Precision requirements of mechanical seals for installation machines

Pumps

The accuracy of the installation of the mechanical seal machine has a great influence on the amount of leakage in the mechanical seal performance. Generally, an industrial pump (speed ≤3600r/min) is used as an example, and the allowable values ​​are introduced as follows.

1. Radial deflection of the shaft

Take the static sealed box as the benchmark for measuring the radial deflection of the shaft, as shown in Figure 11-1, fix the dial indicator on the end face of the sealed box, as close as possible to the end face, and measure the radial deflection of the shaft. Pendulum value, radial yaw value is read the value of the dial indicator when the shaft rotates 1 circle, and shows the difference of the magnitude value.

The radial deflection of the rotating shaft should be less than √d/120mm.

2. Verticality

The perpendicularity between the shaft at rest and the end face of the sealing box is shown in Figure 11-2. Fix a dial indicator on the shaft, and measure the value at the inner diameter of the end face of the sealing box that is close to the seat Z. The vertical degree value is the difference between the major and the decimal read on the dial indicator when the shaft rotates 1 revolution.

Examples of industrial pumps should comply with √d/150mm or less.

3. Coaxiality

The coaxiality between the stationary shaft and the inner diameter of the sealing box, as shown in Figure 11-3, fix the dial indicator on the shaft to measure the inner diameter of the sealing box. At this time, install the dial indicator as far as possible at the left end on the bracket, as close as possible to the end face. In addition, the value of the coaxiality of the outer diameter can also be measured during processing. When the shaft rotates once, the dial indicator reads the difference between the large and small values. In the case of industrial pumps, it should meet: 0.002*dmm.

4. Shaft movement

The clearance between the stationary bearings determines the amount of movement of the shaft. As shown in Figure 11-4, a dial indicator is installed on the shaft to measure the movement relative to the end face of the sealed box. The shaft movement value is the difference between the large and small values ​​of the dial indicator when the shaft movement is read.

In the example of an industrial pump, since the clearance of the bearing is specified to be less than 0.2mm, it rotates in one direction during continuous operation at ordinary times, so it is considered that there is no turbulence, and only violent turbulence occurs at startup. Below 0.2mm. In addition, in order to avoid the slow relative extension of the rotating shaft due to overheating during operation, all axial play values ​​should be below 1mm.

5. Dimensional tolerance and allowable value of surface roughness

When the mechanical seal is installed, as shown in Figure 11-5, the allowable value of the installation dimension tolerance and the surface roughness of the installation part P of the static ring and the installation part of the shaft seal ring are very important.

In the case of an industrial pump, the dimensional tolerance of the static ring installation part P is specified to be a fit accuracy of H7 or higher, and the seal ring installation part to be h7 or higher. In addition, the surface roughness at P, Q, R is different due to the different materials of the secondary seal, see Table 11-5.

6. Precision requirements for machine operation

It is not enough to only pay attention to the accuracy of the machine when it is stationary, because the machine sometimes cannot maintain its original accuracy when it is running. The reasons for this are:

(1) The relative displacement caused by the thermal expansion difference between the casing and the shaft caused by the fluid or machine operation.

(2) The deformation of the machine itself is caused by the expansion and contraction of the piping.

(3) The deformation of the casing is caused by the pressure.

(4) Cavitation occurs due to the reduction of machine efficiency or the increase of the vapor pressure of the liquid, which in turn causes vibration of various parts of the machine.

(5) The movement and vibration of the shaft are caused by the pressure fluctuation caused by the imbalance of the liquid flow. In view of the above, the machine should also be checked and readjusted if necessary. The allowable value of radial runout of the shaft is given as a reference in Figure 11-6.

Stirring transmission equipment (reaction kettle)

The stirring transmission equipment is composed of transmission equipment (including electric motor, coupling, reducer, transmission shaft, bracket, stirring shaft, paddle) and shaft seals. Referring to the technical documents of imported stirring transmission equipment, the main requirements are as follows.

(1) The radial runout of the stirring shaft at the seal should meet the following requirements.

(2) The verticality between the stirring shaft and the sealing flange surface should meet the following requirements.

(3) The coaxiality between the stirring shaft and the sealing flange surface should meet the following requirements.

(4) The radial runout at the end of the stirring shaft should be ≤(√d+√L)/200mm.