Summary
Bearings are very important components of centrifugal pumps and are also normal wear parts that are most prone to failure. Improper selection/design and use will directly affect the safe and reliable operation of the pump unit. This article will be based on the relevant provisions of the API 610 standard, taking API OH2 type pump bearings as an example, and discuss improvements in aspects such as selection, bearing box structural design, lubrication, cooling, installation maintenance and monitoring, and the application of new technologies and new materials. The path to operational reliability of centrifugal pump bearings.
Keywords: centrifugal pump bearing reliability approach
Preface
Like mechanical seals, bearings are also very important parts of the centrifugal pump body, and they are also the normal wear parts that are most prone to failure. Bearings support the shaft and reduce friction on the pump’s moving parts by keeping the rotor rotating smoothly. Bearings also bring stiffness and damping to the rotor-support system. Improper selection/design and use will directly affect the safe and reliable operation of the pump unit. An equipment reliability study conducted at a large refinery concluded that 40% of rotating equipment failures (pumps, mixers, etc.) were attributed to bearing failure. It is further estimated that 48% of bearing failures are caused by particle contamination and 4% by corrosion (from liquids in oil). In fact, bearing oil contamination accounts for 52% of bearing problems and 21% of rotating equipment failures [1].
This article will be based on the relevant provisions of the API 610 11th edition standard [2], taking the API OH2 type pump bearing as an example, and combined with practical engineering experience, from selection, bearing box structural design improvement, lubrication, cooling, installation maintenance and monitoring, The application of new technologies and new materials will be used to explore ways to improve the operational reliability of centrifugal pump bearings. I hope it can be used as a reference for colleagues.
Bearing selection
Technology and experience have led to advancements in manufacturing, materials and design, improving the overall reliability of single-stage overhung (OH2) centrifugal pumps. The basic design criteria of the OH2 type pump have remained relatively unchanged, including a bearing housing with radial and thrust bearings, and an impeller suspended on a shaft outside the bearing housing. Industry standards such as API 610, purchasing recommendations and design considerations have been steadily revised to help improve the overall reliability of pumps.
Bearing type
The standard states that each shaft should be supported by two radial bearings and a double-acting axial (thrust) bearing…The bearings should be one of the following combinations:
- Radial rolling bearings and thrust bearings;
- Radial hydrodynamic bearings and rolling thrust bearings;
- Radial hydrodynamic bearings and thrust bearings.
The standard also limits the application of bearings:
a) The rotational speed of the rolling bearing: shall not exceed the nominal speed limit published by the bearing manufacturer. For ball bearings, the factor ndm shall not exceed 500,000 for a single bearing lubricated with thin oil and 350,000 for a bearing lubricated with grease…
c) If the energy intensity (that is, the product of the pump’s rated power kW and rated speed r/min) is 4,000,000 or greater, hydrodynamic radial bearings and thrust bearings must be used.
Almost all types of bearings are used in centrifugal pumps. The same pump model often even uses two or more different types of bearings, depending on different operating conditions or buyer preference. Most process pumps use antifriction or oil film (sliding) bearings as follows:
1) Anti-friction bearings (rolling bearings)
- Single row deep groove ball bearings
- Double row angular contact ball bearings
- Single row angular contact ball bearing pair
- Cylindrical Roller Bearings
- Tapered roller bearing set
Single row angular contact bearings are often used in pairs. They can be used in series for large one-way thrust loads, or back-to-back for two-way thrust loads. Double row angular contact bearings or their equivalent configuration (bearings mounted in back-to-back pairs) have been found to be very suitable for pumps producing high thrust loads in any direction. Back-to-back bearings last approximately twice as long as comparable double-row bearings. Angular contact bearings require a certain amount of preload.
2) Sleeve bearings (sliding bearings)
3) Tilt pad thrust bearing
Sleeve bearings and tilt pad thrust bearings are commonly used in large pumps and motors with high thrust and/or radial loads that exceed the antifriction bearing capacity [3].
