Deep groove ball bearing seals and sealing the description of the principle of

Kunshan Bearing: O-rings O-ring seals referred to, is a cross-sectional shape is circular rubber ring. O-ring hydraulic and pneumatic systems most widely used as a seal. O-ring has a good sealing performance, both for static sealing, can also be used movable seal; not only can be used alone, but also a lot of the basic modular seal component. Its use is very wide, if the material is properly selected, to meet a variety of media and a variety of sports terms.
O-ring seal is an extrusion, extruded seal the basic principle relies on the seal is elastically deformed, causing the seal contact pressure of the contact surface, the contact pressure is greater than the internal pressure of the sealed medium, does not occur leakage, otherwise leak.
O-ring design, improper use will accelerate its damage, loss of sealing performance. Experiments show that the various parts such as seals designed, simply increase the pressure, and will not cause damage to the O-ring. In the high pressure, high temperature operating conditions, O-ring damage is mainly due to the O-ring material and permanent deformation of the sealing O-ring is extruded into the gap caused by the O-ring gap bite level in motion when distortions.
1, permanent deformation
Since the O-ring material is a synthetic rubber is a viscoelastic material, so the amount of the initial setting compression and rebound clogging after prolonged use, it will gradually be lost permanently deformed and eventually leak. Disappearance of permanent deformation and elastic O-ring sealing performance lost the main reason, the following is the main reason causing permanent deformation.
1) compression ratio and the amount of stretch clutch bearing the permanent deformation
O-ring used for making various formulations of rubber in a compressed state, the compression stress relaxation phenomenon is generated at this time, the growth of the compressive stress decreases with time. Use of the longer, the greater the compression ratio and the amount of stretch, the stress relaxation caused by the rubber decrease the greater the stress, lack of flexibility so that the O-ring, loss of sealing capacity. Therefore, the allowable conditions of use, to lower the compression ratio is desirable. Increase the cross sectional dimensions of the O-ring is to reduce the compression ratio the easiest method, but this will bring an increase in structure size.
Should be noted that, in calculating the compression ratio it is often overlooked when the O-ring in the assembly caused by stretching a cross-sectional height is reduced. O-ring cross-sectional area change is inversely proportional to the change of its circumference. Meanwhile, the role of the tension, O-ring cross-sectional shape will change, on the performance of its height reduced. In addition, under the action of surface tension, O-ring outer surface becomes more flat, ie, section height slightly reduced. This is also the O-ring compression stress relaxation of a performance.
O-ring section deformation degree, also depends on the O-ring material hardness. The same amount of the stretching, the hardness of the O-ring, the cross-sectional height greater decreased, from this point of view, should be selected according to the conditions of use as a low hardness material. The liquid under pressure and the tension of the rubber material of the O-ring will gradually plastically deformed, the cross-sectional height is reduced accordingly, resulting in the final loss of sealing capability.
2) temperature and O-ring between the relaxation process
With O-ring temperature is another important factor of permanent deformation. Temperatures will accelerate the aging of the rubber material. The higher the operating temperature, O-ring compression is greater. When the permanent deformation greater than 40%, O-ring sealing ability lost leak. The compression deformation of the O-ring is formed of a rubber material in the initial stress value, as the O-ring of the relaxation processes and the action of temperature decrease gradually decreased so disappear. Working temperature minus the O-ring, the initial compression may decrease due to rapid temperature decrease or disappear completely. -50 ~ -60 ℃ in the case of low-temperature rubber material resistant to completely lose the initial stress; even low temperature resistant rubber material, this time is not greater than the initial stress of 20 ℃, 25% of the initial stress. This is because the O-ring compression depends on the initial linear expansion coefficient. So, select the initial amount of compression, it must ensure that due process and the temperature drops the relaxation caused by stress after falling still sufficient sealing capability.
The temperature at minus work O-ring, special attention should be rubber materials recovery index and deformation index.
In summary, the design should try to ensure that the O-ring with a suitable working temperature, or the selection of high resistance, low temperature O-ring materials to prolong life.
3) medium working pressure and permanent deformation
The pressure of the working medium is caused by permanent deformation of the O-ring of the main factors. Modern hydraulic equipment operating pressures are increasing. Long high pressure causes the O-ring seal permanent deformation. Therefore, the design should be based on the choice of appropriate pressure working pressure rubber material. The higher the pressure, the use of high hardness and resistance to be higher performance.
In order to improve the withstand voltage of the O-ring material properties, to increase the elasticity (especially at low temperatures to increase the elastic material), reduce material compression, generally require improving material formulation, adding a plasticizer. However, a plasticizer, an O-ring, a long soak in the working medium, the working medium can be gradually plasticizer absorption, resulting in volume contraction O-ring, the O-ring and may even have a negative compression (i.e. In the O-rings and seals the surface to be a gap between). Therefore, in calculating the amount of compression and the O-ring mold design should be fully taken into account the amount of shrinkage. Such that the pressing of the O-ring seal in the working medium for 5 to 10 days and nights still maintain the necessary dimensions.
O-ring material compression rate and temperature. When the deformation rate of 40% or more, that there is a leak, so that the heat resistance of several plastic limit of the material: NBR 70 ℃, EPDM rubber 100 ℃, fluorine rubber 140 ℃. So countries on the O-ring makes provision for permanent deformation. Chinese standard rubber O-ring at different temperatures are shown in Table dimensional change. O-ring of the same material, at the same temperature, the cross-sectional diameter of the O-ring pressure large
In the oil situation is different. Since this time the O-ring is not in contact with oxygen, so greatly reducing the adverse reaction. Combined with another material usually causes a certain degree of swelling rubber, the compression due to temperature-induced deformation rate would be offset. Thus, in the oil greatly improved heat resistance. With nitrile rubber, for example, its operating temperature up to 120 ℃ or higher.