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lip seals and mechanical face seals--performance criteria.

by:DMS Seals     2020-08-02
Maze, stuffing box, lip seal, Bushing, spiral-
Grooveseals and mechanical seals made of a large amount of material are commonly used systems for sealing rotating shafts.
The behavior of the seal is determined by the complex interaction of many factors.
The advantage is usually obtained at a disadvantage price in the direction of the order.
For example, an increase in contact pressure reduces leakage if the roughness remains the same, but wear and friction heat increase.
In contrast, increasing leakage can reduce friction and heat production, but the effectiveness of the device as a seal is reduced.
Similarly, high friction will not only lead to increased wear, but also cause considerable leakage loss due to thermal deformation, or may cause sealing fracture due to thermal stress cracks.
Depending on the application, the sealed rubber should be strong, heat-resistant or resistant to chemical corrosion.
These features must be frequently combined;
Some are compatible with each other.
In any case, good friction performance is required for all sealing rubber applications: high wear resistance and low friction coefficient.
2 The performance of friction and wear seals in dynamic contact seals is characterized by sealing degree, service life, power loss, degree of damage to the contact surface in operation, etc.
Tightness and wear life 【t. sub. w]
The most important feature of sealing performance is performance factor I. (
Dallas Argus 2003)
In addition to the above factors, the temperature will also affect the performance of the dynamic seal, and the temperature depends on the role of the joint.
Given that the temperature has a major effect on the friction effect in the contact area, the leakage is due to the reduction of the contact area and the distortion of the geometry of the friction surface, the increase of deformation, and so on.
In some cases, these factors are interdependent.
According to the combination of the above factors, the conditions of use of sliding contact seals in machinery are very diverse.
Face seal (fig2)
The axial force presses the rotating floating ring 5 on the fixed collision surface 6.
The axial leakage path between the floating ring and the shaft is sealed through static (such as O-ring 7. (Mayer, 1987)[FIGURE 1. a OMITTED][FIGURE 1. b OMITTED][
Figure 2:
The static and sliding surfaces of the traditional stuffing box are effectively interchanged, and if the sealing surface can now be produced more accurately and less than the geometry, and the shaft or shaft sleeve will no longer have any wear and tear, this will be an advantage. (
George Wu, Argesanu, 1996).
In order to compensate for any non-alignment of the sealing surface and the longitudinal thermal expansion of the machine and seal as well as the wear of the sealing surface, the surface seal must contain at least one flexible member, such as diaphragm, bellows, elastic seal or spring 1, 3. (fig2). (
Dallas Argus 2003)
When selecting a sliding material, the operating conditions, the difficulty of manufacturing, and the cost of the material should be taken into account.
Chemical activities and physical and mechanical properties must be considered.
With additional cooling, lubrication and load \"balancing\", select the material with the appropriate thermal conductivity.
The sealing medium also has a considerable impact on the life of the mechanical seal.
Installing the seal on the elastic ring has a very beneficial effect on wear because of the damping effect of the elastic ring.
The durability of the seal is usually not determined by the wear of the seal, but by the aging resistance of any elastic body used.
The increase in contact pressure, friction coefficient, sliding speed and temperature can reduce the life.
Due to the effects of adhesive wear, corrosion wear and erosion wear, not to mention the effects of vibration, temperature and material, can be accumulated.
If it defines the power strength of the friction loss in the contact area as the power ratio of friction and land sliding loss (
George Wu, Argesanu, 1996): [P. sub. fr]/[A. sub. al]= ([mu]* [p. sub. d]* v). sub. a](1)where: [mu]--
Coefficient of friction in contact area; [p. sub. d]--
Pressure in the contact area; v--relative speed.
This may give some insight into the value limits of the sealing operation.
If we consider [mu]= 0. 1 . . . 0.
3 for lipseal (fig. 1. b. )or [mu]= 0. 005 . . . 0.
1 for rubber lipseal (fig. 1. a. )
, 3MPa sliding speed with a working pressure of 12 m/s :[P. sub. fr]/[A. sub. al]= 3. 6 W/[mm. sup. 2]for PTFE and[P. sub. fr]/[A. sub. al]= 7. 2W/[mm. sup. 2]for elastomers.
3 The finite element simulation of the friction contact problem includes solving the motion equation of the floating ring, which is associated with the interaction between the two rings, which is due to the determination of the functional factors of the surface seal.
When friction is considered, the tangent displacement on the interface means energy consumption.
This problem is solved by incremental calculation. (
Wells, 1992)
A part of the structure can have a gap area that can be opened, closed, or sliding with each other.
Similarly, the boundary conditions can also change the nonlinear analysis.
Distribution configuration of equivalent stress under formal insosurfaces (fig. 3)exprimed in [Mpa]
This reveals the areas of most concern for mechanical seals.
The configuration of these quantities is the expected quantity with the largest inner radius of the mechanical seal ring.
By mathematical means, finite element analysis is the only way to establish the distribution of friction contact pressure from the end face sealing interface.
This is allowed.
Evaluation of mechanical and functional influencing factors of sealing performance.
4 Performance Standard tab describes the comparison between surface seals and lip seals based on technology, operation and cost. 1.
When comparing these values, it must be remembered that the sealing pressure p1 of the lip seal is lower than the corresponding mechanical seal.
Nevertheless, it is clear that the mechanical seal is much better than the lip seal due to the smaller leakage of buffer fluid and sealing products, reduced operational safety and maintenance.
Although the initial price of the lip seal is lower than the price of the face seal, the position will be opposite after installation and put into use. The labor-
The intensive maintenance cost of Leap seals is about 20 times higher.
Although the spare parts of mechanical seals are more expensive, due to the long service life of mechanical seals, their total cost is lower than that of lip seals. (Mayer, 1987, (
Was, Waschle, 1990)
Also taking into account that due to the labor savings, the leakage loss is reduced, the operation safety is improved, and-
Downtime, faceseals is even more economical than it looks.
Through the metal support sheath in the carbon ring, due to its slow elastic modulus, the deformation of the carbon ring must be much larger than that of the hard alloy seal under high pressure load, good working properties of conventional thermal fluid dynamics seals can be further improved at higher pressure.
In the seal, the fluid dynamics of the circular groove is a better design using a stable sealgap.
The sealing gap is less sensitive to pressure changes and has a longer service life. 5.
Conclusion The behavior of the seal is determined by the complex interaction of multiple factors.
The advantage is usually obtained at a disadvantage price in the direction of the order.
If we compare the specific loss caused by friction: the lip seal is \"uncharged\" or the classic \"charged\" with the usual pressure [theta]= [F. sub. cr]/[pi]* d (2)
We can notice the net advantage of his lip print, which is larger in size and lower in cost.
However, face seals are still irreplaceable in high-speed, high-pressure and hard working environments. (fig. 4)[
Figure 3 slightly]6.
References Argesanu, V; Madaras, L,(2003).
Analysis of leakage, wear and friction of mechanical surface by finite element method, ROTRIP Galati, Gheorghiu, Romania; Argesanu,V,(1996).
Performance Comparison of lip and face seals, Arad nothe, K. ; Welles, H, (1992).
Introduction to engineers, Springer-
New York, London, Paris, Tokyo, Hong Kong, Barcelona, Budapesta Mayer, E ,(1987).
Mechanical seals, Hewnes--
Butterworth Hotel London, Boston MuellerK; Waschle, P,(1990). EWDR-
A new type of seal, Anbetriebstechnik 29 Nr.
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