Which parts of magnetic suspension blower are prone to wear and need maintenance?

The magnetic suspension blower relies on electromagnetic force to suspend the rotor to realize non-contact operation. Theoretically, the risk of wear is low. However, due to working conditions, maintenance and other factors, some components may still wear or fail due to abnormal conditions. The following are the parts that are easy to wear or need to pay attention to and the main points of maintenance:

First, the core easy to wear parts and cause analysis

1. Bearing system (magnetic bearing)

Wear form:

There is no mechanical contact during normal operation, but "rub-impact" wear may be caused if:

Electromagnetic system failure: sensor failure or power fluctuation leads to insufficient suspension force, and the rotor and bearing are in physical contact (such as axial displacement exceeding the limit);

Foreign body invasion: dust and metal chips in the air enter the bearing gap (usually < ＜0.1mm) and scratch the bearing surface;

Sudden power failure: when the standby power supply fails, the rotor falls due to inertia and rubs against the bearing wear-resistant coating (such as ceramics and tungsten carbide).

Maintenance features:

If the bearing surface is scratched and the coating is peeled off, it is necessary to judge whether it needs to be replaced by dynamic balance detection (the allowable residual unbalance is ≤ 2g mm/kg).

2. Impeller and volute

Wear reason:

The medium contains impurities: inhaled dust, fibers or liquid particles (such as water droplets condensed by humid air), which scour the impeller surface (especially the blade inlet edge) for a long time;

Surge impact: the working condition deviates from the design point, which leads to periodic oscillation of air flow and high-frequency vibration and friction between impeller and volute;

Corrosion and wear: When corrosive gas (such as SO-containing flue gas) is transported, the impeller materials (such as aluminum alloy and titanium alloy) undergo electrochemical corrosion.

Typical phenomenon:

There are pits and notches in the impeller blades, and the local wear thickness of the inner wall of the volute is more than 10% of the original wall thickness, so it is necessary to repair it by surfacing welding (using alloy covered electrode matched with the base material) or replace it with new parts.

3. Seal assembly

Wear type:

Labyrinth seal: the gap (0.2-0.5mm) between the rotor and the sealing teeth becomes larger due to vibration, and the sealing teeth are worn by particles entrained by airflow, resulting in an increase in leakage (allowable leakage rate ≤ 1% of rated flow);

Shaft end seal: the dynamic and static rings of mechanical seal are scratched due to dry friction due to insufficient cooling or dielectric crystal deposition (grinding is required when flatness deviation is greater than ＞0.005mm).

Maintenance measures:

Replace worn sealing teeth (usually made of copper alloy or engineering plastic), and check the spring force (standard value 5%) and the aging of O-ring for mechanical seal.

4. Motor rotor and stator

Abnormal wear scene:

Insufficient cooling: the cooling fan fails or the air duct is blocked, and the insulation layer between rotor silicon steel sheets is worn due to overheating of the motor, resulting in turn-to-turn short circuit;

Shaft current corrosion: when the high-frequency current generated by magnetic suspension system passes through the bearing, tiny electric corrosion pits (diameter < ＜0.1mm) are formed on the surface of the rotor journal, and the long-term accumulation leads to the deterioration of the journal roughness (Ra > 1.6 μ m).

Detection method:

The stator temperature (allowable temperature difference ≤15℃) is detected by infrared thermal imager, and the wear degree of the journal needs to be evaluated by roughness meter and roundness meter (roundness error ≤0.01mm).

Second, the auxiliary system vulnerable parts and maintenance

1. Cooling system

Wear/failure point:

Impeller of cooling water pump: When the water contains sand, the impeller blades wear, which leads to the decrease of lift (rated lift deviation > 5% needs to be replaced);

Heat exchanger pipes: scaling or corrosion leads to the thinning of the inner wall thickness (the remaining wall thickness is less than 80% of the original wall thickness, so it is necessary to clean or replace the pipes).

