16.1.1 Composition of Rolling Bearings
Rolling bearings are generally composed of four parts: the outer ring, the inner ring, the rolling body and the cage.
The inner ring is assembled on the shaft and rotates with the shaft, while the outer ring is assembled with the housing hole to support the bearing.
Rolling body is the core element of rolling bearing, it makes the sliding friction between the relative moving surfaces into rolling friction. Cage will be rolling body equal distance arrangement apart, in order to avoid rolling body direct contact, reduce heat and wear.
16.1.2 Materials and characteristics of rolling bearings
The inner ring, outer ring and rolling bodies of rolling bearings are made of high strength, wear-resistant bearing steel, and the working surfaces are required to be ground and polished to achieve high precision.
Bearing cage has stamping and entity of two kinds, stamping cage is generally made of low carbon steel plate stamping, and rolling body has a large gap between. Entity cage commonly used copper alloy, aluminum alloy or plastic made of cutting process, has a better centering effect.
Rolling bearings and sliding bearings, compared with its characteristics are as follows: rolling bearings have the characteristics of rolling friction, frictional resistance is small, startup and running torque is small, startup sensitivity, power loss is small and bearing unit width bearing capacity is larger, lubrication, installation and maintenance is convenient. Compared with the sliding bearing, the disadvantage of rolling bearing is radial profile size, high contact stress, high speed and heavy load bearing life is low and noise, poor impact resistance.
16.2 Types of rolling bearings and their code
16.2.1 Structural characteristics of rolling bearings
Nominal contact angle. Rolling bearing rolling body and outer ring raceway contact point of the normal and bearing radius direction of the angle α, known as bearing nominal contact angle (referred to as contact angle). The size of the nominal contact angle reflects the ability of the bearing to withstand axial load, the larger the contact angle, the greater the ability of the bearing to withstand axial load.
Clearance. Rolling bearing rolling body and inner ring, outer ring raceway clearance between, known as rolling bearing clearance. Clearance is divided into radial clearance and axial clearance, which is defined as when a bearing collar is fixed, another collar along the radial or axial maximum amount of movement, known as the bearing radial clearance and axial clearance. Bearing standard radial clearance is divided into basic clearance group and auxiliary clearance group, should give priority to the basic clearance group value, axial clearance value can be radial clearance value according to a certain relationship between the conversion.
16.2.2 Types of rolling bearings
There are many types of rolling bearings, which can be categorized from different angles. According to the shape of the rolling body is divided into ball bearings and roller bearings. Spherical rolling body and inner and outer ring contact is point contact, running friction loss is small, bearing capacity and impact resistance is weak; roller rolling body and inner and outer ring is line contact, bearing capacity and impact resistance is strong, but running friction loss is big. According to the number of rolling elements, rolling bearings are divided into single-row, double-row and multi-row.
According to the direction of the load borne by the bearing or the nominal contact angle, rolling bearings can be divided into the following types.
Radial bearings. Radial bearings are mainly used to bear radial loads, 0° ≤ α ≤ 45°. Radial bearings are further divided into radial contact bearings (α=0°) and centripetal angular contact bearings (0°<α≤45°).
Thrust bearings. Mainly used to bear axial load, 45 ° & lt; α ≤ 90 °. Thrust bearings can be further divided into axial contact bearings (α=90°) and thrust angular contact bearings (45°<α<90°).
16.2.3 Rolling bearing code
In order to uniformly characterize the characteristics of various types of bearings, to facilitate the production and selection of stop, Gb/T 272-1933 and JB/T 2974-2004 provides for the preparation of general-purpose rolling bearing code. Rolling bearing code by letters and numbers, and by the front code, the basic code and rear code three parts. The basic code is the main body of the bearing code, on behalf of the basic type, structure and size of the bearing, by the bearing type code, diameter series, width series and inner diameter code. Front code and rear code is the bearing in the structure shape, size, tolerance, technical requirements and other aspects of the change, in the basic code around the increase in the supplementary code.
