With the development of industrial technology and sealing technology, pumps in the power, chemical, petroleum and other chemical pump mechanical seal industry, the use of the pump seal the sealing and reliability requirements are higher and more stringent. The sealing of the chemical pump plays an important role in the operation of the whole equipment. The leakage of the sealing system of the chemical pump will seriously affect the normal operation of the equipment. Especially the development of high temperature and high pressure pump, but also makes the seal of the pump more stringent. At present, China's mechanical seal pump used mainly in the following ways: packing seal, labyrinth seal, floating ring seal, mechanical seal, oil seal, gasket seal, thread seal, power seal, the following on these Sealed form for a brief introduction.
First, chemical pump oil seal
Chemical pump oil seal is a self-tight lip seal, its structure is simple, small size, low cost, easy maintenance, resistance torque is small, both to prevent media leakage, but also to prevent external dust and other harmful substances intrusion, and The wear and tear have a certain degree of compensation, but not high pressure, it is generally used in low-voltage chemical pump on the occasion.
Chemical pumps rely on the principle of centrifugal extraction of liquid materials, special materials made of chemical pumps for bottles, barrels, tanks, tanks or other containers to extract corrosive liquids. As the chemical pump extraction of the media corrosion, evaporation, explosion and other dangerous existence of the sealing performance requirements of the pump, much higher than other types of pumps.
Chemical pump oil seal should be installed in the manufacturing accuracy of h8 ~ h9, surface roughness of 1.6 ~ 0.8μm and surface hardening of the shaft. The sealing medium should not contain solid particles and impurities, otherwise it will cause the oil seal and the shaft to wear quickly and make the seal fail.
In the choice of this sealing method is to give full consideration to the chemical pump to the material to the performance and requirements to avoid unnecessary leakage, to prevent accidents.
Resulting in oil seal the main factors
Seal of the oil seal is the main factor causing oil spills. When the shaft wear to form a groove, even if the replacement of the new oil seal can not be sealed, because the oil seal lip and the contact pressure drop, resulting in the installation of the oil seal diameter and shaft diameter of the interference is too small. Is the S195 diesel engine crankshaft seal, for example, analysis of the main reasons for its lax is:
Poor quality of oil seal manufacturing;
Poor quality of shaft or bearing;
Improper use of maintenance;
Improper storage, environmental pollution caused by adverse effects.
Seal of oil seal and oil spill
master and identify the basic knowledge of fake and shoddy products, buy high quality, standard oil seal.
the installation, if the shaft diameter of the outer surface roughness or rust, rust, burr and other defects, to use fine sand or linoleum polished smooth; in the oil seal or shaft diameter corresponding to the location of cleaning oil or grease. Oil seal on the outer ring coated with sealant, with the hard paper on the shaft of the keyway parts wrapped up to avoid scratching the oil seal lip, with a special tool to seal the oil into the inside, do not hard to hit the hard to prevent oil seal deformation Or crush the spring and failure; if there is lip flanging, spring off and oil seal skew must be removed when reloaded. It should be noted that: When the shaft diameter is not worn and the oil seal spring is sufficient, do not tighten the inner spring.
the application of the mechanical oil seal in general working conditions, environmental temperature difference, dust and more frequent vibration of the machine to make mechanical conditions continue to change, to check, maintenance and maintenance.
such as shaft diameter and bearing wear serious; oil seal rubber aging or spring failure, etc., should be promptly repaired and replace the corresponding parts.
the abnormal heat of the parts or assembly should be promptly troubleshooting; to avoid mechanical speeding, overload operation, to prevent oil seal lip temperature rise, rubber aging, early wear and tear mouth.
to always check the oil level, if the oil too much impurities, there are alloy powder, metal iron scraps to completely replace the new oil. Change the brand and quality of oil to meet the requirements of the season. It is recommended to add Meitre Super Sealant & Lubricant to the oil. It is an excellent gearbox additive that can form an inert film on the part that can slow the leakage of the oil seal and extend the use of the oil seal Life, can also reduce the noise of the gear box, this kind of Maitrele super seal lubricant use will not cause oil pollution or oil deterioration.
Second, the chemical pump gasket seal
Chemical pump commonly used sealing method, a gasket sealing method. Gasket is the basic components of centrifugal pump static seal, the use of a very wide range. The selection of the gasket is mainly determined by factors such as chemical pump conveying medium, temperature, pressure and corrosivity.
Gasket Sealing Mechanism:
Leakage is the phenomenon that the medium does not want to occur from the inside of the finite space or from the outside into the limited space. The media flows through the interface between the inside and outside of the space, that is, the sealing surface leaks. The root cause of the leakage is due to the existence of gaps on the contact surface, and the contact surface on both sides of the pressure difference, the concentration difference is the driving force of leakage. Due to the form of sealing surface and processing accuracy and other factors, there is a gap on the sealing surface is inevitable, which will cause the sealing surface is not fully consistent, resulting in leakage. To reduce the leakage, it is necessary to make the contact surface to the greatest degree of fitting, that is, to reduce the leakage channel cross-sectional area, increase the leakage resistance, and make it greater than the leakage driving force.
