The use of rolling bearings in mechanisms makes it possible to produce machines of a higher accuracy class. Machines based on these structural elements are more reliable and have a longer service life. In addition, their use reduces operating costs.
The capabilities of the assembly in which the rolling bearing is used is determined by how accurately this part is installed. The distance from the base to the axis of rotation and from the base to the end of the shaft, as well as the radial and end runout, must be within certain limits of accuracy.
During the assembly process, it is necessary to strive so that the bearing races are not deformed. Form seats in the bearing housing and on the shaft must satisfy the shape and roughness technical requirements, no scratches or burrs.
Differences from plain bearings
There are two types of moving parts in mechanisms: bearings based on sliding friction and bearings based on rolling friction.
When using the former, the working surfaces of the housing and shaft mutually move and interact, being separated most often by lubricants and a sliding liner. The support works when there is pure sliding in the parts that come into contact.
In the second version of the supports, rolling elements (these can be rollers or balls) are placed in the gap between the surfaces that move mutually. In this case, the bearings work using rolling friction. In such cases, instead of bronze, babbitt or plastic liners in bearings where rolling friction is applied, ball or roller bearings of steel.
In accordance with the nature of the load of rotation supports, they are radial, when a radial load acts on the support, thrust, when the support is subjected to only axial loads, and radial-thrust, when both types of loads act on the support together.
Each type of support is characterized by its size, design, specifications for production, installation and maintenance.
Rolling bearings and plain bearings have a different mechanism for resistance to movement and for determining the wear of parts of movable bearings. The type of required node is determined on the basis of an assessment of the operating procedure of the mechanism or its individual nodes.
Advantages and disadvantages
Rolling and sliding bearings have both pluses and minuses. Rolling bearings can be preferred over plain bearings due to the lower level of friction at low speeds and when starting from a standstill. Also, rolling bearings have smaller dimensions along the axes, which makes it easier to assemble the structures of self-aligning bearings, without requiring a long time for difficult individual fitting of the liners and their running-in. This is especially important for trunnions with large diameters, operating under heavy loads, with high rotational speeds and temperatures.
When a rolling bearing is used, the quality of lubrication of machine parts and assemblies is improved, the quality of their maintenance is improved, the life of the seating surfaces of the cylinder necks and shafts is extended. Thus, they are the best fit for the vast majority of equipment supports.
True, in addition to the advantages, rolling bearings have a number of disadvantages.
For example, large dimensions. Such structural elements are widely represented in machine-building equipment, are produced in small batches and are very expensive. The rolling bearing is inferior to competitors in such parameters as radial dimensions, weight and rigidity.
It is very difficult to choose them correctly when high rotational speeds are combined with the action of high loads. It is well known that with an increase in the load and speed of rotation of the unit, its durability decreases. For example, if the load is increased by a quarter compared to the previous one, then the service life is halved, and if the load is doubled, the durability becomes 10 times less.
Marking and dimensions according to GOST
Requirements for assemblies and parts are formulated by GOST. Rolling bearings are described by GOST 520-2002.
The following parameters formed the basis of the symbols:
- the diameter that the bearing hole has;
- series of widths (or heights) and series of diameters;
- types of bearings;
- technical implementation.
How to correctly determine the dimensions of rolling bearings by marking? The notation table will help to cope with this task.
All of the above parameters are indicated by signs (or numbers). What numbers the bearing marking consists of depends on the places they occupy in its symbol if read from left to right:
Dimensions
To find out how the dimensions of bearings depend on their series, the table of bearing sizes allows. It allows you to link the series to the outer and inner diameter and width.
Dimensions of rolling bearings. Table 1.
Width | External diameter | Inner diameter | |
This is a table of rolling bearings, one of many tables describing this species structural elements.
Classification
One of the features by which rolling bearings are classified is the shape of the rolling elements. In accordance with it, bearings can be ball and roller. Ball rolling bodies, as the name implies, are exclusively spherical in shape. Roller rolling elements can be cylindrical, barrel-shaped or cone-shaped.
The next sign of classification is the direction of load perceived by the rolling bearing. By given feature distinguish bearings:
- radial, which perceive only radial or mainly radial loads;
- radial-thrust, able to perceive both radial and axial loads.
It should be noted that adjustable bearings are not able to function without axle load. Thrust are able to perceive only axial forces. Thrust-radial type work both with axial and with small radial loads.
There is also a classification of rolling bearings depending on how many rows of rolling elements they consist of. They are single row and double row.
