Shafts and axles

The rotating parts of the machines are mounted on axles or shafts. Shafts always rotate with parts and transmit torque; the axes, whether they rotate with the parts or remain stationary, do not transmit moment and only support the parts. Therefore, the axles are loaded only by bending forces, and the shafts, in addition to them, are loaded with torques.

Shafts are straight, cranked and flexible (Figure 3.8). When the diameter of a worm or gear is close to the diameter of the shaft, they are manufactured as one piece, for example, a shaft with a worm, a shaft with a gear wheel.

Shafts

a - straight lines; b - cranked; c - flexible.

Figure 3.8.

Shafts and rotating axles are supported by bearings (trunnions). Trunnions that take axial load are called heels.

Bearings

The shafts and the parts rotating around them are supported on bearings. A distinction is made between plain and rolling bearings.

Plain bearings(Figure 3.9). Depending on the magnitude and direction of the loads occurring on the shafts supported by plain bearings, a distinction is made between radial bearings, which can absorb radial loads, and thrust bearings, which can take axial and radial forces.

The surface of the journal in radial bearings slides relative to its inner surface. A decrease in the frictional forces between the rubbing surfaces is created by a layer of lubricant. During operation, the journal takes an eccentric position in the bearing, and therefore the grease between the surfaces of the bearing and the journal takes the shape of a wedge. The journal, rotating, carries the grease into a narrow gap, where an oil cushion is created that supports the journal. A layer of oil separating the journal and bearing is also created if oil is fed into the gap using an oil pump.

Plain bearings are installed for heavy shafts when disassembly of the bearing is required, or when the latter works in corrosive environments or in case of heavy contamination.

Split housing plain bearing

1 - cover; 2 - bolts; 3 - inserts; 4 - case; 5 - cap oiler.

Figure 3.9.

Friction bearing(Figure 3.10) consists of outer and inner rings with raceways. Balls or rollers are installed between the rings in the raceways and roll along the raceways. In order for the rollers or balls to be at the same distance from each other, cages are provided in the bearings, which are pressed rings with holes for rollers or balls.

The main types of rolling bearings

Figure 3.10.

Roller bearings are widely used (for small diameters of rollers, they are called needle bearings).

Rolling bearings can be divided into three types: radial, bearing radial loads and allowing small axial loads; radial thrust, perceiving both radial and axial loads, but the value of the latter should not exceed 0.7 of the difference between the permissible and effective radial loads; persistent, taking only axial loads.

Couplings

To connect shafts that are a continuation of each other, or located at an angle, as well as to transfer torque between the shaft and the parts sitting on it, couplings are used.

According to their purpose, they are divided into permanent clutches (uncontrolled) and coupling clutches (controlled).

Couplings connecting shafts rigidly, the following types are distinguished:

- Sleeve couplings simple in design, small in size (Figure 3.11). Their disadvantage is that in order to connect the shafts, the latter must be moved apart. Couplings are used for shaft diameters not exceeding 120 mm.

Sleeve couplings:

a - with parallel keys; b - with segment keys; c - with pins; d - with slots.

Figure 3.11.

- Flange couplings(Figure 3.12) usually consist of two half-couplings and are of two types. In one type of couplings, the bolts are installed without play while the bolts are sheared. In another type of couplings, the bolts are installed with a gap. In this case, the torque is transmitted by the frictional moment created by the tightening of the bolts.

Couplings connecting shafts with some mutual displacement or misalignment as a result of inaccuracies in manufacturing, installation or deformation during operation are called compensating.

There are several types of expansion couplings:

The simplest coupling consists of two half couplings, the same as for rigid couplings, only the bolt in one of the half couplings abuts against rubber gaskets, which makes it possible to compensate for inaccuracies in the position of the shafts.

- Cross couplings used to connect shafts when there may be large axle displacements. They consist of two half-couplings with grooves at their ends. A disc is placed between the half-couplings, at the ends of which there are projections perpendicular to one another. The disadvantage of these couplings is the high wear of the grooves, since during operation the middle disc moves relative to the half of the couplings. Friction forces arise between the disc and the coupling halves, causing radial forces that are transmitted to the shaft.

