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Sealing test of soft filler of water pump combination
Packing seal has the characteristics of wide source of packing, easy processing, low price, reliable sealing and simple operation, so it has wide application scope. In recent years, with the development of sealed packing, packing seal has been greatly improved in material, structure and various characteristics, so the packing seal in the machinery industry has been more widely used, and good economic benefits have been obtained.

Working mechanism of 1 packing seal

In mechanical industry, packing seals are mainly used for dynamic seals. It is often used as centrifugal pump, compressor, vacuum pump and mixer's rotating shaft seal. In the design selection of packing seal, the working conditions of mechanical equipment should be considered as the main factors. The selection of packing should consider the following conditions:

(1) there is a certain plasticity. Under the action of compacting force, it can generate certain radial force and contact with the tight shaft.

(2) enough chemical stability, no pollution of the medium, filler is not soaked in medium, impregnating agent in the filler is not dissolved by medium, and the packing itself does not corrode the seal surface.

(3) the self lubrication property of the filler is good, wear resistance and friction coefficient are small.

(4) when the shaft has a small offset, the filler should have enough floating elasticity.

(5) simple manufacturing and convenient filling

Therefore, it is necessary to adjust the compaction of the packing to make the lubricants in the packing run out for some time and then squeeze out some lubricants, and compensate the relaxation of the compacting force caused by the volume change of the filler. Of course, this often squeezing fillers will eventually dry up the impregnant, so it is necessary to regularly replace fillers. In addition, in order to maintain the liquid film and carry out the frictional heat, it is necessary to intentionally leak a small amount of leakage.

Problems in the use of 2 coil root fillers in the use of water pumps

The shaft seal of water pump usually adopts oil impregnated asbestos packing or oil immersed cotton yarn packing. The oil immersed asbestos disk has the advantages of heat resistance, good softness and high strength, but it also has the fatal shortcomings: rough surface after the formation, large friction coefficient, leakage phenomenon, and the lubricant that has been immersed for a long time is easy to lose. Oil soaked cotton packing will become very hard in the long-term immersion in water, and because the expansion coefficient, the larger friction. In actual production, there is often such a situation: the new repair equipment, the starting operation shaft seal condition is good, but not long, the leakage amount is constantly increasing, the adjustment of the cover and replacement of packing work is also gradually frequent, running less than a cycle, the sleeve is worn into vase like, when serious will also appear shaft sleeve grinding, and water seal ring behind the replacement of the root of the coil root. It is rotten and can not act as a seal.

In general, the packing has the following shortcomings (1) the direct contact with the shaft of the packing and the shaft, and the relative rotation, causing the wear of the shaft and the shaft sleeve, so the shaft sleeve must be replaced regularly or unregularly. (2) in order to dissipate the friction heat between the packing and shaft or shaft sleeve, the packing seal must maintain a certain amount of leakage and it is not easy to control. (3) the friction between the packing shaft and the shaft or shaft sleeve causes the effective power of the motor to be reduced, and the power consumption can sometimes reach an alarming ratio of 5% to 10%. In general, the packing has the following shortcomings: from the principle of packing seal, there are three leaks in the fluid in the seal cavity: one is the leakage of the fluid through the fiber material; the other is leakage between the packing and the packing box, and the third is leakage between the packing and the surface of the shaft. Therefore, the most important measures to prevent the leakage of water pump are: (1) the rational selection of sealing packing; (2) the design of a reasonable seal cavity to adjust the appropriate sealing pressure.

Design of 3 combination soft packing seal

The design of the packing cavity is shown in Figure 2. A good sealing soft material is filled in the packing chamber. It is made up of carbon fiber, high purity graphite, polytetrafluoroethylene and organic sealant. It is heat-resistant, 18 - 200 - C, the maximum pressure is 0.7Mpa, the maximum line speed is 8m/s, the corrosion resistance is strong, and the medium pH range is 4-13. It is mainly applied to water medium. The soft filler state is clay like, low friction coefficient and small molecular attraction between the mixtures. During the operation of the shaft, the fiber in the packing will be twisted on the shaft and rotates with the shaft to form a "rotation layer". The "rotation layer" plays the role of protecting the shaft or sleeve, avoiding the wear of the shaft sleeve and reducing the power consumption; with the gradual increase of the diameter of the "rotation layer", the winding ability of the shaft to the fiber will gradually weaken, and the shaft is not entangled with the shaft and fills with the filling.  The inner wall of the cavity remains relatively stationary, and a "shear layer" is formed in the cavity of the filler. At this time, the friction shear zone of the relative rotation movement exists in the middle of the filler rather than between the packing and the shaft. In addition, the polytetrafluoroethylene packing material is pressed on both ends of the injected filler, and the mixed soft packing is pressed by using the packing end ring. In order to make the shaft in the high-speed rotation process, the mixed soft filler is not crushed out, specially designed and processed the spiral groove in the packing cavity and the cover. It is worth noting that the direction of the spiral groove on the two ends of the packing should be opposite, so that the shaft rotation can produce the inward pumping effect of the mixed packing and effectively prevent the splash of the packing.

4 water pump test

After the design and fabrication of the combined packing is completed, the test is carried out on the pump test stand. The design conditions of the test stand are as follows: the motor speed is 1500r/min, the working pressure is 1MPa, the medium is clear water, the medium temperature is at room temperature.

The filling process is carried out according to the following steps: (1) cleaning the packing chamber, checking whether there are any scratches and burrs on the shaft surface, so as to ensure the roughness of the shaft.

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