Dry gas seals used in the centrifuge

Improvement of the mechanical seal
Centrifuge traditional mechanical seals, mechanical seals are the advantages of simple structure, mature technology, machining accuracy is not required; drawback is that life is short, power consumption, there must be a liquid medium to lubricate and cool the sealing surface, the production process parameter fluctuations great seal. Since the operation centrifuges, mechanical seal life has been very short, only five months longest, replace the mechanical seal needs 28h, seriously affecting production. And after the mechanical seal (referred mechanical seal) failure is leaking liquid hexane, hexane is flammable, explosive media, not only the existence of a significant security risk, but also caused serious pollution to the environment. Based on this, we decided to change it to dry gas seal, to enhance economic efficiency and eliminate security risks. Dry gas seal is the most advanced form of a non-contact seal, mainly by the rotating ring, stationary ring, ring, spring, spring seat and sleeve components.
After rotating ring sealing surface grinding and polishing process, and the processed fluid at the dynamic pressure grooves, Figure 2. Dry gas seals rotary ring is rotated, the dynamic pressure of the sealing gas is sucked into the tank, the throttling effect of the sealing weir, into the sealing surface of the gas is compressed under the action of the gas pressure, the sealing surface is open, the gas flow forming a thin gas film between the two sealing surfaces and a thickness of 3 ~ 5um,high security cable seals when the reaction force together with aerostatic air film and the formation of the spring force is equal to the thickness of the air film is very stable, thus ensuring the seal reliability.

We analyze the structure of the centrifuge, decided not to change the device structure, the use of double-end dry gas seal, the same size as the original seal size, and a similar structure, easy to install, see Figure 3. Taking into account the process medium plastic powder, using hexane for cleaning sealed chamber for cleaning. Dynamic pressure dry gas seal ring groove machined end face, using tungsten carbide ring (WC) material, which has a high surface hardness, wear resistance, thermal conductivity coefficient, etc.; static ring using impregnated graphite material, which has high strength, good lubricating properties and high temperature, etc. from.
Seal gas is nitrogen, provided by external network, the maximum pressure is 0.7MPa, the normal operating pressure of 0.5-0.6MPa, the minimum pressure of 0.4MPa, the nitrogen flow is greater than l0 standard m3 / h.
0.7MPa nitrogen is passed through the filtration unit under reduced pressure to 0.5 MPa, into the sealed chamber through a flow meter. To prevent the pipe network in the nitrogen pressure fluctuations for emergency spare bottle with nitrogen gas source, alternate air source can supply 2h. Dry gas seal leakage from the flow meter showed normal operation, the nitrogen leak kept within a stable range,identification cable ties if the leakage continues to increase, the seal chamber pressure will drop, when the pressure drops Bian 0.3MPa, interlock parking to Centrifuge ensure safety. From the actual operation situation, the nitrogen pressure in the 0.5MPa, to ensure the good functioning at this time, nitrogen consumption was 0.48 standard m3 / h, less than the design of a standard m3 / h.