In accordance with such a characteristic as sensitivity to misalignment, self-aligning bearings are distinguished. They are able to function normally even if a misalignment of up to 3 ° occurs.
Tolerance and landing system
Rolling bearings are widely used. They are produced at special factories and have full interchangeability in terms of surfaces, which are determined by the diameters of the rings: D - the outer diameter of the outer ring and d - the inner diameter of the inner ring.
The interchangeability of rolling bearings depends on the accuracy requirements:
- ring width accuracy B;
- accuracy of ring diameters d, D;
- accuracy of ring surfaces;
- radial and axial runout of the raceways, which determines the accuracy of rotation;
- the accuracy of the gap that is formed at operating parameters between the raceways and the rolling elements.
The accuracy of assembly units is set by GOST. Rolling bearings must comply with the accuracy requirements of GOST 520-89, according to which there are 5 classes of their accuracy: 0; 6; 5; 4; 2. Most of the mechanisms use nodes of accuracy class 0. Nodes of accuracy classes above zero are used on high speeds rotation and in situations that require high accuracy of shaft rotation (for example, in precision machine tools). The accuracy class is indicated before marking through a dash.
To maintain the interchangeability of rolling bearings, the average taper and ovality of the bore and ring surfaces should not be more than half the tolerance for the average diameters Dc, dc. These parameters are calculated as the arithmetic mean of the maximum and minimum diameters, which are measured in 2 extreme sections of the ring.
Therefore, the tolerances of rolling bearings are assigned to the dimensions:
- D and d;
- Dc and dc;
The tolerances of the rings are determined only by the accuracy class of the bearing and its dimensions, regardless of the properties of the connection to the shaft and housing. Thus, a reduction in the range of bearings is achieved. The connection parameters of the rings with the shaft and the housing are determined by changing the tolerance fields of the shaft and hole.
Rolling bearing fits must be determined in such a way that the ring that rotates sits with an interference fit that would prevent running in and slipping of the ring along the seating surface during operation in the loaded mode.
Landings depend on such factors:
- accuracy class;
- type and size of loads;
- type of loading.
Loading can be local, circulating and oscillatory.
In the case of local loading, only a radial load of constant magnitude and direction works at a single point on the bearing seating surface, transferred to a single point on the surface of the housing or shaft.
The ring, loaded in this way, must be installed so that there is a gap, and then gradually turn the ring, avoiding the local development of the ring, shaft and housing.
If circulating loading occurs, only the radial load, transmitted over the entire circumference of the bearing race, is exerted and is taken up sequentially by the housing or shaft surface. The ring, which experiences circulation loading, is installed on the housing or shaft with an interference fit.
When oscillatory loading occurs, two different radial loads come into play. One of them has a constant magnitude and direction, and the other is rotating. The resultant of these loads affects a limited section of the raceways of the rings, being transferred to some part on the seating surface of the housing or shaft.
Calculation
Calculation of rolling bearings for durability is carried out according to the method of fatigue spalling and for the prevention of plastic deformations.
For a constant mode, these structural elements are calculated according to the equivalent dynamic load, taking into account the nature and direction of the forces acting on the node. The equivalent load is assumed to provide the same service life as under real load conditions.
The load capacity of bearings is characterized by such parameters as the basic dynamic load rating C and the basic static load rating C0.
The first is a radial or axial load that can be sustained at a service life of 1 million revolutions. Base durability - durability under 90% reliability conditions.
Estimated life can be defined as number of revolutions in millions or hours of operation if, as a result, there is no evidence of metal fatigue in the form of flaking or spalling on the surfaces of 90% of the parts of the batch.
Single row deep groove ball bearings
The most popular type of rolling bearings. Often used in the construction of a wide variety of equipment. Among them are rollers of cardboard machines, gearboxes, electric motors. Used to resist radial loads, but can also be prepared to accept bilateral axial loads. Often they are used exclusively for axial loads, especially if the number of revolutions of the shaft is high and thrust bearings cannot be used. If the radial clearance increases, then the axial load carrying capacity of the bearing also becomes larger, since in this situation the bearings acquire the characteristics of angular contact bearings. Operation of bearings is possible if the relative misalignment of the inner and outer rings is not more than 20°.
