Electric insulation bearing is introduced, the typical case of over current lead to 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 coating can prevent current through, with insulation ability. Hybrid bearings made from ceramic roller, therefore also has the insulating ability. It is by the rolling body to prevent electric current passes through. Second, the choice of the bearing insulation methods in general, completely eliminate bearing internal potential difference is very difficult. However, if we can prevent or greatly reduced through the current bearing, can prevent the corrosion of the bearings. At present all kinds of insulation bearing are designed for this purpose. According to different types of generating 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. One reason for this kind of shaft voltage generated is due to the uneven distribution of motor internal magnetic flux, especially in some very logarithm less motor. At this point, as long as the insulation end bearing can be completely 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 current through each bearing will be in the same direction. This is mainly used for frequency converter caused by common-mode voltage. In this case, the motor at the ends of the bearing should be insulated, see figure 2. Choose time characteristic of the determinants of the insulation is current voltage. If it is a dc voltage or low frequency ac voltage, insulation effect depends on the insulation layer of pure resistance; If it is 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 three voltage, over current result in bearing damage of typical case 1, the trace of raceway and rolling body regardless of bearing by direct current (dc) or an alternating current ( Below the frequency in MHz) , we always can find the same inside the bearing damage forms. In most cases, we can found in raceway and rolling body surface uniform dark gray. But the visual features is not certain, sometimes may also be caused by other factors, such as the lubricant 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 bearing caused by electric current, as shown in figure 4. Figure 4 bearing electric erosion trench, under a microscope to see over current bearing damaged structure only by scanning electron microscope ( SEM) , we can clearly see almost all damage to the surface with the potholes and mu m class welds ( As shown in figure 5) , and this is confirmed with current through bearings. Figure 5 five bearing damage under the scanning electron microscope (sem) structure, bearing damage hair process such pits and the formation of solder joints is due in raceway and rolling body surface of small discharge current caused by the contact point. In the fluid lubrication state, current will breakdown of oil film vulnerabilities, electric spark generated energy is the surface of the adjacent molten metal in a flash. In the condition of mixed friction ( Metal to metal contact) , can also occur fusion adjacent surface, however, as the bearing running would be quickly separated. In both cases, there will be material from the metal surface from, then immediately solidified into a solder joint. There are some solder joints with lubricant, and the other - Some will deposit on the surface of raceway. With the continuous operation of bearing, the solder joint and pits will be crushed flat. Under the action of constant current, on very thin surface layer on the surface of the adjacent repeated the process of melting and solidification. However, in most electric corrosion bearing internal, more easy 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, displacement depends on the bearing internal geometry size, speed and bearing load. When rolling body back and forth, the thickness of lube film change, will produce more of the spark discharge in the area at the same time, the self-exciting process was stimulated. After a period of time, the ring raceway of the entire circumference direction was full of electric erosion. This will cause the obvious bearing vibration, eventually lead to the failure of the bearing. Which shows that the evaluation of bearing over-current risk grade of a reliable principle is calculated by 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 through the current will not result in bearing damage. However, when the current density is equal to or greater than 1 mm - A 2, bearing internal will appear obvious electric erosion. Six, lubricant impact current through the lubricant will have negative impacts. The base oil and additives oxidation and cracking happens. In the infrared spectrogram can clearly see the changes. Premature aging and iron concentrations of metal particles cause lubricant performance is bad, can also lead to bearing temperature operation.