Influence of bearing structure on vibration and noise

Rolling sound

    The rolling sound is caused by the rolling of the rolling elements in the raceway when the bearing rotates to excite a smooth and continuous noise, which only attracts people's attention when its sound pressure level or tone is extremely large. In fact, the sound energy stimulated by the rolling track is limited. For example, under normal conditions, the quality of the 6203 bearing raceway is 25 to 27 dB. This type of noise is the most typical of single row deep groove ball bearings that can withstand radial loads. It has the following characteristics: a. noise and vibration are random; b. vibration frequency is above 1 kHz; c. no matter how the speed changes, the noise main frequency Almost constant and the sound pressure level increases with increasing speed; d. When the radial clearance increases, the sound pressure level increases sharply; e. The rigidity of the bearing housing increases, and the lower the total sound pressure level, even if the speed increases The total sound pressure level also increases little; f. The higher the viscosity of the lubricant, the lower the sound pressure level, but for grease lubrication, the viscosity and shape of the soap fiber can affect the noise value.

    The source of the rolling sound is caused by the natural vibration of the ferrule after the load. Due to the elastic contact of the ferrule and the rolling body, a nonlinear vibration system is formed. When the lubrication or machining accuracy is not high, the natural vibration associated with this elastic characteristic is excited, and when it is transmitted to the air, it becomes noise. It is well known that even with the most advanced manufacturing techniques used to process bearing parts, there are always small geometric errors in the working surface, which causes small fluctuations between the raceway and the rolling elements to excite the natural vibration of the vibration system. Although it is unavoidable, it is possible to use high-precision machining of the working surface of the part, the correct selection of the bearing and the precise use of the bearing to reduce noise and vibration.

    2. Falling body

    This noise is generally found in large bearings that are subjected to low radial loads and subjected to radial loads. When the bearing is running under radial load, the bearing load zone and the non-load zone are in the bearing. If the bearing has a certain radial clearance, the rolling element in the non-load zone does not contact the inner raceway, but it may be external due to the centrifugal force. Ring contact, for this reason, at low speed, when the centrifugal force is less than the weight of the rolling element, the rolling element will fall and collide with the inner race or cage and stimulate the natural vibration and noise of the bearing, and have the following characteristics: a. Grease lubrication It is easy to produce and is not easy to produce when oil is lubricated. It is more likely to be produced when using inferior grease. b. Winter often occurs. c. It is also easy to produce when only radial load is applied and the radial clearance is large. d. Bearings that are also produced within a certain range and of different sizes have different speed ranges. e. It may be continuous or intermittent. f. The forced vibration often excites the second-order and third-order bending natural vibrations of the outer ring to emit the noise. By using the preload method, the noise can be effectively reduced, and the radial clearance of the bearing after installation can be reduced. The use of a good lubricant can also be improved. Some foreign companies use light rolling elements such as ceramic rollers or hollow rollers. To prevent this noise from being generated.

    3. Whistling

    It is a squeaking of the metal between the sliding friction, although the temperature rise of the bearing is not high, it has little effect on the bearing life and grease life, and does not affect the rotation, but the unpleasant sound is disturbing, especially Large short cylindrical roller bearings bearing radial loads often have this noise, which is characterized by: a. The bearing radial clearance is easy to produce. b. Usually appears in grease lubrication, oil lubrication is rare. c. As the bearing size increases, it decreases, and often occurs within a certain speed range. d. It often appears in winter. e. Its appearance is irregular, unpredictable, and related to the amount of grease and performance, installation and operation conditions. This noise can be prevented by reducing the radial play of the bearing and using a shallow outer ring raceway structure.

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Pump bearings and seals are not resistant to wear and high temperatures

(1) Problems occur: the shaft deviation causes high vibration, shortens the life of the mechanical seal, and generates noise.

    Solution: Use the impeller mouth ring of polyimide carbon fiber composite material to fit the stainless steel pump casing ring; replace the original graphite bushing with the throat bushing of our material.

    The result: reduced vibration amplitude, which extends seal life and bearing life and enhances pump free operation. Many pumps use packing as a filler in their use. The main function of the packing is to prevent leakage, but it also acts as a bearing to stabilize the shaft. At present, many pumps have changed the packing to a mechanical seal. With the change of the mechanical seal, the bearing influence is gone, and the shaft deviation (high vibration and related influence) becomes a problem.