- Swivel couplings(Figure 3.13) is used to transfer motion between shafts located at an angle. The possibility of transmitting rotation at an angle of up to 45 ° is ensured by the fact that the coupling has two hinges located mutually perpendicular.

Blind couplings. Long shafts are sometimes made composite according to the conditions of manufacture, assembly and transportation. In this case, separate parts of the shaft are connected with blind couplings. In some cases, these couplings are used to ensure the alignment of the unit shafts.

The sleeve coupling (fig. 10.1) is a sleeve that fits with a gap on the shaft ends. The coupling is small in diameter, but complicates the installation due to the need for large axial displacements of the connected units. The material of the bushings is structural steel (art. 5, art. 3). Sleeve couplings are used to connect shafts up to 70 mm in diameter.

Flange couplings. The flange coupling (Fig. 10.2) consists of two identical half couplings, made in the form of a hub with a flange. The flanges are bolted together. There are two designs:

1. Half of the bolts are installed in the flanges of the half couplings without a gap. In this case, the centering of the coupling halves is carried out by these bolts. As a result of screwing the nuts, the flanges are pressed by the tightening forces of the bolts, and a frictional moment arises at the ends of the flanges. The torque from one coupling half to the other is transmitted by the bolt rods, supplied without clearance, and by the frictional forces on the flanges.

2. All bolts in the flanges of the coupling halves are installed with a gap. At the same time, no

it is necessary to provide for the centering of the half-couplings. In this case, the entire torque from one coupling half to the other is transferred by frictional forces on the flanges.

Compensating couplings.

For economic and technological reasons, machines are usually made of separate units (assemblies), which are connected by couplings. However, accurate installation of the shafts of such units is impossible due to: manufacturing and installation errors; installation of units on a deformable (non-rigid) base; misalignment of shafts as a result of thermal deformations of the housings of the units during their operation, as well as due to elastic deformations of the shafts under load.

Compensating couplings are used to connect shafts with mismatched axes. Due to their design, these couplings ensure the operability of the machine even with mutual displacements of the shafts.

Gear couplings. A double gear coupling (Fig. 10.3) consists of two identical hubs 1 (bushings) with external gear rims and two identical to both 2 with internal gear rims. The clips are tightened with bolts 3 evenly spaced around the circumference. In the covers 4, which cover the inner cavity of the coupling, there are special rubber seals that hold the liquid lubricant inside the coupling. Plug 5 is used to fill the clutch with oil. The belts 6 on the bushings are used to control the alignment of the shafts, and the threaded holes are used to fasten the indicator stands. The number of teeth and their sizes are selected so that the teeth of the sleeve rim are located with a certain gap between the teeth of the cage, forming toothed connections.

To reduce the intensity of the wear of the teeth, the blanks of the bushings and clips are made forged or cast (for large sizes). Forged blanks are made from steels of grades 35XM, 40, 45, and cast from steels of grades 40L, 45L. The hardness of the surfaces of the teeth of the bushings and clips should be 42 - 50 HRC e.

Articulated couplings. The hinge couplings use the principle of the Hooke hinge. These couplings are used to transmit torque between shafts with large skew angles up to 40-45 °, which change during operation.

The coupling (Fig. 10.4) consists of two identical half-couplings in the form of a hub with a fork (the forks of the half-couplings are turned 90 °) and a cross connecting the half-couplings. The crosspiece is connected to the forks of the half-couplings by hinges. This provides freedom of rotation of each half of the coupling relative to the cross.

Elastic couplings.

Elastic couplings are distinguished by the presence of an elastic element and are universal in the sense that, having some torsional flexibility, these couplings are also compensating.

Flexible couplings are capable of:

· Mitigate shock and torque shock caused by the technological process or the choice of clearance when starting and stopping the machine. In this case, the kinetic energy of the impact is accumulated by the clutch during deformation of the elastic element, turning into potential energy of deformation.

· Protect the machine drive from harmful torsional vibrations;

· Connect shafts with mutual displacements. In this case, deform

The elastic element of the clutch is lifted, and the clutch functions as a compensating one.

Couplings with non-metallic (rubber) elastic elements. Up-

Other couplings with rubber cord and rubber elastic elements received

whether it is very widespread due to the simplicity of structures, low cost of manufacture, ease of operation (do not require maintenance), high torsional flexibility and good damping ability. The last two important properties are determined by the properties of the rubber from which the elastic element of the coupling is made.