Type code. Type code with numbers or letters. If the code is "0", it can be omitted.
Size series code. Size series code from the bearing width series code and diameter series code combination. For the same inner diameter of the bearing, when bearing different sizes of load, can use different sizes of rolling elements, so that the outer diameter and width of the bearing changes accordingly. Width series refers to the same inner and outer diameter of the centripetal bearings have several different widths, width series code 8,0,1,2,3,4,5,6, corresponding to the same inner diameter bearings of the width of the size of the sequential increase. Diameter series refers to the same inner diameter bearings have several different outer diameter, diameter series code 7,8,9,0,1,2,3,4,5, corresponding to the same inner diameter bearings of the outer diameter size in ascending order.
Inner diameter code. The inner diameter code indicates the size of the inner ring aperture of the bearing, rolling bearing inner diameter can vary from 1mm to several hundred mm. For commonly used inner diameter d = 20 ~ 480mm bearings, the inner diameter is generally a multiple of 5, the two digits of the inner diameter code indicates that the size of the bearing inner diameter is 5 divided by the quotient. For the inner diameter of 10mm, 12mm, 15mm, 17mm bearings, the inner diameter code for 00,01,02 and 03. For the inner diameter of 500mm, 22mm, 28mm, 32mm bearings, with the nominal inner diameter millimeters directly, but in the size of the series code with "/" between the separation.
Internal structure
Internal structure code. Internal structure code indicates the internal structure of the bearing changes. The meaning of the code varies with different types and structures.
Tolerance grade code. Indicates the precision level of the bearing, is divided into 2, 4, 5, 6, 6X and 0, ***6 levels, in order from the senior to the lower level, the code were /P2,/P4,/P5,/P6,/P5X,/P0. Tolerance level, 6X level is only applicable to the tapered roller bearings, 0 for the ordinary level, in the bearing code is not marked.
Clearance code. Commonly used bearing radial clearance series is divided into 1 group, 2 groups, 0 groups, 3 groups, 4 groups, and 5 groups, *** 6 groups, in order from small to large. 0 group clearance is commonly used clearance groups, in the bearing code is not marked out. The rest of the clearance groups in the bearing code with /C1,/C2,/C3,/C4,/C5 respectively. Tolerance grade code and clearance code at the same time, can be simplified to take the tolerance grade code plus clearance group number combination, such as /P63 that tolerance grade 6, radial clearance 3 groups.
Configuration code, indicating a pair of bearing configuration.
Set of bearings sub-part code. Indicates the sub-parts of the bearing, expressed in letters. Rolling bearing sub-parts indicate that can be freely separated from the bearing with or without rolling elements, or bearing rings or bearing washers with cages and rolling elements, as well as can be freely separated from the bearing with rolling elements and cages of the assembly.
16.3 Selection of rolling bearings
16.3.1 Bearing load
The size, direction and nature of the load on the bearing are the main basis for selecting the type of bearing.
According to the magnitude of the load on the bearing. In the choice of bearing type, due to rolling bearings in the main components are line contact, suitable for bearing larger loads, bearing deformation is also small. And ball bearings in the main point of contact, suitable for bearing lighter or medium load, so in the load is small, should prioritize the use of ball bearings.
According to the direction of the load bearing. In the choice of bearing type, for pure axial load, general selection of thrust bearings; for the smaller pure axial load can choose thrust ball bearings; larger pure axial load can choose thrust roller bearings. For pure radial load, generally use deep groove ball bearings, cylindrical roller bearings or needle roller bearings. When the bearings in the radial load, and at the same time, there is not big axial load, can choose deep groove ball bearings or contact angle is not big angular contact ball bearings or cylindrical roller bearings; When the axial load is bigger, can choose the contact angle is bigger angular contact ball bearings or cylindrical roller bearings, or choose the combination of centripetal bearings and thrust bearings in the structure.
