Mechanical seal design steps
First, in the design of mechanical seals, we should first understand and analyze the conditions and requirements for the use of seals.
(1) Design conditions for mechanical seals
1 Use the pump type of the shaft seal and the part of the shaft seal.
2 working parameters: including pressure, temperature, peripheral speed (speed and shaft diameter).
3 medium properties: including the density of the medium, viscosity, saturated vapor pressure, particle size and concentration of solid particles, corrosivity (pH) and crystallization, polymerization, decomposition and other conditions.
4 host working characteristics: continuous operation, number of starts and stops, cycle, steering.
5 Host working environment: installed indoors or outdoors, ambient atmosphere, ambient temperature and pressure, including environmental conditions such as pollution, corrosion, vibration, available coolant, lubricant, etc. and shaft seal position.
(2) Requirements for mechanical seals
1 Determine the allowable leakage, leakage point, leakage direction (internal leakage or external leakage) of the mechanical seal to ensure safe and reliable operation.
2 The service life of mechanical seals reflects the comprehensive results of wear resistance, corrosion resistance, temperature resistance and vibration resistance of mechanical seals. For petrochemical enterprises, it requires long life of shaft seals of machine pumps to ensure continuous production of process equipment.
3 mechanical seals reliability and stability.
4 The mainframe limits the dimensions and structural conditions of the mechanical seal.
5 save energy and material consumption.
6 operation and stability of the production process.
7 materials and prices.
Secondly, according to the design requirements and conditions, determine the design plan, including selecting the structure type and determining the material according to the requirements and conditions, determining the main dimensions of the auxiliary devices and seals such as lubrication, cooling, rinsing, filtering, and the selection of the existing series of products. Comparison. Then determine the material of the main components, design and calculate the main components and auxiliary devices such as sealing pair, auxiliary seal, elastic element, fasteners, etc. Finally, draw the whole set of drawings and propose the main technical conditions.
Second, the structural selection of mechanical seals
(1) According to the working parameters p, v, t
1 Working pressure P The working pressure p of the seal refers to the pressure of the sealing medium in the sealed chamber. Since the medium pressure in the sealed chamber is not equal to the medium pressure in the pump, the pressure of the sealing medium may be higher than, equal to or lower than the pressure of the medium in the pump. Therefore, it is necessary to report the specific structural type of the pump to determine the working pressure of the seal. For example, a single-stage cantilever pump has a balance hole that not only balances the axial force, but also reduces the shaft seal pressure. At this time, the shaft seal pressure is equal to the suction pressure plus the resistance loss through the balance hole: before and after the ring Balance the axial force with a balance tube. The shaft seal pressure is equal to the balance tube inlet pressure plus the balance tube resistance loss. If the throttle sleeve is used, the bottom sleeve resistance loss should be added: the back blade is used to reduce the shaft seal pressure. The pressure of the centrifugal action is estimated approximately, and the pressure loss of the throttle sleeve can also be estimated based on the flushing pressure and the given flushing amount; for the multistage pump, it should be determined according to the interstage arrangement, and the approximate distribution is estimated by the number of stages. Intermediate pressure: For the case of balancing the axial force with measures such as a flat disc or a balance drum, the suction pressure plus the balance tube resistance loss can be considered. See the books and literature for details. However, the exact data can only be determined by relying on the test values ​​of the same type of machine.
Generally, when the medium has high viscosity, good lubricity, p below 0.8 MPa or low viscosity, poor lubricity, and p below 0.5 MPa, non-equilibrium can be used. When p exceeds 15 MPa, it is difficult to achieve the sealing requirement in the single-end balanced structure. It is possible to use a series multi-end multi-stage seal and step down the pressure step by step.
The 2nd speed v usually represents the peripheral speed of the seal at the peripheral speed of the average diameter of the sealing surface. According to the magnitude of the v value, it is determined whether the elastic element rotates with the shaft to adopt a spring rotation type or a spring static type. When the peripheral speed is lower than 20~30m/s, the spring rotary seal is used, and the peripheral speed is high-speed sealing at 25m/s. In order to avoid strong vibration caused by the unbalanced mass of rotation, in order to avoid the influence of centrifugal force and stirring heat, the spring should be static. Sealed. High weekly speed and high pv value, the intermediate ring mechanical seal can be used to reduce the peripheral speed and thus reduce the value. Hydrostatic seals or hydrodynamic seals can be used when the pressure and peripheral speed are relatively high.