For the OH2 type pump, it is basically a combination of “radial rolling bearings and thrust bearings”. Its standard configuration is: the non-drive end radial bearing uses a deep groove ball bearing or a cylindrical roller bearing + a drive end thrust bearing, which is a 40° angular contact (7000 series) with a machined brass cage, installed back to back in pairs Angular contact ball bearings.
Determination of thrust bearing load
Regarding the load-bearing capacity of thrust bearings, the standard stipulates that they should be designed to operate continuously under all specified operating conditions, including maximum pressure differential and meet the following requirements:
a) The loads on all bearings should be determined based on (single) internal design clearance and twice the internal design clearance…
b) If the direction of rotation is opposite to the normal direction of the pump, the thrust bearing should be able to withstand the full load.
The bearing load is related to the pump structure, impeller type (single suction and double suction), impeller structure (with or without balance holes, back blades), orifice ring diameter, inlet pressure and bearing type.
Special note: Regarding the selection of bearing load capacity, the standard configuration is usually twice the maximum force. It should not be too small or too large. If it is too small, the bearing temperature will be high and the service life will be reduced due to insufficient load-bearing capacity. If it is too large, the rolling bearing will slip and be damaged due to insufficient load.
Bearing life requirements and calculations
Bearing selection is limited by mean time between maintenance (MTBR) or service life or fugitive emissions requirements. The standard stipulates that the bearing system life (the calculated life of the pump bearing combination system) requires continuous operation of at least 25,000 hours under rated operating conditions; at least 16,000 hours under maximum radial and axial loads and rated speed.
The standard provides a formula for calculating the life of the bearing system. Judging from the results displayed by the formula, the system life is shorter than the life of the bearing with the shortest life in the system. For example: If the life of each bearing is 37,500 hours, according to the formula, the life of the bearing system is only 25,000 hours. In other words, to meet the bearing system life of 25,000 hours, the life of each bearing must reach at least 37,500 hours.
When selecting/designing centrifugal pump bearings, the service life of the bearing must be evaluated by calculating the rated life of the bearing and the load, speed and other parameters under actual working conditions. For the calculation of bearing life, please refer to the literature [4].
Basic requirements for bearing boxes
In order to ensure operational reliability, the standard stipulates the structure and configuration of the bearing box:
1) The bearing housing should be arranged so that the bearings can be replaced without moving the pump driver or mounting bracket.
2) All equipment should be designed to allow rapid and economical maintenance work. Major parts such as pump casing components and bearing housings should be designed and manufactured to ensure accurate alignment during reassembly. Alignment can be accomplished by using shoulders, dowels and keys.
3) For thin oil self-lubricating bearings, the bearing box should be equipped with ventilation caps and blocked oil filling holes and oil drain holes. The hole diameter is at least DN 15. The bearing housing shall be equipped with a visual constant oil level oiler with a capacity of at least 1.2 dl, equipped with a positioner to determine the oil level, an oil container with heat-resistant glass and a metal mesh protective cover. The bearing box should be equipped with a glass window (bull’s eye) for observing the oil level. The appropriate oil level should be in the middle of the glass window. A permanent marking of the oil level should be accurately determined…
4) For pressure oil lubricated bearing boxes, they should be designed to minimize foam formation, and the oil drainage system should maintain the oil level so that the foam level is lower than the shaft end seal.
5) In addition, corresponding regulations are also made for the structure/configuration of bearings and bearing boxes with pure oil mist lubrication and purge oil mist lubrication.
lubricating
Lubricants are used to isolate the rolling and sliding contact surfaces of bearings, prevent wear and reduce friction and excessive heat generation. Lubricants also prevent corrosion, remove heat (like oil lubrication), and help block contaminants (like grease lubrication) [5].
