Supports of shafts and axles rolling bearings. Structural elements of shafts and axles. Disadvantages of plain bearings
5.1. What do the shafts and axles support in a running machine?
Shafts and pivot axles are mounted on supports that provide rotation, take loads and transfer them to the base of the machine. The main part of the supports are bearings that can accommodate radial, radial-axial and axial loads.
By the principle of work, they are distinguished:
● Plain bearings.
● Rolling bearings.
5.2. What is a plain bearing?
The simplest plain bearing is a hole bored directly in the machine body, into which a bushing (liner) made of antifriction material is usually inserted. The shaft journal slides over the bearing surface.
5.3. Advantages and disadvantages of plain bearings.
Advantages:
● Small dimensions in the radial direction.
● Good shock and vibration resistance.
● Can be used at very high shaft speeds.
● Can be used when working in water or aggressive environment.
Disadvantages:
● Large dimensions in the axial direction.
● Significant consumption of lubricant and the need for systematic monitoring of the lubrication process.
● The need to use expensive and scarce antifriction materials for liners.
5.4. Basic requirements for materials used in plain bearings.
Liner materials paired with a trunnion must provide:
● Low coefficient of friction.
● High wear resistance.
● Good break-in ability.
● Corrosion resistance.
● Small coefficient of linear expansion.
● Low cost.
Neither of known materials does not possess the whole complex of these properties. Therefore, various anti-friction materials are used that best suit specific working conditions.
5.5. Basic materials used in plain bearings.
Liner materials can be divided into three groups.
● Metallic. Babbits (alloys based on tin or lead) have high antifriction properties, good running-in properties, but are expensive. Bronzes, brass, and zinc alloys have good antifriction properties. At low speeds, antifriction cast irons are used.
● Sintered metal. Porous bronze-graphite or iron-graphite materials are impregnated with hot oil and used when it is impossible to provide liquid lubrication. These materials are able to work for a long time without a lubricant supply.
● Non-metallic. Polymer self-lubricating materials are used at significant sliding speeds. Fluoroplastics have a low coefficient of friction, but a high coefficient of linear expansion. Bearings with rubber inserts are used with water lubrication.
5.6. Serviceability criteria for plain bearings.
The main criterion is wear resistance rubbing couple.
The work of the frictional forces in the bearing is converted into heat, so another criterion is heat resistance.
5.7. What is a rolling bearing?
A finished unit, which consists of an outer 1 and an inner 2 rings with raceways, rolling elements 3 (balls or rollers) and a cage 4 separating and guiding the rolling bodies.
5.8. Advantages and disadvantages of rolling bearings.
Advantages:
● Low friction losses.
● High efficiency.
● Slight heating.
● High load capacity.
● Small overall dimensions in the axial direction.
● High degree of interchangeability.
● Easy to operate.
● Low consumption of lubricant.
Disadvantages:
● Sensitivity to shock and vibration.
● Large radial dimensions.
● Noise at high speeds.
5.9. How are rolling bearings classified?
● By the shape of the rolling elements - ball and roller, and roller: cylindrical, conical, barrel-shaped.
● In the direction of the perceived load - radial (perceive radial loads), radial thrust (perceive radial and axial loads) and thrust (perceive axial loads).
● By the number of rows of rolling elements - single-row, double-row and multi-row.
5.10. The main reasons for the loss of performance in rolling bearings.
● Fatigue chipping after prolonged use.
● Wear - with insufficient protection against abrasive particles.
● Cage failure, which is characteristic of high-speed bearings, especially those with axial loads or skewed rings.
● Splitting of rings and rolling elements - in case of impermissible shock loads and misalignment of the rings.
● Residual deformations on raceways in the form of dimples and dents - for heavily loaded low-speed bearings.
5.11. How is the selection of rolling bearings carried out?
When designing machines, rolling bearings are not designed, but selected from standard ones.
Distinguish the selection of bearings:
● By basic static load capacity to prevent permanent deformation - at a speed of no more than 10 rpm.
● By basic dynamic load capacity to prevent fatigue failure (spalling) - at a speed of more than 10 rpm.
Couplings
6.1. Purpose of couplings.
Coupling - a device, the main purpose of which is the connection of shafts and the transmission of torque from one shaft to
the other without changing its size and direction.
Shaft coupling is a common, but not the only, purpose of couplings.
Some types of couplings additionally:
● Compensate for mounting inaccuracies.
● Disconnect and connect shafts without stopping the engine.
● Protect the machine from breakdowns in emergency modes.
● Absorb shock and vibration.
6.2. How are couplings classified?
● Permanent (non-disengaging) couplings providing permanent shaft connection.
● Couplings, which provide connection (coupling) or disengagement of shafts while the machine is running.
Controlled clutches connect (disconnect) the shafts on command.
Self-guided clutches work automatically, connecting and disconnecting the shafts, depending on the specifics of the machine and the principle of the clutch.
6.3. Types of shaft misalignment.
Due to manufacturing and installation errors, there is some inaccuracy in the relative position of the geometric axes of the shafts to be connected. There are three types of deviations from the nominal (coaxial) shaft arrangement:
● Radial displacement, or eccentricity, D.
● Axial (longitudinal) displacementl , which can also occur due to deformation of the shafts when the temperature changes.
● Angular misalignment, or misalignment,g .
6.4. What is a blind coupling?
The blind coupling forms a rigid shaft connection. It does not compensate for manufacturing and installation errors and requires accurate shaft alignment.
● Sleeve coupling - the simplest representative of blind couplings. The bush is fastened to the shafts using pins or keys.
● Flanged coupling - two half-couplings connected by bolts.
6.5. What is a compensating coupling?
The compensating coupling compensates for manufacturing and installation errors, namely shaft misalignment. Compensation provided design features: torque
is transferred from one coupling half to another through an intermediate disc or elastic elements made of rubber.
6.6. Controlled couplings.
Controlled couplings allow shafts to be connected or disconnected using a control mechanism:
● A clutch whose operation is based on engagement (cam or toothed). Consists of two half-couplings, on the ends of which there are projections (cams). In the working position, the protrusions of one coupling half enter the depressions of the other. For switching on and off, one of the coupling halves is movably mounted on the shaft in the axial direction.
● Friction based clutch (frictional). Consists of two coupling halves, one of which moves along the shaft and is pressed against the second coupling half with a certain force.
6.7. Self-driving couplings (self-acting).
● Safety clutch with destructible element. Consists of two half-couplings connected by a cylindrical safety element (pin). In the event of an overload, the safety element shears off and the coupling halves open.
