Sometimes mechanical seal leakage , not due to leakage caused by face , but because ring, stationary ring seal or sleeve seal leak caused . For the following reasons :
Machine rubber seals leak
Actuating ring, stationary ring "O" type rubber seals, rubber finish is not enough because the hardness inappropriate , good elasticity , friction coefficient, geometry failure , heat resistance, corrosion resistance and other good reasons, often cause seal leakage .
Machine shaft seal ring in contact with leaking
When a sleeve repeated use in contact with ring seal and sleeve at the sleeve surface will have a rough grinding marks and spots , often caused by seal leakage . The main reasons are:
( 1) Since the rail car seals ring and the sleeve exists between the small amount of relative movement , or other hard abrasive grains embedded impurities into the softer seal . Produce a friction rub on the sleeve , and the sleeve surface without surface hardening treatment or processing of poor quality , resulting in wear and tear.
( 2 ) the result of friction rub , the metal surface passivation film sleeve damage present on the surface of the metal sleeve electrode potential difference , the formation of electrochemical corrosion. Also, because of the contact at the leak itself and in the micro crevice corrosion when they have the condition , therefore , the corrosion rate is higher . Furthermore , seal ring side in contact with the atmosphere , due to the presence of oxygen , more complex and harsh etching conditions , so wear marks and spots more obvious.
PTFE sealing ring group polytetramethylene used in the ring , due to the smaller coefficient of friction than the rubber , high finish , easy to move with the ring , thus , is better than the rubber seals . Rubber seals used in the stationary ring , due to good elasticity, low hardness, therefore , the reliability is better than the PTFE ring seal . Therefore, a reasonable choice of ring material is also very important, and we based on the specific circumstances of corrosion on the mechanical seal made the following adjustments: the media side stationary ring with Teflon rings or rubber ring temperature corrosion in the atmosphere quiet side always use rubber ring ring ; ring PTFE seals are generally used , the effect is more ideal .
Bushings eliminate fretting , except try to use the sleeve surface hardness, good corrosion resistance, and maternal affinity, high surface finish of better spraying spraying materials and processes , but also pay attention when installing bushings wear, timely replacement of bushings, new security seals, in many ways to ensure sealing reliability.
pull tight security seals
pull tight security seals
2013年10月27日星期日
2013年10月26日星期六
Pump mechanical seal failure analysis
Mechanical seal means two sealing elements perpendicular to the axis of the smooth and flat surface bonded to each other and constituting the sealing relative to the rotation of the device. It usually consists of stationary ring , ring , spring loading device ( including the thrust ring , spring , spring seat , fixing screws , drive pin ) , the auxiliary ring ( ring ring seals and static seals ) and other components . Anti-rotation pin fixed to the gland to prevent static ring rotation.
From a structural point of view, the mechanical seal is easy to leak mainly axial seal , change the seal easily leaks . Because of mechanical seal has sealing performance , reliable, leak less , long life, low power consumption , does not require frequent maintenance, etc. , and can meet the production automation and high temperature , releasable cable ties low temperature, high pressure, high vacuum , high speed, a variety of explosive , corrosive and corrosive media sealing requirements , thus to obtain more rapidly than other sealing the development and promotion of more and more alternative packing seal and other seals .
Early failure of the mechanical seal now common phenomenon , causes and remedies described below:
A new face early wear and tear causes and solutions
Mechanical seal face common cause early wear and tear are the following .
1.1 motorized ring and stationary ring material selection is appropriate
By the ring and static friction ring is composed of the most important parts of the mechanical seal . Seal life and work quality ( leakage index ) are and it has a direct relationship .
Mechanical seal friction material according to the nature of the pump working medium , working pressure , temperature, rotation speed and other factors to choose, especially for old products on mechanical seal or packing seal retrofit transformation of the original mechanical seals , mechanical seals rational choice material is very important. When the mechanical seal in a corrosive medium, it is subjected to a chemical and galvanic corrosion , particularly in the friction surface , the corrosion rate is great , it is just because the end surface of the corrosion product is generated ( to reduce the corrosion rate ) was friction cause damage .bolt security seals This generated by corrosion-resistant surface to rub off , periodic cycles of more than, often referred to abrasion phenomenon . The abrasion rate of about no friction surface corrosion rate of 10 to 50 times . Therefore, the friction should choose both corrosion resistance and good wear resistance of materials . Generally , graphite impregnated with phenolic resin acid not alkali , acid and also alkali impregnated furan resin , epoxy resin impregnated alkali resistance , impregnated with PTFE resin and ceramic capability corrosive media .
