**Analysis and Solutions for the High Noise of Roots Blowers**
**1、 Classification of noise sources**
|Noise type | Frequency characteristics | Main generation location | Proportion|
|----------------|------------------|---------------------|-------|
|* * Aerodynamic noise * * | Medium high frequency (500-4000Hz) | Inlet and outlet airflow pulsation | 45|
|* * Mechanical noise * * | Low frequency (<500Hz) | Gear/bearing/rotor | 35|
|* * Structural noise * * | Broadband | Shell vibration radiation | 20|
**2、 Diagnostic process for causes of excessive noise**
```mermaid
graph TD
A [Excessive Noise] -->B {Measurement Spectrum}
B -->| Peak value below 500Hz | C [Mechanical troubleshooting]
B -->| Peak above 1kHz | D [Pneumatic noise control]
C -->E [Check gear meshing]
C -->F [Bearing state detection]
D -->G [Muffler Evaluation]
D -->H [Pipeline Vibration Analysis]
```
**3、 Special analysis of mechanical noise**
1. * * Gear noise (25-35dB contribution)**
-* * Root cause * *:
-Gear accuracy<level 7 (ISO 1328 standard)
-Side clearance>0.12mm
-Poor lubrication (oil film thickness<1 μ m)
-* * Solution * *:
-Replace the 6th level precision gear (tooth surface roughness Ra0.8)
-Adjust the side clearance to 0.08-0.10mm
-Switching to ISO VG320 synthetic gear oil
2. * * Bearing noise (15-25dB contribution)**
-* * Fault characteristics * *:
-6206 bearing vibration value>4.5mm/s (ISO 10816)
-Temperature>75 ℃
-* * Handling measures * *:
-Replace SKF/C&U brand bearings
-Install bearing isolation sleeve
**4、 Pneumatic noise control technology**
1. * * Comparison of muffler selection**
|Type | Noise Reduction (dB) | Pressure Loss (kPa) | Applicable Scenarios|
|--------------|-----------|----------|---------------------|
|Resistance muffler | 15-20 | 1-2 | Low frequency noise dominant|
|Resistive muffler | 20-25 | 2-3 | Medium high frequency noise (commonly used)|
|Composite muffler | 25-30 | 3-5 | Broadband noise control|
2. Pipeline noise reduction design**
-Flow rate control:<15m/s (main pipeline),<8m/s (branch pipeline)
-Adopting:
-Rubber flexible joint (vibration isolation)
-30 ° angled tee (reduces eddy currents)
-Wrap the pipeline with 2mm thick damping material
**5、 Structural noise control plan**
1. Vibration isolation measures**
-Install shock absorbers with a frequency ratio greater than 3 (W-shaped rubber shock pads are recommended)
-Basic quality ≥ 5 times the quality of the fan
-The pipeline adopts elastic hangers (spacing ≤ 2m)
2. Shell reinforcement**
-Add 6mm thick reinforcement bars (to reduce resonance risk)
-Internal 3mm polymer damping plate (ST-2 type)
**6、 On site rectification case**
**55kW Roots blower noise reduction project for a certain sewage treatment plant**
-* * Original noise value * *: 98dB (A) @ 1m
-* * Rectification measures * *:
1. Replace the 7th gear with 6th gear (-5dB)
2. Install impedance composite muffler (-18dB)
3. Install shock-absorbing foundation (-7dB)
4. Pipeline wrapped with sound-absorbing cotton (-3dB)
-* * Final noise * *: 65dB (A) (meets GB 12348 Class II standard)
**7、 Maintain preventive measures**
1. * * Daily Inspection Checklist**
-Weekly: Check belt tension (deflection ≤ 10mm)
-Monthly: Iron spectrum analysis of gear oil (wear particles<100 μ m)
-Quarterly: Measurement of impeller clearance (plug gauge inspection)
2. * * Predictive maintenance technology**
-Online vibration monitoring (set alarm threshold of 4.5mm/s)
-Infrared thermal imaging (warning when bearing temperature difference>15 ℃)
**8、 Application of New Noise Reduction Technology**
1. * * Active noise control**
-Adopting phase cancellation technology (effectively reducing 100-800Hz noise)
-The noise reduction can reach 10-15dB
-Cost: Approximately 20% of the fan price
2. * * Magnetic levitation bearing renovation**
-Mechanical friction noise
-The overall noise level has been reduced to below 70dB
-Investment payback period: 2-3 years (through energy-saving compensation)
**9、 Noise prevention during the selection stage**
1. * * Low noise design selection**
-Priority selection:
-Three blade rotor (6-8dB lower than two blade noise)
-Spiral gear (3-5 dB lower than spur gear noise)
-Water cooled models (4-6dB lower in noise than air-cooled models)
2. * * Noise commitment value verification**
-Request the manufacturer to provide:
-ISO 3744 Test Report
-Spectrum diagram of sound pressure level at 1m
-Octave band analysis data
**Note: When the noise level is greater than 90dB, a soundproof cover (NR ≤ 85dB standard) must be equipped, while ensuring ventilation and heat dissipation requirements. It is recommended to prioritize mechanical troubleshooting before gradually implementing pneumatic and structural noise reduction measures.
