Quality Inspection Process of Mechanical Sealing

Mechanical seal is a sealing device composed of two sealing elements (stationary ring and rotating ring) with smooth and flat surfaces that are perpendicular to the axis and rotate relative to each other. It relies on the pressure of the sealing medium to generate appropriate compressive force on the contact surface (end face) of the rotating and stationary rings in order to tightly bond the two end faces and maintain an extremely thin liquid film between them to achieve the sealing purpose. This liquid film plays a role in lubrication and balance by exerting liquid dynamic pressure and static pressure.

Cleaning and inspection of mechanical seals

• The working principle of mechanical seals requires that there be no impurities inside the mechanical seal. Before assembling the mechanical seal, thoroughly clean the rotating ring, stationary seal ring, shaft sleeve, and other components of mechanical seal.

• Check whether there are scratches, cracks, and other defects on the surface of the rotating and stationary seal rings is one of the most important parts of mechanical seal. These defects will cause serious leakage of the mechanical seal. If conditions permit, special tools can be used to check whether the sealing surface is flat. If the sealing surface is not flat, pressure water will enter the sealing surface of the rotating and stationary seal rings of the assembled mechanical seal, causing the rotating and stationary seal rings to separate and the mechanical seal to fail. If necessary, a fixture can be made for hydraulic pressure testing before assembly.

• Check whether there are any defects that affect the sealing of the dynamic and stationary seal ring seats, such as defects on the mating surface of the dynamic and stationary seal ring seat and the sealing ring.

• Check whether the compensating spring of the safematic mechanical seal is damaged or deformed and whether the stubbornness coefficient has changed.

• Check whether there are defects such as burrs and grooves on the sealing shaft sleeve.

• Clean and check whether there are any defects such as cracks and air holes on all sealing gaskets, and measure the diameter of the gasket to see if it is within the tolerance range.

• Mechanical seals with pumping mechanisms also need to check whether there are defects such as cracks or broken lines on the screw pump's helix.

Dimensional verification of mechanical seal assembly technology

• Measure the size of the sealing surface of the rotating and stationary rings. This data is used to verify the radial width of the rotating and stationary rings. When different friction materials are used, the radial width of the hard material friction surface should be 1-3mm larger than that of the soft material. Otherwise, the sharp corners of the hard material end face will embed in the end face of the soft material, causing damage to the mechanical seal function.

• Check the clearance between the dynamic and stationary rings and the shaft or shaft sleeve. The inner diameter of the stationary ring is generally 1-2mm larger than the shaft diameter, and for the rotating ring, in order to ensure floatability, the inner diameter should be 0.5-1mm larger than the shaft diameter to compensate for the vibration and deflection of the shaft. However, the clearance cannot be too large, otherwise, the sealing ring of the rotating ring will be stuck, causing damage to the mechanical seal function.

• Verification of the tightening force of the mechanical seal. The so-called safematic mechanical seal tightening force is also known as the end face specific pressure. The end face specific pressure should be appropriate. If it is too high, the friction surface of the mechanical seal will heat up, accelerate end face wear, and increase friction power. If it is too low, leakage is easy to occur. The end face specific pressure is determined during the mechanical seal design, and we can only determine it by measuring the tightening force of the mechanical seal during assembly. The usual measurement method is to measure the vertical distance from the installed static ring end face to the gland end face, and then measure the vertical distance from the dynamic ring end face to the gland end face, and the difference between the two is the tight force of the mechanical seal.

• Measure the length of the compensation spring is not changed. Spring performance changes will directly affect the mechanical seal end face than the pressure. In general, the length of the spring will be shortened after a long period of operation, compensation springs in the mechanical seal on the moving ring will also be deformed because of centrifugal force.

• Measure the length of the static ring anti-rotation pin and the depth of the pin hole to prevent the pin from being too long static ring can not be assembled in place. This situation will damage the mechanical seal.

Mechanical seal moving ring and static ring end face grinding

• After removal of the moving mechanical seals ring, grinding process, first rough grinding, then fine grinding, polishing conditions can be.

• Rough grinding, choose 80 ~ 160 # size of abrasive, first grinding away processing traces. Then use more than 160# abrasives for fine grinding to make the finish meet the design requirements. Carbide or ceramic dynamic ring needs to be polished by polishing machine after fine grinding. The strength of the polishing machine can be used M28 ~ M5 boron carbide. After polishing to reach the mirror surface. Ceramic ring available M5 agate powder fine grinding after polishing with chromium oxide.

• Graphite filled PTFE static ring, because the material is soft, available kerosene, gasoline or water fine grinding, no need to add abrasive. In the process of running together can also be self-research, so the requirement of finish is not too high.

• The method of grinding, there is a grinding machine can be ground on the grinding machine, no grinding machine can be used in the flat glass on the figure of eight manual grinding method.