Types of seals: guidelines for selecting the correct seal

What is a seal?

Seals are data or parts that prevent fluid or solid particles from leaking from adjacent joint surfaces and prevent external impurities such as dust and moisture from invading the internal parts of machines and equipment.

Application of seals

Although rubber and plastic seals are small, their functions make them basic components and accessories in national defense, chemical industry, petroleum, coal, transportation, machinery manufacturing and other major industries of the national economy, and they play a very important role in the development of the national economy.
Industrial shaft seals are used for sealing between rotating parts and fixed parts or between two relatively moving parts. The main sealing functions include: sealing lubricant, anti fouling, isolation of two different media and sealing under pressure.

Classification of seals

Seals are divided into four categories: sealant, filler seal, rubber seal and mechanical seal.
Sealant classification: glass sealant, waterproof sealant, steel barrel sealant, elastic sealant, polyurethane sealant, PVC mastic, polysulfide sealant, acrylic sealant, flame retardant sealant, epoxy sealant, nitrile sealant, etc.
Packing seal classification: packing, metal spiral wound gasket, graphite composite gasket, tooth type gasket, octagonal gasket, steel gasket, asbestos gasket, non asbestos gasket, flexible graphite plate, graphite coiled material, graphite gasket, asbestos rope, oil resistant plate, filled modified tetrafluoroethylene plate, polytetrafluoroethylene plate, etc.
Classification of rubber seals: U-ring, Y-ring, O-ring, rubber gasket, combined gasket, rubber diaphragm, rubber plate, nylon plate, nylon rod, rubber tube, rubber sealing strip, etc.
Classification of gaskets: nitrile rubber gasket, fluoroprene rubber gasket, silicone rubber gasket, fluororubber gasket, polyamine grease gasket, polytetrafluoroethylene gasket.
Mechanical seal:

• ① According to the rotation or standstill of the spring element, it can be divided into: rotary inner flow unbalanced single face seal, referred to as rotary type; static outer inner flow balanced single face seal, referred to as static type. According to the location of the static ring inside or outside the seal face, it can be divided into: inner and outer type.
• ② According to the leakage direction of sealing medium, it can be divided into internal loss and external flow.
• ③ According to the unloading caused by the media on the end face, it can be divided into balanced and unbalanced.
• ④ According to the logarithm of sealing face, it can be divided into single face and double face.
• ⑤ According to the number of springs, it can be divided into single spring type and multi spring type.
• ⑥ Classified by elastic elements: spring compression type and bellows type.
• ⑦ According to the non-contact mechanical seal structure classification: hydrostatic, hydrodynamic, dry gas seal.
• ⑧ Classification according to the temperature of sealing chamber: high, medium, common and low temperature sealing.
• ⑨ Separate according to the pressure of sealing chamber: ultra-high, high, medium and low pressure mechanical seal.

1. Gasket

What is a gasket?

GasketIt is a mechanical seal between two objects, which is usually used to prevent pressure, corrosion, and natural thermal expansion and contraction leakage of the pipeline between two objects. Since the machined surface cannot be perfect, the use of gaskets can fill the irregularity. Gaskets are usually made of sheet data, such as pad paper, rubber, silicone rubber, metal, cork, felt, neoprene rubber, rubber, fiberglassVinyl or plastic polymers (e.g. polytetrafluoroethylene). Gaskets for specific applications may contain asbestos.
The washer is a hole (usually in the middle) in the thin plate (usually circular). It is usually used as a fastener to distribute the load thread. Other uses are as spacers, springs (Belleville gaskets, wave gaskets), wear pads, pre display devices, and locking devices. Rubber gaskets are also used in faucets (valves)To cut off flowing liquid or gas. Rubber or silicon gaskets can also be used to reduce fan vibration. Usually, the outer diameter of the gasket is about twice the inner diameter.
Application of gaskets
From the design idea, spring washer (also called spring washer)It has pretension, and after being compressed, it will rebound. In actual use, due to the characteristics of the thread, the nut is easy to rotate in the direction of the helix after being tightened, resulting in nut loosening. In order to solve this problem in the early days, spring washer appeared. Because of the pretension of spring washer, after the nut compresses the spring washer, under the effect of pretension, the nutThe inner triangle thread and one side of the bolt triangle thread are tightly attached together. Under the action of friction, the nut will no longer be loose. The ordinary washer (also called circular hole washer or flat washer or ordinary washer)Is a support under the pretension of the spring washer, which increases the pressing area of the preload of the spring washer. Generally speaking, the spring washer and the ordinary washer are used together, and it is unreasonable to use the ordinary washer alone. Of course, it does not exclude the design and actual needs of individual uses. For example, when the plastic shell of an electrical appliance is screwed with self tapping screws, the following separate ordinary washerThe circle is just to increase the force area.
Classification of gaskets
1. Non metallic gasket

• Rubber gasket
• Non asbestos fiber rubber gasket
• Flexible graphite metal composite gasket
• PTFE gasket
• PTFE coated gasket
• Other types of non-metallic material gaskets

2. Metal nonmetal composite gasket

• Corrugated gasket
• Spiral wound gasket
• Metal toothed composite gasket
• Metal clad gasket
• Metal wave tooth composite gasket
• Other types of metal composite gaskets

3. Metal gasket

• Metal flat gasket
• Metal corrugated gasket
• Metal toothed gasket
• Metal ring gasket
• Metal lens gasket
• Metal O-ring gasket

The metal ring gasket can be divided into:

• Octagonal ring gasket
• Oval ring gasket
• RX and BX type self tightening sealing ring gaskets.