3 Temperature t The working temperature t is expressed by the temperature of the sealed medium in the sealed box. The material of the auxiliary seal, the cooling method of the sealing surface and the auxiliary system are usually determined according to the temperature. For easy vaporization medium, the working temperature should be considered to be lower than the boiling point of 14 °C, otherwise the liquid film cannot be guaranteed, and measures need to be taken to improve the working conditions.
Generally, mechanical seals with a medium temperature of 80 to 150 ° C are sealed for high ordinary thermal products (Pursing), and mechanical seals with a temperature higher than 150 ° C are called high temperature mechanical seals, and corresponding cooling measures should be taken. Typically the auxiliary sealing element material is temperature limited. Generally, the seal with a temperature lower than -20 °C is a common low temperature mechanical seal, and the seal with a temperature lower than -50 °C is a cryogenic mechanical seal. Mechanical seals operating at high and low temperatures require not only measures in terms of materials and construction, but also cooling and insulation measures in terms of auxiliary measures. The temperature of the sealing medium is below 80 °C. Generally, the mechanical seals are suitable. The auxiliary sealing ring is usually a nitrile rubber O-shaped sealing jaw. The temperature of the sealing medium is -50~+150°C. According to the corrosive strength of the medium, the sealing ring of fluororubber, silicone rubber or PTFE forming filler (O-shaped, square, V-shaped, wedge-shaped, etc.) is selected. When the temperature of the sealing medium is lower than -50 °C, the rubber and PTFE will produce low temperature embrittlement. When the temperature of the sealing medium is lower than 150 °C, the rubber and PTFE will have high temperature aging, so the metal bellows should be used for sealing.
(2) Selection according to the nature of the medium
For the less corrosive medium, the built-in mechanical seal can be used, and the end force state and the medium leakage direction are more reasonable than the external type; for the strong corrosive medium, it is difficult to solve due to the selection of the spring in the elastic element, then the externally mounted machine is selected. Sealed or Teflon bellows seal, but generally only suitable for medium pressures in the range of 0.2 to 0.3 MPa. For products that are easy to crystallize, easy to solidify and high viscosity, a single large spring rotary structure should be used, which is better than a multi-point small spring structure because it is not easy to block. For flammable, explosive and toxic products, double seals, cascade seals or multi-stage seals with sealant (separator) must be considered to ensure absolute sealing. It must be noted that for seals with flushing or blocking fluids, the properties of the media should be considered on a case-by-case basis, depending on the nature of such fluids.
(3) According to the shaft diameter selection
Series products generally have a shaft diameter greater than 120 mm and are called large shaft diameter seals, while seals smaller than 25 mm are called small shaft diameter seals with a general seal. Non-series products require additional consideration. (Source: Hebei Innovation Sealing Material Co., Ltd.) Tel. 15631678132 Contact: Business Manager
Our main products are: packing series: carbon packing, PTFE packing, graphite packing, high water-based packing, aramid packing, PTFE split wire packing, PTFE packing, expansion PTFE packing, asbestos packing, carbon fiber packing, butter cotton yarn packing, oil-impregnated cotton packing, linseed packing, canvas reel packing, ceramic fiber packing, nylon packing, composite fiber packing, Ceramic packing, and other products.
Two: various gasket series: PTFE gasket, toothed gasket, asbestos gasket, ladle gasket, metal wound gasket, graphite gasket, high strength graphite composite gasket, PTFE gasket gasket, rubber flange Pad, asbestos manhole pad, asbestos hand hole pad, special seal ring for autoclave, asbestos flange pad, etc.
Three: rubber products: silica gel, fluorine rubber, nitrile rubber, neoprene and other special-shaped products.
Four: PTFE products series: PTFE rods, belts, membranes, mats, etc.
Five: insulation products: glass wool, rock wool, aluminum silicate, silicate, rubber, phenolic and other insulation materials.
Products are widely used in national defense, power, machinery, petroleum, chemical, metallurgy, paper, shipbuilding, transportation, aviation and other fields of the national economy. Our company wholeheartedly welcomes new and old customers to negotiate business with us by means of "quality for survival, reputation for development".
Great Wall Texture PU Sandwich Panel
Sandwich Panel,Composite Insulated Panels,Composite Siding Panels,Great Wall Texture Pu Sandwich Panel
Jinan Zhengtang Insulation Decoration Material Co.Ltd , http://www.ztwallsiding.com