In a properly designed, sophisticated processing, assembly intact, speed is high, with labyrinth seals with good results. However, in practical applications, the resulting leakage are many, of which the main reasons are:
1, sealing (such as shafts and bearing gland) with the gap is too large, and this gap is inversely proportional with the sealing effect. With the surface roughness,seal strap it is obvious marks spiral car in some cases also increased the leakage tendency.
2, the amount of grease into the bearing interior too, the overflow pressure exceeds seal resistance.
3, the oil window or the oil level gauge installation location is incorrect, misleading the people to the correct amount of lubricant oil chamber judgment.
4, the operation oil temperature reduces its viscosity, increasing the possibility of leakage.
5, the back tank or back to the hole size is too small, or by other obstacles, so that the liquid can not be blocked smooth return and cause leaks.
Oil seals
Self-tight seal is a lip seal, its simple structure, small size, low cost, easy maintenance, resistance torque is small, both to prevent media leaks, but also to prevent external intrusion of dust and other harmful substances, but also to wear have a certain ability to compensate, but the impatience high pressure, it is generally used in low pressure applications. Seal should be installed in the manufacturing precision of h8 ~ h9, the surface roughness of 1.6 ~ 0.8μm and after surface hardening treatment of the shaft. Sealing medium should not contain solid particles and impurities, which will cause rapid wear of the shaft seal and leaving the barrier seals failure.
plastic padlock security seals
plastic padlock security seals
2013年11月5日星期二
2013年11月4日星期一
Rubber O-ring plane static sealing introduction
Plastic and rubber looks a clear distinction between two kinds of substances or materials, it is not true ,numbered security seals they are the same substance in different rendering. They are polymers, and at a certain temperature conditions can be transformed into each other . This transformation temperature is the polymer glass transition temperature Tg, which is one of the characteristic temperature of polymer .
Tg is bounded to , polymers exhibit different physical properties : Tg less polymer material is plastic ; Above the Tg , the polymer material is rubber . From the engineering point of view , the glass transition temperature is the upper limit temperature engineering plastics , use lower limit of rubber .
If a recipe EPDM sample test measured by obtaining the glass transition temperature is -53.6 ℃, after the glass transition sample starts to melt ( elasticity began to recover ) , near the peak position at 31.4 ℃ . This peak temperature is the maximum melting temperature of the material at this temperature for maximum heat absorption , and thus also the largest of its expansion , the greatest contribution to the sealing .
January 28, 1986 , the U.S. space shuttle Challenger exploded, the reason is on solid fuel propulsion rubber O-ring seal structure caused by improper design :
1, O -ring material selection improperly ;
2 , the night before take-off extremely low temperatures , resulting in decreased elasticity O-ring seal compression decline ;
3, O -ring should be designed to the outside rather than the inside , as in the inside of the combustion and expansion of the metal rapid heat transfer , so that compression of the O- ring is insufficient , security seals resulting in tragedy. So the problem is not trivial seal , seal design or choice worth pondering.
Tg is bounded to , polymers exhibit different physical properties : Tg less polymer material is plastic ; Above the Tg , the polymer material is rubber . From the engineering point of view , the glass transition temperature is the upper limit temperature engineering plastics , use lower limit of rubber .
If a recipe EPDM sample test measured by obtaining the glass transition temperature is -53.6 ℃, after the glass transition sample starts to melt ( elasticity began to recover ) , near the peak position at 31.4 ℃ . This peak temperature is the maximum melting temperature of the material at this temperature for maximum heat absorption , and thus also the largest of its expansion , the greatest contribution to the sealing .
January 28, 1986 , the U.S. space shuttle Challenger exploded, the reason is on solid fuel propulsion rubber O-ring seal structure caused by improper design :
1, O -ring material selection improperly ;
2 , the night before take-off extremely low temperatures , resulting in decreased elasticity O-ring seal compression decline ;
3, O -ring should be designed to the outside rather than the inside , as in the inside of the combustion and expansion of the metal rapid heat transfer , so that compression of the O- ring is insufficient , security seals resulting in tragedy. So the problem is not trivial seal , seal design or choice worth pondering.
Analysis of typical failure of the mechanical seal
General analysis of the mechanical seal common seal failure cause is usually experienced after analysis using derived through the process .
a. seal working gas shock ( splash and sputtering ) .
b. seal leakage and Grand icing .
c. steady drip sealing surface .
d. working seal screaming.
e. Gran outer ring graphite powder build-up.
f. pump and ( or ) axis vibration .
g. seal life is short.
