Routine Fan Maintenance

Proper maintenance and care are important guarantees for the safe and reliable operation of fans and for extending their service life. Therefore, sufficient attention must be paid when using fans.

Impeller Maintenance:

During the initial operation of the impeller and at all regular inspections, whenever possible, the impeller must be checked for defects such as cracks, wear, and dust accumulation.

Whenever possible, the impeller must be kept clean, and accumulated dust and rust should be regularly brushed off with a wire brush. As operating time increases, these deposits cannot adhere uniformly to the impeller, which causes imbalance and leads to rotor vibration.

If the impeller has been repaired, it must undergo dynamic balancing again. If conditions permit, a portable dynamic balancer can be used for on-site balancing. Before performing dynamic balancing, all locking bolts must be checked to ensure they are tight. Since the impeller has operated in an unbalanced state for some time, these bolts may have loosened.

Bearing Maintenance:

Regularly check the lubricating oil supply to the bearings. If oil leakage occurs in the housing, tighten the end cover bolts slightly. If this does not resolve the issue, it may be necessary to replace the sealing packing with new material.

Under normal use of bearing lubricating oil, it should be changed at least once every six months. For first-time use, change the oil after approximately 200 hours of operation. The second oil change should be performed within 1 to 2 months. Thereafter, check the lubricating oil weekly. If the oil has not deteriorated, the oil change interval can be extended to once every 2 to 4 months. When changing the oil, use the specified grade of lubricating oil (as specified in the general assembly drawing). Completely drain the old oil from the tank and clean it thoroughly before filling with new oil.

If fan bearings need to be replaced, observe the following precautions:

Before installing new bearings, ensure that both the bearings and the bearing housing are thoroughly clean. Heat the bearings in oil at a temperature of approximately 70 to 80 °C before mounting them on the shaft. Do not force the assembly to avoid damaging the shaft.

Maintenance of Other Auxiliary Equipment:

For maintenance of auxiliary equipment, including motors, electric actuators, instruments, and meters, please refer to their respective user manuals. These manuals are provided by the respective manufacturers and are included in the shipment by this manufacturer for the user.

Fan Casing Maintenance

Apart from regularly checking for severe wear inside the casing and intake chamber and removing heavy dust accumulation, no other special maintenance is required for these areas. Regularly check that all fastening bolts are tight. For fans with clamping bolts, compress the disc springs on the base feet to the installation height specified in the drawings.

Emergency Shutdown of Fans

Emergency Shutdown: During the trial operation of the unit, if any of the following situations occur, an immediate emergency shutdown is required. To perform an emergency shutdown, press the main motor stop button, and then carry out post-shutdown procedures.

1. 

The centrifugal fan suddenly experiences severe vibration exceeding the trip value;

2. 

There is scraping or abnormal friction noise inside the housing;

3. 

Smoke appears at any bearing or seal, or the temperature of a bearing rises rapidly to the alarm value;

4. 

Oil pressure falls below the alarm value and cannot return to normal;

5. 

The oil tank level is low, causing cavitation;

6. 

When the shaft displacement value shows a clear and continuous increase, reaching the alarm value;

Normal shutdown of the fan

1. 

Gradually open the vent valve while gradually closing the exhaust valve;

2. 

Gradually reduce the intake throttle gate to 20~25 degrees;

3. 

Press the stop button and monitor for any abnormalities during the shutdown process;

4. 

After the unit stops, oil supply can be stopped 5~10min later, or when the bearing temperature drops below 45 degrees Celsius. For units with floating ring seals, the seal oil pump must continue to supply oil until the body temperature is below 80 degrees Celsius;

After the unit shuts down, regularly rotate the rotor 180 degrees within 2~4 hours

Fan fault classification

Common faults:

In the cement industry, the working medium of fans often contains solid particles of varying sizes and shapes, such as induced draft fans in dust removal systems and blowers in pneumatic conveying. Since these fans operate in dusty airflows, the dust particles both wear down the fan and accumulate on the fan blades unevenly. This disrupts the balance of the fan rotor, causing vibration, shortening the fan's lifespan, and in severe cases, preventing normal operation. Particularly, blade wear is severe, not only disrupting flow characteristics within the fan but also easily leading to major accidents like blade fracture and runaway.

Wear in transmission components is a common issue in fans, affecting areas such as bearing seats, bearing housings, keyways, and threads on various shafts, rollers, gearboxes, motors, and pumps. Traditional repair welding and machining methods can easily cause material damage, leading to component deformation or fracture, and have significant limitations. Brush plating and spray coating followed by machining often require outsourcing, resulting in long repair cycles and high costs. Moreover, since the repair materials are still metallic, they do not fundamentally address the causes of wear (poor impact resistance and compliance of metals). Many components can only be scrapped and replaced, significantly increasing production costs and inventory spare parts, causing idle and wasted corporate resource advantages.

Vibration faults:

The fan and motor are connected via a coupling, transmitting motion and torque. Misalignment is the most common fault in fans, with 60% of fan faults related to misalignment. Fan misalignment refers to the tilt or offset between the axis lines of the fan and motor rotors and the bearing centerlines. Rotor misalignment in fans can be categorized into coupling misalignment and bearing misalignment. Once misalignment occurs in the fan rotor system, it generates a series of dynamic effects detrimental to equipment operation during rotation, causing coupling deflection, bearing wear, oil film instability, and shaft bending deformation. This not only changes the relative position of the rotor journal and bearing and the operating state of the bearing but also reduces the natural frequency of the shaft system, leading to abnormal fan vibration and premature bearing damage due to additional forces on the rotor and bearings, posing significant hazards. Laser alignment tools can conveniently and quickly resolve fan misalignment issues.