Mechanical seal failure to take measures to deal with

If the mechanical seal parts fails, you need to replace parts or increase machining precision parts, precision mechanical seals to improve the precision and the pump itself, other components of the mechanical seal is very favorable. In order to improve the sealing effect of the movement of the ring and the friction surface finish roughness higher. Width of the friction surface of the ring movement is not, generally between 2 to 7 mm.
Mechanical seal vibration, heat treatment
If the gap between the sealing ring and the movement of the small chamber, the inner diameter of seal chamber should increase or decrease the outer diameter of rotation, a gap of at least 0.75mm guaranteed. If the friction pair is improper, it is necessary to change the static ring material to temperature, corrosion resistance. This will reduce the mechanical vibration and heat sealed.
Handling mechanical seal leakage
Mechanical seal leakage is due to a variety of causes, we have to deal with specific issues. In order to minimize the amount of leakage, must be strictly in accordance with the technical requirements for the installation of mechanical seal assembly, but also pay attention to the following matters.
(1) assembly to be clean and smooth. Mechanical seal parts, tools, lubricants, wiping material to be very clean. Movement ring seal face use a soft gauze wipe. (2) trimming chamfer rounding. Shaft seal cover, such as chamfers to trim and smooth, rounded shaft and cover related to sanding polish. (3) secondary seal assembly, the auxiliary seal rubber gasoline, kerosene can not be soaked and washed to avoid swelling deformation,bolt security seal premature aging. After the static ring assembly, hand pressed compensation loop, checking is in place, is flexible; elastic snap ring is positioned reliable. Ring is installed, you must ensure that it is flexible shaft axial movement.
Shaft channeling large processing
Rational design of axial force balance device, eliminating axial channeling. To meet this requirement, the multi-stage centrifugal pumps, design options are: balance disc plus axial thrust bearing, the balance disc balance the axial force, the axial thrust bearing on the shaft axial limit.
Adding auxiliary flushing system
Seal chamber sealing medium containing particles, impurities must be flushed, because otherwise the precipitated crystals, particles, deposition of impurities, the mechanical seal spring failure, if the particles entering the friction will cause rapid destruction of the mechanical seal. Therefore, secondary mechanical seal flush system is very important, it can effectively protect the sealing surface, played cooling, lubrication, wash away debris and so on.
Pump vibration treatment measures
In the manufacturing assembly process pump products in strict accordance with the standards and procedures to perform, to eliminate vibration source. Pumps, motors, chassis, piping and other auxiliary equipment on site during on-site installation, to strictly eliminate vibration source.
Studied more than simple mechanical seals on rotating equipment applications and emerging fault,metal seals later encountered mechanical seal failure problems, we must first consider the impact factors of mechanical seals itself, and then also consider some factors outside of the mechanical seal. For example: In analyzing the causes of the accident quality mechanical seal, taking into account the impact on other parts of the pump mechanical seal operation, take measures to continuously improve the mechanical seal effect.

DME-resistant rubber sealing material standards

From Yunnan Coal Chemical Institute of Applied Technology released the "dimethyl ether rubber sealing material" corporate standard at June 1, 2010 implementation. This is currently the dimethyl ether rubber sealing material products first corporate standards.
Yunnan Institute of Applied Technology in formulating released "dimethyl ether rubber sealing material" corporate standard, the DME-resistant rubber material is divided into A and B categories.plastic truck seals A class suitable for long term or full contact with the case of DME, such as liquefied DME cylinder valve cylinder; B class or parts suitable for intermittent contact with the case of use of dimethyl ether, such as adjusting the valve or valves. Standard proposed product of the technical control indicators, DME-resistant rubber sealing material product quality to provide a detection method and the application of judgment basis.
New DME rubber sealing material and the successful development of "dimethyl ether rubber sealing material" corporate standard release, will be conducive to dimethyl ether product application and promotion.
Currently, DME as a clean fuel has been widely recognized. Since the conventional DME liquefied petroleum gas, diesel and other physical and chemical properties of the fuel there is a big difference in resistance, the sealing material as a constraint DME DME application is an important factor. To this end, Yunnan Academy of play in the rubber research in technology, research and development of new thematic groups established DME-resistant rubber seal materials research through several tests, to obtain better results. self-locking cable ties They have developed resistance to dimethyl ether rubber sealing material by Yunnan Rubber Product Quality Supervision and Inspection Station and the National Gas Appliances Quality Supervision and Inspection Center, the performance indicators meet the sealing material material requirements, especially in the anti-media volume change rate and quality changes rates have a greater breakthrough.

