Industry News
Improvement of pump seal structure and application of ---2009-10-30
Yanshan Petrochemical Company Refinery 100y-type oil pump, the original bearing box gland and the shaft seal structure between the labyrinth seal, the labyrinth seal along with a dust ring, poor sealing performance. As the pump speed higher under the influence of centrifugal force, bearing along the axis from the lubricant inside cover thrown, oil spills is widespread, resulting in bearing box, coupling and the surrounding ground covered with oil, to the safety in production bring hidden dangers, also causing an unnecessary waste lubricating oil, but also serious pollution of the production environment, the impact of civilization upgrade set standards for production and business. If the operator can not discover, but also may result in pump damage. Therefore, the improved oil seal structure, and develop a good sealing performance and long service life of the new structure to replace the oil seal closure is necessary.
2 of the original seal structure problems
Pump oil level due to operation restrictions, nut oil immersion bottom of the pool, and the lubricating oil stir up, along the inner surface Tangxia gland, directly dripping rotating shaft, the shaft a lot of product oil has been driven rotating shaft, oil along the axis to crawl into the gland and shaft labyrinth seal gap, due to a larger labyrinth seal gap, and the seal resistance is small, oil enters the maze is difficult to fight back, which have been thrown along the axis, in the shaft at the formation of product oil, so that maze and dust sealing ring would not achieve the role that the oil spill occurred. From the above analysis we can see that the structure of crude oil closed the main problems is the locking nut bearing labyrinth seal gap is too big and too there is no effective sealing effect.
3 to improve program demonstration and preliminary selection
A new anti-leakage structure should meet the following requirements: First, to ensure that combines part of the airtight. Also, compact structure, simple, easy to use manufacturing maintenance, finished lower, reliable, long service life. The main reason for the oil spill, the following two-pronged approach should be improved to prevent oil spills.
(1), to reduce oil rejection
Bearing lock nut oil immersion depth (surface and locking nut relative distance) that affect the size of oil rejection an important factor. Reduce the nut diameter, can reduce the depth of immersion oil, reducing the stir the oil, thereby reducing the amount of oil fell axis and indirectly reduce the amount of oil leakage. ?
(2), improving the structure of crude oil seal
Their structural analysis, from the perspective of sealing principle may consider filling or blocking, segregation, leads to, or injection and flow resistance, anti-lost, as well as the combination of these programs and other methods. First separated, mechanical seals can be taken. According to mechanical seal performance, scope of application, life expectancy, mechanical seals can be applied, but the mechanical seal expensive, complex structure, the required space for larger disassembly inconvenience, not suitable for such a small spatial structure. Second, consider using extraction or injection methods, to achieve sealing requirements, but need assistive devices, complex structure, and thus undesirable. Further consider the use of packing and blocking methods require a longer life due to a number of contact-type seal, such as carpet circle, stall ring, sealing ring, oil seal and other contact with the shaft wear and tear, lifespan is limited, not suitable for high-speed long-period operation, but also prone to hold-axis, and thus excluded. Finally consider the flow resistance or anti-lose, or use integrated programs. Flow resistance is the use of a narrow gap sealing means or the twists and turns needed to create a sealed fluid resistance. Anti-lose is the use of seals on the leakage of fluid caused by counter-pressure, so that part of the balance or full balance, the fluid lost to the anti-upstream, in order to achieve sealing purposes. Its characteristics are no mechanical friction, compact structure. Fluid Anti-lose (also called dynamic pressure), including spiral labyrinth seals, dynamic seals, spiral seals. Consider the space is small, long life, power consumption is small, simple structure, demolition of convenience, low price requirements, use of flow resistance, or opposing the importation of its integrated program of the best. In the flow resistance or anti-lose scenario, the spiral seal the most comprehensive to meet the above requirements, so give priority to screw seal. In view of centrifugal seal may be used in conjunction with other seals, in order to ensure close results, the selected spiral seal and centrifugal seal form of combination. As shown in Figure -1:
4 For the 100y pump design calculations:
According to the theoretical analysis, spiral seal helix angle ¦Á in 5 ¡ã 6 'when the power of the smallest, while the 15 ¡ã 39' take the same length of the seal when the highest pressure, combined with practical experience in some of the information is given, taking into account the pressure seal, power consumption and the structure length, and stay a certain margin of safety, design is as follows:
4.1 The design and calculation of parameters of helical seal
(1), helix angle
For the 100y pump, shaft diameter d = 65mm, outer extension shaft seal length of the screw can be used in paragraph l0 = 56.5mm, its shaft associated with the coupling, leaving 7mm spacing, so they chose seal length l = 39.5mm. As the length and diameter are small, from the sealed pressure formula (see later) [1], sealing pressure of the smaller, so the larger helix angle selection, taken as ¦Á = 5 ¡ã 49 '. Then the tangent of ¦Á t = tan¦Á = 0.1019 (this value is calculated by the following).
