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The company OU "Vibromera" is engaged in the development and manufacture of various devices for technical diagnostics and dynamic balancing of industrial equipment.

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Subject to the rules of consumer transportation, storage and use in the event of failure of the device manufacturer guarantees free appliance repair at his place of manufacture within twelve months from the date of its receipt to the consumer.
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Estonia, Narva linn, Kreenholmi 39v
Phone :+372 56630018

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Some practical approaches to problem solving to reduce fan noise and vibration in their manufacture and use.

1.Puti improve vibro-acoustic characteristics of the fans at the stage of their production.

     Vibration and noise, along with their energy parameters, are some of the most important performance fans, which draws the attention of the consumer in choosing them.
    As is known, the main sources of forced oscillations fans, causing their noise and vibration are:

• Power imbalances associated with manufacturing and assembly errors of parts of the fan, and appearing on the rotor speed - FO;
• aerodinamcheskie forces associated with the design of the impeller and fan housing, and manifested in the blade frequency - FO * Zl (where Zl- number of impeller blades) and its harmonics;
• mechanical strength of interaction associated with defects in rolling bearings that appear at frequencies - FO; FO * (1 - d / D * COS β) / 2; ZT * FO * (1 - d / D * COS β) / 2; ZT * FO * (1 + d / D * COS β) / 2; FO * D ​​/ d * [1 - (d / D) ² * COS ² β] / 2 (where D, d, β - the geometric dimensions of the bearing, and ZT - the number of rolling elements);
• electromagnetic forces associated with the design and quality of manufacturing of electric motors, and are manifested at a frequency - FO * Zm (where Zm- number of magnets in the motor) and its harmonics.

     Thus, as can be seen from the foregoing, the fan at a constant speed there is a certain finite set of discrete values ​​of the forced vibration frequency.
     During production Manufactured by improving the design and accuracy of manufacture and assembly of parts quality fans seeks to minimize the impact of these forces, thereby ensuring acceptable level of vibration and noise of the fans.
     However, in practice, said the problem can be technically successful and cost-effectively solved only if knowledge Manufacturer dynamic characteristics fan design (primarily natural frequencies of its parts and components).
    The need for knowledge of these characteristics is the fact that in the case of coincidence of forced and natural frequencies of oscillations in the resonant vibrations of the fan. However, even under the influence of a relatively small excitation force, vibration and / or noise of the fan can reach quite high values.
    In this case, the Manufacturer before a dilemma - either by increasing the accuracy of the manufacture of parts of the fan to reduce to the minimum value of the exciting force, or (if possible) by introducing structural changes in the product to carry the detuning from resonance.
     Typically, the second way is more preferable because it requires less manufacturing costs with the release of a batch production. However, manufacturers, without objective data on the natural vibration frequencies of fans, often forced to tighten the requirements for the performance of individual process steps (eg when balancing the fan impeller), which leads to increased production costs.
    Especially important is the dynamic testing for fans with variable speed, as in this case, the above frequency forced oscillations vary over a wide range, proportional band changes the fan speed FO. This significantly increases the probability of their coincidence with the natural frequencies of the components and parts of the fan.
    Practice Test individual types of ducted fans with variable speed, which were carried out by OU "Vibromera" on one of the fan, the factories of St. Petersburg, showed that the vibration spectra of these fans are areas of convergence of natural and forced oscillation frequencies at which resonances are observed body parts fan Accompanying-Esja marked increase in noise and vibration. Moreover, depending on the design features of the fans, as well as the quality of their construction and assembly of these resonant oscillation sources were all the above types of excitatory forces (including unbalance forces, electromagnetic forces, aerodynamic forces and interactions).
     It should be noted that the development of more powerful fans novyh- danger displays resonances when operated will increase.
     On the one hand this is due to the fact that an increase in fan power increase strength, exciting forced oscillations. On the other hand with an increase in the dimensions of the fan will decrease the natural frequency of its units, which in turn increases the probability of coincidence frequencies of natural and forced vibrations and challenges to the detuning from resonance.
    In view of the above it seems appropriate to the stage of development and manufacturing of prototype models of powerful fans as well as fans with variable speed, to conduct their dynamic testing, which should improve the quality of manufacture of fans and will reduce the cost of their finishing.
    The experience gained by our experts in solving these problems shows that the study of dynamic characteristics of fans in general should include the following activities:
▪ calculation of the theoretical spectrum of potential components of forced oscillations of the fan;
▪ measurement and narrowband spectral analysis of fan noise and vibration of its main units in the operating speed range;
▪ experimental determination of the natural vibration frequencies of the basic units and parts of the fan;
▪ analysis of the results and the identification of the main sources of forced oscillations and resonance of the fan;
▪ development (if necessary) in light of the results of a set of measures aimed at reducing noise and vibration of the fan, including:
      - The quality of manufacturing units and parts that reduce excitatory
         power source fluctuations;
       - Recommendations for changing the stiffness of individual structural elements
         fan for the purpose of detuning from resonance.
       To carry out these studies can be used modern equipment vibroacoustic, widely represented in the present market of instrumentation products, such as domestic vibration spectrum analyzers "Quartz" and "Topaz", manufactured by "Diameh" SD-12, manufactured by "VAST" and several others.
      When selecting the specified equipment must be borne in mind that it should be capable of measuring and narrowband spectral analysis of noise and vibration mechanisms, as well as to determine the natural frequencies of their structural elements.

