The application of oil monitoring - - The main exhaust fan fault diagnosis of sliding bearings

The application of oil monitoring - - The main exhaust fan fault diagnosis of sliding bearings 2020 - 10 - 05 ( Source: Shanghai RanChao) A preface sliding bearing, bearing under sliding friction work. Sliding bearing work steady, reliable, no noise. In liquid lubrication condition, the sliding surface is lubricating oil without direct contact, also can greatly reduce the friction loss and wear of surface oil film also have certain vibration absorbing ability, but starting frictional resistance is bigger. Sliding bearing is one of the most common mechanical parts in machinery and equipment, is the key in large rotating machinery such as fan, motor friction pair. From the point of the wear form of sliding bearing, mainly has slight wear, wear and tear on severe form, etc. Through the analysis of a large number of failure of sliding bearing, the main reason causing abnormal wear has the following kinds: 1, bad lubrication. Due to design error or improper maintenance sliding bearing oil supply shortage in the work, the hydrodynamic oil film rupture and cause scratches, eventually killed; Or because the bearing in the external fault occurred after running-in oil, such as oil absorption network congestion, oil pump is flawed, oil blockage or leakage and pressure reducing valve spring failure cause oil circulation, such as the final result in failure. 2, the assembly is not correct or the centerline deviation. It will make one end of the bearing or local serious wear and tear and generate heat, or due to the uneven load and wear to one side. 3, the overload. The resulting overheat in the metal fatigue and cause bearing surface of the metal surface broken flake. 4, dust or external impurities to enter. Big and hard dust particles into the bearing clearance of soft bearing surface scratch, sink or particles embedded in soft and strain journal bearing surface. 5, corrosion. Corrosion caused by the acid in lubricating oil bearing surface, forming a thin pitting surface and a large area of metamorphic bearing materials. Besides oil hollow the formation of bubbles and crashes can result in high local stress, the so-called 'cavitation effect, cause local bearing surface fatigue and pitting. Two fault diagnosis have a exhaust fan in one power plant, the main parameters as follows: the main exhaust fan exhaust 21000 m3 / min, 2000 mmh2o wind pressure, motor power 9300 kw, sliding bearing with lead-based babbitt ( Tin 5% ~ 11%), Bushing, its ability to resist Mosaic is wonderful, sintering resistance, corrosion resistance are good. In the process of using, often on the sample analysis, in early February, found that the direct reading ferrograph analysis data analysis than the previous data has obvious rising trend, reading DL have dramatically increased (especially big grits Table 1. ) 。 Spectral analysis of lead and tin element content is higher. Spectrum analysis ferrograph on-chip except a few normal sliding wear particle position sedimentary more non-ferrous metal particles, size in 10 ~ 20 & micro; M, rough surface, as a blob of the granular surface, its color is deeper, with a small spot color, blue, and purple is an effective suction light body, under the polarized light is not bright shining luster, random arrangement on ferrographic pieces arranged along the direction of magnetic field lines, thus it can be ruled out as a black oxide ( FeO） The possibility of. The non-ferrous metal abrasive is from sliding bearing on babbitt, show that bush had abnormal wear and tear, is due to bad lubrication, so this warning. Due to the oil analysis and vibration analysis are synchronized, and vibration analysis results show that the vibration of point values are within the normal range, so the prosecutors did not take any measures. Again after a month of oil analysis, collected, including tank system, a total of five sample sample to conduct a comprehensive analysis of the results found that every point in the sample containing more babbitt metal abrasive surface has obvious melting phenomenon, and some have even become globular, bearing wear has the tendency of further development, the conclusion is still a warning, and suggests that some prosecutors down, check the spare parts such as bearing wear condition. After half month point prosecutors to overhaul the main exhaust fan shell, find four sample sliding bearing all have different degrees of bruises, babbitt metal surface has obvious scratch, some still appeared crack and spalling phenomena. After the replacement bearing shell, and adjusted if appropriate, working properly. If left alone, will probably appear killed phenomenon, and eventually lead to electrical fire accident. This is a case of a typical through oil monitoring technology can earlier than vibration analysis technique to forecast the problems of case, then the main exhaust fan fault is still in the initial stage, does not cause the vibration of the large value of change, on the measured vibration value, not for spectrum analysis. Three conclusions sliding bearings are widely used in metallurgical machinery, iron spectrum analysis on the working condition monitoring is feasible in theory, it can be earlier than vibration analysis technique to forecast the fault hidden trouble, but in the process of practical application of concrete, due to its wear quantity is small, plus babbitt is a ferromagnetic material again, and iron spectrum technology is mainly for the ferromagnetic material is responsive, so it is difficult, the accurate forecast fault through the oil monitoring technology, is the effect of many years of experience, has important practical significance.