Gasket Selection Guide
The data for selecting shims mainly depends on the following three factors: temperature、Pressure and medium

• Temperature: It is very important to determine the temperature of gasket. The temperature limit of gasket depends on its data. For high temperature environment, the gasket data resistant to high temperature should be selected, such as silicone rubber or PTFE.
• Pressure: It is also important to select the pressure limit of the gasket. The gasket should be able to withstand the working pressure of the relevant equipment. For high-pressure environment, high-strength gaskets should be selected.
• Medium: It is also important to determine the medium that the gasket will contact. Some media may corrode some data, so it is necessary to select a corrosion resistant gasket.

In addition, other factors, such as size, shape, thickness, etc., need to be considered to ensure that the gasket can meet the requirements of relevant equipment. In general, selecting a suitable gasket requires a comprehensive evaluation of the use environment and requirements.

Matters needing attention

• The two flanges must be on the same centerline and parallel. It is not allowed to insert bolts or pointed steel into the bolt hole to correct the flange, so as to prevent the bolts from bearing large stress. Before installation, carefully clean the flange sealing surface and water line (sealing line). Spiral wound gasket is best used for flanges without dense sealing line.
• Only one gasket can be added between two flanges. It is not allowed to eliminate the defect of excessive clearance between two flanges by adding more gaskets. The gasket must be installed correctly without deflection to ensure uniform pressure and avoid the gasket from being eroded by medium and causing eddy current when it is inserted into the pipeline.
• When tightening the nut, use a torque wrench when the nut is below M22, and use a pneumatic wrench when the nut is above M27. To ensure that the gasket is evenly pressed, the bolts should be tightened symmetrically and evenly in 2-3 times.

2. Sealing strip

What is a sealing strip?

The sealing strip is a product that seals something so that it is not easy to open, and plays the role of shock absorption, waterproof, sound insulation, heat insulation, dust prevention, fixation, etc. The sealing strip is made of rubber, paper, metal, plastic and other materials.
Application of sealing strip
The door sealing strip is mainly applied to the door frame, side window, front and rear windshield, engine hood and trunk lid, playing the role of waterproof, dust-proof, sound insulation, temperature insulation, shock absorption and decoration. EPDM rubber sealing strip has excellent anti-aging, high and low temperature resistance and chemical drug resistance performance, good elasticity and compression deformation resistance, and long-term use does notIt will crack or deform, and its original high sealing performance can be maintained between – 50 ° and 120 °.
Classification of sealing strips
The rubber data of the sealing strip includes three types: dense rubber, sponge rubber and hard rubber. The hardness of hard rubber can reach Shore A95. The rubber material of the sealing strip is mainly aging resistant, low temperature resistant, moisture resistant, chemical resistant, especially ozone resistant ethylene propylene diene monomer (EPDM)EPDM can be compounded with steel belt, steel wire braid, TPE, flannelette, flocking, PU coating, organic silicon coating, etc. to ensure the waterproof, dust-proof, sound insulation, heat insulation, vibration reduction, abrasion prevention and decoration functions of the interior and the outside of the car. Generally, EPDM sealing strips can be used stably for more than ten years. Neoprene rubber with good ozone resistance and aging resistance can also be selected (CR). In consideration of the process properties of common rubber compounds, it is sometimes necessary to select rubber blends, such as natural rubber (NR), CR and styrene butadiene rubber (SBR), or polyethylene (PE), EPDM and NR rubber and plastic blends to improve ozone resistance. With the development of thermoplastic elastomer (TPE)With the continuous development and maturity of science and technology, the application field continues to expand. Among the raw materials used to manufacture sealing strips, EPDM, the main raw material used in the past, is also constantly updated and developed. The new EPDM with excellent physical properties and good processing properties can control the medium and long chain branching of molecules, improve its vulcanization performance, and increase the extrusion speed and product output. NewThe data of TPO and TPV are also increasingly used in automobile sealing strips. These data not only have the excellent engineering performance of elastomers, but also have the excellent characteristics of plastics. They are not only convenient for processing, but also recyclable. These data are gradually replacing EPDM products.
Selection guide of sealing strip

• 1. Determine the size of the sealing strip to avoid that the sealing strip is too long or too short, or the height and width of the sealing strip are inconsistent with the size of the door and window frame.
• 2. Select the appropriate type of sealing strip, and determine the type of sealing strip to be purchased, including Type I, D, E, etc., to avoid that the purchased sealing strip cannot be installed and used.
• 3. Select the material of the sealing strip, and determine the material of the sealing strip according to the different use environment, characteristics, functions, etc. For example, EPDM sealing strip is mainly used for sealing in high-temperature steam environment. In short, select the material of the sealing strip according to the use status of doors and windows.
• 4. Check the sealing strip. When selecting the door and window sealing strip, pay attention to whether there are obvious cracks and uneven concave and convex on the sealing strip. The surface of the sealing strip is required to be clean, free of scratches, bruises, rust, flat and smooth, uniform thickness, and free of pores.