● Friction safety clutch. In the event of overload, the coupling halves open. The machine's operability is automatically restored after the overload has ceased.
● Overrunning clutch (freewheel). Serves to transmit torque in one direction only.
● Centrifugal clutch (starting). Automatically connects the shafts only when the angular velocity exceeds a certain preset value.
List of references
1. Ivanov M.N., Finogenov V.A. Machine parts: Textbook. - M., Higher School, 2008 .-- 408 p.
2. Kuklin N.G., Kuklina G.S., Zhitkov V.K. Machine parts: Textbook. - M., Higher School, 2008 .-- 406 p.
3. Markhel I.I. Machine parts: Textbook. - M., Forum, Infra-M, 2011 .-- 336 p.
4. Roshchin G.I., Samoilov E.A. Machine parts and design basics: Textbook. - M., Bustard, 2006 .-- 415 p.
5. Sukhikh R.D. Machine parts and design basics: A Brief Explanatory Dictionary. - St. Petersburg, Petersburg state University ways of communication, 2010. - 43 p.
1. General information about machines and mechanisms …………….… ..1
2. Connections of machine parts ………………………… ... …… .5
2.1. One-piece connections ……………………… ......... 6
2.2. Detachable connections …………………………… ..... 9
3. Mechanical transmissions ………………………………… .... 12
3.1. General information about mechanical transmissions ……… .12
3.2. Gears ………………………………… ... 13
3.3. Chain drives …………………………………… .22
3.4. Friction gears …………………………… ... 22
3.5. Belt drives …………………………… ......... 24
4. Shafts and axles ……………………………………………… ..25
5. Supports of shafts and axles ……………………………………… ... 27
6. Couplings ………………………………………………… ......... 31
References …………………………………… .... 35
Supports of shafts and axles are designed to support the rotary or rocking motion of the shafts and axles and transfer forces from them to the housing. The accuracy of the action and the reliability of the mechanism as a whole largely depend on the design of the supports. Supports designed to accept a radial or combined (radial and axial) load are commonly called bearings, and supports that take only axial loads are called thrust bearings.
According to the type of friction, they are divided into rolling bearings and sliding bearings. The choice of one or another type of support is determined by the operating conditions, loads acting on the support, dimensional constraints, the required durability and cost of the mechanism.
Rolling bearings
Friction bearing Is a ready-made subassembly consisting of an external 1 and internal 2 rings with raceways between which the rolling elements are located 3 and separator 4, holding the rolling bodies at a certain distance from each other and directing their rotation (Figure 4.72, and). Rolling bearings are the most common complete assembly unit and are used in almost all mechanisms with rotating parts (with the exception of mechanisms with slide bearings).
Rolling bearings are standardized and produced at specialized state bearing plants (GPP). The domestic industry occupies one of the leading places in Europe in the production of bearings. In the late 1980s. up to 1 billion bearings per year of various standard sizes were produced - from 1 mm of inner diameter to 3 m of outer diameter.
Benefits: relatively low friction losses; relatively low cost of bearings for their mass production; relatively short support length; less consumption of lubricant; small starting moments; complete interchangeability, which facilitates assembly and repair of mechanisms. In the designs of shafts and axles with rolling bearings, the issues of axial fixation and compensation of thermal deformations are easier to solve, they are less sensitive to misalignments and deflections of the shafts under load, to misalignment of the bearings.
disadvantages: high sensitivity to shock loads; limited speed associated with kinetic
Figure: 4.72
mathematics and dynamics of rolling bodies (centrifugal forces, gyroscopic moments, etc.); high cost for single or small-scale production; relatively large radial dimensions of the support; limited operating temperature range; noise during operation due to form errors; General purpose bearings do not work in corrosive environments.
Bearings for general use, which are used in general engineering, railway transport, automobile construction and other industries, are produced in five accuracy classes, which differ in the values \u200b\u200bof the tolerances for the dimensions of the rings and rolling elements. With an increase in manufacturing accuracy, the cost of bearings increases, so the choice of an accuracy class must have an appropriate justification. Table 4.22 shows the comparative cost of bearings of different accuracy classes.
Table 4.22
By the shape of the rolling bodies bearings are divided into ball and roller. The rollers can be short cylindrical, barrel-shaped, conical, twisted and long cylindrical (Fig. 4.72, b).
By direction of perceived load bearings are divided into radial, which perceive only radial or radial and some axial loads; radial bearing, serving for the perception of radial and significant axial loads; thrust-radial, perceiving radial loads along with axial ones; thrust, designed to absorb axial load.
By self-installation method bearings can be non-self-aligning and self-aligning.
By the number of rows of rolling elements bearings are divided into single-row, double-row and multi-row.
By ratio of overall dimensions bearings of the same type are divided into series: ultra-light, extra light
Figure: 4.73
(fig. 4.73, and), light (Figure 4.73, b), light wide (Figure 4.73, in), medium (fig. 4.73, d), medium wide (Fig.4.73, d) and heavy (Fig.4.73, e). Bearings of light and medium series are the most common and, accordingly, have a low cost in mass production.
Let's consider some basic types of bearings for general use.
Radial bearings.Deep groove ball bearing (fig. 4.74, and) designed to accept radial loads, but can also accommodate axial loads up to 70% of unused radial loads. These bearings fix the position of the shaft in two axial directions, at low speeds they allow slight misalignments of the shafts (up to 8 "), the size of which depends on the internal clearances between the rings and rolling elements.
Double-row spherical deep groove ball bearing (self-aligning) (Figure 4.74, b) perceives a radial load with mutual rotation of the axes of the rings up to 2–3 ° and an axial load, which is up to 20% of the unused radial. Self-aligning bearings are advantageous with significant shaft deflections and bearing misalignment. In swinging motion, these bearings perform better than single-row radial bearings.
Radial roller bearings with short cylindrical rollers (fig. 4.74, in) Accepts a radial load 1.7 times that of a ball bearing of the same dimensions. In the design of such bearings, one of the rings has guide collars, while the other is not fixed relative to the rollers. These bearings do not accept any axial load. In case of misalignment of the supports, additional pressure arises along the edges of the rollers,
Figure: 4.74
dramatically reducing the durability of bearings. They are used in electric motors, gearboxes, gas turbines and other machines.
Double row spherical roller bearing (self-aligning) (fig. 4.74, d) accepts increased radial load and axial load up to 25% of unused radial. The rollers of this bearing are barrel-shaped and the outer ring is free to rotate axially relative to the inner ring. Such bearings can compensate for misalignment and shaft deflections when the rings are misaligned up to 2.5 °. They fix the shaft axially in both directions within the available clearances. These bearings are used in the bearings of pumps, rolling mills and other machines, where there are large radial loads and shaft misalignments are possible.
