Some customers purchase sealing rubber components and, despite the sealing components appearing to be of good quality, they lose their sealing effect. What is the main cause of this problem?

1. Opening of the sealing faces

When repairing a mechanical seal, 85% of seal failures are not caused by wear, but by leakage that occurs before wear develops.

When the sealing faces open, solid particles in the medium enter the sealing faces under the action of liquid pressure. After the sealing faces close, these solid particles become embedded in the surface of the soft ring (usually the graphite ring), effectively forming a “grinding wheel” that damages the surface of the hard ring.

Because the rotating ring or rubber component is secured to the shaft (shaft sleeve), when the shaft moves axially, the rotating ring cannot make contact in time, causing the sealing faces to open. The delayed closing of the sealing faces then allows solid particles to enter between them.

At the same time, solid particles may also be present between the shaft (shaft sleeve) and the sliding components, affecting the sliding of the rubber component or rotating ring (a common failure in relative dynamic sealing points). In addition, the medium may produce crystalline deposits at the friction area between the rubber ring and the shaft (shaft sleeve), and solid substances may also accumulate around the springs. All of these conditions can cause the sealing faces to open.

2. Overheating

Because heat is generated on the sealing faces, the operating temperature of the rubber component should be lower than the design specification. The operating temperatures of fluoroelastomer and PTFE are 216℃ and 216℃ respectively, while that of nitrile rubber is 162℃. Although these materials can withstand relatively high temperatures, the heat generated by the sealing faces may cause the rubber ring to continue vulcanizing, eventually resulting in loss of elasticity and leakage. (Cold brittleness should be considered in cold zones.) Heat may also cause the medium between the sealing faces to crystallize, such as through carbon deposits, causing the sliding components to stick and the sealing faces to become bonded. Some polymers may become charred due to overheating, while some fluids may lose their lubricating properties or even ignite.

In addition to changing the condition of the medium, overheating also accelerates its corrosion rate. It can cause deformation of metal components, cracking of alloy surfaces, and cracks in certain coatings. A balanced mechanical seal should be selected during design to reduce the specific pressure and prevent overheating.

3. Excessive tolerances

Correct assembly tolerances are essential for installing a mechanical seal. The shaft (shaft sleeve) must have suitable surface roughness and correct dimensions, but manufacturers rarely provide tolerance data, even though this information is critical for installation. The dimensional accuracy and geometrical tolerances of the mechanical seal must comply with the drawing requirements. Excessive deviations will cause premature seal failure.