(2), the relative slot width u normally take u = 0.5 ~ 1.0, where u = a / (a + b) = 0.75.
(3), the relative groove depth generally take ¦Ô ¦Ô = 2 ~ 10, taken as ¦Ô = (c + h) / c = 5.
(4), seal gap c Recommended c = (0.6 ~ 2.6) / 10000m take c = 0.26mm, due to centrifugal spiral before sealing sealing sealing performance can be guaranteed, taking a large gap in order to prevent errors due to processing errors and installation, and shaft friction.
(5), groove depth h, h by the formula h = c * (¦Ô-1) obtained: h = 0.26 * (5-1) = 1.04, taken as h = 1.0mm.
(6), the first few i, from the first few i discussed earlier by the choice of screw heads a few principles: high-speed (n> 5000r/min), menu head; low speed (n <5000rmin) selected long. As the pump n = 2950r/min, according to the information recommendation, taking i = 4.
(7), spiral lead s, taking s = 16 (rounded to facilitate processing); from?
s = ¦Ðd * tan¦Á, ¦Á = 5 ¡ã 49 '.
(8), spiral slot width a, tooth width
By the formula were a = ¦Ðu * d * tan¦Á / i = 3.00mm
b = ¦Ð * (1-u) * d * tan¦Á / i = 1.0mm
(9), axis angular velocity ¦Ø and spiral circumferential velocity v of the calculation:
¦Ø = 2¦Ðn/60 = 308.9rad / s
v = ¦Ðn/60 = 7.6m / s
(10), spiral structure, selected according to the length of l = 39.5mm
(11), spiral seal pressure
tu (1-u) (¦Ô-1) (¦Ô3-1) - $
Where: cp = -----------------------------------
(1 + t2) ¦Ô3 + t2u (1-u) (¦Ô3-1)
To u = 0.75, t = 0.1019, ¦Ô = 5.0-generation Entering: cp = 0.178, according to cp = 0.178, thin oil lubrication coefficient of viscosity is too small to take ¦Ì = 0.00223 ¡Á 9.8pa / s, ¦Ø = 308.9rad / s, d = 0.065m, l = 0.0395m, c = 2.6 ¡Á 10
m on behalf of the income, calculated ¦Ä p `= 35800pa.
(12), spiral seal power calculation n
n = ¦Ð¦Ø2d3lcn/4c6ei?
cn obtained by the formula: cn = 0.46,
Then n = 14 watts
Pump motor rated power 90kw, shaft power 75kw, spiral seal consumes 14w, can see that power is very small, the original does not affect the pump operation.
4.2 Calculation of Impeller Centrifugal Seal
Vice-impeller centrifugal effect generated by the sealing pressure difference ¦Äp "formula as follows:
¦Äp "= k2¦Ø2 (r22-r12) r / 2%
= 0.52 ¡Á 308.92 ¡Á (0.0352-0.0252) ¡Á 800
= 6403
Where: r1, r2 -------- impeller diameter, respectively, gas-liquid interfacial radius of the outer diameter
k ------------ factor, and smooth disc approximation, k = 0.5dR
4.3 screw seals and seal combination of centrifugal sealing the total pressure difference
Combination seal pressure difference ¦Äp as the spiral seal pressure difference ¦Äp 'and centrifugal sealing pressure difference ¦Äp "sum that is: ¦Äp = ¦Äp' + ¦Äp" = 35800 +6403 = 42203
As basic as the atmospheric pressure bearing box, box pressure and atmospheric pressure outside the bearing box are similar, so the total pressure difference ¦Äp combination of sealing is to prevent the oil sealing the pressure outside the string, the seal structure pressure 0.04mpa, fully in line should be slightly higher than the Machine internal pressure requirements.
