Problems that should not be ignored in the maintenance and installation of high-speed diaphragm couplings

Problems that should not be ignored in the maintenance and installation of high-speed diaphragm couplings:

High-speed diaphragm coupling is a kind of flexible coupling. The compensating element is composed of several sets of thin metal sheets (usually stainless steel sheets) that are staggeredly connected with the two halves of the coupling with bolts. Each set of diaphragms is composed of several sheets, so it is often called a laminated coupling. . Diaphragm couplings rely on the elastic deformation of the diaphragm to compensate the relative displacement of the connected two shafts. The diaphragm is not affected by temperature and oil pollution, and has the characteristics of acid resistance, alkali resistance and corrosion resistance. It is suitable for high temperature, high speed and corrosive medium conditions. Environmental shaft transmission is a coupling that is mainly promoted in my country.

Problems and suggestions for maintenance and installation:

1. About the calibration standard

At present, the alignment standards only require radial runout and end face runout. For diaphragm couplings, the requirements of "General Specifications for Construction and Acceptance of Mechanical Equipment Installation Engineering" GB50231-1998, radial ≤ 0.15mm, end face runout ≤ 0.1 mm, the standard of the Ministry of Chemical Industry is also equivalent to it. But it should be noted that this standard does not apply to all diaphragm couplings during normal maintenance and installation.

2. The diaphragm of the coupling is mainly subjected to 4 kinds of forces

(1) Membrane stress due to torque. The force generated by the torque on one side is evenly distributed on the four bolt holes at intervals. On the taken 1/4 diaphragm, the force acts on the middle part of one side of the middle bolt hole along the circumferential direction to fix the radial displacement and axis to the displacement.

(2) Centrifugal stress generated by centrifugal inertial force. The centrifugal inertial force of high-speed machinery is very important in the stress calculation of the structure. The centrifugal inertial force can be loaded according to the radial unit body force f=2rρ(2πn/60), and the direction is radially outward. In the formula, n is the rotational speed , r is the radius, and ρ is the density. The radial displacement, circumferential displacement and axial displacement of the middle bolt hole are fixed, and there is no other load on the periphery.

(3) Bending stress caused by axial installation error. Due to the actual installation error in the axial direction, the diaphragm is bent and deformed in the axial direction. The displacement is loaded in the axial direction of the middle bolt hole, and the radial displacement and axial displacement are fixed.

(4) Bending stress (periodic stress) caused by angular installation error. Due to the actual installation error in the angular direction of the axis, the diaphragm undergoes periodic bending deformation along the axial direction, and it is the main factor determining the fatigue life of the diaphragm.

From the analysis of the relevant formula (omitted), the size of the additional stress is not only related to the relative angular displacement of the two axes, the relative axial displacement of the two axes, and the relative radial displacement of the two axes, but also related to the number of bolts of the coupling, the thickness of the diaphragm, and the coupling. It is related to factors such as the distribution radius of shaft bolts. Therefore, it is suggested that the specific alignment standard should be carried out according to the design requirements of the equipment, and it cannot be carried out according to the radial direction ≤ 0.15mm and the end runout ≤ 0.1mm. Diaphragm coupling picture

3. The deviation of the distance between the end face of the coupling

The requirements for the distance deviation of the end face of the diaphragm coupling are proposed based on the formula of the additional stress generated by the relative displacement of the two axes. In the case of an axial installation distance deviation, when the coupling bolts are tightened, a force will be generated on the diaphragm (assuming 6 coupling bolts). And when there is angular and radial deviation, the force b of the diaphragm. Generally, these two conditions will exist at the same time during installation, which will produce a superposition of forces.

Coupled with the axial displacement generated during the operation of the equipment, it is possible to accelerate the damage of the diaphragm. Correspondingly, the axial stress caused by the axial distance deviation may in turn affect the operating parameters of the equipment (vibration, bearing temperature).

Therefore, it is recommended to strictly control the distance deviation between the two halves of the coupling during the actual maintenance and installation. The deviation between the distance between the two halves of the coupling and the installation thickness of the short joint and the diaphragm in the middle is within 0~0.4mm (except for the diaphragm with pre-tension and pre-compression design). Of course, the design of each coupling manufacturer may be different, so it should also be adjusted according to the design requirements.

4. Problems that should not be ignored during installation

(1) Dynamic balance. As the speed of the machine increases, there is an eccentricity between the main axis of inertia of any rotary component and the axis of rotation. The unbalanced moment of inertia generated during operation will inevitably cause the vibration of the drive shaft and cause the failure of the machine component. There are parts in the flexible coupling that can be displaced relative to each other, which is more likely to cause imbalance. Therefore, the diaphragm coupling itself in many high-speed equipment has been dynamically balanced, and the half coupling is installed on the shaft and then dynamically balanced to ensure the dynamic balance of the system.