Maintenance of sealing strip
First, check whether the sealing strip is cracked or broken. If the sealing strip is broken or has large cracks, use adhesive to repair.
In particular, it is easy to repair large cracks in the sealing strip with special adhesive for sealing strip. Of course, if the sealing strip is seriously damaged or aging, it is usually better to replace it with a new one.
It is not difficult to replace the sealing strip, but if you want to do a better job, you’d better ask professionals to do it.
The daily maintenance of the sealing strip mainly includes the following items: first, use car detergent to clean, and then apply a layer of high permeability protective agent to prevent the sealing strip from aging.
In addition, the gaps between the sealing strips are easily filled with sand and dust, which may lead to corrosion. Therefore, the sand and dust should be removed with a brush.
Matters needing attention
The sealing strip plays a sealing and waterproof role in plastic steel doors and windows, aluminum alloy doors and windows, and wooden doors and windows. The sealing strip has high requirements for materials. First, it must have strong tensile capacity and elasticity, as well as good temperature resistance and aging resistance. At the same time, in order to ensure the close contact between the sealing strip and the profile, the sectional structure of the sealing strip must match the profile of the door and windowIt is generally applicable to suspended windows and folding doors and windows.The wool sliver is usually installed on the sash of the Dolby special door and window to seal the gap between the frame and the sash. The specification of the wool sliver can greatly affect the watertight performance of the door and window, and also can affect the opening and closing of the door and window. If the specification of the wool sliver is too large or the vertical hair is too high, it will be very difficult to assemble, and after assembly, it will also be when the door and window are movingThe resistance becomes larger. If the fire specification is too small or the vertical hair is too low, the doors and windows are prone to bracket phenomenon, reducing the sealing of the doors and windows. There are generally two types of wool slivers that have been silicified and that have not been silicified. Generally, the use effect of the treated wool slivers will be better. The qualified wool slivers have the following characteristics: no obvious defects in appearance, flat surface, bottom plate and verticalThe hair is relatively smooth and free from bending, and there are no pockmarks and other problems on the bottom plate, meeting the size requirements.

3. Packing

What is packing?

Packing is also called sealing packing, which is usually woven from soft linear objects. Usually, rectangular or circular strips with a cross sectional area are filled in the sealing cavity.
Working principle of packing
Working principle of packing The shaft surface is very uneven under microscopic conditions, and can only partially fit with the packing. Therefore, there is a small gap between the packing and the shaft, just like a labyrinth. The medium is intercepted many times in the labyrinth, so as to achieve the sealing effect of the packing.
The packing seal is installed in the stuffing box by the packing, and the packing is pressed on the surface of the shaft through the packing gland. Because the shaft surface is always somewhat rough, it can only be partially bonded with the packing, and some of it does not contact, which forms numerous labyrinths. When the pressurized medium passes through the shaft surface, the medium is throttled for many times, with this “labyrinth effect”So as to achieve sealing. The fit and friction between the packing and the shaft surface are also similar to sliding bearings. There should be enough liquid for lubrication to ensure a certain life of the seal, which is the so-called” bearing effect “. It can be seen that a good packing seal is a combination of labyrinth effect and bearing effect.
The compression force of the packing on the shaft is generated by tightening the gland bolts. Since the packing is an elastoplastic body, the friction force will be generated when it is compressed axially, which will gradually reduce the compression force along the axial direction. At the same time, the generated radial compression force will make the packing close to the shaft surface and prevent the leakage of media. The radial compression force is distributed from the outer end (gland)To the inner end, the pressure of the medium decreases gradually from the inner end to the outer end. When the pressure of the medium at the outer end is zero, there is little leakage. When the pressure is greater than zero, there is leakage.
With the continuous emergence of new materials, the structural type of packing has also changed greatly, which will undoubtedly promote the wider application of packing seals. The data used as packing should have the following characteristics: a certain degree of elastic-plastic. When the packing is compressed axially, it can produce a large radial compression force to obtain a seal; when the machine and shaft have vibration or the shaft has runout and eccentricity, it can have a certain degree ofCompensation capability (following); chemical stability. It is neither corroded or swelled by the medium nor polluted by the medium; impermeability. The medium has some penetration to most fibers, so the filler is required to be compact, so it is often necessary to dip and fill various lubricants and fillers when making the filler; it has good self lubrication, small friction coefficient and wear resistance; and temperature resistance. It can withstand a certain temperature after friction heatingEasy disassembly, simple manufacturing and low price.
Application of packing
As a static seal, it is widely used in containers, heaters, manholes, covers, etc. It can also be used for heat insulation and fire protection of pipes, etc. It is suitable for neutral media, and can be used for water, steam, air, oil and other services. Jinfang fiber packing is specially imported and customized with high strength,
High resilience, soft and wear-resistant high-performance novel synthetic fiber packing, superior to the commonly used yellow aramid and white aramid, generally golden yellow, commonly known as “golden aramid”According to needs, it can also be customized as orange or blue. This packing also makes up for many shortcomings of tetrafluoro packing. It is thermally stable, low thermal expansion, dimensional stability under the condition of alternating temperature and pressure, high strength, but no shaft grinding, easy cutting, and excellent chemical resistant media, especially for acids, organic solvents, oils and fuels. Application: high-performance general-purpose packing for pumps and valves, widely usedIt is used in various industrial fields, especially for the medium that needs cleaning and easy to wear in the food and paper industries where the graphite composition is not suitable.
Classification of packing
1. Aramid series
Gold aramid fiber packing, yellow aramid fiber packing, aramid fiber interweaved white tetrafluoro packing, aramid fiber interweaved black tetrafluoro packing This series of packing takes aramid fiber as the main data, and is precisely prepared by repeatedly dipping lubricants, tetrafluoro emulsion, etc. It has good high resilience, chemical resistance, low cold flow, and high linear speed. Compared with other types of packing, it can resist granular crystallization mediumHigh quality and higher temperature. It can be used alone or combined with other packing. It is mainly used under the condition of many medium particles and easy to wear.
2. Tetrafluoro series
White tetrafluoroethylene packing, black tetrafluoroethylene packing, white tetrafluoroethylene interweaved aramid fiber packing, black tetrafluoroethylene interweaved aramid fiber packing, tetrafluoroethylene pre oxygenated wire packing, white tetrafluoroethylene impregnated silicone oil packing, white tetrafluoroethylene impregnated rubber core packing This series of packing takes polytetrafluoroethylene as the main data. It has excellent chemical stability, corrosion resistance, sealing performance, high lubrication and non adhesion, and good anti-aging endurance+It can work for a long time under the temperature of 250 ℃ to – 180 ℃. It can resist all other chemicals except molten metal sodium and liquid fluoride, and it will not change when boiled in aqua regia. It is mainly used in the working conditions where pollution is not allowed, such as sanitary grade, strong corrosiveness, high linear speed, wear and tear, etc.
3. Graphite series
Flexible graphite packing, metal reinforced graphite packing, carbon fiber reinforced graphite packing, carbon fiber metal reinforced graphite packing This series of packing characteristics are carefully compiled based on the data of graphite as the main body. It has the advantages of good self-lubricating and thermal conductivity, small friction coefficient, strong versatility, good flexibility, high strength, and protection for the shaft rod. According to different requirements, it can be usedThe data of carbon fiber, copper wire, 304, 316L, Yinke nickel alloy wire, etc. are strengthened. They are mainly used under the working conditions of high temperature and pressure.
4. Carbon fiber series
Carbon fiber reinforced graphite packing, carbon fiber metal reinforced graphite packing This series of packing mainly uses carbon fiber as the theme data. Carbon fiber is a new material with excellent mechanical properties. Carbon fiber has no creep, good fatigue resistance, small coefficient of thermal expansion, good corrosion resistance, and good thermal conductivity. It is mainly used in high-temperature and high-pressure wear resistant conditions.
5. Series with rubber core
It is woven by wrapping super elastic silicone core in high-quality synthetic fiber and repeatedly dipping in tetrafluoro emulsion, lubricant and barrier agent. It can effectively absorb mechanical vibration and control leakage of cracks caused by vibration. It has excellent resilience, self lubrication, flexibility, wear resistance, high tensile strength, good chemical resistance, etc.
6. High temperature and ultra-high temperature packing
The disc root is precisely woven from high-quality synthetic fiber, with fine structure, excellent high temperature and high pressure resistance, low thermal conductivity, non combustibility and other advantages. It is widely used in water, steam, acid, alkali and other media under extreme high temperature and high pressure. It is used for thermal insulation and fire protection of pipes, containers, heaters, manholes, furnace door heaters, high-temperature flanges and other placesIt is used in steel works at high temperature and is specially used for blast furnace combustion valve.
In addition to the above materials, there are acrylic packing, high water-based packing, and hemp packing to meet the needs of various working conditions.