Typical mechanical seal failure
General analysis of the mechanical seal common seal failure cause is usually experienced after analysis using derived through the process .
a. seal working gas shock ( splash and sputtering ) .
b. seal leakage and Grand icing .
c. steady drip sealing surface .
d. working seal screaming.
e. Gran outer ring graphite powder build-up.
f. pump and ( or ) axis vibration .
g. seal life is short.
Vaporization ( flash )
When the sealing surface friction heat accumulation , the end faces of the occurrence of local film boiling .
Symptoms seal pronunciation or take gas ( intermittent shock ) . Stationary ring bitten eclipse , comet -like texture generating process leads to a narrow ring outer edge trimming . Hard rings of thermal cracking . End at the inner edge of graphite dust accumulation .
Corrective measures checking seal design parameters ; improve circulation conditions .
Dry Running
Face between the liquid insufficient or no liquid.
Symptoms are severe wear stationary ring and groove . Hard surface polished ring marks, or radial cracks ( thermal cracking ) and discoloration. Aprons sclerosis. There LP graphite ring -shaped grooves.
Corrective measures chosen balanced seal ;releasable cable ties choose high thermal conductivity of rigid material ; Inspect the exhaust situation ; improve circulation conditions .
Blister scars
Between the end faces of the high viscosity fluid shear stress exceeds the breaking strength of the graphite . When the pump stops , the temperature drop of liquid viscosity increases so that the pump restart problems.
Symptoms of carbon graphite particles emerge from the end face ; hard ring with polished traces ; tiny gap in the residual graphite particles.
Corrective Action Check the loop condition ; using 15 ~ 30min ※ steam preheat or low pressure steam heat .
Abrasive wear
Grinding medium containing solid particles.
Symptoms of solid particles or residues accumulate in the face and tiny gaps , etc..
Corrective measures as using resistant material end ; improve cycling conditions : hydrocyclone , external cleansing rinse ......
Face deformation
Symptoms pump starts ,high security cable seals the seal leakage and leakage occurs over time. Will face light research on the platform , there are signs of deformation .
Corrective measures natural aging deformation, reground ; improper assembly , carefully re- assemble ; pump pair bad , bearing damage , adjust pump .
a. seal working gas shock ( splash and sputtering ) .
b. seal leakage and Grand icing .
c. steady drip sealing surface .
d. working seal screaming.
e. Gran outer ring graphite powder build-up.
f. pump and ( or ) axis vibration .
g. seal life is short.
Typical mechanical seal failure
General analysis of the mechanical seal common seal failure cause is usually experienced after analysis using derived through the process .
a. seal working gas shock ( splash and sputtering ) .
b. seal leakage and Grand icing .
c. steady drip sealing surface .
d. working seal screaming.
e. Gran outer ring graphite powder build-up.
f. pump and ( or ) axis vibration .
g. seal life is short.
Vaporization ( flash )
When the sealing surface friction heat accumulation , the end faces of the occurrence of local film boiling .
Symptoms seal pronunciation or take gas ( intermittent shock ) . Stationary ring bitten eclipse , comet -like texture generating process leads to a narrow ring outer edge trimming . Hard rings of thermal cracking . End at the inner edge of graphite dust accumulation .
Corrective measures checking seal design parameters ; improve circulation conditions .
Dry Running
Face between the liquid insufficient or no liquid.
Symptoms are severe wear stationary ring and groove . Hard surface polished ring marks, or radial cracks ( thermal cracking ) and discoloration. Aprons sclerosis. There LP graphite ring -shaped grooves.
Corrective measures chosen balanced seal ;releasable cable ties choose high thermal conductivity of rigid material ; Inspect the exhaust situation ; improve circulation conditions .
Blister scars
Between the end faces of the high viscosity fluid shear stress exceeds the breaking strength of the graphite . When the pump stops , the temperature drop of liquid viscosity increases so that the pump restart problems.
Symptoms of carbon graphite particles emerge from the end face ; hard ring with polished traces ; tiny gap in the residual graphite particles.
Corrective Action Check the loop condition ; using 15 ~ 30min ※ steam preheat or low pressure steam heat .
Abrasive wear
Grinding medium containing solid particles.
Symptoms of solid particles or residues accumulate in the face and tiny gaps , etc..
Corrective measures as using resistant material end ; improve cycling conditions : hydrocyclone , external cleansing rinse ......
Face deformation
Symptoms pump starts ,high security cable seals the seal leakage and leakage occurs over time. Will face light research on the platform , there are signs of deformation .