Mechanical seals are the primary method of modern shaft seal

Modern shaft seal mechanical seal is the main method, though use of it is not easy to achieve completely leak, but the reach of tiny, it is perfectly acceptable amount of leakage is entirely possible. However, the operation of the pump, but often embarrassing situation, then the mechanical seal failure because what is it?
1, the mechanical seal material selection inappropriate. Mechanical seal material and the transmission medium does not match. In operation, the sealing element will soon be corrosion, dissolution or wear, thus losing the sealing capability. Therefore, according to the nature of the transmission medium and the choice of the mechanical seal material is to ensure its sealing function and the normal life of the prerequisites.
2, the mechanical seal flush condition does not meet the design requirements. In conveying easy to crystallize or fine particles of the medium, there must be a certain pressure and a certain flow of fluid to wash, or their crystals or particles will accelerate the sealing wear and affect the sealing of worn automatic compensation leak. Therefore, according to the nature of the transmission medium not only to configure the appropriate flushing lines, but also to install a monitoring and regulation instruments and devices to ensure that fluid pressure and flow to meet the design requirements, in order to maintain the normal operation of the mechanical black cable ties, which is often overlooked by users.
3, each of the mechanical seal can withstand the pressure is limited, due to the seal chamber pressure measurement are not allowed, resulting in the seal chamber pressure exceeds the mechanical seal can withstand the pressure of the leak, is a common sealing One reason for failure.
4, the mechanical seal operating temperature can not exceed the specified value. In the design of a cooling circuit, often due to insufficient flow of the cooling medium leaving the cooling effect is reduced; without the cooling circuit design, the seal cavity often as harbored in the air and cause mechanical seal dry friction condition. In both cases, the movement of the mechanical seal sealing temperature is too high and accelerated wear, resulting in seal failure.
5, the use of a single spring mechanical seals ignored when spring pump rotor rotation direction and the direction of rotation correct combination also occurs. Or design without instructions or assembly negligence, failed to do so because of the rotation of the rotor mechanical seal leaving but on the contrary increase the spring force, resulting in the ring and stationary ring friction pairs formed insufficient pressure leak.
6, bearing severe wear or damage, so that axial movement of the shaft produce severe, but also one of the reasons mechanical seal leakage. With the scientific and technological development, new marker cable ties and sealing materials, emerging forms, which is bound to the pump seal technology have a direct impact and promoted. Long life, zero leakage pump products in a growing number of occasions to get promotion and application.

