Why is greater than the shaft vibration and bearing vibration and the dynamic characteristics of rotor bearing what kind of?

Why is greater than the shaft vibration and bearing vibration and the dynamic characteristics of rotor bearing what kind of? 2018 - 11 - 22 rotor rotating equipment and support with rigid and flexible characteristics, different dynamic characteristics, vibration characteristics have great differences. Because within the page can't edit formula, so all adopt the text description, not intuitive, some might seem tired. A, rigid rotor and flexible rotor working speed is lower than the first critical speed of the rotor is called the rigid rotor, is the work speed is less than 0. 75 times the critical speed, because more than 0. 75 has been in the critical speed zone, in order to ensure the safe operation of the general work actually speed must be less than zero. Five times the critical speed. For rigid rotor, due to the low work speed, unbalance centrifugal force caused by small, rotating the rotor axis bending deformation can be ignored. Working speed is higher than the first critical speed of the rotor is called flexible rotor, the speed is greater than 1. 3 times the critical speed of flexible rotor and rigid rotor compared to the actual is a rigid, when rotating a for elasticity, when the rotor is elastic, will inevitably because of the unbalance rotor of the centrifugal force generated by bending, the bending direction is associated with critical speed ratio, when the speed is far greater than the critical speed, rotor bending direction and unbalance caused by the unbalanced centrifugal force in the opposite direction, the unbalanced centrifugal force and elastic restoring force equilibrium, this is known as the rotor from the centre, after a lot of people know the rotor critical vibration will be more and more small, but I do not know reason, this is the answer, further explanation is as follows: when the speed is less than the critical speed, the deflection increases with the increase of rotational speed and rotor, and the deflection and eccentricity in the same direction, the arc bending deformation is less than the eccentricity, often ignored the rotor in the operation of the bending deformation, when the rotation speed is equal to 0. 707 times the critical speed, the bending deformation will be equal to the eccentricity; When rotation speed is equal to the critical speed, produce resonance; When the speed is greater than the critical speed, the direction of the deflection and eccentricity on the contrary, the deflection of the rotor decreases with the increase of rotational speed, when the speed is far greater than the critical speed, the deflection tend to eccentricity, center of mass in the center of the rotating rotor online at this time. Second, critical speed, critical speed is refers to the rotor in these or nearby, the running speed itself will appear a large deformation, and make a bow, cause the vibration of the mechanical system is very strong, and outside the scope of a certain rotational speed in the specific of, vibration leveled off, these cause dramatic vibration when the speed is called the critical speed. That is to say, the inherent frequency is equal to the speed of rotor system itself, the rotor's unbalanced force and the speed of the rotor system resonance occurs, the axis deflection of approaching infinity, centrifugal force approaching infinity, the only factor that limits the amplitude is the damping system. Critical speed is completely determined by the inherent character of the rotor bearing system ( The structural characteristics, mainly has the quality of the rotor, material, diameter of axle, length, and the size of the concentrate quality, and distribution, the bearing span and the stiffness of the bearing, quality, etc. ） , has nothing to do with the external conditions ( Such as the unbalanced force, load, etc. ) 。 Critical speed and natural frequency of the object, there are a lot of order, such as order, The first critical speed) , the second order, and n order, general field devices have little higher than the third order. Three, rigid support working with flexible support support is greater than the natural frequency of the rotor speed, known as the rigid support; Support work is less than the natural frequency of the rotor speed, known as flexible support. We often encounter, a rigid rotor frequency conversion fan or other device, when the speed to hundreds of vibration, but raising speed after vibration instead of smaller. The general descriptions on the natural frequencies of the infrastructure is less than rated speed frequency of the equipment. General view is that the bearing vibration is transmitted to bearing seat. In the process of transmission, vibration attenuation gradually. As a result, the shaft vibration will be greater than the vibration. Axial vibration, vibration ratio is about 2 ~ 10 times. But the reality is, as a result of the existence of the flexible support, some kind of tile under the condition of vibration will be significantly greater than the axial vibration. When the shaft vibration and vibration are hours, shows that the vibration stability. On the rotor vibration force is small, stiffness of supporting system is normal. When the shaft vibration and vibration are big, vibration is large. The increase of vibration may be derived from the exciting force, or the stiffness of the supporting system to reduce. When the shaft vibration, vibration small, supporting system stiffness showed normal or larger, vibration is caused by rotor vibration. When the shaft vibration, vibration small, tile if it is a rigid support, if it is a new installation equipment, to analysis and design is in line with the rigid support stiffness requirement, if long-term normal operation of equipment, should check bearing system connectivity, block contact condition, bearing fit clearance is too large. If it is a flexible supporting, should increase the support stiffness, or avoid support critical speed running, the actual effective way is to reduce rotor vibration force is commonly used to reduce the amplitude. For the rigid support, and the vibration characteristics of the bearing should conform to the rules shown below, the vibration amplitude is gradually increasing from bottom to top bearing vibration; Empty side to load side vibration increases gradually; Bearing seat left and right sides two vibration should be equal, there is at the same vibration should be symmetrical distribution; Close to parallel and away from the vibration of the rotor position is greater than the vibration amplitude of rotor parts such as motor bearing end cover and the chassis vibration. When the measured amplitude does not accord with the above features, usually indicates a portion of the support stiffness problem.