An elastic sleeve-finger coupling is shown in Fig. 10.5.

The elastic elements are rubber-cord bushings fitted on the connecting pins.

An elastic coupling with a rubber sprocket is shown in fig. 10.6

In fig. 10.7 depicted flexible sleeve in the form of an inner torus. Two identical half-couplings 2 are connected by a toroidal elastic element 1, the edges of which are pressed to the half-couplings by pressure rings 3 and screws 4, evenly spaced around the circumference.

Rubber conical washer sleeve shown in Fig. 10.8. The rubber-metal elastic element 6 is attached to the half-couplings 1 and 2 with screws 5 evenly spaced around the circumference. Modern methods of vulcanizing rubber to metal make it possible to obtain a bond strength not lower than that of the rubber itself. The coupling does not have high compensating properties. However, it is successfully used in machine drives for damping harmful torsional vibrations. By varying the angle of the taper, the required torsional stiffness of the coupling can be obtained.

In fig. 10.9 shows a coupling with elastic elements in the form of steel rods, working in bending under the action of a torque.

The half-couplings 1 and 7 are connected by cylindrical steel rods (springs) 5, evenly spaced around the circumference. Cover 3 and casing 4 keep the rods from falling out and keep the lubricant in the coupling thanks to seals 2 and 8. To reduce the wear of the springs and their seats, the coupling is filled with oil with EP additives through the oiler 6.

The half-couplings are made of 45, 40X steels, the rods are made of high-alloy spring steels, the covers and casings are made of Сч12 cast iron.

Mechanical couplings

Couplings, with which you can easily separate the shafts (often during operation), are called clutch. These couplings include form-fit couplings and couplings.

Form-fit couplings. Form-fit couplings are classified according to the shape of the engaging elements.

A coupling with rectangular teeth (Fig. 10.10, a) can transmit torque in both directions. Its left side is rigidly attached (keyed) to the shaft. The right side is attached to the other shaft with a sliding key and engages or disengages from the left side by moving a lever in the slot. The main disadvantage of such a clutch is the difficulty in engaging. A gear clutch, which engages more easily, but transmits torque in only one direction, is shown in Figure 10.10, b.

The material of the cam clutches must provide a high hardness of the working surfaces of the cams. Steel grades are used: 20X, 12XH3A with case hardening and quenching to a hardness of 54 - 60 HRc. With frequent inclusions, steels are used: 40X, 40XH, 35XGSA with hardening of the working surfaces of the teeth to a hardness of 40 - 45 HRc.

Freewheel clutches

These couplings serve to transmit torque in only one direction, when the angular speeds of the driving and driven half couplings are equal. If the angular velocity of the driven coupling half exceeds the angular velocity of the driving coupling half, the coupling will automatically disconnect the coupled units.

Roller freewheel is shown in Fig. 10.11. The clutch consists of a cage 1 and a sprocket 2, which are half couplings, rollers 3, spaced evenly around the circumference, and pressure devices consisting of a piston and a spring 7. The rollers hold the side covers 4, which fix the spring rings. The key 5 keeps the cage from turning. The leading link of the coupling can be either an asterisk or a cage. When the cage starts to overtake the sprocket, the roller frictional forces against the sprocket and the cage shifts to the wider part of the wedge gap and the half-couplings open.

Torque limit couplings

In fig. 10.12 shows a friction clutch used in crane rotation mechanisms and on rotary winches. This sleeve is at the same time a connecting piece. It connects the motor shaft to the gearbox. The clutch is equipped with a brake pulley, the connection between the engine and the mechanism is via discs. Some of the disks are fixed through the splines on a bushing rigidly connected to the gearbox shaft, the other part of the disks is fixed to the disk. Rigidly connected to the electric motor. The discs are pressed against each other by a constant force developed by compressed springs. The amount of compression of the springs, which determines the amount of torque transmitted by the clutch, is regulated by the threaded ring.

