Various guidelines for the life of mechanical seals for kettles

Mechanical seals are one of the basic mechanical components with precision and complex structure, and are the key components of various pumps, reaction synthesis kettles, turbo compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as model selection, machine accuracy, correct installation and use, etc.

1. Selection method

Depending on the working conditions and the properties of the medium, mechanical seals include high-temperature and low-temperature-resistant mechanical seals, high-pressure and corrosion-resistant mechanical seals, particle-resistant mechanical seals, and mechanical seals adapted to easily vaporized light hydrocarbon media. The use of mechanical seals of different structural types and materials is selected.

The main parameters for selection are: sealed cavity pressure (MPA), fluid temperature (°C), working speed (M/S), fluid characteristics and effective space for sealing installation.

The basic principles of selection are:

1: According to the pressure of the sealing cavity, determine whether the sealing structure is balanced or unbalanced, single-end or double-end, etc.

2: According to the working speed, determine whether to use rotary or static, hydrodynamic or non-contact.

3: According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal circulation protection system such as lubrication, flushing, heat preservation, cooling, etc.

4: According to the effective space of the installation seal, it is determined to use multiple springs or single springs or wave springs, built-in or external.

2. Installation and use requirements of mechanical seals

1: The requirements of the mechanical seal on the machine accuracy (take the mechanical seal for the pump as an example)

(1) The radial runout tolerance of the shaft (or shaft sleeve) where the mechanical seal is installed 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 surface of the shaft (or shaft sleeve) shall not exceed 0:04~0:06MM.

2: Confirmation of seals

(1) Confirm whether the installed seal is the same as the required model.

(2) Before installation, carefully check with the general assembly drawing to see if the number of parts is complete.

(3) For mechanical seals driven by parallel springs, the springs are divided into left and right rotations, which must be selected according to the rotation direction 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. The installation steps and precautions are as follows:

(1) Determination of installation size

During installation, 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 should be in good condition; the seals, shaft, sealing cavity and gland should be cleaned. In order to reduce frictional resistance, the part where the mechanical seal is installed on the shaft should be coated with a thin layer of oil for lubrication. Considering the compatibility of rubber O-rings, if oil is not suitable, soapy water can be applied. The structure of floating static ring without anti-rotation pin should not be oiled, and should be installed in the gland dry.

(3) Install the static ring together with the gland on the shaft first, being careful not to collide with the shaft, and then install the moving ring assembly. The set screw of the spring seat or transmission seat should be evenly tightened several times.

Before the gland is not fixed, push the compensation ring by hand for axial compression. After loosening, the compensation ring can automatically spring back without jamming, and then the gland bolts are evenly locked.

4: use

(1) When the temperature of the conveying medium is too high, too low, or contains impurity particles, flammable, explosive or toxic, corresponding measures such as blocking, flushing, cooling, and filtration must be taken.

(2) Turn the car by hand before running, pay attention to whether the torque is too large, whether there is friction and abnormal sound.

(3) Pay attention to the direction of rotation, whether the coupling is centered, whether the addition of lubricating oil in the bearing part is appropriate, and whether the piping is correct.

(4) Before operation, first open the medium and cooling water valves, check whether the gas in the sealing chamber is fully discharged, and prevent leakage caused by static pressure, and then start the operation.

(5) Whether the work is normal and stable after driving, whether there is abnormal torque caused by shaft rotation, abnormal noise and overheating.