The sealing problem of moving equipment is always accompanied by the operation of the equipment. Today, we have specially sorted out various sealing forms, application scope and characteristics commonly used in mobile devices, so that everyone can have a deeper understanding of the sealing problem.
First, packing sealing.
Packing seal according to its structural characteristics can be divided into:
Soft packing seal
Hard packing seal
Molded packing seal
1, soft packing seal
Flexible packaging type: packaging
The filler is usually made of flexible wire and filled in the sealed cavity through a strip with a square cross-sectional area. The gland produces a pressing force to press the packing, forcing the packing to press on the sealing surface (the outer surface of the shaft and the sealing cavity), generating a radial force with sealing effect, thus playing a sealing role.
Flexible packaging applications:
The sealing effect of the filler is determined by the manufacturing material selected for the filler. Generally speaking, the materials used for packing are limited by the temperature, pressure and pH value of the working medium, and the surface roughness, eccentricity and linear velocity of the mechanical equipment where the packing works also require the selection of packing materials.
Graphite packing is one of the most effective products to solve the problem of high temperature and high pressure sealing. Corrosion resistance, good sealing performance, stable and reliable performance.
Aramid packing is a kind of high-strength organic fiber, and woven packing is impregnated with PTFE emulsion and lubricant.
PTFE filler is made of pure PTFE dispersion resin, which is first made into green sheets and then twisted and woven into filler. It can be widely used in valves and pumps in foods, pharmaceuticals, papermaking, chemical fibers and other media with high cleanliness requirements and strong corrosiveness.
2, hard packing seal
There are two types of hard packing seals: split ring and split ring.
Second, the mechanical seal
Mechanical seal always consists of two parts: the rotating part (yellow part) and the stationary part (orange part), and two relatively moving dynamic and static torus surfaces become the main sealing surfaces of the seal.
Mechanical seal, also known as face seal, refers to a device that keeps contact with at least one pair of face perpendicular to the rotating shaft and slides relatively under the joint action of fluid pressure, elastic force (or magnetic force) of compensation mechanism and auxiliary seal to prevent fluid leakage.
Third, dry gas seal.
Dry gas seal, that is, "dry running gas seal", is a new type of shaft end seal with slotted sealing technology, which belongs to non-contact seal.
Features:
Good sealing performance, long service life, no need of sealing oil system, low power consumption, simple operation and low operation and maintenance cost. Dry gas seal, as a maintenance-free sealing system that does not need any oil to cool and lubricate the sealing end face, is replacing floating ring seal and labyrinth seal and becoming the main seal of high-speed centrifugal compressor shaft seal in petrochemical industry.
Applicable occasions:
High-speed fluid machinery, such as centrifugal compressor, is suitable for the condition that a small amount of process gas leaks into the atmosphere without harm, such as air compressor and nitrogen compressor.
Fourthly, labyrinth seal.
Labyrinth seal is to set a number of annular sealing teeth around the rotating shaft in turn, and a series of intercepting gaps and expansion cavities are formed between the teeth. When the sealing medium passes through the gap of the labyrinth, it will produce throttling effect to prevent leakage.
Labyrinth seal is the most basic seal form between the stage and shaft end of centrifugal compressor. According to different structural characteristics, it can be divided into four types: smooth type, sawtooth type, step type and honeycomb type.
1, smooth labyrinth seal
There are two structures of smooth labyrinth seal: integral type and plug-in type. Simple structure and easy manufacture, but poor sealing effect.
2. Sawtooth labyrinth seal
Sawtooth labyrinth seal is also divided into two structures: integral type and plug-in type. The structural characteristics of this labyrinth seal are that the protruding heights of the sealing teeth are different, the high and low teeth are staggered, and the mating shaft surface is a special concave-convex groove. The structure that the high and low teeth are matched with the concave and convex grooves makes the smooth sealing gap zigzag, thus increasing the flow resistance and improving the sealing efficiency. However, it can only be used for cylinders or partitions with horizontal split faces, and the sealing body should also be made into horizontal parting.
3. Step labyrinth seal
Stepped labyrinth seal is similar to smooth labyrinth seal in structure, but the sealing effect is similar to sawtooth labyrinth seal, which is often used in impeller cover plate and balance plate.
4. honeycomb labyrinth seal
The sealing teeth of honeycomb labyrinth seal are welded into honeycombs, forming an expansion chamber with complex shape. Its sealing performance is superior to the general sealing form, and it is suitable for occasions with large pressure difference, such as the balance disk sealing of centrifugal compressor. The manufacturing process of honeycomb labyrinth seal is complicated, the strength of the sealing sheet is high, and the sealing effect is good.
Verb (abbreviation of verb) oil seal
Oil seal is a self-tightening lip seal with simple structure, small volume, low cost, convenient maintenance and small resistance moment. It can not only prevent the leakage of medium, but also prevent the invasion of harmful substances such as dust. It has certain compensation ability for wear and tear, but it is not resistant to high pressure, so it is generally used in chemical pumps in low-pressure situations.
Vi. Dynamic sealing
When the chemical pump is running, the pressure head generated by the auxiliary impeller balances the high-pressure liquid at the outlet of the main impeller, thus achieving sealing. When parking, the auxiliary impeller does not work, and a parking sealing device must be equipped to solve the possible leakage of the chemical pump when parking. The auxiliary impeller has the advantages of simple sealing structure, reliable sealing and long service life, and can be watertight during the operation of chemical pumps, so it is often used in pumps conveying impurity media.
Seven, spiral seal
Spiral seal is also a form of dynamic seal, which is to process a spiral groove on the rotating shaft or the sleeve of the shaft and fill a sealing medium between the shaft and the sleeve. The rotation of the shaft makes the spiral groove produce a conveying effect similar to that of a pump, thus preventing the leakage of sealing liquid. Its sealing ability is related to spiral angle, pitch, tooth width, tooth height, tooth action length and the gap between shaft and sleeve. Because there is no friction between seals, the service life is long, but due to the limitation of structural space, its spiral length is generally short, so the sealing ability is also limited. When the pump is used at a reduced speed, its sealing effect will be greatly reduced.