Corrective measures natural aging deformation, reground ; improper assembly , carefully re- assemble ; pump pair bad , bearing damage , adjust pump .
2013年11月3日星期日
Industrial pump mechanical seal failure analysis of external causes
A large shaft axial channeling
Mechanical seal sealing faces have a certain pressure ratio , so as to play seal, mechanical seal which requires to have a certain amount of compression spring , a force to the seal faces , the sealing surface rotating together produce the desired ratio of the sealing pressure . In order to ensure that a specific pressure, mechanical shaft seal requires channeling can not have too much , generally guaranteed within 0.5 mm . However, in practical designs, due to improper design , channeling tends to have a great amount of shaft , the use of mechanical seals are very unfavorable. This phenomenon often occurs in a multi- stage centrifugal pumps , especially during startup of the pump , channeling a greater amount .
When working at the equilibrium balance disc and balance automatically changing the axial gap between the ring b, thereby changing the front and rear sides of the pressure balance disc , generates a force in the opposite direction to the axial force to balance the axial force. The inertia of the rotor runout and transient fluctuations in pump mode , operation will not be resting on a rotor axial equilibrium position . Always in balance disc ran around the state . In normal operation, the balance disc axial channeling is only 0105 ~ 011 mm, to meet the mechanical seal to allow the amount of 015 mm axial channeling requirements, but the balance disc in the pump start, stop , drastic changes in working conditions are likely when the axial channeling greatly exceeds the permissible axial mechanical seal channeling .
Industrial pumps after a long run, the balance disc and balance ring friction and wear , the gap b with increasing the amount of mechanical seal axial channeling increasing . The axial force on the suction side of the sealing surface of the pressing force increases , the sealing surface wear increased , until the sealing surface is damaged , lost seal. The discharge side of the mechanical seal , with the balance of the wear plate , the axial direction of the rotor member is greater than the sealing requirements channeling channeling the axial sealing surface of the pressing force decreases , id cable ties less than sealing requirements , the final side of the pump lost all mechanical seal seal.
2 axial force is too large
In the course of the mechanical seal is not able to withstand the axial force , if there is an axial force of the mechanical seal is serious. Sometimes, because of the axial pump unreasonable force balance mechanism design and manufacture , installation, use and other reasons , resulting axial force is not balanced out . Mechanical seals to withstand an axial force , the operation temperature is high gland , the polypropylene of the medium may be melted at high temperatures , thus the pump starts soon lost sealing effect of the sealing face when the pump is stationary there intermittent spray drain phenomenon .
3 shaft deflection is too large
Mechanical seals known face seal is a rotary seal axially movable contact , which is in a fluid medium and the role of the elastic member , the two lines perpendicular to the axis of the seal faces close contact , relative rotation , so as to achieve sealing effect ,security seal labels thus requiring two sealing force between to evenly. However, the unreasonable design of the pump , pump operation, the mechanical seal installation deflection generated at the larger the discontinuity between the sealing surface , resulting in good sealing effect .
4 no auxiliary flushing system or auxiliary flushing system set unreasonable
Auxiliary mechanical seal flush system is very important, it can effectively protect the sealing surface, for cooling , lubrication, and other debris washed effect. Sometimes designers no rational allocation of auxiliary flushing system , reach the sealing effect ; although sometimes designers designed the support system, but because there are impurities in flushing fluid , fluid flow, pressure is not enough, rinse mouth position unreasonable design and other reasons , also reach the sealing effect.
Mechanical seal sealing faces have a certain pressure ratio , so as to play seal, mechanical seal which requires to have a certain amount of compression spring , a force to the seal faces , the sealing surface rotating together produce the desired ratio of the sealing pressure . In order to ensure that a specific pressure, mechanical shaft seal requires channeling can not have too much , generally guaranteed within 0.5 mm . However, in practical designs, due to improper design , channeling tends to have a great amount of shaft , the use of mechanical seals are very unfavorable. This phenomenon often occurs in a multi- stage centrifugal pumps , especially during startup of the pump , channeling a greater amount .
When working at the equilibrium balance disc and balance automatically changing the axial gap between the ring b, thereby changing the front and rear sides of the pressure balance disc , generates a force in the opposite direction to the axial force to balance the axial force. The inertia of the rotor runout and transient fluctuations in pump mode , operation will not be resting on a rotor axial equilibrium position . Always in balance disc ran around the state . In normal operation, the balance disc axial channeling is only 0105 ~ 011 mm, to meet the mechanical seal to allow the amount of 015 mm axial channeling requirements, but the balance disc in the pump start, stop , drastic changes in working conditions are likely when the axial channeling greatly exceeds the permissible axial mechanical seal channeling .