Selection Guide of Packing

• ① The working condition requirements should be consistent with the packing performance. The packing that best meets the requirements can be selected according to the relevant technical data. If there is any doubt, please consult the sales representative.
• ② The packing size must be correctly selected according to the sealing requirements. In order to determine the cross section, please use the following formula: cross section=(stuffing box diameter – valve stem diameter)/2 damaged device may need a packing with a slightly larger cross section to compensate for the damage.

Maintenance of packing

• 1. After the packing seal assembly is completed, it can be put into operation. Before the formal start-up, it is necessary to use manpower to slowly start and test run (turning gear). During the operation, if the torque is too large, which may be caused by the tightness of the packing gland, it is appropriate to loosen the gland bolts and adjust them until the friction resistance becomes smaller and the seal does not leak. When packing seal starts to operate, if it is found that the friction torque is large and the temperature of packing box is long, it may be caused by lack of lubricant or excessive preload. Measures should be taken to adjust, and if allowed, appropriate seal leakage should be controlled. For most harmless centrifugal pumps, a small amount of drip leakage should be kept under normal conditions to cool and lubricate.
• 2. After the packing seal is officially started, it is necessary to insist on patrol observation on time, and pay attention to whether the leakage of braided packing and the temperature of the stuffing box meet the requirements. If the braided packing is abnormal, it should be adjusted immediately. If the leakage of the packing seal is greater than the allowable value, the gland can be tightened, but not more than one turn at a time, and the allowable leakage of the packing seal should still be maintained to prevent sudden friction heatIncrease and burn the sealing packing.
• 3. For the packing seal on the dynamic seal, especially the sealing part with high linear speed, cooling water or lubricant shall be poured continuously, which is a powerful measure to improve the sealing effect and extend the service life of the packing.

Matters needing attention

• 1. After the packing seal assembly is completed, it can be put into operation. Before the formal start-up, it is necessary to use manpower to slowly start and test run (turning gear). During the operation, if the torque is too large, which may be caused by the tightness of the packing gland, it is appropriate to loosen the gland bolts and adjust them until the friction resistance becomes smaller and the seal does not leak.
• When packing seal starts to operate, if it is found that the friction torque is large and the temperature of packing box is long, it may be caused by lack of lubricant or excessive preload. Measures should be taken to adjust, and if allowed, appropriate seal leakage should be controlled. For most harmless centrifugal pumps, a small amount of drip leakage should be kept under normal conditions to cool and lubricate.
• 2. After the packing seal is officially started, it is necessary to insist on patrol observation on time, and pay attention to whether the leakage of braided packing and the temperature of the stuffing box meet the requirements. If the braided packing is abnormal, it should be adjusted immediately. If the leakage of the packing seal is greater than the allowable value, the gland can be tightened, but not more than one turn at a time, and the allowable leakage of the packing seal should still be maintained to prevent sudden friction heatIncrease and burn the sealing packing.
• 3. For the packing seal on the dynamic seal, especially the sealing part with high linear speed, cooling water or lubricant shall be poured continuously, which is a powerful measure to improve the sealing effect and extend the service life of the packing.

