Author:Site Editor Publish Time: 2020-10-29 Origin:Site
In the selection of mechanical seals, working conditions must be considered, including the appropriate form and material of the seal, and the installation structure. The working conditions that need to be considered generally include: temperature, pressure, and medium. It also needs to consider the selection of the mechanical seal in combination with the characteristics of the equipment itself.
According to different working conditions and media properties, mechanical seals include high temperature and low temperature resistant mechanical seals, high pressure resistant and corrosion-resistant mechanical seals, particle resistant mechanical seals, and mechanical seals suitable for light hydrocarbon media that are easy to vaporize. Choose mechanical seals of different structure types and materials according to different uses.
The main parameters of the selection are: sealed cavity pressure (MPA), fluid temperature (℃), working speed (M/S), fluid characteristics, and effective space for installation and sealing.
Regarding temperature, for example, the operating temperature range of NBR materials is generally -40 to +120°C. If the temperature exceeds 120°C, FKM or even PTFE should be considered. Low-temperature conditions are relatively rare. Generally speaking, cold-resistant NBR should be considered at -20 to -40°C. Normal NBR materials will harden the material under low-temperature environments and cause leakage, such as railway locomotives in the northern winter. Such problems often occur.
As for the pressure, it affects the form of the seal to be selected. Generally speaking, the low pressure and medium pressure of mechanical seals will not have much problem with rubber or PU seals. However, an impact pressure must be considered. For example, when starting in construction machinery, its impact pressure is much greater than the normal working pressure when it is closed. Therefore, HBY or SPGW with a pressure resistance of up to 70MPA is often used as the main choice seal. PTFE composite seal is also a commonly used choice.
The problem of the medium is relatively simple. Just need to pay attention to some special minor issues, such as the metallurgical industry often use water-glycol and phosphate hydraulic oil. Sometimes, although the working temperature is not high, you still need to be very careful when choosing the material. When hydraulic oil is the latter, FKM should be used.
The selection of the mechanical seal is very important, and it must be selected based on the equipment itself. For example, if you need to be responsive and precise control, of course, you should choose the stuffongley circle. If high reliability is required, Hunger's GD1000K series or NOK's SPGW are often chosen. For another example, construction machinery working in the field often has impacts and low-temperature weather when working, and its dust ring will use an exposed metal framework to avoid falling off. Cylinders, compressor piston rings, high-pressure oil seals, and oil pumps in various scientific instruments require special structures to meet the requirements.
1. According to the pressure of the sealed cavity, determine whether the sealing structure adopts a balanced or unbalanced, single end face or double end face, etc.
2. According to the working speed, determine the use of rotating or static, fluid dynamic pressure, or non-contact type.
3. According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal circulation protection system such as lubrication, flushing, heat preservation, and cooling.
4. According to the effective space for installation and sealing, it is determined to adopt multiple springs, single springs or wave springs, built-in or exterior-mounted.
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