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Location:News / Industry News / Method to reduce cavitation damage of centrifugal pump
Anti-leakage treatment of feed water pump motor bearing seat
Time:2021-06-26Click volume:

At present, the problem of oil leakage in the bearing box of the feedwater pump motor of the domestic thermal power plant is widespread. Analyzing the reasons, it can be roughly divided into two types: poor sealing of the motor oil shield or long-term operation damage; the original casting bearing box has casting defects such as blisters, pores, cracks, and shrinkage due to poor casting technology, which occur after long-term operation leakage.

(1) Existing problems

In a power plant 8#, 9# unit electric feedwater pump motor bearing box, oil leakage occurred after long-term operation, turbine oil loss was serious, oil replenishment was frequent, feedwater pump output was affected, and the environment was also affected to a certain extent Pollution.

(2) Cause analysis

Units 8# and 9# of the power plant are two old units, which were put into production in 1985 and 1990 respectively. The bearing seat of the feedwater pump motor adopts a casting process, which inevitably has some defects such as blisters, pores, cracks, and shrinkage. In the past, due to the short operating time, these shortcomings could not be quickly exposed. After 10 or even 20 years of operation, oil leakage occurred in the bearing seat of the feedwater pump motor.

(3) Improvement plan

Consult a large amount of relevant information, and formulate this plan based on full investigation and combined with the actual situation on the spot. The HT series products produced by the domestic Huitian glue industry are used for leakage coating treatment. Due to the leakage of casting defects, it is generally difficult to confirm the location of the leakage. Therefore, the entire inner surface is coated with an anti-leakage coating to completely eliminate the leakage. . The operation process is as follows: First, clean the inner surface of the bearing housing and dry it, and then impregnate the inner cavity of the bearing housing with special impregnating glue. After the impregnating glue fills and solidifies the casting defects such as cracks and micro seams in the casting, then use Corrosion-resistant repair agent is used for the outer layer of anti-corrosion and anti-leakage treatment.

The specific operation method is as follows.

① Use high-efficiency cleaning agent HT755 to clean the surface oil, and remove the surface paint with scavenger HT790.

②Use an acetylene flame to drive out the oil stains in the dead corners and cracks.

③Use emery cloth, wire brush and other tools to polish to the casting body, clean and dry.

The upper bearing (deep groove ball bearing) is basically not bad; the lower bearing is broken and the bearing and bearing cavity are filled with cinder, sand and water.

It is analyzed that the life of the upper bearing is longer than that of the lower bearing, and the fracture of the lower bearing causes the electric pump to fail to operate; the cinder, sand and water filled in the lower bearing and the bearing cavity are the direct and main reasons for the rapid failure of the lower bearing; the lower bearing and the bearing The cinder, sand, and water filled in the cavity come from the motor cavity, and the cinder, sand, etc. in the motor cavity come from the working condition water because of the skeleton oil seal.

5, 10, 14 and other wear failure.

(4) Problem solving

In view of the above analysis, a QS20-75/5-7.5 submersible deep well pump was improved and processed in October 2002. The improvements are as follows: The skeleton oil seal 5 was modified with a single-end mechanical seal to prevent water and other debris in the motor cavity from entering The bearing accelerates the wear failure of the bearing; the bearing cavity 7 is filled with oil for the purpose of lubricating the bearing, lubricating and cooling the mechanical seal, and improving the working environment of the lower bearing. The improved prototype was put into trial use in a coal mine on October 15, 2002. The first failure occurred during 75 days of operation-the upper bearing was broken. The coal mine continued to use the bearing for 30 days and then failed again, so the prototype was returned to the factory. . The first life span was 2.5 times the original, and it was an initial success. After inspection and dissection, it was found that the motor was in good condition; the upper shaft was willing to break and the bearing and bearing cavity were filled with cinder and sand; the skeleton oil seal 2 was severely worn, and the cinder and sand entered the upper bearing from the gap between the skeleton oil seal and the shaft ; The lower bearing has been used for 105 days (3 to 4 times of that before the improvement) intact. There is no cinder or sand in the bearing cavity, and there is a small amount of water in the single engine oil.

In this way, the problem is transformed into solving how to extend the life of the upper bearing to be consistent with that of the lower bearing. Since the problem of the lower bearing has been solved, a similar solution is adopted to solve the problem of the life of the upper bearing; the skeleton oil seal 2 is modified into a single-end mechanical seal that can be installed on the shaft to prevent cinders, sand, etc. from entering the upper bearing, improving the upper bearing The working environment is improved, thereby increasing its life.

(5) Summary

Since February 2003, more than 70 improved QS pumps have been put on the market. They are used for deep well pumping and mine drainage (this type is the main one). The longest use time is 5 months. , So far only one has failed, but it is not a bearing problem. According to this method, the life problem of the lower bearing of the QS submersible electric pump can be completely solved.

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