4. Oil seal

What is an oil seal?

Oil seal is the customary name of general seals, which is simply the seal of lubricating oil. It is a mechanical element used to seal grease (oil is the most common liquid substance in the transmission system, and also generally refers to general liquid substances). It separates the parts that need lubrication in the transmission parts from the output parts, so as not to let the lubricating oil leak. Static seal and dynamic seal(General reciprocating movement) seal is called oil seal.
The representative form of oil seal is TC oil seal, which is a double lip oil seal with self tightening spring completely covered by rubber. Generally speaking, oil seal refers to tc framework oil seal.
Operating principle of oil seal
During normal operation, oil first passes through capillarity and rough structure (oil seal narrow band and shaft roughness)The pumping function of the oil seal enters into the narrow band where the oil seal contacts the shaft. When the oil seal enters this contact surface, the pumping function starts to work. The cascade micro pump at the atmospheric side has a high potential pumping capacity, and on this basis, the fluid dynamic pressure balance is formed. Now, the seal operates on the oil film to maintain the sealing state. At this time, the operating state is the lean oil lubrication state. This is the oil sealMicroscopic model of mechanism.
The macro model is as follows: in fact, the oil seal rarely keeps absolutely perpendicular to the axis during operation, and the entire seal is generally inclined; or it is manufacturing error, such as angular eccentricity or the hole in the cavity is not parallel to the axis. The final performance is that when the shaft rotates, the oil seal performs low amplitude reciprocating axial movement relative to the shaft, the frequency is the shaft speed, and the stroke depends on the size of the angular eccentricityThere is a phenomenon that oil will be pumped to the area with steep contact pressure gradient for reciprocating seals with asymmetric pressure distribution.
Application of oil seal
Engine: crankshaft – crankshaft front and rear oil seal valve – valve oil seal (engine repair kit o-ring) (distributor oil seal, water pump oil seal, balance shaft oil seal, oil pump oil seal…); camshaft – camshaft oil seal; transmission: transmission – transmission front and rear oil seal gear lever oil seal (transmission repair kit o-ring) (transfer case – transfer case front and rear oil seal); Rear axle: axle shaft – rear axle shaft oil seal differential – (front) rear quarter oil seal rear wheel oil seal steering gear oil seal (steering gear repair kit o-ring) steering booster oil seal (front axle shaft oil seal).
All parts in the operating body box that have liquid lubricating oil and are connected with the outside need oil seals. Some are rubber, some are metal, and most are steel reinforced rubber, such as the rear crankshaft oil seal, the front and rear transmission oil seal, the left and right half shaft oil seal, the front oil seal of the main reducer, the crankshaft oil seal of the air compressor, etc.
Classification of oil seals
Oil seals are generally divided into single type and assembly type. The assembly type is that the skeleton and lip data can be freely combined, which is generally used for special oil seals.
From the sealing function, characteristics, structural type, working state and sealing mechanism of oil seal, it can be divided into many forms and different names. However, it is customary to call rotary shaft lip seal oil seal, and static seal and dynamic seal (generally reciprocating) seal.
The representative form of oil seal is TC oil seal, which is a double lip oil seal with self tightening spring completely covered by rubber. Generally speaking, oil seal refers to tc skeleton oil seal. See Fig. for skeleton oil seal schematic diagram.
Selection Guide of oil seal
Similar to the selection principle of other seals, the oil seal type and data shall also be selected according to the sealing medium and working conditions. The working conditions mainly consider the operating pressure, operating linear speed and operating temperature range.
When selecting the oil seal data, the compatibility of the data with the working medium, the adaptability to the operating temperature range, and the ability of the lip to follow the rotating shaft at high speed must be considered. Generally, the lip temperature of the oil seal is 20~50 ℃ higher than the working medium temperature when it is working, so attention should be paid to the selection of oil seal materials. For details, please refer to the table of rubber types and general characteristics.
Under the condition of the same diameter, oil seals manufactured with different data have different ability to adjust the linear speed of shaft surface rotation, and the relationship is shown in the figure below. The linear speed range used by oil seals is generally less than 15m/s
The operating pressure of ordinary oil seal generally does not exceed 0.05MPa. When the working pressure exceeds this value, pressure resistant oil seal shall be selected.
The working range of oil seal is related to the data of oil seal use: – 40~120 ℃ for NBR, – 30~180 ℃ for ACM and – 25~300 ℃ for FPM.
Maintenance of oil seal

• a. If there is slight leakage after the pump is started, it should be observed for a period of time. If the leakage does not decrease after 4 hours of continuous operation, the pump should be stopped for inspection.
• b. The operating pressure of the pump shall be stable, and the pressure fluctuation shall not exceed 1kg/cm2.
• c. During the operation of the pump, evacuation shall be avoided to avoid dry friction on the sealing surface and seal damage.
• d. The sealing condition shall be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil shall not be more than 5 drops/minute, and the light oil shall not be more than 10/minute. If there is no improvement trend within 2-3 days, the pump shall be stopped to check the sealing device.