16.3.2 Bearing speed
From the working speed of the bearing requirements, the following points can be determined: ball bearings and roller bearings, compared with a higher limiting speed, so in the high speed should be preferred to use the ball bearings; in the same conditions of the inner diameter, the smaller the outer diameter, the smaller the rolling body, the smaller the centrifugal inertia force of the rolling body added to the raceway of the outer ring, and thus more suitable for higher speeds. It is more suitable for working at a higher speed; cage material and structure of the bearing speed has a great influence on the entity cage than the stamping cage allows higher speed, bronze entity cage allows higher speed; the limit speed of the thrust bearings are very low, when the working speed is high, if the axial load is not very large, you can use the angular contact ball bearing to withstand the pure axial force; if the working speed is a little more than the sample provisions of the limit speed, you can improve the bearing capacity. Limit speed, you can improve the tolerance level of the bearing, or appropriately increase the radial clearance of the bearing, the choice of circulating lubrication or oil mist lubrication, strengthen the cooling of the lubricant and other measures to improve the high-speed performance of the bearing.
16.3.3 Alignment of bearings
The ability of bearings to automatically compensate for the relative skewness of the centerline of the shaft and the box, and thus maintain the normal working condition of the bearings, becomes the alignment of the bearings. Self-aligning ball bearings and spherical roller bearings have good self-aligning performance, and their allowable axial skew angle is 3° and 1°~2.5° respectively.
Cylindrical roller bearings and needle bearings are the most sensitive to bearing deflection, and the load carrying capacity of these bearings in the state of deflection may be lower than that of ball bearings. Therefore, the use of these bearings should be avoided when the rigidity of the shaft and the supporting rigidity of the bearing bore are low.
16.3.4 Mounting and dismounting of bearings
Ease of mounting and dismounting is also a factor to be considered when selecting a bearing type. When the bearing housing has no split surface and the bearing components must be mounted and dismounted axially, preference should be given to bearings with separable inner and outer rings. When the bearing is installed on the long axis, in order to facilitate the installation and dismantling, you can choose its inner ring hole for 1:12 tapered hole (used to install in the tight bushing) bearings.
16.3.5 Running accuracy
The axial and radial running accuracy of shafts supported by rolling bearings is related to the accuracy and elastic deformation of the bearing parts, as well as the accuracy and elastic deformation of the adjacent parts. Therefore, for the high running accuracy requirements of the bearing, need to choose the interference fit.
16.3.6 Economic requirements
Ball bearings are cheaper than roller bearings, spherical bearings are more expensive. Under the premise of meeting the use of function, should try to use ball bearings, low precision, low price bearings.
In addition, the choice of bearing type should also consider the overall design requirements of the bearing device, such as the configuration of the bearing use, travel and other requirements, such as support stiffness requirements are high, can be used in pairs of angular contact bearings, radial clearance adjustment is appropriate to use the bearings with tapered holes, pivot points across the distance, the shaft deformation, or multi-pivot axle, it is desirable to use the self-aligning bearings, space constraints, the needles can be used needle roller bearings.
16.4 Rolling bearing load analysis, failure form and design guidelines
16.4.1 Rolling bearing work analysis
Rolling bearing work between the components of the movement relationship. A rolling bearing is a supporting member that carries a load and rotates. Acting on the bearing load through the rolling body by a ring to another ring. Inner and outer ring relative rotation, rolling body both self-transfer and around the bearing center rotation.
Load distribution in rolling bearings. To radial bearings, for example, assuming that the bearing is only subject to radial load, consider a rolling body center is located in the radial load on the line, the upper half of the circle of the rolling body does not bear load, the lower half of the circle of the rolling body by the load, and the rolling body in different locations by the size of the load is also changing.
Load and stress changes on the bearing element. By the bearing load distribution can be seen, rolling bearing work, the rolling body is located in a different position, the bearing components of the load and stress at any time are changing. In the bearing area, the rolling body loaded by 0 gradually increased to the maximum value, and then gradually reduced to 0. The rolling body is subject to variable load and variable stress.