Needle roller bearing (fig. 4.74, ∂ ) perceives large radial loads at small radial overall dimensions... It is used for pallet speeds up to 5 m / s, as well as for swinging movements. The rolling bodies are rollers with a diameter of 1.6–6 mm and a length of 4–10 roller diameters, which are installed without a cage. Sometimes bearings are used without an inner ring, and the rollers are rolled over the surface of the shaft. These bearings are very sensitive to shaft deflections and seat misalignments. The needle bearing is used in the bearings of crank and rocker mechanisms, cardan shafts, milling machine assemblies, etc.
Angular contact bearings.Single row angular contact ball bearing (fig. 4.74, e) perceives radial and one-sided axial loads. These bearings have a bevel on the outer ring on one side, which makes it possible to install a larger (45%) number of balls and increase the radial load capacity by 30–40%. The perceived axial load is 70-200% of the unused radial load, depending on the contact angle of the balls with the rings. Bearings are made with contact angles of 12, 18, 26 and 36 °. With an increase in the contact angle, the perceived axial load increases and the speed of the bearings decreases. For the perception of alternating axial load, bearings are often installed in two or more in one support. Angular contact ball bearings are installed in machine tool spindles, electric motors, worm gearboxes etc.
Tapered roller bearings (fig. 4.74, g) perceives simultaneously significant radial and one-sided axial loads. The rolling element of this bearing is a tapered roller. They are used at speeds up to 15 m / s. At very high loads (in rolling mills), multi-row tapered roller bearings are installed, which can accommodate double-sided axial loads. The magnitude of the perceived axial load depends on the taper angle of the outer ring, with an increase in which the axial load capacity increases and the radial load capacity decreases. When installing these bearings, it is necessary to adjust the axial clearances. Very small or excessively large clearances can lead to destruction of bearing parts. These bearings are used in the wheels of aircraft, automobiles, in spur and worm gearboxes, gearboxes, in the spindles of metal-cutting machines.
Angular contact ball bearings(fig. 4.74, s) are designed to absorb axial loads, but can also take small radial loads. The angle of inclination of the contact line is 45–60 °. They are used at low speeds.
Thrust bearings.Thrust ball bearing (fig. 4.74, and) designed to accept only axial load at shaft speeds up to 10 m / s, works best on vertical shafts. At high speeds, the operating conditions of the bearing deteriorate due to centrifugal forces and gyroscopic moments acting on the balls. They are very sensitive to the accuracy of installation, they allow mutual misalignment of rings up to 2 ". They are used in screw-nut gears, for jacks, crane hooks, etc.
Thrust roller bearing (fig. 4.74, to) designed to accept only axial loads, mainly on vertical shafts with low speeds. They are characterized by high carrying capacity. They are very sensitive to misalignment of rings: permissible misalignment is no more than 1.
Special bearings. In addition to bearings of general use, special bearings are also produced, for example, aircraft bearings, corrosion-resistant, self-lubricating, low-noise, etc. Aircraft bearings include heavy-loaded high-speed bearings for gas turbine engines, bearings for control mechanisms of aircraft (AC), performing rocking motion under heavy loads , bearings for electric units with rotation speeds up to 100,000 rpm. Bearings for aircraft control mechanisms are produced without a cage, fully filled with balls, grease and shields that keep the lubricant in the space between the rings. Corrosion-resistant bearings are made of chromium steel 95X18, 11X18, the cage is made of fluoroplastic-4. Self-lubricating bearings are installed in the mechanisms of special equipment operating in conditions of deep vacuum, ultra-low or ultra-high temperatures (mechanisms of space technology). Under these conditions, plastic and liquid lubricants lose their viscosity and therefore solid lubricants are used, which are molybdenum disulfite MoS2, graphite, fluoroplastic, and special grades of plastics. The raceways are coated with special silver, nickel and gold coatings. These bearings operate at speeds 2 times lower than the usual ones, since there is no heat removal from the friction zone. Low-noise bearings are used in mechanisms that operate for a relatively long time in the presence of a person (life support systems for an astronaut, mechanisms household appliances etc.). Reducing the level of vibrations and, accordingly, noise is achieved by reducing the gaps between the rolling elements and the bearing rings, increasing the accuracy of their manufacture.
The bearings are made of ball bearing high-carbon chromium steels ShKh15, ShKh15SG with a carbon content of 1–1.5%. The number in the designation of the steel grade indicates the chromium content in tenths of a percent. Also used are case-hardened alloy steels 18KhGT, 20Kh2N4A, 20NM. The hardness of the rolling elements and bearing rings is 60–65 HRC. For bearings operating in aggressive environments, corrosion-resistant steels 9X18, 9X18SH are used. Separators are most often made of stamped or riveted steel strip. At relative circumferential velocities of the rings more than 10 m / s, separators made of bronze, brass, aluminum alloys and non-metallic materials are used.
Selection of bearing type.When choosing a rolling bearing, the size, nature of action and direction of load, speed, required durability, installation conditions, environmental influences, etc. are taken into account. Bearings can be used for the same operating conditions different types, and in their selection, economic factors and operating experience of similar structures are taken into account. Initially, they consider the possibility of using deep groove single-row ball bearings of light or medium series as the cheapest and easiest to operate. The choice of other bearing types must be justified. The dimensions of the bearing are determined by the requirements for the carrying capacity, the diameter of the shaft journal (determined by the strength), and the conditions for placing the supports. Thus, the choice of the bearing is an important and crucial moment in the design phase of the mechanism.
Calculation of bearings. The calculation of the bearing life is based on its dynamic load capacity. When the bearing rotates with a load at the point of interaction of the rolling body with the ring, contact voltages, changing in a zero cycle. The criterion for their performance is the resistance to fatigue failure of the contact surface. Based on the experimental data, the following relationship was established between the effective load and durability:
where L - bearing durability, million revolutions; - coefficients; FROM - dynamic load capacity, which is a constant radial load that a bearing with a fixed outer ring can withstand 1 million revolutions; R - equivalent load acting on the bearing; - exponent (for ball bearings and for roller bearings).
The reliability of bearings for general applications corresponds to the probability of failure-free operation. If it is necessary to increase the reliability, the coefficient of durability is introduced (Table 4.23).
