Electric welding. Electrode coatings: purpose and composition. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric welding. Electrode coatings: purpose and composition. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / welding equipment

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Depending on the ratio D/d (where D is the diameter of the coating, d is the diameter of the electrode wire) electrodes are divided into 4 types:

M - thin coated electrodes D/d≤l,2;
С - electrodes with medium coating l,2≤l,45;
D - electrodes with a thick coating l,45≤l,8;
G - electrodes with a particularly thick coating D/d>l,8.

Thin coating It is designed only to stabilize the arc and does not create protection for the molten weld metal, which leads to oxidation and nitriding of the deposited metal.

Thin-coated electrodes cannot be used when making critical welds, since the weld is brittle, porous with various non-metallic inclusions. The simplest thin coating is made from finely sifted chalk diluted on liquid glass.

For 100 weight parts of chalk, 25-30 weight parts of liquid glass are taken. The resulting mixture is stirred in water until a creamy state is obtained. The coating is applied to the electrode wire by dipping, followed by drying at a temperature of 30-40°C.

Higher quality welds produce coated electrodes based on titanium concentrate.

Welded joints of high quality are made by electrodes with medium, thick and extra thick coatings.

In addition to stabilizing the arc, these coatings can perform a number of other functions.:

Function 1. To protect the molten weld metal from the effects of oxygen and nitrogen in the air.
Function 2. Deoxidize the oxides formed during the welding process.
Function 3. Change the composition of the deposited metal by introducing alloying impurities into it.
Function 4. Remove sulfur and phosphorus from the molten weld metal.
Function 5. Form a slag crust over the weld metal.

To perform the listed functions, the electrode coating must contain the following components:

Component 1. Ionizing substances that facilitate the excitation of the welding arc and maintain its stable combustion. Chalk, marble, potash, feldspar, etc. are used as ionizing substances.
Component 2. Protective substances that decompose and burn during welding, releasing a large amount of gases that protect the weld pool from contact with atmospheric gases. Thanks to these substances, the weld metal is protected from the effects of oxygen and nitrogen in the air. Such gas-forming substances are starch, wood flour, cellulose, etc.
Component 3. Deoxidizers have a high affinity for oxygen and therefore restore the weld metal, improving its quality. Ferroalloys, aluminum, graphite, etc. are used as deoxidizers.
Component 4. Alloying substances allow you to get various useful properties of the weld. Good alloying substances are ferromanganese, ferrosilicon, ferrochrome, ferrotitanium.
Component 5. Slag-forming substances form slag, which, hardening on the surface of the weld, prevents its rapid cooling, and also protects from the effects of the atmosphere. Feldspar, quartz, marble, rutile, manganese ore, etc. are used as slag-forming substances.
Component 6. Binders designed to mix all components of the coating, as well as to hold the coating on the electrode and give it sufficient mechanical strength after drying. Usually liquid glass is used as a binder. Less commonly used dextrin.

To increase productivity, i.e., to increase the amount of deposited metal per unit time, iron powder is sometimes introduced into the electrode coatings. The iron powder introduced into the coating improves the technological properties of the electrodes (facilitates the re-ignition of the arc, reduces the cooling rate of the deposited metal, which is beneficial when welding at low temperatures).

Quality coatings are divided into four main groups:

Group 1. Acid coatings containing ores in the form of iron oxide, manganese, silicon, sometimes titanium.
Group 2. Basic coatings based on calcium fluoride and calcium carbonate. Welding with basic coated electrodes is carried out at direct current and reverse polarity. Due to the low tendency of the metal to form crystallization and cold cracks, electrodes with this coating are used for welding large sections.
Group 3. Cellulosic coatings based on cellulose, flour or other organic compounds that create gas shielding of the arc and form fine slag during melting. Cellulosic coated electrodes are generally used for welding thin steel.
Group 4. Rutile coatings, the main component of which is rutile. For slag and gas protection, appropriate mineral and organic components are introduced into coatings of this type. When welding on direct and alternating current, metal spatter is insignificant. The stability of arc burning, the formation of welds in all spatial positions is good.

Author: Koryakin-Chernyak S.L.

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