The outer skin of the welding rod should be fine and smooth, free of air holes and mechanical damage, no eccentricity of the coating, no corrosion of the welding core, chamfering at the arc starting end, and clear marking of the clamping end.
Lift the welding rod to a height of 1m and drop it freely onto a smooth thick steel plate, as shown in Figure Test method for solder skin strength. If the coats does not fall off, the coats strength is qualified.
welding rod eccentricity As shown in Figure Welding rod eccentricity, T1 in the figure represents the sum of the maximum thickness of the coating on the section of the welding rod and the diameter of the welding core, and T2 represents the sum of the minimum thickness of the coating on the same section and the diameter of the welding core. The eccentricity of the welding rod should be within the allowable tolerance range. If the eccentricity is too large, the arc will be deflected and the coating will fall off in pieces during welding, which will affect the quality of welding. The calculation of eccentricity can be calculated by formula.
The qualified standard for welding rod eccentricity is: for welding rods with a diameter not greater than 2.5 mm, the eccentricity should not be greater than 7%; for welding rods with a diameter of 3.2 mm and 4.0 mm, the eccentricity should not be greater than 5%; The degree should not be greater than 4%.
Welding rod manufacturability inspection mainly includes inspection items such as arc stability, re-strike performance and slag removal. In the welding test with the inspected welding rod, if the arc is easy to start, the arc combustion is stable, and the spatter is small, the coating is melted evenly, the weld is well formed, and the slag is easy to remove, the processability of the welding rod is good. Among them, the inspection of the arc breaking length in the arc stability inspection is very important. The method is to clamp the welding rod vertically on a special bracket, place a steel plate under the welding rod, and the welding rod and the steel plate are the two poles of the power supply, and connect Current, voltmeter. After the power is turned on, the arc is ignited with a carbon rod. With the melting of the welding rod, the length of the arc gradually increases. When it reaches a certain length, the arc extinguishes itself. Record the values of current and voltage, and measure from the weld seam after the power is cut off.The distance from the tip to the end of the welding core, this distance is the arc breaking length. As shown in Figure Schematic diagram of measuring arc break length. Generally, the average value of three times is the arc-breaking length of the welding rod, and the larger the arc-breaking length, the better the arc stability.
(1) Roll a few welding rods on the palm of your hand. If the welding rods collide with each other and make a crisp metallic sound, the welding rods are dry; if there is a low rustling sound, the welding rods have been damp and need to be dried before use.
(2) Short-circuit the welding rod in the welding circuit for a few seconds. If the surface of the welding rod sweats or has granular spots, the welding rod is damp and cannot be used normally.
(3) If there are rust marks on the welding core, the welding rod will be damp.
(4) For thick-coated welding rods, bend slowly to 120°. If a large piece of coating falls off or there is no crack on the surface of the coating, it means that the welding rod is damp. When the dry welding rod is slowly bent, there is a small brittle sound. Continue When it is bent to 120°, small cracks appear on the stretched surface of the drug skin.
(5) If the coating falls off in pieces during welding, a large amount of water vapor is generated or there is violence, it means that the welding rod has been damp.
If the coating of the damp welding rod falls off, it should be discarded. Although it is damp, it is not serious and can be used after drying. The welding core of the acid welding rod has slight rust spots and can basically guarantee the quality when welding, but the basic welding rod used for important welding structures cannot be used after rusting.
The welding rod coating is very easy to absorb moisture in the air and get damp. If the water content of the welding rod coating exceeds a certain level, it will seriously affect the process performance and welding quality of the welding rod during operation. If there is too much moisture in the coating, it will cause huge splashes during welding, and form pores in the weld seam. When welding some alloy steels, it will also promote the formation of delayed cracks. At the same time, too much water will also cause yellow spots and rust on the welding core. Therefore, it is of great significance to strengthen the storage and storage of welding rods to ensure the quality of welding.
(1) welding rods must be stored in a dry, well-ventilated indoor warehouse. Welding rods are stored in the warehouse, harmful gases and corrosive media are not allowed, and the room should be kept clean.
(2) welding rods should be stored on the shelf, the distance from the shelf to the ground should not be less than 300mm, and the distance from the wall should not be less than 300mm, and a desiccant should be placed indoors to prevent the welding rods from getting wet.