Table 4.23
The coefficient depends on the material from which the bearing is made and the operating conditions. For mechanisms of general use, one can take
The equivalent load for radial and angular contact ball and tapered roller bearings is determined by the relationship
where X and Y - coefficients of radial and axial loads (see table. 4.16); V– a rotation factor of 1 if the inner ring rotates and 1.2 when the outer ring rotates; and - radial and axial loads; - safety factor, taking into account the nature of the acting load; - temperature coefficient equal to one at the operating temperature of the bearing C.
Safety factor under load without jerks; at light jolts and vibrations; with moderate shock and vibration; with strong shock and high overload.
The equivalent load for bearings with short cylindrical rollers is found by the formula
and for thrust bearings - according to the formula
With an increase in the equivalent load R durability is reduced by 2 times by 8–10 times, therefore it is necessary to determine the load acting on the bearing as accurately as possible.
Bearing durability (in h) is compared with the resource of the mechanism:
where p - bearing ring rotation speed, rpm; Г - resource of the mechanism, h.
The calculation of durability by dynamic load capacity is carried out for bearings with a rotational speed; rpm. In bearings with rocking motion or rotating at a frequency of rpm, the acting load is considered as static and compared with the static load capacity Q. static load capacity understand a force such that the residual deformation of the rolling elements and rings does not exceed the allowable value, where D - the diameter of the rolling body. For static and dynamic load ratings, refer to the bearing catalogs.
Lubricants.Is of great importance right choice lubricant, the presence of which reduces friction losses, promotes heat removal from the friction zone, softens the impact of rolling elements on the cage and rings, protects against corrosion, and reduces noise levels. The choice of one or another type of lubricant for bearings depends on operating modes and conditions, mechanism design, environment, special requirements, etc. For lubrication, plastic and liquid lubricants are used. Plastic lubricants of the CILTIM-201 brands,
Litol-24, VNII NP-207, etc. are used in the temperature range -60 ... + 150 ° С, moderate loads and rotational speeds; liquid lubricants (oils) - for high-speed and heavily loaded bearings. The latter provide more efficient heat dissipation and have better penetration to the friction surfaces. They are also used in friction units that are difficult to access for changing the lubricant and, if necessary, constant monitoring of the presence of lubricant. The main brands of liquid oils: industrial I-5A, I-12A, transmission TAD-17, aviation MS-14, MK-22, etc.
Sealing of bearing units... An important condition for the reliable operation of bearings is a reasonable choice of seals that protect the bearing cavity from dust, moisture, abrasive particles from the environment and prevent the leakage of lubricant. The design of the selected seal depends on the type of lubricant, the conditions and operating mode of the bearing assembly, and the degree of its tightness.
According to the principle of operation, the seals are divided into contact ones, in which the sealing is carried out due to the tight fit of the sealing elements to the moving surface of the shaft; non-contact - sealing in which is carried out due to the small gaps of the mating elements; combined, consisting of a combination of contact and non-contact seals.
Contact seals. The main types of contact seals are stuffing box and lip th. Felt ring seals (stuffing box) used to seal the cavities of bearings operating on a plastic lubricant up to peripheral speeds v \u003d 8 m / s and T \u003d 90 ° C. Ring contact 2 with shaft 1 (fig. 4.75, and) provide due to preload. Before being installed in the groove in the body part, the felt rings are impregnated with a heated mixture of lubricant (85%) and graphite. It is not recommended to use these seals in overpressure and dusty environments. The efficiency and durability of packing gland seals is increased when installed in combination with other seals (slotted and labyrinth).
Lip seals (fig. 4.75, b) have an o-ring 3, made of rubber with a protruding working edge that contacts the surface of the shaft 1. The contact of the working edge of the cuff with a width of 0.2-0.5 mm with the shaft is ensured by preloading, as well as by pressing it against the shaft with a bracelet spring 2. The seal is installed so that the working edge is pressed against the shaft by excess pressure of the sealed medium. Cuffs for working in a clogged environment are made with an additional working edge-anther 5. To increase rigidity, the cuff body can be reinforced with a steel ring 4. Lip seals are used in bearing units at speeds V \u003d 25 ÷ 30 m / s and overpressure P \u003d 0.2 ÷ 0.3 MPa. Work efficiency is increased by sequential installation of two cuffs at a distance of 3–8 mm.
Figure: 4.75
Sealing of bearing assemblies at any lubricant and speed v\u003e 5 m / s can be provided with shaped washers 2 (Figure 4.75, c). The thickness of the washers depends on their size and is 0.3-0.5 mm. The washer is fixed with a nut 1. It is not recommended to seal self-aligning bearings with large axial clearances with shaped washers due to the possibility of breaking the contact between the washer and the bearing race.
Disadvantage contact seals - the presence of friction between the contacting surfaces, which leads to additional energy costs, as well as heating and wear of the surfaces. The friction and wear of the contact pair limits the life and scope of contact seals.
Non-contact seals. These seals work by resisting the flow of lubricant through narrow slots or channels with rapidly changing bore sizes. They do not provide absolute tightness, but serve to limit leaks. The main advantage of non-contact seals is increased durability and reliable operation at all temperatures and speeds. By their principle of operation, they can be divided into static and dynamic. In static seals, slot and labyrinth seals, the amount of leakage depends only on the geometric characteristics of the connection of mating elements. The effectiveness of dynamic seals depends on the geometry of the joint and the relative rotational speed of the mating elements.
Throat seal (fig. 4.75, d) used for grease and speeds v \u003d 5 m / s. The degree of sealing of the seal depends on the size of the gap and the length of the gap /. The clearance is determined by the deflection of the shaft at the place of the seal installation, the eccentricity of the shaft surfaces 2 and housing 1 in relation to the axis of rotation, bearing clearance, etc. Reducing the gap is achieved by applying mastic to the stationary part 3 prepared on powdered graphite.
Sealing of bearing assemblies operating on plastic and liquid lubricants at temperatures T \u003d 80 ÷ 400 ° C and speeds v \u003d 30 m / s, it is possible to provide fat grooves (Fig. 4.75, E), which are filled with a plastic lubricant during assembly. The dimensions of the grooves and the size of the gap are assigned depending on the diameter of the shaft. For example, for d \u003d 20 ÷ 95 mm r \u003d 1 ÷ 1.25 mm and δ \u003d 0.3 ÷ 0.4 mm.
Labyrinth seal used at speeds v\u003e 30 m / s. Depending on the number of slots, they can be single or multi-stage. Radial seal (fig.4.75, e) allows relative sleeve displacement 2 with respect to the support cover 1, therefore it is used for floating bearing supports. In the axial labyrinth seal (Fig.4.75, g) with one-piece housing 3 use a compound labyrinth sleeve 4. This seal is installed with axial shaft displacements.