16.4.2 Failure forms of rolling bearings and design guidelines
The main failure forms of rolling bearings:
Fatigue pitting. Rolling bearing in the work, the rolling surface of the rolling body or collar repeatedly subjected to pulsating cyclic changes in the role of contact stress, after a period of time, fatigue cracks and continue to develop, so that the metal surface pits or flake peeling, resulting in fatigue pitting. Usually fatigue pitting is the main form of rolling bearing failure, bearing design is for this kind of failure and start.
Plastic deformation. In the larger static load and impact load, the rolling contact surface will produce a permanent pit, will increase the frictional torque, strong vibration and noise in the bearing operation, reduce the operating accuracy, that is, bearing failure due to plastic deformation. Therefore, the bearings under such working conditions need to do static strength calculation.
Wear and tear. Due to poor sealing, dust and impurities into the bearings caused by rolling body and raceway surface abrasive wear, or due to poor lubrication caused by early bearing wear or burns.
Other forms of failure. Due to installation and dismantling operations, maintenance caused by improper component rupture.
Rolling bearing design guidelines, after selecting the bearing type, decide the bearing size, should be calculated for the main forms of failure. Fatigue pitting failure is the main basis for fatigue life calculation, plastic deformation is the main basis for static strength calculation. For general working conditions to do rotary rolling bearings should be contact fatigue life calculation, should also do static strength calculation; for not rotating, oscillating or low-speed bearings, the requirements of the control of plastic deformation, should do static strength calculation; high-speed bearings due to the heat prone to wear and burns, in addition to life calculation, but also to verify the limit of rotational speed.
In addition, the factors that determine the working ability of bearings and bearing combination of reasonable structure, lubrication and sealing, etc., they are to ensure that the bearings work properly its important role.
16.5 Rolling bearing size selection calculation
16.5.1 Basic rated life L
The life of a rolling bearing refers to the bearing in any one of the rolling body or raceway first fatigue expansion before a collar relative to the other ring of the number of revolutions, or at a certain speed of the number of hours of work.
Rolling bearing life is quite discrete, due to manufacturing precision, material homogeneity and other differences, even if it is the same material, the same size and the same batch of bearings produced in the exact same conditions of work, their life will not be the same.
For a batch of bearings can be used mathematical and statistical methods, analyze and calculate a certain degree of reliability R or the probability of failure n under the bearing life. Generally in the calculation of R = 0.9, then Ln = L10, known as the basic rated life.
16.5.2 Basic dynamic load rating C
The life of the bearing is related to the size of the load, the larger the working load, the greater the contact stress caused by the contact stress, and thus in the occurrence of pitting corrosion before the destruction of the number of changes in the stress that can be accepted is also less, that is, the shorter the life of the bearing. The basic rated life bearings can withstand the maximum load taken as the basic dynamic load rating. The basic dynamic load rating refers to the size and direction of the load is constant, is the center bearing to withstand pure radial load or thrust bearing to withstand pure axial load capacity.
16.5.3 Equivalent dynamic load P
In order to carry out life calculations, the actual load must be converted into an assumed load with the same properties as the C load. Under this assumed load, the life of the bearing is the same as under the actual load, and the assumed load is called the equivalent dynamic load, denoted by P. The bearing life is then calculated as follows Under the constant radial load Fr and axial load Fa, the equivalent dynamic load is P=XFr+YFa . Where, X,Y are radial dynamic load coefficient and axial dynamic load coefficient. P=Fr for radial bearings and Fa for axial bearings.