10.2. Bearings

Bearings are the most common parts in mechanical engineering. Not-

it is possible to imagine any modern mechanism without a bearing, the functions of which are, on the one hand, in a significant reduction in friction between the rotating and stationary parts of the mechanism, and on the other, in the ability to carry a certain load. The seal also plays an important role in protecting the bearing from external influences and retaining the lubricant in it.

The durability and reliability of any mechanism largely depends on the correct choice and quality of bearings, seals and lubricants used. Bearings by the type of parts used in them and their interactions during operation are subdivided into rolling bearings and plain bearings. The most common rolling bearings, which, in turn, are classified according to the direction of the perceived load relative to the shaft (radial, angular contact, thrust-radial and thrust); the form of rolling bodies: ball, roller; the number of rolling bodies: single-row, double-row, etc. (see Table 10.1).

Table 10.1
Roller bearings
Characteristic	View	Characteristic	View
Single row radial roller bearing		Radial spherical single row bearing
Double row radial roller bearing		Double row spherical roller bearing
Angular contact roller bearing		Spherical roller thrust bearing
Continuation of Table 10.1
Tapered roller bearing		Axial radial roller bearing
Ball bearings
Deep groove ball bearing, single row		Double row spherical deep groove ball bearing
Split deep groove ball bearing		Single row thrust ball bearing
Angular contact ball bearing		Double thrust ball bearing
Double row angular contact ball bearing		Angular contact ball bearing
Needle bearings
Needle bearing with cage without rings		Double row needle bearing
Needle bearing with cage without rings, double row		Needle roller bearing with extruded cup and open end
Single row needle roller bearing		Needle roller bearing with extruded outer ring and closed end
The end of the table. 10.1
Combined bearings
Combined bearing (radial needle and angular contact ball)			Combined bearing (radial needle
Insert bearings

Fastening connections

In mechanical engineering, four main types of threaded fasteners are used: bolts with nuts (Figure 10.13, a), screw bolts (screws) (Figure 10.13, b ), pins (fig. 10.13, v ) intermediate (Fig.10.13, G).

1. Bolting is applicable only if it is possible to make through holes in the mating parts.

2. Connection with screw-in bolts is used with blind threaded holes (Figure 10.13, d), when it is impossible to use a bolt with a nut, or with a through threaded hole, when it is possible to install the bolt on only one side of the connection.

Parts with a threaded hole are made of steel, ductile and ductile iron, titanium alloy, bronze. In soft alloy parts (aluminum, magnesium, zinc, etc.), intermediate threaded bushings of a harder metal are required.

3. Stud connection is used for parts made of soft (aluminum and magnesium alloys) or brittle (gray cast iron) materials, as well as for blind or through threaded holes in cases where frequent twisting of the studs is undesirable.

4. In addition to the described basic types of compounds, intermediate ones are also used. These include, for example, the connection used, shown in Figure 10.13, f ... The bolt is secured with a nut in a smooth hole in one piece; the other part is tightened with a nut screwed onto the free end of the bolt.

General-purpose fasteners are made most often from steel 35, critical parts (connecting rod bolts, power pins, etc.) - from chromium steels of the 40X type, chromium steels of the 30HGS type, heat-resistant steels of the 30XM, 50XFA, 25X12M1F types, of corrosion-resistant steels type 30X13, 40X13.
In serial and mass production, threads are cut using the vortex cutting and milling methods. The most productive and at the same time providing the highest thread strength is the thread rolling method.

Industry Standards

They are compiled for products used only in a specific industry.

Every engineering plant or group of plants in any industry has its own standards and norms. These are technical documents prescribing the use of only certain metal profiles, die sizes, processing methods. They also set the dimensions of fasteners: nuts, bolts, washers, etc. And when a designer develops a machine, he must adhere to those standards and norms that are accepted at the manufacturing plants. The more standard devices, apparatuses and parts there are in the new machine, the easier the machine is to manufacture and the more reliable it is to operate. After all, such parts are produced in large quantities, and, therefore, they are cheaper, they can be easily replaced in case of damage.

State and industry standards regulate the technical data of products, mandatory types and methods of their testing and verification. The manufacturer is obliged to strictly observe all this and does not have the right to produce products with a deviation from GOST or OST.

For products that are produced in small quantities, standards are not developed. Instead, the factories draw up technical specifications, which also determine all the parameters of the product and are strictly adhered to by the manufacturers.

