Defect repair technology of the hottest large cast

2022-08-08
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Defect repair technology of large castings through the repair results of several traditional welding repair processes in the defects of machine tool castings, the reasons for the poor repair results of machine tool castings are analyzed. Through the research on the repair results of casting defect repair machine in machine tool castings, a feasible new technology and process for repairing machine tool castings are determined

1. Welding repair results and analysis of traditional welding repair process

material HT200, guide rail defect area s < 1000mm2, depth h < 8mm. Heat treatment status: 3 pieces have not been surface quenched, and 1 piece has been surface quenched. Use nickel based welding powder F103, cast iron welding rods for arc welding: Z308, z248. 2.1.2 spray welding equipment, arc welding equipment, nickel based welding powder F103 (C ≤ 0.15 8.0 < Cr < 12 2.5 < Si < 4.5 1.0 < B < 1.7 Fe ≤ 8 other Ni), cast iron electrode: Z308, z248

1.1 spray welding

according to the spray welding process, it is enough to set the tension range of the guide rail surface at 300 Newton; Preheat to above 150 ℃, after the preliminary welding powder spraying, heat the spraying surface to above 900 ℃ -1200 ℃, so that the welding powder melts and forms a flat surface. Due to the long preheating and heating time, the heating area of the workpiece is larger and the thermal stress is larger, which is easier to produce cracks than arc welding, and the linear shrinkage has a greater tendency to produce cracks. As the crack tendency is affected by factors such as spray welding time and spray layer thickness, the size of defects is limited to a certain extent, and the defects of welding repair need to be cleaned up. Due to the high proportion of Fe in the powder, the color of the spray layer formed is more similar to that of the base metal than that of arc welding. However, due to a certain amount of Ni, it cannot be closer to the color of the base metal, and machining can be carried out after welding repair

1.2 arc welding

cast iron electrode z248 is used for welding repair. There are two kinds of welding repair processes. The first kind: preheat to 550 ℃ -650 ℃ before welding, and keep the temperature for hours after welding repair; The second kind: the workpiece is not preheated before welding, and it is kept warm for hours after welding. Both methods are prone to cracks and hard spots, and it is not easy to carry out machining after welding repair. Welding rods are cheap. The nickel base cast iron electrode Z308 electrode is used for welding repair. The welding layer and the welding layer should be stopped and cooled to below 60 ℃. There are few pores and cracks in the welding repair area. The machinability is good, the bonding strength is high, and there is no falling off. Due to the influence of oil absorption and electrode blowing force after the machining of machine tool guide rail, undercut is easy to occur and "welding repair trace" is formed. The color of the welding repair area is very different from the base metal, and the electrode is expensive

1.3 result analysis

the traditional spray welding and arc welding processes are easy to produce cracks after welding repair, the workpiece is easy to be heated and deformed, and it is easy to have secondary pores. The common characteristics of the weld repair are the large difference between the metal color and the base metal, which is also the fundamental reason why the traditional welding repair process can not completely solve the defect repair of machine tool guide rail. Technora para aramid fiber

2. Repair effect and analysis of casting defect repair adhesive:

now there are many kinds of fillers used in enterprises, and the quality is also far from each other. This paper is only based on the experimental results of fillers that can meet the requirements of casting quality standards (AK and AKB models of orco brand casting defect repair adhesive are selected)

2.1. Surface treatment before sizing:

there are several pores and sand holes of ¢ 2 - ¢ 10mm on the surfaces of two (100x100 X50) unprocessed HT250 test blocks; There are two processed HT250 test blocks (100x100x50), with a surface roughness of 3.2 and several pores of ¢ 2 - ¢ 10mm. First, remove sand and oxide skin with electric tools or shovel tools, and then clean the surface with acetone

2.2. Glue mixing and coating:

for the defect filling of the unmachined surface, the non machined surface defect repair glue (AK) should be selected. Take 2 parts of a glue and 1 part of B glue respectively according to the weight or volume ratio of 2:1, mix them well (stir in one direction) and scrape the glue with a special glue mixing knife or hard rubber. Pay attention to the elimination of air in the hole, and the mixed glue should be used up within minutes; To fill the defects on the processing surface, select the processing surface defect repair glue (AKB) and mix the colloids A and B evenly according to the proportion specified in the manual. During the gluing process, pay attention to the flatness of the surface and the protection of the datum plane

