GENERAL KNOWLEDGE ABOUT ENGINEERING SEALS

Leakage is a direct cause of many major accidents today. In today’s high-tech era, even if production processes equipped with the latest technology and modern management methods are implemented, in complex production and natural environments, due to continuous erosion of media, changes in temperature, pressure, and vibration, changes of season and geology, it will inevitably lead to the problem of seal failure in some parts. Today we mainly introduce the common problems of engineering seals.

1. The correct installation of engineering seals

1) Confirm the type and size of the mechanical seals, and install it according to the instruction manual or sample of the product.

2) Before installing the mechanical seal, check that whether the bearing is in good condition. The seal, shaft, seal cavity, and gland should be cleaned. In order to reduce the frictional resistance, apply a thin layer of oil to the part where the mechanical seal is installed for lubrication. Considering the compatibility of the rubber seal ring, if oil is not suitable, soapy water can be applied.

3) First install the static ring and the gland together on the shaft. Be careful not to touch the shaft, and then install the moving ring assembly. The set screw of the spring seat or transmission seat should be tightened evenly in several times. Before fixing the gland, 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. Here the gland packings you can choose is the spring seals.

2. The use of engineering seals

1) When the temperature of the conveying medium is too high or too low, or contains foreign particles, flammable, explosive, and toxic, take appropriate measures such as blocking, washing, and filtering.

2) Pay attention to the direction of rotation, whether the coupling is aligned, whether the addition of lubricating oil at the bearing is appropriate, and whether the piping is correct.

3) Before operation, first open the medium and water valve, check whether the gas in the sealed cavity is completely discharged to prevent leakage caused by static pressure, and then start the operation.

3. The processing technology of engineering seals

The end face of the mechanical seal adopts the porous processing method. First, understand the notch (orifice) of the end face processing. People have explored a variety of processing methods, mainly the following: photochemical etching (lithography), EDM (electrodischarge machining), electrochemical machining and laser machining.

Compared with the traditional seal processing technology, laser processing has a wide range of applications, suitable for different materials and different shapes of processing surfaces. It has the characteristics of no mechanical deformation of the workpiece, fast speed, good repeatability and high degree of automation. Obviously, for the porous end face mechanical seal ring, the processing method is forceful, and only the laser processing method can obtain satisfactory results.

In the friction performance test, the common seal ring and the laser mechanical end face porous device seal ring were compared and tested under the same end load. The end face dimensions, surface roughness, end load and speed of the two seal rings are all the same. From the point of the coefficient of friction, the porous device on the end face of the mechanical seal is lower, so it has better wear resistance and extends the life of the seal.

4. Five major phenomena that cause leakage of engineering seals

1) There is too much wear on the sealing end face between the dynamic and static rings. The load factor of the mechanical seal specifications and models is unreasonable, which causes cracks, deformation and damage on the sealing end face.

2) The mechanical seal is damaged because of improper assembly or auxiliary seal ring components. Therefore, a reasonable auxiliary seal ring must be selected according to the engineering machinery media.

3) After the spring has been running for a long time, its preload is reduced, causing corrosion, fracture, coking, and accumulation of suspended particles or crystals in the spring gap for a long time, resulting in the failure of the spring seals or elastomer bellow seals, the compensation seal ring cannot float, and leakage happens .

4) Due to the excessive deviation of the verticality of the sealing end face of the moving ring and the static ring and the axis, the end face of the mechanical seal is not tightly bonded and causes leakage.

5) Because the axial movement of the shaft is large, the fittings related to the mechanical seals are not well matched or the quality is not good, and it is easy to cause leakage.