In bearing arrangements with liquid lubricant use dynamic seals, which work when rotating vata, but lose their effectiveness when stopped. These seals are often used in combination with static contact or non-contact seals to prevent leakage in non-operating machinery. Spiral (threaded) seal (Fig. 4.75, h) is performed in the form of a single or multiple cut of a rectangular or triangular profile. When the shaft rotates, the lubricant is thrown into the cavity of the gearbox. On-
Figure: 4.76
the cutting direction must be coordinated with the direction of rotation of the shaft. The spiral seal should not be used in reversing applications.
In fig. 4.76 shows the combined seal of the gearbox bearing unit of the AI-14V aircraft engine, consisting of an oil flinger 2 and elastic metal rings 1. In an idle gearbox, sealing is ensured by the contact of elastic rings with the bearing cap 4. When the shaft rotates under the action of centrifugal forces, the liquid lubricant is thrown to the periphery of the ring 2 and flows down to the lower part of the case, where there is a channel 3 to drain it.
The shafts and axles are supported by special parts that act as supports. The name "bearing" comes from the word "thorn" ( english shaft, it.zappen, goll.shiffen - shaft). This is how the shanks and shaft journals used to be called, where, in fact, the bearings are installed.
The purpose of the bearing is that it must provide a reliable and accurate connection between the rotating (shaft, axis) part and the stationary housing. Consequently, the main feature of the bearing is the friction of the mating parts.
By the nature of friction, bearings are divided into two large groups:
sleeve bearings (sliding friction);
rolling bearings (rolling friction).
Plain bearings
The main element of such bearings is a liner made of an antifriction material, or at least with an antifriction coating. The liner is installed (inserted) between the shaft and the bearing housing.
Sliding friction is definitely greater than rolling friction, however, the advantages of plain bearings lie in a variety of applications:
in split designs (see figure);
at high rotation speeds (gas-dynamic bearings in turbojet engines at n 10,000 rpm );
if necessary, precise centering of the axes;
in machines of very large and very small dimensions;
in water and other aggressive environments.
The disadvantages of such bearings are friction and the need for expensive antifriction materials.
In addition, sleeve bearings are used in auxiliary, low-speed, low-responsibility mechanisms.
Typical defects and failures in plain bearings are caused by friction:
temperature defects (sticking and melting of the liner);
abrasive wear;
fatigue failure due to load pulsation.
With all the variety and complexity of the design options for sliding bearing units, the principle of their design is that a thin-walled sleeve made of antifriction material, usually bronze or bronze alloys, is installed between the housing and the shaft, and for lightly loaded mechanisms made of plastics. There is a successful experience of operating thin-walled bimetallic liners with a thickness of not more than 4 mm, made of steel strip and aluminum-tin alloy AO 20-1, in locomotive diesel engines M753 and M756.
Most radial bearings have a cylindrical liner, which, however, can also take axial loads due to fillets on the shaft and rounding of the liner edges. Tapered bush bearings are rarely used, they are used for light loads, when it is necessary to systematically eliminate ("track") the bearing wear clearance to maintain the accuracy of the mechanism.
For the bearings to function properly without wear, the journal and bushing surfaces must be separated by a layer of grease of sufficient thickness. Depending on the operating mode of the bearing, it may contain:
semi-fluid frictionwhen the irregularities of the shaft and the liner can touch each other and in these places they seize and detach the liner particles. Such friction leads to abrasive wear even without external dust entering.
Providing the fluid friction mode is the main design criterion for most plain bearings. At the same time, performance is ensured according to the criteria of wear and seizure.
The criterion for the strength and, consequently, the performance of the plain bearing is the contact stresses in the friction zone or, which, in principle, is the same, the contact pressure. The calculated contact pressure is compared with the allowable p = N / (l d ) [ p ] ... Here N - power normal pressure shaft to bushing (support reaction), l - working length of the bearing sleeve, d - diameter of the shaft journal.
Sometimes it is more convenient to compare the calculated and permissible product of pressure and sliding speed. The sliding speed can be easily calculated by knowing the diameter and speed of the shaft.
The product of pressure and sliding speed characterizes the heat generation and bearing wear. The most dangerous is the moment of starting the mechanism, because at rest, the shaft descends ("lies") on the liner and at the beginning of the movement dry friction is inevitable.
ROLLING BEARINGS
The principle of their design lies in the presence between the shaft and the body of a group of identical round bodies, called rolling bodies.
It can be either balls, or rollers (short thick or long needle-shaped), or tapered rollers, or barrel-shaped, or even spiral springs. Typically, the bearing is made as an independent assembly unit, consisting of an outer and inner rings, between which the rolling elements are placed.
In order to avoid unnecessary contact with each other and uniform distribution around the circumference, the rolling bodies are enclosed in a special ring-shaped cage - a separator ( lat.Separatum - share).
In some designs, where one has to struggle to reduce the radial dimensions, so-called. "slip-free" bearings when the rolling elements are mounted directly between the shaft and the housing. However, it is not hard to guess that such structures require complex, individual, and, therefore, expensive assembly and disassembly.
Advantages of rolling bearings:
low friction, low heating;
saving grease;
high level of standardization;
saving expensive antifriction materials.
Disadvantages of rolling bearings:
high dimensions (especially radial) and weight;
high requirements for optimizing the choice of standard size;
weak vibration protection, moreover, the bearings themselves are vibration generators due to even a very small inevitable difference in the size of the rolling bodies.
Rolling bearings are classified according to the following main characteristics:
the shape of the rolling bodies;
dimensions (axial and radial);
dimensional accuracy;
direction of perceived forces.
By the shape of the rolling elements, bearings are divided into:
Ball (high-speed, capable of self-installation due to the possibility of some deviation of the axis of rotation);
Roller - tapered, cylindrical, needle-shaped (more lifting capacity, but due to the precisely fixed position of the axis of rotation, they are not able to self-align, except for barrel-shaped rollers).
Bearings are grouped into seven series in terms of radial dimensions:
According to axial dimensions, the bearings are grouped into four series:
Bearings are distinguished by accuracy classes as follows:
"0" - normal class;
"6" - increased accuracy;
"5" - high accuracy;
"4" - extra high accuracy;
"2" - ultra high precision.
When choosing a bearing accuracy class, remember that "the more accurate, the more expensive."