Proper lubrication is the key to long, trouble-free centrifugal pump bearing life. Survey results in some industries indicate that more than 30% of bearing failures are caused by poor lubrication [6]. Poor lubrication can be divided into:
1) The lubricant is incorrectly selected;
2) The amount of lubricant is incorrect;
3) The lubricant is contaminated;
4) Lubricant deterioration.
Standard states: Unless otherwise specified, bearings and bearing housings shall be designed to be lubricated with mineral oil (hydrocarbon oil).
Viscosity is the most important property of a lubricant. Using a lubricant with the correct viscosity for speed, operating temperature and load ensures a complete oil film between rotating parts. When an incorrect viscosity is used, the load-carrying capacity of the lubricant is negatively affected.
For viscosity recommendations, the OEM operating manual should be consulted, but it is also important to measure the sump operating temperature because viscosity decreases with increasing temperature. Table 1 shows the lubricating oil viscosities recommended by SKF for ball bearings at different operating temperatures.
Table 1: Selection of ball bearing lubricant viscosity at different operating temperatures (SKF recommendation)
插入图一
Oils in process pumps are usually ISO VG32, 46, 68 or 100. The oil is usually a hydrocarbon oil, although synthetic oils are sometimes used in specific lubrication applications.
The viscosity of synthetic oils is less sensitive to temperature changes and is more widely used when temperature fluctuations are present. If the temperature exceeds 100°C, it is recommended to use synthetic oil because the oxidation rate of mineral oil increases at higher temperatures [7].
For the combination of “radial rolling bearings and thrust bearings”, there are four main lubrication methods: grease lubrication, thin oil self-lubrication, oil mist lubrication and pressure oil lubrication.
The selection of lubricant should comprehensively consider factors such as load, working temperature, operating speed, working environment temperature and service life requirements. The general principles for selection are:
1) For high speed, light load and stable working conditions, use low viscosity lubricating oil or low consistency grease. On the contrary, use high viscosity lubricating oil and grease with higher consistency.
2) In working conditions with low working and ambient temperatures, lubricating oil with smaller viscosity or grease with low consistency should be used. On the contrary, a lubricating oil with a higher viscosity or a grease with a high consistency and a high dropping point should be used. The viscosity of summer oil is generally higher than that of winter oil. Lubrication under high temperature conditions should consider the flash point of the lubricating oil and the dropping point of the grease. Lubrication under low temperature conditions should consider the freezing point of the lubricating oil. If the temperature range changes greatly, a tackifier can be used to improve the viscosity-temperature properties of the lubricating oil.
3) For humid environments, lubricants with strong emulsification resistance, oily properties, and good rust resistance should be selected. Sodium-based grease without water resistance should not be used.
4) The smaller the gap between the friction surfaces, the lower the viscosity of the lubricating oil used should be. Generally, the lubricating oil viscosity during the running-in period of new parts should be lower than that during the normal use period.
5) If the friction surface is roughened, the lubricating oil required has a high viscosity and the grease has a high consistency. On the contrary, when the surface finish is high, use lubricating oil with low viscosity and low consistency.
6) The consistency of the grease used in the centralized lubrication system should be lower to facilitate transportation. Lubricating oil with a higher viscosity should be used for manual intermittent refueling to avoid loss too quickly [8].
grease
Grease is the preferred bearing lubricant because it is simple to apply, can be retained in the bearing housing more easily, and improves sealing. The use of grease is mainly limited to low power pumps.
If the estimated grease life is less than 2,000 hours, grease lubrication should not be used.
Where operating conditions permit, sealed “lubricated for life” bearings are an attractive alternative, eliminating the need for relubrication and associated maintenance.
Thin oil self-lubricating (oil bath, oil ring and oil slinger)
Thin oil lubrication is usually used when grease cannot be used due to limitations such as speed, temperature or lubricant life. Advantages are ease of filling/draining, increased rotational speed, reduced heat and filtration capabilities.