16.5.4 Lifetime Calculation
16.5.4 Relationship between bearing load P and basic rated life L10 P?L10=C?x1=constant , where n=ε, the same as below; P is the equivalent dynamic load; L10 is the basic rated life; C is the basic dynamic load; ε is the life index; and P is the equivalent dynamic load; L10 is the basic rated life; and C is the basic dynamic load. load; ε is the life index, for ball bearings ε = 3, roller bearings ε = 10/3. can be obtained rolling bearing basic rated life L10 for L10 = (C / P)? In the actual engineering calculations, the bearing life is commonly used in hours, then the basic rated life Lh (in hours) for Lh = (10 of the 6th power / 60n) - (C / P)? . Where, n outside the nth power n is the speed of the bearing, unit r/min.
If the load P and speed n is known, the expected calculated life Lh' is also determined, then the required bearing should have the basic dynamic load rating C' can be calculated C'=P(60nLh'/6th power of 10) bracketed by the opening of the εth power . If this value is to be used for high-temperature bearings, it is necessary to multiply C by the temperature coefficient Ft, i.e. to correct the C value. Considering the impact of shocks and vibrations on the bearing load when the machine is working, the equivalent dynamic load should be corrected by multiplying P by the load factor Fp.
After correction, the formula becomes L10=(FtC/FpP)? , Lh=(6 times 10/60n)-(FtC/FpP)? , C'=FpP(60nLh'/6th power of 10) open in parentheses to the εth power/Ft . These three formulas are commonly used in the design calculation of the bearing life calculation formula, from which the bearing life or type can be determined.
16.5.5 Angular contact radial bearing axial load calculation
In order to make the angular contact radial bearing internal axial force to get balanced, so as not to avoid the axis of fluctuation, usually this kind of bearings should be used in pairs, symmetrical mounting. Fa is the axial load, F' is the radial load Fr generated by the internal axial force. O?, O? point for the center of the pressure of the bearings 1 and bearings 2, that is, the support reaction point. reaction force action point. The direction of the internal axial force F' and the direction of the applied axial load Fa consistent with the bearing labeled 2, the other end of the bearing labeled 1. Take the shaft and its mating bearing inner ring for the separation of the body, such as to achieve axial equilibrium, it should satisfy the Fa + F?'= F?'.
If you find that does not satisfy the above equation, there are two situations. When Fa + F?'> F?', the shaft has a tendency to leap to the right, equivalent to bearing 1 is "compressed", bearing 2 is "relaxed", but in fact, the shaft must be in the equilibrium position, so it is "compressed" bearing. "The total axial force Fa? and Fa + F?' must be balanced, that is, Fa? = Fa + F?', while the "relaxed" bearing 2 only by its own internal axial force F?', that is, Fa? = F?'. When Fa+F?'<F?', the same as before, bearing 1 is only subject to its own internal axial force F?', that is, Fa?=F?', bearing 2 is subject to the total axial force Fa?=F?'-Fa .
In summary, the method of calculating the axial force on angular contact radial bearings can be summarized as follows: first, through the calculation and analysis of internal axial force and external axial load, determine the bearing that is "relaxed" or "compressed"; then determine the bearing that is "relaxed". The axial force of the "relaxed" bearing is only its own internal axial force, and the axial force of the "compressed" bearing is the algebraic sum of the remaining axial forces after removing its own internal axial force.
16.5.6 Static loads on rolling bearings
The basic static load rating C0. For rolling bearings with very low speeds or slow oscillations, fatigue pitting does not normally occur. However, in order to prevent excessive plastic deformation of the rolling element and internal and external causes, static strength calculation should be carried out. Shaft bearing force is the largest rolling body and raceway contact center caused by the contact stress reaches a certain value of the load, as the bearing static load limit, known as the basic rated static load, expressed in C0. To the centripetal bearings, the basic static load rating is to make the bearing collar only produce relative pure radial displacement of the radial component of the load, called the basic radial static load rating, with C0r said. For thrust bearings, the basic static load rating refers to the center of the axial load, called axial basic static load rating, with C0a.
