Welding repair of diesel generator set refers to the use of welding technology in the maintenance of generator equipment. Welding repair makes the matric and electrode powder melt together under the action of heat energy and get good intergranular bonding strength. However, the influence of heat energy will change the microstructure and shape of the matric, which is the key problem of welding repair.
Welding repair can be divided into arc welding, gas welding and plasma welding according to different ways of providing heat energy. According to the process and method of welding repair, it can be divided into welding repair, surfacing welding, spray welding and brazing.
Because of its outstanding advantages, ordinary cast iron is still the main material for making basic parts with complex shape, large size, easy processing and anti-vibration and anti-wear. In mechanical equipment, cast iron type and weight account for more than half. The failure or failure of cast iron is mainly due to the hole, sand hole, crack, loose, insufficient pouring and equal pressure casting defect of castings. For the machined parts, most of them are cracks and wear in the process of use. The production process of castings is relatively long, and the process costs account for a large proportion of the value of castings, especially cast iron parts with large size, complex shapes and large quantities of processing, which condense most of the raw materials and manufacturing costs of machinery and equipment. Many large castings, such as machine bed, machine base, large box and so on, generally lack the ability to cast blanks and machining by themselves.
Therefore, in the diesel generator maintenance process, we should try every means to repair the old and waste, to compensate for their natural wear. The welding repair of cast iron is not only suitable for the repair of invalid parts, but also as the repair of local defects of castings, which can greatly reduce the production cost. It is of great significance to further study the repair of cast iron. Because the temperature of hearing and cooling of cast iron changes greatly during welding repair time, the solder ability of cast iron is poor, which will lead to many difficulties.
Some necessary technical measure should be taken to ensure the quality of the cast iron structure of diesel generator set. Good performance of cast iron electrode should be selected, preparation before welding should be done, such as cleaning, preheating, etc., cooling rate should be controlled, slow cooling after welding, etc. The following introduction by the small-sized start generator cast iron welding repair matters needing attention.
1. The time-smelting melting zone is small, the cooling rate is fast, and the influence of graphitization makes the weld seam easy to produce both the fragile and hard white iron, and the slag is formed, the weld metal base material is not fused, and the post-weld processing is difficult, crack occur, local overheating deteriorates the performance of the base metal, the grains are coarse, the structure is loose, the stress is unbalanced, and cracks are generated, even brittle.
2. The iron has a high carbon content, and the aged structure of the casting is aged, the performance is attenuated, and the strength is lowered. Especially for cast iron which has been working in high temperature or corrosive medium for a long time, the matric is loose, the internal structure is oxidized and corroded, the grease is absorbed, the weldability is further reduced, and even the welding is not possible.
3. The variety of welding requirements of iron structure and part structure shape complicates the cast iron welding repair process. Major parts need to be welded in all directions, but the cast iron has poor welding performance, low melting point and high fluidity of molten iron, which brings trouble to the welding repair.
4. Casting damage, stress release, coarse grain is easy to misplace, it is not easy to restore the original shape and dimensional accuracy.