I. There are four methods to check the crack and fracture of diesel generator crankshaft.
Crankshaft cracks often occur at the end of connecting rod journal or at the joint of crankshaft arm and crankshaft journal. The inspection method is as follows.
1. Magnetic flaw detection method.
Use a magnetic flaw detector for inspection. First magnetize the crankshaft with a magnetic flaw detector, and then spread iron powder on the parts to be inspected. At the same time, gently tap the crankshaft with a small hammer. Observe carefully at this time. If there are cracks, clear crack lines will be found in the middle of iron powder accumulation.
2. Hammering method.
First remove the oil stains on the surface of the crankshaft. Then soak the whole crankshaft with kerosene or diesel oil, take it out and wipe it clean. Then support both ends of the crankshaft on a wooden frame, and gently tap each crankshaft arm with a small hammer. If there is "clang" (continuous sharp metal sound), it means there is no crack. If "wave, wave" (discontinuous, short dumb metal sound) is emitted, it means there is crack. Then, use your eyes or a magnifying glass to carefully observe the area near where cracks are likely to occur. If you find oil stains emerging or forming a black line, that is where the cracks are located.
3. Powder method.
After cleaning and drying the crankshaft with kerosene or diesel oil, evenly coat a layer of talcum powder on the surface of the crankshaft, and then gently tap the crankshaft arm with a small hammer. If the crankshaft has cracks, the oil stains will seep out from the cracks, making the talcum powder on the surface of the crankshaft become yellow brown.
4. Lime milk method.
Wash the crankshaft and immerse it in hot oil (engine oil) for about 2h, let the oil enter the crack, take it out and wipe it dry, spray "lime lotion" on the crankshaft with a spray gun to make it dry. E lime lotion is a mixture of clean chalk and alcohol, with a ratio of (1:10)~(1:12). Or use gas welding flame to heat the spray layer on the crankshaft to 70~80 ℃. At this time, the chalk absorbs the oil stored in the crack, and this part of the chalk becomes dark, showing the shape of the crack.
II. Repair of cracks and fractures in the crankshaft of diesel generators.
If the crankshaft is cracked or broken, it can be repaired by "welding repair". The key points of the process are as follows.
1. Preparation before welding repair.
First, boil and clean the crankshaft in alkaline water to remove oil stains, and then use a chisel to chisel a U-shaped groove along the crack surface. The groove depth should be free of cracks. The bottom of the groove is circular arc, and the width of the groove shall be determined according to the depth, length and shape of the crack. Then correct it so that the bending runout of the crankshaft does not exceed the specified range. Finally, install the crankshaft on the special welding frame or on the cylinder block, and place iron lining between the crankshaft and the welding frame or cylinder block. Then fasten the bearing cover with bolts to avoid bending and deformation of the crankshaft during welding. If the broken crankshaft is welded, it is necessary to find out the central seam according to the original crack of the crankshaft, spot weld several points on both sides of the broken seam with electric welding, and then slot on both sides of the crack without electric welding before welding.
2. Repair welding.
Before welding repair, first heat the repair area with a gas welding flame to 350~450 ℃, and then conduct electric welding with a low-carbon steel electrode with a diameter of 3~4mm. During welding, the method of opposite welding (moving the electrode perpendicular to the crack) shall be adopted, and the welding slag shall be removed immediately after each layer is welded, and then the next layer shall be welded.
3. Finishing after welding.
After welding, the repaired part shall be chiseled flat, and the oil passage shall be drilled through to check whether there are cracks at the welding part and whether the crankshaft is bent or deformed. Then use a grinder to grind the weld to make the surface smooth and smooth, and heat treatment can be carried out on the working surface of the crankshaft to increase the anti-wear performance of the working surface.
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