According to the perceived forces, all bearings are divided into four groups. Calculating the radial F r and axial F a reactions of the shaft supports, the designer can choose:
Radial bearings (if F r << F a ), which perceive only radial load and insignificant axial load. These are cylindrical roller (if F a = 0 ) and deep groove ball bearings.
Angular contact bearings (if F r > F a ), perceiving more radial and less axial loads. These are angular contact ball and tapered roller with a small taper angle.
Thrust radial bearings (if F r < F a ), perceiving more axial and less radial loads. These are tapered roller bearings with a large taper angle.
Thrust bearings, "foot pads" (if F r << F a ), taking only axial load. These are thrust ball and thrust roller bearings. They cannot center the shaft and are only used in combination with radial bearings.
Rolling bearing materials are selected taking into account the high requirements for the hardness and wear resistance of the rings and rolling elements.
It uses high-carbon ball bearing chromium steels ШХ15 and ШХ15СГ, as well as case-hardened alloy steels 18ХГТ and 20Х2Н4А.
The hardness of rings and rollers is usually HRC 60 65 , and the balls have a little more - HRC 62 66 because the ball has a smaller contact pressure area. Cages are available in mild carbon steel or anti-friction bronze for high speed bearings. Separators made of duralumin, cermets, textolite, and plastics are widely introduced.
Causes of breakdowns and design criteria for bearings
The main feature of bearing dynamics is alternating loads.
Cyclic rolling of the rolling elements can lead to micro fatigue cracks. Constantly rolling rolling elements press the lubricant into this microcrack. The pulsating pressure of the lubricant expands and loosens the microcrack, leading to fatigue chipping and, in the end, to ring breakage. Most often, the inner ring breaks. it is less than the external one and there, therefore, the specific loads are higher. Fatigue spalling is the main type of rolling bearing failure.
In bearings, static and dynamic overloads are also possible, destroying both rings and rolling elements.
Therefore, when designing a machine, it is necessary to determine, firstly, the number of revolutions (cycles) that the bearing is guaranteed to withstand, and, secondly, the maximum permissible load that the bearing can withstand.
Conclusion: bearing performance is maintained if two criteria are met:
Durability.
Carrying capacity.
Calculation of the nominal bearing life
The rated life is the number of cycles (or hours) that a bearing must operate before the first signs of fatigue appear. There is an empirical (found from experience) relationship for determining the nominal durability L n = ( C / P ) , [ million revolutions ] ,
where FROM - carrying capacity, R - equivalent dynamic load, = 0,3 for balls, = 0,33 for rollers.
Nominal life can be calculated in hours
L h = (10 6 / 60 n ) L n , [ hours ] ,
where n - shaft rotation frequency.
Equivalent dynamic load is a constant load such that the bearing life is the same as under actual operating conditions. Here, for radial and angular contact bearings, the radial load is meant, and for thrust and radial thrust bearings, the central axial load.
Equivalent dynamic load is calculated using the empirical formula
P \u003d ( V X F r + Y F a ) K B K T ,
where F r , F a - radial and axial reaction of supports;
V - the coefficient of rotation of the load vector ( V = 1 if the inner ring rotates, V = 1,2 if the outer ring rotates)
X , Y - the coefficients of radial and axial loads, depending on the type of bearings, are determined from the reference book;
TO B - safety factor, taking into account the influence of dynamic working conditions ( TO B = 1 for gears, TO B = 1,8 for rolling stock),
TO T - temperature coefficient (up to 100 about FROM TO T = 1 ).
Lifting capacity is the constant load that a group of identical bearings can withstand for one million revolutions. Here, for radial and angular contact bearings, the radial load is meant, and for thrust and radial thrust bearings, the central axial load. If the shaft rotates slower than one revolution per minute, then we are talking about static load capacity C 0 , and if the rotation is faster than one revolution per minute, then they talk about the dynamic load capacity C ... The load capacity is calculated during the design of the bearing, determined on an experimental batch of bearings and entered into the catalog.
Method for selecting rolling bearings
An experienced designer can designate a specific bearing type and size and then make a verification calculation. However, this requires a lot of design experience, because in the event of an unsuccessful choice, the strength condition may not be met, then it will be necessary to select another bearing and repeat the verification calculation.
In order to avoid numerous "trials and errors", it is possible to offer a bearing selection method based on the principle of design calculation, when the loads are known, the required durability is set, and as a result, a specific bearing size from the catalog is determined.
The selection technique consists of five stages:
The required bearing life is calculated based on the speed and the customer's specified machine life.
Based on the previously found reactions of the supports, the type of bearing (radial, angular contact, thrust-radial or thrust) is selected, the radial and axial load factors are found from the reference book X , Have .
The equivalent dynamic load is calculated.
The required lifting capacity is determined C = P * L ( 1/ α ) .
According to the catalog, based on the required load capacity, a specific size ("number") of the bearing is selected, and two conditions must be met:
lifting capacity according to the catalog is not less than the required one;
the inner diameter of the bearing is not less than the diameter of the shaft.
Design features of bearing assemblies
THEME 3. SHAFT AND BEARINGS. LECTURE 13. SUPPORTS OF AXES AND SHAFT. SLIDE BEARINGS. Questions outlined in the lecture: 1 Supports of axles and shafts. General information. Classification. 2 Plain bearings. General information. 3 Modes of operation of sleeve bearings. 4 Lubrication of sleeve bearings. 5 Calculation of plain bearings
Axle and shaft supports. Classification Shafts and rotating axles are supported by bearings and thrust bearings. Bearing The part of the shaft or axle bearing that interacts directly with the journal. Accepts radial and axial loads and transfers them to the body or frame of the machine. Foot pad - perceives axial loads, mainly vertical. Classification: 1 In the direction of the force load perceived by the support: 1.1 radial bearings perceive the load directed perpendicularly (along the radius) to the axis of rotation; 1.2 thrust bearings take a load directed along the axis of rotation (thrust bearings are called thrust bearings); 1.3 angular contact bearings perceive both radial and axial loads at the same time, while the radial load is usually greater than the axial one; 1.4 thrust radial bearings take both radial and axial loads, but in this case the radial load is less than the axial load. 2 Depending on the type of friction: 2.1 rolling bearings; 2.2 sleeve bearings
Plain bearings are divided according to their design features into one-piece (deaf) and split. One-piece plain bearings (Figure 1) are widely used where loads and sliding speeds are low (v ck 3 m / s) - in devices and control mechanisms. Plain bearings. General information Figure 1 - One-piece (blind) plain bearings: a) built into the body; b) flanged Figure 2 - Split plain bearing Split bearings (Figure 2) are mainly used where axial assembly is impossible or undesirable (journals of the internal combustion engine crankshafts), as well as in heavy engineering for fastening heavily loaded shafts. A sleeve bearing is a support or guide in which the trunnion slides over the liner surface.