Matters needing attention
1. Preparations and precautions before startup

• a. Comprehensively check whether the mechanical seal, accessory devices and pipeline installation are complete and meet the technical requirements.
• b. Before starting the mechanical seal, carry out static pressure test to check whether the mechanical seal has leakage. If there is a lot of leakage, find out the cause and try to eliminate it. If it is still invalid, disassemble, check and reinstall it. Generally, the static pressure test pressure is 2-3 kg/cm2.
• c. Turn the pump according to the rotation direction and check whether it is light and even. If the turning is hard or does not move, check whether the assembly size is wrong and the installation is reasonable.

2. Installation and shutdown

• a. Before starting, the sealing chamber shall be kept full of liquid. When transporting solidified medium, the sealing chamber shall be heated by steam to melt the medium. Before starting, the turning gear must be turned to prevent sudden start from causing soft ring fragmentation.
• b. For the mechanical seal using the external sealing oil system of the pump, the oil sealing system shall be started first, and then the oil sealing system shall be stopped after shutdown.
• c. After the hot oil pump is shut down, the cooling water of the seal oil chamber and the end face seal cannot be stopped immediately. The cooling water can only be stopped when the oil temperature at the end face seal drops below 80 degrees to avoid damaging the sealing parts.

Troubleshooting

• 1. Master and identify the basic knowledge of fake and inferior products, and purchase high-quality and standard oil seals.
• 2. During installation, if the outer surface of the shaft diameter has low roughness or defects such as rust spots, rust, burrs, etc., it should be polished with fine emery cloth or oilstone; clean engine oil or lubricating grease should be applied to the oil seal lip or the corresponding position of the shaft diameter. The outer ring of the oil seal should be coated with sealant, and the key slot on the shaft should be wrapped with hard paper to avoid scratching the oil seal lip. Use special tools to rotate and press the oil seal inward,Never hit or punch hard to prevent the oil seal from deforming or breaking the spring, which will lead to failure. If lip flanging, spring falling off and oil seal deflection occur, it must be removed and reinstalled. It should be noted that when the shaft diameter is not worn and the oil seal spring has sufficient force, do not tighten the inner spring without authorization.
• 3. The oil seal applied to machinery shall be inspected, maintained and maintained frequently when its working conditions are generally bad, the ambient temperature difference is large, there is much dust, and the mechanical conditions of the parts are constantly changing due to frequent vibration of machines and tools.
• 4. If the shaft diameter and bearing are seriously worn; the oil seal rubber is aging or the spring is invalid, repair and replace the corresponding parts in time.
• 5. The abnormal heating parts or assemblies shall be timely troubleshooting; mechanical overspeed and overload operation shall be avoided to prevent oil seal lip temperature rise, rubber aging, lip early wear, etc.
• 6. Always check the oil level of the engine oil. If there are too many impurities in the engine oil and there are alloy powders and metal iron filings in the engine oil, completely replace the engine oil. The brand and quality of the replaced engine oil should meet the requirements of the season. It is recommended to add Metley super sealant&lubricant to the engine oil. It is an excellent gearbox additive, which can form an inert data film on the components, which can slow downThe leakage of oil seal can extend the service life of oil seal gear, and also reduce the noise of gearbox. The use of Metre super sealing lubricant will not pollute or deteriorate the oil.

5. Mechanical seal

What is a mechanical seal?

Mechanical seal is one of the precision and complex mechanical basic elements. It is the key component of various pumps, reaction synthesis kettles, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as model selection, machine accuracy, correct installation and use.
There are mainly the following four types of components. a. Main seals: moving rings and stationary rings. b. Auxiliary seals: sealing rings. c. Fasteners: springs, push rings. d. Driving parts: skip seats and keys or fixing screws
Operating principle of mechanical seal
Mechanical seal refers to a sealing device formed by two sealing elements sticking together and rotating relative to each other on a smooth and straight surface perpendicular to the axis. It usually consists of static ring, dynamic ring, spring loading device (including push ring and spring box), auxiliary sealing ring (dynamic ring sealing ring, static ring sealing ring)The anti rotation pin in the anti rotation sleeve is fixed on the outer gland to prevent the stationary ring from rotating.
The end faces of the moving ring and the stationary ring form a pair of friction pairs. The moving ring presses its end face against the end face of the stationary ring by the pressure of the liquid in the seal chamber, produces appropriate specific pressure on the end faces of the two rings, and maintains an extremely thin liquid film to achieve sealing. Therefore, from the structural point of view, the mechanical seal is mainly to change its axial seal that is very easy to leak into an end seal that is not easy to leakIn the actual operation process, mechanical seal is not a separate component, it is combined with other parts to operate.
Application of mechanical seals
The mechanical seal is a device to prevent fluid leakage, which is composed of at least one pair of end faces perpendicular to the rotating axis under the action of fluid pressure and the elasticity of the compensation mechanism and the cooperation of the auxiliary seal. In light mechanical seals, rubber corrugated pipes are also used as auxiliary seals. The rubber corrugated pipes have limited elasticity, and generally need to be supplemented with springs to meet the requirements ofThe elastic loading mechanism and auxiliary seal are mechanical seals of metallic corrugated pipes, which are called metal corrugated pipe seals.
Classification of mechanical seals

