The carbon steel electrode for carbon steel and low-strength low alloy steel.
Select the electrode based on the steel chemical composition, mechanical properties, crack resistance requirements, taking into account the comprehensive analysis of welded structures, plate thickness, working conditions, stress, welder performance and other factors. Necessary, to do the welding test, formulate corresponding measures to determine the selection of the electrode.
â’ˆ carbon steel welding is generally used in steel strength grade corresponds to the electrode, taking into account the complex structure, slab stiffness, dynamic load, poor weldability is generally used in good plasticity, impact toughness, good crack resistance of low hydrogen electrodes. Special requirements of the welding position, using the corresponding special electrode, such as vertical down welding rod, the base Copper Electrode. Iron powder type electrode can be used to improve the welding efficiency.
â’‰ fast on the weld cooling rate, increased strength, weld cracks easily, lower than the parent material strength level electrode can be used; between the low-carbon steel and low alloy steel, dissimilar steel welding is generally used with low strength grade steel electrode, and considering the factors of low-alloy steel, in order to use low-hydrogen type is appropriate.
â’Š welding of medium carbon steel, due to higher carbon content of steel, increasing the tendency of welding cracks, generally used in low-hydrogen electrodes and preheating and slow cooling method and adapt welding processes and other measures.
â’‹ cast steel weldable poor generally higher carbon content, the workpiece Heavy, complex structure, easy to produce a weld crack cast steel alloying elements for a long time, it is more prominent. Generally used in low-hydrogen electrodes, and to take measures to warm-up, slow cooling method and the corresponding welding process.
â’Œ as to ensure the quality of welding, the workpiece weld should be clean, not allowed to have oil, rust, water, paint and dirt, is particularly important to use low-hydrogen electrodes.
â’ low hydrogen type electrode, Welding Electrodes shall be subject to 350 ° C baking 1h as baking, or easy to produce pores folder slag, cracks and other defects. Cellulose electrode without baking in general, if damp, temperature welding instructions provided before baking, but the temperature will destroy the electrode welding performance.
Welding current specified in â’Ž instructions as a reference value, the actual operation should be specific to master, such as workpiece preheat than normal current 5% to 15%; vertical welding and overhead welding flat welding current 10% to 15%; DC than AC decreases about 10%. Attention to the instructions provided in DC welder, welding class nature, or affect the welding process.
â’ low hydrogen type electrode generally should not be repeated baking to prevent drug skin crisp, fall off.
SMAW SMAW is a manual manipulation of the arcCarbon Steel Welding Electrodefor welding method. SMAW, the heat generated by the burning of the arc between the electrode end of the workpiece electrode drugs leather and welding die and workpiece melting solder core end deepen the rapid formation of small metal droplet, the transition to the arc column partial melting of the workpiece surface, fusion with the formation of the molten pool. Gas and slag generated in the melting process of the drug skin, not only the weld pool and arc around the air isolated, and the molten solder core, the base metal to a series of metallurgical reaction, to ensure the formation of the weld performance. With the arc to the arc length and speed continue to move forward in their work, the bath of liquid metal gradually cooling and crystallization, to form the weld.
SMAW has the following advantages:
1) The equipment used is relatively simple, relatively cheap and lightweight. Electrode electric arc welding using the AC and DC welding machine is relatively simple, does not require complex auxiliary equipment in the welding operation, only equipped with simple tools. Therefore, the purchase of equipment investment, and easy maintenance, this is one of the reasons it is widely used.
2) does not require auxiliary gas protection. The electrode can not only provide the filler metal in the welding process can produce a protective gas to avoid oxidation to protect the weld pool and welding, and has strong wind resistance.
3) flexible and adaptable. SMAW welded one-piece or small batch of products, short and irregular, anywhere in space, and other mechanized welding the weld is not easy to achieve. Where the electrode can be achieved can be welded.
