Views: 2504 Author: Site Editor Publish Time: 2020-10-10 Origin: Site
Although the common contacting mechanical seal has a wide range of applications, it has its own limitations in a sealed environment. Under the compulsion of modern fluid dynamic pressure lubrication theory, new non contacting mechanical seals have been continuously developed. Therefore, compared with the ordinary contacting mechanical seal, the non-ordinary one can more easily achieve zero leakage or even zero escape of the sealed medium, which completely eliminates pollution to environment.
At the same time, due to the absence of direct solid friction and wear between the sealing end faces, it has the technical advantages of greatly extending service life, significantly improving seal reliability, greatly reducing prices, and significantly improving economic benefits. Therefore, it is one of the cost-effective seals. Today, we will briefly introduce the sealing principle and structural classification of non contacting seal.
Non contacting type is divided into two types: fluid static pressure and fluid dynamic pressure. Fluid static pressure seal refers to a seal that uses externally introduced pressure fluid or the sealed medium itself to produce a fluid static pressure effect through the pressure drop at the end of the seal. Fluid dynamic pressure seal refers to a seal that uses the relative rotation of the end surface to generate a fluid dynamic pressure effect, such as a spiral groove end surface seal.
The fluid static pressure mechanical seal is to introduce the sealing liquid with sufficient pressure to balance the end face compression load or the sealed self-medium between the seal end faces, so that it forms a static pressure fluid film with sufficient lubrication and cooling effect on the seal end face. Let's take a look at the sealing structures of several typical fluid static pressure mechanical seals.
The self-pressing groove type is formed with thousands of holes on the outer periphery of the static ring and communicated with the annular groove opened on the end surface. The fluid film on the end face has high rigidity and stable working performance, but it is necessary to prevent clogging of small holes. The self-pressing step type is processed into a step shape on one end face. The rigidity of the fluid film on the end surface is a little lower, and the grinding process on the end surface is more difficult. One end surface of the self-pressing cone type is a convergent cone surface, and its liquid film rigidity is lower than that of the self-pressing groove type and the self-pressing step type, and the fluid static pressure is distributed parabolically along the radius. All three types rely on the pressure of the medium itself to form a static pressure fluid film on the end face. The thickness of the fluid film changes with the fluctuation of the medium pressure. It is suitable for the situation where the working pressure of the medium is relatively stable.
The fluid lubricating structure of the externally pressing groove type is similar to the self-pressing groove type, except that the outer circumferential opening of the static ring is not in communication with the medium, but the sealing liquid is introduced from the outside into the end surface primary groove to establish the static pressure fluid film. This structure is suitable for the situation where the working pressure of the medium fluctuates, but a fluid with good lubricating performance and compatible with the medium should be selected as the sealing liquid. At the same time, an additional sealing liquid circulation adjustment system must be equipped.
The fluid static pressure mechanical seals require that the input lubricating medium pressure is equivalent, so the control is more complicated, and now have fewer applications. Now the gland packings we use most are mainly spring seals, elastomer bellow seals and pump seals.