As for the housing of rolling bearings, it is most often made of gray cast iron. The material for single-row bearing cages is steel stamping or anti-friction materials such as textolite, brass, bronze, duralumin. Recently, polyamide resins have been used for the production of separators. If the bearings are high class accuracy and massive turned cages, the centering of which occurs on the outer ring when using effective lubrication modes, then their operation is possible even at rotation speeds that exceed the limit described in the reference books.
Design types of single-row radial bearings:
- having one protective washer;
- having two protective washers;
- having a groove on the outer ring and a setting ring;
- having an adjusting ring and a protective washer;
- having one-sided and two-sided seal;
- having a groove for introducing balls without a cage.
Ball bearings with one shield
Manufactured exclusively with cages made by stamping. Their use at high speeds is undesirable. When working with such bearings, greases. A metal shield that is pressed into a groove in the outer ring can only hold grease on one side. WITH reverse side the grease that is packed into the bearing is limited by the cap or seal in the assembly. The resulting space is partly filled with lubricants selected for special operating conditions. This version of the design of the part always makes it possible to inspect it (in the place of the cover or seal) and carry out additional lubrication in the course of work.
Ball bearings with two shields
They have the same separators and speed parameters as the previous part, but the working lubricant of the rolling bearings is laid between the washers during assembly at the factory. This type of assembly is used in situations where it is impossible to make a seal in the assembly. So the design becomes simpler and the overall weight of the assembly is reduced. The internal parts of such a bearing cannot be inspected during operation.
Ball bearings with a groove on the outer ring
By means of a split mounting ring, which enters the groove on the ring from the outside, it is possible to fix the bearing inside the housing, which does not require the stop of the outer ring, into the shoulders of the housing for support. However, their ability to perceive radial loads is much greater than for axial ones. The use of adjusting rings makes the design simpler, reduces the size of the nodes and makes it possible to bore through the housing holes.
Sealed ball bearings
Bearings with a double-sided seal are widely used. It is a rubber membrane. The nodes where this seal is applied are characterized by good tightness. As a result, the factory grease does not leak and the ingress of third-party particles into it is excluded. The cages of such ball bearings are usually machined textolite or bronze. Although sealing them and contact type, they have the ability to work at higher rotation speeds.
Sealed ball bearings are often used in motor mounts. In these units, brush dust is released so intensely that it can quickly lead to breakage of other types of ball bearings.
Ball bearings with a groove for inserting balls without a cage
Their difference from other bearings of the classical design is the presence of milled grooves in the sides of the rings. Balls are inserted through these grooves. Since such a rolling bearing has more balls than a cage bearing, this gives a gain in load capacity. Their purpose is to work at low rotation speeds due to excessive friction of the rolling elements in contact. Where there are axial loads, it is better to abandon their use, since under their action the balls are often displaced in relation to the axis of the raceways.
As a constructive version of such ball bearings, there are nodes where there is a groove for inserting balls and protective washers.
These units are used without the use of lubrication in drying chambers and units that use rocking motion.
Many mechanisms currently in existence have bearings that allow them to rotate. Therefore, no rotating movement can be carried out without them. But even such a seemingly irreplaceable, but at the same time inconspicuous part of the mechanism, can be different both in size and in its technical characteristics, the diameter is especially taken into account, the dimensions of which are usually presented in the table. But whatever this detail may be, whatever it looks like, and whatever its specifications, it should perform only one task - to provide parts with rotation or the necessary rotation.
Rules for working with bearings
The bearing must be reliable, but sometimes the conditions under which it has to rotate do not correspond to its normal functioning. Also precisely and conditions can affect the fact that the bearing even in good conditions may suddenly fail.
That's why exist special rules exploitation this part, and they should be taken very seriously so that your part can work for as long as possible. For example, you should not overload it and make sure that it works only for the prescribed time period, and no more. Another rule should be considered that it should be selected so that it fits perfectly in size, diameter and other technical characteristics.
For example, in terms of size, you can find a variety of bearings: from miniature to the most gigantic sizes. There is another division: high-speed, low-speed, most accurate and others. All these divisions depend on where and how you are going to use this important element of the rotational movement.
Bearing design
Continuing the conversation about bearings, you can not miss its design. But in the element itself, which provides rotation, there are a lot of details of which it consists. And each of them should be taken very seriously, because if one of them fails, further operation of the bearing becomes simply impossible.
Bearing accessories:
- Rolling bodies.
- Bushings.
- nuts.
- Washers.
- Rings.
- screws.
- Staples.
- Balloons.
Of course, this list of bearing parts could go on and on, but it's still worth it study in practice and understand each element separately so that you can easily find it later.