From a structural point of view, the mechanical seal is easy to leak mainly axial seal , change the seal easily leaks . Because of mechanical seal has sealing performance , reliable, leak less , long life, low power consumption , does not require frequent maintenance, etc. , and can meet the production automation and high temperature , releasable cable ties low temperature, high pressure, high vacuum , high speed, a variety of explosive , corrosive and corrosive media sealing requirements , thus to obtain more rapidly than other sealing the development and promotion of more and more alternative packing seal and other seals .
Early failure of the mechanical seal now common phenomenon , causes and remedies described below:
A new face early wear and tear causes and solutions
Mechanical seal face common cause early wear and tear are the following .
1.1 motorized ring and stationary ring material selection is appropriate
By the ring and static friction ring is composed of the most important parts of the mechanical seal . Seal life and work quality ( leakage index ) are and it has a direct relationship .
Mechanical seal friction material according to the nature of the pump working medium , working pressure , temperature, rotation speed and other factors to choose, especially for old products on mechanical seal or packing seal retrofit transformation of the original mechanical seals , mechanical seals rational choice material is very important. When the mechanical seal in a corrosive medium, it is subjected to a chemical and galvanic corrosion , particularly in the friction surface , the corrosion rate is great , it is just because the end surface of the corrosion product is generated ( to reduce the corrosion rate ) was friction cause damage .bolt security seals This generated by corrosion-resistant surface to rub off , periodic cycles of more than, often referred to abrasion phenomenon . The abrasion rate of about no friction surface corrosion rate of 10 to 50 times . Therefore, the friction should choose both corrosion resistance and good wear resistance of materials . Generally , graphite impregnated with phenolic resin acid not alkali , acid and also alkali impregnated furan resin , epoxy resin impregnated alkali resistance , impregnated with PTFE resin and ceramic capability corrosive media .
New seal ring fragmentation causes and prevention measures
mechanical security seals seal ring fragmentation is a common phenomenon of early failure . Graphite stationary ring main is broken off , ceramic , tungsten carbide ring is mainly Seals cracks and deformation . Graphite ring broken off , a serious leak sealing , sealing medium pressure greater than the pressure can not be guaranteed . Although ring crack , causing leakage increased, but in most cases, but also to maintain operation . Resulting graphite ring broken off for many reasons , mainly the following .
( 1 ) Rubber seals or PTFE V-ring and graphite ring and stationary ring seat fit too tight , graphite by squeezing , under the dynamic fragmentation .
( 2 ) Install the seal chamber and pump in shock when heavy or pump seal chamber heavily skewed .
( 3 ) the swing axis and the string exceeds the specified value.
( 4 ) seal water interruption friction dry friction, high temperature , sealing ring thermal cracking , but suddenly sent to seal water , violent contraction of the seal ring fragmentation .
Ring crack main reasons are:
( 1 ) carbide ring , there is a greater stress on moving ring operation, in force , under the combined effects of internal forces cracks . These cracks are diverging radially dense fine cracks.
( 2 ) Temperature: non-metallic materials for the seal ring ( such as ceramic , WC), due to thermal conduction is not good , the ring is very uneven temperature distribution , even in normal conditions, the temperature may reach several Baidu , the temperature difference due to the presence and, thus, thermal stress caused by thermal deformation . When the thermal stress reaches a certain level , resulting in stress exceeds the ultimate strength of the material . At this time, the sealing ring on brittle materials tend to produce surface cracking , thereby enabling the sealing surface of the friction and wear and tear and failure. Due to thermal deformation of the sealing surface will fit clearance distortion, thus increasing the leakage .
Ring face with carbide , due to the thermal expansion coefficients of these materials are small , and the substrate materials, the thermal expansion coefficient difference between the larger ( stainless steel carbide thermal expansion coefficient than 3 to 4 times ) , so when the sealing temperature l exceeds a certain value , it will cause surfacing carbide seal ring deformation or cracks.
Solving dynamic and static bad fragmentation and deformation effective measures , in addition to strictly control the quality of spare parts processing , careful installation and maintenance , enhance operational management , the guarantee can be fully cable seals face lubrication and cooling are important measures. However, in practice, not any time to ensure adequate lubrication and cooling , seal water pressure fluctuations , disruption and misuse of workers , will cause the seal to lose sufficient lubrication and cooling.
( 1 ) Rubber seals or PTFE V-ring and graphite ring and stationary ring seat fit too tight , graphite by squeezing , under the dynamic fragmentation .
( 2 ) Install the seal chamber and pump in shock when heavy or pump seal chamber heavily skewed .
( 3 ) the swing axis and the string exceeds the specified value.
( 4 ) seal water interruption friction dry friction, high temperature , sealing ring thermal cracking , but suddenly sent to seal water , violent contraction of the seal ring fragmentation .
Ring crack main reasons are:
( 1 ) carbide ring , there is a greater stress on moving ring operation, in force , under the combined effects of internal forces cracks . These cracks are diverging radially dense fine cracks.