4.4 Material Selection
Pressure due to the role of bearing gland can not afford, optional a3 steel, while the rejection not only from the oil Deputy impeller rejection role of oil and oil resistance, but also bearing clasp, in order to prevent damage caused by repeated removal may make use of 45 steel.
5 application
After transformation of the oil seal, in April 1998, in the ketone benzene plant pump 305 (Model 100y-120 ¡Á 2) carried out a trial run, and later the pump 430, pump 351 installed on the pump and so on, after four more than a year of operation, the bearing box office no gland seal leakage, fully meet the design requirements. Prior to this, the original seal structure due to frequent leaks, Secretary pump operator jobs heavy workload, in the hour inspection of lubricating oil pump must be right to supplement, but also occurred in two causes of oil spills Equipment hold shaft accident, led to production fluctuations, due to the universality of oil spills also made on-site sanitation has been difficult to resolve, to the device brings site management difficult. After the transformation, the drain of the oil inside the pump does not require substantial additional basic, thus greatly reducing the labor intensity of workers, on-site condition has been markedly improved, but also for the smooth running of production has created favorable conditions.
6 Conclusion
Gland at the original labyrinth seal bearing box sealed with screw seal centrifuge into a combination of sealing structure, the use of centrifugal seal leakage as the initial cutting resistance seal, the use of spiral seal as a secondary seal, can guarantee no leaks at shaft head. This improved method requires transformation of bearing lock nut and bearing boxes gland, a small alteration to the original structure, that can meet the sealing requirements, but also to adapt to the original structure can be little use of space restrictions. The kinds of sealing simple structure, manufacture, easy to install and consume little power. From the practical effects, a total improvement of the original structure of the equipment and the surrounding environment caused by oil pollution situation, eliminating the production of hidden dangers; reduce labor intensity of workers, promoting the production of civilization. In addition, by adjusting the structural parameters, the structure has been successfully applied 65y, 150y-type pump, the same achieved satisfactory results. Therefore, the structure is also applicable to other similar problems in the pump, there is a great promotional value.
2 of the original seal structure problems
Pump oil level due to operation restrictions, nut oil immersion bottom of the pool, and the lubricating oil stir up, along the inner surface Tangxia gland, directly dripping rotating shaft, the shaft a lot of product oil has been driven rotating shaft, oil along the axis to crawl into the gland and shaft labyrinth seal gap, due to a larger labyrinth seal gap, and the seal resistance is small, oil enters the maze is difficult to fight back, which have been thrown along the axis, in the shaft at the formation of product oil, so that maze and dust sealing ring would not achieve the role that the oil spill occurred. From the above analysis we can see that the structure of crude oil closed the main problems is the locking nut bearing labyrinth seal gap is too big and too there is no effective sealing effect.
3 to improve program demonstration and preliminary selection
A new anti-leakage structure should meet the following requirements: First, to ensure that combines part of the airtight. Also, compact structure, simple, easy to use manufacturing maintenance, finished lower, reliable, long service life. The main reason for the oil spill, the following two-pronged approach should be improved to prevent oil spills.
(1), to reduce oil rejection
Bearing lock nut oil immersion depth (surface and locking nut relative distance) that affect the size of oil rejection an important factor. Reduce the nut diameter, can reduce the depth of immersion oil, reducing the stir the oil, thereby reducing the amount of oil fell axis and indirectly reduce the amount of oil leakage. ?
