Causes and solutions for oil leakage of centrifugal fan bearing housing
Centrifugal fans are mechanical devices that use input energy to increase gas pressure and move air. These systems are commonly used in ventilation, dust removal, and cooling applications across factories, mines, tunnels, cooling towers, vehicles, ships, and buildings. However, during operation, oil leakage from the bearing housing can occur, leading to various issues. What causes this problem, and how can it be resolved?
**Causes and Solutions for Oil Leakage in Centrifugal Fan Bearing Housings**
During operation, the shaft seal on the impeller side of the bearing often experiences significant oil leakage. This not only results in a waste of lubricating oil but also contaminates both the equipment and the surrounding area. The blower bearings frequently operate at low oil levels, which poses a risk to the safe functioning of the fan. Additionally, frequent oil replenishment increases the workload for operators.
To address the oil leakage issue, engineers have tried multiple methods over time, but few were effective. After extensive testing and analysis, the main cause was identified: when the fan is running, the impeller-side bearing housing and impeller are under positive pressure, allowing air to enter the bearing chamber through gaps between the casing and outer sleeve. Moreover, there is a design flaw in the bushing between the impeller and the bearing housing, leading to loosening after prolonged use. This loosening causes friction between the bushing and the shaft, increasing the clearance and allowing more air to enter, which then carries oil out, worsening the leak.
By adding an external guide ring inside the bearing sleeve, the oil leakage problem was fully resolved.
**Cause Analysis and Solutions**
To tackle the oil leakage, a vacuum device was installed to modify the oil leakage from the bearing housing. While this solution reduced oil leakage and contamination, it led to lubricating oil being drawn into the blower, causing pollution and increasing oil consumption. Various improvements, such as enhancing the labyrinth seal, installing exhaust caps, and using felt seals, had some success, but the problem wasn’t completely solved.
After careful observation, it was found that when the oil cover on the bearing housing was removed, a strong airflow came out. This high-pressure airflow caused the lubricating oil to be blown out. When oil was added via a funnel, the air would push the oil into a parabolic shape. Under normal conditions, the bearing rotates at high speed, and air enters the bearing chamber through the gap between the casing and outer sleeve. Due to the labyrinth seal and end cover, the cavity becomes slightly pressurized, creating strong airflow.
The sleeve positions the bearing inner ring and the fan impeller. It fits with the shaft in a clearance fit. Over time, the sleeve may loosen, and although set screws help temporarily, they often fail within a month. To solve this, a strong fill was needed to close the clearance. Addressing the "hurricane" effect caused by the blower on the bearing housing required high-pressure injection into the sleeve and shaft gap. A guide ring was also welded onto the sleeve to redirect airflow and prevent oil leakage.
During a minor repair in December 2006, four 7mm holes were drilled around the circumference of the No. 1 furnace, and M10 threads were tapped. Using a high-pressure injection gun, rubber was injected three times symmetrically to prevent the sleeve from tilting and avoid friction with the bearing or casing. A guide ring was welded 5cm from the casing.
After the modification, over one year of operation showed no oil leakage, the sleeve remained properly positioned, and no loosening occurred. The transformation eliminated collisions and friction between the bushing, shaft, and impeller, effectively preventing oil leaks. Bearings now operate under normal lubrication conditions, reducing the risk of overheating and fire accidents. It also improved the working environment, reduced noise, decreased maintenance efforts, and provided significant economic benefits.
This case study provides valuable insights into solving oil leakage problems in centrifugal fan bearing housings and can be applied to similar situations.
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