Plain bearings are radial (Figure 3 a) and axial (Figure 3 b) by type of perceived load. Plain bearings. General information Figure 3 - Plain bearings: a) radial; b) axial Figure 4 - Self-aligning bearing Self-aligning bearing is a bearing capable of changing the angular position of the longitudinal axis in relation to the base surface, that is, tracking the angular position of the shaft journal (Figure 4). Self-aligning bearings are used with long trunnion lengths and possible misalignment of support units.
Advantages: 1 small dimensions in the radial direction; 2 good susceptibility to dynamic loads (shock and vibration); 3 high precision pairing; 4 good break-in ability; 5 high durability in conditions of abundant liquid lubrication; 6 the ability to work in an aqueous, abrasive and corrosive environment (with appropriate selection of materials); 7 possibility of assembly both in axial and radial directions Disadvantages: 1 large dimensions in the axial direction; 2 significant consumption of lubricant; 3 the need to monitor the constant supply of lubricant to the working surfaces; 4 high starting torque and high wear during starting; 5 the need to use expensive antifriction materials in the bearing. Plain bearings. General information
Depending on the amount of lubricant in the sliding bearing, the following friction modes are distinguished: 1) liquid friction - the surfaces of the shaft journal and bearing are separated by a continuous layer of grease, there is no direct friction between them; 2) semi-fluid friction - the continuity of the oil layer is broken; the surfaces of the bearing and the shaft journal are in contact with the tops of microroughnesses in the areas of greater or lesser extent; 3) semi-dry (boundary) friction - the surfaces of the shaft journal and bearing are in almost constant contact with each other, there is no separating layer of lubricant, oil is on the surfaces in the form of an adsorbed film; 4) dry friction - there is no lubricant in the gap between the surfaces of the shaft journal and the bearing, as a result of which these surfaces are in a state of continuous contact. Operating modes of plain bearings Characteristic of the operating mode of the bearing: - dynamic viscosity of the grease; - the angular velocity of the shaft; - the average pressure on the bearing surface.
Operating modes of plain bearings Examples of self-regulation of plain bearings. Liquid friction mode: 1 Increases decreases decreases decreases heat generation increases stable equilibrium. 2 Increases decreases decreases decreases decreases heat release stable equilibrium. Semi-fluid friction mode: Any factor contributing to a decrease (decrease in oil viscosity, increase in load), causes an increase in the coefficient of friction, as a result, an increase, increase in the coefficient of friction. The way out of the situation is to control the speed
The grease used for lubricating sliding bearings is classified according to the degree of consistency (density, hardness): - solid - graphite, molybdenum disulfide, some enveloping metals, for example, indium; - plastic (consistent, not dropping) - solid oil, lithol, some CIATIM lubricants; - liquid - organic and mineral oils, sometimes water and other liquids; - gaseous - air, nitrogen, inert gases (argon). The higher the viscosity of the lubricant, the more difficult it is to squeeze out of the bearing operating clearance and, therefore, the thicker its layer between the journal and the bearing surface can be during their joint operation. The most widespread in industrial conditions are liquid and grease lubricants. When using liquid lubrication, hydrostatic and hydrodynamic methods of lubrication are distinguished depending on the method of supplying lubricant to the bearing working clearance and the separation of hard surfaces with a layer of liquid lubricant. Sleeve Bearing Lubrication
The hydrostatic method is based on the separation of the rubbing surfaces due to the static head (pressure) of the lubricant supplied to the bearing, created by an external source (pump). Therefore, with the hydrostatic lubrication method, the lubricating fluid is supplied against the main loads (Figure 6) acting on the shaft journal, and the pump pressure is chosen so that the shaft journal floats on the lubricant layer. This method of supplying grease is used to lubricate the bearings of heavily loaded low-speed shafts (for example, to lubricate bearings of rolling mill shafts), for hydrostatic shaft alignment in precision machines. Figure 6 - Hydrostatic lubrication of sleeve bearings Lubrication of sleeve bearings
The hydrodynamic method is realized only during the rotation of the journal in the bearing after reaching the critical rotation speed (Figure 7). At rest, the shaft journal lies on the bearing surface (Figure 7 a). As the angular velocity of the journal increases (Figure 7 b), particles of lubricating oil, due to adhesion to its surface, are drawn into the wedge gap between the journal and the bearing. Figure 7 - Hydrodynamic lubrication of a sliding bearing As a result, the shaft journal floating up, comes off the bearing surface, and the friction surfaces are completely separated. The pressure that develops in the wedge gap increases in direct proportion to the dynamic viscosity of the oil, shaft speed and inversely to the thickness of the oil layer. The pressure in the wedge layer can be high, and therefore the oil is supplied to the vacuum zone, which does not require large power inputs for lubrication and high-pressure lubrication systems (pumps, filters, radiators, pipelines, etc.). Sleeve Bearing Lubrication
In the practice of operating sleeve bearings, the following types of wear can be observed: 1) abrasive (occurs when solid particles enter the bearing working clearance); 2) fatigue chipping under the action of pulsating loads; 3) overheating, which is a consequence of dry friction and ultimately leads to jamming of the journal in the bearing, the appearance of scoring or melting of the antifriction layer of the material. Thus, the main criterion for the performance of a sliding bearing is the wear resistance of the friction pair. Types of destruction of sliding bearings Requirements for the materials of the friction pair: 1) low coefficient of friction; 2) high wear resistance and fatigue resistance; 3) good thermal conductivity; 4) run-in and oil wettability.
