The common problems with SMC cylinders during use can be divided into several sections
The force situation of SMC cylinder during operation is very complex. In addition to static loads such as the pressure difference between the gas inside and outside the cylinder and the weight of various components installed inside it, it also has to bear the reaction force of steam flowing out of the stationary blade on the stationary part, as well as the force of various connecting pipelines in cold and hot states on the cylinder. Under the interaction of these forces, the cylinder is prone to plastic deformation and leakage.
The load on SMC cylinders increases or decreases too quickly, especially during rapid start-up, shutdown, and changes in operating conditions, with large temperature fluctuations, incorrect cylinder warming methods, and premature opening of insulation layers during shutdown maintenance, resulting in significant thermal stress and deformation in the cylinder and flanges.
SMC cylinders generate stress during mechanical processing or after welding repair, but the cylinders are not tempered to eliminate it, resulting in significant residual stress and deformation during operation.
During the installation or maintenance of SMC cylinders, due to the maintenance process and techniques, the expansion gaps of the inner cylinder, cylinder partition, partition sleeve, and gland sleeve are not suitable, or the expansion gaps of the hanging ear pressure plate are not suitable. After operation, a huge expansion force is generated, causing deformation of the cylinder.
The quality of the cylinder sealant used in SMC cylinders is poor, there are too many impurities, or the model is incorrect; If there are hard impurities particles in the cylinder sealant, it will make it difficult for the sealing surface to bond tightly.
The tightening force of SMC cylinder bolts is insufficient or the material of the bolts is unqualified. The tightness of the cylinder joint surface is mainly achieved by the tightening force of the bolts. The thermal stress and high temperature generated during the start stop or load increase/decrease of the unit can cause stress relaxation of the bolts. If the stress is insufficient, the pre tightening force of the bolts will gradually decrease. If the bolt material of the cylinder is not good, the bolt will be stretched under the action of thermal stress and cylinder expansion force during long-term operation, resulting in plastic deformation or fracture, insufficient tightening force, and leakage of the cylinder.
The sequence of tightening SMC cylinder bolts is incorrect. Generally, when tightening cylinder bolts, they are tightened from the middle to both sides simultaneously, that is, from the place with the largest vertical arc or the place with the largest deformation under force. This will transfer the gap at the place with the largest deformation to the free ends of the front and rear of the cylinder, and the gap gradually disappears after the maximum deformation. If it is tight from both sides to the middle, the gap will concentrate in the middle, forming a bow shaped gap on the cylinder joint surface, causing steam leakage.
SMC cylinders are generally caused by eccentric installation of the piston rod, insufficient supply of lubricating oil, wear or damage of the sealing ring and sealing ring, impurities in the cylinder, and scratches on the piston rod. Therefore, when there is internal or external leakage in the cylinder, the piston rod should be readjusted to ensure its coaxiality with the cylinder barrel; Regularly check the operation of the oil mist device to ensure good lubrication of the actuator components; When the sealing ring and sealing ring are worn or damaged, they must be replaced in a timely manner; If there are impurities in the cylinder, they should be dealt with promptly; When there are scars on the piston rod, it should be replaced with a new one.
The insufficient output force and unstable movement of SMC cylinders are generally caused by the piston or piston rod being stuck, poor lubrication, insufficient air supply, or condensation water and impurities in the cylinder. For this, the piston rod should be adjusted; Check if the oil mist device is working properly; Is the gas supply pipeline blocked. When there is condensed water and impurities in the cylinder, it should be done promptly.
The poor buffering effect of SMC cylinders is generally caused by wear of the buffering sealing ring or damage to the adjusting screw. At this point, the sealing ring and adjusting screw should be replaced.
Damage to the piston rod and cylinder head of a cylinder is usually caused by eccentric installation of the piston rod or ineffective buffering mechanism. For this, the position of the piston rod should be adjusted; Replace the buffer seal ring or adjust the screw.
Solution
1. For the joint surface of SMC cylinder with significant deformation or severe steam leakage, the method of grinding and scraping the joint surface is adopted
If the deformation of the upper cylinder joint surface is within 0.05mm, use the upper cylinder joint surface as the reference surface, apply red lead or imprint blue paper on the lower cylinder joint surface, and scrape the lower cylinder according to the trace. If the deformation of the joint surface of the upper cylinder is large, apply red lead to the upper cylinder, use a large ruler to scratch the mark, and flatten the upper cylinder. Alternatively, mechanical processing can be used to level the joint surface of the upper cylinder, and then the joint surface of the lower cylinder can be scraped off 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 forward and backward, and scrape according to the condition of the lower cylinder joint surface. This method is suitable for high-pressure cylinders with strong structural rigidity.
⑵ It is a bolt that tightly fits the joint surface. Based on the inspection of the tightness of the joint surface with a feeler gauge, the numerical value and pressure marks are measured, and the joint surface is scraped. This method can eliminate the influence of cylinder sag on the clearance.
2. Use appropriate cylinder sealing materials
Due to the lack of unified standards and specifications for steam turbine cylinder sealants, the production materials and formulas are also different, resulting in uneven output; When selecting a sealing agent for a steam turbine cylinder, it is necessary to choose one that is both internally produced and has a regular output, in order to ensure the tightness of the cylinder after maintenance and treatment.
Method of local welding repair
Due to steam erosion or corrosion on the joint surface of SMC cylinder, appropriate welding rods should be used to level the groove marks. The marks should be ground out with a flat plate or ruler, and the weld bead and joint surface should be scraped in the same plane. When there is significant deformation or severe steam leakage on the joint surface of the cylinder, one or two 10-20mm wide sealing strips should be welded to the joint surface of the lower cylinder to eliminate the gap. Then, use a ruler or buckle the upper cylinder to measure and apply red lead to scrape until the gap is eliminated. The process of this operation is also very simple. Preheat the cylinder to 150 ℃ before welding, and then perform segmented back welding or skip welding at room temperature. Use austenitic welding rods such as A407 and A412, and cover them with asbestos cloth for insulation and slow cooling after welding. After cooling to room temperature, polish and scrape.
Coating or spraying of SMC cylinder joint surface
When there is a large area of steam leakage on the SMC cylinder joint surface with a gap of about 0.50mm, in order to reduce the workload of grinding and scraping, the coating process can be used. Using a cylinder as the anode and a coating tool as the cathode, repeatedly apply electrolytic solution on the joint surface of the cylinder. The thickness of the coating should be determined according to the size of the gap between the joint surfaces of the cylinder, and the type of coating should be determined according to the material of the cylinder and the scraping process. Spraying is a method of using a high-temperature flame spray gun to heat and melt metal powder or spray it onto the surface of a treated cylinder after reaching a plastic state, forming a coating with the required properties. Its characteristics are simple equipment, easy operation, and firm coating. After spraying, the cylinder temperature is only 70 ℃ -80 ℃, which will not cause deformation of the cylinder. Moreover, a heat-resistant, wear-resistant, and corrosion-resistant coating can be obtained. It should be noted that the cylinder surface should be polished, degreased, and roughened before coating and spraying. After coating and spraying, the coating should be scraped and the joint surface should be tight.