What are the main common causes of failures in container mechanical seals?

What are the main common causes of failures in container mechanical seals?

Machine sealing is a device that prevents liquid leakage. It consists of at least one pair of ports perpendicular to the axis of rotation that maintain adhesion and relative sliding under the combined action of fluid pressure, compensation mechanism elasticity (or magnetism), and auxiliary sealing.

Damage to the dynamic and static ring ports causes leakage of the machine seal

Regardless of the type of seal, its core feature is the protruding surface perpendicular to the axis of rotation, that is, from the axial seal that is prone to leakage to the end face seal that is less prone to leakage. Therefore, an important method for ineffective sealing is the wear failure between the stationary ring and the moving ring. The friction pair at the top of the moving and stationary rings mainly relies on the thrust of the torsion spring to avoid leakage. The tighter the sound ring, the less likely it is to leak, but the friction between them will increase. Under the influence of high friction, the contact surface of the acoustic ring is rapidly damaged, resulting in ineffective and leakage.

Mechanical seal leakage is caused by unstable operating conditions and poor installation

The unstable nature of the work, vibrations caused by poor installation, and equipment evacuation and gasification can all damage the liquid film between the machine seal and the static ring, causing the machine seal to operate "dry" without lubrication The temperature of the sealing ring will rapidly rise, some will ignite immediately, while others will rapidly cool down during the pump's resumption of operation, leading to thermal shock and rupture. Poor flushing fluid and operating conditions can also cause thermal shock, leading to axial cracks in the seal and increasing the probability of wear and failure of the dynamic and static rings. At the same time, when the temperature of the graphite ring exceeds the operating temperature, crystals will precipitate on the surface of the graphite ring, carbonization will occur around the high-temperature friction pair, and particles will enter the friction pair, causing rapid damage to the acoustic ring.

Invalid sealing ring is an important reason for seal leakage

Poor installation of dynamic and static sealing rings; The surface smoothness of the shaft or sleeve matched with the seal is insufficient or the matching specifications are too small; Physical or chemical changes, corrosion, deformation, and aging between seals and sealing materials can all lead to leakage.

Improper installation causes leakage of the machine seal

Confidential seals not cleaned, parts scratched or scratched; Inadequate assembly; The total stroke of the torsion spring (assembly) is tilted, and the fastening screws are not tightened; The damage to the machine seal during disassembly and assembly is the cause of early failure of the seal.

Improper selection and design of mechanical seals result in seal leakage

Due to the diverse characteristics of process materials in chemical plants, improper sealing design and use, excessive or insufficient pressure on the sealing end face, and high shrinkage rate of sealing materials, it is easy to cause ineffective sealing and leakage.

Twisted spring reduction adjustment

Adjusting the compression of the spring is the main parameter related to the sealing performance and service life of the mechanical seal end face, as well as its sealing structure type, torsion spring size, and material pressure. If the port pressure is too high, the friction pair will be damaged; If the pressure is too low, it is easy to leak, so manufacturers generally provide a suitable range, usually 3kg/cm2 to 6kg/cm2. The free length a of the spring, the spring stiffness k (the load that the enterprise needs to bear when shrinking), and the specified specific pressure p are all parameters provided by the manufacturer. When the size is reduced to b, P/(ab)=k，b=ap/k， That is to say, the assembly of torsion springs has reduced the specifications. If the specifications of the torsion spring are too large after installation, an adjusting pad can be added between the spring seat and the spring to increase its thickness. If the specification is too small, the thickness of the adjustment pad can be reduced accordingly. Measure the thickness of the adjustment pad with a micrometer.

Sealing performance of dynamic ring closure

Overtightening the dynamic ring seal is harmful and detrimental. One is that it will exacerbate the wear between the sealing ring and the shaft sleeve, causing premature leakage; The second is to enhance the radial adjustment and motion resistance of the dynamic ring. When the working conditions frequently change, the dynamic ring cannot be corrected in a timely manner; 3. Twisted springs are prone to damage due to excessive fatigue; 4. The sealing ring of the moving ring may deform, endangering the sealing effect. In order to ensure the fluctuation characteristics of the dynamic ring, its inner diameter is 0.5-1mm larger than the shaft diameter, used to compensate for shaft vibration and deflection, but the gap should not be too large, otherwise it will get stuck in the sealing ring of the dynamic ring and damage the mechanical seal of the machine seal. Performance. After applying lubricant, the tightness of the sealing ring should be easy to press by hand.

Sealing performance of static ring closure

The static ring seal is basically in a static state, and the sealing effect is relatively good. However, if it is too tight, it will cause: 1. The static ring seal will change too much, endangering the sealing effect; Excessive pressure can easily cause fragmentation; 3. Assembly and disassembly are difficult, and it is easy to damage the stationary ring. Therefore, the inner diameter of the static ring is generally 1mm to 2mm larger than the shaft diameter. Use both hands to install the pressure and feel the tightness of the sealing ring (after applying lubricant). If the hand can gently press, it means it is too loose; If the hand cannot press hard, then it is too tight.

Disassemble and replace old and new seals

Relatively speaking, the application effect of new machine seals is better than that of old machine seals, but when the quality or material type of new machine seals is not suitable, dimensional errors can affect the sealing effect. In aggregatable and deeply permeable media, if the static ring is not excessively worn (protruding cracks, detachment, scratches, dents, burrs, and partial wear), and scratches and dents penetrate the entire protruding surface, it is called excessive damage, Try not to disassemble or replace as much as possible. Due to the long-term static state of the stationary ring, polymers and impurities accumulate as a whole, resulting in a better sealing effect.