Equivalent static load P0. If the actual load of the bearing is different from the basic static load rating assumption, the actual static load should be converted to a hypothetical load. In the hypothetical load bearing in the maximum loaded rolling element and raceway contact with the permanent deformation produced by the actual load under the same, the hypothetical load is called equivalent static load. Its calculation formula for P0 = X0Fr + Y0Fa, which X0, Y0 is the radial static load factor and axial static load factor.
Selection of bearings according to static load. Formula for C0 ≥ S0P0, where S0 is the static strength safety factor, P0 is the equivalent static load. S0 value depends on the conditions of use of the bearing, when the bearing is required to rotate very smoothly, S0 should be greater than 1, in order to avoid excessive amount of localized plastic deformation of the rolling surface of the bearing; when the bearing rotational smoothness requirements are not high, or the bearing is only to do the oscillating motion, S0 can be taken as 1 or less than 1, in order to make the bearing under normal operating conditions as far as possible. Bearing in order to ensure that the normal operation of the conditions to play the maximum static load capacity.
16.6 Combined design of rolling bearings
16.6.1 Stiffness and coaxiality of the shaft and housing bore
The shaft and the housing or housing where the bearing is mounted, as well as other parts subjected to force in the bearing combination, must have sufficient stiffness. Because the deformation of these parts are to hinder the rolling body rolling and lead to premature failure of the bearing.
In order to ensure that the bearings work properly, should ensure that the shaft of the two journals of the coaxiality and box on the coaxiality of the two bearing holes. The most effective way to maintain the coaxiality is to use the overall structure of the box, and the installation of bearings in the two holes machined at once.
16.6.2 Bearing configuration
Reasonable bearing configuration should ensure that the shaft and shaft parts in the work of the correct position, to prevent axial fluctuation, fixed axial position, when subjected to axial force, the force can be transmitted to the body, at the same time, in order to avoid the shaft due to thermal elongation of bearings over the excessive additional load, or even jammed, but also to allow it to have a certain amount of axial travel. To this end, the configuration of the following three methods:
Double pivot point each one-way fixed. By each of the two bearings to limit the axial movement in one direction. Taking into account the thermal elongation of the shaft, a certain clearance is left between the outer ring of the bearing at one end and the end face of the bearing cover. For adjustable clearance bearings, the clearance is left inside the bearing during assembly.
One bearing is fixed in both directions, and the other end of the bearing is free. For a larger span and high operating temperature shaft, its thermal elongation is larger, should be used a point of two-way fixed, the other end of the pivot point of the support structure. As a fixed support bearing, should be able to withstand two-way axial load, so the inner and outer rings in the axial direction should be fixed.
Two pivot points full travel. When the shaft and the parts on the shaft have been axially fixed from other sources, the two supports should be fully free.
16.6.3 Axial fixing of rolling bearings
The inner and outer rings of the bearing should be reliably fixed, and the choice of fixing method depends on the nature, size and direction of the load on the bearing, as well as the type of bearing and its position on the shaft. When the shock vibration is more serious, the greater the axial load, the higher the speed, the fixing method used should be more reliable.
The bearing inner ring axial fixed common methods are: with shaft with elastic retaining ring and shoulder fixed, mainly used to bear axial load and speed is not very high single row radial ball bearings; with shaft end retaining ring and shoulder fixed, can be used for the occasion of the larger diameter of the shaft, can withstand a large axial load in the high speed; with a round nut and stop washer fixed, disassembled and installed easily, used for axial load, high speed occasions; with tight bushings, with the tightening of the bearing inner ring, the axial load, high speed, the axial load is large. The bearing is fixed with a round nut and stop washer, easy to disassemble, used for large axial load and high speed; fixed with a tight bushing, stop washer and round nut, used for axial force and rotational speed are not large on the optical axis, the inner ring for the tapered hole bearings.
