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Chemical mechanical seal technology introduced

 

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Regardless of seals, the seals have a common requirement, namely: tight, leak less; reliable, long life; simple and compact structure; easy maintenance; low cost; cheap; interchangeability. For chemical mechanical seal leakage can generally be controlled in the 0.2 ~ 3mL; life in general up to more than one year.

Theory, most chemical mechanical seal, less wear rate in the hydrodynamic lubrication conditions at run time, it means that the seal should always durable, but it was not, the reason usually is the existence of the seal can not be overcome by chance conditions, including: chemical mechanical seal of quality problems; human error (the machine is running error); installation error; flushing system failure; the sharp fluctuations of operating conditions.

1 to determine the mechanical seal damage criteria

1.1 the amount of leakage observed discrimination

1.2 leakage measurement of discrimination

Chemical mechanical seal shaft diameter 50mm, leakage shall not exceed 3mL/min; shaft diameter more than 50mm, 120mm below the amount of leakage shall not exceed 6mL/min.

1.3 leakage definition of discrimination

Normal leak: to meet the requirements and relatively stable leakage. Abnormal leakage: short-term more than the standard leak.

Based on the above three, according to the actual situation, and ultimately concluded that the chemical mechanical seal failure. For example, the newly installed seal in the running-in period, disabled seal is restarted, voltage fluctuations, process status change are likely to produce abnormal leakage of the above, after a period of observation of leakage can be eliminated by sealing still can continue to use, not self-eliminate the need to be demolished check.

2, the chemical mechanical seal failure

2.1 wash. Work characteristics of the chemical machinery, the mutual friction of the rotating ring and stationary ring, and will continue to generate frictional heat, the friction pair temperature, chemical machinery to cause the following: ① friction Vice film evaporation, vaporization caused by dry friction; (2) the friction pair liquid film viscosity decreases, poor lubrication; ③ friction the Vice medium vapor pressure increases, resulting in leakage; ④ accelerate the corrosion medium; ⑤ secondary seal aging, loss of elasticity, and even decomposition; ⑥ The static ring deformation.

In order to eliminate the impact of frictional heat, to ensure the sealing work properly and prolong service life, must be taken to adapt to different media conditions of the chemical machinery cooling, so that the face between the liquid film exists, the grease, which is the basic conditions of the chemical machinery to work properly . Medium containing suspended particles and impurities of the chemical machinery, static ring seal to lose floating solid particles into the friction pair, severe wear of the static ring, the spring loses its elasticity causing seal failure, so take the cleaning liquid or steam cleaned on the friction pair The way to wash or take a filter medium particles and impurities removed in order to ensure the normal operation of the chemical machinery.

Rinse and chemical mechanical failure: the rinse liquid pipeline filter blockage causes the flushing fluid flow; due to the lack of filters, the impurities in the flushing fluid into the sealing surface; washing liquid pipeline check valve leading to process The liquid retrograde into the washing fluid pipes, and impurity particles increase the flushing fluid, led to the use of the flushing liquid chemical mechanical failure.

2.2 Static seal failure. Static seal points leak mostly due to the defects of the ring such as ring size difference is too large or injury, aging deterioration. , Seals done carefully examined and carefully install the static seal can guarantee the quality of design (structure and material selection). The early localization of the chemical machinery, chemical mechanical failure caused by O-ring selection mistakes.

2.3 dynamic seal failure. Dynamic sealing effect theoretically affect mainly the following aspects: ① media impact: medium pressure the higher the leakage the more; low viscosity of the medium than the high viscosity, easy to leak: with particles and ease of scaling media than clean stable easy to leak. Impact ② axis: In general, the more wide-axis is the coarser the sealing surface on the vertical deviation more sensitive, it is more easy to leak; axis of the operation more easy to shimmy, more easy to leak; the higher the speed the more easy to leak. (3) sealed structure: The most important is sealed floating, floating sex best bellows seal best poor, PTFE plastic ring. The ④ sealing face in the manufacture and installation of quality in the face flatness and perpendicularity of the shaft axis of the most important.

2.4 Vibration large. Chemical mechanical seal vibration is too large, and ultimately result in the loss of sealing effect. But often the reason for the chemical mechanical seal vibration large chemical mechanical seal itself reason, the other parts of the pump is the source of vibration, such as shaft design is unreasonable, for processing reasons, the bearing accuracy is not enough, the parallel degree of coupling the radial force, the reason of cavitation phenomena.

3 to improve the sealing effect of the measures of chemical machinery

3.1 running smoothly. Increasingly stable plant operation, there is little change of the stop, start and run conditions, the normal operating procedures for the operation of the pump provides a well-run environment, chemical machinery to reduce damage in harsh dynamic conditions and sudden parking caused by the moment the possibility of damage, thus sealing the life expectancy has increased considerably.

3.2 continuous flushing. Flush, including the work of media self-flushing and relatively clean process solution rinse, rinse the media does not meet the design requirements is an important reason for the leakage of chemical machinery. On the one hand, through targeted inspections, adjustments, the wash medium pressure, flow, temperature meet the design requirements; the other hand, regular cleaning of the filter of the washing fluid and a reasonable increase in the non-return valve on the flush pipe, fundamentally, to avoid flushing causes the seal is broken.

3.3 devices improved. Constantly sum up experience in the operation of the mechanical properties of the pump and other equipment to guarantee, through technical transformation. For example: DA302 tower circulation pump after the replacement of the chemical machinery, frequent instantaneous seal is broken. The reason is that the sealing ring of the pump casing and impeller mouth ring gap between the friction caused by the irregular movement of this friction lead to seal damage to the pump vibration. Sandy Bay after processing with the gap to reach 1.4mm, the premise does not affect the use of the pump performance, so that this problem has been the ultimate solution.

3.4 installation. The practice shows that the prevention of random interference and changing environment to achieve reliable sealing, eliminating the random mechanical seal, seals and the installation of equipment errors became the main reason for seal failure. Sealing has been sufficient to ensure the normal operation of the pump in the servicing intervals, but the installation error and the cause of adverse vibration and shaft and shell unreasonable relative motion are harmful to the pump and sealing, so in order to reduce the shaft vibration and to ensure that the chemical machinery of life, we must ensure that accurate and detailed installation process. Correct assembly tolerance shaft (sleeve) suitable surface roughness and the correct size, carefully measured, careful record of the equipment installation process is to achieve an effective process control. The same time, the maintenance team of the quality of education, training technically effective guarantee.

4, Conclusions

Through the above analysis, it can be concluded with the raising the level of process operation, maintenance quality improvement, spare parts, quality assurance, mechanical seal more and more able to reach its design life of its unexpected failure will be reduced accordingly . At the same time, accidental chemical mechanical seal failure can also be solid theoretical training for staff, skilled operators drill, accurate knowledge of a wealth of accumulated experience and operating procedures to avoid the greatest degree. This is also to ensure the long period of enterprises, economic and efficient operation.

 

 

 
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