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| Slag is one of the common defects in hot melt castings. Slag formation is caused by molten slag entering the weld. If not all molten metal blocks or other metals are mixed with steel; in the thermal reaction of aluminum, the molten slag will not float in time, be washed away in the cavity, and adhere to the surface of the rail to solidify to form slag. In the welding joint autometallographic structure is the grain size is coarse or uneven in part or all parts, called feed grain. The grain size of the weld is required to be lower than that of the rail. If the grain size of the PD3 rail transport is 6, the grain size of the weld should not be lower than 5. If the rail gap is too large, the sand box is not placed or the phenomenon of "running iron" is set, and the molten steel is insufficient, the slag cannot be completely discharged into the cavity, and the slag is most likely to be generated on the upper part of the rail; the static time is not enough, and the reaction is not complete. The slag will continue to be produced in the furnace, and the slag will not have time to form a slag due to the rapid solidification. Sand formation is caused by the type of sand entering the weld. Such as: sand and refractory dirt, the disposable crucible of sand holding material is mainly mixed alumina and manganese sulfide in molten steel. Can be produced under the influence of welds and heat. Combined with the solidification of the welded joint, the strength is lower than a certain freezing point temperature range, and cracks or fractures occur due to shrinkage stress or strengthening the boundary of the steel in the temperature range. The aluminothermic welding will produce a certain degree of welding thermal stress during the cooling process. It is generally required that there should be no bolt holes adjacent to the welding, so as to avoid the welding thermal stress acting on the holes to form cracks and cause damage. During the running of the train, the cracks develop and expand, eventually leading to rail fracture. The cracks formed in the high temperature zone are called hot cracks. Its surface is often oxidized blue in color. Like screw hole welding, try to adjust the rail joints to meet the requirements of welded rails. When there is a necessary track, we must cut off 10〜13mm from both ends of the track, so that the screw holes are too close to the rail joints, causing hidden dangers. The impact of thermal cracking on the quality of welded joints will lead to rail fracture. Removing the box prematurely puts the solder joints into effect prematurely. Especially under low temperature conditions, the weld seam is stimulated by cold, accelerates shrinkage, increases shrinkage stress, and forms regional high temperature thermal cracks. Removing the box prematurely puts the solder joints into effect prematurely. Especially under low temperature conditions, the weld seam is stimulated by cold, accelerates shrinkage, increases shrinkage stress, and forms regional high temperature thermal cracks.
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