In cases where state standards immediately cover a group of machines of the same purpose, separate technical conditions are also drawn up for each separate type of machine to clarify the standard.

When performing a working drawing of gear wheels, there are various forms of a bore hole in the wheel hub. It depends on the type of connection between the wheel and the shaft.

9.4.1. Keyway connection

The main elements of this connection are shown in Fig. 9.7. In this case, the key is about half of its height enters the groove (groove) of the shaft and half into the groove of the wheel hub. The side working faces of the key transfer rotation from the shaft to the wheel and vice versa.

Rice. 9.6. Spur gear drawing

Table 9.2

Dimensions of keyway elements

Shaft diameter

Dimensions of the section of the keys

Groove depth

Shaft diameter

Dimensions of the section of the keys

Groove depth

t 1

t 1

Rice. 9.8. Elements of keyway connection: a) keyway on the hub;

b) keyway on the shaft; c) keyed connection of the shaft and hub

9.4.2. Splined connection

The spline connection of the wheel hub with the shaft is carried out by means of several protrusions (splines) made as one piece with the shaft, and the corresponding grooves cut in the hub (Fig. 9.9).

Spline joints of various profiles are made: straight-sided, trapezoidal, involute and triangular. The straight-sided profile is the most common.

The rules for performing conventional images of spline shafts and wheel hubs on working drawings are established by GOST 2.409-74. An example of an image is shown in Fig. 9.10.

Rice. 9.10. Conditional images of elements of the splined shaft and hub

The symbol for the hole or shaft splines is indicated on the leader line shelf or in the specifications. Example of a symbol for a hub: 8 x 42 x 48, where Z = 8- the number of teeth; d = 42- inner diameter; D = 48- outside diameter. Tooth width “ b”Is affixed to the image.

4.2.1 Reading an assembly drawing. To read an assembly drawing means to determine the device, the principle of operation, the purpose of the product depicted on it, to represent the interaction of parts, their shape and methods of connection with each other. The sequence of reading the assembly drawing: - familiarization with the product. According to the main inscription, determine the name of the product, the designation of the drawing, the scale of the image, the mass of the assembly unit; - reading the image. Determine the main view, additional and local types, sections and sections, the purpose of each of them; - study of the constituent parts of the product. Determine according to the specification the number and name of the parts included in the assembly unit, and according to the drawing, determine their shape, relative position and purpose. Find the image of the part first on the view on which the position number is indicated, and then on the others. It should be remembered that the same part on any cut (section) is hatched in the same direction with the same step; - study of the functional purpose of the product and its constructive solution. Establish a method for connecting individual parts to each other, the interaction of component parts in the process of work, the external relationship with other assembly units and products. For detachable connections, identify all fasteners. Determine the mating surfaces and the dimensions along which the mating of the parts is carried out; - study of the design of the product. Establish the nature of the connection of parts, their functional interaction in the process of work, connection and interaction with other assembly units. For moving parts, establish the process of their movement during the operation of the mechanism, determine the rubbing surfaces and methods of lubrication; - determination of the order of assembly and disassembly of the product - the final stage of reading the drawing.

