Views: 2454 Author: Site Editor Publish Time: 2020-07-26 Origin: Site
Packing seals is also known as Gland Packings, commonly known as Packings seals. Packings seals is the oldest sealing structure. In the ancient water-lifting machinery in China, the method of plugging cotton yarn was used to stop the leak. The first steam engine in the world also adopted this seal form. The production and development of oil and natural gas mining technology in the 19th century have led to new developments in materials for packing seals. In the 20th century, packing seals were favored by many industrial sectors because of their relatively simple structure, low price, and wide source.
The felt seals is a sealing structure composed of felt rings filled in the grooves of the casing.
Among the contact sealing devices, felt seals is the simplest one. It is widely used in low-speed, normal-temperature, normal-pressure motors, gear boxes and other machinery, sealing butter and lubricating oil. Felt seals is also suitable for dustproof, but not suitable for gas sealing. When the felt seals is used as a liquid seal, the greater the viscosity of the medium, the better the sealing effect. For liquids with lower viscosity such as kerosene, the effect of the felt seals is very poor. If thick felt is used for felt sealing, the circumferential speed of the shaft is only allowed to be less than 3 meters/second. If high-quality fine felt is used, the speed can be increased by 2-3 times, but not more than 10 meters/second. If the design is proper, and the shaft has high hardness, good surface brightness, and sufficient lubrication, then in some cases, the felt sealing can also work normally at a high speed of 20 meters/second. The operating temperature of the felt seals generally does not exceed 90℃, and the operating pressure is generally an atmospheric pressure. The packing seal wraps the packing between the shaft and the casing (packing box), and then is pressed tightly with a gland and screws. Packing seals are widely used for pump seals (such as water pumps, vacuum pumps, etc.), as a sealing device for liquid or gaseous media.
Packing seals can be used for high temperature and high pressure environment. For example, the sealing pressure of oil-immersed asbestos packing can reach 12 kg/cm, and the medium temperature can reach 250 ℃. But the packing sealing speed is lower. For example, when used in a water pump, the upper limit of its speed is 6 meters/second. This is because the packing is not wear-resistant, and the contact friction surface between the packing and the shaft is large, and the pressure of the packing on the shaft is also large, so heat generation and wear are serious. If the pressure of the sealing medium is high, the screws must be tightened more tightly so that the packing force can be greater, so as to ensure that the high-pressure seals does not leak. At this time, the speed of the shaft must be lowered. It can be seen that pressure and speed are related to each other. When the pressure is low, the speed can be allowed to be higher. If the pressure is higher, the speed must be reduced to meet the requirements of high-pressure sealing. Generally, the reason for packing leakage is due to the high temperature caused by friction, which causes some components in the packing to volatilize or carbonize to form a leakage gap. At this time, a new packing can be replaced to restore its sealing performance. Packing cost is very low, which is inferior to other various high-pressure seals. However, the volume and weight of the packing seals is very large, which is far less compact and lightweight than the graphite seal and the expanding ring seal.
In addition to the above two types of packing seals, there are spring seals, elastomer bellow seals, mechanical seals, etc., you can choose different sealing methods according to the use scenario.
1) Have some flexibility. Under the action of the pressing force, it can generate a certain radial force and tightly contact the shaft.
2) It has sufficient chemical stability. The medium is not contaminated, the filler is not swollen by the medium, the impregnant in the filler is not dissolved by the medium, and the filler itself does not corrode the sealing surface.
3) Good self-lubricating performance. Wear resistance and low friction coefficient.
4) There is a small amount of eccentricity in the shaft, the packing should have sufficient floating elasticity.
5) Simple manufacturing and convenient loading.