1、 STD-AGHA 97FTMZ-ENGL L997 m Ob87575 DD050b3 3Tb m , 97FrM2 Determining Sound Power Levels of Enclosed Gear Drives Using the Sound Intensity Method by: Craig Burriss, Amarillo Gear Company COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services- STD-AGMA 97FT
2、M2-ENGL 1997 - Ob87575 00050b4 232 D Determining Sound Power Levels of Enclosed Gear Drives Using the Sound Intensity Method Craig Burriss, Amarillo Gear Company The statements and opinions contained herein are those of the author and should not be construed as an official action or opinion of the A
3、merican Gear Manufacturers Association. Abstract This paper will examine use of the sound intensity measurements to calculate sound power levels of enclosed gear drives under full load. important characteristics of the test environment will be discussed. Acoustic intensity concepts and theory will b
4、e presented. Equipment requirements and acoustic requirements of the sound field for collecting accurate data will be discussed. Actual sound intensity data with a discussion of measurement quality indicators are included. Finally, a case study will be presented that illustrates how this data was us
5、ed to validate a design improvement. Copyright Q 1997 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Virginia, 22314 November, 1997 ISBN: 1-55589-696-0 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services STDaAGMA 77FTMZ-EN
6、GL 1997 Ob87575 00050b5 179 Determining Sound Power Levels of Enclosed Gear Drives Using the Sound Intensity Method Craig Burriss, Engineer Amarillo Gear Company space. Introduction Sound power measurements are important for making direct comparisons between different enclosed gear boxes because sou
7、nd power is independent of the measurement environment. Sound power levels can be used to determine resulting sound pressure levels at a distance from the source or can be used to select appropriate acoustical treatments. The ability to supply customers with accurate sound power levels is becoming m
8、ore important. First, some international trade regulations require conformance to noise standards. Secondly, a quieter enclosed gear drive has the perception of being higher quality. Consumers demand quieter products and quieter industrial gear drives make for better working environments. The final
9、reason for the increased popularity of sound power measurements is the reduced cost of obtaining the data by using the sound intensity method. What is sound intensity? The sound intensity in a specified direction at a point is the average rate of sound energy transmitted in the specified direction t
10、hrough a unit area normal to this direction at the point considered (1). More simply, sound intensity is a vector. that describes the net amount and direction of acoustic power at a given point in I = W/A Where I is intensity, W is power, and A is area Since sound intensity is a vector quantity, it
11、can be used to calculate the net power emanating from a surface. Sound power is computed by measuring the normal spacial-averaged intensity over an area that encloses the gear drive and multiplying it by the measurement surface area enclosing the source. How is sound intensity measured? Sound intens
12、ity can be calculated from measurements of pressure and particle velocity due to the following relationship: I = W/A = F*V/A = P*V Where F is force, P is pressure, and V is velocity. The pressure term is easy to measure using a single microphone, so the challenge in measuring sound intensity is to a
13、ccurately measure the particle velocity. From Newtons Second Law: Where pois the density of air, the probe, the analyzer, and the post processor. The probe holds the two phase matched microphones separated by a fixed spacer, and may have a remote control to start and stop data collection. Probes com
14、e in two styles: side-by-side and end-to-end. Side-by-side probes usually have higher pressure measurement error due to diffraction and shadow effects. In this configuration, the microphone spacing should be 2 to 3 microphone diameters to minimize reflections. For measurements meeting ANSI S12.12-19
15、92, microphones should meet the requirements for use in a Type 1 precision sound level meter. For higher accuracy measurements of low frequency sound levels, use a better grade of microphone with improved phase mismatch. For frequency ranges between SOH2 and 6300 HZ, 1/2 inch diameter microphones ar
16、e normally used. For measurements up to 10 KHZ, smaller 1/4 inch diameter microphones are used (4). The analyzer can be a real time type using digital filters or any FFT analyzer with two channels. The frequency response of the system should be flat within the frequency range of interest within the
17、limits given in the applicable sound intensity standard. Some analyzers can calculate sound power directly, while others processors can also be used for source ranking, intensity mapping, contour plots, or other computations. need a post-processor. Post ProCaaura for mcasurng sod intensity: 1. Make
18、sure calibration of the instrument is current. 2. Perform a field calibration check after each equipment Set-up. The normal procedure is to take an intensity measurement of the source, then rotate the probe 180 and position it with the same acoustical center. The two measurements should have opposit
19、e signs and equal magnitudes within 1.5 dB. 3. Prepare the source by placing it in a way that represents normal usage and operate it in the condition to be tested. 4. Select the appropriate spacer for the frequency range of interest and configure the analyzer. 5. Determine a measurement surface that
20、 totally encloses the source. Distance from the gear drive surface should be at least 200 mm (5). The measurement quality indicators will indicate if changes should be made in the location of measurement surfaces. 6. Take initial measurements using surface scanning technique (IS0 9614-2 or ANSI S12.