Thin oil lubrication is divided into two categories: thin oil self-lubrication and pressure oil lubrication. The most common thin oil self-lubricating methods are: oil bath lubrication, oil ring lubrication and oil throw plate lubrication.
In oil ring lubrication, the oil ring is suspended on a horizontal shaft with its lower end immersed in an oil pool below the bearing. Oil rings are more dependent on shaft speed than immersion depth and are prone to overlubrication if not properly designed. But a good rule of thumb is to submerge 3/8″ at the deepest point.
Oil sling pan lubrication is commonly used in Europe, usually made of stainless steel. Oil slinger pans are less prone to overlubrication problems because they are connected directly to the rotating shaft, and they should also be immersed in oil approximately 3/8″[9].
Experience shows that at ndm > 150,000, to meet the minimum requirements in reliability-focused factory environments, shaft-mounted stainless steel sling pans generally perform well. This sling pan is less likely to cause unforeseen downtime than many other methods currently popular. The oil ring is sensitive to the levelness of the shaft, the viscosity of the lubricating oil, the immersion depth of the oil ring, the concentricity of the ring and the surface roughness [10].
Oil mist lubrication
The basic concept of the oil mist lubrication system is to disperse oil aerosol into the bearing housing, and it is a centralized low-pressure lubrication system [7].
Oil mist lubrication is divided into two types: pure oil mist lubrication and purge oil mist lubrication. Oil mist lubrication is suitable for rolling bearings. Radial hydrodynamic sliding bearings should be lubricated with purge oil mist, but oil mist lubrication is not suitable for tilting pad thrust bearings.
Oil mist lubrication produces the least friction of all pump bearing lubrication methods (allowing speed to be determined based on bearing design rather than lubrication limitations) and creates positive pressure within the bearing housing, which prevents the intrusion of contaminants.
Special Note:
1) The currently commonly used oil mist lubrication method is pure oil mist lubrication;
2) When using oil mist lubrication, a slight positive pressure must be maintained in the oil tank;
3) In order to prevent oil mist from leaking from the seals at both ends of the bearing box, the bearing box should use magnetic oil seals or INPRO oil seals with better sealing effects [11].
Pressure oil lubrication
According to standard regulations, hydrodynamic radial bearings and thrust bearings must be used if the energy intensity is four million or more. For pumps equipped with such bearings, pressure oil lubrication must usually be provided.
However, for pressure oil lubricated centrifugal pump units, once a sudden power outage occurs, it may cause very fatal injuries. Therefore, in order to ensure long-term safe and reliable operation of key pumps used in important industries such as petrochemicals, power stations, and large chemical fertilizers, during the system design process, we have to carefully consider “how to shut down safely in the event of a sudden power outage (while the bearings cannot damaged)” problem. Detailed information on this aspect can be found in [12].
cool down
For different lubrication methods, the standard provides limit requirements for the temperature and temperature rise of bearing lubricating oil and bearing metal temperature. For this reason, bearing applications must consider cooling to ensure their long-term safe and reliable operation.
Fan + heat sink
Fan cooling is usually used in conjunction with heat sink cooling. It has a simple structure and is the preferred cooling method for centrifugal pumps from the perspective of energy saving and environmental protection. See Figure 1. The fin geometry of the box and the fan used to increase the airflow through the box to exchange heat with the surrounding atmosphere help reduce the temperature of the bearing box/bearing and extend the service life of the bearing. According to research, a larger surface area can reduce the operating temperature of the bearing by nearly 4.4°C and extend the service life of the bearing by about 13%.
图片2
Figure 1: Fan + heat sink cooling
Larger/Deeper Oil Pool
During operation, heat is transferred from the pump bearings to the oil and to the outside air through the bearing housing frame walls. A larger/deeper oil sump, not only helps dissipate heat, but also allows contaminants to settle away from the moving parts, resulting in a cleaner oil layer near the ball bearings. Contamination of bearing races and balls is responsible for microscopic degradation of the load surface, leading to failure. Statistics show that cleaner lubricants can extend bearing life by nearly 2.1 times. Likewise, the rate at which air oxidizes oil decreases for larger and deeper oil pools due to the decrease in air concentration. For the pump type studied in this article, bearing life can be extended by 2% [13].