The bearing outer ring axial fixed by the common methods: embedded in the box groove hole with elastic retaining ring and cam fixed, commonly used in single-row centripetal ball bearings; with the shaft with elastic retaining ring embedded in the bearing outer ring of the stop groove fixed, applicable to the box is not set up cam and the outer ring with the stop groove of the bearings; with the bearing end cap and cam fixed, applicable to high-speed and bear a lot of axial load all kinds of centripetal and centripetal thrust bearings; with the bearing bearing end cap and cam fixed, applicable to high speed and bear a lot of axial load all kinds of radial and Centripetal thrust bearings; fixed with the bearing cover and cup of the tab, suitable for the box is not suitable for the setting of the tab and other occasions; fixed with threaded ring, suitable for bearing speed is very high, axial load, not suitable for bearing fixed occasions.
16.6.4 Adjustment of rolling bearing clearance
In order to ensure the normal operation of the bearing, the bearing should be left with a certain internal clearance, known as bearing clearance. Adjustment of the clearance of the common methods are:
Thickening or thinning of the end cap and the box between the gasket to adjust the clearance; through the adjusting screw, through the bearing outer ring gland, move the outer ring to achieve, in the adjustment of the anti-loosening nut should be tightened; rely on the shaft to adjust the round nut, but this method due to the necessity of the production of the shaft in the stress concentration of serious thread, weakening the strength of the shaft.
When there are parts such as bevel gears or worm gears on the shaft, in order to obtain the correct meshing position, it is necessary to have a device for proper adjustment of the clearance and position of the bearings when installing or during work.
16.6.5 Rolling bearing preload
Rolling bearing preload, that is, in the installation of bearings with a certain method to make the rolling body and the inner and outer ring to produce a certain amount of initial pressure and pre-deformation, in order to ensure that the bearing inner and outer rings are in the state of compression, so that the bearings in the working load, in the negative clearance state operation. The purpose of preloading is: to increase the stiffness of the bearing; to enable the rotating shaft in the axial and radial direction to correctly locate and improve the rotational accuracy of the shaft; to reduce the vibration and noise of the shaft, reduce the moment of inertia caused by the rolling body relative to the inner and outer ring raceways of the sliding; to compensate for wear and tear caused by changes in the internal clearance of the bearings; to extend the life of the bearings.
Commonly used preload device: clamp a pair of tapered roller bearings and preload the outer ring; in a pair of bearings in the middle of the sleeve of unequal length and preload; clamp a pair of narrowed bearing inner or outer ring and preload; the above three devices due to the temperature rise during the work of the dimensional relationship between the parts change, the size of the preload force is also changed, the use of preloaded springs, you can get a stable Pre-tensioning spring, you can get a stable pre-tensioning force.
16.6.6 Rolling bearing fit and mounting/dismounting
In order to prevent the inner ring of the bearing and the shaft as well as the outer ring and the hole of the housing from sliding relative to each other when the machine is running, it is necessary to choose the correct fit. Rolling bearings are standardized, the inner ring of the hole for the reference hole, and the shaft with the base hole system; outer ring of the outer cylindrical surface for the reference axis, and the bearing housing hole with the base axis system.
When choosing the type of bearing fit, the general principle is that for high speed, high load, high temperature, vibration bearings should be selected with a tighter fit, and often disassembled bearings, should be selected with a looser fit.
When designing the bearing combination, the mounting and dismounting of the bearings should be considered so that the bearings and other parts are not damaged during the mounting and dismounting process.
When disassembling, it is common to use a disassembler or press to remove the bearing from the shaft.
16.6.7 Lubrication of rolling bearings
The main purpose of lubrication is to reduce friction and wear. In addition, it also reduces contact stress, heat dissipation, vibration absorption, rust prevention and so on.
The main lubricants for bearings are grease and lubricating oil. In addition, there is also the use of solid lubricants.
Grease lubrication. For ball bearings dn<160000, cylindrical, tapered bearings dn<100000~120000, spherical roller bearings dn<80000, thrust ball bearings dn<40000, the general use of grease lubrication. Adopt grease lubrication structure is simple, grease is not easy to lose, by the temperature effect is not big, on the nature of the load, the change of the speed of movement has a greater adaptability, the use of time is longer. Commonly used grease for calcium-based grease and sodium-based grease.