2.Podderzhanie vibration characteristics of fans in operation.

      As the experience of exploitation and control of vibration characteristics of the fans at the stage of their operation, the main reasons leading to the exit of these mechanisms of action are associated with high dynamic loads acting on the bearing assemblies and lead to premature damage and destruction.
     The values ​​of these dynamic loads are primarily dependent on the level of operational imbalance of the fan impeller, as well as the quality of the implementation of the alignment of the merged via the rotor sleeve (for large fans and smoke exhausters) and on the technical condition of the bearing fans that may deteriorate in service.
     In [1] provides a formula for calculating the permissible level of residual unbalance analysis which shows that the increase in the actual level of imbalance mechanism twice in relation to the maximum allowable, shorten the life of the bearings 8 times. Similar data are available for dynamic loads associated with misalignment of rotors mechanisms and defects of bearings.
     In practice, the technical condition of the fan is usually assessed in terms of vibration measured on its bearing assemblies. Studies of domestic and foreign experts [1] have shown that long-term operation is possible with machines bearing vibration load levels to speed not exceeding 0.1 g, that depending on the rotor speed of the machine corresponds to approximately 2 - 6 mm / sec rms vibration velocity.
      These requirements are formalized in the international standard GOST ISO 10816-1-97 [2], which establishes tolerances for different types of vibration machines in accordance with their capacity.
      Compliance with these requirements avoids fatigue failure of the bearing elements associated primarily with high alternating loads. In addition, reducing to an acceptable value of the vibration level of the fan reduces the probability of failure of the oil film separating the moving parts of the bearing.
     This in turn leads to a reduction in the intensity of abrasive wear in direct contact, which also has a positive effect on the increase in the lifetime of the fan bearings. In view of the foregoing it is evident the need for periodic technical inspection of the instrument fans. Experience shows that, for these purposes have enough service operation at least two devices, including a device for controlling bearings (e.g., bearing condition indicator 77D11) and a device for measuring vibration and balancing fan rotors (e.g., device "Balkom-1", manufactured by OU "Vibromera"). With their help it is possible to timely identify and reduce excessive vibration fans by performing work on balancing impellers, replacement of defective bearings, etc. This allows for a significant increase in the service life of the fans and eliminate situations related to their emergency outage, resulting in significantly reduced costs of operation and maintenance of the fans. The foregoing is confirmed by a number of companies in the milling industry, which is already one year after the introduction of instruments for measuring vibration and balancing the fan impeller need for bearings used in the repair of fans, decreased approximately twice. In addition, these companies have been excluded almost entirely accidental damage to the rotors and stators of electric motors, which previously took place in the destruction of the bearings.

3.Literatura:

• 1. The vibrations in the art. Directory. In 6 volumes. Volume 6, pp. 39,40. M .: Mechanical Engineering, 1981
• 2. GOST ISO 10816-1-97 "Evaluation of machine vibration by measurements on non-rotating parts." Part 1: General requirements.

21 декабря 2013

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