(3) When stacking welding rods, they should be stacked according to type, grade, batch, specification, and storage time. Each stack should be clearly marked to avoid confusion.
(4) After the welding rod is supplied to the user, it can be guaranteed to continue to be used for at least six months.
(5) The storage and storage of special welding rods should be stricter than general welding rods, and should be stacked in the designated area of the warehouse. Wet or packaged damaged welding rods are not allowed to be stored without treatment.
(6) Welding rods with damp coating, discoloration of the drug skin, and rust on the welding core must be dried for quality evaluation, and the performance indicators in all aspects can meet the requirements before they can be put into the warehouse.
(7) The amount of welding rods out of the warehouse at one time generally cannot exceed the amount used for two days, and the welding rods that have been out of the warehouse must be properly kept by the welder.
(8) Thermometers and hygrometers should be installed in the welding rod storage. The indoor temperature for storing alkaline welding rods should not be lower than 5C, and the relative air humidity should be lower than 60%.
(9) welding rods that have been stored for more than one year should be re-tested for various performances before distribution, and they can be distributed only when they meet the requirements, otherwise they should not be released from the warehouse.
(10) welding rods should be dried in strict accordance with regulations before use. The dried welding rod should be placed in a heat-insulating plate at 100~150C, and the heat-insulating plate must be connected to the output terminal of the electric welding machine, and it can be used at any time.
(11) The alkaline welding rod should not be placed at room temperature for more than 4 hours, and should be re-dried after the time is exceeded, and the number of repeated drying should not exceed 3 times.
(12) When drying the welding rod, it is forbidden to put the welding rod into the high-temperature cylinder suddenly, or take it out of the high-temperature cylinder to cool it suddenly, so as to prevent the welding rod from cracking and peeling due to sudden cooling and sudden heating.
(13) When drying the welding rods, the welding rods should not be stacked or stacked in bundles, but should be laid in layers. The stacking of each layer of welding rods should not be too thick, generally 1 to 3 layers, to avoid heat and moisture when the welding rods are dried .
(14) A record should be made when the welding rod is dried, and the record should include the grade, batch number, temperature and time.
The selection of welding rod is a very important part of welding preparation. The following basic principles should be followed when selecting welding rods:
For structural steel weldments, when welding the same kind of steel, the welding rod should be selected according to the principle of the same tensile strength as the steel; when welding dissimilar steel, the steel on the side with lower strength should be selected; The room temperature performance of the weld metal is more important to choose according to the high temperature performance; when welding stainless steel, it is necessary to ensure that the weld composition is compatible with the parent material composition, thereby ensuring the special performance of the welded joint; for the weld under dynamic load, it is necessary to The electrode with high impact toughness of the deposited metal should be selected; for the weld under static load, only the electrode with the same tensile strength as the base metal should be selected.
For weldments with complex structures and high rigidity, due to the large stress generated when the weld metal shrinks, electrodes with better plasticity should be selected: when selecting the same electrode, not only the mechanical properties, but also the influence of the shape of the welded joint should be considered . Because, when welding butt welds, if the strength and plasticity are moderate, the strength will be high and the plasticity will be low when welding fillet welds; , oil and other insensitive acid electrodes can better ensure the quality of the weld.
The weldment has high rigidity, and when the content of carbon, sulfur, and phosphorus in the base metal is high or the external temperature is low, the weldment is prone to cracks. It is best to use a basic electrode with high crack resistance for welding.
During the welding process, the arc should be stable, with less spatter, beautiful weld shape, easy slag removal, and suitable for all-position welding. For this reason, try to use acidic electrodes, but first of all, the performance and crack resistance requirements of the weld must be guaranteed.
In the absence of a DC welding machine, low-hydrogen electrodes without special arc stabilizing agents cannot be selected; when the weldment cannot be turned over and all-position welding must be performed, electrodes suitable for spatial position welding under various conditions should be selected ; When welding in a closed container, in addition to considering enhanced ventilation, it is also necessary to avoid using alkaline low-hydrogen electrodes as much as possible, because this electrode will emit a lot of harmful gases and dust during the welding process.
Under the condition that the performance requirements of the weld can be guaranteed, the welding rod with lower cost should be used first. For example, the cost of ilmenite-type electrodes is much lower than that of titania-calcium electrodes. Under the premise of ensuring performance, ilmenite-type electrodes should be selected.