(2), improving the structure of crude oil seal
Their structural analysis, from the perspective of sealing principle may consider filling or blocking, segregation, leads to, or injection and flow resistance, anti-lost, as well as the combination of these programs and other methods. First separated, mechanical seals can be taken. According to mechanical seal performance, scope of application, life expectancy, mechanical seals can be applied, but the mechanical seal expensive, complex structure, the required space for larger disassembly inconvenience, not suitable for such a small spatial structure. Second, consider using extraction or injection methods, to achieve sealing requirements, but need assistive devices, complex structure, and thus undesirable. Further consider the use of packing and blocking methods require a longer life due to a number of contact-type seal, such as carpet circle, stall ring, sealing ring, oil seal and other contact with the shaft wear and tear, lifespan is limited, not suitable for high-speed long-period operation, but also prone to hold-axis, and thus excluded. Finally consider the flow resistance or anti-lose, or use integrated programs. Flow resistance is the use of a narrow gap sealing means or the twists and turns needed to create a sealed fluid resistance. Anti-lose is the use of seals on the leakage of fluid caused by counter-pressure, so that part of the balance or full balance, the fluid lost to the anti-upstream, in order to achieve sealing purposes. Its characteristics are no mechanical friction, compact structure. Fluid Anti-lose (also called dynamic pressure), including spiral labyrinth seals, dynamic seals, spiral seals. Consider the space is small, long life, power consumption is small, simple structure, demolition of convenience, low price requirements, use of flow resistance, or opposing the importation of its integrated program of the best. In the flow resistance or anti-lose scenario, the spiral seal the most comprehensive to meet the above requirements, so give priority to screw seal. In view of centrifugal seal may be used in conjunction with other seals, in order to ensure close results, the selected spiral seal and centrifugal seal form of combination. As shown in Figure -1:
4 For the 100y pump design calculations:
According to the theoretical analysis, spiral seal helix angle ¦Á in 5 ¡ã 6 'when the power of the smallest, while the 15 ¡ã 39' take the same length of the seal when the highest pressure, combined with practical experience in some of the information is given, taking into account the pressure seal, power consumption and the structure length, and stay a certain margin of safety, design is as follows:
4.1 The design and calculation of parameters of helical seal
(1), helix angle
For the 100y pump, shaft diameter d = 65mm, outer extension shaft seal length of the screw can be used in paragraph l0 = 56.5mm, its shaft associated with the coupling, leaving 7mm spacing, so they chose seal length l = 39.5mm. As the length and diameter are small, from the sealed pressure formula (see later) [1], sealing pressure of the smaller, so the larger helix angle selection, taken as ¦Á = 5 ¡ã 49 '. Then the tangent of ¦Á t = tan¦Á = 0.1019 (this value is calculated by the following).
(2), the relative slot width u normally take u = 0.5 ~ 1.0, where u = a / (a + b) = 0.75.
(3), the relative groove depth generally take ¦Ô ¦Ô = 2 ~ 10, taken as ¦Ô = (c + h) / c = 5.
(4), seal gap c Recommended c = (0.6 ~ 2.6) / 10000m take c = 0.26mm, due to centrifugal spiral before sealing sealing sealing performance can be guaranteed, taking a large gap in order to prevent errors due to processing errors and installation, and shaft friction.
(5), groove depth h, h by the formula h = c * (¦Ô-1) obtained: h = 0.26 * (5-1) = 1.04, taken as h = 1.0mm.
(6), the first few i, from the first few i discussed earlier by the choice of screw heads a few principles: high-speed (n> 5000r/min), menu head; low speed (n <5000rmin) selected long. As the pump n = 2950r/min, according to the information recommendation, taking i = 4.
(7), spiral lead s, taking s = 16 (rounded to facilitate processing); from?
s = ¦Ðd * tan¦Á, ¦Á = 5 ¡ã 49 '.
