Question
1.The cylinder is made of casting, and the cylinder must undergo aging treatment after leaving the factory, so that the internal stress generated by the cylinder during the casting process is completely eliminated. If the aging time is short, the machined cylinder will be deformed in the subsequent operation.
2.In addition to the static load such as the pressure difference of the gas inside and outside the cylinder and the weight of the various parts installed in the cylinder, it also bears the reaction force on the static part when the steam flows out of the stator, and the various Under the interaction of these forces, the cylinder is prone to plastic deformation and leakage.
3.The load of the cylinder increases or decreases too quickly, especially when the temperature changes rapidly during rapid start-up, shutdown and working condition changes, the method of warming up the cylinder is incorrect, and the insulation layer is opened too early during shutdown and maintenance, etc. Large thermal stress and thermal deformation.
4.Stress is generated in the cylinder during machining or after repair welding, but the cylinder is not tempered to eliminate it, resulting in large residual stress in the cylinder and permanent deformation during operation.
5.In the process of installation or maintenance, due to the maintenance process and maintenance technology, the expansion gap of the inner cylinder, the cylinder diaphragm, the diaphragm sleeve and the steam seal sleeve is not suitable, or the expansion gap of the hanging lug pressure plate is not suitable. A huge expansion force is generated to deform the cylinder.
6.The quality of the cylinder sealant used is not good, there are too many impurities or the wrong type; if there are hard foreign particles in the cylinder sealant, it will be difficult for the sealing surface to be tightly combined.
7.The tightening force of the cylinder bolts is insufficient or the material of the bolts is not qualified. The tightness of the cylinder joint surface is mainly achieved by the tightening force of the bolts. The thermal stress and high temperature generated when the unit starts and stops or increases or decreases the load will cause the stress relaxation of the bolts. If the stress is insufficient, the preloading force of the bolts will gradually decrease. If the bolt material of the cylinder is not good, the bolt will be elongated under the action of thermal stress and cylinder expansion force during long-term operation, plastic deformation or fracture will occur, the tightening force will be insufficient, and the cylinder will leak.
8.The cylinder bolts are tightened in the incorrect order. Generally, the cylinder bolts are tightened from the middle to both sides at the same time, that is, from the place where the vertical arc is the largest or the place where the force and deformation are the largest, so that the gap at the place with the largest deformation will be adjusted to the freedom of the front and rear of the cylinder. End transfer, and finally the gap gradually disappears. If it is tight from both sides to the middle, the gap will be concentrated in the middle, and the joint surface of the cylinder will form a bow-shaped gap, causing steam leakage.
Reason
1. The internal and external leakage of the cylinder is generally caused by the eccentric installation of the piston rod, the insufficient supply of lubricating oil, the wear or damage of the sealing ring and the sealing ring, the impurities in the cylinder and the scar on the piston rod. Therefore, when internal and external leakage occurs in the cylinder, the center of the piston rod should be re-adjusted to ensure the coaxiality of the piston rod and the cylinder; it is necessary to check whether the lubricator works reliably to ensure that the actuators are well lubricated; When the rings and sealing rings are worn or damaged, they must be replaced in time; if there are impurities in the cylinder, they should be removed in time; if there are scars on the piston rod, they should be replaced.
2. Insufficient output force of the cylinder and unstable action are generally caused by the stuck piston or piston rod, poor lubrication, insufficient air supply, or condensed water and impurities in the cylinder. In this regard, the center of the piston rod should be adjusted; check whether the lubricator works reliably; whether the air supply line is blocked. When there is condensed water and impurities in the cylinder, it should be removed in time.
3. The buffering effect of the cylinder is not good, which is generally caused by the wear of the buffer sealing ring or the damage of the adjusting screw. At this time, the sealing ring and adjusting screw should be replaced.
4. The damage to the piston rod and cylinder head of the cylinder is generally caused by the eccentric installation of the piston rod or the ineffectiveness of the buffer mechanism. In this regard, the center position of the piston rod should be adjusted; the buffer sealing ring or adjusting screw should be replaced.
solution
1. For the joint surface with large deformation of the cylinder or serious steam leakage, the method of grinding and scraping the joint surface is adopted.