Bearing types
There are several divisions of bearings into different types. At the heart of each such division is some sign, which is the main one for attributing important element to rotate to one type or another.
The first such division is based on how the load acts on the bearing and makes it work. But the load is also different. Accordingly, the bearing groups will be involved depending on how the load acts on it.
Groups depending on the action of the load:
- Radial.
- Persistent.
- Radial thrust.
Let's take a closer look at each of these groups. So, the first group is radial. Such bearings can only act under the influence of a radial load. Rarely, they also act under axial load, if roller elements are used for rotation, which have the required diameter.
The second group - thrust elements for rotation. They work perfectly only when they feel the effects of axial loads. The third group is radial-thrust, which can act under any kind of load. They are not afraid of either radial or stubborn loads.
There is another division of bearings, which is based on the shape of the rolling elements, as well as their diameter. There are two types: ball and roller. The first type is ball. They are based on the rolling of such a body, which is similar in shape to balls and has a small diameter. The second type, roller, is based on a different form of rolling, that is, rollers of a certain diameter.
According to their design, bearings can be divided into two types: self-aligning and non-self-aligning. Such elements for rotation are also called spherical. Usually the division into these two species does not require any further explanation, but the main thing is not to forget about the diameter and as often as possible look into special tables, where they are presented with explanations.
There is another division of bearings, which depends not only on its diameter or size, but primarily on the rolling of the bearing bodies itself, which can be either roller or ball. Such an element for rotation can be, despite the shape of balls or rollers, one-, two-, three- or four-charged.
Bearing applicability
Knowing the diameter of the bearing, its design and dimensions, as well as the form of rolling: balls or rollers, it will be possible to determine how important this element will be for the user to rotate. This is especially important for those who are engaged in any kind of repair of equipment. For example, automotive, tractor or motorcycle equipment. But there is another applicability of bearings, which lies in knowing its size.
It is worth dwelling in more detail on how bearings are indicated in the tables. Usually, something is written on each element for rotation in letters and numbers. Such symbols indicate and diameter including. How accurately the part is made is indicated by the letter that comes before the number.
The numbers indicate the size of the hole, what is special about its design, for example, ball or roller shapes of bodies. Usually the first two digits on the parts to be rotated indicate the diameter. But even diameter may vary., so you should be very attentive to the numbers.
So, the sliding parts that are needed for automobile structure, are not very strict about the diameter, and the fact that balls or rollers are used. Another thing is the part for rolling, where everything must be strictly instructions.
For example, sliding ball piece is widely applied for the manufacture of automotive parts. To load in this case was larger, it is necessary to use the balls correctly. It is worth remembering that the gutter must be larger than the ball. By the way, ball parts allow their use at different angles.
But roller parts provide high speed b, which is needed very often. You should not mix all types of bearings, otherwise, during operation, the balls will interfere with the operation of the rollers and vice versa. Therefore, it is worth monitoring the shape of the rolling, if it is a ball, then such a ball part must be used for its intended purpose. Nowadays, ball parts for rotation are used much more often than anything else.
A bearing is a special assembly, which is a part of the support for supporting the shaft and designed to rotate or roll the latter without losing energy to friction. There are several varieties of such structural elements. At the same time, the dimensions of bearings are in most cases regulated by GOST.
Varieties
Knots of this type are widely used in industry and other sectors of the economy. There are hydrostatic, gas-static, magnetic and other groups of bearings. However, the most common varieties are sliding and rolling units. According to the perceived load, both of these groups are divided into:
radial-thrust.
radial;
Rolling bearings
The main elements of this type of units are balls or rollers located at a certain distance from each other in a special cage called a separator. During the operation of the bearing, they roll along the treadmills of two rings, one of which is static in most cases. Knots of this type are used most often in industry. The fact is that, in comparison with plain bearings, they have whole line benefits. These include, first of all, low friction and low lubricant consumption. Ease of operation and installation is also what distinguishes such bearings. The standards (their sizes are regulated by GOST) of such nodes are presented in special tables. Therefore, finding a suitable bearing in one case or another will not be difficult. A node of this type can be matched to absolutely any standard design.
Sensitivity to vibration and shock loads is the only drawback that distinguishes such bearings. Standards in their manufacture must be observed. Otherwise, they won't last too long.
