Welding is the process of joining two metal surfaces at the intermolecular level. For welding metal required apparatus (inverter), electric current, electrodes and protective equipment. It is necessary to answer the questions: how to cook with electrodes, how to choose them correctly, how to ignite an arc and what are the welding parameters?
The scheme of the electrode for welding.
Selection of welding electrodes
Electrode - metal rod in the shell. It is designed to make the compound by melting (when the materials are heated to the melting temperature and form intermolecular bonds). The metal core is an additive material that fills the void between the parts (forms a seam).
The core of the electrode, which is boiled, is covered with an external coating. It is necessary to protect the molten metal. The coating melts along with the rod, floats on the surface of the melt (it is lighter) and forms a protective slag film. The film protects the molten metal from oxidation and saturation with nitrogen.
Electrode welding technique.
Gaseous substances are also introduced into the coating. They are released upon melting and surround the arc with protective gas. Gas is a barrier to oxygen and nitrogen, it prevents the reaction of the metal with air components.
Different rods are used for different parts to be welded. Their differences are in the material and diameter. In individual construction or on the plot, two diameters are most in demand: 3 and 4 mm.
The size of the cross section of the rod (its diameter) is determined by the thickness of the surfaces to be joined. The wider the part, the thicker the rod should be. The largest diameter of the rod is 5 mm.Back to table of contents
Parameters of arc welding: what is it?
In order to cook with electrodes qualitatively, it is necessary to choose the right process parameters. What is it and how to determine their meaning?
For a novice welder working with ordinary steel, it is important to know the meaning of the following parameters:
- electrode diameter;
- welded current;
Welded current is the amount of current that forms an arc between the part and the electrode. Its value should correspond to the diameter of the rod. The thicker the diameter, the greater the current value. Often the value of the correspondence of the current and the diameter of the rod is depicted on the packaging container (box) of the inverter.
The polarity of the current is the direction of its movement. The welding inverter has two terminals with clamps at the ends. One is labeled "+", the second - "-". An electrode is inserted into one of the terminals, the second is fixed on one of the parts to be welded.
The influence of the angle of inclination of the electrode on the shape of the seam.
The current moves from "-" to "+". Between the plus and minus of the arc, a temperature difference of 700-800º C is formed. For example, at the anode end of the arc a temperature of 4000 ºC is formed, at the cathode - 3200 ºC.
With direct polarity, the “-” terminal holds the rod, and the “+” terminal is attached to the part. The flow of electrons moves from the electrode to the part, a higher temperature forms on the surfaces to be joined, the parts melt faster. This mode is used in welding parts from conventional alloys (without special properties).
With reverse polarity, the rod is attached to the “+” terminal. In this scheme, the electron flow moves from the part. This mode of welding is used for thin-sheet products and low-melting alloys in order to prevent their excessive melting and burning (the formation of a through hole in the part).
In household use, the most demanded mode of direct polarity.
The most common parameters for household electrode welding are 100 A with direct polarity and an electrode of 3 mm.Back to table of contents
Metal welding: how to cook with electrodes?Back to table of contents
Start welding: how to ignite the arc?
For welding, the metal is cleaned of rust, old paint. One of the terminals (“+”) is fixed on the part, the electrode is inserted into the second one. The value of the welding current (100 A) is set on the inverter, the terminal with the rod is taken in hand and the voltage is applied. Dip the eye shield with a protective glass (light filter).
To properly boil the electrode, you need to learn how to ignite an arc.
The classification of the arc.
Arc ignition can be performed in two ways:
- Chirping. The terminal in the terminal strikes the surface of the metal, as when igniting a match. In this case, the appearance of the arc is accompanied by a characteristic crackle and a bright luminescence observed in the light filter. Before ignition in the glass filter is not visible almost nothing. Striking is used for ignition of the arc "on the cold" (first or when changing the rod).
- Bring the electrode to the minimum distance. This method is used for "hot" metal, when the arc a few seconds ago was burning and went out. The end of the rod is brought closer to the distance of the arc (3-5 mm), the electrons pierce the air gap, and an arc is formed.
In order to facilitate ignition, it is necessary to beat the edge of the rod to remove the coating. For welding, the angle of inclination of the rod to the surface of the parts to be welded is selected at 70-80º (almost vertically, with a slight slope).Back to table of contents
Movement of the electrode and the weld pool
When welding electrodes with metal melting, the formation of a welded bath occurs. This is a pool of melt in which materials of the surfaces to be welded and the core are mixed. For high-quality welding, the end of the rod should move along the seam not straight, but reciprocating (back and forth or in a spiral).
Semi-automatic arc welding with consumable electrode in shielding gas.
Behind the core moves the weld bath. Its size affects the speed of movement of the terminal with the rod. The slower the welding, the wider the bath and the deeper the melting. There is a danger of through-burning.
With the accelerated movement of the rod is not ensured sufficient penetration. Welding contains discontinuities, indicating poor quality compounds.
The welded bath freezes and forms a weld. Its surface is coated with flux. The protective layer is removed with a hammer (knock) and visually inspect the seam, determine the presence of penetration, discontinuities, voids.
Welding is a technological operation of a strong connection of two metals. In order to successfully master the welding skills and use it in their own construction, it is necessary to purchase a welding inverter, choose the right electrodes and determine the welding parameters.
By showing patience and perseverance, you can learn to cook metal products at home (grilles on the windows) and in the garden (frames for greenhouses and for construction).