Sequence and basic techniques for reading drawings

Read the assembly drawing - it means to present the shape and design of a product, to understand its purpose, principle of operation, assembly procedure, and also to identify the shape of each part in a given assembly unit. When reading the general arrangement drawing, you should: 1. Find out the purpose and principle of operation of the product. The necessary information on the purpose and principle of operation of the product is contained in the title block and product description. 2. Determine the composition of the product. The main document for determining the composition of the product is the specification, in which the component parts of the product are classified into sections. To determine the position of a specific component of the product on the drawing, you need to determine the item number in the specification by its name, and then find the corresponding leader line on the drawing. The specification also allows you to determine the number of products for each item. 3. Determine the purpose and configuration of the component parts of the product. The purpose and configuration of the product is determined by the functional characteristics of the product as a whole and its component parts. The configuration of the components is due to their purpose and interaction during operation. When determining the configuration of the components, attention should be paid to the way they are connected. 4. Identify ways of connecting the component parts of the product with each other. The methods of connecting parts are due to the peculiarities of the interaction of the elements of the product during its operation. Connection methods can be identified from the general arrangement drawing and classified as detachable or non-detachable. 5. Determine the sequence of assembly and disassembly of the product. One of the main requirements for the design of the product is the ability to assemble and disassemble it during operation and repair. Only a design that allows assembly (disassembly) with a minimum number of operations can be considered rational. The following sequence of reading the drawing is recommended: 1. Based on the title block, establish the name of the product, the number, scale of the drawing, the weight of the product, the organization that issued the drawing. 2. Find out the content and features of the drawing (identify all the images that make up the drawing). 3. According to the specification, establish the name of each part of the product, find its image in all images, and understand its geometric shapes. Since in the drawings, as a rule, there is not one, but several images, the shape of each part can be identified unambiguously by reading all the images in which this part is present. You should start with the simplest parts (rods, rings, bushings, etc.). Having found a part on one (usually on the main) image using the reference designation and, knowing the design purpose of the part, imagine its geometric shape. If this one image uniquely determines the shape and dimensions of the part, then proceed one by one to identifying the shapes of other parts; if one image does not reveal the shape or dimensions of at least one element of the part, then you should find this part in other images of the assembly drawing and make up for the lack of one image. Clarification of the shape of the part is facilitated by the fact that on all cuts and sections the same part is shaded with the same slope and distance between the hatching lines. At the same time, they use the knowledge of the basics of projection drawing (projection connection of points, lines and surfaces) and the conventions established by the ESKD standards. 4. Read the product description. If the description is missing, if possible, familiarize yourself with the description of a similar design. 5. Establish the nature of the connection of the component parts of the product to each other. For permanent connections, define each connection element. For detachable connections, identify all fasteners included in the connection. For moving parts, establish the possibility of their movement during the operation of the mechanism. 6. Establish which parts are lubricated and how the lubrication is carried out. 7. Find out the order of assembly and disassembly of the product. It should be borne in mind that in the specification and on the assembly drawing, the order of recording and designation of component parts is not related to the assembly sequence. It is recommended to record the order of assembly and disassembly of the product on paper in the form of a diagram or in the form of a record of the sequence of operations. The ultimate goal of reading a drawing, as a rule, is to clarify the device of the product, the principle of operation and establish its purpose. In the educational process, the central place in reading a drawing is the study of the forms of individual parts, as the main means of clarifying all other issues related to reading a drawing.

Detailing the drawing

Detailing is the execution of working drawings of a part according to a general arrangement drawing. Detailing - this is not a simple copying of an image of parts, but a complex creative work, including an individual assessment of the complexity of the shapes of each part and the adoption of the best graphic solution for it: the choice of the main image, the number and content of images. The dimensions of the parts are measured in the drawing taking into account the scale indicated in the title block. The exception is the dimensions shown on the assembly drawing. The sizes of standard elements (threads, tapers, "turnkey", etc.) are specified according to the relevant standards. Detailing process it is advisable to divide into three stages: reading the general drawing, detailed identification of the geometric shapes of the parts and the execution of working drawings of the parts. 1. Reading a general arrangement drawing. The result of reading the general drawing should be an understanding of the composition of the parts included in the assembly, their relative position and methods of connection, interaction, the design purpose of each part separately and the product as a whole. 2. Detailed identification of geometric shapes of parts to be drawn in order to correctly select the main image, the number and content of other images in the working drawings. As the shapes of the parts are identified, it is necessary to decide on the choice of the main image and the need to perform other images for each part, select the image scale, format. 3. Execution of working drawings of parts. make the layout of the drawing, i.e. outline the placement of all images of the part in the selected format. draw the necessary views, cuts, sections and detailing elements in thin lines. draw extension and dimension lines. Determine the true dimensions of the elements of the part and put them on the drawing. Pay particular attention to ensure that the dimensions of the mating parts do not have discrepancies. Determine the necessary structural and technological elements (chamfers, grooves, slopes, etc.), which are not shown in the general arrangement drawings. The dimensions of the identified structural elements should be determined not according to the general drawing, but according to the relevant standards for these elements. put down the roughness based on the manufacturing technology of the part or its purpose. circle the drawing and hatch cuts and sections. check the drawing and, if necessary, make corrections. fill in the title block, write down the technical requirements.