• According to the rotation or standstill of spring elements, it can be divided into: rotary inner flow unbalanced single face seal, referred to as rotary seal; static outer inner flow balanced single face seal, referred to as static seal.
• The stationary ring can be divided into built-in type and external type according to whether it is located inside or outside the seal face.
• According to the leakage direction of sealing medium, it can be divided into internal loss and external flow.
• According to the unloading caused by the media on the end face, it can be divided into balanced and unbalanced.
• According to the logarithm of sealing face, it can be divided into single face and double face.
• According to the number of springs, it can be divided into single spring type and multi spring type.
• Classified by elastic elements: spring compression type and bellows type.
• According to the non-contact mechanical seal structure classification: hydrostatic, hydrodynamic, dry gas seal.
• Classification according to the temperature of sealing chamber: high, medium, common and low temperature sealing.
• Separate according to the pressure of sealing chamber: ultra-high, high, medium and low pressure mechanical seal.

Selection Guide for Mechanical Seals

• 1. According to the pressure of the sealing chamber, determine whether the sealing structure is balanced or unbalanced, single end or double end.
• 2. According to the working speed, the rotary type or static type, hydrodynamic type or non-contact type shall be adopted.
• 3. According to the temperature and fluid properties, determine the friction pairs and auxiliary sealing materials, and correctly select the lubrication, flushing, insulation, cooling and other mechanical seal cycle protection systems.
• 4. According to the effective space of the installation seal, it is determined to use multiple springs or single springs or wave springs, internal or external.

Maintenance of mechanical seals
1. Preparations and precautions before startup

• a. Comprehensively check whether the mechanical seal, accessory devices and pipeline installation are complete and meet the technical requirements.
• b. Before starting the mechanical seal, carry out static pressure test to check whether the mechanical seal has leakage. If there is a lot of leakage, find out the cause and try to eliminate it. If it is still invalid, disassemble, check and reinstall it. Generally, the static pressure test pressure is 2-3 kg/cm².
• c. Turn the pump according to the rotation direction and check whether it is light and even. If the turning is hard or does not move, check whether the assembly size is wrong and the installation is reasonable.

2. Installation and shutdown

• a. Before starting, the sealing chamber shall be kept full of liquid. When transporting solidified medium, the sealing chamber shall be heated by steam to melt the medium. Before starting, the turning gear must be turned to prevent sudden start from causing soft ring fragmentation.
• b. For the mechanical seal using the external sealing oil system of the pump, the oil sealing system shall be started first, and then the oil sealing system shall be stopped after shutdown.
• c. After the hot oil pump is shut down, the cooling water of the seal oil chamber and the end face seal cannot be stopped immediately. The cooling water can only be stopped when the oil temperature at the end face seal drops below 80 degrees to avoid damaging the sealing parts.

3. Operation

• a. If there is slight leakage after the pump is started, it should be observed for a period of time. If the leakage does not decrease after 4 hours of continuous operation, the pump should be stopped for inspection.
• b. The operating pressure of the pump shall be stable, and the pressure fluctuation shall not exceed 1kg/cm2.
• c. During the operation of the pump, evacuation shall be avoided to avoid dry friction on the sealing surface and seal damage.
• d. The sealing condition shall be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil shall not be more than 5 drops/minute, and the light oil shall not be more than 10/minute. If there is no improvement trend within 2-3 days, the pump shall be stopped and the sealing device shall be checked.

Matters needing attention
1. Precautions during installation
a. Pay great attention to avoid installation deviation during installation

• (1) The gland shall be tightened after the alignment of the coupling. The bolts shall be evenly supported to prevent the end face of the gland from deflecting. Check each point with a feeler gauge, and the error shall not be greater than 0.05 mm.
• (2) Check the fit clearance (i.e. concentricity) between the gland and the outer diameter of the shaft or shaft sleeve. The circumference should be even. Use a feeler gauge to check that the tolerance of each point is not more than 0.01mm.

b. The compression amount of the spring shall be carried out according to the regulations. It is not allowed to be too large or too small, and the required error is 2.00 mm. If it is too large, the specific pressure of the end face will be increased, and the other end face will be worn. If it is too small, the specific pressure will be insufficient and the sealing effect will not be achieved.
c. The movable ring shall be able to move flexibly on the shaft after installation, and it shall spring back automatically after pressing the movable ring against the spring.
2. Precautions during disassembly

• a. When disassembling the mechanical seal, be careful. It is forbidden to use a hammer or flat shovel to avoid damaging the sealing elements. A pair of wire hooks can be made to extend into the notch of the transmission seat in the direction of self financing and to pull out the sealing device. If the scaling cannot be removed, it should be cleaned before removal.
• b. If mechanical seals are used at both ends of the pump, take care of each other during assembly and disassembly to prevent neglect of one thing and loss of another.
• c. For the operated mechanical seal, if the gland is loose and the seal moves, the moving and stationary ring parts must be replaced and should not be tightened again for continued use. Because after the sample moves, the original running track of the friction pair will change, and the sealing of the contact surface will be easily damaged.