Oil lubrication. From the rolling bearing lubrication and heat dissipation effect, oil lubrication is better, but need complex oil supply system and sealing device. Oil lubrication, commonly used lubrication methods are as follows: oil bath lubrication, the bearing local immersion in lubricant; oil drop lubrication, with the oil feeder to make the oil into drops, oil due to the rotating part of the churning, the formation of oil mist in the bearing box, the drop of oil will be the movement of friction in the heat away from the role of cooling; splash lubrication, with the oil into the oil pool in the gears or the oil ring will be splashed by rotating the oil to lubricate; oil spray lubrication, with the oil pump to lubricate oil pressurization, with the Oil pump will lubricating oil pressurization, through the oil pipe or the body of the special oil holes, through the nozzle will be sprayed to the bearings in the oil, flow through the bearings of the lubricating oil, after filtering and cooling and then recycling; oil mist lubrication, ultra-high-speed bearings can be used for oil mist lubrication, lubricating oil in the oil mist generator into an oil mist.
Solid lubrication. Commonly used solid lubrication methods are: bonding agent will be solid lubricant bonding in the raceway and cage; the solid lubricant into the engineering plastics and powder metallurgy materials, made of self-lubricating properties of the bearing parts; with electroplating, high-frequency sputtering, ion plating, chemical deposition and other technologies to make solid lubricant or soft metal in the friction surface of the bearing parts to form a layer of uniformly dense thin film. Commonly used solid lubricants are molybdenum disulfide, graphite, PTFE and so on.
16.6.8 Sealing of rolling bearings
Sealing is to prevent dust, moisture and other impurities from entering the bearing, and to organize the loss of lubricant in the bearing.
There are many methods of sealing bearings, which can usually be summarized into two main categories, namely contact seals and non-contact seals
Contact seals. This type of sealing seals in contact with the shaft. When the shaft rotates during operation, there is friction and wear between the seal and the shaft, so it is not suitable for use when the shaft speed is high.
Felt ring seal. Rectangular cross-section felt ring installed in the trapezoidal groove of the bearing end cap, the use of felt ring contact with the shaft to play a sealing role.
Seal ring seal. The sealing ring is made of oil-resistant rubber, leather or plastic. Installation with a spiral spring to seal the lip hoop tight on the shaft, have a better sealing effect, applicable to the shaft circumferential speed v & lt; 7m / s, operating temperature of -40 ~ 100 ℃ with paper or oil lubricated bearings.
Non-contact seal. This type of sealing using the gap (or add oil ring) sealing, rotating parts and fixed parts are not in contact, so it allows the shaft to have a very high rotational speed.
Gap seal. In the bearing end cap and the shaft to leave a small radial gap between the seal, the smaller the gap, the longer the axial width, the better the sealing effect.
Labyrinth seal. In the bearing end cap and fixed on the shaft between the rotating parts of the system out of the curved road gap and get sealed, there are two kinds of radial labyrinth and axial labyrinth.
Oil ring seal. Oil retaining ring and bearing hole by a small radial clearance, and the oil retaining ring protrudes out of the bearing hole end face? =The oil retaining ring rotates with the shaft when working, and the centrifugal force is used to throw away the oil and debris falling on the oil retaining ring, which plays the role of sealing.
Oil dumping seal. Oil lubrication, in the shaft groove or a ring, can be lost to the outside of the oil flung away, and then through the bearing end cover of the oil collection cavity and the bearing cavity connected to the oil hole flow back. Or in close proximity to the bearing to install a throw oil ring, on the axle car has a spiral oil feeding groove, can effectively prevent the oil outflow.
Combined seal. Combination of the above sealing methods together to give full play to its sealing performance, improve the overall sealing effect.