put mastics and secondary primer. The internal surfaces of the parts and the bottom are hand-operated with a pneumatic sprayer (how much depends on the conscientiousness of the worker!), The front ones are electrostatically sprayed.

Dry the body for 20 minutes at a temperature of 150 degrees. Then the rest of the mastics is applied, bitumen sound insulation is glued to the floor. After the final straightening and rubbing with white spirit, the “iron” finally finds the clothes that customers will meet with it - ordinary single-layer paint or two-layer “metallic” (for details, see ЗР, 2000, No. 4). Thanks to 30–40 microns of varnish covering the color base, the elegant “metallic” is better able to withstand mechanical stress and is aging more slowly. Automata are responsible for the appearance of the car, and the insides and inaccessible places are painted manually.

After controlling the quality of the paint, the bottom of the doors and thresholds are coated with a two-component gray acrylic paint, the hidden cavities are treated with the Oremin preservative.

On cars of the VAZ 2105 family, black AK-142 is painted with door frames, on “Samaras” it also has thresholds from below.

So, having covered a considerable distance in 10 hours (only the length of the drying chambers is more than 270 meters), the body wears an anticorrosive “armor” with a thickness of only 90 - 120 microns. But it is precisely this thin layer that is called upon to fight one of the main enemies of motorists - corrosion.

Volunteers The plant somehow equips cars for the war against rust. Many owners, considering the standard protection is insufficient, call for all kinds of anti-corrosion compounds to help. Nobody seems to doubt the benefits of additional processing, but try to specify: how long does it extend the life of the body? And not in a special chamber with salt fog, but in real use?

To finally answer this question, we decided on an experiment. For clarity, we chose the least classically protected plant. We additionally processed the half of the freshly purchased diesel “four” (see “Operational Experience”) with an anticorrosive, installed two wing liners and … placed the car in an aggressive environment, that is, it was released onto public roads. I wonder what will come of it?

Newly welded VAZ 2110 body: galvanized metal parts can be easily distinguished by a light gray matte finish.

The phosphated dark gray body is immersed in a cataphoretic bath with a VEP primer. To the "stern" is attached a "negative" wire. The body will come out of the drying chamber in light gray.

After final priming, plastisol mastic is applied to the bottom.