Industrial pumps after a long run, the balance disc and balance ring friction and wear , the gap b with increasing the amount of mechanical seal axial channeling increasing . The axial force on the suction side of the sealing surface of the pressing force increases , the sealing surface wear increased , until the sealing surface is damaged , lost seal. The discharge side of the mechanical seal , with the balance of the wear plate , the axial direction of the rotor member is greater than the sealing requirements channeling channeling the axial sealing surface of the pressing force decreases , id cable ties less than sealing requirements , the final side of the pump lost all mechanical seal seal.
2 axial force is too large
In the course of the mechanical seal is not able to withstand the axial force , if there is an axial force of the mechanical seal is serious. Sometimes, because of the axial pump unreasonable force balance mechanism design and manufacture , installation, use and other reasons , resulting axial force is not balanced out . Mechanical seals to withstand an axial force , the operation temperature is high gland , the polypropylene of the medium may be melted at high temperatures , thus the pump starts soon lost sealing effect of the sealing face when the pump is stationary there intermittent spray drain phenomenon .
3 shaft deflection is too large
Mechanical seals known face seal is a rotary seal axially movable contact , which is in a fluid medium and the role of the elastic member , the two lines perpendicular to the axis of the seal faces close contact , relative rotation , so as to achieve sealing effect ,security seal labels thus requiring two sealing force between to evenly. However, the unreasonable design of the pump , pump operation, the mechanical seal installation deflection generated at the larger the discontinuity between the sealing surface , resulting in good sealing effect .
4 no auxiliary flushing system or auxiliary flushing system set unreasonable
Auxiliary mechanical seal flush system is very important, it can effectively protect the sealing surface, for cooling , lubrication, and other debris washed effect. Sometimes designers no rational allocation of auxiliary flushing system , reach the sealing effect ; although sometimes designers designed the support system, but because there are impurities in flushing fluid , fluid flow, pressure is not enough, rinse mouth position unreasonable design and other reasons , also reach the sealing effect.
Power plants pump seal Precautions
According to the White Horse in Neijiang power plant pumps renovation and maintenance of such experiences , needs attention to the following matters .
Transformation can only be carried out in the positive pressure pump
If the vacuum pump ( eg fire pumps ) on the transformation , fillers easily sucked into the pump , stainless steel cable tie the White Horse stage steam turbine power plant has been transformed plant industrial pumps , supplementary pumps, circulating pumps , dredging pumps and boiler shop some of the low-pressure pump , running good effect.
Do not overtighten packing gland
After the installation of tight packing gland packing when not too tight , there should be loose.
Injecting a filler material so that the filler gun , according to the gland packing tightness to determine whether or filled . Tighten the gland by the loose , it means that the filler has been filled .
Filler added
Test pump, leak situation should be based on supplemental filler.
With the pump start , before injection of the filler of the rotary friction part will be extruded to the outside of the pump and generate a certain gap , resulting in leakage. At this time instant injection of filler until no leakage. Injectable fillers should be split into multiple transactions , action should be slow , at intervals of about 5min. If the packing is too tight and smoke , you can loose about packing gland, packing room while pouring cold water to cool . After a period of rotation of the pump , the filler and the sleeve has a good run , will no longer smoke.
Connector on the pump cover the requirements of the injection hole
Hole injection pump cover joints should closely,colored cable ties available raw tape winding , there should be soft gland gasket .
Filled with a filler after the injection pressure connector , and then tightly gland .
Injection can not be forced too fast
Filler gun high pressure ( up to 10MPa), therefore can not be forced when injected too fast , I feel a certain pressure to grip .
Transformation can only be carried out in the positive pressure pump
If the vacuum pump ( eg fire pumps ) on the transformation , fillers easily sucked into the pump , stainless steel cable tie the White Horse stage steam turbine power plant has been transformed plant industrial pumps , supplementary pumps, circulating pumps , dredging pumps and boiler shop some of the low-pressure pump , running good effect.
Do not overtighten packing gland
After the installation of tight packing gland packing when not too tight , there should be loose.
Injecting a filler material so that the filler gun , according to the gland packing tightness to determine whether or filled . Tighten the gland by the loose , it means that the filler has been filled .
Filler added
Test pump, leak situation should be based on supplemental filler.