4) a wide range of applications, applies to most industrial metals and alloys welding. The the SMAW appropriate choice of electrode can not only welding of carbon steel, low alloy steel, but also welding of high alloy steel and nonferrous metals, not only can be welded with metal and welding dissimilar metals can also be cast iron Types Of Welding Electroderepair surfacing of various metal materials.
However, the SMAW has the following disadvantages:
1) the welder operating technical requirements, welder training costs. SMAW welding quality, in addition to close to the electrode with the appropriate welding parameters and welding equipment, mainly to ensure that rely on operating skills and experience of the welder, SMAW welding quality to a certain extent depends on the welder operating technology. Must always welder training, training costs.
2) poor working conditions. SMAW mainly rely on manual and eye observation of the welder to complete the whole process of the labor intensity of the welder and always baked at high temperature and toxic smoke environment, working conditions are relatively poor, to strengthen the labor protection.
3) low production efficiency. SMAW mainly rely on manual operations, and welding parameters to select a smaller range, In addition, welding electrodes must be frequently changed, and regular clean-up of weld slag, and automatic welding, welding productivity is low.
4) is not suitable for the welding of special metals and sheet. Active metals (eg Ti, Nb, Zr) and refractory metals (such as Ta, Mo, etc.), due to oxygen contamination of these metals is very sensitive to the electrode protective effect is not sufficient to prevent the metal oxide, the protective effect is not good enough. welding quality is below standard, so can not be used SMAW; arc temperature is too high in terms of its low melting point metal such as Pb, Sn, and Zn in its alloys, etc., so it can not be used SMAW welding. In addition, the SMAW welding workpiece thickness is generally more than 1.5mm, 1mm below the sheet is not suitable for SMAW.
SMAW with simple equipment, convenient operation, strong adaptability, can be anywhere in the space welding is widely used in various industrial fields, is one of the most widely used welding method.
Static characteristics of an SMAW arc
SMAW welding current is low, especially in smaller current density, so the SMAW arc static characteristic in the horizontal section shown in Figure 2. SMAW arc level range, the arc length remained unchanged, within a certain range to change the current value of the arc voltage almost does not change, and thus the change within a certain range of welding current, arc stable burning.
Second, the arc temperature distribution
SMAW arc in the electrode end of the workpiece burn, electrode and workpiece electrode, the maximum temperature of the arc yin and yang poles close to the boiling point of the material, welded steel cathode about 2400 â„ƒ, the anode of about 2600 ° C, the arc temperature â„ƒ 60 ~~ 7000. With the increase of welding current, the arc column temperature is increased. AC arc two electrode polarity is constantly changing, so the two electrodes, the average temperature is equal to the DC arc cathode temperature than the negative high 200 ° C or so.
Welding process, due to air turbulence, magnetic field or electrode eccentric impact of the arc center from the electrode axis phenomenon known as arc blow.
1, resulting in arc blow
(1) electrode eccentric blow the eccentricity of the electrode through the large, resulting in uneven skin thickness electrode drugs, drug skin thicker heat absorbed when one side is thinner than the drug skin side of the melting, thin skin of drug side quickly melting leaving arc exposed, forcing the arc to blow as shown in Figure 3.
(2) arc around the airflow to blow the arc gas flow around the strong will blow. Caused by the arc around the gas flow is too strong by many factors, mainly the air flow and thermal convection in the atmosphere. Welding operations in the open gale, arc blow is very serious;, due to the air flow rate of the larger tubes, the formation of "drafts" in the pipeline welding, the arc blow; then docking the gap in also have a blow under the influence of thermal convection.
(3) when the welding arc, magnetic blow DC arc welding, the arc generated by the electromagnetic force generated by the welding circuit blow, known as the welding arc, magnetic blow. Magnetic blow causes are:
1) the grounding line location inappropriate caused by magnetic blow, shown in Figure 4. Space through the welding current produces a magnetic field, when the welding rod and welding vertical arc left side of the density of magnetic field lines, magnetic field lines of the arc the right of the sparse, uneven distribution of magnetic field lines resulting in density on one side of the arc produce thrust , so that the arc deviation from the axis.
