The cracks in the cylinder block and the cylinder head of diesel generator set are often related to their structures and have certain regularity. Generally speaking, there are three main aspects.
I design and manufacturing deficiencies
1. The speed and power of some improved engine are significantly higher than that of the original engine. At high speed, the inertia force and stress of the engine are also increased, and cracks are easy to appear.
2. The structure of cylinder block is complex and the wall thickness is uneven. In some weak parts, the stiffness is low and cracks are easy to appear.
3. The stress concentration will be produced at the transition of different parts of the wall thickness between the processed and the unworked parts. When these stresses are superimposed with the residual stresses in casting, cracks will also easily occur.
II Improper use
1. In the cold winter, no antifreeze is used or no cooling water is released according to the specified time (cooling water is cooled to normal temperature) after shutdown, which results in the freezing of the cooling water in the water jacket, or in the cold winter, the condensation of hot water with high temperature and the cracking of the cooling water.
2. When the diesel engine is working at high temperature, the sudden addition of cold water causes the thermal stress of the cylinder block and the cylinder head to be too large, resulting in cracks in the cylinder block and the cylinder head.
3. Carelessness in disassembly or handling causes cracks in cylinder block or cylinder head due to severe vibration or collision. During the operation of diesel engine, the material is subjected to excessive thermal stress. For example, long hours of overload work lead to increased stress in the cylinder block, too thick scale in the water jacket, reduced cooling water passing area, and poor heat transfer performance of the water scale, which reduces the heat dissipation performance of the engine, especially between cylinders. When the waterway between the valve seat and the intake and exhaust hole is blocked, the heat dissipation will be seriously affected, the local working temperature will be raised and the thermal stress will be too large, resulting in cracks.
4. In the absence of sufficient heating, the load increases rapidly, which results in a sharp change in the heat and cold of the cylinder block and the cylinder head, and cracks occur inhomogeneously.
III Repair quality is not high
In the course of maintenance, the technical requirements have not been strictly carried out, such as the failure of the cylinder head nut to tighten the torque in the prescribed order, the uneven tightening force, the use of the cylinder head nut which does not conform to the requirements, and so on. According to the material of valve seat and machining precision, no proper input interference is selected to make it crack.
Cylinder head nuts should be accurately counted with torsion wrench, press first middle and then on both sides, 2-3 times to tighten. For the engine with reloaded cylinder head, after the first heating and cooling to normal temperature, the engine should be twisted again according to the above requirements to achieve the specified torque.
The order of disassembly of cylinder head nuts is opposite to the above order, in the order of first two sides and then middle, split into two or three times of symmetrical loosening.
Repair method for cracks in cylinder Block and cylinder head of Diesel generating set
The repair of cylinder block and cylinder head crack of diesel generator set should be determined according to the degree of rupture, the site of damage, the condition of repair and the condition of equipment. There are five kinds of repair methods in common use.
Epoxy resin adhesive
Epoxy resin adhesive has the advantages of strong adhesion, small shrinkage, fatigue resistance, simple technology, easy operation and low cost. The main drawback is that it is not resistant to high temperature and impact. In the next repair, it will come off after the hot alkali water is boiled and washed, so it needs to be bonded again. So the cylinder block and cylinder head can be repaired by this method except combustion chamber and valve seat.
This method is suitable for some plane parts with small force, small strength requirement and short crack range (generally less than 50 mm). The quality of repair is higher, but when it is more difficult to work, the specific filling process is as follows:
1. Drill a hole at each end of the crack to prevent the crack from extending further.
2. Drilling along the crack, tapping the thread, the diameter of the hole depends on the diameter of the thread, enduring that the hole and hole overlap 1/3 aperture.
3. In the tapping thread, screw in the copper rod with pre-hinged thread, and cur off the copper rod after twisting, so that the cutting place is 1-1.5 mm higher than the crack surface.
4. To make the fill tight, use a hammer to gently tap the cut screw, file it, and solder it if necessary to prevent leakage.
Patch plate seal
In the cylinder block, where the cylinder head has little force, if the crack is longer or there is a hole, the patch plate is used around the damaged area. The specific process is as follows:
1. Drilling at the end
2. With a copper plate of 3-5mm thick or an iron plate of 1.5mm-2mm thickness, a patch plate with a contour similar to that of a break is cut and is larger than 1520mm in width.
3. In the patch every 1015 mm drill diameter 4mm 6 mm hole, about 10 mm from the edge of the patch. According to the position of mending plate drilling, make drilling mark on cylinder block, then drill the hole about 10 millimeters deep to break out the thread.
4. Insert an asbestos liner with white paint between the cylinder block and the patch board, then fasten the patch plate to the cylinder block with a flat head bolt.
The cracks between the cylinder block and the cylinder head are repaired by welding method if they occur in the parts where the force is high or the temperature is higher and where the above methods are not easy to operate. The specific process is as follows:
1. Drill a 3mm hole at each end of the crack.
2. Chisel the crack into a V-shaped groove of 60 ~ 90 degrees.
3. In direct current welding and acetylene welding, the cylinder block or cylinder head should be flattened, the welding zone should be preheated slowly to about 500 ℃, the welding area should be heated to 500,550 ℃ for 1 hour, and then cooled to normal temperature in not less than 16 hours.
When using plugging agent to repair cracks, the location of leakage is found first, and the length and width of cracks or aperture of sand holes are determined. If the crack width is greater than 0.3 mm, it is best not to use this method.
The cylinder block or cylinder head should be replaced if the crack is in the key position, such as the cylinder hole edge, the main bearing seat and so on. Any repaired cylinder block and head of generator set should be tested for leakage.