With the development of science and technology, the application range of fluid machinery and fluid engineering continues to expand, high temperature sealing, sealing temperature, paper super low temperature, strong corrosion, inflammable, explosive, toxic, radioactive medium, high pressure sealing, high vacuum sealing and sealing with various impurities such as suspended particles in the medium have come into being. To ensure the reliability and service life of seal is one of the most important subjects in sealing research, design, manufacture and application.
The function of the seal is to prevent leakage. Sealed parts are called seals, referred to as seals. A more complex seal, especially one with an attached system, is called a sealing device.
The fluid seal includes a fluid static seal and a fluid seal. The seal between the opposite stationary surfaces (i.e., the sealing surface) is called a static seal; the joint of the opposite motion is called a dynamic seal. The fluid machinery and fluid engineering, sealing is indispensable in many parts, machinery and equipment, although the seal is generally only small proportion of the whole machine, but often directly determines the safety, reliability and durability of the whole machine and even the whole equipment. Therefore, it becomes an important index to evaluate the quality of many mechanical products. Especially in the petrochemical industry, transportation, handling and storage of many fluid is flammable and explosive, corrosive and poisonous kind of medium, once the seal failure, even failure, the consequences are serious, it will affect the quality of products, pollute the environment, endanger the surrounding people's health, will lead to serious ecological environment fire the explosion, casualties, and even large area, long time the deterioration of the former Soviet Union at Norian nuclear fuel leak and cause serious accidents, is a profound lesson.
In addition, for the nuclear power plant's circulating pump, high pressure polyethylene compressor, poly propylene combustion reactor and other equipment, where the seal is a decisive technology.
Sealing is also directly related to the conservation of material and energy. Among the total energy consumption, the power, machinery and fluid machinery account for the largest proportion. And these machines due to leakage and leakage, resulting in volumetric efficiency is often very low, the loss can reach more than 10% of the total power, small machines and even 40~50% situation. The friction power consumption of some sealing devices is not small. Friction losses such as piston rings account for 2/3 of the entire engine friction loss. The power consumption of the centrifugal impeller seal may reach 1/3 of the total shaft power. As for improving the seal, stop running, take, drop and leak, reduce material loss. It is a direct benefit. Such as oil refinery with the use of packing seal, each pump leakage volume of about 10m3 years, the promotion of the use of mechanical seal, in the amount of oil below 0.1m3, with 1000 pumps per annum on saving the nearest 1000m3, if all kinds of fluid machinery are used properly or advanced seal technology in saving material and energy saving the benefits will be very considerable.
In the use of fluid machinery operation, sealed maintenance and repair work, accounted for a considerable proportion of the petrochemical industry, seal failure is the main reason causing unplanned shutdown, according to statistics, more than 60% of the non planned parking events are related with fault sealing. Take the pump as an example, the maintenance of fluid dynamic seal and fluid dynamic seal almost accounts for about 50% of the total maintenance. More than half of the faults of rocket engines are caused by sealing failures or failures. In this sense, it can be said that sealing is one of the weakest links of machinery and equipment. Therefore, advanced and reliable sealing technology is also an important link of automation, continuous production and civilized production.
Structural features of mechanical seals
In order to meet the needs of different working conditions, there are many different types of mechanical seals.
1, according to the sealing end of the logarithm, divided into single end, double end and other mechanical seals.
Single end - only one pair of sealing faces in the seal. The utility model has simple structure and is a common mechanical seal type.
Double end face with two pairs of sealing ends in the sealing device. The utility model has the advantages of complicated structure, and is suitable for occasions of strong corrosion, inflammable and explosive, poisonous and harmful medium and vacuum.
2 、 according to the sealing fluid, the pressure on the sealing end surface is unloading or not unloading, and can be divided into balanced and unbalanced mechanical seals.
Balance - the sealing fluid acts on the end face of the seal, unloading or unloading all parts of the pressure.
Non balanced type - the pressure acting on the end face of the sealing fluid does not unload.
The balance type applies to the mechanical seal in the medium and high pressure condition; the unbalanced type is suitable for the mechanical seal under the low pressure condition.
3, according to whether the spring placed in the sealed fluid, divided into spring, built-in and spring, external mechanical seal.
Spring is built-in - spring is placed in sealed fluid.
Spring is external - spring is placed outside the sealed fluid.
The inner end of the spring is in good state of force, the leakage is small, and the cooling and lubrication are good. Therefore, in addition to corrosive media, it should be possible to use built-in structure.
4, according to the number of springs in the compensation structure, divided into single spring type and multi spring type mechanical seal.
Single spring type - there is only one spring in the compensating mechanism. The utility model is used for occasions with light load and small shaft diameter.
Multiple springs - there are multiple springs in the compensating mechanism. For larger axle diameter. The spring force on the end face of the seal face is more uniform, but the diameter of the spring wire is small, and the corrosion affects the spring greatly.
5, according to whether the compensation mechanism rotates with the axis, divided into rotating and stationary mechanical seals.
Rotation -- the compensating ring rotates with the shaft.