However, when switching to a larger/deeper oil sump, care should be taken to ensure that the span between bearings is minimized wherever possible, and the mechanical sealing surface and shaft diameter at the bearings are increased to increase the dynamic stiffness of the rotor. These improvements provide opportunities to increase mechanical seal and bearing life and reduce overall vibration [14].
Jacket cooling
Jacket cooling is the most common cooling method for the bearing housing of OH2 pumps. If the bearing housing is cooled by a water-cooling jacket, there should be only external joints between the water-cooling jackets of the upper and lower bearing housing halves. There should be no sealing gaskets on the water-cooling jackets, nor should there be threaded joints, sealing seams and Threaded fittings may allow water to leak into the tank.
Special attention should be paid to the fact that the water-cooling jacket should be designed to cool the oil pool rather than the bearing outer ring (the shrinkage of the bearing outer ring due to cold will cause the internal clearance of the bearing to decrease, leading to bearing failure). See Figure 2.
图3
Figure 2: Jacket cooling (picture from EGP)
coil cooling
Standard regulations: It is best to use cooling coils where water cooling is required. Embedded fin cooling coils provide better cooling than jackets. However, coils (including pipe fittings) should be made of non-ferrous metal or austenitic stainless steel and should not have joints to withstand internal pressure.
Bearing seal
The bearing housing of rolling bearings should be designed to prevent contamination by moisture, dust and other impurities. The bearing housing should be equipped with replaceable labyrinth or magnetic face seals and an oil retaining pan with the shaft passing through the bearing housing. Lip seals should not be used. Seals and oil traps should be constructed of non-sparking materials. Seals and oil retaining pans should be designed to effectively retain oil within the bearing housing and prevent foreign matter from entering the bearing housing.
图4
Figure 3: Some common sealing methods for bearing boxes (picture from HI)
Figure 3 shows some common bearing housing seals, such as lip seals, labyrinth seals and magnetic seals. These seals also help reduce oil contamination to maintain oil quality [15].
The labyrinth seal is a non-contact shaft seal that works well as long as the shaft is rotating. It is very effective in preventing shaft seal leakage and external water splash, but it is not effective in preventing condensation water intrusion. The traditional labyrinth seal is shown in Figure 4, and the improved labyrinth seal is shown in Figure 5.
This seal will not damage the pump shaft and is available in both integral and split configurations; also available in a variety of materials and internal configurations. Due to its relatively simple structure and easy maintenance, it is the most commonly used form of oil seal.
Picture 图5
Figure 4: Traditional labyrinth seal
Picture 图6
Figure 5: Improved labyrinth seal
Currently, manufacturers have developed more advanced labyrinth seals that prevent all types of contamination. For example, a seal that is non-contacting during operation to avoid shaft wear uses patented dynamic lift technology to prevent breathing problems that cause 52% of bearing failures to focus on contamination. This dynamic lift technology uses the centrifugal force of rotating equipment to open a temporary, tiny gap, allowing the oil and air mixture in the bearing housing to expand, allowing the equipment to “breathe”.
When the device stops rotating, the tiny gap closes immediately, creating a perfect seal. This prevents dust and moisture from being drawn into the bearing housing, thus preventing contamination (see Figure 6).
Picture 图7
Figure 6: More advanced labyrinth seal
Magnetic face seals have been around for many years, see Figure 7. It occupies very little axial space, is very effective in preventing moisture and solids from entering, and is also effective in preventing the intrusion of external moisture.
Picture 图8
Figure 7: Magnetic Face Seal
However, some people are uncomfortable with magnets located close to bearings.
