Marine centrifugal pump should be how to reduce vibration noise?

With the rapid development of the shipbuilding industry, the stability and safety requirements for the operation of marine centrifugal pumps have become higher and higher. In order to improve the crew's working environment, ensure the physical and mental health of the crew, and reduce the vibration and noise generated by the pump operation, ensure that The stability of the pump equipment operation has become the direction of future development of marine pumps. This article analyzes the vibration reduction and noise reduction of a marine centrifugal pump on an ocean-going freighter and verifies it through experiments.

Marine centrifugal pump should be how to reduce vibration noise?

2. Introduction to Retrofit Marine centrifugal pumps are mainly used to inhale seawater from the outboard and are sent to various water equipments or water offices through the system piping after pressurization. They are discharged outboard after completing the predetermined function. The original design parameter is the flow rate Q矣85dB. The pump is a single-shell pump. The pump and the motor are rigidly connected and the motor takes axial thrust. Its structure is as shown.

3 Causes of Vibration and Noise in Centrifugal Pumps Analysis Marine centrifugal pumps are rotary fluid machines that generate vibration and noise due to mechanical and fluid dynamics. The vibration and noise are partly from the inside of the pump housing and are directly related to the hydraulic pulsation of the fluid in the pump. The other part is directly related to the pump, that is, related to the manufacture, installation and use of the pump itself. It is specifically divided into the following aspects: Vibration noise due to poor design The internal structure design is unreasonable, resulting in uneven distribution of the pump's internal flow field. Pressure pulsation in the local area will cause the pump to generate vibration and noise; if the design is rigid to the pump, Basic board stiffness and other considerations are not comprehensive, there are errors in the calculation of the critical speed of the pump, etc., which will also cause the pump to produce vibration and noise.

Vibration noise caused by low manufacturing quality If the marine centrifugal pump is manufactured with poor concentricity of the rotating parts, uneven distribution of the pump impeller mass, uneven blade thickness, or partial thickness distribution of the impeller front and rear cover plate, etc. Appears, will make the rotor in the rotation of the entire pump group to generate periodic excitation force, so that the pump body produces forced vibration, resulting in noise; impeller blade space shape is inconsistent, each blade in the rotation generated by the different head, The resulting hydraulic imbalance leads to increased vibration and can also cause the pump to generate vibration and noise.

When the pump is installed, the base is not leveled and the reference plane, the pump shaft and the motor shaft do not meet the requirements of the coaxiality, the piping configuration is unreasonable, the pipeline has stress deformation, the foundation bolt is not firm enough, and the vibration isolation device or component design, selection and installation Inappropriate layout or quality problems can also cause vibration and noise in the pump. When the fixed frequency of the centrifugal pump coincides with the excitation force frequency such as some unbalanced force, there is a possibility that resonance will occur and the vibration and noise of the pump group will become more severe.

Inappropriate use caused by vibration caused by the operation of the pump in non-recommended conditions, and sometimes deviated from the design conditions are too large, generate a large radial force, the pump rotor force offset, or the pump body under tension or pressure According to past experience, when the centrifugal pump operates at a small flow rate that deviates from about 60% to 70% of the design condition, there is a possibility of so-called “surge”; if the pump operation status is not strict, external vibration is detected. Incoming, etc. can also cause pump vibration noise.

4 improvement measures from the above points to study the measures to reduce vibration and noise, and marine centrifugal pump design and production process to be improved.

4.1 Design Improvement Change the pump and motor from rigid connection to elastic connection; change the structure of the pump casing, design the pump body from single casing to double casing, increase the strength of the pump casing, reduce the radial force; improve the accuracy of pump assembly , Such as: to improve the fitting accuracy between parts, the pump impeller, rotor parts and motor rotor balance accuracy level from G6.3 to G2.5; change the pump foot plate rib position and increase the number of pump inlet settings to strengthen Ribs; Motor bearings changed from weldments to castings to increase the ability to absorb vibration; reasonably arrange the bearings to ensure that the bearings of the pump itself bear axial forces after the elastic coupling. The structure of the pump after the improvement is as shown.

Some new equipment and process methods are adopted in the process: The turning of the pump shaft is changed from the original ordinary horizontal car processing to the numerical control horizontal car processing; the turning of the bearing is changed from the ordinary vertical turning to the digital vertical turning, and at the same time, the bearing is rough. An annealing heat treatment is added between the finishing and finishing to better eliminate the internal stress generated during the process of casting and ensure the stability of the processing dimensions.

In order to ensure that the size of the inner hole matching the impeller and the shaft is improved from level 7 to level 6, the process is changed from the original turning to grinding; in addition, the turning of the arc surfaces on the front and rear covers of the impeller is also performed by the original. Ordinary sleeper processing is changed to CNC sleeper processing.