With the pump start , before injection of the filler of the rotary friction part will be extruded to the outside of the pump and generate a certain gap , resulting in leakage. At this time instant injection of filler until no leakage. Injectable fillers should be split into multiple transactions , action should be slow , at intervals of about 5min. If the packing is too tight and smoke , you can loose about packing gland, packing room while pouring cold water to cool . After a period of rotation of the pump , the filler and the sleeve has a good run , will no longer smoke.
Connector on the pump cover the requirements of the injection hole
Hole injection pump cover joints should closely,colored cable ties available raw tape winding , there should be soft gland gasket .
Filled with a filler after the injection pressure connector , and then tightly gland .
Injection can not be forced too fast
Filler gun high pressure ( up to 10MPa), therefore can not be forced when injected too fast , I feel a certain pressure to grip .
2013年11月1日星期五
Vertical condensate pump seal transformation is widely
According to the customer's general response , the transformation has the following outstanding advantages:
A transformation of short implementation time - only in power plant condensate pump overhaul the way transformation, security seals almost no maintenance valid time
2 sealed high integration - an integrated part of the whole transformation only ( cartridge mechanical seal ) , a significant reduction in spares inventory , spare error rate is zero
3 does not modify the equipment original structure - the transformation only cancel the original packing and gland on the pump without any modifications , greatly reducing the risk of transformation , which in the initial implementation of the transformation of the unit is more important
4 reduces spare parts consumption - the seal life of four years , no longer need packing, bushings, and other spare parts inventory , reducing inventory capital
5 lower operating costs - because of mechanical seal packing friction power consumption is much lower than the friction consumption, increased running stability , reducing the running load , save operating costs
6 save labor - Routine maintenance is almost zero ,vehicle seals no longer have to frequent replacement of the packing and bushings .
A transformation of short implementation time - only in power plant condensate pump overhaul the way transformation, security seals almost no maintenance valid time
2 sealed high integration - an integrated part of the whole transformation only ( cartridge mechanical seal ) , a significant reduction in spares inventory , spare error rate is zero
3 does not modify the equipment original structure - the transformation only cancel the original packing and gland on the pump without any modifications , greatly reducing the risk of transformation , which in the initial implementation of the transformation of the unit is more important
4 reduces spare parts consumption - the seal life of four years , no longer need packing, bushings, and other spare parts inventory , reducing inventory capital
5 lower operating costs - because of mechanical seal packing friction power consumption is much lower than the friction consumption, increased running stability , reducing the running load , save operating costs
6 save labor - Routine maintenance is almost zero ,vehicle seals no longer have to frequent replacement of the packing and bushings .
Common seal rubber material introduced
NBR seals
1 , mainly oil resistance , abrasion resistance,cable tie oil resistance, widely used in applications that require high
2 common seals , O-rings commonly used materials
3 Operating temperature range : -40 ℃ -120 ℃
EPDM.
1 general acid -resistant , chemical resistance , chemical resistance , water resistance
(2) resistant to mineral oil, suitable for superheated steam (200 ℃)
3 Operating temperature range : -40 ℃ -120 ℃
Viton FPM (FKM, VITON)
1 oil, heat , acid and alkali resistance and excellent chemical resistance
(2) commonly used in high-temperature , corrosion-resistant occasion
3 Operating temperature range : -20 ℃ -210 ℃
Silicone MVQ (SILICONE)
1 heat, cold, tamper evident seal weather resistance and excellent resistance to compression set , good dyeing but poor mechanical properties impatience wear
(2) for high precision under low temperature sealing applications , are food, medical, widely used in the electronics industry
3 Operating temperature range : -70 ℃ -230 ℃
1 , mainly oil resistance , abrasion resistance,cable tie oil resistance, widely used in applications that require high
2 common seals , O-rings commonly used materials
3 Operating temperature range : -40 ℃ -120 ℃
EPDM.
1 general acid -resistant , chemical resistance , chemical resistance , water resistance
(2) resistant to mineral oil, suitable for superheated steam (200 ℃)
3 Operating temperature range : -40 ℃ -120 ℃
Viton FPM (FKM, VITON)
1 oil, heat , acid and alkali resistance and excellent chemical resistance
(2) commonly used in high-temperature , corrosion-resistant occasion
3 Operating temperature range : -20 ℃ -210 ℃
Silicone MVQ (SILICONE)
1 heat, cold, tamper evident seal weather resistance and excellent resistance to compression set , good dyeing but poor mechanical properties impatience wear
(2) for high precision under low temperature sealing applications , are food, medical, widely used in the electronics industry
3 Operating temperature range : -70 ℃ -230 ℃
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