Knowledge!Mining axial fan bearing box fault analysis and solutions

Posted on 2024-08-05

The main fan ventilator used in coal mine is the main large-scale equipment to ensure the safe production of coal mine and gas discharge, in the process of coal mine production, it adopts one use and one backup two fans, which can not stop running every moment. The bearing box is the core of normal operation of the fan. It is one of the most precise parts of the fan. If the bearing box fails when the fan is running, it will cause the fan to stop working and serious quality accidents will occur.

The bearing box of AGF type fan adopts integral box structure, and its inner cavity is equipped with two support bearings and two thrust bearings each, all sealed in the inner cavity of the box. Compared with 2BY, 70B2, 2K60 double-support bearing housings, this type of bearing housings do not need to adjust the bearings when the fan is installed, and the bearings in the bearing housings are lubricated by a mixture of oil bath and splash lubrication using 46# liquid mechanical oil. This design has many advantages over the old front and rear bearing box fans, such as compact structure, simple and convenient grease replacement, and low daily maintenance. The bearing box assembly is shown in Figure 1.

Although there are many advantages of AGF type fan bearing box, some problems have also appeared in actual use. During the operation of the fan, individual fans will sometimes appear oil seepage, oil leakage phenomenon; sometimes there are also oil level is not allowed and bearing temperature is too high. The following is a brief introduction and analysis of the causes of these problems.　

1.Problem analysis and solution

1.1 High bearing temperature

There are four sets of bearings in the bearing box of the fan, i.e. two sets of thrust bearings and two sets of cylindrical roller bearings. Each bearing is equipped with a Pt100 temperature sensor for monitoring. An alarm is raised when the operating specified bearing temperature is exceeded. Causes of elevated bearing temperatures:

(1) There are impurities in the lubricating oil and other poor lubrication. Fan in normal operation for a long time, after several refueling, oil change, may be due to impurities in the oil or hard particles into the inner cavity of the bearings, thus leading to fan operation process occurs in a bearing temperature suddenly increased, oil discharge powder or copper floating, is likely to be copper cage damage and lead to localized spalling. As a result, for the cage localized spalling, such as not serious and does not affect the roller movement, can continue to move. And repeatedly replace the new oil flushing cavity can be. On the contrary, the direct replacement of bearings.

(2) oil system blockage, lubricant is not in place. Oil supply pipe is composed of many pipes, and the pipes must be connected with joints combination, sometimes in the removal of joints to reassemble, must only be coated with a uniform layer of grease, and can not be arbitrarily coated, due to the small area of the pipeline, more coated with the residual oil after the oil finger will be clogged oil pipe, and refueling in the wrong way lubricants are in place. A driving operation, resulting in bearing burnout. So in the fan repair and maintenance must check the oil circuit system is smooth.

1.2 During fan operation, the oil level is not stable

In the fan debugging operation oil level is not stable or oil level drop fast, although after a long time operation, oil level display is still unstable, this phenomenon is caused by the following two reasons. (1) debugging the initial oil level is not stable, need to refuel often, this is due to the lubricating oil need to fill the pipeline, the bearing box cavity and spindle rotation splash to the bearing cavity above the wall, need to consume more oil, generally need to be counted for 3 hours, replenishment of oil less and less, the oil cavity can be shown to stabilize, Z long in 6-8 hours this phenomenon disappeared.

(2) bearing box inside and outside the pressure difference caused by this reason will also cause the bearing box oil leakage, the two exist with each other. To eliminate this phenomenon must make the bearing box inside and outside the pressure to maintain the same. The solution will be in dealing with the oil leakage problem on the specific instructions.

1.3 Bearing box oil leakage

According to the bearing box working environment and its structural characteristics, can be found in addition to the bearing box various parts of the processing accuracy and assembly accuracy, or seal aging caused by oil leakage. In the previous design of the fan lubrication system ignored an important factor, that is, in the fan operation of the main body of the wind cylinder in the ring-type flow channel and the inner ring cavity, the inner ring cavity and the bearing box cavity exists in the pressure difference. As shown in Figure 2:

-P, -P': the negative pressure at the point relative to the external atmospheric pressure, respectively,

Po: external atmospheric pressure

As the main body of the inner ring of the wind tube is not sealed, so in the operation of the fan in the inner ring cavity will exist with the impeller outlet pressure is approximately the same pressure, the pressure relative to the atmospheric pressure is negative, that is, lower than the outside world atmospheric pressure. So it can be derived from the analysis of the figure:

　　① -P <-P′ can be considered -P ≈ -P′

　　② Po>-P′

This makes the lubricant in the cavity by a squeeze pressure from the inside out, so that the lubricant is pressed out through the gap that exists between the inner and outer rings of the oil seal in contact with the bonding surface.

For the elimination of the air pressure difference between the inside and outside of the bearing box, the treatment can be used: as shown in Figure 3:

(1) will be used to wear the oil pipe and the sensor cable channel, that is, the fan body shell through and in the guide vane inside, connected to the inner ring cavity of the opening, the gap with the material sealed tightly, or make a cover, to prevent the external atmosphere from this channel into the periphery of the bearing box.

(2) in the fan body outside the upper part of the oil level observation gauge, connected to a pressure balance pipe, the other end of the body of the inner ring cavity, to ensure that the pipeline seal, can not breathe.

(3) Add a venting nozzle to the upper part of the bearing box in order to make the pressure of the inner ring cavity of the main body the same as the pressure of the inner cavity of the bearing box.

-P<-P′ can be considered -P≈-P′

　　P box ≈ -P′ (after not communicating with the atmosphere)

After the above treatment, the atmospheric pressure outside the fan can be isolated from the inner annular cavity in the main body of the fan; so that the inner cavity of the bearing box has the same pressure as the inner annular cavity of the main body, which is close to the pressure of the airflow in the annular flow channel of the fan. Existing pressure difference is eliminated, the problem of oil leakage is solved, while the problem of unstable oil level is also solved.

The above three major points are the bearing box is prone to problems, there are, for example, oil system piping joints are not tightened, seals are not installed correctly, oil system air balance pipe local blockage and so on. When dealing with bearing box failure, these problems must also be noted.