With the rapid development of the shipbuilding industry, the requirements for the stability and safety of marine centrifugal pumps are getting higher and higher. In order to improve the working environment of the crew, ensure the physical and mental health of the crew, reduce the vibration and noise generated by the pump operation, and ensure The stability of pump equipment operation has become the development direction of marine pumps in the future. In this paper, the vibration and noise reduction analysis of a marine centrifugal pump on a certain type of ocean-going cargo ship is carried out and verified by experiments.
Introduction to the modified object Marine centrifugal pumps are mainly used to suck in seawater from outboard, pressurized and then send it to various water-using equipment or water-use places through the system pipeline, and discharge it outboard after completing the predetermined function. The original design parameter is a flow rate of 85dB. The pump is a single-shell pump. The pump and the motor are rigidly connected, and the motor bears the axial thrust. Its structure is as shown.
Analysis of the reasons for vibration and noise of centrifugal pumps Marine centrifugal pumps are a kind of rotating fluid machinery, which will produce vibration and noise due to both mechanical and fluid dynamics during operation. Part of the vibration and noise comes from the inside of the pump casing, which is essentially directly related to the hydraulic pulsation of the fluid in the pump, and the other part is directly related to the pump, that is, related to the manufacture, installation and use of the pump itself. Specifically, it is divided into the following aspects: the internal structure of vibration and noise caused by poor design is unreasonable, resulting in uneven distribution of the internal flow field of the pump, and the presence of pressure pulsation in a local area will cause the pump to produce vibration and noise; Incomplete consideration of the rigidity of the foundation plate and errors in the calculation of the critical speed of the pump will also cause the pump to produce vibration and noise.
Vibration and noise caused by poor manufacturing quality If the concentricity of the rotating parts of the marine centrifugal pump is poor, the pump impeller is unevenly distributed, the thickness of the blade is uneven, or the thickness of the front and rear cover plates of the impeller is not distributed in local areas, etc. Occurs, it will cause the rotor to generate periodic excitation force for the entire pump set when it rotates, and force the pump body to vibrate, thereby generating noise; the spatial shape of each blade of the impeller is inconsistent, and the head generated by each blade is different when rotating, so The imbalance of the hydraulic power will increase the vibration, and the pump will also produce vibration and noise.
When the pump is installed, the base is not leveled and the reference plane is aligned, the pump shaft and the motor shaft do not meet the coaxiality requirements, the pipeline configuration is unreasonable, the pipeline produces stress and deformation, the foundation bolts are not strong enough, the vibration isolation device or component design, selection and installation Improper layout or quality problems can also cause the pump to produce vibration and noise. When the fixed frequency of the centrifugal pump coincides with the frequency of the excitation force such as some unbalanced force, resonance may occur, which makes the vibration and noise of the pump group more intense.
Improper use causes vibration during operation. The pump runs under non-recommended working conditions, and sometimes deviates too much from the design working conditions, resulting in large radial forces, which cause the pump rotor to be stressed, or the pump body is under tension or pressure. Deformation caused by excessive external force. According to past experience, when centrifugal pumps deviate from the design conditions by about 60%-70% of the small flow operation, there is a possibility of so-called "surging"; if the pump operation status is not strictly checked and external vibrations Incoming, etc. can also cause pump vibration and noise.
Improvement measures From the above points to study the measures to reduce vibration and noise, and to improve the design and production process of marine centrifugal pumps.
Design improvements change the pump and motor from rigid connection to elastic connection; change the pump casing structure, design the pump body from a single casing to a double casing, increase the strength of the pump casing and reduce the radial force; improve the processing and assembly accuracy of the pump, Such as: improve the matching accuracy between the parts, increase the balance accuracy of the pump impeller, rotor components and the motor rotor from G6.3 to G2.5; change the position and increase the number of reinforcement ribs on the pump foot plate, and install reinforcement ribs at the pump inlet The motor support is changed from welding parts to castings to increase the vibration absorption capacity; the bearings are arranged reasonably to ensure that the bearings of the pump itself can withstand the axial force after the elastic connection. The structure of the improved pump is as shown.
