subject: Why Is "taking The Time" Is The Biggest Mechanical Seals "the Enemy"? [print this page] Typically, the mechanical seals design life of at least 8060 to 1 000 hours. In the meantime, seal ring in a soft (mostly a carbon graphite manufacturing) in Taiwan was first worn bearing wear, the wear volume between the 2 ~ 3mm, then smooth the surface although the basic, but spring can not compensate or the specific pressure is too low (due to the sealing surface wider) loss of ability of the seal, the other part is basically no wear. This seal failure is a natural wear and tear, called the aging failure. Clearly, this wear and tear is inevitable. In practice, some of the wear of sealing ring is far from reach 2 ~ 3mm, but the sealing surface will have a scar (not smooth), or other component failure, life has not yet reached the expected value, usually such prominent onset of fault known as the accidental failure. Statistics show that the aging failure is the failure of 10% to 30%, while the number of the fault belongs to the latter. Therefore, to reduce and prevent the accidental failure to extend the seal on the lifetime and improve the average water sealing technology has great practical significance. To reduce the incidents of failure, we must first clarify the causes of the incident. To answer this question, we first survey of the United States. The report summarizes the 24 U.S. chemical plants and petrochemical plants heat pump (232 above) the type of seal failure and the percentage. By the table can be seen from the stationary ring bit and pump cavitation, etc. should be taking the time to type pump failure, the two together account for 45%. In addition, severe wear of graphite ring (30%), secondary seal failures (25%) and thermal crack (52%), and also for taking the time to pump or pump after taking the time to failure increased due. That is in addition to corrosion (28%) and sealing their own poor performance, the other most of the seal failure are directly or indirectly related with the pump for taking the time. So we can say that high-temperature pump seal failures caused mainly by taking the time. The so-called taking the time to failure, that is, internal steam pump hole (or cavitation) produced intense hydraulic shock, lead seal axial oscillation phenomenon caused by seal failure.
Cavitation is the process for taking the time and conditions and medium properties (such as media saturation vapor pressure and light fraction content) determined the structure can not avoid any seal. Some people think that using static welded metal bellows mechanical seals to avoid taking the time and cavitation damage, it is not correct. Real cause cavitation is still not clear just from the stationary ring by the static pressure difference between inside and outside the proceeding to consider the problem of the conclusions. Is worth noting that the "question and answer tool that is mentioned in the United States 191 24 factory seal failure statistics, almost all with welded metal bellows seal, cavitation, and taking the time to a very high ratio, further illustrates the fact that, steam Water erosion is the result of impact or shock, rather than due to static pressure difference. from the sealing structure can not avoid cavitation production, but can reduce cavitation damage seal. First of all, should reduce the occurrence of frictional heat, the heat appears to make lost in time. So the diameter of the sealing surface to minimize the width of a narrow selection of material to try to have good self-lubrication, the friction Friction coefficient group. To prevent the ring from the static position, should be floating static Central to fixed. ring stopper, and only allowed after the seal faces wear compensation to the static ring direction, refused to reverse direction (spring side) of the string too large. This of course increases the installation of degree, but the set can be used cartridge seal to resolve that prior to the sealing of all (including the gland and sleeve) after pre-installed package put something good. can balance the seal, the introduction of equipment from the point of view, no matter how much pressure process flow pump, almost have adopted a balanced mechanical seals. analysis because, in addition to lower pV value, reduce heat generation, but also reduces the ability of cavitation break. balanced seal ring, the direction of displacement to the spring at 2mm Right, if use of container seals, the value can be reduced, if cavitation is not to be away from the ring bit (not from the reseller and turning anti-), also reduce the damage of dynamic seals, reducing the performance of the seal damage. In addition, the increase in diameter or box made of dense conical cavity, excluding gas and mechanical impurities on the beneficial, after all, a measure for consideration.