If the deformation of the joint surface of the upper cylinder is within the range of 0.05mm, the joint surface of the upper cylinder shall be used as the reference surface, and the joint surface of the lower cylinder shall be painted with red dan or embossed blue paper, and the lower cylinder shall be ground and scraped according to the traces. If the deformation of the joint surface of the upper cylinder is large, apply red elixir to the upper cylinder, use a large flat ruler to grind out traces, and grind the upper cylinder to level. Or take the method of machining to level the joint surface of the upper cylinder, and then grind and scrape the joint surface of the lower cylinder based on the upper cylinder. There are generally two methods for grinding and scraping the joint surface of the cylinder:
⑴ It is a bolt that does not tighten the joint surface. Use a jack to slightly push the upper cylinder to move back and forth, and grind and scrape according to the coloring of the red dan on the joint surface of the lower cylinder. This method is suitable for high-pressure cylinders with strong structural rigidity.
(2) It is the bolt that tightens the joint surface. Check the tightness of the joint surface according to the feeler gauge, measure the value and the traces pressed out, and repair and scrape the joint surface. This method can eliminate the influence of the vertical arc of the cylinder on the gap.
2. Use proper cylinder sealing material
Because there is no unified national standard and industry standard for steam turbine cylinder sealant, the raw materials and formulations are also different, and the product quality is uneven; Guaranteed regular manufacturer to ensure the tightness of the cylinder after overhaul.
3. The method of local repair welding
Since the joint surface of the cylinder is scoured by steam or corroded to form groove marks, select appropriate electrodes to level the groove marks, use a flat plate or a ruler to grind out the marks, and scrape the weld bead and the joint surface in the same plane. When the deformation of the joint surface of the cylinder is large or the steam leakage is serious, repair and weld one or two 10-20mm wide sealing tapes on the joint surface of the lower cylinder to eliminate the gap, and then measure with a flat ruler or buckle the upper cylinder, and apply red dan to grind it. , until the gap is eliminated. The process of this operation is also very simple, preheat the cylinder to 150 ℃ before welding, and then perform segmental de-soldering or jump-soldering at room temperature. Use austenitic electrodes, such as A407 and A412, and cover with asbestos cloth to keep warm and cool after welding. After cooling to room temperature, polish and scrape.
4. Coating or spraying of cylinder joint surface
When there is a large area of steam leakage on the joint surface of the cylinder and the gap is about 0.50mm, in order to reduce the workload of grinding and scraping, the coating process can be used. Use the cylinder as the anode and the applicator as the cathode, and repeatedly brush the electrolytic solution on the joint surface of the cylinder. The thickness of the coating depends on the size of the gap between the joint surfaces of the cylinder. Process depends. Spraying is to use a special high-temperature flame spray gun to heat the metal powder to melt or reach a plastic state and spray it on the surface of the treated cylinder to form a coating method with the required properties. Its characteristics are simple equipment, easy operation, firm coating, and the temperature of the cylinder after spraying is only 70℃-80℃, which will not cause deformation of the cylinder, and can obtain heat-resistant, wear-resistant and corrosion-resistant coatings. It should be noted that the surface of the cylinder should be polished, degreasing and roughened before coating and spraying, and the coating should be ground and scraped after coating and spraying to ensure the tightness of the joint surface.
5. The method of padding the joint surface
If the local gap leakage of the joint surface is not very large, the hardness of the 80-100 mesh copper mesh can be reduced by heat treatment, then cut into an appropriate shape, laid on the leakage of the joint surface, and then equipped with a cylinder sealant. If the gap of the joint surface is large and the leakage is serious, a groove with a width of 50mm and a depth of 5mm can be opened on the upper and lower joint surfaces, and a toothed pad of IGr18Ni9Ti is embedded in the middle. It can be adjusted with stainless steel washers of the same shape.
6. Methods of controlling bolt stress
If the deformation of the joint surface of the cylinder is small and uniform, new bolts can be replaced at the gaps, or the pre-tightening force of the bolts can be appropriately increased. Tighten from the middle to both sides at the same time, that is, tighten the bolts from the place with the largest vertical arc or the place with the largest stress and deformation. In theory, the pre-tightening force of the control bolt can be calculated by the formula d/L≤A, but since the data and measurement methods of this calculation are still under study, they have not been promoted, and they are mostly within the allowable maximum stress of the bolt according to experience.
7. Polymer material methods adopted in the new era
With the further development of technology, polymer composite materials have gradually achieved successful application in cylinder maintenance. Compared with traditional methods, polymer composite materials have excellent temperature resistance, good pressure resistance, and better sealing performance, and have good plasticity. They will not be cured when heated, and the sealing film will not be In addition, it is easy to remove, and the used sealing surface can be easily wiped off with absolute ethanol or acetone without adhering to the sealing surface; due to its excellent performance, it is gradually subjected to more and more More and more cylinder enterprises are favored.