Hydraulic equipment damaged by the impact of seals

Mechanical processing industry, hydraulic transmission is widely used, such as lathes and other types of semi-automatic hydraulic transmission . These machines during use , such as the impact of frequent , reptiles and other faults , diagnostic repair, often in the hydraulic control components ( such as various types of pumps, valves ) can not find the cause of the malfunction , resulting in maintenance trouble. The final such failure or normally found on the actuator causes the cylinder piston sealing element due to severe wear . Such phenomena especially "O" ring seal see more .
Example 1: a CE7120 hydraulic copying lathe, turret profiling occurs in the work cited by the sword turn longitudinal feed line cutting die cutter , resulting knife fight , scrap living phenomenon frequently, the machine does not work.
Inspection and Maintenance : Check no fault of the hydraulic control components , maintenance work one o'clock into blind spots. Overhauling vertical turret tank, found that the piston seal "O" ring seal has been polished cylindrical , cylindrical piston also found substandard size requirements ( genus machine tool manufacturing reasons ) , the diameter direction is less than standard size 0.8mm, piston and cylinder body clearance large, causing vertical cylinder two chambers communicate channeling oil . Maintenance, and replacement of the piston passing "O" -ring after the die cutter machine troubleshooting. Analysis of the reasons cited in the profiling tool holder in place of the instantaneous line of the sword , the whole holder to receive a momentum F ', the force is decomposed F'1 a horizontal force acting on the cylinder piston rod longitudinal direction , at the same time , the solenoid valve 34E1-25B work turned vertical cylinder rod chamber pressure oil chamber connected rodless return oil control valve , the piston rod chamber by the force F by the two partially completed , one for F'1, the other is F1 = A1P1, where A1 is rodless chamber force area , then F = F'1 + F1. Under normal circumstances , the piston under the action of the force F rod chamber began to move , as incompressible hydraulic oil , hydraulic oil pressure rodless abrupt increase cavity to form a back pressure piston , the piston control valve according to the force balance it is set to go steady speed knife . The moment due % F'1 role in longitudinal cylinder chamber pressure P2 will be greater than P1. In practice, the two-chamber cylinder gap channeling due to the P2> P1 moments, hydraulic fluid from the high pressure zone with rod chamber rod chamber to the low pressure area flow trends , liquidity , once produced , P2 reduced , P1 rises , F1 increase large , unbalanced force piston , the piston driven turret quickly moves to the rod chamber . And moments later, the end result of profiling tool slide downward acting on the piston in the cylinder longitudinal horizontal thrust F'1 disappear on their own fast-moving piston end , take the knife stabilized turret , Fixed Length plastic seal red knife phenomenon ends.
Example 2: a CB3463-1 semi-automatic programmable hexagon turret lathes, during use , the emergence of the turret feed rate can not adjust the failure phenomenon , globe valve 2 is closed there is still crawling, pediment , and has been to bottom of the tank to stop the machine does not work properly .
Inspection and Maintenance : Inspect all hydraulic control components , especially the governor components have not found any problems. Replace some of the control valve , the failure persists . After dismantling the cylinder after the discovery piston "O" ring seal badly worn , so that the two chambers of hydraulic oil cylinder channeling each year. Analysis of the reasons , because "O" -ring wear, cylinder rod chamber and the rod chamber gap increases interoperability, when closing valve control valve 3 or 2:00 , it means cutting off the cylinder rod chamber oil return road. Theoretically , the pressure oil into the cylinder rod chamber when the piston is formed without a force F , the piston rod chamber to move the trend, as the cylinder rod chamber back to the oil off the rapid formation of the oil cavity back pressure , so that the force balance across the piston stationary , F a = F no time , no fluid pressure chamber due to the piston force different size and different, that is, P a > P no .
In practice, a gap is formed due to the two chambers communicate with each cylinder , the cylinder chamber with pressure oil from the high pressure region to the low flow area trends , mobile one generation,security seals a lower chamber pressure P , P without elevated ends of the thrust acting on the piston F No > F Yes, loss of balance piston rod chamber to move to find a new balance . And so forth, the piston has been moved to an external force barrier to stop. The phenomenon of the maintenance work to the machine brought great impact , replace the cylinder piston "O" ring seal , the machine fault elimination , running back to normal.

These aspects of mechanical seals how to do these problems

Graphite ring ( or ceramic ) fracture
PTFE o-ring friction is small , stationary ring with snap ring rotation , the contact pin after the break.
Symptoms at the pin groove cracking or destroyed a graphite ring .
Corrective measures making pin sets ; self-locking cable ties using other types of seals or static ring structure.
o-ring overheating
Usually because the heat conduction unfavorable end result .
Symptoms rubber ring hardening and cracking. PTFE blue or black. Near the seal face the worst .
Corrective measures checking seal design ; Check and improve circulation status .
o-ring extrusion
o-ring part is forced through a small gap . Assembly or assembly of components when the force is too large, or the sealing gap is too large .
Symptoms o-ring is cut or torn skin .
Corrective Action Check the assembly method .
o-ring corrosion, swelling
Symptoms inappropriate material selection occurs when swelling , fracture , deformation and other faults.
Corrective measures based on the actual conditions, re-select the material .
Graphite erosion ( element )
When the fluid pressure is too large or contains grinding particles .
Symptoms of flushing fluid inlet is on the element at a erosion pits .
Corrective measures to reduce the fluid pressure ; using hydrocyclones .
Evacuated
System pressure fluctuations or cavitation generated at the seal faces
Symptoms: plastic security seals the dregs at the end round and round Zhoucheng Bo striated , 0 laps extrusion, static ring from the bit .
Corrective Action: change the system operation process , increase the amount of rinse