    The use of polyimide carbon fiber composite material to improve the pump successfully solved the customer's problems, mainly in the following two points:

    1) Polyimide carbon fiber composite is a metal-free, non-biting material. This allows the running clearance to be reduced (only half of the gap between the metal gaps specified by the API), the bushing with smaller clearances can stabilize the shaft, and the smaller gap ring can further limit leakage and leakage speed.

    2) Polyimide carbon fiber composite is a high strength, high performance thermoplastic material. It is easy to injection and absorbs vibrations and shocks, while the metal being replaced can cause vibration and shaft wear.

Parts: with removable sealing bushings and Teflon bearings

    (2) There is a problem: the support bearing is severely worn. The factory tried a lot of different materials such as carbon, graphite, and filled Teflon materials, trying to find a suitable solution to the problem of wear and shaft deviation. All materials were scrapped in two to three months. Among them, the product of polytetrafluoroethylene causes wear of the shaft, causing great leakage, resulting in failure of the mechanical seal.

    Solution: Replace the previously used filled PTFE bearing with a polyimide carbon fiber composite.

    RESULTS: After the polyimide carbon fiber composite support bearing was installed, it has been successfully operated for more than 13 months. At the 8th month after use, the center part of the agitator was removed and temporarily used for other equipment. At that time, the staff tested it. The agitator bearing found that the leakage per inch per inch was less than 0.005, and the average failure interval increased by 300% to 400%.

    (3) Problems: This pump is made of stainless steel and stainless steel with a hard outer casing as a ring and bushing. In general, the dry running of the pump is caused by a decrease in the amount of suction during operation, and the main dry running conditions often lead to premature pump damage and metal parts are also greatly damaged. The average time between failures of these pumps is only six months.

    Solution: Replace the stainless steel impeller ring and bushing with a polyimide carbon fiber composite material, reducing the operating clearance by approximately 50%.

    The result: Pumps modified with polyimide carbon fiber composites have been in use for more than a year now. Some unfavorable conditions often occur during the previous operation, causing intermittent dry rotation, which makes the pump inoperable, but this phenomenon has been delayed by the renewal of polyimide carbon fiber composites. In addition, the customer also issued a report: by using polyimide carbon fiber composite material to transform it, reducing the operating gap, the pump output flow has increased by 400gpm, and the other two multi-stage pumps have also been updated.

    (4) Problems occur: severe vibration, low pump efficiency

    Solution: Polyimide carbon fiber composite material is used as the pump casing ring and bushing. The running clearance was reduced from the API standard to 0.0015 inches per inch of turning diameter.

    Result: The initial vibration was 0.600 inches/second, the improved vibration was 0.094 inches/second, and the efficiency was increased by 5%.

    Vibration: The reason for the vibration reduction is as follows:

    1) Recirculation flow and its effect on rotor instability is reduced;
    2) The clearance is reduced and the running of the shaft is reduced;
    3) Natural thermoplastic materials have easy injection molding properties and absorb shock or impact.

    Efficiency: The efficiency gain is due to the reduced clearance between the pump casing and the impeller ring. The gap here in the pump will in turn reduce internal recirculation.

    Reliability: This pump has been working continuously for more than four years, and the refinery has already been? Polyimide carbon fiber composites are used on more than ten pumps.

    Advantages and applications of polyimide carbon fiber composite anti-abrasive materials:

    a. Excellent wear resistance. It is superior to rubber, bronze, carbon graphite and other materials in the case of abrasive particles.

    b. Widely used in bushings for sewage pumps, sea water pumps (working environment is sand and other abrasive particles), line pump bearings and bowl wear rings.

    c. Recommended only as a fixed part (due to temperature limits of the material).

    d. Anti-abrasive composites have better chemical resistance than other non-metallic materials.

    e. Polyimide carbon fiber composite materials have a very low coefficient of friction compared to rubber bushings and other metallic materials.

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Bearing seal type

In order to maintain good lubrication conditions and normal working environment, fully utilize the bearing performance and extend the service life, the rolling bearing must have a proper seal to prevent leakage of lubricant and invasion of dust, moisture or other dirt. .

