Standard notation
RDS - manual arc welding (mainly in the Soviet literature); MMA - Manual Metal Arc (Welding) - manual metal arc welding; SMAW - Shielded Metal Arc Welding - metal arc welding in a protective atmosphere; E - the international symbol for manual arc welding.
Manual arc welding Technology
To form and maintain an electric arc to the electrode and the workpiece (see figure) is supplied from the power supply welding current (AC or DC).
If the positive pole of power source (anode) attached to the product, saying that the manual arc welding is done on the line polarity. If the negative pole of the product, then the polarity is reversed. Under the action of the arc melted metal rod electrode (electrode metal), its covering and metal products (base metal). The electrode metal in the form of individual droplets, covered with slag goes into the weld pool, where it is mixed with the base metal and molten slag floats to the surface.
Size of the weld pool depends on the mode and the spatial position of the welding arc moving speed of the workpiece surface, the design of the welded joint, the shape and size of the cutting edges of the weld, etc. They are usually found within the following limits: depth of 6 mm, width 8-15 mm, 10-30 mm.
The arc length - the distance from the active spots on the surface of the weld pool to the other active spots on the molten surface of the electrode. As a result of melting of the electrode coating around the arc and weld pool formed on the gas atmosphere, the air is pushed from the weld zone to prevent its interaction with the molten metal. In the gas atmosphere also contains a pair of alloying elements, the main electrode and the metal.
The slag, covering a drop of molten metal electrode and the weld pool surface, preventing their interaction with the air, and helps cleanse impurities from molten metal.
With the removal of the metal arc weld pool is crystallized to form a joint that connects the welded parts. On the surface, a layer of solidified weld slag.
Methods of arc ignition in manual arc welding
The arc is ignited briefly touch the electrode to the workpiece. As a result of current flow and the availability of short-circuit end of the electrode contact resistance is rapidly heated to high temperatures at which the electrode after the formation of ionization of the gas gap and there is a welding arc. For reliable ignition of the arc welder to take products from the electrode to a height of 4-5 mm, since a larger distance between the end of the electrode and the workpiece an arc does not occur.
Usually, the ignition of the arc is carried out either by direct separation of the electrode after a short-circuit current, or the end of the sliding movement of the electrode.
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| Ignition of the arc for manual arc welding |
Moving electrode manual welding
During the welding electrode is reported movement in three directions. The first movement - forward, is directed along the axis of the electrode. This movement is supported by a constant arc length, depending on the rate of melting of the electrode. The length of the arc for manual welding depending on the welding electrode and the mark should be in the range (0,5-1,2) d e . Excessive reduction in the length of the arc affects the formation of the joint and can cause a short circuit. An excessive increase in the length of the arc leads to a decrease in the depth of penetration, increasing the spray electrode metal and the weld quality deterioration both in form and in the mechanical properties and welding electrodes coated basic type - and to cavitation.
The second movement - the movement of the electrode along the axis of the roller to form a seam. The speed of this movement is determined depending on the current strength, electrode diameter, its rate of melting, the type of suture, and other factors. In the absence of transverse motion of the electrode is obtained by a narrow seam (needles cushion) with a width of about 1.5 diameter of the electrode. These joints are used when welding thin sheets, application of the first (root) layer laminated seam welding by the method of bearing, and in other cases.
The third movement - the movement of the electrode across the joint to obtain the required joint width and depth of penetration. The transverse vibrational motion of the end of the electrode are determined by the form of cuts, sizes and position of the seam welded material properties, welding skill. Width of the joints obtained with the transverse vibrations, typically 1.5-5 diameters of the electrode.
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| The main types of trajectories of transverse movements at the end of the electrode at low (A, B), enhanced (E-H) heating the welded edges, one edge of the strong heating (W, S), heating the weld root (R). |
Technique manual arc welding depends on the spatial position of the weld. When welding distinguish lower (0-60 °), vertical (60-120 °) and ceiling (120-180 °) position
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| Various provisions in the product manual arc welding |
In manual welding in the down position the main problem is to ensure full penetration without the formation of cross burn-through.
The figure shows various embodiments of the joints in the lower position. When welding seams on unilateral weight (Figure A) is usually very difficult to avoid burn-through or fusions, so one-sided welds commonly used ways to keep the weld pool:
- Welding on a removable copper lining (Figure B);
- welding on the steel lining of the remaining (Figure B);
- imposition of podvarochnogo seam (figure D);
- cutting, followed by lack of fusion welding the root pass (figure D).
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| Ways to keep the weld pool 1 - removable copper lining, and 2 - the remaining steel lining, 3 - the main seam, 4 - podvarochny seam |
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| How you perform fillet welds in manual arc welding: A - "in the boat", B - slanted electrode |
In manual welding in the vertical position of the molten metal and runoff has a significant influence on the weld penetration and depth (see figure). Vertical joints are usually performed on the rise. In this case it is possible to provide the desired penetration and to maintain the molten metal at the edges. However, the low productivity of welding and welding increases the trigger. However, due to the shallow depth of penetration is possible only for thin metal and the use of special electrodes.
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| Manual arc welding of joints in vertical position |
Manual arc welding in the overhead position
Quite complex and manual welding in the overhead position. The molten metal in the weld pool in this case is kept from leaking out of the surface tension force (see figure). It is therefore necessary that the weight of the molten metal does not exceed that power. To do this, seek to reduce the size of the weld pool, performing periodic short-circuit welding, allowing the weld metal is partially crystallize. Also used the reduced diameter of the electrodes, reducing the welding current force, special electrodes are used to ensure receipt of the viscous puddle.
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| Formation of the bath and the joint in manual arc welding in the overhead position |
- the possibility of welding in all spatial positions;
- the possibility of welding in areas with limited access;
- relatively rapid transition from one material to be welded to another;
- the possibility of welding of various steels with a wide choice of brands produced by the electrodes;
- simplicity and portability of welding equipment.
- low efficiency and performance compared to other techniques of welding;
- quality of the connection depends on the qualifications of the welder;
- adverse conditions of the welding process.
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| Photo: Manual arc welding |
The welding equipment used in manual arc welding:
- welding transformers
- welding rectifiers
- welding inverters
- welding machines (welding generators)
- welding inverters (inverter welders)
Welding technology:
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