Cause analysis

Summarizing fan fault phenomena and their causes reveals patterns. Based on their causes and classifications, fan faults fall into the following categories:

Design reasons:

Improper design, poor dynamic characteristics, leading to forced or self-excited vibrations during operation

Unreasonable structure, stress concentration

Designed operating speed close to or within the critical speed range

Inaccurate calculation of thermal expansion, leading to poor hot-state alignment

Manufacturing reasons:

Poor processing and manufacturing of components, insufficient precision

Poor material quality of parts, insufficient strength, manufacturing defects

Rotor dynamic imbalance does not meet technical requirements

Installation causes:

Improper mechanical installation, misalignment of components, excessive preload

Poor shaft alignment

Improper adjustment of machine geometric parameters (such as fit clearance, interference fit, and relative position)

High piping stress alters dynamic characteristics and installation accuracy under operating conditions

Improper long-term storage of the rotor compromises dynamic balance accuracy

Maintenance not performed according to procedures, damaging the original fit characteristics and precision of the machine

Improper operation:

Process parameters (such as medium temperature, pressure, flow rate, load, etc.) deviate from design values, resulting in abnormal operating conditions

Operation at overspeed or overload changes the machine's operating characteristics

Operating point approaches or falls within the critical speed range

Poor lubrication or cooling

Local rotor damage or fouling

Improper operation during startup/shutdown or speed ramping, insufficient warm-up, uneven thermal expansion, or excessive dwell time in the critical zone

Equipment deterioration:

Long-term operation leads to increased rotor deflection or degradation of dynamic balance

Local rotor damage, detachment, or cracking

Component wear, pitting, or corrosion

Deterioration of force distribution on mating surfaces, causing insufficient interference fit or looseness, which compromises fit characteristics and precision

Uneven settlement of the machine foundation and deformation of the machine housing.

Fan maintenance

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1. 

The operating environment should be kept clean at all times. Keep the fan surface clean, and ensure no debris is present at the air inlet and outlet. Regularly remove dust and other debris from the fan and ducts.

2. 

Operate the fan only when it is in fully normal condition. Ensure adequate power supply capacity and stable voltage. Operation with phase loss is strictly prohibited. The power supply line must be a dedicated circuit; do not use temporary lines for long-term power supply.

3. 

If abnormal noise, severe motor overheating, electrified casing, circuit breaker tripping, or failure to start occurs during fan operation, shut down the unit immediately for inspection. To ensure safety, maintenance during fan operation is not permitted. After maintenance, perform a trial run for approximately five minutes to confirm there are no abnormalities before resuming operation.

4. 

Supplement or replace the bearing lubricant at irregular intervals based on operating environmental conditions (sealed motor bearings do not require lubricant replacement during their service life). To ensure proper lubrication of the fan during operation, the interval between lubrications shall be no more than 1000 hours per application. For sealed bearings and motor bearings, fill 2/3 of the inner and outer bearing rings with ZL–3 lithium-based grease. Operation without lubricant is strictly prohibited.

5. 

The fan should be stored in a dry environment to prevent moisture absorption by the motor. When stored outdoors, rain protection measures must be implemented. Prevent impacts and collisions during storage and handling to avoid damage to the fan.

When selecting the fan housing, primarily consider the thickness of the cold galvanized coating. Thin coatings are prone to rust and should be avoided. The fan inlet hood is available in 2 materials: galvanized steel sheet and glass fiber; galvanized steel sheet is preferred. Matching motor powers are available in 2 options: 750 W and 1100 W; selecting the 1100 W motor is recommended. There are many fan types with materials including stainless steel, galvanized steel sheet, aluminum alloy, and color-coated steel sheet. In terms of performance, stainless steel fan blades are recommended. Fan blade profiles vary widely; high-performance profiles and manufacturing processes are complex. The rotating assembly is available in 2 types: die-cast aluminum and cast iron; die-cast aluminum offers better performance. Louver automatic opening devices include centrifugal hammer type, gravity hammer type, and wind-driven type. Experience shows that the centrifugal hammer type is more stable, while the gravity hammer type is susceptible to dust accumulation, leading to malfunction in opening and closing. The wind-driven type is mainly used for 36-inch fans. For louvers, primarily evaluate the quality of their sealing.

Fan equipment widely used in industries such as electric power, steel, cement, and papermaking handles gas media containing large amounts of hard dust particles and acidic gases. The wetted parts of these equipment suffer from severe erosion and corrosion, especially the impeller, which is the core component. The linear speed at the tip of the impeller blades reaches 160 m/s, resulting in more severe wear than other parts. Statistics show that impellers made of ordinary carbon steel or general wear-resistant steel 16Mn typically have a service life of only half a year, with the shortest being only a few dozen days. Although various surface anti-wear measures such as surfacing welding, spraying, spray welding, and coating with polymer wear-resistant materials have been used, the service life is difficult to significantly improve. Among commonly used methods, surfacing welding is frequently used with acceptable results, generally allowing operation for over one year without major repairs. Its disadvantage is that surfacing welding inputs a large amount of heat; if not controlled properly, it can cause impeller deformation, and repeated repairs are not feasible. Thermal spraying and spray welding have similar issues, greatly limiting their application.

A better method is to bond or inlay wear-resistant ceramics on the surface of the impeller or volute casing. Due to the excellent wear resistance of wear-resistant ceramics, this can significantly improve the wear resistance of the fan.