Troubleshooting of mechanical seals
1. Sealing surface open
When repairing mechanical seals, 85% of seal failures are not caused by wear, but have leaked before wear.
As soon as the sealing surface is opened, solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface is closed, these solid particles are embedded on the surface of the soft ring (usually the right ink ring), which is actually a “grinding wheel” that will damage the surface of the hard ring.
Since the moving ring or rubber ring is fastened on the shaft (shaft sleeve), when the shaft is in series, the moving ring cannot fit in time, which causes the sealing surface to open and the sealing surface to close behind time, so that solid particles enter the sealing surface.
At the same time, there are also solid particles between the shaft (shaft sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (relative moving sealing point, common fault). In addition, the medium will also produce crystals at the friction part between the rubber ring and the shaft (shaft sleeve), and there will also be solid substances at the spring, which will open the sealing surface.
2. Overheating
Since heat will be generated on the sealing surface, the use temperature of the rubber ring should be lower than the design specification. The use temperature of fluororubber and polytetrafluoroethylene is 216 ℃, and the use temperature of nitrile rubber is 162 ℃. Although they can withstand higher temperatures, the rubber ring is in danger of continuing vulcanization due to the high heat generated on the sealing surface, and eventually loses elasticity and leaks. (Cold brittleness is considered for cold zone)
Heat can also cause crystallization of media between sealing surfaces, such as carbon deposition, which can cause the sliding parts to be stuck and the sealing surface to be condensed. Moreover, some polymers are coking due to overheating, some fluids lose lubrication due to overheating, and even flash.
Overheating can not only change the condition of the medium, but also aggravate its corrosion rate. It will cause deformation of metal parts, cracking of alloy surface, and some coating cracks. Balanced mechanical seals should be selected in the design to reduce the specific pressure to prevent overheating.
3. Out of tolerance
Correct assembly tolerance is necessary for the installation of mechanical seal. The shaft (shaft sleeve) must have proper surface roughness and correct size, but the manufacturer rarely provides tolerance data, which is critical for installation. (Rely on experience and common sense)
The dimensional accuracy and geometric tolerance of the mechanical seal must meet the requirements of the drawing, and out of tolerance will lead to premature failure of the seal.

Selection Guide for Seals

We hope that the seals can maintain good sealing performance in their life cycle, with low friction and wear, and also have good performance in harsh working environment. In order to meet the different requirements in the above aspects, we should choose seals more reasonably. Since many factors will affect the selection of seals, we should choose sealsIt is necessary to understand the application environment of the oil cylinder and make a choice after analyzing and studying its performance requirements.
When we select seals, we must consider the following important factors:
1. Pressure
The high or low pressure and the length of pressure cycle change have a great impact on the damage of seals. The higher the pressure, the greater the impact of other factors on the performance of seals, such as temperature, speed, seal data, clearance between piston and cylinder barrel, and clearance between piston and cylinder head.
2. Temperature
It is difficult to describe the maximum service temperature and minimum service temperature of a kind of seal data, because this is the result of the comprehensive influence of a series of factors. As the working temperature of piston and piston rod are different, they should be selected differently.
3. Friction
The friction between seals and sealing surfaces depends on many factors: surface roughness, surface characteristics, pressure, medium, temperature, seal data, seal type and movement speed.
4. Surface treatment
Experience shows that the characteristics of the surface of the cylinder piston and piston rod have a great impact on the life of the seals. The surface characteristics are usually defined by the value of surface roughness Ra, which is the arithmetic mean of the absolute value of the surface shape deviation from the centerline. However, these values do not fully represent the impact of surface conditions on the seals, because even under the same roughness, different surface shapesThe shape feature can lead to different degrees of seal wear.
Matters needing attention
(1) Select proper seal material and hydraulic oil, as well as adaptability to working temperature and oil compatibility.
(2) The geometric position accuracy (concentricity) of the sliding parts relative to the seals is high, and the good materials (such as hard chrome plating) and the fine surface roughness can extend the service life.

• ① For the oil seal used for hydraulic pump and motor journal, not only the roughness of the sliding surface is required to be within 0.25m Ra, but also the surface is required to be plated with hard chrome. During specific use, the radial spring force of the oil seal lip needs to be properly adjusted according to the specific situation to make it moderately tight. In addition, during installation, an installation sleeve or thin gasket should be used to protect the seal ring to prevent the lip from rolling and twisting,Causes the spring to slip out.
• ② The common rolling processing method for the inner surface of hydraulic cylinder barrel not only improves the surface roughness, but also makes its surface undergo cold work hardening treatment, which is conducive to extending the service life of the seal ring. In addition, the pressure used, the length and type of sliding surface also have a great impact on the service life. Therefore, the “regular inspection” time should be determined according to these conditions.
• ③ It is required that the sealing surface should be well lubricated to prevent dirt from invading people. It is also necessary to use the oil with the specified cleanliness level and the correct installation method.

(3) Before installing the seals, ensure that there are no impurities and cracks in the seal groove, and apply operating oil to the seal groove and the surface of the seals respectively; gradually install the seals in order; avoid sharp edges during installation, and straighten the seals to avoid distortion and skew; in case of split groove, tighten the gland at the end.

How to select the correct seal manufacturer?

The following points need to be considered when selecting the correct seal manufacturer:

• Quality: ensure that the seals produced by the selected manufacturer have good quality and reliability.
• Product range: ensure that the manufacturer provides the seals you need and has sufficient product range to adjust your needs.
• Price: consider whether the price provided by the manufacturer is reasonable, and compare the prices of multiple manufacturers to ensure that the most cost-effective option is selected.
• Customer service: ensure that the manufacturer has good customer service to help you solve any problems or difficulties.
• Brand image: study the brand image of the manufacturer to ensure that a manufacturer with good reputation is selected.
• Supply chain stability: ensure the stability of the manufacturer’s supply chain to ensure that you can get the products you need at any time.

By considering these factors, you can choose a high-quality and trustworthy seal manufacturer.