( 2 ) Temperature: non-metallic materials for the seal ring ( such as ceramic , WC), due to thermal conduction is not good , the ring is very uneven temperature distribution , even in normal conditions, the temperature may reach several Baidu , the temperature difference due to the presence and, thus, thermal stress caused by thermal deformation . When the thermal stress reaches a certain level , resulting in stress exceeds the ultimate strength of the material . At this time, the sealing ring on brittle materials tend to produce surface cracking , thereby enabling the sealing surface of the friction and wear and tear and failure. Due to thermal deformation of the sealing surface will fit clearance distortion, thus increasing the leakage .
Ring face with carbide , due to the thermal expansion coefficients of these materials are small , and the substrate materials, the thermal expansion coefficient difference between the larger ( stainless steel carbide thermal expansion coefficient than 3 to 4 times ) , so when the sealing temperature l exceeds a certain value , it will cause surfacing carbide seal ring deformation or cracks.
Solving dynamic and static bad fragmentation and deformation effective measures , in addition to strictly control the quality of spare parts processing , careful installation and maintenance , enhance operational management , the guarantee can be fully cable seals face lubrication and cooling are important measures. However, in practice, not any time to ensure adequate lubrication and cooling , seal water pressure fluctuations , disruption and misuse of workers , will cause the seal to lose sufficient lubrication and cooling.
2013年10月24日星期四
How to choose the right repair seals
Notice for users in the purchase of maintenance repair seals , most users will be according to the sample size and color to buy, this will only increase the difficulty of purchasing , but not necessarily be able to select the appropriate product. The following procedures are recommended to improve the accuracy of purchase seals :
1 the direction of movement - first determine the location of the sealing member movement direction , such reciprocating , rotary ,ss cable ties screw or fixed .
2 Sealed focus - such as deciding the point of activity in the inner diameter of the rod seal or activity point is at the outer diameter of the piston seal.
3 Temperature Class - Instructions for use machinery from the factory to inspect or assess the actual working environment temperature, determine the required use of materials . For a description of the temperature level of production users can refer to the following precautions .
4 pressure levels - from factory machinery access to the relevant data for use , or by observing the original seals and structural inference softness working pressure rating, a description of the relevant pressure level production users can refer to the following precautions .
5 size - most users will by used to buy old samples , but seals in use for some time, will be the temperature,colored cable ties pressure and wear and tear and other factors significantly affect its original size, press the select sample only as a reference , a better approach is to measure the location of the metal seal tank size , accuracy will be higher .
1 the direction of movement - first determine the location of the sealing member movement direction , such reciprocating , rotary ,ss cable ties screw or fixed .
2 Sealed focus - such as deciding the point of activity in the inner diameter of the rod seal or activity point is at the outer diameter of the piston seal.
3 Temperature Class - Instructions for use machinery from the factory to inspect or assess the actual working environment temperature, determine the required use of materials . For a description of the temperature level of production users can refer to the following precautions .
4 pressure levels - from factory machinery access to the relevant data for use , or by observing the original seals and structural inference softness working pressure rating, a description of the relevant pressure level production users can refer to the following precautions .
5 size - most users will by used to buy old samples , but seals in use for some time, will be the temperature,colored cable ties pressure and wear and tear and other factors significantly affect its original size, press the select sample only as a reference , a better approach is to measure the location of the metal seal tank size , accuracy will be higher .
The main characteristics of polysulfide sealant
Because liquid polysulfide polymer main chain containing -ss- bond , and is saturated , so the sealant made with unique properties : oil, water , solvent resistance to atmospheric aging , resistance to radiation , low temperature , good song , excellent air tightness . Can be used for construction projects , large reservoirs, diversion works , sewage treatment , bolt security seals roads, bridges , doors, windows and other joints , settlement is sealed.
l, adhesion : polysulfide sealant for cement , steel, glass, wood , natural stone , etc. have good adhesion. General building and water conservancy projects on the appropriate use of low modulus, high elongation polysulfide sealant , its bond strength ≥ 0.2Mpa, Elongation ≥ 300%.
2, the water resistance : polysulfide sealant for water, tap water, distilled water, the role of stability , compared to seawater ( salt ) the minimum change in weight .
3 , acid and alkaline able to: polysulfide sealant resistant to strong acids, alkalis . However, the dilute mineral acid, vehicle seals alkali and various salts , or stable .
4 , heat aging properties : polysulfide sealant heat aging performance very good, long-term in a 40 ℃ ~ 120 ℃ working conditions .
l, adhesion : polysulfide sealant for cement , steel, glass, wood , natural stone , etc. have good adhesion. General building and water conservancy projects on the appropriate use of low modulus, high elongation polysulfide sealant , its bond strength ≥ 0.2Mpa, Elongation ≥ 300%.