TO Category:

Repair and construction machines

Shafts, axles, their supports and connections

Shafts and axles are the supporting and rotating parts of the machine elements. The axles only support the parts, while the shafts transmit torque. The parts of shafts and axles that transfer loads to the supports are called journals, and if they are located at the ends of the shafts, studs or trunnions. Bearing parts of vertical shafts and axles that transmit the longitudinal load are called heels.

Shafts are smooth, stepped, cranked, cardan, flexible, etc. (Fig. 2.11). Smooth and stepped shafts are used in gearboxes, open and closed gears.

Crankshafts are used in crank mechanisms. Flexible and cardan shafts are used to transmit motion with frequent changes in the relative position of the connected nodes with a relatively large distance between them.

Rice. 2.11. Shaft types: a - smooth; b - stepped; в - cranked; g - flexible

Rice. 2.12. Plain bearings: a - one-piece with a sleeve; b - detachable with inserts; 1 - bushing (insert); 2 - self-aligning support; 3 - case; 4 - hole for lubrication

Plain bearings can take significant loads, are convenient when mounting large shafts, when disassembly of bearings is required, are reliable when working in highly contaminated environments, and are relatively durable.

Rolling bearings (fig. 2.13) consist of outer and inner rings with raceways, made of alloyed wear-resistant chromium steel. Balls (for ball bearings) or rollers (for roller bearings) move along raceways between the rings. The position of the rolling elements is fixed using separators - steel rings with holes for balls or rollers. Rolling bearings have a friction force 5 ... 10 times less than plain bearings. Roller bearings have a significantly higher load capacity than ball bearings, but their permissible rotational speed is about half that.

Rolling bearings are divided into six series depending on the load capacity (from ultra-light to super-heavy) and nine types according to their design.

Rice. 2.13. Rolling bearings: a - ball bearings with a cage; 6 - ball in the body; в - ball thrust; g - double-row ball; d - roller; e - roller tapered; w-roller self-aligning; z - roller multi-row

To reduce wear, rolling bearings are packed with grease and various seals (oil seals) made of felt, leather, etc. are used.

Couplings are used to connect shafts, as well as to transmit torque to parts and shafts of the kinematic chain of machines. By purpose, couplings are divided into connecting (elastic) and coupling. An example of couplings of the first type are sleeve (Figure 2.14, a) and flanged (Figure 2.14, b). In sleeve couplings, the element connecting the shafts is a sleeve with a pin or hairpin. The connection of these couplings is made by longitudinal movement of shafts, gearboxes, drums, etc.

Connectors, pins and keys are calculated. When using flange couplings, flanges are put on the ends of the shafts to be connected, which are then bolted together.

Rice. 2.14. Couplings: a - sleeve; b - flanged

Couplings are cam and friction clutches. Cam couplings (Fig. 2.15, a) consist of two half couplings, one of which is permanently rigidly connected to the shaft, and the second can move along the shaft on a key or splines. At the ends of the half-couplings there are cams - protrusions and depressions, which, when the half-couplings approach, engage. With cam clutches, their stops or slow, you can turn on the mechanisms when rotating.

Couplings are intended for connecting shafts or other rotating parts, for transmitting torque. They are used to transfer rotation from the engine to the mechanism, turn it on and off, change speeds and perform other functions.

By purpose, design and operating conditions, couplings are divided into permanent (connecting) and coupling (controlled and self-steering). In this article, we will only talk about couplings. When choosing a coupling design, it is necessary to take into account its purpose, layout and assembly features, the magnitude and nature of the load and operating conditions. Couplings are designed for permanent connection of rotating parts. They are divided into two groups: blind, rigidly connecting the shafts, and movable, allowing for some inaccuracy of assembly. For shafts transmitting insignificant torques, a blind coupling is used, connected by conical pins (Fig. 1, a). For the transmission of significant torques, a deaf clutch with keys (Fig. 1.6) or a disc clutch (Fig. 1, c) is used. The pins are positioned at 90 ° to each other. The sleeve can be made of any material. Approximate dimensions: L = (3 ... 5) d; D = 1.5d; dm = (0.25 ... 0.3) d. The sleeve is designed for torsion, and the pins or dowels are for shear and crush.