Some new equipment and methods are used in the process: the turning of the pump shaft is changed from ordinary horizontal turning to CNC horizontal turning; the turning of the support is changed from ordinary vertical turning to numerically controlled vertical turning. At the same time, the support is rough. , An annealing heat treatment is added between finishing processes to better eliminate the internal stress generated during the processing of steel castings and ensure the stability of processing dimensions.
In order to ensure that the inner hole size of the impeller and the shaft is increased from level 7 to level 6, the process is changed from the original turning process to the grinding process; in addition, the turning process of each arc surface on the front and rear cover of the impeller is also changed from the original turning process. Ordinary horizontal lathe machining is changed to CNC horizontal lathe machining.
In order to ensure that the dynamic balance accuracy of impeller and rotor components is improved from the original G6. 3 to G2.5, a high-precision dynamic balancing machine is used for dynamic balancing, and the minimum achievable residual unbalance (Umar) is 0.1gmm/kg, and compiled The corresponding work instructions control the quality of this key process. In order to better ensure that the rotor unbalance is controlled, special tooling is designed, namely the impeller static balance and dynamic balance mandrel, to control the impeller unbalance first, and then perform the dynamic balance test of the entire rotor component.
For the hydraulic test of the pump body, pump cover and other pressure-bearing parts, a hydraulic test operation guide is compiled to control the quality of the process. After the parts are roughed, a hydraulic test is performed first. If small defects such as sweating and leakage are found, repair them by welding, infiltration, etc., and perform a hydraulic test after the parts are finished.
In view of the improvement of pump assembly accuracy requirements, a reasonable assembly process is formulated, especially to control the beating of the impeller port ring position on the pump body. After the pump body is installed, a meter cannot be used to check the impeller port ring position bounce, and a special pressure is designed. The cover is positioned instead of the stop of the pump body. In addition, during the assembly process, the following procedures are also checked: the beating of the outer circle of the motor shaft to the end face of the motor flange, the beating of the outer circle of the pump shaft to the support stop, the gap between the bearing gland and the end face of the bearing, to Ensure that the coaxiality of the pump and the motor meets the requirements.
The improvement of the casting process improves the casting process of the two key parts that affect the hydraulic performance of the pump: the pump body and the impeller.
After the pump body is changed from a single shell to a double shell, the pump body is divided into two parts by the water dividing rib. Because the water dividing rib is of a twisted shape, and the volume of the whole pump body is small, this undoubtedly increases the difficulty of casting. Therefore, the core bone tooling is designed, the runner sand cores are separately made, and the runner sand cores are connected by the core bone to form a whole, so as to ensure the integrity and compliance of the runner. The mold design adopts a metal mold combined with a plastic stripping structure to ensure the uniform wall thickness of the casting; the casting adopts the whole body cold iron, resin sand molding, and core making, which is equivalent to metal mold casting, which improves the compactness of the casting body structure and meets the pressure requirements.
Change the wooden mold to the plastic mold to minimize the impact of the deformation on the pump performance due to the mold casting process; when making the mold, strictly follow the size and technical requirements of the drawing to make the model of each section of the blade and the runner, and use the model for inspection Dimensions of each section. Due to the many unstable factors in the casting process, the casted impeller has a certain deviation from the design. The three-dimensional coordinate instrument is used to measure and compare the casted impeller and the designed impeller to guide the modification of the impeller casting and mold. At the same time, the casting impeller adopts the principle of selecting the best, and select the impeller that meets the design requirements as much as possible and is very consistent with the design for the assembly of the pump, so as to eliminate the influence of the manufacturing error of the impeller on the performance of the pump.
Improvement effect: Flow field simulation and bottom plate modal analysis were performed on the improved pump design, and vibration and noise tests were performed on the improved pump.
The total pressure distribution in the front pump is improved. It can be seen that after the pump body adopts a double shell, the non-axisymmetric distribution of the flow field is greatly reduced, thereby reducing the radial pressure and reducing the vibration of the entire pump.
