Encountered a mechanical seal issue
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This post was last edited by tianyewei on 2018-1-24 08:26. I encountered a problem with the mechanical seal: it’s used to drive the mixer, with a rotation speed of around 700 rpm. The pressure inside the main tank during operation is 4 bar; I applied 5 bar of pressure in the siphon tank (which has cooling coils), using nitrogen to maintain this pressure. The mechanical seal is of the double-end type with a diameter of 100 mm, and its working height is relatively short. The siphon tank is equipped with cooling systems, and the cooling water used is deionized water. The rotating ring is made of antimony-doped graphite, while the upper and lower stationary rings are made of silicon carbide. During operation, the pipes and tanks could be touched by hand without feeling hot, but in reality, the mechanical seal did not last long – the water level in the tank dropped after a short time, and the seal at the atmospheric side started leaking. The water also became cloudy. When the stationary ring seals were removed, they were found to be severely deformed. I don’t understand why this happens (the customer specified that oil cannot be used as the sealing fluid). The lifespan of the mechanical seal is very short – sometimes around two months, but other times just two or three days. Additionally, would it be better to replace the rotating ring with one made of conventional resin-doped graphite, or to incorporate silicon carbide into it?
It’s my own problem; please give some help. I hope the knowledgeable netizens can offer some guidance
The mixer rotates at 700 revolutions per minute – such a high speed. What is the sealing compression ratio, and what is the cooling method? Considering reducing the temperature.
Carefully inspect the removed old machine seal (try to keep it) to determine where the problem lies; check the tolerances and play of the mixing shaft, as well as whether there are sliding bearings on the mixing base – measure the clearance to see if it is within the acceptable range Friction pairs are prone to deformation; try using a solid alloy or a solid silicon carbide ring! Try changing the seal ring material to PTFE!
The effect of thermal siphon is not very noticeable; it would be good to have a sealed cross-sectional view. The sealed flushing pipeline should ensure a continuous upward flow, which helps bubbles to be discharged upward. Check whether the contact surface of the mechanical seal is ensured to be submerged in the liquid. As shown, the contact point between the stationary and rotating rings is located at the center of the flushing hole, ensuring that there is always liquid on the contact surface. In some cases, the sealing flush holes are drilled at a lower position, with the ring surface in contact with the upper edge of these holes. When a pipe is connected to the flush interface, due to the thickness of the pipe walls, it may be possible for air to remain trapped in the area where the ring surfaces are in contact. The liquid film on the sealing surface is unstable, which may lead to dry grinding. High temperatures after dry grinding can cause the O-ring to age and deform.
Is this the first time you’ve seen a friction pair lubricated and cooled with ionized water? ! In this way, no oil film can be formed in the friction pair; it’s no wonder that the stationary and rotating rings deform due to high temperatures!
A liquid film is formed at the friction pair; it isn’t necessarily an oil film. Since the water pump uses a mechanical seal, where does the oil film come from?
The material of the static ring seal was not chosen correctly, right?