2.3. Effect detection and analysis:

12 hours later, the unprocessed test block was shot blasted, and there was no falling off, and the surface state and color were close to the reference plane; After 12 hours, the processed test block was turned and milled again, and no peeling was found, and the color was close to the processing surface of more than 1000 tons of high-pressure polyethylene recycled particles per year

2.4. Conclusion:

the tested rubber can meet the requirements of shot blasting, sand blasting, turning, milling, plutonium and grinding without falling off, and can meet the repair requirements of performance; The color is close to the substrate surface, which can not meet the strict color difference requirements. The colloid is non-metallic and needs to be recognized by customers. However, the repair cost is low, the use is convenient, and the efficiency is high. It has gradually become a wide range of repair methods

3. Welding repair effect and analysis of casting defect repair machine:

3.1 production and analysis of test bar

prepare a piece Φ 30mm × 200mm test bar, material HT250, surface roughness Ra0.8, drill on the surface Φ The hole 5mm deep and mm deep shall be welded and repaired with akzqb-2000c casting defect repair machine. The repair material shall be 0.8 × 0.25mm thick metal sheet and 0.4mm thick HT250 iron filings. There is no obvious boundary at the weld repair, the transition area is small, there is no carbide precipitation near the weld repair point, the metal structure at the weld repair is dense, and there is no crack. Near the weld repair point and the whole test bar at room temperature, the metal color of the weld repair point is the same as that of the base metal, the weld repair point with the repair material of 0.8 # is denser than that of the base metal, and the weld repair point with the same material has the same density as the base metal. Metallographic structure analysis: no crack, no change in peripheral metallographic structure, no internal stress, no hardening and softening

3.2 welding repair effect and analysis of guide rail defects

material: HT200; Heat treatment state: 2 pieces of surface quenching, hardness 50-56hrc; 2 pieces without surface quenching, hardness Hb, defect Φ 1- Φ 6mm; There are several mm deep defects. Akzqb-2000c casting defect repair machine, with 0.8 # Φ 0.8mm wire and HT200 iron filings

welding repair effect and analysis: according to the macro inspection, the metal color of the welding repair point is the same as that of the base metal, without undercut and burn marks, and the vicinity of the welding repair point and the whole workpiece are at room temperature. The 30 times magnifying glass and hardness tester are used to detect the welding repair on site. The results show that there is no obvious dividing line, the metal of the welding repair point is dense, free of cracks and sand holes, the 0.8 × repair material welding repair point is hard, and the heat insulation degree Hb of the test piece can be expanded by ethanol or liquid nitrogen, the hardness Hb of the HT200 repair material welding repair point, and the hardness HB near the welding repair point of the UN quenched guide rail surface. The hardness near the weld repair point of the quenched guide rail is HRC, no annealing and softening are found, and it is qualified through the flaw detection agent. It can be machined, and the metal color at the weld repair is the same as that of the base metal, meeting the quality inspection requirements of defect repair on the machined surface

4. Conclusion:

4.1 the traditional spray welding, arc welding and other processes have certain limitations on the defect repair of castings. The machinability of spray welding is good, but it is easy to produce cracks, thermal deformation, annealing and other phenomena. The color is greatly different from the parent. It is a mechanical combination, and the bonding strength is lower than that of arc welding. The repair effect of arc welding is directly related to the selection of welding rods. The machinability and non generation of cracks of Z308 are good, but the difference between the repair trace and color and the parent is difficult to eliminate, and the price is high. In the traditional welding repair process, the temperature rise before welding and the heat preservation after welding of castings also cause some inconvenience to the welding repair of large castings. Casting defect repair glue is easy to use, low price and high efficiency, but it is non-metallic, and the color cannot be completely consistent, which is not suitable for castings with strict color requirements

4.2 use the casting defect repair machine to repair the defects of castings. During the repair process, the castings do not rise in temperature, do not deform, do not produce cracks, and the metal at the weld repair point is dense, do not produce hard spots, and do not have annealing phenomena. Any mechanical processing can be carried out. The selection of filler materials is not restricted by materials. Through the selection of filler materials of different materials, the unity of the performance and color of the weld repair point and the matrix can be achieved. The filler material and the matrix are metallurgically combined, with high bonding strength, and will not fall off. The welding repair quality meets the quality inspection standard of casting products. It is a new technology worthy of wide promotion. However, the welding repair scope of the casting defect repair machine is Φ 1.5- Φ In the process of repeated melting and accumulation of 1.2mm weld repair points, the repair efficiency is the only factor that restricts its wide application in the process of large-area defect repair. For large defects, the combined application of traditional welding repair process and casting defect repair machine is recommended. (end)

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