21、12-1992) or by measuring at discrete points (IS0 9614-1 or ANSI S12.12-1992). 7. Calculate sound power and quality indicators. 8. Verify adequacy of measurement by evaluating sound field conditions. These may vary from standard to standard, but the commonly used criteria are: a) The pressure intensi
22、ty index (Lpi) at each octave band is compared to the residual intensity found using the calibrator. The measured pressure-intensity index must be lower by at least 7 dB for an engineering grade measurement and 5 dB for a survey grade measurement. This quality indicator assesses the adequacy of the
23、measuring equipment. b) The negative partial power indicator (F+/-) detects error due to extraneous sound sources on nearby reflecting surfaces. This quality indicator of the measurement environment should be less than 3 dB at each octave band (5). c) The partial power repeatability check assesses t
24、he source and/or environment variability when surface scanning is used. This quality indicator compares sound power levels computed from two scans of the same surface. When taking discrete sound intensity measurements, a similar measure called “field non-conformity indicator is used. This field indi
25、cator describes the adequacy of the chosen measurement array. 4 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSTD-AGMA 97FTM2-ENGL 1997 m 0b87575 0005b9 814 W 9. If any of the measurement quality indicators fail, then apply a corrective action as gui
26、ded by the standard being used. Then, repeat the measurement. Sample Sound Intensity Data The test specimen was a two stage enclosed gear drive with one spiral bevel and one helical gear set. The total ratio was 11:l and the input speed was 1800 RPM. The gear drive was driven with an electric motor
27、and an air-actuated disc brake applied the 75 HP load. The dimensions of the gear drive and measuring surfaces are shown in Figure 2. Two of the surfaces were divided in half due to protruding shafts. Each surface was scanned twice in orthogonal directions. The equipment used was a HP 3569A sound in
28、tensity analyzer with a 12m spacer separating two k“ class I Em however, under full load (300Hp 1760RPM) the gears had a sound power level of 104 to 108 dBA depending on positioning of the gear set in the enclosed drive. Vibration levels taken during the load test were well within acceptable limits.
29、 Summary changes were made in order to lengthen the contact pattern on the concave side and the gear set was developed to avoid flank contact on the gear and face contact on the pinion. A 6.00 inch radius cutter was used for both gear sets because it is a standard cutter set. The actual full load co
30、ntact pattern for each case is shown in Figure 3. The summary changes resulted in a 5 dBA drop in sound power due to the improvement in full load contact. One of the lessons learned was that a square heel bearing resulted in a longer contact pattern. The sound intensity method allowed the collection
31、 of accurate sound power data, in-situ with both driving and driven equipment in operation. By eliminating the influence of background noise, the actual improvement in sound level was measured. ORIGINAL CONTACT CONTACT PATiERN AFIER PATTERN SUMMARY CHANGE GEAR (CONVEX SIDE) GEAR (CONVEX SIDE) PINION
32、 (CONCAVE SIDE) PINION (CONCAVE SIDE) Figure 3 -1 Load Contact Patterns Conclusion The benefits of sound intensity data are demonstrated by the case study and the actual data presented. Quality indicators are easily calculated to provide a measure of the data quality. If some data are unacceptable b
33、ased on quality indicator tolerances, the standards offer corrective actions to improve the measurement. In addition, the sound power radiating from each surface is obtained using sound intensity scanning. In this example, the sound power was calculated within 1.5 dB of actual with a certainty of 95
34、%. This level of error is possible using sound pressure data only if the sound field is well controlled and background noise is well below the source noise level. References 1. “Engineering Method for the Determination of Sound Power Levels of Noise Sources Using Sound Intensity”, ANSI Standard S12.
35、12-1992. 1986. Application”, Navcon Engineering Network, 1996 4. “Sound Power Meas-nts”, Hewlett-Packard Co., 1992 5. “Acoustics - Detexmination of Sound Power Levels of Noise Sources Using Sod Intensity Part 2 : Measurament by Scanning”, ISO/DIS 9614-2 2. “Sound Intensity”, Briiel & Kjr, 3. “Acoustic Intensity Theory h 7 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services
