Analysis of causes of mixer seal damage
Thread Content
Multiple polymerization kettle stirrers, the stirring shaft is about 8 meters long, the number of revolutions is about 100, the motor power is 55kw, the internal blades have five layers, the pressure of the polymerization kettle is -0.1 to +0.3Mpa, the mechanical seal is Dandong Clone, the mechanical seal journal is 140mm, the flushing plan is PLAN54 The mixer stops running for about 16 hours each time and starts again after the next batch of materials is fed. The number of starts is about 200 times per year. Damage occurs one after another after running for about a year. After disassembly, the cross section of the dynamic and static rings is analyzed to have large and small pits. Experts, what is the cause? Is it because during the reaction process, the material quality is uneven, the dynamic load during stirring and rotation is relatively large, and the dynamic and static rings of the machine seal are collided? Is there any solution?
1. The viscosity and temperature of the material need to be provided before we can answer it later. 2. Whether the mixing structure has a bottom support (commonly known as the bottom swing) and a middle support. These two supports are generally PTFE sleeve structures and whether they should be replaced every six months. 3. Whether the polymerization tank is cleaned regularly to improve reaction efficiency. 4. Whether the mixing structure rack has a single pivot point or a double pivot point depends on your structure. The probability of a double pivot point is higher. 5. Count the current fluctuations during a stirring cycle and analyze the time period with the largest current fluctuations. Refer to my immature suggestion, go to the site to analyze more, make a list, and find a more professional manufacturer to analyze it.
Whether the quality of the dynamic and static ring materials is imported or domestic is also very important and has a lot to do with its lifespan.
However, there are other similar kettles in the device category, which also start and stop frequently, and the mechanical seals are from the same manufacturer. The only difference is that the kettle contains the medium that has completed the reaction, which may be of uniform quality. In addition, the number of blades in the kettle is only 2-3, and the motor power is smaller. The mechanical seals in these kettles are not damaged.
The material is nitrile latex, with a viscosity similar to that of milk. The normal reaction temperature is more than 40 degrees. The bottom is supported and made of PEEK. The polymerization kettle is basically cleaned once a month, but it is steamed before each cleaning. The cooking temperature is 90 degrees, and then a manhole is opened for cleaning.
The superposition of the starting shock caused by frequent starts and stops and the thermal expansion and contraction caused by temperature changes will make the working environment of the mechanical seal even worse. Under this synergistic effect, the stress distribution on the surface of the dynamic and static rings will be more complex, and the local stress concentration may be more serious, thus accelerating the damage of the sealing surface and leading to the formation of potholes.
Many phenomena of mechanical seals need to go deep into the microscopic level. The pits shown at the macro level actually belong to the later stage. The early stage is "bubbles", that is, there are bulges on the surface of the sealing end face. After a period of time, cracks will appear in the blisters, and the fragments will fall off, leaving pits. In fact, this is a mechanical process. During the startup process, high shear force will act on the sealing surface, causing blistering, micro-cracks and pits. ； This process will be repeated every time it is started, eventually leading to fatigue failure of the seal face. If the viscosity of the fluid in contact with the sealing end face is high at this time, the failure will occur faster.