| The mechanical seal, also called the end face seal, relies on the pressure of the spring and the sealing medium to produce a suitable pressing force on the contact surface of the rotating moving ring and the stationary ring, so that the two end faces are closely fitted. A very thin oil film is maintained between the end faces. When the medium passes through, the resistance is large, which prevents the liquid from leaking, thereby achieving the purpose of sealing, and at the same time lubricating the moving ring and the stationary ring. Adjusted well can be completely leak-free. 1 mechanical seal features The main advantage of mechanical seal is that the seal is reliable. During a long period of use, there is little leakage; the service life is long, generally it can be used for about 5 years; the maintenance period is long. However, the mechanical seal structure is complex, the manufacturing and installation precision is high, the cost is high, and the technical requirements for the maintenance personnel are Seeking high, because the mechanical seals used on the oil pipelines are all built-in type, the oil pump is often dismantled when repairing mechanical seals, and the workload is large. Therefore, it is very important to ensure the mechanical seal work is reliable and extend the service life of the mechanical seal. 2 Mechanical seals are prone to problems The main problems that are prone to mechanical seals during use are excessive leakage and excessive temperatures. Touch the mechanical seal gland by hand. If it cannot stay on it, the temperature is too high. The amount of leakage should not exceed 60 drops/min per side. If it is flowing in a line, it indicates that the leakage is too large, and it can be determined whether to observe the operation; if the oil is sprayed outward, it should be stopped immediately. 3 Control measures taken 3.1 Guarantee the quality of parts The mechanical seal must be tested for sealing performance before leaving the factory and has a certificate of conformity. After long-term operation of the mechanical seal, the moving ring and the static ring wear, the spring and shaft corrosion wear, the sealing rubber ring wear, aging, deformation, etc., can cause leakage of the seal, and new parts must be repaired or replaced. The sealing surfaces of the moving ring and the stationary ring shall not have cracks, corners, scratches, pitting, flashing and eccentric wear, and scratches and pitting may not penetrate the entire sealing end face. If the repaired static and dynamic ring is used, the height of the boss of the static and dynamic ring is not less than 3 mm, and the height of the single boss is not less than 1 mm, so as not to affect the heat dissipation. After the moving ring is installed, it should be able to move flexibly on the shaft. After pressing the moving ring to the spring, it should be able to bounce back freely, keeping the static and vertical rings parallel and parallel. The specifications of the static and dynamic ring sealing rubber ring are in accordance with the drawings. The surface shall not be damaged, uneven thickness and uneven hardness. The sealing rubber ring shall be replaced during overhaul. The outer surface of the spring is clean and free of rust and should be used before use. Length profile detection and pressure test, the pressure difference of each set of springs in the specified compression length should meet the requirements, and the pressure error of each set of springs in the specified compression length meets the requirements. The free length tolerance does not exceed 0.5mm, and the compression amount cannot be too large or too small, requiring an error of ±2mm. The sealing sleeve and the pump shaft cannot be of the same material, and the parallelism tolerance of the end faces on both sides and the non-perpendicularity tolerance to the axis do not exceed ±0.20 mm. 3.2 Ensure adequate cooling and lubrication Adjust the opening of the cooling line regulating valve to ensure that the mechanical seal cooling line is unobstructed. When the tank pump is opened, the venting valve should be drained to clean the gas in the sealed chamber. 3.3 Guaranteed installation accuracy When disassembling the mechanical seal, the static and dynamic rings should be cleaned, and a small amount of clean lubricating oil should be applied to the friction auxiliary surface. The high pressure end and the low pressure end should be taken into consideration. When installing the static ring gland, the force should be even to prevent the pressure deviation. Check with the feeler gauge. The deviation between the upper and lower positions is not more than 0.05mm. Check the matching clearance between the gland and the outer diameter of the shaft. The circumference should be even. More than 0.1 ram. The radial runout of the pump shaft where the mechanical seal is installed does not exceed 0.05mm. Before putting the pump cover and sealing the end cover, carefully check the installation and positioning dimensions of the mechanical seal. If the positioning size does not meet the requirements, the steel pad can be adjusted between the bushings, but the steel pad has high precision and the thickness difference does not exceed 0.01mm. . Measuring the radial runout of the mechanical gland and the end face bounce of the sealing surface meet the requirements. For the mechanical seal that has been run, if the gland is loose and the sealing surface is moved, the static and dynamic ring parts must be replaced, and should never be re-tightened for continued use. Because the original trajectory of the friction pair changes after such loosening, the sealing performance of the contact surface is easily destroyed. 4.4 Adjusting the end face specific pressure End face specific pressure is an important parameter related to sealing performance and service life, and it is related to the sealed structure type, spring size and medium pressure. If the end face is too large, the friction pair will be added; if the pressure is too small, it will leak easily, and the manufacturer will give a suitable range. The specific pressure is generally 3 to 6 kg/cm2. Adjusting the specific pressure is to adjust the compression size of the spring. The free length of the spring is indicated by A. The spring stiffness (the load that is generated when the unit compression is generated) is k, and the specified specific pressure is indicated by P. These are the parameters given by the manufacturer. The size after compression is denoted by B, then P / (A-13) = k, resulting in 13 = Ae / k, which is the size of the spring after compression. If the size of the spring after installation is too large, the thickness of the adjustment pad can be increased between the spring seat and the spring. If the size is too small, the thickness of the adjustment is reduced, and the thickness of the adjustment pad is measured by a micrometer. |
According to Professor Hu Xiaosong, Ph.D. supervisor of the School of
Food Science and Nutritional Engineering, China Agricultural University,
Instant Noodles are often criticized by people who think eating is not
good for health mainly for the following reasons:
First, high fat content, because most of the instant noodles are fried way to dry the noodles. However,
Professor Hu pointed out that compared with French fries, hamburgers
and other instant noodles in the fat content is not very high, with an
average of about 16% -18% of fat, of which 11% are palm oil, that is, Human health beneficial vegetable oil, and a hamburger in an average
of about 30% of fat, nearly twice as much as instant noodles.
Second, contain certain additives. Professor
Hu said that when it comes to additives we talk about change, I think
it is not conducive to the health of the material, which is the concept
of a misunderstanding. The food industry can not do without thickeners, stabilizers and other
additives, the country allows the use of, are strictly tested to prove
harmless to the human body, we can rest assured that consumption.
Third, many people are concerned about the problem of acrylamide. Professor
Hu pointed out that all starch-based foods in the high-temperature
cooking (over 120 ℃) will produce this carcinogen, therefore, there
are french fries, instant noodles, there must be.
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