Filler seal has a wide source of filler, easy processing, low prices, reliable sealing, easy operation and so on, so the scope of application is broader. In recent years, with the development of sealing packing, packing sealing has been greatly improved in material, structure and various characteristics, so packing sealing in the machinery industry has been more widely used, and achieved good economic benefits.
First, the working principle of packing seal
Stuffing seals in the machinery industry are mainly used as dynamic seals. Commonly used for centrifugal pumps, compressors, vacuum pumps, rotary shaft seal mixer, seal design in the choice of the mechanical equipment should be the working conditions as the main consideration, the choice of filler should consider the following conditions:
1, a certain degree of plasticity, under the action of compression can produce a certain radial force and contact with the close axis.
2, have sufficient chemical stability, do not pollute the medium, the filler is not swelled by the medium, the impregnating agent in the filler is not dissolved by the medium, and the filler itself does not corrode the sealing surface.
3, filler self-lubricating performance is good, wear-resistant, small friction coefficient.
4, the shaft there is a small amount of offset, the filler should have sufficient floating flexibility.
5, easy to manufacture, easy to fill
For this reason, it is necessary to adjust the degree of packing of the packing frequently so that the lubricant in the packing runs out for a period of time and then some lubricant is squeezed out, and at the same time, the packing pressure is relaxed due to the volume change . Of course, this often squeeze the filler, the impregnator will eventually dry up, so regular replacement of the filler is necessary. In addition, in order to maintain the liquid film and take away the frictional heat, it is necessary to deliberately allow a small amount of leakage at the packing.
Second, packing the pump in the use of the existing problems
Pump seal commonly used oil asbestos packing or oil-impregnated cotton packing. Oil asbestos packing with heat resistance, good softness, high strength, but it also has a fatal flaw: knitting surface roughness, friction coefficient, there is a leakage phenomenon, in addition to the use of a long immersion lubricant easy to drain. Soaked cotton yarn packing in the water will become very hard to soak for a long time, and because of the large coefficient of expansion, larger friction. In actual production, it is often the case that the newly-built equipment has a good shaft seal at the beginning of operation, but it does not take long before the amount of leakage increases and the work of adjusting the gland and changing the filler is also frequent and inoperable One cycle, the sleeve has been worn into a vase-shaped, serious cases will occur when the bushings worn, and replace the water seal ring behind the roots have been decayed, can not play the role of seal.
In general, the packing has the following disadvantages: (1) The packing packing directly contacts with the shaft and relatively rotates, resulting in wear of the shaft and the shaft sleeve. Therefore, the shaft sleeve must be replaced periodically or irregularly. (2) In order to make the friction between the packing and the shaft or shaft sleeve promptly dissipated, the packing seal must maintain a certain amount of leakage, and not easy to control. (3) Friction between the packing and the shaft or sleeve causes the motor to reduce its effective power, consume electric energy, and sometimes even reach an astonishing proportion of 5% -10%. In general, the packing has the following disadvantages: From the principle of packing sealing, there are three channels through which the fluid can leak in the sealing cavity: one is that the fluid leaks through the fiber material; the other is leakage from the packing and packing Leakage between the box; the third is leakage from the filler and the shaft surface. Therefore, to prevent the pump leakage is the most critical measures: (1) a reasonable choice of packing; (2) a well-designed sealed chamber, adjust the appropriate sealing pressure.
Third, the combination of soft packing seal design
Design of the filler chamber structure shown in Figure 2. Filler cavity filled with a good sealing soft material, which is made of carbon fiber, high purity graphite, PTFE, organic sealants and other components. It heat -18 ℃ ~ 200 ℃, the maximum pressure of 0.7Mpa, the maximum linear velocity of 8m / s, corrosion resistance, the applicable medium PH value range of 4 to 13, mainly for aqueous media. This soft filler is in the form of a masonry with a low coefficient of friction and low molecular attraction between the mixtures.
During operation of the shaft, the fibers in the filler wrap around the shaft and rotate with the shaft to form a "rotating layer," which serves as a protective shaft or bushing to prevent shaft sleeve wear , Reducing the power consumption; as the "rotating layer" diameter increases, the winding capacity of the shaft will be gradually weakened, not wrapped with the shaft, and remain relatively static with the inner wall of the packing chamber in the packing chamber to form a " Shear layer "where the frictional shear zone of the relative rotational motion is present in the middle of the filler instead of between the filler and the shaft. In addition, both ends of the injected filler are pressed into the PTFE braided filler, and the braided filler end ring is used to compress the mixed soft packing. In order to enable the shaft to rotate at a high speed, the mixed soft packing is not crushed and thrown out. The spiral groove is specially designed and manufactured in the packing cavity and the gland. It is noteworthy that the spiral grooves on the two ends of the packing should be opposite to each other, Ensure that the shaft rotates to produce a mixed material by the inward pumping effect, effectively prevent the filler splashing.
Fourth, the pump test situation
Combination packing design and production is completed, the pump test bench test. Test bench design conditions are as follows: motor speed 1500r / min, working pressure 1MPa, medium water, medium temperature at room temperature.
Filler filling process according to the following steps (1) clear the packing chamber, check the shaft surface for scratches, burrs and other phenomena to ensure that the shaft roughness to meet the requirements of the drawings Ra1.6; (2) with a dial indicator to check the seal Radial parts of the beating, the tolerance should be within the range of 0.03mm-0.08mm. (3) When packing, it is best to take a piece of wood rod with the same size as that of the shaft, to knit PTFE wrapped around the wooden stick, cut off with a knife, and the incision is preferably made into a 45o bevel, Use a wooden half sleeve with the same size as the packing chamber to push the braided packing into the deep part of the cavity and apply a certain pressure to the wooden sleeve with the gland so as to precompress it and keep the braided packing at the bottom of the cavity smooth. (3) into the mixed clay-like filling must be injected into the side while using wooden sleeve compression, and finally re-woven PTFE pressure outside the packing chamber, uniform gland, while hand rotating the spindle, so that after filling Pressure tends to parabolic distribution, and then slightly relax the gland, packing filling is completed. Run the test, just start running, the leakage of intermittent drip-based, when the leak increases, the appropriate tighten the gland bolts. If the heat is too large, relax the bolts. After running normally, the leak basically stops. After 60 hours of trial operation, the packing sealing chamber was opened and the shape of the PTFE ring was braided. The mixed soft packing did not fall out and there was no signs of wear on the shaft.
Fifth, the conclusion
1, the combination of soft packing effectively improve the mechanical efficiency of the pump, reducing the shaft wear. As the packing gland can keep long-term drip, protect the environment.
2, easy maintenance, large leakage, can be injected into the non-stop filling, extending the pump's continuous working time, saving labor and maintenance costs. According to preliminary estimates of energy savings per pump savings of tens of thousands of dollars.
3, modular soft filler has broad application value.