Spring-loaded face seals are a relatively new form of oil seal and may be the best alternative to all of the oil seals mentioned above. Like magnetic face seals, they are very effective at preventing the intrusion of moisture, solids and external moisture. Unlike a lip seal, it will not damage the shaft or sleeve.
As long as there is air in the bearing box and a breather is installed on the bearing box, oil seals alone cannot prevent moisture intrusion and condensation. Therefore, the best solution is: spring-loaded face seal + bearing housing expansion chamber + breather with desiccant. The expansion chamber (see Figure 8) is designed to limit the pressure increase in an enclosed volume; creating a larger volume for trapped air will cause its pressure to decrease. A breather with desiccant is used to prevent condensation from forming in the hot air after the bearing housing has cooled.
Picture 图9
Figure 8: Bearing box expansion chamber
Picture 图10
Figure 9: Bearing housing with expansion chamber and desiccant breather
As shown in Figure 9, at the original breathing valve interface on the top of the bearing box, an expansion chamber is installed horizontally, and the breather with desiccant is located vertically at the top.
Note: This configuration is relatively expensive. In actual engineering applications, in order to prevent the intrusion of moisture, dust and other debris contamination, the simplest and most commonly used configuration is: labyrinth seal + dustproof disk, or only an improved labyrinth seal, or only a magnetically loaded end face seal [ 16].
Installation, maintenance and monitoring
Install
Including assembly of the pump head and on-site installation (alignment) of the pump unit.
For some important pumps, only professionally trained and qualified personnel are usually allowed to perform installation/assembly work. At the same time, installation should be carried out in accordance with good mechanical engineering practice.
Bearings can easily be damaged or installed incorrectly when the wrong tools or incorrect installation techniques are used. The environment should be clean and free of any pollutants or corrosive liquids. This includes work surfaces, hands/gloves, and tools.
Most bearings are mounted mechanically, preheated and hydraulically. For small and medium-sized bearings with an outer diameter of 4 inches or less, mechanical (or cold) mounting is preferred. Thermal mounting and hydraulic mounting can be used for all bearings, but are mainly used for large and medium-sized bearings.
Mechanical mounting uses a mounting force sufficient to overcome the interference fit between the bearing and the shaft or housing components. Appropriate installation tools should be positioned to apply installation force to the ring with an interference fit. Mounting forces should never pass directly through the rolling elements.
Hot mounting involves heating the bearing to a specific temperature before mounting, causing the bore to expand radially. This short-term, temporary extension is easy to install. Once the bearing returns to room temperature, it returns to its original dimensions and tolerances. Induction heaters with adjustable thermostat and degaussing function are the cleanest and most reliable technology for heating bearings. Never use an open flame!
For large bearings or applications with precision requirements, hydraulic technology can be used, including hydraulic pumps, oilers, and hydraulic nuts. They help maintain accuracy, installation speed and repeatability. They minimize damage, require less manual work and increase safety [5].
maintain
Bearings should always contain a small amount of lubricant (oil or grease), otherwise damage to the bearing surface will affect the service life of the bearing. This damage can be avoided with proper cleaning and/or relubrication.
For critical process pumps, the grease in the bearings should be replaced every 12 to 18 months. If there is a possibility of water or moisture intruding into the bearing housing, cleaning and relubrication intervals should be more frequent. The new grease will expel the old grease under pressure. The amount of grease added depends on the size and design of the bearing housing and the size of the bearings. The grease should completely soak into the bearing and fill approximately 25% of the bearing housing. Too much grease will cause the bearings to overheat. The specific amount should be added according to the requirements of the pump supplier.
With thin oil self-lubricating pumps, it’s easy to tell when the bearings need oil – check the oil level indicator.
