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You are here : Mechanical face seal
Axial mechanical face seal is a seal, referred to as mechanical seals, also known as seal, is a common rotary shaft seal. And other forms of seal (such as soft-packing gland), compared with a low leakage, friction and wear, long service life, reliable, no maintenance and a series of advantages. Therefore, in modern industrial production in a wide range of applications, especially the application of pump devices become more prevalent and important occasions using more than 85% of the mechanical seal pumps. In addition, the mechanical face seal in a number of high-pressure, high temperature, high-speed, flammable, explosive and corrosive media, such conditions have also made good use of effects.
Mechanism of mechanical seal sealing the main focus of hydrodynamic effects. Either contact or non-contact type mechanical seal mechanical seal, and hope that through the hydrodynamic bearing effect to improve the sealing ability to reduce friction, wear and leakage and improve the reliability of sealing to extend the seal life. Determine the mechanical seal in the theory of hydrodynamic effects is based on the famous British scientist Reynolds (Reynolds) 1886 was proposed in the basic equation of lubrication theory - Reynolds equation. Mechanical seal on the hydrodynamic effect of the early 60s from the beginning of this century, has been made a lot of research results, but there are still some unresolved issues, the study focused on the following three aspects.
1 flat seal in the effect of hydrodynamic
Standard balanced and unbalanced mechanical seal is usually working under boundary lubrication conditions, the friction coefficient is generally f = 0.07 ¡À 0.03. In this condition, although the gap exists in the sealed liquid layer, but the liquid layer may partly interrupted, and almost no pressure and, therefore, no significant viscosity effect. Friction due to high heat, even with the best heat transfer and cooling characteristics of face matching material, the pressure - speed limit is very low PV limit value. To improve the sealing of the PV value limit, expand the use of surface seal, seal face must be by means of hydrodynamic fluid film effects. Denny (1961) first observed by testing the two seal faces is a thin film of the isolation. Since then, in order to better understand the working mechanism of mechanical face seals, many researchers have done a lot of work, which mostly involved in the mechanism of fluid film pressure. Seal end surface of the fluid film pressure depends on face shape and size of the gap, the fluid film geometry and thickness.
Despite flat seal a thin layer of fluid film can bear some of the load, but in general, this thin fluid film is not complete, there is direct contact with some asperity. In the high-pressure, high-speed and low viscosity conditions, direct contact asperities will be the main bearing part of the friction generated at this time sealing and wear large, may lead to a sharp rise in seal face temperature, liquid gasification, as well as seal failure. In order to overcome the contact type mechanical seal problems, proposed non-contact type mechanical seal - hydrodynamic and hydrostatic mechanical seal.
2 hydrodynamic mechanical seal in the effect of hydrodynamic
Hydrodynamic non-contact type mechanical seal is a seal, the sealing surface is a layer of full thickness of several microns for the fluid film are separated from the fluid friction and lubrication of the state is pure conditions. These seals used in high-pressure differential, high speed and poor lubrication medium seal (gas, boiling liquid, cryogenic liquid, etc.) conditions.
In the hydrodynamic seal in order to face friction wedge open, use the kinetic energy of the sealing surface. In the stationary seal face contact, to eliminate leakage. When the sealed high-speed rotation, the sealing surface of thin fluid film will separate from the limited leakage, or no leakage. In order to maintain the sealing surface of the non-contact condition, the sealing surface of the liquid medium or gas gap dielectric fluid film to bear the compressive load, the fluid film should have the fluid stiffness.
In the hydrodynamic seal friction surface in the separation and compression under load, depending on the liquid under the action of the friction part is pressed from the convergence of the gap and generate force to achieve. Convergence towards the sliding velocity direction paragraphs gap sealing surface can also be slotted, openings or steps to produce. The structure is the most widely used step-Ray out, slant-type and spiral groove face seals.