1) antifriction cast irons (AShS, AChV, etc.) - at a quiet load, specific pressure up to 20 MPa and sliding speeds up to 5 m / s; 2) tin bronzes (BrOTsS5-5-5; BrOF10-1, etc.), lead and tin-lead (BrS-30; BrO5S25, etc.), tinless (BrA9Zh3L; BrA10Zh4N4L, etc.) at sliding speeds up to 12 m / s and specific pressures up to 25 MPa; 3) brass (LAZhMts, LKS, etc.) - at sliding speeds up to 2 m / s and specific pressures up to 12 MPa; 4) babbits, for example B89 (89% tin, 9% antimony, residual copper) - for conditions of abundant lubrication and good heat removal at sliding speeds up to 15 m / s and specific pressures up to 12 MPa; 5) light alloys on an aluminum base for irrelevant bearings (foundry AL3, AL4, AL5, wrought AK4, AK4-1); 6) non-metallic materials (chipboard, textolite, polycarbonates, nylon, nylon, fluoroplastics, rubbers) - at sliding speeds up to 5 m / s and specific pressures up to 10 MPa, some of these materials (chipboard, rubber) allow the use of water as a lubricant ; PS friction pair materials
7) cermets (bronze-graphite, iron-graphite) - at sliding speeds up to 3 m / s, specific pressures up to 6 MPa and lack of lubrication. The cermet is distinguished by high porosity (pores occupy up to 40% of the volume), as a result of which it is capable of absorbing large amounts of oil, this oil reserve is usually enough for several months of bearing operation without lubrication. To work with the bearing, the shaft journals must be subjected to thermal or chemical - thermal treatment in order to obtain a high hardness of the working surface (HRC\u003e 50 ... 55). The accuracy of manufacturing the diametrical dimensions of the trunnion is 6 ... 7 grade ESDP, and the surface roughness R a - 2.5 ... 0.25 microns. A higher surface smoothness of the journal is undesirable (less lubricant retention). Materials of the friction pair PS The height of the microroughness of the journal R z 1 and the liner R z 2 must ensure the mode of liquid lubrication. Because in real conditions, when installing bearings, shaft misalignments, shape errors and temperature deformations take place, take: the minimum thickness of the oil layer. 50 ... 55). The accuracy of the diametrical dimensions of the pins is 6 ... 7 of the ESDP grade, and the surface roughness R a is 2.5 ... 0.25 microns. A higher surface smoothness of the journal is undesirable (it retains the lubricant worse). Materials of the friction pair PS The height of the microroughness of the journal R z 1 and the liner R z 2 must ensure the mode of liquid lubrication. Because in real conditions, when installing bearings, shaft misalignments, shape errors and temperature deformations take place, take: the minimum thickness of the oil layer. "\u003e 
To check the basic dimensions of the bearing journal - length l and diameter d, the calculated and permissible pressure in the bearing are compared. In this case, the strength condition for the average pressure p between the contact surfaces of the shaft journal and the bearing can be written as: where R is the radial load acting on the shaft journal, [p] is the permissible value of this pressure. In the design calculation, the following assumption is made: the specific pressure is considered uniformly distributed both along the diameter of the journal and along its length. In the design calculation, they are set by the value of the bearing length factor. For non-self-aligning supports, it is recommended to take \u003d 0.4 ... 1.2 (in domestic technology, most often \u003d 0.6 ... 0.9). The use of a self-aligning bearing allows the length factor to be increased to \u003d 1.5 ... 2.5. Calculation of plain bearings
For a given bearing length coefficient, its diameter can be found by the ratio: The value of the energy release in a running bearing is characterized by the product of the average pressure p and the sliding speed v. In order to prevent overheating of the bearing, it is also checked according to this criterion: where n is the rotational speed of the shaft journal. Based on the last expression, with known materials of the friction pair of the journal - bearing liner, it is convenient to find the bearing length as follows: Calculation of sleeve bearings and then you can calculate the required journal diameter:
Shafts and rotating axles are mounted on supports that determine the position of the shaft or axis, provide rotation, take the shaft loads and transfer them to the base of the machine. The main part of the supports are bearings.
By the type of friction, they are distinguished: sleeve bearings,in which the shaft journal slides on the bearing surface; rolling bearings,in which the rolling elements of the bearing are located between the surfaces of the rotating part and the supporting surface.
The performance, durability and efficiency of the machine largely depend on the quality of the bearings.
There are many designs sleeve bearings,which are divided into two types: one-pieceand detachable.
A one-piece bearing (Figure 3.5) consists of a housing and a sleeve (liner) made of antifriction material, on which the journal of the shaft or axle rests directly. The bushing can be fixedly fixed in the bearing housing or freely embedded in it ("floating bushing"), a lubrication device is provided in the bearing design. One-piece bearings are commonly used in low-speed applications.
A split bearing (Figure 3.6) consists of a base and housing cover, a split liner, a lubricator, and a bolted or studded base / cover. The wear of the liners during operation is compensated by pressing the cover against the base. Split bearings are used in general and especially in heavy engineering.
Plain bearings advantages:
High performance at high speeds and shock loads;
Silence and vibration resistance of the shaft when the bearing is operating in fluid friction(the oil layer between the surfaces of the journal and the liner has the ability to damp vibrations);
Small dimensions in the radial direction;
Sufficiently high performance under special conditions (chemically aggressive media, with poor or contaminated lubricant).
Disadvantages of sleeve bearings:
Large friction losses (does not apply to bearings operating in the fluid friction mode, the efficiency of which is greater than 0.99);
Significant dimensions in the axial direction;
The need to use expensive and scarce antifriction materials for liners;
Significant consumption of lubricant and the need for systematic monitoring of the lubrication process;
Bearing interchangeability during repair is not ensured, since most bearing types are not standardized.
Rolling bearingsin most cases consist of an external 4 (fig. 3.7, and)and internal 1 rings with raceways, rolling elements 3 (balls or rollers), cage 2, separating and guiding rolling body. Some bearings may have one or both rings missing. In them, the rolling elements are rolled directly over the grooves (pins) of the shaft or housing.
Advantages of rolling bearings:
Significantly lower friction losses, and therefore a higher efficiency (up to 0.995) and less heating;
Saving scarce colored materials;
Less consumption of lubricant;
High degree of interchangeability (mass production).
Disadvantages of rolling bearings:
Sensitivity to shock and vibration loads;
Large dimensions in the radial direction;
Low reliability in high speed drives.
Rolling bearing classification (see fig. 3.7):
According to the shape of the rolling bodies: ball (a, 6, g, i), roller (with cylindrical (c), conical (h), barrel-shaped (d), needle (e) and twisted (e) rollers;
By the number of rows of rolling elements: single-row (a, c, g), double-row (6, d), multi-row;
In the direction of the perceived load: radial (a ... e), perceiving (mainly) radial loads, i.e. loads directed perpendicular to the geometric axis of the shaft; persistent (u, k), taking only axial loads from the shaft; radial thrust (w) and thrust radial (h) can simultaneously perceive radial and axial loads, while thrust radial bearings are designed for the prevailing axial load.
By overall dimensions. Depending on the ratio of the dimensions of the outer and inner diameters, bearings are divided into series - ultra-light, extra light, light, medium, heavy; in width on the series - narrow, normal, wide, extra wide.
3.3. TYPICAL MECHANISMS OF METAL CUTTING MACHINES