(8), spiral slot width a, tooth width
By the formula were a = ¦Ðu * d * tan¦Á / i = 3.00mm
b = ¦Ð * (1-u) * d * tan¦Á / i = 1.0mm
(9), axis angular velocity ¦Ø and spiral circumferential velocity v of the calculation:
¦Ø = 2¦Ðn/60 = 308.9rad / s
v = ¦Ðn/60 = 7.6m / s
(10), spiral structure, selected according to the length of l = 39.5mm
(11), spiral seal pressure
tu (1-u) (¦Ô-1) (¦Ô3-1) - $
Where: cp = -----------------------------------
(1 + t2) ¦Ô3 + t2u (1-u) (¦Ô3-1)
To u = 0.75, t = 0.1019, ¦Ô = 5.0-generation Entering: cp = 0.178, according to cp = 0.178, thin oil lubrication coefficient of viscosity is too small to take ¦Ì = 0.00223 ¡Á 9.8pa / s, ¦Ø = 308.9rad / s, d = 0.065m, l = 0.0395m, c = 2.6 ¡Á 10
m on behalf of the income, calculated ¦Ä p `= 35800pa.
(12), spiral seal power calculation n
n = ¦Ð¦Ø2d3lcn/4c6ei?
cn obtained by the formula: cn = 0.46,
Then n = 14 watts
Pump motor rated power 90kw, shaft power 75kw, spiral seal consumes 14w, can see that power is very small, the original does not affect the pump operation.
4.2 Calculation of Impeller Centrifugal Seal
Vice-impeller centrifugal effect generated by the sealing pressure difference ¦Äp "formula as follows:
¦Äp "= k2¦Ø2 (r22-r12) r / 2%
= 0.52 ¡Á 308.92 ¡Á (0.0352-0.0252) ¡Á 800
= 6403
Where: r1, r2 -------- impeller diameter, respectively, gas-liquid interfacial radius of the outer diameter
k ------------ factor, and smooth disc approximation, k = 0.5dR
4.3 screw seals and seal combination of centrifugal sealing the total pressure difference
Combination seal pressure difference ¦Äp as the spiral seal pressure difference ¦Äp 'and centrifugal sealing pressure difference ¦Äp "sum that is: ¦Äp = ¦Äp' + ¦Äp" = 35800 +6403 = 42203
As basic as the atmospheric pressure bearing box, box pressure and atmospheric pressure outside the bearing box are similar, so the total pressure difference ¦Äp combination of sealing is to prevent the oil sealing the pressure outside the string, the seal structure pressure 0.04mpa, fully in line should be slightly higher than the Machine internal pressure requirements.
4.4 Material Selection
Pressure due to the role of bearing gland can not afford, optional a3 steel, while the rejection not only from the oil Deputy impeller rejection role of oil and oil resistance, but also bearing clasp, in order to prevent damage caused by repeated removal may make use of 45 steel.
5 application
After transformation of the oil seal, in April 1998, in the ketone benzene plant pump 305 (Model 100y-120 ¡Á 2) carried out a trial run, and later the pump 430, pump 351 installed on the pump and so on, after four more than a year of operation, the bearing box office no gland seal leakage, fully meet the design requirements. Prior to this, the original seal structure due to frequent leaks, Secretary pump operator jobs heavy workload, in the hour inspection of lubricating oil pump must be right to supplement, but also occurred in two causes of oil spills Equipment hold shaft accident, led to production fluctuations, due to the universality of oil spills also made on-site sanitation has been difficult to resolve, to the device brings site management difficult. After the transformation, the drain of the oil inside the pump does not require substantial additional basic, thus greatly reducing the labor intensity of workers, on-site condition has been markedly improved, but also for the smooth running of production has created favorable conditions.
6 Conclusion
Gland at the original labyrinth seal bearing box sealed with screw seal centrifuge into a combination of sealing structure, the use of centrifugal seal leakage as the initial cutting resistance seal, the use of spiral seal as a secondary seal, can guarantee no leaks at shaft head. This improved method requires transformation of bearing lock nut and bearing boxes gland, a small alteration to the original structure, that can meet the sealing requirements, but also to adapt to the original structure can be little use of space restrictions. The kinds of sealing simple structure, manufacture, easy to install and consume little power. From the practical effects, a total improvement of the original structure of the equipment and the surrounding environment caused by oil pollution situation, eliminating the production of hidden dangers; reduce labor intensity of workers, promoting the production of civilization. In addition, by adjusting the structural parameters, the structure has been successfully applied 65y, 150y-type pump, the same achieved satisfactory results. Therefore, the structure is also applicable to other similar problems in the pump, there is a great promotional value.