Maintenance points:

Regularly clean the heat exchanger with chemicals (the pH value is controlled at 6-8), and install a filter with accuracy ≤50μm at the inlet of the water pump.

2. Lubrication system (if there are spare bearings)

Wear risk:

Some magnetic levitation blowers are equipped with mechanical backup bearings, which are started when the magnetic levitation fails. If the lubricating oil is polluted (granularity > NAS8), the bearing raceway will be worn (the surface fatigue pitting area is more than ＞1cm² and needs to be replaced).

Detection index:

When the viscosity change rate of lubricating oil is more than 15% and the acid value is more than 0.5 mg KOH/g, it is necessary to replace the oil and clean the oil circuit.

Third, wear early warning and preventive maintenance strategy

1. Online monitoring parameters

Abnormal threshold in normal range of monitoring project (to be repaired) Associated wear parts

Bearing vibration speed ≤ 2.5 mm/s (10-1000 Hz) > 5.0 mm/s (lasting for 10 minutes) Bearing and impeller

Motor current fluctuation ≤ 3% Rated current > 10% and motor rotor and bearing keep rising.

Inlet and outlet pressure difference design value 5% < design value 20% (excluding blockage) Impeller and volute

Bearing temperature ≤ 80℃ (when ambient temperature is 25℃) > 95℃ (temperature rise rate > 5℃/min) Magnetic bearing and mechanical bearing.

2. Regular maintenance projects

Every 1000 hours:

Clean the air inlet filter (filtering accuracy ≤1μm) and check the impeller dynamic balance (residual unbalance increment > 10% needs to be corrected);

Every 8000 hours:

Disassemble the bearing cavity, inspect the surface of the magnetic bearing with an endoscope (slight scratches ≤0.05mm deep are allowed), and measure the axial movement of the rotor (≤ 0.03 mm is allowed);

Every 24,000 hours:

Replace all seals and carry out nondestructive testing on the impeller (such as penetrant inspection, cracks ≥0.5mm are prohibited).

Four, typical fault maintenance cases

Case 1: Impeller wear leads to efficiency decrease.

Phenomenon: After one year's operation of the magnetic suspension blower in a sewage treatment plant, the air volume decreased by 15% and the vibration value increased from 2.0mm/s to 4.5 mm/s..

Cause: No dehumidifier was installed in the air inlet, and the wet air washed the impeller with sludge particles, and the wear thickness of the blade inlet edge reached 0.8mm (the original thickness was 2mm).

Repair: The blade surface was sprayed with tungsten carbide coating (thickness 0.3mm) by HVOF, and the balance was rebalanced (the residual unbalance was reduced from 12 GMM/kg to 3 GMM/kg), and the efficiency was restored to over 95%.

Case 2: Bearing rubbing causes shutdown

Phenomenon: Restart after sudden power failure, the motor sounds abnormally and the bearing temperature rises suddenly (from 70℃ to 110℃ within 10 minutes).

Cause: The switching of standby power supply was delayed (> ＞50ms), the rotor fell into hard contact with the mechanical standby bearing, and the raceway of the inner ring of the bearing was scratched with a width of 0.2mm.

Treatment: replace the mechanical bearing (model 6205-2RS), recalibrate the clearance of magnetic bearing (axial 0.1mm, radial 0.08mm), and install UPS power supply (switching time < ＜10ms).

summary

The wear risk of magnetic suspension blower is mainly concentrated in bearing system, impeller and sealing assembly, and its core incentives include abnormal working conditions, foreign body intrusion and lack of maintenance. By on-line monitoring vibration, temperature, current and other parameters, combined with periodic disassembly detection (such as dynamic balance, nondestructive testing), the hidden danger of wear can be found in advance. For key components (such as impellers and bearings), it is suggested to use wear-resistant coatings (such as ceramics and tungsten carbide) or corrosion-resistant materials (such as 316L stainless steel) to improve the service life, and at the same time strictly control the intake air quality (filtration accuracy ≤1μm, moisture content ≤70%) to reduce the wear incentives and ensure the long-term stable operation of the equipment.