Types of rolling bearings
In addition to the perceived load, nodes of this type are classified into groups according to the following criteria:
The shape of the rolling elements. In this regard, a distinction is made between ball and roller bearings. The rolling elements of the latter type can be conical, cylindrical, needle-shaped, twisted, barrel-shaped, etc.
By the ability of self-establishment. In this case, a distinction is made between spherical and non-self-aligning bearings.
By the number of rolling bodies. There are single row and double row bearings.
By size. All bearings produced today are divided into several series on this basis.
Depending on the series, with the same inner diameter, the width of the bearing and its outer D may vary. Rolling bearings can be used when assembling cars, bicycles, windmills, etc.
Dimensions
The dimensions of nodes of this type are determined by GOST 3478-79. If it is followed, very strong and durable bearings are obtained. These standards apply to all types of rolling units, with the exception of models special purpose having a special design. In the latter case, the nodes can be made the most different sizes most suitable for a given design.
You can find out the standard dimensions of bearings of each series, as already mentioned, from special tables that indicate the outer and inner diameters, the smallest limit dimensions (Rmin), as well as the nominal width of the inner and outer rings (B). As an example, below we bring to your attention a table for a series of bearings with diameters 8 (abbreviated).
Size B for series | |||||||||
1 for Series 7, 1.5 for Series 1-6 |
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More detailed tables can be found in specialized literature. There are also bearing standards in Compass, a graphic editor designed for computer-aided design (in the design library). There are tables for different node diameters.
Accuracy classes
Standard sizes rolling bearings can thus be found in special tables. However, in some cases, some deviations in dimensions from GOST are allowed. According to the accuracy class, rolling bearings are divided into:
normal "0";
increased accuracy "6";
high "5";
extra high "4";
ultra high "2".
Assemblies designed for different designs may have strictly defined tolerances. So, for example, the standards for bicycle bearings (type 608) are as follows:
ball tolerances - 0/-0.005;
inner track - +0.0001/-0.0003;
outer track - +0.0001/-0.0005.
Notation
The standards of rolling bearings must be adhered to during their manufacture. In order for the consumer to be able to see what kind of node is in front of him and for what purposes it can be used, special markings are used. Rolling bearings are usually designated by an engraved set of numbers. Sometimes standard markings include letters. Wherein:
The first number or letter indicates the bearing type.
The next two digits define the series of the node. The first indicates a group of width or height, the second indicates a diameter.
The last two digits are the hole diameter code. If you multiply it by 5, you can get the value of d in mm.
Standard sizes of bearings 66414 (fits in this case are chosen according to GOST 3325-85), for example, such:
width - 42 mm;
weight - 5.74 kg.
Plain bearings
Units of this type consist of two main elements: a strong body and an insert, between which there are special lubricants. The main advantages of such bearings include, first of all, small diameters, as well as the ability to make them split and use them for shafts of a very complex design. The disadvantages of nodes of this variety are considered not too long term service and the need to use expensive lubricants.
Types of plain bearings
At the moment there are nodes of this group:
high speed;
detachable (used, for example, in;
precision machines, accurately guiding the shafts and making it possible to adjust the gap;
cheap low-speed mechanisms;
designed to work in special conditions (water, aggressive environments).
Depending on the mode of operation in a bearing of this type, there may be liquid or semi-fluid friction. In the first case, the working surfaces of the housing and shaft are separated by a rather thick layer of oil. In semi-fluid friction, boundary friction is added to liquid friction (through the thinnest oil film formed by molecular bonds).
Plain bearing dimensions
The dimensions of the nodes of this group are determined by GOST 2795. Data from special tables is also something that must be taken into account when manufacturing such bearings. The standards in this case apply to parameters such as:
chamfer size (C);
tolerances (limit deviations).
outer and inner diameter;
The table below (abbreviated) shows the standard sizes of plain bearings in different rows.
D for rows | L for rows |
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Design features and materials
Plain bearing standards are thus strictly defined by GOST. Some requirements are also imposed on the quality of the materials used for their manufacture. sliding, as already mentioned, can be one-piece or split. In the latter case, special studs or bolts are used to connect the parts. The sleeve of the plain bearing is made in the form of a sleeve. In a one-piece assembly, it can be made of two halves. On shafts subject to deformation, self-aligning plain bearings are usually mounted.
For the manufacture of nodes of this type, the following materials can be used:
cast iron (for the body);
bronze, cast iron or plastic (for bushings).
In some cases, but of course, very rarely, the bushings are made of wood or even chipboard.