In order to ensure that the impeller and rotor components dynamic balance accuracy from the original G6. 3 to G2.5 level, using high-precision balancing machine for dynamic balance, the minimum up to the amount of residual unbalance (Umar) is 0.1gmm/kg, and prepared Corresponding job instructions to control the quality of this critical process. In order to better ensure that the unbalanced amount of the rotor is controlled, special tooling is designed, that is, the impeller static balance and dynamic balance mandrel are used to control the unbalanced amount of the impeller first, and then the dynamic balance test of the entire rotor assembly is performed.

For hydrostatic tests on pressure parts such as pump bodies and pump covers, hydraulic pressure test work instructions were prepared to control the process quality. After the parts are rough-processed, a hydrostatic test shall be conducted first. If any small defects such as sweating or leakage are found, repair shall be carried out by means of repair welding and infiltration, and a hydrostatic test shall be conducted after the parts are finished.

For the improvement of the assembly precision of the pump, a reasonable assembly process is developed, in particular to control the impeller ring position on the pump body, because the pump body can not be used after the pump is installed to check the ring position of the impeller, and the special pressure is designed. The cover replaces the positioning of the pump body. In addition, during the assembly process, the following processes are also inspected: the runout of the outer periphery of the motor shaft to the end face of the motor flange, the runout of the outer periphery of the pump shaft to the support seat, and the clearance between the bearing gland and the bearing end surface. Ensure that the coaxiality of the pump and the motor meets the requirements.

4.3 Casting Process Improvements Two key components affecting the hydraulic performance of the pump: The casting process of the pump body and the impeller is improved.

After the pump body is changed from a single shell to a double shell, the pump body is divided into two parts by water diversion ribs. Since the water diversion ribs are twisted and the entire pump body is small, this undoubtedly increases the difficulty of casting. Therefore, the core tooling is designed and the runner cores are separately formed. The cores are linked to form the flow runner cores as a whole, thereby ensuring the integrity and conformity of the runners. The mold design adopts the metal mold combined with the plastic debiliary structure to ensure the uniform wall thickness of the casting; the casting adopts the whole body cold iron, the resin sand modeling and the core making, which is equivalent to the metal mold casting, improves the denseness of the casting body structure, and satisfies the pressure requirements.

Change the wood mold to plastic mold to minimize the influence of the deformation during the mold casting process on the performance of the pump; in the mold making, strictly follow the size and technical requirements of the pattern to make the model of each section of the blade and runner, and use the model for inspection. Each section size. Because there are many unstable factors in the casting process, there is a certain deviation between the cast impeller and the design. The measured impeller is compared with the designed impeller with a three-dimensional coordinate instrument to guide the impeller casting and mold modification. At the same time, the principle of selecting the best from the cast impeller is selected, and the impeller that meets the design requirements and fits the design as much as possible is selected 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.

5 Improvement Effect The flow field simulation and floor modal analysis of the pump with improved design were performed, and the improved pump was tested for vibration and noise.

To improve the distribution of the total pressure in the front pump, 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.

Table 1 shows the former tenth-order frequency of the original welding floor and the improved casting base. In the entire pump system, the pump's rotation axis frequency is about 50 Hz, and the pump's leaf frequency is about 300 Hz. Through comparison, the casting base is known. Compared with welding bases, they have higher natural frequency of each order, and the first, second, and third-order natural frequencies that affect them are much larger than the leaf frequency of the pump and are less prone to resonance. Therefore, the use of a cast base is more conducive to vibration reduction and noise reduction.

Table 1 Improved Front and Back Floor Natural Frequency vs. Hz Natural Frequency Welding Base Casting Pedestal - Ranked Second Order Third Order Fourth Order Fifth Order Sixth Order Seventh Order Eighth Order Nineth Order Tenth Order Table 2 shows the improved pump's vibration when operating under rated conditions. The test results of the noise index can be seen from the table: All measured values ​​are lower than the required values, and the improvement effect is obvious.

Table 2 Comparison of Measured and Requested Values ​​for Vibration Noise after Improvement Table Foot Vibration Vibration Airframe Vibration Air Noise Level Index (dB) Index (dB) Required Value Measured Value 6 Conclusion Starting from the factors that produce vibration noise from the centrifugal pump, The marine centrifugal pump has been designed and manufactured to improve the flow field simulation and floor modal analysis of the improved pump, and the vibration noise of the pump is tested. The final test results show that the improved pump vibration and noise indicators meet the requirements. . It can be seen that the pump and the motor are changed from a rigid connection to an elastic connection, and a modified design of the pump body is used to make the flow in the pump smoother, the accuracy of the pump processing and assembly is improved, the position of the pump foot plate ribs is increased, and the quantity is increased. Ribs are used to change the bearing of the motor from the welding part to the casting. The bearings are arranged rationally to ensure that the bearing of the pump itself bears the axial force after the elastic coupling. These improvements can effectively reduce the vibration and noise of the marine centrifugal pump.