2) asymmetric ferromagnetic material caused by the magnetic blow, shown in Figure 5. Welding, the arc side of the place a steel plate (resistive magnet), the permeability of the ferromagnetic material capacity is far greater than the air, most of the magnetic field lines of the ferromagnetic material side through the ferromagnetic material to form a closed curve, resulting in arc with iron The lower density of magnetic material between the magnetic field lines under the action of electromagnetic force arc blow to the side of the ferromagnetic material.
3) arc movement to the end of the steel plate caused by the magnetic blow, shown in Figure 6. This is the change of magnetic area because of the arc to reach the plate ends, caused by the increase of the space magnetic field lines in the local density near the edge of the weldment, under the action of electromagnetic force to produce a point to weld the inside of the magnetic blow.
Measures to prevent arc blow
1) Welding encountered during electrode eccentricity caused by the blow, should immediately stop the arc. If the eccentricity is small, rotating electrode will move the eccentric position to weld the forward direction, to adjust the electrode angle before welding; eccentricity larger, new electrode must be replaced.
2) the welding process when the airflow caused by the blow, To stop welding, identify the reasons for the shelter and other methods to solve.
3) When the magnetic blow occurs, the welding rod can be to the magnetic blow opposite the direction of tilt, in order to change the size of the space around the arc, so that the density of the magnetic field lines tends to be uniform to reduce the degree of blow; to change the location of the grounding line or in the weldment two opposite sides of the ground wire can reduce the magnetic blow caused due to the wire grounding position. AC current and the direction of the magnetic field is constantly changing, so the AC arc welding power to prevent the magnetic blow, another short arc welding, can also reduce the magnetic blow.
Droplet and weld pool forces
Welding arc is not only a heat source, as well as a power source, the droplet transfer process in the droplet and weld pool will be subject to a variety of external forces. Process measures the force on the droplet and weld pool can be changed to ensure the stability of the welding process to control the weld forming, reduce spatter, good welded joints.
1) Gravity gravity objects always have a tendency to under the weight. Flat welding, the gravity of the droplet will promote droplet transfer and bath under the action of gravity, if the temperature is too high, the bath is too large, it will produce welding in the tumor and burn. Li a welder Yang welding, gravity hinder the transition of the droplet to the weld pool, short arc welding can overcome the effect of gravity.
2) surface Zhang Liping welding, the liquid droplet surface tension will hinder the droplet transfer overhead position welding, droplet surface tension can make it difficult to drip, the transition to the molten bath. Bath of liquid metal surface tension of the bath strive tends to keep the plane to a certain extent to prevent gravity-induced surface depressions. The same time, the droplet contact with the bath short-circuit, the weld pool surface tension droplet pulled into the molten bath to accelerate the droplets of the short-circuit transition.
3) the arc gas blowing force SMAW electrode melting rate of the drug skin than the melting rate of the solder core slower, melt the ends to form a casing, the gas-making agent in the composition of drug skin melted in the welding rod gas emitted from the casing and the formation of Cobalt straight airflow and volume in the high-temperature state of rapid expansion in the axial direction along the electrode, the droplet blown into the molten bath. In any welding position, the arc gas blowing force have contributed to the droplet transition.
4) the electromagnetic compression force SMAW is the electrode and the electrode end of the droplet as conductor after the passage of the welding current will produce magnetic fields around them, and compression to the center of the electromagnetic force generated from the surrounding. The electrode end of the droplet necking part of the current density, electromagnetic compressive force is also higher, can contribute to the droplet from the electrode end of the transition to the molten pool.
5) the pole pressure in the welding arc, the pole pressure hinder the droplet transfer of power. When using DCSP, the pressure of the cation hinder the droplet transition; electronic pressure hinder the droplet transfer when using DCRP. Cation mass, cation current than the pressure of the flow of electrons is also large, DCRP, it is easy to produce fine-grained transition are connected is not easy.