Primary requirements
Thus, bearing standards (or rather, compliance with them) allow us to produce the highest quality, durable and with excellent operational characteristics. The requirements for the nodes of this group are as follows:
The materials and design of plain bearings must be such as to provide a minimum between housing and bushing.
The strength and stiffness of the assembly must be such that it can withstand any necessary loads.
The maximum simplicity of the bearing design is welcomed. When installing it, there should not be any difficulties.
Bearings should be manufactured in such a way that their surface has an area sufficient to remove the heat generated during operation.
How do they do
Sliding and rolling bearings are manufactured at specialized large enterprises, which usually include two main workshops: thermal and mechanical. The assembly lines of such factories most often operate in automatic mode. In addition to them, modern spraying machines are also installed in the workshops.
In our country, the most popular are the nodes produced on domestic factories, as well as in Switzerland (SKF). SKF bearing standards are the same as Russian ones.
In order not to make a mistake when choosing a suitable bearing, you need to know its number. Since there is not always access to a replacement part, for example, when the bearing is part of a working mechanism, there are several options for how to calculate it.
If possible, measure as much of the bearing's technical data as possible: height, inside and outside diameter. This will ensure maximum search accuracy and save time. The main way to search for a number is electronic catalogs. There are enough databases on the Internet with information about all kinds of bearings. To calculate, you need to enter the bearing parameters in the filter fields. If there is no data about the diameter and height, some catalogs allow you to search for a number only by brand.
Even a non-specialist can find out the bearing number. But if there are doubts about the choice, it would be useful to consult with professionals in their field who will help with advice and take into account all the nuances.
The use of rolling bearings in mechanisms makes it possible to produce machines of a higher accuracy class. Machines based on these structural elements are more reliable and have a longer service life. In addition, their use reduces operating costs.
The capabilities of the assembly in which the rolling bearing is used is determined by how accurately this part is installed. The distance from the base to the axis of rotation and from the base to the end of the shaft, as well as the radial and end runout, must be within certain limits of accuracy.
During the assembly process, it is necessary to strive so that the bearing races are not deformed. The shape of the seats in the bearing housing and on the shaft must meet the technical requirements in shape and roughness, without scratches and burrs.
Differences from plain bearings
There are two types of moving parts in mechanisms: bearings based on sliding friction and bearings based on rolling friction.
When using the former, the working surfaces of the housing and shaft mutually move and interact, being separated most often by lubricants and a sliding liner. The support works when there is pure sliding in the parts that come into contact.
In the second version of the supports, rolling elements (these can be rollers or balls) are placed in the gap between the surfaces that move mutually. In this case, the bearings work using rolling friction. In such cases, instead of bronze, babbitt or plastic liners in bearings where rolling friction is applied, steel ball or roller bearings are used.
In accordance with the nature of the load of rotation supports, they are radial, when a radial load acts on the support, thrust, when the support is subjected to only axial loads, and radial-thrust, when both types of loads act on the support together.
Each type of support is characterized by its size, design, specifications for production, installation and maintenance.
Rolling bearings and plain bearings have a different mechanism for resistance to movement and for determining the wear of parts of movable bearings. The type of required node is determined on the basis of an assessment of the operating procedure of the mechanism or its individual nodes.
Advantages and disadvantages
Rolling and sliding bearings have both pluses and minuses. Rolling bearings can be preferred over plain bearings due to the lower level of friction at low speeds and when starting from a standstill. Also, rolling bearings have smaller dimensions along the axes, which makes it easier to assemble the structures of self-aligning bearings, without requiring a long time for difficult individual fitting of the liners and their running-in. This is especially important for trunnions with large diameters, operating under heavy loads, with high rotational speeds and temperatures.
When a rolling bearing is used, the quality of lubrication of machine parts and assemblies is improved, the quality of their maintenance is improved, the life of the seating surfaces of the cylinder necks and shafts is extended. Thus, they are the best fit for the vast majority of equipment supports.
True, in addition to the advantages, rolling bearings have a number of disadvantages.
For example, large dimensions. Such structural elements are widely represented in machine-building equipment, are produced in small batches and are very expensive. The rolling bearing is inferior to competitors in such parameters as radial dimensions, weight and rigidity.
It is very difficult to choose them correctly when high rotational speeds are combined with the action of high loads. It is well known that with an increase in the load and speed of rotation of the unit, its durability decreases. For example, if the load is increased by a quarter compared to the previous one, then the service life is halved, and if the load is doubled, the durability becomes 10 times less.