The disadvantage of these couplings is the requirement for strict alignment of the connected shafts. The displacement and misalignment of the shafts causes additional bending deformations in them and increases the pressure on the supports. Movable couplings are divided into expansion couplings, allowing axial displacement of the shaft; cross, allowing radial shaft displacement; leash; membrane and elastic, allowing axial and radial displacement of the shafts. In fig. 2, a shows an end expansion sleeve, 2.6 - a sleeve with a driving pin. The dimensions of the couplings are selected based on the conditions of crushing of the contacting surfaces. Usually 1 = d, 6 = (0.25 ... 0.3) d, dm = (0.25 ... 0.3) dv. Expansion couplings used only when transferring small loads and low angular velocities due to intensive wear of the working surfaces. Cross couplings (Fig. 3) consist of two fixed flanges with cutouts or protrusions 1 and 2, fixed on the connected shafts. A movable part 3 with protrusions or cutouts is placed between these flanges. The perpendicular arrangement of the grooves allows you to compensate for misalignment of the shafts due to the sliding of the protrusions of the cross in the grooves half-couplings... To increase the efficiency, lubrication of the rubbing surfaces and their precise running-in are required. Coupling parts are usually made of steel. The protrusions of the cross and the grooves of the half-couplings are cemented. If the shafts are to be electrically isolated from each other, then the cross is made of an electrically insulating material. Table 1 shows the main dimensions of the couplings.
Disadvantage cross couplings is the increase in backlash as the protrusions wear. In cases where backlash (MPX) is unacceptable, clearance-free designs of cross couplings with a clamping device are used. Drive couplings (Fig. 4) consist of two discs with hubs rigidly attached to the ends of the rollers. On the disk 1 of one half of the coupling, a pin 2 is fixed, which slides into the radial groove of the second half of the coupling 3.
The disadvantage of drive couplings is the presence of MPX due to the landing of the finger in the groove; the value of MPX increases with the wear of the rubbing surfaces of the groove and the pin and is determined by the size of the resulting gap. To improve the working conditions of the driver clutch, it is preferable to use a two-finger driver. In this case, the wear of the rubbing parts of the coupling is reduced, and the radial pressure on the roller, observed in single-finger drives, is also eliminated. However, double-finger drivers are more difficult to manufacture and, moreover, require complete alignment of the connected shafts, which complicates the assembly of the mechanism. Table 2 shows the dimensions of the single-finger drive couplings.

In my school years, I was engaged in a ship modeling circle, and so there we connected the engine shaft with the propeller shaft of the ship model using the hinge shown in Figure 5. This connection resembles a cardan transmission of a car. I think the structure of this connection is clear from the figure. The closer the coupling halves are to each other, the longer the grease is stored in them, but at the same time there must be a corresponding alignment of the shafts. The photo below shows one of the half couplings, which miraculously survived from those times, and this is almost fifty years. There is also a spring connection, I have not drawn it. In short, if the shafts have the same diameters, and the forces are minimal, then a suitable spring is simply put on the shafts. It can be fixed simply by soldering or a sleeve with a clamping screw can be put on over the spring.

Homemade coupling

I want to tell you about one more shaft connection. The first time I saw this miracle was in 1971, when I was on a collective farm harvesting potatoes. I liked it so much that I immediately took it into my arms. It stood on the KIR-1.5 mower. Mower - chopper, rotary KIR-1.5 is designed for harvesting annual and perennial seeded and natural grasses. Modern kirs do not have such a connection. The connection can handle a decent amount of torque. To make it, you will need an asterisk (photo 1) from the engine crankshaft from the Zhiguli classics, where the camshaft has a chain drive. The chain itself is photo 3. And it is necessary to grind out the half-couplings, in the figure they are green. The asterisk is cut in half. A sprocket half is welded onto each coupling half (Fig. 1). Then a part of the chain is separated with the number of links equal to the number of teeth on the sprocket. The resulting half-couplings are wrapped with this piece of chain and the links are connected with a new pin using a rivet (Photo2). Bolts can be used to fasten the coupling halves if the efforts are not large, but it is better, of course, to use a keyed connection. Well, that seems to be all, if I remember what is interesting, I will definitely post it. Goodbye. K.V.Yu.