2, the water resistance : polysulfide sealant for water, tap water, distilled water, the role of stability , compared to seawater ( salt ) the minimum change in weight .
3 , acid and alkaline able to: polysulfide sealant resistant to strong acids, alkalis . However, the dilute mineral acid, vehicle seals alkali and various salts , or stable .
4 , heat aging properties : polysulfide sealant heat aging performance very good, long-term in a 40 ℃ ~ 120 ℃ working conditions .
2013年10月23日星期三
Selection of gasket
Widely used in the gasket pipes, pressure vessels and various body joint surface static seal . There are non-metallic gaskets gaskets , non-metallic gaskets and metal combination and metal gasket three categories. The commonly used materials are rubber, leather , asbestos nylon zip ties, cork , PTFE , steel, iron, copper and stainless steel .
Gasket leaks in three forms : the interface leakage, infiltration leaks and destructive leak. Where previously the two as the main form .
Gasket selection :
Gasket selection principle is that, for less demanding situations, can be empirically selected sub- city again when replaced. But for those demanding applications such as explosive, toxic and combustible gases and highly corrosive liquids equipment, reaction tank and pipeline systems, etc. , should be based on operating pressure , operating temperature, sealed.
Flange surface roughness . The surface roughness of the sealing flange great effect , especially when using non- flexible gasket , the sealing surface roughness is caused by leakage of a large value of the main. For example , turning the blade flange is a spiral line pattern , using the metal gasket , if the roughness is large, it can not block the knife profile gasket is formed of spiral grooves which , under pressure , the media will along this trench leaked . Soft gasket to the flange surface finish is required is much lower, this is because it is easily deformed , fixed length plastic strap seal to block the machining tool pattern, thereby preventing leakage. Right soft gasket and flange surface is too smooth detriment .
Gasket leaks in three forms : the interface leakage, infiltration leaks and destructive leak. Where previously the two as the main form .
Gasket selection :
Gasket selection principle is that, for less demanding situations, can be empirically selected sub- city again when replaced. But for those demanding applications such as explosive, toxic and combustible gases and highly corrosive liquids equipment, reaction tank and pipeline systems, etc. , should be based on operating pressure , operating temperature, sealed.
Flange surface roughness . The surface roughness of the sealing flange great effect , especially when using non- flexible gasket , the sealing surface roughness is caused by leakage of a large value of the main. For example , turning the blade flange is a spiral line pattern , using the metal gasket , if the roughness is large, it can not block the knife profile gasket is formed of spiral grooves which , under pressure , the media will along this trench leaked . Soft gasket to the flange surface finish is required is much lower, this is because it is easily deformed , fixed length plastic strap seal to block the machining tool pattern, thereby preventing leakage. Right soft gasket and flange surface is too smooth detriment .
Heat pump mechanical seal Precautions
Heat pump according to the conditions of use of the different installation of different forms of mechanical seals , such as the built-in single-ended flat horizontal and non- balanced ,high security cable seals double-end balanced and unbalanced type , externally mounted mechanical seals , etc. Therefore , according to the choice of seals in different forms, its using methods and precautions are also different, generally have the following specific conditions :
1, the general mechanical seal suitable for cleaning medium without suspended particles , on the newly installed piping system should be carefully cleaned reservoir together to prevent solid impurities into the mechanical seal faces .
2, in the crystallization medium using mechanical seals , attention should be cleaned regularly , before the restart after stopping to get crystal mechanical seal clean .
3 , the mechanical seal should be carefully disassemble , prohibited by hand cone, iron and other percussion . Demolition should be clear dirt.
4 , strict inspection ring and the stationary ring for face grinding , does not allow any minor scratches, Pengpo other defects.
5 , the right to adjust the amount of compression springs , making it an appropriate degree of tightness to avoid excessive wear or leakage.
6, there is an external mechanical seal flush , start should be preceded by open cavity filled with fluid sealing liquid is sealed ,adjustable length plastic seals stopping when the first stop the pump, close the seal flush fluid.
1, the general mechanical seal suitable for cleaning medium without suspended particles , on the newly installed piping system should be carefully cleaned reservoir together to prevent solid impurities into the mechanical seal faces .
2, in the crystallization medium using mechanical seals , attention should be cleaned regularly , before the restart after stopping to get crystal mechanical seal clean .
3 , the mechanical seal should be carefully disassemble , prohibited by hand cone, iron and other percussion . Demolition should be clear dirt.
4 , strict inspection ring and the stationary ring for face grinding , does not allow any minor scratches, Pengpo other defects.
5 , the right to adjust the amount of compression springs , making it an appropriate degree of tightness to avoid excessive wear or leakage.
6, there is an external mechanical seal flush , start should be preceded by open cavity filled with fluid sealing liquid is sealed ,adjustable length plastic seals stopping when the first stop the pump, close the seal flush fluid.
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