Introduced electric insulation bearing, over current from typical condition of bearing damage

A, the purpose of the electric insulation bearing the so-called electric insulation bearing is insulation bearing, electric insulation bearing including all can prevent the current through the rolling bearing. Both inner ring and outer ring bearing are called insulation bearing with ceramic coating. Ceramic coatings can avoid the current passes through, with insulation ability. Hybrid bearings made from ceramic roller, and therefore has insulation ability. It is by the rolling element to avoid current through. Second, the choice of the bearing insulation way ordinary, complete alleviation off bearing internal potential difference is very difficult. But, if we can prevent or greatly reduced through bearing current, electric corrosion can avoid bearing attack. At present all kinds of insulation bearing are designed for this purpose. Based on different types of voltage to select bearing insulation way. 1, along the shaft of the induced voltage along the shaft of the induced voltage will produce after bearing 1 at the same time, the bearing and bearing 2 current loop, shown in figure 1. Such a reason is due to the motor shaft voltage internal magnetic flux distribution inequality, especially in some less polar logarithmic motor. At this point, just insulation end bearing can complete cut off the current loop. Usually the drive end bearing insulation. Bearing A = 1; Figure 1 B = bearing 2 along the shaft of the induction voltage of 2, between shaft and bearing seat if the voltage between the shaft and bearing seat, the current will be in the same direction after each bearing. This is mainly used in inverter brought on by the common mode voltage. Under this condition, the motor at the ends of the bearing should be insulated, see figure 2. Select the resolution of the insulation factor is the time characteristic of the current voltage. If be dc voltage or low frequency ac voltage, insulation effect depends on the insulation layer of pure resistance; If be the high frequency ac voltage ( The common use of frequency converter device) , depending on the capacitive reactance value of the insulating layer. Figure 2 between shaft and bearing seat of three voltage, over current cause bearing damage of typical condition 1, the trace of raceway and rolling body regardless of bearing after direct current (dc) or an alternating current ( Below the frequency in MHz) , we always can find the same inside the bearing damage. In most cases, we can found in raceway and rolling table in vitro, on average, the dark grey. But the visual features is not certain, sometimes may also be provoked, other factors such as smooth agent contained abrasive ingredients, as shown in figure 3. Figure 3 marks on the bearing raceway and rolling body 2, electric erosion trench of electric erosion ditch refers to the raceway surface has a continuous cyclical in running direction. This kind of phenomenon is mostly due to the bearing, incurred after the current is shown in figure 4. Figure 4 bearing electric erosion trench, under a microscope to see over-current damage of bearing structure through the scanning electron microscope ( SEM) , we can clearly see it all damage appearance full of pits and mu m class welds ( As shown in figure 5) , it also proves that the current through the bearing. Figure 5 under the scanning electron microscope (sem) bearing damage damage process of the five, bearing such pits and the structure of the solder joints due to the raceway and rolling body table tiny contact points between attacks by electric exile electric. In full flow smooth state, the current will breakdown of oil film thin point, spark energy to condense in the elusive adjacent metal appearance. In the condition of mixed friction ( Metal to metal contact) Fusion, adjacent appearance will attack, but with the bearing operation would be tantivy apart. In both cases, there will be data out from the metal appearance, then immediately solidified into a solder joint. There are some solder joint with smooth agent, and the other - Some also can accumulate in the raceway appearance. As the bearing running from time to time, the solder joint and pits can also smooth rolling. Under the action of sustained current in adjacent looks very thin surface will be repeated again and again the condensation and the process of solidification. However, in most electric corrosion of bearing internal, it is easier to find electric erosion trench ( Pictured above 4) 。 This type of raceway and rolling body is a continuous current and cycle type trace on the vibration caused by the combined influence of bearing parts. When rolling body rolled a large enough pits, it can produce pure radial displacement, the displacement of the level will depend on the bearing internal geometry size, speed and bearing load. When rolling body back and forth, smooth the oil film thickness will change, will produce more of the spark discharge in the area at the same time, the self-exciting process has been aroused. After a period of time, the ring raceway of the entire circumference direction was full of electric erosion. This provoked compare with obvious bearing vibration, and eventually cause the failure of the bearing. Thus marked, evaluate bearing over-current risk level of a firm line is calculated through the current density of bearings, in other words, the effective amps were divided by the rolling element and the inner ring and outer ring raceway contact area. It has to do with bearing type and operating condition. When the current density is less than 0. 1 A mm- 2, according to our current experience forms through the current will not bearing damage. But when the current density is equal to or greater than 1 mm - A 2, bearing internal will present obvious electric erosion. Six, the impact on the smooth agent current through the smooth agent also can have negative effects. The warp and woof of the oxidation and the cracking oil and additives will attack. In the infrared spectrogram can clearly see the changes. Premature aging and iron metal particle collection of smooth agent will incur performance becomes bad, also can cause bearing overheating.