Industrial pump mechanical seal failure and these reasons

Vibration is too large
Mechanical seals vibration is too large , resulting in loss of seal. But the reasons for larger vibration mechanical seal mechanical seal itself is often not the cause , the other parts of the pump is the source of vibration , such as shaft design is unreasonable ,container seals processing reasons, lack of precision bearings , couplings parallelism poor, radial force and other reasons .
Pump cavitation causes
Since the unit and the pump inlet system operation unreasonable cavitation performance is not good, the high speed of the pump , the pump inlet localized cavitation , cavitation occurs, the water will bubble one hand, it will impact the mechanical seal faces an outer surface , so that the surface damage ; hand side anastomosis ring movement causes a flow membrane also contains bubbles can form a stable flow of film, resulting in movement of the ring fit surface friction, the mechanical seal device is damaged .
Lack of precision machining
Machining accuracy is not enough , there are many reasons , some precision mechanical seal itself is not enough, the reason for this is easy to arouse people's attention , but also easy to find. But sometimes the other components of the pump is not precision , the reason for this is not likely to cause people 's attention . For example: shaft , bushings ,security seals  pump, seal chamber to increase accuracy is not enough other reasons . The presence of these reasons, the sealing effect of the mechanical seal is very unfavorable .

The transformation of plant water pump seal

Rotating machinery as a pump , the shaft and the casing there is a gap between the necessity , in order to prevent discharge of liquid out of the pump or leakage of air into the pump ( inlet of vacuum ) , generally between the shaft and the pump casing provided with a shaft sealing device . Recent years due to the continuous development of high-temperature high-pressure pump , the pump seal problems have an impact on safety is one important factor . Shaft sealing device currently used generally have the following forms: packing seal , mechanical seals, labyrinth seals, floating ring seal , and for many of the low-pressure pump power plant , generally soft packing seal .
Multi-use asbestos , carbon fibers, PTFE resin and other materials woven into a square or circle. Soft packing seal has a versatile, cheap and so on . Plus the usual soft fillers such as leaking water pump , generally tight gland plate method . If not , you must stop the pump again for filler. And soft filler cycle is generally short and right sleeve wear larger , which makes routine maintenance increases, and not the economy. At this stage able to use other methods to use it instead of packing ? Foreign experience combined with China 's actual thermal power plant , the available injectable filler gun wadding method to replace the use of packing .
Soft packing filler gun injection principle is to pulpy soft packing high pressure pump filler injected into the chamber ,releasable cable tie which was replaced rope -like packing. Other parts of the packing room remains unchanged .
A transformation step
Because at this stage low-pressure pumps and more thermal power plant with packing seal , which faces an example of how to transform based on the original problem , based on experience and are summarized below .
1.1 clean packing room
Thoroughly clean the pump before the transformation good original packing room , does not allow any impurities and dirt. If seal ring, can be abandoned. This work must be carried Uncovery in order to save time and materials , it is best when the pump overhaul . This allows the overhaul and reconstruction synchronization.
1.2 water pump cover drilling
In order to inject fillers, must cover the installation of the injection hole connector. Joints need special processing, the threads need to cooperate with the filler gun fittings and connectors to be processed gland , for a water pump seal , seal tube can be removed directly in the water seal on the drilling and tapping.
1.3 plus packing
In order to prevent leakage and internal leakage filler is required at each end of the packing chamber before and after the installation of a circle packing, you can add carbon fiber packing or PTFE packing.security seal labels Because it is Uncovery added packing, so care must be taken plus packing clearance fit to close .
1.4 plus filler
First hand pressed into the filler packing room , without too tight. Then close the pump cover with gland packing rope , and then put the gun filler filler can be injected under pressure . At this time packing should be tight .

