Mechanical seals belong to one of the mechanical basic components of precision and complex structure, and are the key components of various pumps, reaction synthesis reactors, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as selection, accuracy of the machine, correct installation and use.
1. Selection method:
The main parameters of mechanical seal selection: seal chamber pressure (MPA), fluid temperature (℃), working speed (M/S), fluid characteristics and effective space for installing seals.
Mechanical seal according to the different working conditions and the nature of the medium, there are high temperature resistance, low temperature resistance mechanical seal, high pressure resistance, corrosion resistance mechanical seal, resistance to particle medium mechanical seal and adapt to the mechanical density of light hydrocarbon medium that is easy to vaporize
Mechanical seals of different structural types and materials should be selected according to different uses.
The basic principles of selection are:
1: According to the pressure of the sealing chamber, the sealing structure is determined to be balanced or non-balanced, single or double.
2: According to the working speed, determine the use of rotary or static, hydrodynamic pressure or non-contact type.
3: According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, as well as the correct selection of lubrication, washing, insulation, cooling and other mechanical seal cycle protection systems.
4: According to the effective space of the installation seal, determine the use of multi-spring or single spring or waveform spring, built-in or external.
Second, mechanical seal installation and use requirements:
1: Mechanical seal requirements for machine accuracy (taking pump mechanical seal as an example)
(1) The radial runout tolerance of the shaft (or sleeve) of the installation of the mechanical seal part shall not exceed 0:04 ~ 0:06MM.
(2) The axial movement of the rotor does not exceed 0:3MM.
(3) The runout tolerance of the positioning end of the sealing cavity combined with the sealing end cover facing the shaft (or sleeve) surface is not more than 0:04 ~ 0:06MM.
2: Confirmation of seals
(1) Confirm whether the installed seal is consistent with the required model.
(2) Before installation, carefully compare with the final assembly drawing to check whether the number of parts is complete.
(3) The mechanical seal with parallel coil spring transmission has left and right rotation of the spring, which must be selected according to the rotation of the rotating shaft.
3: Installation
The installation method varies with the type of mechanical seal and the type of machine, but the installation essentials are almost the same, and the installation steps and precautions are as follows:
(1) Determining the installation size When installing, the installation size of the mechanical seal should be guaranteed according to the product instruction manual or sample.
(2) Before loading, the shaft (sleeve) and gland should be free of burrs, and the bearing is in good condition; Seals, shafts, sealing cavities, gland should be cleaned.
In order to reduce friction resistance, the part of the shaft installed mechanical seal should be thinly coated with oil for lubrication, considering the compatibility of the rubber O-ring, if it is not suitable for oil, it can be coated with soapy water.
The floating static ring does not have the structure of anti-rotating pin, should not be oiled, and should be dry loaded into the gland.
(3) First install the static ring with the gland on the shaft, taking care not to touch the shaft, and then load the dynamic ring assembly. The setting screw of the spring seat or transmission seat should be tightened evenly in several times.
Before the gland is not fixed, push the compensation ring for axial compression. After releasing the compensation ring can automatically spring back without stuck phenomenon, and then lock the gland bolt evenly.
4: Use
(1) When the temperature of the conveying medium is high, too low, or contains impurity particles, flammable, explosive, toxic, corresponding measures must be taken to block, flush, cool, filter and so on.
(2) Turn the car by hand before operation, pay attention to whether the torque is too large, there is no friction and abnormal sound.
(3) Pay attention to the rotation, whether the coupling is in alignment, whether the lubricating oil addition of the bearing part is appropriate, and whether the piping is correct.
(4) Whether the work is normal and stable after driving, there is abnormal torque caused by shaft rotation, as well as abnormal noise and overheating phenomenon.
(5) Before operation, first open the medium and cooling water valve, check whether the gas in the sealing chamber is completely discharged, prevent leakage caused by static pressure, and then start up and run.