The compression surface is applied to the sealing surface to produce the pressing stress, which can improve the contact degree of the sealing surface. When the stress increases enough to cause obvious plastic deformation on the surface, the gap of the sealing surface can be filled and the leakage channel can be blocked. The purpose of the use of gasket is the use of gasket material under the action of the compression load is more prone to plastic deformation characteristics, so that the flange sealing surface of the small bumps, in order to achieve sealing.
Chemical pump gasket selection Chemical pump extraction of the media corrosion, evaporation, explosion and other dangerous existence of the sealing performance requirements of the pump, much higher than other types of pumps. Chemical pump commonly used sealing method, a gasket sealing method. Gasket is the basic components of centrifugal pump static seal, the use of a very wide range. The selection of the gasket is mainly determined by factors such as chemical pump conveying medium, temperature, pressure and corrosivity.
When the chemical pump delivery medium, the temperature and pressure is not high, the general use of non-metallic gasket;
When the chemical pump delivery medium for the medium-pressure high temperature, the choice of non-metallic and metal combination gasket.
Non-metallic gaskets are most commonly used on pumps, and their materials are generally paper, rubber and polytetrafluoroethylene. When the temperature does not exceed 120 ℃, the pressure below 1.0Mpa, the general use of green shell paper or paper paper gasket. If the chemical pump delivery medium for the oil, the temperature at -30 ~ 110 ℃, the general use of anti-aging performance better Dingqing rubber. Dangdang chemical pump delivery medium, at -50 ~ 200 ℃, the choice of fluorine rubber is more appropriate. Because it is in addition to oil and heat, the mechanical strength is also its main feature. In the chemical pump due to the transmission medium is corrosive, so the general choice of polytetrafluoroethylene as a gasket material. With the chemical pump used in the field more and more widely, the transmission medium types are more and more, so the choice of gasket material should be consulted when the relevant information or through the experiment and make the right choice.
Third, chemical pump packing seal
Chemical pump packing seal is the compression and resilience of the filler into the stuffing box, relying on the axial compression of the gland into a radial sealing force, which play a sealing effect. This seal is called a packing seal, and this filler is called a seal filler. Due to the simple form of packing structure, easy to replace, low price, to adapt to speed, pressure, wide media in the chemical pump design has been widely used.
The principle of packing seal
In the machinery industry, packing seal is mainly used for dynamic sealing, commonly used as centrifugal pump, compressor, vacuum pump, mixer shaft seal. After the packing is packed in the packing chamber, it is axially compressed by the cap screws. When the shaft is relatively moved with the packing, the radial force of the packing is brought into contact with the shaft due to the plasticity of the packing. At the same time, the impregnated lubricant in the filler is extruded to form an oil film between the contact surfaces. As the contact state is not particularly uniform, the contact area will appear boundary lubrication state, known as the "bearing effect"; and not contact the concave to form a small oil tank, a thick oil film, contact parts and non-contact parts of the irregular Maze, from the role of blocking the flow of leakage, this is called "maze effect." This is the mechanism of the packing seal. A good seal is to maintain the "bearing effect" and "maze effect". In other words, to maintain good lubrication and proper compression, if the lubrication is bad, or too tight pressure will make the oil film interruption, resulting in dry friction between the filler and the shaft, and finally lead to burning shaft and serious wear and tear. Therefore, we need to often adjust the degree of compression of the filler, so that the lubricant in the lubricant for some time after the loss, and then squeeze some of the lubricant, while compensating the load due to changes in volume caused by the relaxation of relaxation The Of course this is often squeezed packing, and finally will make the impregnant dry, so regular replacement of the filler is necessary. In addition, in order to maintain the liquid film and take away the friction heat, it is necessary to have a small amount of leakage at the packing.
Packing seal form
Packing seal in the use of chemical pump problems
Chemical pump shaft seal is generally used with wear resistance, heat resistance, good flexibility, high strength, we use packing packing and found that it has the following shortcomings: filler surface roughness, friction coefficient, there is leakage Phenomenon, and the use of a long time to immerse the lubricant easily lost. the newly repaired equipment, the beginning of the operation of the shaft seal in good condition, but it will not take long, the leakage will continue to increase, adjust the gland and replace the packing work is also gradually frequent, less than a cycle, the sleeve has been worn into a vase Shaped, serious will appear when the sleeve wear, and the water ring after the replacement of packing packing have been rotten, can not play a sealing effect. The filler is in direct contact with the shaft and is relatively rotated to cause wear of the shaft and the sleeve, so the sleeve must be replaced on a regular or irregular basis. In order to make the packing and the shaft or the sleeve between the friction heat generated in time to disperse, packing seal must maintain a certain amount of leakage, and difficult to control. packing with the shaft or the friction between the axle, resulting in the principle of effective packing of the motor to reduce the power consumption, power consumption.
