What are the methods to extend the service life of container mechanical seals?

What are the methods to extend the service life of container mechanical seals?

The sealing of machines working in liquid media typically relies on the liquid film generated between the dynamic and static friction surfaces of the liquid substance. Therefore, maintaining a liquid film between the friction surfaces is a necessary condition for ensuring the smooth operation of the machine seal and extending its service life.

Several types of strengthening lubrication structure

Port 1 slotting:

It is difficult for high-pressure and high-speed machinery to maintain a liquid film between the friction surfaces, and the liquid film is often destroyed by the frictional heat generated by high pressure and high speed. In this case, strengthening lubrication through grooving is very effective. Both the dynamic and static rings can be grooved, usually set on more wear-resistant materials. The dynamic and static rings cannot be grooved at the same time, as they will reduce the lubrication effect. In order to prevent dirt or debris from entering the friction surface as much as possible, the liquid flows in the direction of centripetal force (loss) and is sealed. The groove should be set on the static ring to prevent centripetal force from introducing dirt into the friction surface. On the contrary, when the liquid flows in the opposite direction of centripetal force (internal flow), the groove should be set on the moving ring, and centripetal force is beneficial for removing dirt from the groove.

The friction surface has small grooves in the shape of squares, wedges, or other shapes. The groove should not be too many or too deep, otherwise it will increase leakage.

2. Pressure lubrication:

The so-called static pressure lubrication refers to immediately introducing pressurized lubricating fluid into the friction surface for lubrication. The introduced lubricating fluid is provided by independent liquid sources such as hydraulic pumps. Using this type of pressure lubricant to resist fluid pressure in machinery is commonly referred to as a hydrostatic seal.

The sealing of gas media should take measures to create gas film lubrication, such as gas negative pressure controllable film sealing or solid lubrication, using self-lubricating materials as dynamic or static rings. As long as conditions permit, gas medium standards should be converted into liquid substance standards as much as possible for lubrication and sealing.

3-axis axial force:

Generally speaking, the core of the moving ring, the core of the stationary ring, and the axis of the shaft are all in a straight line. If the port core of one of the moving or stationary rings deviates from the axis by a certain distance, the ring can continuously introduce lubricant during rotation, providing lubrication between the sliding surfaces.

It should be pointed out that the axial force specification should not be too large, especially for high pressure. Axial force will cause uneven pressure at the port, resulting in uneven damage. For high-speed seals, dynamic rings should not be used as axial force rings, otherwise the equipment will vibrate due to the balance of centripetal force.

According to different standards, the friction between the motion of the machine seal and the static ring may exhibit the following situations:

(1. Semi liquid lubrication:

There is liquid at the concave groove on the sliding surface, and a thin liquid film is maintained in the middle of the contact surface, so thermal wear is good because the liquid film between the moving and stationary rings has interfacial tension at the inlet and outlet, which limits liquid leakage.

(2. Thoroughly lubricate with liquid:

When the pressure between the moving and stationary rings is insufficient, and the gap widens, the liquid film thickens, and there is no solid contact, so there is no friction. However, due to the large gap between the moving and stationary rings, the sealing effect cannot be exerted, resulting in severe leakage. In practical applications, this situation is generally not allowed to occur (except for controllable membrane machine seals).

The working conditions between machine seals and static rings are mostly in the state of boundary lubrication and semi liquid lubrication, and semi liquid lubrication can achieve sealing effect under relatively satisfactory frictional resistance, namely damage and heat.

Machine seals can work in a better lubrication environment, but factors such as medium characteristics, pressure, temperature, and rolling rate also need to be fully considered. However, selecting appropriate motion, static ring intermediate pressure, reasonable lubrication structure, and improving the quality of motion and static ring friction surfaces are key factors to ensure effective sealing operation.

(3 Dry Friction:

There is no liquid entering the sliding friction surface, so there is no liquid film, only dust and oxide layer and their absorbing gas molecules. When the motion and static ring are running, the result must be that the friction surface heats up, the damage worsens, and leakage occurs.

(4 Boundary lubrication:

When the pressure between the moving and stationary rings increases or the ability of the liquid to form a liquid film on the friction surface is weak, the liquid will be squeezed out from the gap. Due to uneven surface but uneven height, contact damage occurs when raised, but the concave surface maintains liquid wetting properties, resulting in boundary lubrication. The wear and heat levels of boundary lubrication are moderate.