Marking and dimensions according to GOST
Requirements for assemblies and parts are formulated by GOST. Rolling bearings are described by GOST 520-2002.
The following parameters formed the basis of the symbols:
- the diameter that the bearing hole has;
- series of widths (or heights) and series of diameters;
- types of bearings;
- technical implementation.
How to correctly determine the dimensions of rolling bearings by marking? The notation table will help to cope with this task.
All of the above parameters are indicated by signs (or numbers). What numbers the bearing marking consists of depends on the places they occupy in its symbol, if you read from left to right:
Dimensions
To find out how the dimensions of bearings depend on their series, the table of bearing sizes allows. It allows you to link the series to the outer and inner diameter and width.
Dimensions of rolling bearings. Table 1.
Width | External diameter | Inner diameter | |
This is a table of rolling bearings, one of many tables describing this type of structural element.
Classification
One of the features by which rolling bearings are classified is the shape of the rolling elements. In accordance with it, bearings can be ball and roller. Ball rolling bodies, as the name implies, are exclusively spherical in shape. Roller rolling elements can be cylindrical, barrel-shaped or cone-shaped.
The next sign of classification is the direction of load perceived by the rolling bearing. On this basis, bearings are distinguished:
- radial, which perceive only radial or mainly radial loads;
- radial-thrust, able to perceive both radial and axial loads.
It should be noted that adjustable bearings are not able to function without axle load. Thrust are able to perceive only axial forces. Thrust-radial type work both with axial and with small radial loads.
There is also a classification of rolling bearings depending on how many rows of rolling elements they consist of. They are single row and double row.
In accordance with such a characteristic as sensitivity to misalignment, self-aligning bearings are distinguished. They are able to function normally even if a misalignment of up to 3 ° occurs.
Tolerance and landing system
Rolling bearings are widely used. They are produced at special factories and have full interchangeability in terms of surfaces, which are determined by the diameters of the rings: D - the outer diameter of the outer ring and d - the inner diameter of the inner ring.
The interchangeability of rolling bearings depends on the accuracy requirements:
- ring width accuracy B;
- accuracy of ring diameters d, D;
- accuracy of ring surfaces;
- radial and axial runout of the raceways, which determines the accuracy of rotation;
- the accuracy of the gap that is formed at operating parameters between the raceways and the rolling elements.
The accuracy of assembly units is set by GOST. Rolling bearings must comply with the accuracy requirements of GOST 520-89, according to which there are 5 classes of their accuracy: 0; 6; 5; 4; 2. Most of the mechanisms use units of accuracy class 0. Units of accuracy classes above zero are used at high rotation speeds and in situations requiring high shaft rotation accuracy (for example, in precision machine tools). The accuracy class is indicated before marking through a dash.
To maintain the interchangeability of rolling bearings, the average taper and ovality of the bore and ring surfaces should not be more than half the tolerance for the average diameters Dc, dc. These parameters are calculated as the arithmetic mean of the maximum and minimum diameters, which are measured in 2 extreme sections of the ring.
Therefore, the tolerances of rolling bearings are assigned to the dimensions:
- D and d;
- Dc and dc;
The tolerances of the rings are determined only by the accuracy class of the bearing and its dimensions, regardless of the properties of the connection to the shaft and housing. Thus, a reduction in the range of bearings is achieved. The connection parameters of the rings with the shaft and the housing are determined by changing the tolerance fields of the shaft and hole.
Rolling bearing fits must be determined in such a way that the ring that rotates sits with an interference fit that would prevent running in and slipping of the ring along the seating surface during operation in the loaded mode.
Landings depend on such factors:
- accuracy class;
- type and size of loads;
- type of loading.
Loading can be local, circulating and oscillatory.
In the case of local loading, only a radial load of constant magnitude and direction works at a single point on the bearing seating surface, transferred to a single point on the surface of the housing or shaft.
The ring, loaded in this way, must be installed so that there is a gap, and then gradually turn the ring, avoiding the local development of the ring, shaft and housing.
If circulating loading occurs, only the radial load, transmitted over the entire circumference of the bearing race, is exerted and is taken up sequentially by the housing or shaft surface. The ring, which experiences circulation loading, is installed on the housing or shaft with an interference fit.
When oscillatory loading occurs, two different radial loads come into play. One of them has a constant magnitude and direction, and the other is rotating. The resultant of these loads affects a limited section of the raceways of the rings, being transferred to some part on the seating surface of the housing or shaft.
