Views: 2 Author: Site Editor Publish Time: 2022-08-01 Origin: Site
5. The slag
Phenomenon: Non-metallic inclusions such as oxide, nitride, sulfide, phosphide and so on were found in the weld by nondestructive testing, forming a variety of irregular shapes, the common ones are conical, needle and other slag. Slag inclusion of metal weld will reduce the plastic and toughness of metal structure, but also increase the stress, resulting in cold and hot brittleness easy to crack, so that the component is destroyed.
Reason: The weld base metal is not clean, the welding current is too small, so that the molten metal solidifies too fast, and the slag is too late to surface. The chemical composition of the welding base metal and electrode is not pure, such as oxygen, nitrogen, sulfur, phosphorus, silicon and other components in the welding pool, it is easy to form non-metallic slag. The welder is not skilled in operation and the improper method of running strips makes the molten slag and molten iron mixed together inseparable, hindering the floating of molten slag. The welding groove Angle is small, and the electrode coating falls off in blocks and is not melted by the arc; In multi-layer welding, the slag is not cleaned, and the slag is not removed in time when the operation is caused by slag inclusion.
Prevention and control measures: Use only good welding process performance of the electrode, the welded steel must meet the requirements of the design document. Select reasonable welding process parameters by welding process evaluation. Pay attention to the cleaning of welding groove and edge range, electrode groove should not be too small; For multi-layer welds, the welding slag of each layer should be carefully removed. When using acidic electrode, the slag must be in the back of the molten pool; In the use of alkaline electrode welding vertical Angle seam, in addition to the correct selection of welding current also need to use short arc welding, at the same time the strip should be correct, so that the electrode swing properly, so that the slag surface. Preheating before welding, heating during welding, and heat preservation after welding, so that it is slowly cooled to reduce slag inclusion.
Phenomenon: The gas absorbed in the molten weld metal during the welding process is not discharged from the molten pool before cooling, and the residual hole is formed inside the weld. According to the part of stomata can be divided into inner and outer stomata; According to the partial situation and shape of the pore defects, the existence of pores in the weld will reduce the weld strength, but also produce stress concentration, increase the low temperature brittleness, hot crack tendency, etc.
Reason: the electrode itself is inferior, the electrode damp not according to the requirements of drying; The electrode coating deteriorates or flakes off; Weld core corrosion, etc. Residual gas exists in base metal smelting; The electrode and welding parts are stained with rust, oil and other impurities, in the welding process, due to high temperature gasification gas. The welder is not skilled in operation or has poor eyesight to distinguish the molten iron from the drug skin, so that the gas in the drug skin and the metal solution are mixed together. Excessive welding current can reduce the protection effect of red electrode; Arc length is too long; Power supply voltage fluctuation is too large, resulting in unstable arc combustion.
Prevention AND CONTROL measures: the selection of qualified electrode, do not use drug skin cracking, peeling, deterioration, eccentricity or welding core serious corrosion of the electrode, should be near the electrode and the surface of the electrode oil, rust, clean up. If the size of the current is appropriate, control the welding speed. Preheat the workpiece before welding. When the welding is finished or stopped, the arc should be evacuated slowly, which is conducive to slowing down the cooling rate of the molten pool and the discharge of gas in the molten pool, so as to avoid the occurrence of pore defects. Reduce the humidity at the welding site and increase the temperature of the operating environment. When welding outdoors, if the wind speed reaches 8m/s, rain, dew, snow, etc., effective measures should be taken to prevent wind and put up a canopy before welding operation.
7. Do not clean up spatter and welding slag after welding
Phenomenon: THIS is the most common kind of common disease, neither beautiful, harm is very big. The melting spatter will increase the hardened structure on the surface of the material, and it is easy to produce defects such as hardening and local corrosion.
Reason: The welding material in the preservation of traditional Chinese medicine skin due to moisture deterioration, or the selection of electrode and base metal does not match. The selection of welding equipment does not meet the requirements, the AC and DC welding equipment does not meet the welding material, the welding secondary line polarity connection method is incorrect, the welding current is large, the weld groove edge has debris and oil scale pollution, the welding environment does not meet the welding requirements, etc. The operator is not skilled, not according to the rules of operation and protection.
Prevention and control measures: according to the welding base metal selection of appropriate welding equipment. The electrode should have drying constant temperature equipment, in the drying room with dehumidifier, air conditioner, distance from the ground, the wall is not less than 300mm, the establishment of electrode transceiver, use, storage and other systems (especially for pressure vessels). Clean the edges of the welds to remove moisture, oil and debris rust. Winter and rainy season construction lap protection shed to ensure welding environment. For non-ferrous metal and stainless steel before welding, the base metal on both sides of the weld line can be coated with protective coating as protection. Also available are electrode, thin-coated electrode and argon gas protection to eliminate spatter and reduce slag. Welder operation requires timely cleaning of welding slag and protection.
8. Arc scar
Phenomenon: Due to the careless operation of the electrode or handle and weldment contact, or ground wire and workpiece contact is not good short time caused arc, and leave arc scar on the surface of the workpiece.
Reason: The welding operator is careless and does not take protective measures and maintenance of tools.
Prevention and control measures: welders should always check the insulation of welding wire and grounding wire, and timely wrap up if any damage is found. The grounding wire should be firmly and reliably installed. Do not arc outside the weld pass when welding. Welding tongs should be placed in isolation from the base metal or properly hung. Cut off the power supply when not welding. If arc abrasion is found, the grinding wheel must be polished in time. Because in stainless steel and other corrosion resistance requirements of the workpiece, arc scar will become the starting point of corrosion, reduce the performance of the material