How to judge whether the impeller of magnetic suspension blower needs to be replaced?

To judge whether the impeller of the magnetic suspension blower needs to be replaced, it is necessary to comprehensively evaluate it from three dimensions: wear degree, performance impact and potential safety hazard, and make a decision based on the test data and operation status. The following are specific criteria, detection methods and typical replacement scenarios:

First, the quantitative judgment standard based on physical wear

1. Impeller surface damage degree

Repairable scope:

Local shallow scratches (depth < ＜0.5mm) and slight corrosion pits (diameter < 2 mm and density < 5/cm) on the blade surface can be repaired by grinding or repair welding;

The abrasion at the inlet edge of the impeller is less than 20% of the original thickness (for example, the original thickness is 3mm and the residual after abrasion is ≥2.4mm).

The scene must be changed:

Penetrating crack (length > ＞10mm), notch (area > 1 cm) or fracture of the blade;

Wear causes the blade thickness to remain less than 50% of the original thickness, or the hub hole diameter to wear out of tolerance (fit tolerance > ＞0.05mm).

2. Dynamic balance performance attenuation

Detection method:

Using dynamic balancing machine, the impeller was tested for high-speed rotation (rotating speed ≥ 110% of rated speed), and the residual unbalance was measured.

Replacement threshold:

The residual unbalance exceeds 2 times of the design allowable value (e.g., the design value is ≤ 5 GMM/kg and the measured value is > 10 mm/kg);

After dynamic balance correction, it still cannot meet the standard, or the amount of repair welding exceeds 5% of the blade weight during correction (which may cause stress concentration).

3. Geometric dimension deviation

Key parameter detection:

Blade outlet angle deviation > 2 (affecting airflow direction);

Roundness error of impeller outer diameter > ＞0.1mm (resulting in uneven clearance with volute);

Runout of hub end face > ＞0.05mm (axial vibration occurs during operation).

Handling principle:

If the deviation can be corrected by mechanical processing (such as turning and grinding) without affecting the strength, it can be repaired; Otherwise it needs to be replaced.

Second, anomaly characterization based on operational performance

1. The efficiency dropped significantly.

Judgment basis:

Under the same working conditions (the inlet and outlet pressure and temperature are the same), the air volume decreases by > 10% or the energy consumption increases by > 15%;

The pressure head-flow curve of the fan deviates from the design value by more than 5% (compared by the performance test bench).

Typical reasons:

Impeller wear leads to distortion of blade profile, and airflow produces vortex or leakage in the channel (for example, the gap between blade and volute is expanded from 0.5mm to 1.5mm, and the leakage is increased by 3 times).

2. Abnormal vibration and noise

Monitoring indicators:

The vibration speed of the bearing seat is > 5.0 mm/s (normally ≤2.5mm/s), and the frequency spectrum analysis shows that the frequency amplitude of 1X speed increases sharply (for example, from 2.0mm/s to 4.5 mm/s);

Operating noise > 90dB (a) (original design ≤85dB), accompanied by obvious metal impact sound or airflow howling.

Risk warning:

Uneven impeller wear leads to dynamic imbalance, which may further lead to bearing overload, seal failure and even rotor seizure.

3. Abnormal temperature rise and current fluctuation

Correlation phenomenon:

The motor current fluctuates more than 10% of the rated value, and there is no electrical fault;

The temperature of the impeller is higher than the normal working condition by more than 10℃ (excluding the cooling system problem).

Cause analysis:

Friction between impeller and volute generates heat, or wear causes loose cooperation between impeller and shaft, resulting in additional mechanical loss.

Third, the forced replacement scenario under special working conditions

1. Structural damage caused by medium corrosion/scouring

Typical scenario:

After transporting acidic gases (such as SO and Cl), large-area electrochemical corrosion (pit depth > 1 mm, coverage area > 30%) appeared on the impeller surface.

Inhaled dust concentration > 50mg/m (not up to standard), and blade wear after 10,000 hours of operation > ＞1mm (such as aluminum alloy impeller).

Material upgrade suggestion:

Replace the impeller with titanium alloy, Hastelloy or ceramic coating (such as ALO) to improve the wear resistance.

2. Safety assessment after major failure

Faults to be replaced:

The impeller partially falls off during operation (even if the rest seems to be intact);

Due to surge or mechanical collision, the impeller and volute are severely rubbed, and blue annealing marks appear on the surface (material strength decreases).

Testing requirements:

In this case, it is necessary to carry out comprehensive nondestructive testing (such as ultrasonic flaw detection+penetrant testing) on the impeller, and any potential cracks need to be replaced.

Fourth, the cycle and strategy of preventive replacement

1. Plan according to the running time

Normal working conditions (clean air):

It is recommended to replace the aluminum impeller every 3-5 years (about 40,000-60,000 hours), and the titanium impeller can be extended to 5-8 years;

Bad working conditions (dust and corrosion):

The replacement cycle is shortened to 2-3 years, or replaced in advance according to the wear monitoring data (such as the wear amount detected every 10,000 hours).

2. Collaborative replacement with other components

Matching replacement scenario:

When replacing the spindle (e.g. journal wear out of tolerance), replace the impeller synchronously (to avoid insufficient matching accuracy);

When the wear of the inner wall of the volute exceeds the limit (the remaining wall thickness is less than 80% of the original thickness), the impeller should be replaced at the same time to match the gap.

V. Change decision-making process and case reference

1. Standardized judgment process

Vibration > 5 mm/s or efficiency decrease > 10%

Crack/thickness < 50%/unbalance > 2 times | Yes

Repairable damage | No

Performance recovery

Performance not recovered.

Find abnormality

Vibration/efficiency detection

Disassembly impeller detection

Surface damage/dynamic balance?

Replace impeller

Grinding/Repair Welding/Dynamic Balance Correction

Installed test

Continue to use

2. Practical case: impeller replacement in sewage treatment plant

BACKGROUND: The magnetic suspension blower of a sewage plant runs for 25,000 hours, conveying air containing sludge particles (dust concentration is about 80 mg/m).

Test data:

The wear thickness of the inlet edge of the impeller reaches 1.2mm (the original thickness is 2.5mm, and the remaining 52%);

The residual unbalance of dynamic balance is 18 GMM/kg (design value ≤ 5 GMM/kg);

The air volume decreased by 12%, and the vibration value was 4.8 mm/s.

Decision: Because the wear amount is close to the critical value and the dynamic balance can't be corrected, replace it with a new impeller with WC-Co coating on the surface. After operation, the air volume will be restored and the vibration will be reduced to 2.2 mm/s.

summary

The replacement decision of the impeller of magnetic suspension blower should be comprehensively judged by combining the quantitative data of physical damage (such as wear thickness and crack size), the attenuation degree of operational performance (air volume, vibration and energy consumption) and the particularity of working conditions (corrosion and dust). For minor repairable wear (such as shallow scratches and local corrosion), the service life can be extended by surface treatment or dynamic balance correction; However, in case of structural damage (crack, fracture), out-of-tolerance of key dimensions or significant performance degradation, it must be replaced. At the same time, it is suggested to use wear-resistant materials or coatings to prevent wear in severe working conditions, establish a wear trend file through regular inspection (every 10,000 hours), and plan the replacement cycle in advance to avoid sudden failures.