During routine maintenance, the bearing box/bearing temperature should be monitored or measured. Once an unknown increase in temperature is found, it may indicate that a failure is about to occur and must be investigated [17].
monitor
With the continuous advancement of technology, digitalization or digital transformation has become an inevitable trend in enterprise development. Condition-based monitoring is a maintenance strategy for the operating status of rotating equipment. For centrifugal pumps, the most commonly used condition monitoring is bearing/bearing housing temperature and vibration monitoring. By monitoring these two parameters, the operating status of the pump can be determined. With the development of machine learning, cloud computing and other technologies, it will also be possible to predict the service life of mechanical parts and when failures may occur, and correct problems within the expected or specified period [18].
Other measures to improve bearing reliability
Material
In particularly demanding pump applications, such as those in the oil and gas and hydrocarbon processing industries, bearings often must accommodate contaminated and corrosive environments, insufficient lubrication, high and low loads, and high or low temperatures. At the same time, they must provide high levels of service, reliability and security.
As an upgrade, SKF’s hybrid ceramic bearings that integrate rolling elements made of bearing-grade silicon nitride can significantly improve reliability and operational robustness. This bearing is dimensionally interchangeable with a similarly sized all-steel bearing without the need to reconfigure or otherwise change the pump equipment.
Bearing-grade silicon nitride is an engineering ceramic material with a uniform and clean microstructure. It is extremely hard and has a density 40% lower than bearing steel. As a result, the rolling elements are lighter and have lower inertia, which reduces stress on the bearing cage during rapid starts and stops and significantly reduces friction at high speeds. Lower friction means cooler operating temperatures and longer lubricant life.
In addition, silicon nitride exhibits a higher elastic modulus than steel, which helps increase bearing stiffness and extend bearing life in contaminated environments. The lower thermal expansion of silicon nitride rolling elements allows for more precise preload control and is less likely to cause over-preload when there are temperature gradients within the bearing.
Hybrid ceramic bearings also improve bearing reliability and service life in other ways. No smearing occurs between silicon nitride and steel, allowing hybrid ceramic bearings to last longer in applications with severe dynamics or improper lubrication conditions.
coating
To overcome several common causes of bearing failure, a low-friction, wear-resistant carbon coating can be applied to the bearing’s rolling elements and inner ring raceways.
Coated bearing surfaces retain the toughness of the underlying material – the coating is actually harder than steel, while using the coating’s hardness to improve friction and wear resistance.
Upgraded coated bearings can withstand many harsh operating conditions, including tailing effects, insufficient lubricant film, lubricant contamination, sudden changes in load, light loads, rapid changes in rotational speed, vibration and oscillation, and the risk of high operating temperatures. The expected results of these features include increased reliability, extended service life, and a reduced likelihood of premature bearing failure due to friction, wear, and related factors.
Changing the contact angle of paired-mounted bearings
The 40° contact angle has become the standard for pairs of single-row angular contact bearings in API pumps. For conventional double-row bearings used in ANSI pumps, the typical contact angle for matching is 30°.
For 40° matched single row bearings, changing the opposing contact angle (such as a combination of 40° and 15°) can benefit many centrifugal pump applications by promoting smoother operation and longer service life to support the load.
This 40°/15° angular contact ball bearing arrangement is ideal for applications where axial loads are high in one direction and do not change direction during operation. The bearing set can accept momentary reversals of axial loads, including those that occur during pump startup and shutdown.
In centrifugal pumps with lighter thrust loads and predominantly radial loads, such as double-suction impeller pumps, a bearing configuration with only a 15° contact angle provides another upgrade option.
The design of these 15° bearings contributes to cooler operation, significantly reduced vibration and extended service life in applications with high radial loads compared to conventional 40° contact angle bearing arrangements [19].
Summarize
The article discusses in detail ways to improve the operational reliability of centrifugal pump bearings from many aspects, mainly including:
1) Correct selection;
2) Reasonable bearing box structure;
3) Proper lubrication;
4) Necessary cooling;
5) Correct installation, necessary maintenance and monitoring;
6) Application of new technologies, new materials, etc.。
Post time: Mar-30-2024