Failure performance and reason of packing seal
From the principle of packing seal, the fluid in the sealed cavity can leak the channel there are three: one is the fluid through the sealing material caused by leakage; the other is from the filler and packing box leakage; the third is from the filler and the shaft Leak between surfaces. The main causes and causes are the following:
The outer surface of the filler is trapped, the packing gland outer leakage is due to the filler outer diameter is too small.
Packing into the shaft and the ring or the gap between the shaft and the gland, the design gap because of too large or eccentric.
The media leak along the packing gland, because the packing is improperly assembled or the ring is broken.
Leakage is too large, has been unable to adjust, because the filler expansion or destruction, packing cut too short or assembly error.
Fourth, the chemical pump power seal
Chemical pump in the operation, the auxiliary impeller produced by the pressure of the main impeller out of the high pressure liquid outlet, in order to achieve sealing. Parking, the secondary impeller does not work, it must also be equipped with a parking seal to solve the parking may occur when the chemical pump leak. Vice impeller seal structure is simple, reliable sealing, long life, chemical pump operation can be achieved in the water leakage, so the chemical pump to transport impurity medium pump is often used.
Power seal with centrifugal seal, screw seal, magnetic fluid seal, etc., which is very promising spiral seal. Fully enclosed seal with diaphragm and shield type.
Centrifugal power seal
Centrifuge the power seal using the premise. Centrifugal power seal is by centrifugal force, the liquid medium in the radial throw, to prevent the liquid into the leak gap, so as to achieve the purpose of sealing.
Centrifugal seals are only suitable for liquid media and are not suitable for gas media. Therefore, if airtightness is also required in places where centrifugal sealing is used, it is necessary to accommodate the combination seal type in which the centrifugal seal is combined with other types of seals.
The most commonly used centrifugal seal is the oil pan, which is widely used in a variety of gear units for sealing oil or other liquids. If the speed is too low or still does not turn, then the oil seal is invalid. If the speed is too low, In addition, the oil pan seal is not subject to high temperature restrictions. Therefore, this seal can not be used for high pressure, generally used for the case where the pressure difference is zero or closer to zero, and the heat transfer is not suitable for high temperature and high pressure. This is the form of the pump seal.
Centrifugal throttle plate structure is simple, low cost, no friction power consumption, no wear, no maintenance, so widely used.
Centrifugal seal structure. Centrifugal seal it is not thrown oil pan thrown oil seal device: in the smooth axis, the liquid medium with its adhesion is easy to crawl along the axis of the appearance, and thus easy to leak; if the car on the optical axis out of one or two rings Groove, the liquid is difficult to cross the ring groove on the sharp mutation of the interface, this time, by means of the centrifugal force of the shaft is easy to get rid of the liquid to ensure sealing. Centrifugal the oil pan and the shaft 1 into one, it is trying to leak the liquid to block, and under the action of centrifugal force will be thrown to the liquid seal on the circumference of the seal, then flow into the bottom of the oil return to the oil. The ring groove is provided in place where the sealing cap and the oil pan are common, which allows the liquid on the seal cover wall to flow down along the annular groove without flowing into the gap between the seal cap and the shaft.
When designing a centrifugal throttle seal, the radial clearance between the oil pan and the seal cap and the axial clearance should be minimized to minimize the radial clearance between the seal and the shaft. At this point, the seal ring groove should be large enough, seal between the lid and the oil pan between the oil should be large enough, the oil return channel should be as possible circulation.
Shake the oil impeller seal is equivalent to the oil pan on one or both sides of the configuration of a number of pieces, parasitic rotation caused by the role of the impeller, so that the leakage of lubricating oil with the radial flow of the flow to the return hole, thereby reducing the oil along the Axial outward. The leaves of the oil impeller should not be too large, the number should not be too much. Because too strong air and oil mixture will produce a bubble, the oil back to the negative, and the large consumption of large blade power.
Back leaf seal and secondary impeller seal, often used as IS centrifugal pump shaft seal. Vice impeller seal is often located in the sealed chamber inside a number of fixed guide vane, they can be steady flow and partial elimination of the auxiliary impeller smooth surface of the role of pressurization, thereby enhancing the impeller sealing capacity.
Centrifugal power sealing is characterized by its lack of direct contact with the friction pair, can accept a large sealed gap, it can seal the media containing solid impurities, wear small, long life, the design can be done to zero leakage. But the ability to overcome the pressure difference is low, power consumption, and even up to the pump power of l / 3. In addition, because it is a power seal, so a parking immediately lost the sealing capacity, this must be supplemented by parking seal.
Screw power seal
The working principle of the screw dynamic seal is equivalent to a screw capacity pump, the shaft is cut out on the right screw (or on the shell, both are engraved with a spiral groove), the rotation of the axis of the target from right to left as clockwise The purpose of the target, the liquid medium and the friction of the shell for counterclockwise purpose, and the friction F in the right thread on the helix of the component to the right, so the liquid
The medium is like a nut pushing the liquid to the right as the screw loosens the environment. With the capacity of the shrink, the pressure head gradually increased, so that the establishment of the sealing pressure and was