Spiral groove face seal for sealing liquid can be used for the upstream pumping seal. In the upstream pumping seal, the seal is equivalent to a small flow of high-pressure pump, it will seal a small amount of liquid from the low pressure side of the pump along the spiral groove to the high side of the sealed room. Salant and put forward to consider pumping spiral groove face seals swim in the analytical model of cavitation. Salant and other studies in the literature groove (shallow groove) throughout the entire sealing surface of the case, and the shape of the groove (slash slot and spiral groove) on the impact of leakage.
Mechanism of mechanical seal sealing the main focus of hydrodynamic effects. Either contact or non-contact type mechanical seal mechanical seal, and hope that through the hydrodynamic bearing effect to improve the sealing ability to reduce friction, wear and leakage and improve the reliability of sealing to extend the seal life. Determine the mechanical seal in the theory of hydrodynamic effects is based on the famous British scientist Reynolds (Reynolds) 1886 was proposed in the basic equation of lubrication theory - Reynolds equation. Mechanical seal on the hydrodynamic effect of the early 60s from the beginning of this century, has been made a lot of research results, but there are still some unresolved issues, the study focused on the following three aspects.
1 flat seal in the effect of hydrodynamic
Standard balanced and unbalanced mechanical seal is usually working under boundary lubrication conditions, the friction coefficient is generally f = 0.07 ¡À 0.03. In this condition, although the gap exists in the sealed liquid layer, but the liquid layer may partly interrupted, and almost no pressure and, therefore, no significant viscosity effect. Friction due to high heat, even with the best heat transfer and cooling characteristics of face matching material, the pressure - speed limit is very low PV limit value. To improve the sealing of the PV value limit, expand the use of surface seal, seal face must be by means of hydrodynamic fluid film effects. Denny (1961) first observed by testing the two seal faces is a thin film of the isolation. Since then, in order to better understand the working mechanism of mechanical face seals, many researchers have done a lot of work, which mostly involved in the mechanism of fluid film pressure. Seal end surface of the fluid film pressure depends on face shape and size of the gap, the fluid film geometry and thickness.
Despite flat seal a thin layer of fluid film can bear some of the load, but in general, this thin fluid film is not complete, there is direct contact with some asperity. In the high-pressure, high-speed and low viscosity conditions, direct contact asperities will be the main bearing part of the friction generated at this time sealing and wear large, may lead to a sharp rise in seal face temperature, liquid gasification, as well as seal failure. In order to overcome the contact type mechanical seal problems, proposed non-contact type mechanical seal - hydrodynamic and hydrostatic mechanical seal.
2 hydrodynamic mechanical seal in the effect of hydrodynamic
Hydrodynamic non-contact type mechanical seal is a seal, the sealing surface is a layer of full thickness of several microns for the fluid film are separated from the fluid friction and lubrication of the state is pure conditions. These seals used in high-pressure differential, high speed and poor lubrication medium seal (gas, boiling liquid, cryogenic liquid, etc.) conditions.
In the hydrodynamic seal in order to face friction wedge open, use the kinetic energy of the sealing surface. In the stationary seal face contact, to eliminate leakage. When the sealed high-speed rotation, the sealing surface of thin fluid film will separate from the limited leakage, or no leakage. In order to maintain the sealing surface of the non-contact condition, the sealing surface of the liquid medium or gas gap dielectric fluid film to bear the compressive load, the fluid film should have the fluid stiffness.
In the hydrodynamic seal friction surface in the separation and compression under load, depending on the liquid under the action of the friction part is pressed from the convergence of the gap and generate force to achieve. Convergence towards the sliding velocity direction paragraphs gap sealing surface can also be slotted, openings or steps to produce. The structure is the most widely used step-Ray out, slant-type and spiral groove face seals.
Spiral groove face seal for sealing liquid can be used for the upstream pumping seal. In the upstream pumping seal, the seal is equivalent to a small flow of high-pressure pump, it will seal a small amount of liquid from the low pressure side of the pump along the spiral groove to the high side of the sealed room. Salant and put forward to consider pumping spiral groove face seals swim in the analytical model of cavitation. Salant and other studies in the literature groove (shallow groove) throughout the entire sealing surface of the case, and the shape of the groove (slash slot and spiral groove) on the impact of leakage.