Bearing seals can be divided into self-contained seals and external seals. The so-called bearing self-contained seal is to manufacture the bearing itself into a device with sealing performance. Such as bearings with dust cover, sealing ring and so on. The sealing space is small, the installation and disassembly are convenient, and the cost is relatively low.

The so-called bearing-incorporated sealing performance device is manufactured into a sealing device having various properties inside the {TodayHot} such as the mounting end cap.

The choice of bearing seals should consider the following main factors:
1. Bearing lubricant and type (grease and lubricant);
2. The working environment of the bearing, the size of the occupied space;
3. The advantage of the support structure of the shaft allows angular deviation;
4. The circumferential speed of the sealing surface;
5. The working temperature of the bearing;
6. Manufacturing costs.

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Bearing use and storage

Precautions for use
Rolling bearings have higher precision than general mechanical parts, so care should be taken when using them.
1) Keep the bearings and their surroundings clean
2) Careful and careful when using
If it is used carelessly to give the bearing a strong impact, the bearing will be injured, indented, broken and injured.
3) Use the right tools
4) Pay attention to the rust prevention of the bearing
Avoid using it in wet areas, and wear gloves if you don't get sweat on it.
5) Users should be familiar with bearings
6) Develop operating specifications for bearing use
a, the preservation of bearings
b, cleaning of bearings and their surroundings
c. Inspection of the size and processing quality of the installation site
d, installation work
e, post-installation check
f, disassembly work
g, maintenance (regular inspection)
h, lubricant supplement
Bearing storage
The bearings are coated with an appropriate amount of anti-rust oil and packaged with anti-rust paper. As long as the package is not damaged, the quality of the bearing will be guaranteed.
However, for long-term storage, it is recommended to store on a shelf 30cm above the ground at a temperature below 65% and a temperature of about 20 degrees Celsius. In addition, {TodayHot} storage places should avoid direct sunlight or touch with cold walls.
Bearing installation
Pre-installation precautions
1) Bearing preparation
Since the bearings are rust-proofed and packaged, do not open the package until installation.
In addition, the anti-rust oil coated on the bearing has good lubricating properties, and can be used directly for bearings for general purpose or for bearings filled with grease without cleaning. However, for instrument bearings or bearings for high-speed rotation, the cleaning oil should be washed with a clean cleaning oil. The bearing is prone to rust and cannot be placed for a long time.
2) Inspection of the shaft and the casing
Clean the bearing and the casing to confirm the burrs left by scratches or machining. There must be no abrasive (SiC, Al2O3, etc.) sand or chips in the outer casing.
Secondly, check whether the size, shape and processing quality of the shaft and the casing are in accordance with the drawings.
Before installing the bearing, apply mechanical oil to each mating surface of the tested shaft and the outer casing.
Bearing installation method
The mounting method of the bearing varies depending on the type of bearing and the fitting conditions.
Since the shaft is generally rotated, the inner ring and the outer ring can respectively adopt an interference fit and a clearance fit, and when the outer ring rotates, the outer ring adopts an interference fit.
(1) Press-in installation
Push-in installation generally uses a press, and bolts and nuts can also be used. When necessary, the hammer can be used.
(2) Hot sleeve installation
The hot-sleeve method of heating the bearing in the oil to expand it and then mounting it on the shaft can prevent the bearing from being subjected to unnecessary external force and complete the installation work in a short time.
Heating precautions:
1) Do not heat more than 100 degrees Celsius.
2) Do not allow the bearing to contact the bottom of the oil sump.
In addition, the hot-sleeve installation can also use an induction heating device to heat the bearing to expand it and then mount it on the shaft.
Bearing disassembly
When you regularly inspect or replace parts, you need to remove the bearings. Usually the shaft and bearing housing are almost always used, and the bearings are often used. Therefore, the structural design should take into account that when removing the bearing, {HotTag} does not damage the bearing, shaft, bearing housing and other parts, but also prepare appropriate disassembly tools. When removing the statically fitted ferrule, only the pulling force can be applied to the ferrule, and the ferrule must not be pulled by the rolling element.
Bearing maintenance
In order to fully utilize the bearings and maintain their proper performance for a long time, regular maintenance (regular inspection) must be performed.
Through proper periodic inspections, early detection of failures and prevention of accidents are important to improve productivity and economy.

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