Correctly handle automotive sealing problems

Automotive sealing strip (automobile rubber seal strip) is one of the important parts car , widely used in doors, windows , body , seats, sunroof, and other parts of the engine compartment and trunk , with a waterproof, sealing, noise , dust , frost , shock absorption , warmth and energy conservation an important role. It must have a strong tensile strength , good flexibility , but also good heat resistance and resistance to aging. In order to ensure the fastening strips and profiles , strips and profiles section structure dimensions must match .
Fix the sealing flange in the vehicle door , the seal should be noted that repair damaged flanges , flange accurately restore the original shape. To carry out the repair after the door seal inspection, the inspection method is: put a hard disk in a sealed position, shut the door , and then pull the paper , according to the Rally to determine the size seal is good . If the force required to pull the paper too much explanation sealed tight, this will affect the doors close properly , and also due to deformation of the seal over the Omo faster mourning for sealing performance ; if the force required to pull the paper too small , indicating bad seal doors wind does not often appear rain phenomenon. When replacing the door must pay attention to the inner and outer door panels in a new office painted folding plastic flange bite and put some punch hole left when the small craft with the base tape blocked .
In the repair of automotive line , should all body holes , holes worn harness ring is mounted at the place, not only because these seals from the seal, but also play a protective role in the harness . If the seal is damaged or harness can be rotated or ran seals , replace the metal security seals, and compares it with the body holes , hole assembly firmly secure the harness is good .
In the window glass is damaged , changing with the same curvature as the original glass window glass , while the glass to check the guide groove and seal for damage. Because windows often reply after repair is less than its original shape , therefore , when in addition to ensure easy pulling or lifting the window glass , but also pay attention to the window glass in the windows closed after four weeks of the seal.
In changing the roof , the roof should be in place around the lamination coated conductive sealant, after a good to be welded seams in the water tank and folding over the painted plastic , which not only helps the body seal , prevents the body due to more water to produce the weld flange early rust. Assembling the door when the door below the window paste an entire inner panel sealing barrier film , if not forming a seal barrier film , you can use ordinary plastic instead of paper , and then affix the seal spacer film compaction , and finally for interior panels production assembly .
When replacing the entire body , in addition to each of these projects should be completed outside , but also in the lap portion of the weld joints on both coated with sealant layer thickness should be about 1mm, and may not have virtual sticky layer , bubbles and other defects ; should be at the Flap Flap special plastic coated ; across the floor surface and the lower surface of the front cover should be coated 3mm-4mm elastic coatings and anti-corrosion coating ; on the floor surface and the front elevation to paste the plate surface noise, heat , vibration damping film , colored cable ties then covered insulation blankets block , and finally covered with carpets or fitted with decorative flooring. These measures can greatly enhance the sealing and the vehicle speed slows down corrosion of the body , but also can greatly enhance comfort.

Gasket leaks cause analysis

The gasket leakage :
General gasket leaks , there are four forms: interface leak , leak penetration , diffusion leaks, damage leak.
Penetration leak: soft gasket material because the material is mostly fiber, easy to dip appropriate media , in particular pressure . tie wraps Due to capillary phenomenon, the medium will penetrate into the low pressure side to form infiltration.
Interface Leak : The interface is not as gasket compression flange surface finish combined with improper flange deformation etc will leak in the sealed interface . For interface World leakage , the use of padded material can be clamped against the flange surface .
Destruction Leakage: sealing parts relatively poor working conditions , thermal deformation, often affected by vibration, shock , improper installation , fastening force is too large , used repeatedly , deformation , stress concentration, fatigue strength and damage than the material aging , deterioration etc will cause damage leak. This leakage causes the greatest impact hazard is also large , to strengthen prevention.
Diffusion Leakage: poor concentration , driven by the media or by sealing the gap sealing material produced by mass transfer and capillary leak . Diffusion is the result of molecular motion , and not one-way. Minimal pressure or vacuum in a sealed state , or sealed nitrogen, high security seal hydrogen and other permeable substances, as well as highly toxic , radioactive substances should pay special attention penetration and proliferation of two kinds of leaks.