Stability and characteristic influence of diaphragm coupling movement

Large-scale rotor systems are key equipment in important industries such as chemical and electric power, such as the three machines for the production of ethylene, the five machines for the production of fertilizers, and the large-scale steam turbine generator sets in power plants.Due to the high cost of the unit, spare units are generally not equipped in actual production, which requires these equipment to work stably and reliably during the normal production stage, otherwise it will cause major losses.

In the past, in the process of dynamic analysis of the rotor system, some typical components of the system, such as the rotor, support bearing, seal and foundation, have been deeply discussed, but there are not many discussions on the coupling effect of the coupling. .In actual engineering, the rotor system connects several rotor-bearing systems through couplings. To be precise, a large multi-span rotor system can be called a rotor-bearing-coupling system.In a multi-span rotor system connected by couplings, re-recognize the role of couplings in the system.The transmission of energy and motion between the rotors is achieved through the coupling, and the quality of the coupling determines the degree of energy coupling and transmission.People hope that in the process of motion transmission, the coupling can cut off the harmful motion to the system, thereby increasing the stability of the system motion.

Judging from the current status quo, from the perspective of rotor dynamics in the field of linear vibration, more has been done on the inherent characteristics of the rotor-bearing system, including the dynamics of the rotor-bearing system including couplings. analysis.Diaphragm coupling is a new type of flexible coupling introduced in my country in recent years. Most of it is limited to the analysis of rigidity, strength, and life of traditional mechanical parts, while it is used in large-scale rotating machinery. The role played in this has not yet been deepened.Because the diaphragm coupling has no need for lubrication and high misalignment compensation capabilities, some large domestic petrochemical companies have begun to use this type of coupling to replace the traditional gear coupling; The dynamics of the misaligned rotor-bearing system has practical engineering significance.

First, the statics analysis of the diaphragm group is carried out, and the calculation formula for the stress of the diaphragm group is derived under the working condition; then the dynamic model of the diaphragm group is established, and the relationship between the stiffness and the structure of the diaphragm coupling is obtained.Through analysis, it is found that the corner stiffness and axial stiffness of the diaphragm group are not only related to the thickness of the diaphragm and the radius of the bolt distribution circle, but also the angle of the elastic part of the diaphragm between two adjacent connecting bolts has a great influence on it.

In actual engineering, the misalignment of the rotor system is very common, and 60% of the rotor failures are related to the misalignment.Rotor misalignment includes two cases: bearing misalignment and shafting misalignment.The deflection of the shaft diameter in the bearing is called bearing misalignment. Bearing misalignment itself does not produce vibration, and it mainly affects the performance of the bearing oil film.When the rotors of the unit are connected by a coupling, if the axes are not on the same straight line, it is called shafting misalignment.Misalignment is usually referred to as misalignment of multi-finger shafting.After the rotor system is misaligned, it will produce axial and radial alternating forces, causing axial and radial vibration, so a series of dynamic effects that are not conducive to the operation of the equipment will be produced during its movement, such as causing equipment vibration , The deflection of the coupling, the wear of the bearing and the instability of the oil film, the bending and deformation of the shaft, etc., are harmful.Therefore, the dynamic characteristics of the misaligned rotor system are of great significance to the operation of the unit.

Taking the misaligned rotor-bearing system coupled with the diaphragm coupling as the object, the generalized inverse iteration method is used to analyze the influence of misalignment on the dynamic and static characteristics of the symmetrical rotor system bearing and the inherent characteristics of the system. The main conclusions are as follows:

(1) The impact of misalignment at the bearings on both sides of the coupling and both ends of the system on the load distribution of the system is different.The load distribution supported on both sides of the coupling increases with the increase of the misalignment, and decreases under the influence of the misalignment of the bearings at both ends of the system.The load distribution at the bearings at both ends of the system decreases with the increase of the misalignment at the supports on both sides of the coupling, and increases under the influence of the misalignment at its own.Due to the vibration isolation function of the diaphragm coupling, the misalignment at the support of the rotor system of one span has less effect on the dynamic and static characteristics of the rotor bearing of the other span.

(2) The inherent characteristics of the system change under the influence of the misalignment, in which the absolute value of the real part of the eigenvalue decreases, while the imaginary part increases, and the first few modes of the system no longer exhibit symmetrical or antisymmetrical The characteristics are mainly due to the deformation of the rotor of one of the spans, and almost no deformation of the other span.

(3) The stability of the system tends to deteriorate due to the misalignment of the bearings on both sides of the diaphragm coupling.Under the influence of misalignment, the smaller logarithmic decay rate of the system is reduced, and the instability speed drops.

The forced vibration of the rotor can be divided into vibration asynchronous with the rotor and synchronous vibration, and the latter is mainly excited by the unbalance of the rotor.Due to design and structure factors, uneven materials, manufacturing and installation errors, etc., the inertial main shaft of the actual rotor-bearing system is more or less deviated from its axis of rotation.In this way, when the rotor rotates, the centrifugal inertial force of each micro-element mass forms a set of unbalanced force systems.The vibration of the rotor-bearing system under the excitation of unbalanced force or unbalanced torque is called unbalanced response.In general, the unbalance of the rotor system is the main factor causing vibration.

The unbalanced response of the rotor-bearing system coupled with the diaphragm coupling is analyzed.First, the Gaussian elimination method is used to solve the forced vibration caused by the unbalanced amount of the system: the unbalanced response of each node is analyzed.Then, taking the multi-span rotor-bearing system with symmetrically arranged diaphragm couplings as the object, the effects of the stiffness of the diaphragm coupling and the misalignment of the rotor on the unbalanced response of the system are analyzed through numerical simulations; detailed analysis In the misalignment state, the unbalanced response of the system support varies with the speed. The main conclusions are as follows:

(1) For a symmetrical rotor-bearing system, when the radial stiffness of the diaphragm coupling is equal to a certain value, its angular stiffness has a great influence on the unbalanced response of the system.When the radial stiffness of the diaphragm coupling, the corner stiffness determines its vibration isolation effect.When k, is small, there is a significant vibration isolation function.With the increase of k, its vibration isolation effect gradually decreases.Analysis shows that the corner stiffness of the diaphragm coupling is an important factor affecting its vibration isolation effect.

(2) When the system passes through the critical speed area, the misalignment of the rotor has a significant influence on the unbalanced response of the system, but at the working speed, this influence becomes smaller.