Calculation
Calculation of rolling bearings for durability is carried out according to the method of fatigue spalling and for the prevention of plastic deformations.
For a constant mode, these structural elements are calculated according to the equivalent dynamic load, taking into account the nature and direction of the forces acting on the node. The equivalent load is assumed to provide the same service life as under real load conditions.
The load capacity of bearings is characterized by such parameters as the basic dynamic load rating C and the basic static load rating C0.
The first is a radial or axial load that can be sustained at a service life of 1 million revolutions. Base durability - durability under 90% reliability conditions.
Estimated life can be defined as number of revolutions in millions or hours of operation if, as a result, there is no evidence of metal fatigue in the form of flaking or spalling on the surfaces of 90% of the parts of the batch.
Single row deep groove ball bearings
The most popular type of rolling bearings. Often used in the construction of a wide variety of equipment. Among them are rollers of cardboard machines, gearboxes, electric motors. They are used to resist radial loads, but can also be prepared to take double-sided axial loads. Often they are used exclusively for axial loads, especially if the number of revolutions of the shaft is high and thrust bearings cannot be used. If the radial clearance increases, then the axial load carrying capacity of the bearing also becomes larger, since in this situation the bearings acquire the characteristics of angular contact bearings. Operation of bearings is possible if the relative misalignment of the inner and outer rings is not more than 20°.
As for the housing of rolling bearings, it is most often made of gray cast iron. The material for single-row bearing cages is steel stamping or anti-friction materials such as textolite, brass, bronze, duralumin. Recently, polyamide resins have been used for the production of separators. If the bearings have a high accuracy class and massive turned cages, the centering of which occurs on the outer ring when using effective lubrication conditions, then it is possible to operate even at rotation speeds that exceed the limit described in the reference books.
Design types of single-row radial bearings:
- having one protective washer;
- having two protective washers;
- having a groove on the outer ring and a setting ring;
- having an adjusting ring and a protective washer;
- having one-sided and two-sided seal;
- having a groove for introducing balls without a cage.
Ball bearings with one shield
Manufactured exclusively with cages made by stamping. Their use at high speeds is undesirable. When working with such bearings, greases are used. A metal shield that is pressed into a groove in the outer ring can only hold grease on one side. On the reverse side, the grease that is embedded in the bearing is limited by a cover or seal in the assembly. The resulting space is partly filled with lubricants selected for special operating conditions. This version of the design of the part always makes it possible to inspect it (in the place of the cover or seal) and carry out additional lubrication in the course of work.
Ball bearings with two shields
They have the same separators and speed parameters as the previous part, but the working lubricant of the rolling bearings is laid between the washers during assembly at the factory. This type of assembly is used in situations where it is impossible to make a seal in the assembly. So the design becomes simpler and the overall weight of the assembly is reduced. The internal parts of such a bearing cannot be inspected during operation.
Ball bearings with a groove on the outer ring
By means of a split mounting ring, which enters the groove on the ring from the outside, it is possible to fix the bearing inside the housing, which does not require the stop of the outer ring, into the shoulders of the housing for support. However, their ability to perceive radial loads is much greater than for axial ones. The use of adjusting rings makes the design simpler, reduces the size of the nodes and makes it possible to bore through the housing holes.
Sealed ball bearings
Bearings with a double-sided seal are widely used. It is a rubber membrane. The nodes where this seal is applied are characterized by good tightness. As a result, the factory grease does not leak and the ingress of third-party particles into it is excluded. The cages of such ball bearings are usually machined textolite or bronze. Although their seal is of the contact type, they have the ability to operate at higher rotational speeds.
Sealed ball bearings are often used in motor mounts. In these units, brush dust is released so intensely that it can quickly lead to breakage of other types of ball bearings.
Ball bearings with a groove for inserting balls without a cage
Their difference from other bearings of the classical design is the presence of milled grooves in the sides of the rings. Balls are inserted through these grooves. Since such a rolling bearing has more balls than a cage bearing, this gives a gain in load capacity. Their purpose is to work at low rotation speeds due to excessive friction of the rolling elements in contact. Where there are axial loads, it is better to abandon their use, since under their action the balls are often displaced in relation to the axis of the raceways.
As a constructive version of such ball bearings, there are nodes where there is a groove for inserting balls and protective washers.
These units are used without the use of lubrication in drying chambers and units that use rocking motion.
